Sources

Vital signs

Adult ranges. Each says whether it is an ideal (what healthy looks like) or a field threshold (the number that changes what an EMT does).

Life-saving basics

The free CPR, choking, bleeding, stroke, overdose, allergy and seizure lessons anyone can take.

EMT course — every number

Every number with a unit or range in the EMT course was pulled out by script and checked against a named standard. 116 were right as written and one was clarified; nothing had to be removed.

Term glossary

Rules stated inside glossary definitions, checked against the National EMS Education Standards and NREMT EMT curriculum, AAOS Emergency Care and Transportation of the Sick and Injured, and AHA guidelines. ⚑ marks wording that varies by local protocol — follow your agency.

Shockable vs non-shockable rhythms

• Shockable rhythms = ventricular fibrillation + pulseless ventricular tachycardia. Non-shockable = asystole + PEA. (AHA 2020 Guidelines, Adult BLS/ACLS cardiac arrest algorithm.)
• Defibrillation depolarizes the myocardium at once so the intrinsic pacemaker can resume an organized rhythm; a shock cannot start a heart with no electrical activity (asystole). (AHA ACLS.)
• After a shock OR "no shock advised": resume CPR immediately, starting with compressions, for 2 minutes before the next rhythm analysis; pulse checks ≤10 s. (AHA 2020 BLS.)
• Untreated VF deteriorates to asystole within minutes. (AHA.) Kept as "within minutes" — no specific minute count claimed.
• Survival from VF arrest falls ~7–10% per minute without CPR/defibrillation. (AHA Guidelines; Larsen MP et al., Ann Emerg Med 1993;22:1652.)

Reference charts

Pediatric vitals, blood pressure categories, glucose, CPR, oxygen devices and APGAR.

• BP categories: AHA/ACC — normal <120 and <80; elevated 120–129 and <80; stage 1 130–139 or 80–89; stage 2 ≥140 or ≥90; crisis >180 and/or >120. Field hypotension systolic <90.
• Pediatric vitals: AHA PALS 2020 via San Francisco EMS Agency Protocol 14.1 (eff. 10/01/25), verified from the PDF: HR awake neonate 100–205, infant 100–190, toddler 98–140, preschool 80–120, school-age 75–118, adolescent 60–100; RR infant 30–53, toddler 22–37, preschool 20–28, school-age 18–25, adolescent 12–20; hypotension neonate <60, infant <70, 1–10 y <70+(2×age), >10 y <90.
• Glucose: ADA Standards of Care — level 1 hypoglycemia <70, level 2 <54; normal fasting <100 (shown 70–99); 2-h postprandial <140; hyperglycemia >180. DKA shown as a PATTERN (no single glucose cutoff, since the 2024 hyperglycemic-crisis consensus changed the threshold).
• Fever ≥100.4°F (38°C): CDC.
• CPR table: AHA 2020 — adult depth ≥2 in and ≤2.4 in; child ~2 in (1/3 AP); infant ~1.5 in (1/3 AP); 30:2 single rescuer all ages, 15:2 two-rescuer child/infant; rescue breathing adult 1/6 s, child/infant 1 every 2–3 s; pulse check ≤10 s (carotid adult; carotid/femoral child; brachial infant).
• O₂ devices: AAOS ECTSI — NC 1–6 L/min ~24–44%; NRB 10–15 L/min up to ~90% (course uses 15); BVM + reservoir 15 L/min nearly 100%.
• APGAR: AAP/ACOG Committee Opinion 644 — 0/1/2 per sign; pulse <100 = 1, ≥100 = 2; 7–10 reassuring, 4–6 moderately abnormal, 0–3 low.

Emergency identification

Heart attacks, nitroglycerin and ED medications, stroke, cardiac arrest, shock and breathing emergencies.

Heart

• STEMI is named for ST-segment elevation on a 12-lead ECG, the pattern of a completely occluded coronary artery injuring the full thickness of the ventricular wall; NSTEMI shows no such elevation and most often injures the inner (subendocardial) layer.AHA 2020
• NSTEMI and unstable angina are indistinguishable at the bedside and are separated at the hospital by a blood troponin level — a protein released by dying myocardium; troponin rises in NSTEMI and does not in unstable angina.ACC / AHA 2020
• For a STEMI, guidelines target reperfusion at a PCI-capable center within 90 minutes of first medical contact, which is why destination choice and early notification are EMS decisions that affect outcome.AHA 2020 / ACC
• Right ventricular infarction commonly accompanies an inferior MI; those patients are preload dependent, and nitroglycerin can cause profound hypotension. The classic field picture is hypotension with clear lung sounds and jugular venous distension.AAOS Emergency Care & Transportation of the Sick and Injured
• The right coronary artery supplies the SA node and the AV node in the majority of people, which is the anatomic reason inferior MI produces bradycardia and heart blocks.AAOS Emergency Care & Transportation of the Sick and Injured
• Diabetic autonomic neuropathy damages the visceral afferent fibers carrying cardiac ischemic pain, which is why diabetics are over-represented among silent myocardial infarctions.AHA 2020 / NREMT EMT curriculum

Nitroglycerin and ED medications

• Nitrates are contraindicated within 24 hours of sildenafil or vardenafil, and within 48 hours of tadalafil, because of the risk of severe and potentially fatal hypotension.American Heart Association / American College of Cardiology Guideline for the Management of ST-Elevation Myocardial Infarction (2013), nitrate use after phosphodiesterase inhibitors
• Tadalafil has a long duration of action, with effects persisting up to about 36 hours, which is why its nitrate-free window is longer than sildenafil's.FDA-approved prescribing information, Cialis (tadalafil) label, Clinical Pharmacology
• Sildenafil and tadalafil inhibit phosphodiesterase type 5, the enzyme that degrades cyclic GMP; nitroglycerin is a nitric oxide donor that increases cyclic GMP, so the two act on the same pathway and produce potentiated, non-self-limiting vasodilation.FDA-approved prescribing information, Viagra (sildenafil) label, Clinical Pharmacology and Drug Interactions
• Hypotension from a nitrate given after a phosphodiesterase type 5 inhibitor can be profound and may be refractory to fluid and vasopressor therapy; management is supportive until the drug effect wears off.American Heart Association / American College of Cardiology STEMI Guideline (2013); FDA-approved prescribing information, Viagra (sildenafil) label
• Sildenafil is also prescribed for pulmonary arterial hypertension under the brand name Revatio, so a patient on a phosphodiesterase type 5 inhibitor may be a woman or a patient with no erectile dysfunction history.FDA-approved prescribing information, Revatio (sildenafil) label, Indications and Usage
• The inferior wall of the left ventricle and the right ventricle usually share the same coronary supply, so inferior myocardial infarction is frequently accompanied by right ventricular infarction; right ventricular output is preload-dependent, and nitroglycerin can cause profound hypotension in these patients. Treatment of that hypotension is supine positioning and fluid, not further nitrate.American Heart Association / American College of Cardiology STEMI Guideline (2013); AAOS Emergency Care and Transportation of the Sick and Injured, 12th Edition, Cardiovascular Emergencies
• An EMT assists a patient with their own prescribed nitroglycerin only under medical direction, by standing order (offline) or direct order (online), and only when the systolic blood pressure meets the local protocol minimum; the exact threshold and repeat limits are set by the local protocol.AAOS Emergency Care and Transportation of the Sick and Injured, 12th Edition, Medication Administration; National Registry of Emergency Medical Technicians EMT scope of practice
• Aspirin is an antiplatelet that blocks thromboxane-mediated platelet aggregation; it limits growth of the coronary thrombus but does not lyse the existing clot, reopen the artery, or relieve chest pain. It is withheld for true aspirin or NSAID hypersensitivity, active bleeding, and suspected aortic dissection.American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care, Acute Coronary Syndromes; AAOS Emergency Care and Transportation of the Sick and Injured, 12th Edition

