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This is a clinician-written, evidence-based summary aligned to the USMLE Step 2 CK Content Outline. It is intended for medical students preparing for USMLE Step 2 CK. Management reflects current ACC/AHA, USPSTF, and APA guidelines. Always cross-reference with UpToDate, institutional protocols, and clinical judgment.
The Bottom Line
- Shock = tissue hypoperfusion, not just hypotension; early signs include tachycardia, altered mentation, cool skin, oliguria, and elevated lactate.
- Four categories: hypovolemic, cardiogenic, distributive, obstructive.
- Septic/distributive shock: cultures, broad-spectrum antibiotics, 30 mL/kg crystalloid when hypoperfused, norepinephrine first-line vasopressor.
- Cardiogenic shock: avoid indiscriminate fluids; use vasopressors/inotropes and treat the cause.
- Obstructive shock requires mechanical relief: needle decompression, pericardiocentesis, thrombolysis/embolectomy, or other cause-specific intervention.
Overview
Shock is acute circulatory failure leading to inadequate oxygen delivery and cellular dysfunction. It may occur with normal blood pressure early because compensatory vasoconstriction maintains pressure while tissue perfusion is already impaired. Classification guides therapy: hypovolemic shock from fluid or blood loss; cardiogenic shock from pump failure; distributive shock from vasodilation and maldistributed flow; obstructive shock from impaired venous return, filling, or outflow.
Epidemiology
Shock is common in emergency and inpatient care and carries high mortality, especially with sepsis, trauma, massive hemorrhage, myocardial infarction, pulmonary embolism, and tamponade. Septic shock is among the most frequent causes of ICU admission. Trauma-related hemorrhagic shock is a leading preventable cause of death in younger adults.
Clinical Features
Symptoms
Weakness, lightheadedness, syncope, confusion, or sense of impending collapse
Chest pain or dyspnea suggesting MI, PE, tension pneumothorax, or tamponade
Fever, rigors, dysuria, cough, abdominal pain, or skin infection suggesting sepsis
Bleeding, trauma, vomiting, diarrhea, poor intake, or burns suggesting hypovolemia
Urticaria, wheeze, angioedema, or GI symptoms suggesting anaphylaxis
Signs
Hypotension, narrow pulse pressure, tachycardia, or bradycardia in late/preterminal shock
Altered mental status, cool clammy skin, delayed capillary refill, mottling, oliguria
Warm flushed skin and bounding pulses in early distributive shock
Elevated JVP in cardiogenic or obstructive shock; flat neck veins in hypovolemia
Unilateral absent breath sounds, muffled heart sounds, or pulsus paradoxus suggesting obstructive shock
Investigations
First-line
Bedside assessment and vital signsBP, HR, RR, SpO2, temperature, mental status, urine output, skin perfusion, and shock index.
Serum lactateElevated lactate reflects tissue hypoperfusion; repeat to assess response. Lactate >=4 mmol/L is high risk.
CBC, CMP, coagulation studies, blood gasEvaluate anemia, leukocytosis, renal/liver dysfunction, acidosis, electrolyte abnormalities, and coagulopathy.
ECG and troponinAssess MI, arrhythmia, right heart strain, hyperkalemia, and cardiogenic causes.
Second-line
Cultures and infection evaluationBlood cultures before antibiotics if this does not delay treatment; urinalysis, chest X-ray, and source-directed imaging.
Point-of-care ultrasoundRUSH/FAST: LV function, RV dilation, IVC, free fluid, pericardial effusion, pneumothorax, aortic aneurysm.
Chest X-rayPneumothorax, pneumonia, pulmonary edema, widened mediastinum, and line placement.
Specialist
Definitive imaging and monitoringCT angiography for PE/dissection, CT abdomen for source, echocardiography, arterial line, central access, or right heart catheterization in selected refractory shock.
1
Initial resuscitation
- Airway and oxygenation; intubate if unable to protect airway or severe respiratory failure.
- Two large-bore IVs or intraosseous access; place patient on monitor and obtain frequent blood pressure.
- Balanced crystalloid boluses for most hypovolemic/distributive shock; reassess after each bolus.
- Early vasopressors if hypotension persists during/after fluids or fluids are unsafe.
- Identify cause while resuscitating; treat life threats before all diagnostic results return.
2
Hypovolemic / hemorrhagic shock
- Control external bleeding with direct pressure, tourniquet, pelvic binder, or hemostatic dressing.
- Activate massive transfusion protocol for severe hemorrhage; balanced RBC:plasma:platelet resuscitation.
- Avoid excessive crystalloid in hemorrhagic shock because it worsens dilutional coagulopathy and hypothermia.
- Tranexamic acid within 3 hours of traumatic hemorrhage when indicated.
- Definitive control: surgery, interventional radiology, endoscopy, or obstetric management depending on source.
3
Distributive shock
- Septic shock: cultures if feasible, broad-spectrum antibiotics ideally within 1 hour for shock, and source control.
- Initial crystalloid 30 mL/kg for sepsis-induced hypoperfusion, then reassess fluid responsiveness.
- Norepinephrine is first-line vasopressor; add vasopressin or epinephrine if needed.
- Anaphylactic shock: IM epinephrine first, repeated as needed; fluids and airway support.
- Neurogenic shock: fluids plus vasopressors; atropine or pacing if severe bradycardia.
4
Cardiogenic and obstructive shock
- Cardiogenic shock: treat MI/arrhythmia/mechanical complication; norepinephrine for hypotension and inotrope for low output when BP tolerates.
- Tension pneumothorax: immediate decompression followed by chest tube.
- Cardiac tamponade with shock: urgent pericardiocentesis or surgical drainage.
- Massive PE with shock: systemic thrombolysis or embolectomy if no contraindication.
Complications
- Multi-organ dysfunction: AKI, liver injury, encephalopathy, ARDS, and coagulopathy from persistent hypoperfusion
- Cardiac arrest: Shock may progress to PEA or VF/pVT depending on cause
- DIC: Especially in sepsis, trauma, obstetric catastrophe, or malignancy
- Fluid overload: Pulmonary edema and abdominal compartment syndrome after excessive resuscitation
- Ischemic complications: Mesenteric, limb, myocardial, or cerebral ischemia
USMLE Step 2 CK Exam Tips
- 1Shock can exist with normal BP — altered mentation, cool extremities, oliguria, and lactate matter.
- 2Norepinephrine is first-line vasopressor for septic shock.
- 3Septic shock bundle: fluids, lactate, cultures, broad antibiotics, vasopressors, source control.
- 4Hemorrhagic shock in trauma = blood products and hemorrhage control, not liters of normal saline.
- 5Elevated JVP + hypotension + clear lungs suggests obstructive shock or RV infarct, not hypovolemia.
- 6Tension pneumothorax is a clinical diagnosis in unstable patients — decompress before chest X-ray.
- 7Cardiogenic shock after MI needs urgent revascularization plus hemodynamic support.
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