About This Page
This is a clinician-written, evidence-based guide aligned to the MCC Examination Objectives. It is structured by clinical presentation — the way the MCCQE tests and the way patients actually present. Management reflects current Canadian guidelines (CMA, CFPC, CPS). Always cross-reference with institutional protocols and clinical judgment.
The Bottom Line
- Shock is inadequate tissue perfusion, not just low blood pressure — altered mentation, cool extremities, oliguria, high lactate, and mottling matter
- Manage ABCs immediately: oxygen, monitors, IV/IO access, glucose, ECG, fluids/blood when appropriate, vasopressors if persistent hypotension, and early source control
- Classify shock as hypovolemic, distributive, cardiogenic, obstructive, or mixed
- POCUS is high-yield in unstable patients: LV function, RV strain, pericardial effusion, IVC, pneumothorax, free fluid, and volume status clues
- For septic shock, obtain cultures and give broad-spectrum antibiotics early, measure lactate, provide fluid resuscitation, and use norepinephrine if hypotension persists
Approach to the Presentation
Shock is an emergency presentation. The MCCQE1 expects parallel processing: resuscitate while diagnosing. Start with airway, breathing, circulation, disability, and exposure. Place the patient on monitors, obtain IV/IO access, check glucose, give oxygen if hypoxic, order ECG, draw blood work/cultures when indicated, and activate help early. Use bedside clues: warm flushed shock suggests early sepsis or anaphylaxis; cold clammy shock suggests cardiogenic or late shock; flat JVP suggests hypovolaemia; distended neck veins suggest obstructive or cardiogenic shock. Treatment of reversible killers — tension pneumothorax, tamponade, massive haemorrhage, anaphylaxis, sepsis, and massive PE — must not wait for exhaustive testing.
Differential Diagnosis
| diagnosis | likelihood | key features | distinguishing test |
|---|---|---|---|
| Septic shock | must-not-miss | Infection source, fever or hypothermia, tachycardia, tachypnea, altered mentation, warm early/cold late shock, high lactate | Cultures, lactate, CBC, creatinine, source imaging; clinical diagnosis and treatment should not wait |
| Haemorrhagic shock | must-not-miss | Trauma, GI bleeding, ruptured ectopic, postpartum haemorrhage, ruptured AAA, anticoagulation, tachycardia, pallor | FAST/CT if stable, Hb trend, type and crossmatch; clinical recognition and massive transfusion if unstable |
| Cardiogenic shock | must-not-miss | Chest pain, pulmonary oedema, elevated JVP, cool extremities, new murmur, ECG ischemia/arrhythmia | ECG, troponin, POCUS/echo showing poor LV function or mechanical complication |
| Massive pulmonary embolism | must-not-miss | Sudden dyspnea, chest pain, syncope, hypoxia, tachycardia, VTE risk, elevated JVP, RV strain | CTPA if stable; POCUS RV dilation; treat unstable high-suspicion PE emergently |
| Cardiac tamponade | must-not-miss | Hypotension, JVP elevation, muffled heart sounds, pulsus paradoxus, malignancy/uremia/trauma/pericarditis | POCUS/echo: pericardial effusion with chamber collapse |
| Tension pneumothorax | must-not-miss | Severe dyspnea, unilateral absent breath sounds, hypotension, JVP elevation, trauma/ventilation | Clinical diagnosis; needle/finger decompression before imaging |
| Anaphylactic shock | must-not-miss | Acute allergen exposure, urticaria/angioedema, wheeze, GI symptoms, hypotension; skin signs may be absent | Clinical diagnosis; response to IM epinephrine supports |
| Neurogenic shock | less common | Spinal cord injury with hypotension, bradycardia, warm dry skin, neurological deficits | Clinical context and spinal imaging |
| Adrenal crisis | less common | Shock with abdominal pain, vomiting, hyponatraemia, hyperkalaemia, steroid withdrawal/Addison disease | Cortisol/ACTH if feasible, but do not delay hydrocortisone if unstable |
| Toxicologic shock | less common | Overdose, medication access, bradycardia/tachycardia, hypothermia/hyperthermia, altered mental status | ECG, glucose, acetaminophen/salicylate levels, toxidrome-based assessment |
Red Flags & Key History
Symptoms
Altered mental status, syncope, severe dyspnea, chest pain, or mottled/cool extremities
Fever, rigors, immunosuppression, indwelling catheter, recent procedure, or suspected infection source
Trauma, melena/hematemesis, vaginal bleeding, postpartum state, or ruptured AAA symptoms
Allergen exposure with airway, breathing, circulation, skin, or GI symptoms
Recent immobilisation/surgery, cancer, estrogen, pregnancy/postpartum
Steroid use or withdrawal, known adrenal disease, autoimmune disease
Signs
MAP <65, persistent SBP <90, lactate elevation, oliguria