Stroke

• Intravenous thrombolytic therapy for acute ischemic stroke is given within 3 hours of last known well, extended to 4.5 hours in selected eligible patients.AHA/ASA 2019 Update to the 2018 Guidelines for the Early Management of Patients With Acute Ischemic Stroke
• Mechanical thrombectomy for a large vessel occlusion is standardly offered within 6 hours of last known well, and out to 24 hours in selected patients who meet advanced imaging criteria.AHA/ASA 2019 Update to the 2018 Guidelines for the Early Management of Patients With Acute Ischemic Stroke (DAWN and DEFUSE 3 criteria)
• Of all strokes, approximately 87% are ischemic, about 10% are intracerebral hemorrhage and about 3% are subarachnoid hemorrhage — which is the basis for the module's statement that roughly one stroke in eight is a bleed.AHA/ASA Heart Disease and Stroke Statistics Update
• In untreated acute ischemic stroke roughly 1.9 to 2 million neurons are lost each minute, which is the quantitative basis of the phrase time is brain.Saver JL, Time Is Brain — Quantified, Stroke (AHA journal), 2006
• Supplemental oxygen in suspected stroke should be titrated to maintain an oxygen saturation above 94%; routine supplemental oxygen in non-hypoxic stroke patients is not recommended.AHA/ASA Guidelines for the Early Management of Patients With Acute Ischemic Stroke; AHA ECC/ACLS oxygen targets
• A suspected stroke patient without hypotension is transported with the head of the cot elevated approximately 30 degrees to aid venous drainage and reduce aspiration risk, per local protocol.AAOS Emergency Care and Transportation of the Sick and Injured, neurologic emergencies chapter
• After a transient ischemic attack the risk of stroke is front-loaded: on the order of 3 to 10 percent within 2 days and 9 to 17 percent within 90 days without treatment.AHA/ASA Scientific Statement, Definition and Evaluation of Transient Ischemic Attack, Stroke, 2009
• Large vessel occlusions account for roughly a quarter to a third of acute ischemic strokes (reported ranges approximately 24 to 46 percent) but a disproportionate share of stroke death and severe disability.AHA/ASA Recommendations for the Establishment of Stroke Systems of Care, 2019; published LVO prevalence ranges
• Todd's paralysis — focal weakness following a seizure — typically resolves within minutes to hours and by convention within 48 hours.Standard neurology reference on the postictal state (Todd's paresis), consistent with AAOS seizure teaching
• Hypoglycemia, the most important field-correctable stroke mimic, is defined for field purposes as a blood glucose below approximately 70 mg/dL.AAOS Emergency Care and Transportation of the Sick and Injured; NREMT diabetic emergencies scope

Cardiac arrest

• Agonal gasps are a brainstem reflex seen early in cardiac arrest and are not effective breathing; a patient who is unresponsive and only gasping is in cardiac arrest and needs compressions started immediately.AHA 2020 Guidelines for CPR and ECC, Part 3: Adult Basic and Advanced Life Support — recognition of cardiac arrest
• Defibrillation terminates a rhythm by depolarizing a critical mass of myocardium at the same instant, producing a brief period of no electrical activity in which the sinus node, the heart's fastest intrinsic pacemaker, can resume an organized rhythm.AHA 2020 Guidelines for CPR and ECC, Part 3: Adult Basic and Advanced Life Support — defibrillation
• Ventricular fibrillation is sustained by multiple simultaneous disorganized wavefronts in the ventricular muscle, so the ventricles quiver without generating any stroke volume, while pulseless ventricular tachycardia is organized but too rapid to allow ventricular filling.AHA 2020 Guidelines for CPR and ECC, Part 3: Adult Basic and Advanced Life Support — arrest rhythms and defibrillation
• About 1 in 5 EMS-treated out-of-hospital cardiac arrests present in an initially shockable rhythm, and shockable rhythms are considerably more common when the arrest is witnessed and a defibrillator is applied early.AHA Heart Disease and Stroke Statistics 2020 Update — out-of-hospital cardiac arrest initial rhythm data
• Asphyxial arrests — drowning, choking, opioid and other overdoses, respiratory failure, and most pediatric arrests — most often present in asystole or pulseless electrical activity rather than in a shockable rhythm.AHA 2020 Guidelines for CPR and ECC, Part 3 (adult) and Part 4 (pediatric basic and advanced life support)
• Drowning produces a primarily hypoxic arrest; rescuers should emphasize ventilation and oxygenation along with compressions, and should not delay CPR in an attempt to drain water from the lungs.AHA 2020 Guidelines for CPR and ECC, Part 3 — drowning and special circumstances of resuscitation
• The reversible causes of pulseless electrical activity that matter at EMT level are severe blood loss, hypoxia, tension pneumothorax, cardiac tamponade and hypothermia; the AHA groups these with the other reversible causes as the H's and T's to be treated during resuscitation.AHA 2020 Adult Cardiac Arrest Algorithm — reversible causes (H's and T's)
• Needle decompression of a tension pneumothorax is above the EMT scope of practice in most systems; the EMT contribution is recognition, gentle ventilation, an early ALS request and rapid transport.National EMS Scope of Practice Model (2019 edition), EMT-level skills — invasive decompression is an advanced-level skill
• In suspected severe hypothermia, assess breathing and a pulse for 30 to 45 seconds before concluding the patient is pulseless, because profound bradycardia can make a pulse extremely difficult to detect.AHA Guidelines for CPR and ECC — accidental hypothermia (2020 Part 3 special circumstances; the 30 to 45 second assessment is longstanding AHA ECC hypothermia guidance)
• Severely hypothermic patients have survived arrest neurologically intact after prolonged downtime, so resuscitation is continued and rewarming begun, and the decision to terminate efforts belongs to the hospital — the principle stated as no one is dead until they are warm and dead.AHA 2020 Guidelines for CPR and ECC, Part 3 — hypothermia and special circumstances
• Rough handling, jolting or dragging of a severely hypothermic patient can precipitate ventricular fibrillation; move the patient gently and horizontally, remove wet clothing, insulate and rewarm.AHA Guidelines for CPR and ECC — accidental hypothermia special circumstances
• Patient or vehicle motion during AED analysis can corrupt the rhythm assessment, so the analysis is performed with everyone clear of the patient and the ambulance stopped.AHA 2020 Guidelines for CPR and ECC, Part 3 — automated external defibrillator use and analysis artifact

Shock

• Cardiac tamponade classically presents with Beck's triad: distended neck veins, muffled heart tones, and a narrowing pulse pressure with hypotension. Clear, equal bilateral breath sounds distinguish it from tension pneumothorax.AAOS, Emergency Care and Transportation of the Sick and Injured (Chest Trauma)
• Because the fibrous pericardium cannot stretch acutely, as little as 50 to 100 mL of rapidly accumulating blood can mechanically limit ventricular filling and cause tamponade.AAOS, Emergency Care and Transportation of the Sick and Injured (Chest Trauma)
• Pulmonary embolism is most often a thrombus from a deep vein thrombosis in a leg or pelvic vein that lodges in the pulmonary arteries, obstructing flow through the lungs; it presents with sudden dyspnea, sharp chest pain worse on inspiration, tachycardia, and hypoxia with clear lung sounds.AAOS, Emergency Care and Transportation of the Sick and Injured (Respiratory Emergencies)
• Pulmonary embolism risk factors include recent surgery (especially hip and knee), prolonged immobility or travel, casting, malignancy, pregnancy and the postpartum period, oral contraceptives, and prior venous thromboembolism.AAOS, Emergency Care and Transportation of the Sick and Injured (Respiratory Emergencies)
• Neurogenic shock typically follows spinal cord injury at or above roughly the T6 level, where descending sympathetic outflow and the cardiac accelerator fibers arising from T1 through T4 are interrupted, producing hypotension with warm dry skin and bradycardia.AAOS, Emergency Care and Transportation of the Sick and Injured (Spine and Nervous System Trauma)
• Beta blockers occupy beta-1 receptors and blunt the compensatory tachycardia of shock, so a patient taking one may present with a normal or slow heart rate despite significant hypoperfusion; calcium channel blockers and implanted pacemakers can mask it the same way.AAOS, Emergency Care and Transportation of the Sick and Injured (Pharmacology and Shock)
• Pediatric hypotension is defined as a systolic blood pressure below 70 + (2 x age in years) mmHg for children 1 to 10 years old.American Heart Association, Pediatric Advanced Life Support (PALS) Provider Manual
• Capillary refill time longer than 2 seconds is a reliable indicator of poor peripheral perfusion in children under 6 years of age.AAOS, Emergency Care and Transportation of the Sick and Injured (Pediatric Emergencies)
• In adults, hypotension is generally defined as a systolic blood pressure below 90 mmHg, and in shock it is a late finding rather than a screening one.AAOS, Emergency Care and Transportation of the Sick and Injured (Shock)
• Pulse pressure is the systolic minus the diastolic pressure; a narrowing pulse pressure is an early sign of hemorrhagic shock as peripheral vasoconstriction raises the diastolic value.AAOS, Emergency Care and Transportation of the Sick and Injured (Shock)
• Epinephrine auto-injectors deliver 0.3 mg intramuscularly for adults and 0.15 mg for pediatric patients, given in the lateral thigh; epinephrine causes alpha-mediated vasoconstriction and beta-2 mediated bronchodilation.AAOS, Emergency Care and Transportation of the Sick and Injured (Immunologic Emergencies)
• Biphasic anaphylactic reactions can recur roughly 4 to 12 hours after the initial reaction, which is why every anaphylaxis patient is transported even after symptoms improve.AAOS, Emergency Care and Transportation of the Sick and Injured (Immunologic Emergencies)
• A hypotensive anaphylaxis patient should be kept supine, with the legs elevated if tolerated; sudden standing or sitting upright can precipitate cardiovascular collapse. If respiratory distress predominates, allow a position of comfort.AAOS, Emergency Care and Transportation of the Sick and Injured (Immunologic Emergencies)
• Trendelenburg positioning is no longer recommended for shock; the supine position is the current standard for most shock patients, with position of comfort for cardiogenic shock and respiratory distress.AAOS, Emergency Care and Transportation of the Sick and Injured (Shock)
• Supplemental oxygen in shock is titrated to maintain an oxygen saturation of at least 94 percent, with assisted ventilation when breathing is inadequate.American Heart Association, Advanced Cardiovascular Life Support guidelines
• Hypothermia impairs the clotting cascade and platelet function, which is why aggressive prevention of heat loss is a bleeding-control and shock intervention, not a comfort measure; it is one leg of the trauma triad of death with acidosis and coagulopathy.AAOS, Emergency Care and Transportation of the Sick and Injured (Bleeding)
• Non-hemorrhagic causes of hypovolemic shock include severe vomiting and diarrhea, heat exposure and dehydration, extensive burns with plasma loss, and uncontrolled hyperglycemia with osmotic diuresis.AAOS, Emergency Care and Transportation of the Sick and Injured (Shock)
• Septic shock produces both relative hypovolemia from vasodilation and absolute hypovolemia from increased capillary permeability, so the patient is simultaneously dilated and volume depleted.AAOS, Emergency Care and Transportation of the Sick and Injured (Shock)
• Tracheal deviation in tension pneumothorax is a late and frequently absent finding; decompensation with unilateral absent breath sounds, JVD, and hypotension should drive action without it.AAOS, Emergency Care and Transportation of the Sick and Injured (Chest Trauma)
• Baroreceptors located in the carotid sinus and the aortic arch detect falling arterial pressure and trigger the sympathetic response that produces tachycardia and peripheral vasoconstriction in compensated shock.AAOS, Emergency Care and Transportation of the Sick and Injured (Anatomy and Physiology)
• Hypothermic pulse check written as 30–45 s (AHA ECC hypothermia guidance; the 2020 document is less numerically specific).

Breathing

• An average adult tidal volume is about 500 mL, of which roughly 150 mL remains in anatomic dead space and never reaches the alveoli; minute volume is tidal volume multiplied by respiratory rate, which is why rapid shallow breathing ventilates dead space without oxygenating.AAOS, Emergency Care and Transportation of the Sick and Injured (Airway Management and Respiratory Physiology)
• Agonal gasps are present in up to 40 percent of witnessed out-of-hospital cardiac arrests and must be treated as absent breathing; a pulse check is limited to 10 seconds.American Heart Association, 2020 Guidelines for CPR and ECC (Adult Basic Life Support)
• Stridor arises from the extrathoracic upper airway, which is subjected to negative intraluminal pressure on inspiration and narrows further, while wheezing arises from intrathoracic lower airways that are compressed during expiration; breath sounds are generated by turbulent airflow, so an absent or silent chest indicates minimal air movement rather than resolution.AAOS, Emergency Care and Transportation of the Sick and Injured (Respiratory Emergencies)
• Asthma involves three simultaneous processes in the lower airways: bronchospasm of smooth muscle, mucosal edema, and mucus plugging, producing largely reversible expiratory airflow obstruction and air trapping. Albuterol is a beta-2 agonist that relaxes bronchial smooth muscle.AAOS, Emergency Care and Transportation of the Sick and Injured (Respiratory Emergencies and Pharmacology)
• COPD is persistent, not fully reversible airflow limitation; emphysema destroys alveolar walls and elastic recoil, causing air trapping and a barrel chest, while chronic bronchitis is defined clinically as a productive cough on most days for at least 3 months in each of 2 consecutive years.GOLD, Global Strategy for the Diagnosis, Management and Prevention of COPD (GOLD Report)
• In COPD exacerbation, supplemental oxygen should be titrated to a target saturation of 88 to 92 percent rather than to the 94 percent and above target used for most other patients.GOLD, Global Strategy for the Diagnosis, Management and Prevention of COPD (GOLD Report)
• Pursed-lip breathing in COPD generates positive back pressure during exhalation that splints collapsing small airways open, allowing trapped air to empty; it is a self-generated form of positive airway pressure.AAOS, Emergency Care and Transportation of the Sick and Injured (Respiratory Emergencies)
• In acute cardiogenic pulmonary edema, elevated left ventricular filling pressure raises pulmonary capillary hydrostatic pressure until plasma is forced into the interstitium and alveoli, producing basilar crackles that ascend, orthopnea, paroxysmal nocturnal dyspnea, and pink frothy sputum. Interstitial edema can also compress small airways and produce wheezing, known as cardiac asthma.AAOS, Emergency Care and Transportation of the Sick and Injured (Cardiovascular and Respiratory Emergencies)
• CPAP raises intrathoracic pressure, recruits collapsed alveoli, drives alveolar fluid back into the interstitium, and reduces both preload and afterload; it is contraindicated in hypotension, altered mental status, vomiting, inability to protect the airway, suspected pneumothorax, and significant facial trauma.AAOS, Emergency Care and Transportation of the Sick and Injured (Airway Management)
• In pulmonary embolism, alveoli distal to the occluded pulmonary artery are ventilated but not perfused, creating dead-space ventilation and hypoxemia that is out of proportion to clear, equal breath sounds; supplemental oxygen only partially corrects it because the defect is in pulmonary blood flow.AAOS, Emergency Care and Transportation of the Sick and Injured (Respiratory Emergencies)
• Pulmonary embolism risk factors include recent surgery (especially hip and knee), prolonged immobility or long-distance travel, casting, malignancy, pregnancy and the postpartum period, estrogen-containing oral contraceptives, and prior venous thromboembolism.AAOS, Emergency Care and Transportation of the Sick and Injured (Respiratory Emergencies)
• Pneumonia is a focal infection that consolidates alveoli with purulent exudate, producing localized crackles or diminished sounds, fever, chills, pleuritic pain, and a productive cough over days; older adults may present with confusion, weakness, or falls and no fever.AAOS, Emergency Care and Transportation of the Sick and Injured (Respiratory Emergencies)
• Pertussis is transmitted by respiratory droplets and requires droplet precautions (a surgical mask on the provider and, if tolerated, on the patient), whereas tuberculosis is transmitted by airborne droplet nuclei that remain suspended in air and requires airborne precautions (an N95 or higher respirator on the provider and a surgical mask on the patient).CDC, Guideline for Isolation Precautions: Preventing Transmission of Infectious Agents in Healthcare Settings
• Anaphylaxis requires involvement of two or more body systems, or hypotension following exposure to a known allergen; mast cell mediators cause vasodilation, capillary leak with angioedema, and bronchoconstriction. Epinephrine 0.3 mg IM for adults and 0.15 mg for small children in the lateral thigh is first-line, and alpha-mediated vasoconstriction plus beta-2 bronchodilation is why albuterol is an adjunct and never a substitute.AAOS, Emergency Care and Transportation of the Sick and Injured (Immunologic Emergencies)
• Biphasic anaphylactic reactions can recur roughly 4 to 12 hours after the initial reaction, which is why every anaphylaxis patient is transported even after improvement.AAOS, Emergency Care and Transportation of the Sick and Injured (Immunologic Emergencies)
• Croup (laryngotracheobronchitis) is a viral subglottic swelling most common between about 6 months and 3 years of age, with gradual onset after upper respiratory symptoms, a barking cough, inspiratory stridor, and nocturnal worsening; the child can usually still swallow and is not drooling.AAOS, Emergency Care and Transportation of the Sick and Injured (Pediatric Emergencies)
• Epiglottitis is a bacterial supraglottic infection with onset over hours, classically described in children about 2 to 7 years old, presenting with high fever, drooling, dysphagia, a muffled voice, tripod positioning, and no barking cough; routine Haemophilus influenzae type b vaccination has made it rare in vaccinated children, so it is now seen relatively more often in adults.CDC, Haemophilus influenzae Disease (Hib) Clinical Information, with AAOS Emergency Care and Transportation of the Sick and Injured (Pediatric Emergencies)
• Because airway resistance rises steeply as the radius falls, 1 mm of circumferential edema in an infant airway removes a large majority of the cross-sectional area, which is why small amounts of swelling are catastrophic in children and why the cricoid ring is the narrowest point of the pediatric airway.AAOS, Emergency Care and Transportation of the Sick and Injured (Pediatric Emergencies)
• Children have a higher oxygen consumption per unit body weight and a smaller functional residual capacity than adults, so they desaturate markedly faster during apnea or inadequate ventilation; bradycardia in a hypoxic child is a pre-arrest sign.American Heart Association, Pediatric Advanced Life Support (PALS) Provider Manual
• Grunting is expiration against a partially closed glottis, generating endogenous positive end-expiratory pressure to prevent alveolar collapse, and it indicates severe respiratory distress in an infant or child.AAOS, Emergency Care and Transportation of the Sick and Injured (Pediatric Emergencies)
• Carbon monoxide binds hemoglobin with roughly 200 to 250 times the affinity of oxygen, forming carboxyhemoglobin, and shifts the oxyhemoglobin dissociation curve to the left so that the oxygen still bound is released less readily to tissue; skin is typically normal or red rather than cyanotic, and the classic cherry-red appearance is late and unreliable.CDC, Carbon Monoxide Poisoning: Clinical Guidance for Health Care Providers
• Conventional two-wavelength pulse oximeters cannot distinguish carboxyhemoglobin from oxyhemoglobin, so SpO2 reads falsely normal or high in carbon monoxide poisoning; CO-oximetry is required to measure carboxyhemoglobin.CDC, Carbon Monoxide Poisoning: Clinical Guidance for Health Care Providers
• The elimination half-life of carboxyhemoglobin is approximately 4 to 5 hours on room air and roughly 60 to 90 minutes while breathing high-concentration oxygen, which is why high-flow oxygen is the field treatment.CDC, Carbon Monoxide Poisoning: Clinical Guidance for Health Care Providers
• Pulse oximetry accuracy is degraded by poor peripheral perfusion, hypothermia, motion, severe anemia, nail polish, and carbon monoxide, and readings become unreliable at low saturations; treat the patient's presentation, not the number alone.AAOS, Emergency Care and Transportation of the Sick and Injured (Patient Assessment)
• Hyperventilation syndrome produces respiratory alkalosis, which causes cerebral vasoconstriction (dizziness, visual changes) and increases calcium binding to albumin, lowering ionized calcium and causing perioral and digital paresthesia and carpopedal spasm. It is a diagnosis of exclusion, and rebreathing into a paper bag is no longer recommended because it can cause serious hypoxia when the true cause is organic.AAOS, Emergency Care and Transportation of the Sick and Injured (Respiratory Emergencies)
• Kussmaul respirations are both deep and rapid, an increase in tidal volume and rate that compensates for metabolic acidosis such as diabetic ketoacidosis; Cheyne-Stokes respirations are a crescendo-decrescendo pattern separated by periods of apnea, associated with brain injury and terminal illness.AAOS, Emergency Care and Transportation of the Sick and Injured (Patient Assessment and Respiratory Emergencies)
• Spontaneous pneumothorax results from rupture of a subpleural bleb, classically in tall, thin young patients and in patients with COPD, presenting without trauma as sudden unilateral pleuritic chest pain and dyspnea with decreased or absent breath sounds on the affected side; progression to tension pneumothorax produces hypotension, jugular venous distention, and rapid deterioration.AAOS, Emergency Care and Transportation of the Sick and Injured (Chest Trauma and Respiratory Emergencies)
• For a severe foreign body airway obstruction in a responsive adult or child, deliver abdominal thrusts until the obstruction is relieved or the patient becomes unresponsive, at which point begin CPR and look into the mouth before each set of ventilations; infants receive back slaps and chest thrusts instead.American Heart Association, 2020 Guidelines for CPR and ECC (Basic Life Support)
• Opioid overdose causes respiratory depression with slow, shallow breathing and pinpoint pupils; ventilatory support with a bag-valve mask is the priority alongside naloxone administration per protocol.AAOS, Emergency Care and Transportation of the Sick and Injured (Toxicology)
• Flagged, NOT included: pulse oximetry overestimates saturation in patients with darker skin pigmentation (FDA Safety Communication 2021) — left out because the module's source list did not include FDA. Worth adding on Ryan's call.