Raised JVP with clear lungs — obstructive shock; raised JVP with pulmonary oedema — cardiogenic shock
Absent unilateral breath sounds or tracheal deviation
Peritonitis, uncontrolled bleeding, pelvic instability, ruptured AAA signs
Urticaria, angioedema, wheeze, stridor
Approach to Investigation
First-line
Continuous monitoring + ECG + point-of-care glucoseIdentify arrhythmia/ischemia, hypoglycaemia, and immediate reversible causes
CBC, electrolytes/creatinine, liver enzymes, coagulation, blood gas with lactateAssess perfusion, organ dysfunction, anaemia, acidosis, renal/liver involvement, and severity
Blood cultures before antibiotics if this does not delay therapySepsis workup; cultures should not delay antibiotics in shock
Type and screen/crossmatchIf bleeding, trauma, surgery, or possible transfusion
Second-line
POCUS/RUSH examCardiac contractility, pericardial effusion, RV strain, IVC, pneumothorax, abdominal free fluid, aorta, hydronephrosis, DVT
CXRPneumothorax, pneumonia, pulmonary oedema, line position; do not delay decompression of tension pneumothorax
Source-directed imagingCT abdomen/pelvis, CTPA, CTA aorta, ultrasound, or CT head only if stable enough or immediately management-changing
Specialist
ICU / anesthesia / emergency consultant involvementPersistent vasopressor requirement, respiratory failure, severe acidosis, multisystem organ dysfunction
Surgery / interventional radiology / cardiologySource control, haemorrhage control, PCI, pericardiocentesis, thrombectomy, or operative management
Management Principles
CAEP sepsis principles + Canadian ED sepsis guidance1
Universal shock actions
- Call for help, move to resuscitation area, continuous monitoring, two large-bore IVs or IO access
- Airway and oxygenation: high-flow oxygen if hypoxic; prepare for intubation if failing airway/ventilation
- Give isotonic crystalloid when hypovolaemia or distributive shock is likely; reassess after each bolus
- Start norepinephrine early if hypotension persists after fluids or if fluid overload/cardiogenic physiology limits fluid
2
Septic shock
- Measure lactate and repeat if elevated
- Obtain cultures, then give broad-spectrum antibiotics early
- Initial crystalloid resuscitation with frequent reassessment; individualise in HF/CKD
- Source control: drainage, surgery, catheter removal, imaging-guided intervention
3
Haemorrhagic shock
- Control bleeding with direct pressure, pelvic binder, tourniquet when appropriate, urgent endoscopy/IR/surgery/obstetrics
- Activate massive transfusion protocol for major bleeding
- Use balanced blood products, calcium monitoring/replacement, and tranexamic acid in appropriate trauma/postpartum contexts
4
Cardiogenic and obstructive shock
- Cardiogenic MI: ASA, urgent cardiology/cath lab activation, cautious fluids only if appropriate, vasopressor/inotrope support
- Tamponade: urgent pericardiocentesis
- Tension pneumothorax: immediate decompression then chest tube
- Massive PE: anticoagulation and consider systemic thrombolysis or thrombectomy when unstable
5
Anaphylactic shock
- IM epinephrine immediately, repeat every 5-15 minutes as needed, airway readiness, IV fluids, bronchodilators, adjunct antihistamines/steroids after epinephrine
Complications & Pitfalls
- Waiting for BP to fall: Shock can exist with normal BP if perfusion is poor and lactate is elevated.
- Delayed antibiotics/source control: In septic shock, cultures are important but must not delay treatment.
- Over-fluiding cardiogenic shock: Reassess frequently; pulmonary oedema and poor LV function require vasopressors/inotropes rather than repeated litres.
- Missing obstructive shock: Raised JVP with hypotension should trigger PE, tamponade, and tension pneumothorax thinking.
- Failure to give epinephrine: Antihistamines do not treat anaphylactic shock.
MCCQE1 Exam Tips
- 1Next best step in shock: ABCs, monitors, IV access, fluids/blood/vasopressors as indicated
- 2Warm shock = early sepsis/anaphylaxis; cold shock = cardiogenic or late shock, but mixed shock is common
- 3Tension pneumothorax and anaphylaxis are clinical diagnoses — treat immediately before confirmatory tests
- 4Septic shock bundle logic: lactate, cultures, broad-spectrum antibiotics, fluids, vasopressors, source control
- 5Norepinephrine is the first-line vasopressor for most distributive/septic shock scenarios
- 6POCUS distinguishes LV failure, tamponade, RV strain, IVC collapse, pneumothorax, and free fluid
- 7Adrenal crisis: shock plus hyponatraemia/hyperkalaemia/steroid history → give hydrocortisone
practicetest your knowledge on shock & hemodynamic instabilityApply what you've learnt with MCCQE1-style questions from the iatroX Q-Bank — general & constitutional and beyond.
open q-bank