Body systems

What each system does, how, and what it looks like when it fails.

Circulatory

• Cardiac output equals stroke volume times heart rate. A resting adult ejects roughly 70 mL per beat, giving a cardiac output of about 5 litres a minute — the entire blood volume circulating roughly once every minute.AAOS Emergency Care and Transportation of the Sick and Injured; Guyton & Hall Textbook of Medical Physiology (cardiac output)
• Pulse pressure is the systolic pressure minus the diastolic pressure. A narrowing pulse pressure is an early sign of hypovolaemic shock and of cardiac tamponade.AAOS Emergency Care and Transportation of the Sick and Injured (circulation assessment)
• Beck's triad of cardiac tamponade is jugular vein distension, muffled heart tones, and hypotension with a narrowed pulse pressure.AAOS Emergency Care and Transportation of the Sick and Injured (chest trauma)
• A red blood cell lives about 120 days before it is removed and recycled by the spleen and liver.Gray's Anatomy (blood and haematopoiesis)
• About two-thirds of the circulating blood volume sits in the venous system at any moment, which makes the veins the body's blood reservoir.Guyton & Hall Textbook of Medical Physiology (the systemic circulation)
• A capillary wall is a single cell thick — that one-cell gap is where oxygen and nutrients leave the blood and carbon dioxide and waste enter it.Gray's Anatomy (the microcirculation)
• The coronary arteries fill during diastole, while the ventricle is relaxed, so a very fast heart rate shortens filling time and reduces the heart muscle's own blood supply.Guyton & Hall Textbook of Medical Physiology (coronary circulation)
• Blood is roughly 55 per cent plasma and 45 per cent cells, and plasma is about 90 per cent water.Gray's Anatomy (composition of blood)
• Skeletal muscle contraction acting on one-way venous valves is a major mechanism of venous return — the so-called skeletal muscle pump.Guyton & Hall Textbook of Medical Physiology (venous return)

Respiratory

• Room air is about 21 per cent oxygen, and exhaled air still contains roughly 16 per cent — which is why mouth-to-mask rescue breathing works.AAOS Emergency Care and Transportation of the Sick and Injured (airway management)
• A normal adult tidal volume is about 500 mL, and roughly 150 mL of each breath never reaches an alveolus because it remains in the conducting airways — the anatomic dead space.AAOS Emergency Care and Transportation of the Sick and Injured; Guyton & Hall Textbook of Medical Physiology (pulmonary ventilation)
• Minute volume equals tidal volume times respiratory rate, so depth and rate matter equally when judging whether breathing is adequate.AAOS Emergency Care and Transportation of the Sick and Injured (adequate breathing)
• The phrenic nerve, which drives the diaphragm, arises from the cervical nerve roots C3, C4 and C5.Gray's Anatomy (the diaphragm and its innervation)
• The adult lung holds roughly 300 million alveoli, giving a combined gas-exchange surface of about 70 square metres.Gray's Anatomy (respiratory system); Guyton & Hall Textbook of Medical Physiology
• Surfactant produced by cells in the alveolar wall lowers surface tension and keeps alveoli from collapsing on exhalation.Gray's Anatomy; Guyton & Hall Textbook of Medical Physiology (surfactant and alveolar stability)
• Exhalation at rest is passive, produced by elastic recoil of the lung and chest wall rather than by muscular effort.Guyton & Hall Textbook of Medical Physiology (mechanics of breathing)
• Carbon dioxide, sensed as rising acidity by chemoreceptors in the brainstem, is the primary stimulus to breathe; low oxygen sensed by the carotid and aortic bodies is the backup stimulus.Guyton & Hall Textbook of Medical Physiology (regulation of respiration)
• In children, cardiac arrest is most often the end stage of respiratory failure rather than a primary cardiac event.AHA Pediatric Advanced Life Support (PALS), 2020 Guidelines for CPR and ECC
• The trachea divides at the carina into the right and left main bronchi; the right main bronchus is wider and more vertical, so aspirated material tends to go right.Gray's Anatomy (trachea and bronchi)

Nervous

• The brain is about 2 per cent of body weight but consumes roughly 20 per cent of the body's oxygen and receives about 20 per cent of the cardiac output.Gray's Anatomy; Guyton & Hall Textbook of Medical Physiology (cerebral blood flow and metabolism)
• The peripheral nervous system contains 12 pairs of cranial nerves and 31 pairs of spinal nerves.Gray's Anatomy (the peripheral nervous system)
• A reflex arc runs from sensory neuron to spinal cord to motor neuron without involving the brain, which is why withdrawal from a painful stimulus happens before the pain is felt.Gray's Anatomy; Guyton & Hall Textbook of Medical Physiology (spinal cord reflexes)
• The brainstem is composed of the midbrain, pons and medulla oblongata; the medulla holds the respiratory and cardiovascular control centres.Gray's Anatomy (the brainstem)
• Three meninges cover the brain and spinal cord — dura mater outermost, then arachnoid mater, then pia mater on the tissue itself — with cerebrospinal fluid in the subarachnoid space.Gray's Anatomy (the meninges)
• An epidural haematoma is typically arterial, classically from the middle meningeal artery torn by a temporal skull fracture; a subdural haematoma is venous, from torn bridging veins.AAOS Emergency Care and Transportation of the Sick and Injured (head injuries); Gray's Anatomy
• Cerebral perfusion pressure is the mean arterial pressure minus the intracranial pressure, so either a falling blood pressure or a rising pressure inside the skull starves the brain.AAOS Emergency Care and Transportation of the Sick and Injured (head injuries)
• Decorticate posturing is flexion of the arms toward the core; decerebrate posturing is rigid extension and indicates deeper, lower brainstem injury with a worse prognosis.AAOS Emergency Care and Transportation of the Sick and Injured (neurologic assessment)
• Roughly one person in five has a small, long-standing difference in pupil size (physiologic anisocoria), which is why a new or sudden inequality is what signals a brain emergency.Standard clinical neurology / ophthalmology reference (physiologic anisocoria)
• In traumatic brain injury, even a single episode of hypoxia or hypotension is associated with markedly worse outcome, which is why airway and blood pressure take priority over everything else.Brain Trauma Foundation, Guidelines for the Management of Severe Traumatic Brain Injury
• The vagus nerve is the tenth cranial nerve and carries most of the parasympathetic output to the heart, lungs and gut.Gray's Anatomy (cranial nerves)
• Each cerebral hemisphere controls movement and sensation on the opposite side of the body, and language is usually located in the left hemisphere.Gray's Anatomy (the cerebrum); AAOS Emergency Care and Transportation of the Sick and Injured (stroke)

Musculoskeletal

• The adult skeleton contains 206 bones, divided into 80 axial bones (skull, vertebral column, ribs, sternum and hyoid) and 126 appendicular bones (the limbs plus the shoulder and pelvic girdles).Gray's Anatomy (standard human osteology)
• The adult vertebral column has 7 cervical, 12 thoracic and 5 lumbar vertebrae, plus the fused sacrum (5 elements) and the coccyx (4 elements).Gray's Anatomy
• There are 12 pairs of ribs. Pairs 1 to 7 attach directly to the sternum by costal cartilage, pairs 8 to 10 attach indirectly, and pairs 11 and 12 are floating ribs with no anterior attachment.Gray's Anatomy
• Bone stores approximately 99 percent of the body's calcium and releases it into the blood to maintain the serum calcium needed for cardiac conduction, nerve conduction, muscle contraction and clotting.Gray's Anatomy / standard human physiology
• The phrenic nerve arises from cervical nerve roots C3 to C5 and is the sole motor supply to the diaphragm.Gray's Anatomy
• Average adult circulating blood volume is approximately 5 liters (roughly 70 mL per kilogram of body weight), which is why a 1 to 1.5 liter femoral bleed represents a quarter to nearly a third of the supply.AAOS Emergency Care and Transportation of the Sick and Injured
• Approximate internal blood loss from closed fractures: pelvis can exceed 2 liters, femur 1 to 1.5 liters, tibia or fibula up to about 500 mL, and humerus about 500 mL.AAOS Emergency Care and Transportation of the Sick and Injured
• In adults, red (blood-forming) marrow is concentrated in the pelvis, sternum, ribs, vertebrae, cranium and the proximal ends of the femur and humerus, while most long-bone shaft marrow has converted to yellow fatty marrow.Gray's Anatomy / standard human physiology

Integumentary

• Skin is the body's largest organ, covering roughly 1.5 to 2 square meters in an adult and making up about 16 percent of total body weight.Gray's Anatomy / standard human anatomy and physiology
• The epidermis is avascular and is nourished by diffusion from the capillary beds of the underlying dermis.Gray's Anatomy
• Full thickness burns destroy the hair follicles, sebaceous glands, sweat glands and sensory nerve endings within the burned area, so that skin cannot regenerate from within the wound and requires grafting.AAOS Emergency Care and Transportation of the Sick and Injured
• Infection and sepsis are the leading causes of death in burn patients who survive the initial resuscitation period, because the barrier function of the skin has been lost across a wide area.AAOS Emergency Care and Transportation of the Sick and Injured
• In patients with darkly pigmented skin, assess color changes such as pallor, cyanosis and jaundice at the conjunctiva, oral mucosa and inner lip, nail beds, palms and soles, where pigment is thinnest.AAOS Emergency Care and Transportation of the Sick and Injured
• Cooling of the body by sweating depends on evaporation rather than on the presence of sweat, so high ambient humidity, which slows evaporation, substantially reduces the body's ability to shed heat.Standard human physiology (thermoregulation) / AAOS Emergency Care and Transportation of the Sick and Injured
• Vitamin D is synthesized in the skin on exposure to ultraviolet B light, and is required for intestinal absorption of dietary calcium.Gray's Anatomy / standard human physiology

Digestive

• The adult alimentary canal runs approximately 9 meters, about 30 feet, from mouth to anus.Gray's Anatomy
• Gastric acid maintains the stomach contents at a pH of roughly 1.5 to 3.5, which kills most ingested bacteria and activates pepsinogen into the protein-digesting enzyme pepsin.Gray's Anatomy / standard human physiology
• Venous blood from the stomach, intestines, pancreas and spleen drains into the hepatic portal vein and passes through the liver before returning to the heart, so the liver processes all absorbed material first.Gray's Anatomy
• The liver synthesizes most clotting factors and plasma albumin, stores glucose as glycogen, detoxifies drugs and alcohol, converts ammonia to urea for renal excretion, and conjugates bilirubin from worn-out red cells.Gray's Anatomy / standard human physiology
• Digested fats are absorbed into the lacteals, the lymphatic capillaries within the intestinal villi, and travel in lymph rather than entering the portal blood directly.Gray's Anatomy
• The retroperitoneal structures include the kidneys and adrenal glands, the pancreas, the abdominal aorta and inferior vena cava, most of the duodenum, and the ascending and descending colon.Gray's Anatomy
• The visceral peritoneum and abdominal organs carry autonomic innervation, producing dull, poorly localized pain, while the parietal peritoneum carries somatic innervation, producing sharp, well-localized pain, which is why pain in appendicitis migrates and localizes.Gray's Anatomy / AAOS Emergency Care and Transportation of the Sick and Injured
• Esophageal varices arise from portal hypertension in chronic liver disease, in which obstructed portal flow forces blood through collateral veins in the esophageal wall until they distend and rupture.AAOS Emergency Care and Transportation of the Sick and Injured

Urinary

• The kidneys receive roughly 20 to 25 percent of cardiac output, far out of proportion to their size, because their job is to process blood rather than merely be fed by it.Standard anatomy and physiology reference (Marieb, Human Anatomy & Physiology, renal physiology)
• Each kidney contains about one million nephrons, the functional filtering units.Standard anatomy and physiology reference (Marieb, Human Anatomy & Physiology)
• The kidneys filter about 180 liters of fluid per day and reabsorb more than 99 percent of it, producing roughly 1 to 2 liters of urine daily.Standard anatomy and physiology reference (Marieb, Human Anatomy & Physiology; Guyton & Hall Textbook of Medical Physiology)
• Adequate adult urine output is about 0.5 mL per kilogram per hour, roughly 30 mL per hour; less than that signals poor renal perfusion.American College of Surgeons, Advanced Trauma Life Support (ATLS) urine-output benchmark
• Maintenance hemodialysis is typically performed three times a week for about three to four hours per session; missing a session allows fluid, potassium and wastes to accumulate.National Kidney Foundation / KDOQI hemodialysis adequacy guidelines
• Normal serum potassium is about 3.5 to 5.0 mEq/L, and severe hyperkalemia causes weakness, bradycardia, dysrhythmia and cardiac arrest.American Heart Association ACLS guidance on hyperkalemia; standard clinical laboratory reference ranges
• The kidneys secrete erythropoietin, so chronic kidney failure causes anemia, and they activate vitamin D, so chronic failure also causes calcium and bone disease.National Kidney Foundation; standard anatomy and physiology reference (Marieb)
• The female urethra is roughly 4 cm long compared with about 20 cm in the male, which is a main reason urinary tract infections are far more common in women.Standard anatomy and physiology reference (Marieb, Human Anatomy & Physiology)
• A first episode of apparent renal colic in a patient over 50 should raise suspicion for a leaking abdominal aortic aneurysm, which can mimic stone pain exactly.Rosen's Emergency Medicine: Concepts and Clinical Practice (AAA presenting as renal colic)
• Urinary tract infection is among the most common sources of sepsis in older adults, and in the elderly it may present as new confusion, weakness or a fall without fever or dysuria.Infectious Diseases Society of America guidance; CDC healthcare-associated infection guidance for older adults

Endocrine

• The adrenal medulla is functionally an extension of the sympathetic nervous system, releasing epinephrine and norepinephrine directly into the blood so the fight-or-flight response acts within seconds.Standard anatomy and physiology reference (Marieb, Human Anatomy & Physiology; Guyton & Hall Textbook of Medical Physiology)
• Type 1 diabetes results from autoimmune destruction of the pancreatic beta cells, leaving no endogenous insulin, while type 2 arises from insulin resistance with relative insulin deficiency.American Diabetes Association Standards of Care in Diabetes (classification and diagnosis)
• Antidiuretic hormone is released from the posterior pituitary and makes the kidney reabsorb water; its absence causes diabetes insipidus, with large volumes of dilute urine and intense thirst.Standard anatomy and physiology reference (Marieb, Human Anatomy & Physiology)
• Thyroid storm is a life-threatening extreme of hyperthyroidism, typically with fever often above 104°F (40°C), marked tachycardia or atrial fibrillation, agitation and altered mental status.American Thyroid Association guidelines for the diagnosis and management of hyperthyroidism and thyrotoxicosis
• Myxedema coma is the extreme of hypothyroidism, marked by hypothermia, bradycardia, hypoventilation and depressed mental status.American Thyroid Association guidelines for the treatment of hypothyroidism
• Adrenal crisis in a patient on long-term corticosteroids presents with weakness, vomiting, abdominal pain, hypoglycemia and hypotension that does not respond well to fluids alone.Endocrine Society Clinical Practice Guideline on primary adrenal insufficiency
• Glucagon from pancreatic alpha cells raises blood glucose by driving the liver to break down stored glycogen; epinephrine and cortisol raise it too, which is why stress and injury can elevate a reading.Standard anatomy and physiology reference (Guyton & Hall Textbook of Medical Physiology)
• Cerebral edema is a rare but leading cause of death in pediatric diabetic ketoacidosis, which is one reason correction of DKA is done carefully in hospital rather than rushed.American Diabetes Association Standards of Care in Diabetes (hyperglycemic crises)

Lymphatic

• Roughly 3 liters of fluid per day is returned from the tissues to the bloodstream as lymph, entering the venous circulation through the thoracic duct and the right lymphatic duct near the subclavian veins.Standard anatomy and physiology reference (Marieb, Human Anatomy & Physiology; Guyton & Hall Textbook of Medical Physiology)
• The lymphatic system has no pump; lymph is moved by skeletal muscle contraction, respiratory pressure changes and one-way valves in the lymph vessels.Standard anatomy and physiology reference (Marieb, Human Anatomy & Physiology)
• T lymphocytes mature in the thymus and B lymphocytes mature in the bone marrow; neutrophils are the most numerous circulating white blood cell, and normal adult white cell count is about 4,500 to 11,000 per microliter.Standard anatomy and physiology reference (Marieb) and standard clinical laboratory reference ranges
• Lacteals are specialized lymphatic vessels in the lining of the small intestine that absorb digested fat and deliver it into the bloodstream through the lymphatic circulation.Standard anatomy and physiology reference (Marieb, Human Anatomy & Physiology)
• Sepsis is defined as life-threatening organ dysfunction caused by a dysregulated host response to infection; the qSOFA screen flags altered mentation, respiratory rate of 22 or more, and systolic blood pressure of 100 mmHg or less.Sepsis-3 consensus definitions (JAMA 2016) and the Surviving Sepsis Campaign guidelines
• Anaphylaxis requires a prior sensitizing exposure: IgE antibodies made on first contact are parked on mast cells and basophils, and re-exposure triggers mass degranulation with histamine release.NIAID/AAAAI anaphylaxis practice parameters
• Febrile seizures occur mainly in children between about 6 months and 5 years of age, triggered by the rise in temperature rather than by the absolute number.American Academy of Pediatrics clinical practice guideline on febrile seizures
• Patients without a functioning spleen are at risk of overwhelming post-splenectomy infection from encapsulated bacteria such as pneumococcus, which can progress from mild illness to fulminant sepsis within hours.CDC vaccination recommendations for asplenic patients; Infectious Diseases Society of America guidance
• Fever in a neutropenic patient, such as someone on chemotherapy, is a medical emergency requiring urgent evaluation and antibiotics even when the patient appears well.Infectious Diseases Society of America guideline on fever and neutropenia

Reproductive

• A woman's circulating blood volume increases by roughly 45 percent by the end of pregnancy.AAOS Emergency Care and Transportation of the Sick and Injured (obstetrics — anatomy and physiology of pregnancy)
• Maternal resting heart rate rises about 10 to 20 beats per minute during pregnancy, and blood pressure often runs slightly lower than baseline in mid-pregnancy.AAOS Emergency Care and Transportation of the Sick and Injured; ACOG guidance on normal pregnancy physiology
• A pregnant patient can lose 30 to 35 percent of her blood volume before her blood pressure falls.AAOS Emergency Care and Transportation of the Sick and Injured (trauma in pregnancy)
• Pregnancy lasts about 40 weeks in three trimesters; the third trimester begins at about 28 weeks.ACOG — normal pregnancy duration and trimesters
• By about 20 weeks of pregnancy the top of the uterus, the fundus, reaches the level of the navel.AAOS Emergency Care and Transportation of the Sick and Injured (assessing the pregnant patient)
• The umbilical cord contains two arteries, which carry oxygen-poor blood from the fetus to the placenta, and one vein, which carries oxygen-rich blood to the fetus.AAOS Emergency Care and Transportation of the Sick and Injured (obstetrics)
• At term, roughly 500 to 700 mL of blood flows through the uterus each minute, which is why postpartum bleeding can be so rapid.ACOG — uteroplacental blood flow at term / postpartum hemorrhage guidance
• Preeclampsia is defined by a blood pressure of 140/90 mm Hg or higher after 20 weeks of pregnancy, with findings such as headache, visual changes, and swelling.ACOG — Gestational Hypertension and Preeclampsia
• Eclamptic seizures can occur before labor, during labor, or after delivery, including days to weeks postpartum.ACOG — Gestational Hypertension and Preeclampsia
• Breastfeeding releases oxytocin, which contracts the uterus and helps control postpartum bleeding.ACOG — postpartum hemorrhage management
• Free blood under the diaphragm can refer pain to the tip of the shoulder, a clue to intra-abdominal hemorrhage such as a ruptured ectopic pregnancy.AAOS Emergency Care and Transportation of the Sick and Injured (abdominal and gynecologic emergencies)
• When a late-pregnancy patient must remain supine, displace the uterus to the patient's left — a 15 to 30 degree left tilt of the board, or manual left uterine displacement — including during CPR in maternal cardiac arrest.AHA 2020 Guidelines for CPR and ECC — cardiac arrest in pregnancy
• Testicular torsion is a time-critical surgical emergency; the twisted cord cuts off the testicle's blood supply and the organ can be lost within hours.AAOS Emergency Care and Transportation of the Sick and Injured (genitourinary emergencies)

How the systems work together

• An average adult carries roughly 5 liters of blood, about 70 mL per kilogram of body weight.AAOS Emergency Care and Transportation of the Sick and Injured (circulatory system and shock)
• A healthy adult can lose about 15 percent of blood volume, roughly 750 mL, with minimal signs, and blood pressure typically does not fall until about 30 percent is lost.AAOS Emergency Care and Transportation of the Sick and Injured (hemorrhage classification and shock)
• Brain cells begin to die after roughly 4 to 6 minutes without oxygen, which is why airway and breathing outrank everything else.AAOS Emergency Care and Transportation of the Sick and Injured (airway management)
• Bradycardia in an infant or child is presumed to be caused by hypoxia until proven otherwise, and is treated with oxygenation and ventilation first.AHA 2020 Guidelines for CPR and ECC — Pediatric Basic and Advanced Life Support
• Beta blockers such as metoprolol blunt the sympathetic response, so a patient taking one may not develop the expected tachycardia in shock.AHA — beta-adrenergic blocker pharmacology; AAOS Emergency Care and Transportation of the Sick and Injured (pharmacology and geriatric patients)
• Maximum attainable heart rate declines with age, commonly estimated as 220 minus the patient's age in years, which limits how much an older patient can compensate.AHA — target and maximum heart rate estimation
• Adequate adult urine output is roughly 30 to 50 mL per hour; a fall below that is an early sign of poor renal perfusion.AAOS Emergency Care and Transportation of the Sick and Injured (perfusion and the urinary system)
• Chronically hypertensive patients perfuse at higher baseline pressures, so a 'normal' reading can represent significant relative hypotension for that patient.AHA/ACC blood pressure guidance; AAOS Emergency Care and Transportation of the Sick and Injured (geriatric patients)
• Cellular failures such as cyanide poisoning and severe sepsis stop the cell from using delivered oxygen, so saturation and delivery can look adequate while the tissue starves.AAOS Emergency Care and Transportation of the Sick and Injured (toxicology and shock)

Vital organs

Solid vs hollow, what each organ does, and what failure looks like.

Heart

• An adult heart is about the size of the owner's fist and weighs roughly 250 to 350 grams.Gray's Anatomy for Students (thorax: the heart)
• At rest an adult heart moves roughly 5 liters a minute — about 70 mL per beat times about 70 beats a minute.AHA / Gray's Anatomy for Students (cardiac output)
• The coronary arteries arise from the aortic root just above the aortic valve, and coronary blood flow occurs mainly during diastole because systolic contraction compresses the intramural vessels.Gray's Anatomy for Students / AHA coronary circulation
• The left ventricular wall is roughly three times thicker than the right ventricular wall, because it pumps against systemic rather than pulmonary resistance.Gray's Anatomy for Students (chambers of the heart)
• The pericardial sac normally contains only a small amount of clear fluid, about 25 mL; acutely, as little as 100 to 150 mL of blood in the sac can produce tamponade, because the fibrous layer cannot stretch quickly.AAOS Emergency Care and Transportation of the Sick and Injured / Gray's Anatomy
• Commotio cordis is ventricular fibrillation produced by a blunt blow landing in a vulnerable window of roughly 10 to 30 milliseconds on the upstroke of the T wave, in a structurally normal heart.AHA scientific statement on commotio cordis
• The heart's normal pacemaker, the SA node, fires at 60 to 100 a minute; the AV junction escapes at 40 to 60, and ventricular sites at 20 to 40.AAOS Emergency Care and Transportation of the Sick and Injured
• The brain has only about 4 to 6 minutes of reserve before cells begin to die once perfusion stops.AHA Guidelines for CPR and ECC / AAOS Emergency Care and Transportation

Lungs

• The right lung has three lobes and the left has two, the left being smaller because of the cardiac notch.Gray's Anatomy for Students (thorax: the lungs)
• The apex of each lung extends about 2 to 3 cm above the medial third of the clavicle, so wounds at the root of the neck can enter the pleural space.Gray's Anatomy for Students (pleural cavities)
• The right main bronchus is wider, shorter and more vertical than the left — roughly 25 degrees from the midline versus about 45 degrees — so aspirated material and over-inserted endotracheal tubes preferentially enter the right lung.Gray's Anatomy for Students (tracheobronchial tree)
• There are roughly 300 million alveoli in an adult, giving a gas-exchange surface of about 70 square meters, with an alveolar-capillary membrane about one cell thick.Gray's Anatomy / AAOS Emergency Care and Transportation of the Sick and Injured
• The pleural space normally contains only a few milliliters of serous fluid, and the pressure within it is slightly below atmospheric, which is what holds the lung expanded against the chest wall.Gray's Anatomy for Students (pleura and pleural cavities)
• A massive hemothorax is defined as 1,500 mL or more of blood in one pleural space, roughly a third of an adult's total blood volume.AAOS Emergency Care and Transportation of the Sick and Injured / ATLS

Brain

• Normal intracranial pressure in an adult is roughly 5 to 15 mmHg.AAOS Emergency Care & Transportation of the Sick and Injured
• Cerebral perfusion pressure equals mean arterial pressure minus intracranial pressure, which is why a rise in pressure inside the skull or a fall in arterial pressure both reduce blood flow to brain tissue.AAOS Emergency Care & Transportation of the Sick and Injured
• In severe traumatic brain injury, a single episode of prehospital hypotension with a systolic pressure below 90 mmHg is associated with roughly a doubling of mortality, and hypoxia occurring with it worsens outcome further.AAOS Emergency Care & Transportation (Brain Trauma Foundation prehospital guidelines)
• The adult brain weighs about three pounds, roughly 1,300 to 1,400 grams.Gray's Anatomy for Students
• Head-injured patients are commonly transported with the head of the cot or board raised about 30 degrees when local protocol and spinal precautions allow it.AAOS Emergency Care & Transportation of the Sick and Injured

Liver

• The adult liver weighs roughly three pounds, about 1.4 kilograms, and is the largest solid organ in the body.Gray's Anatomy for Students
• The liver lies deep to the right seventh through eleventh ribs and extends across the midline into the left upper quadrant.Gray's Anatomy for Students
• The liver has a dual blood supply and receives roughly a quarter of the cardiac output; the portal vein provides about three quarters of that flow and the hepatic artery the rest.Gray's Anatomy for Students
• Vitamin K, absorbed from the gut along with fat and bile, is required for the liver to assemble several clotting factors.Gray's Anatomy for Students
• In children the liver is proportionally larger and the rib cage more flexible, so blunt abdominal force reaches it more readily than in adults.AAOS Emergency Care & Transportation of the Sick and Injured
• Hypothermia impairs clotting, so preventing heat loss is part of hemorrhage care in the field.AAOS Emergency Care & Transportation of the Sick and Injured

Spleen

• The spleen lies in the left upper quadrant behind the stomach, deep to the ninth through eleventh ribs, and is normally about the size of the patient's own fist.Gray's Anatomy for Students
• The spleen holds roughly a third of the body's circulating platelets and acts as a reservoir of blood.Gray's Anatomy for Students
• Red blood cells circulate for about four months before the spleen and liver remove them and recycle the iron.Gray's Anatomy for Students
• The spleen is supplied by the splenic artery, a branch of the celiac trunk off the abdominal aorta, and is therefore engorged with blood at all times.Gray's Anatomy for Students
• The spleen and the liver are the abdominal organs most frequently injured by blunt trauma, and splenic injury is classically associated with fractures of the left lower ribs.AAOS Emergency Care & Transportation of the Sick and Injured
• A subcapsular splenic hematoma can rupture hours to days after the original impact, which is known as delayed splenic rupture.AAOS Emergency Care & Transportation of the Sick and Injured
• A spleen enlarged by mononucleosis, leukemia or other illness can rupture from minimal force, which is why contact sports are restricted in those patients.AAOS Emergency Care & Transportation of the Sick and Injured
• Patients without a functioning spleen face a lifelong risk of overwhelming infection from encapsulated bacteria such as pneumococcus, and are routinely vaccinated against them.AAOS Emergency Care & Transportation of the Sick and Injured
• In sickle cell disease the spleen can suddenly trap a large share of the blood volume, called splenic sequestration, producing hypovolemic shock in a child with no external bleeding.AAOS Emergency Care & Transportation of the Sick and Injured

Kidneys

• The kidneys are retroperitoneal, lying beside the spine from roughly the twelfth thoracic to the third lumbar vertebra, with their upper poles behind the eleventh and twelfth ribs; the right kidney sits slightly lower because the liver lies above it.Gray's Anatomy for Students
• Each kidney is surrounded by a layer of perirenal fat and a fibrous fascia, which is part of why kidney bleeding tends to stay contained in the flank.Gray's Anatomy for Students
• The kidneys receive roughly twenty to twenty-five percent of the cardiac output.Gray's Anatomy for Students
• The kidneys filter about 180 liters of fluid per day and reabsorb nearly all of it, producing about one to two liters of urine.Gray's Anatomy for Students
• The kidney releases erythropoietin, the hormone that signals bone marrow to produce red blood cells, which is why chronic kidney failure causes anemia.Gray's Anatomy for Students
• Blood in the urine after kidney trauma is often microscopic, and some serious kidney injuries produce no blood in the urine at all.AAOS Emergency Care & Transportation of the Sick and Injured
• Blood at the urethral opening suggests urethral injury and is a contraindication to urinary catheterization.AAOS Emergency Care & Transportation of the Sick and Injured

Pancreas

• The pancreas is retroperitoneal, lying across the upper abdomen at roughly the first and second lumbar vertebrae, with its head in the curve of the duodenum and its tail reaching the spleen; it is about six inches long in an adult.Gray's Anatomy for Students
• The pancreatic duct and the common bile duct join and drain through a single opening into the duodenum, which is why one gallstone can obstruct both.Gray's Anatomy for Students
• Pancreatic protein-digesting enzymes are secreted as inactive precursors and are normally activated only after they reach the small intestine.Gray's Anatomy for Students
• The islets of Langerhans make up only a small fraction of the pancreas by mass; beta cells release insulin and alpha cells release glucagon.Gray's Anatomy for Students
• Gallstones and alcohol account for the large majority of cases of acute pancreatitis.AAOS Emergency Care & Transportation of the Sick and Injured
• Acute pancreatitis can sequester liters of fluid in the retroperitoneum and bowel, producing hypovolemic shock with no external blood loss.AAOS Emergency Care & Transportation of the Sick and Injured
• Handlebar and steering-wheel mechanisms compress the pancreas against the vertebral column, and the resulting injury is often occult for hours.AAOS Emergency Care & Transportation of the Sick and Injured
• Chronic pancreatitis and pancreatic surgery can destroy enough islet tissue to cause diabetes.American Diabetes Association Standards of Care

Stomach

• An adult stomach comfortably holds roughly one to one and a half liters and can distend to about four liters.Gray's Anatomy for Students
• The stomach secretes hydrochloric acid, and resting gastric contents sit at a pH of roughly 1.5 to 3.5.Gray's Anatomy for Students
• The stomach protects itself with a bicarbonate-rich mucus layer, and most peptic ulcers are caused by Helicobacter pylori infection or by nonsteroidal anti-inflammatory drug use.AAOS Emergency Care & Transportation of the Sick and Injured
• A normal meal generally empties from the stomach over about two to four hours, so a recent meal is still an aspiration risk well after eating.Gray's Anatomy for Students
• Bag-mask ventilations should be delivered over about one second with only enough volume to produce visible chest rise, because faster or larger breaths force air into the stomach and provoke vomiting.American Heart Association 2020 Guidelines for CPR and ECC
• The stomach produces intrinsic factor, the substance required for absorption of vitamin B12 further down the small intestine.Gray's Anatomy for Students

Intestines

• The small intestine is roughly 20 feet long in an adult and the large intestine roughly 5 feet.AAOS Emergency Care & Transportation of the Sick and Injured
• Folds, villi and microvilli give the small intestine an absorptive surface on the order of 200 square meters, roughly the area of a tennis court.Gray's Anatomy for Students
• McBurney's point lies about one third of the distance along a line from the right anterior superior iliac spine toward the umbilicus.Gray's Anatomy for Students
• Adhesions from previous abdominal surgery are the most common cause of small bowel obstruction in adults, followed by hernias and tumors.AAOS Emergency Care & Transportation of the Sick and Injured
• Appendicitis commonly progresses over about 12 to 24 hours, and perforation becomes increasingly likely after roughly 24 to 36 hours of symptoms.AAOS Emergency Care & Transportation of the Sick and Injured
• Roughly one to one and a half liters of watery material enters the colon each day, and all but about 100 to 200 milliliters of water is reabsorbed before the residue is passed.Gray's Anatomy for Students

Gallbladder

• The gallbladder holds roughly 30 to 50 milliliters of concentrated bile.Gray's Anatomy for Students
• The liver produces about 500 to 1,000 milliliters of bile per day, which the gallbladder stores and concentrates between meals.Gray's Anatomy for Students
• Bile emulsifies fat rather than digesting it chemically, breaking large globules into small droplets so that enzymes have far greater surface area to act on.Gray's Anatomy for Students
• The gallbladder contracts in response to cholecystokinin, a hormone released by the duodenum when fat and protein arrive from the stomach.Gray's Anatomy for Students
• Gallstones are present in roughly 10 to 15 percent of adults in the United States, and most never cause symptoms.AAOS Emergency Care & Transportation of the Sick and Injured
• Gallstones are about two to three times more common in women than in men, which is the basis of the classic fair, fat, forty, female description.AAOS Emergency Care & Transportation of the Sick and Injured
• An episode of biliary colic typically starts within a few hours of a fatty meal and lasts from about 30 minutes to several hours before easing.AAOS Emergency Care & Transportation of the Sick and Injured

Bladder

• The first urge to urinate is typically felt at roughly 150 to 300 milliliters, and comfortable adult bladder capacity is about 400 to 600 milliliters.Gray's Anatomy for Students
• An empty bladder lies entirely within the bony pelvis below the peritoneum, but as it fills it rises above the pubic bone into the lower abdomen where it is no longer shielded by bone.Gray's Anatomy for Students
• The bladder wall is smooth muscle called the detrusor, and the outlet is guarded by an internal sphincter of smooth muscle under involuntary control and an external sphincter of skeletal muscle under voluntary control.Gray's Anatomy for Students
• The large majority of traumatic bladder ruptures occur together with a pelvic fracture, and bladder injury should be suspected whenever the pelvis is broken.AAOS Emergency Care & Transportation of the Sick and Injured
• A fractured pelvis can bleed several liters into the retroperitoneal space, which is enough to cause fatal shock with no external blood loss visible.AAOS Emergency Care & Transportation of the Sick and Injured
• In men the urethra passes through the prostate, and benign enlargement of the prostate is the most common cause of urinary retention in older men.AAOS Emergency Care & Transportation of the Sick and Injured
• Urinary tract infection is a common cause of new confusion in elderly patients and may present without fever or any urinary complaint, and the urinary tract is a leading source of sepsis in older adults.AAOS Emergency Care & Transportation of the Sick and Injured

Aorta

• The aortic arch gives three branches: the brachiocephalic trunk, which divides into the right common carotid and right subclavian arteries, then the left common carotid and the left subclavian.Gray's Anatomy for Students (thorax: the aorta)
• The aorta passes through the diaphragm at the aortic hiatus at about the level of the twelfth thoracic vertebra and divides into the common iliac arteries at about the fourth lumbar vertebra, roughly the level of the umbilicus.Gray's Anatomy for Students (abdominal aorta)
• The aortic wall has three layers — the intima, the media and the adventitia; a dissection begins as a tear in the intima that lets blood track within the media.Gray's Anatomy / ACC-AHA Guideline for the Diagnosis and Management of Aortic Disease
• A normal adult abdominal aorta is roughly 2 centimeters across; an abdominal aortic aneurysm is defined at 3 centimeters or more, and rupture risk climbs steeply above about 5.5 centimeters.ACC/AHA Guideline for the Diagnosis and Management of Aortic Disease
• A systolic blood pressure difference of more than about 20 mmHg between the arms is a recognized red flag for aortic dissection.ACC/AHA Guideline for the Diagnosis and Management of Aortic Disease
• In blunt deceleration trauma the aorta most often tears at the isthmus, just distal to the left subclavian artery near the ligamentum arteriosum, where the vessel is tethered.AAOS Emergency Care and Transportation of the Sick and Injured / ATLS
• The great majority of patients with a complete traumatic aortic rupture die before reaching the hospital; survivors typically have a contained tear.AAOS Emergency Care and Transportation of the Sick and Injured
• The aorta carries the entire cardiac output, roughly 5 liters a minute in a resting adult.AHA / Gray's Anatomy for Students (cardiac output)

Diaphragm

• The diaphragm performs the majority of the work of quiet breathing, roughly 70 percent, with the intercostal muscles supplying the rest.Gray's Anatomy for Students (thoracic wall and mechanics of breathing)
• In quiet breathing the diaphragm descends about 1 to 2 cm, and up to about 7 to 10 cm with deep breathing.Gray's Anatomy for Students (diaphragm)
• Normal adult tidal volume is roughly 500 mL per breath, about 5 to 7 mL per kilogram.AAOS Emergency Care and Transportation of the Sick and Injured
• On full exhalation the dome of the diaphragm rises to about the level of the fourth or fifth intercostal space, roughly the nipple line, so wounds between the nipples and the costal margin may involve both the thoracic and abdominal cavities.Gray's Anatomy / AAOS Emergency Care and Transportation of the Sick and Injured
• Three structures pass through the diaphragm: the inferior vena cava at about T8, the esophagus at about T10 and the aorta at about T12.Gray's Anatomy for Students (diaphragm openings)
• Traumatic diaphragmatic rupture occurs far more often on the left, because the liver shields and buffers the right hemidiaphragm.AAOS Emergency Care and Transportation of the Sick and Injured / ATLS
• Referred pain from diaphragmatic irritation reaches the shoulder tip because the phrenic nerve and the skin over the shoulder share the C3 to C5 nerve roots — the basis of Kehr's sign.Gray's Anatomy for Students (referred pain and the phrenic nerve)
• A hiccup is an involuntary spasm of the diaphragm followed by sudden closure of the vocal cords.Gray's Anatomy for Students
• Each assisted or rescue breath is delivered over about 1 second, using just enough volume to produce visible chest rise, which limits gastric inflation.AHA Guidelines for CPR and ECC (Adult and Pediatric BLS)

Surface landmarks

• The adult chest has twelve pairs of ribs. Pairs one through seven attach directly to the sternum, pairs eight through ten attach to the cartilage above them, and pairs eleven and twelve are floating, with no attachment in front.Gray's Anatomy for Students, 4th edition (thoracic wall); AAOS Emergency Care and Transportation of the Sick and Injured, 12th edition (the musculoskeletal system)
• On full exhalation the dome of the diaphragm rises to about the level of the nipples, the fourth intercostal space anteriorly, so a penetrating wound between the nipple line and the navel must be treated as both a chest and an abdominal injury.AAOS Emergency Care and Transportation of the Sick and Injured, 12th edition (abdominal and genitourinary injuries)
• Appendicitis classically begins as dull pain near the navel and migrates to the right lower quadrant over roughly twelve to twenty-four hours as the inflammation reaches the parietal peritoneum.AAOS Emergency Care and Transportation of the Sick and Injured, 12th edition (gastrointestinal emergencies)
• Flank bruising from retroperitoneal bleeding typically takes hours to days to appear, so its absence in the prehospital window never rules out a retroperitoneal bleed.AAOS Emergency Care and Transportation of the Sick and Injured, 12th edition (abdominal and genitourinary injuries)
• The retroperitoneal structures are the kidneys and adrenal glands, the ureters, most of the pancreas, the second through fourth parts of the duodenum, the ascending and descending colon, and the abdominal aorta with the inferior vena cava.Gray's Anatomy for Students, 4th edition (abdomen: the peritoneal cavity and retroperitoneum)
• The liver is the largest solid organ in the abdomen, occupying most of the right upper quadrant and extending across the midline into the left upper quadrant.Gray's Anatomy for Students, 4th edition (abdomen: the liver)