Rapid Review·Cardiovascular
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HY Approach
T1Must knowApproach to Shock
Focus on
Shock is inadequate tissue perfusion, not a blood pressure number. Four mechanisms with four hemodynamic signatures — low preload (hypovolemic), pump failure (cardiogenic), low resistance (distributive), and blocked flow (obstructive) — each with its own first move. Neck veins, skin temperature and the lungs sort them at the bedside.
Key takeaways
What shock is
Definition
oxygen delivery below tissue demand, with anaerobic metabolism, a rising lactate and organ dysfunction.Hypotension is late
a systolic blood pressure (SBP) under 90 or mean arterial pressure (MAP) under 65 is common but late.The early signs
tachycardia, altered mentation, cool mottled skin, delayed capillary refill, oliguria (under 0.5 mL/kg/h) and lactate over 2 mmol/L.Compensated shock
normal pressure with tachycardia and vasoconstriction precedes collapse, especially in the young.The equation
MAP = cardiac output x systemic vascular resistance (SVR); every type of shock lowers one of the two.| Type | Cardiac output | SVR | Filling pressure (CVP / PCWP) | Bedside clues | First corrective move | Page |
|---|---|---|---|---|---|---|
| Hypovolemic / hemorrhagic | Low | High | Low / low | Flat neck veins, cool clammy skin, history of loss | Stop the bleeding; blood for hemorrhage, crystalloid for other losses | Hypovolemic & Hemorrhagic Shock |
| Cardiogenic | Low | High | High / high | JVD, pulmonary edema, S3, cold extremities, ischemia | Reperfusion, inotropes and vasopressors, mechanical support; no blind fluids | Cardiogenic Shock |
| Distributive (septic, anaphylactic, neurogenic) | High early, low late | Low | Low or normal | Warm flushed skin, wide pulse pressure, bounding pulses; fever, allergen or spinal injury | Fluids, then norepinephrine (septic) or epinephrine (anaphylaxis); treat the cause | Distributive Shock, Anaphylactic Shock |
| Obstructive | Low | High | High CVP with low PCWP (PE, tension pneumothorax) or equalized (tamponade) | JVD with clear lungs, absent breath sounds, pulsus paradoxus | Relieve the obstruction: decompress, drain or lyse | Obstructive Shock |
Sorting shock at the bedside
A sequence, not a number
work through the signs in order.- Neck veins: flat means hypovolemic or distributive; distended means cardiogenic or obstructive.
- Skin: warm means distributive; cold means everything else.
- Lungs: crackles mean cardiogenic; clear lungs with jugular venous distension (JVD) mean pulmonary embolism (PE), tamponade or tension pneumothorax; one silent hemithorax means tension pneumothorax.
- Point-of-care ultrasound: B-lines (pulmonary edema) versus absent lung sliding (pneumothorax); effusion with chamber collapse (tamponade); dilated right ventricle (massive PE); poor left-ventricular squeeze (cardiogenic); small hyperdynamic left ventricle (hypovolemia or distributive).
- Inferior vena cava: collapsing means low preload; plethoric means high right-sided pressure.
Invasive numbers
a high pulmonary capillary wedge pressure (PCWP) is left-sided pump failure; low is hypovolemia or distributive; high central venous pressure (CVP) with low PCWP is obstruction before the left heart.Mixed venous oxygen saturation
high is distributive (tissues cannot extract); low is every low-output state.Treat the time-critical cause while confirming
Hemorrhage
stop the bleeding and transfuse.Sepsis
antibiotics within the hour.Anaphylaxis
intramuscular epinephrine.Tension pneumothorax
decompress.Tamponade
drain.Massive PE
thrombolysis.Infarction with shock
catheterization laboratory.Adrenal crisis
hydrocortisone.Toxins
antidotes (Beta-Blocker Toxicity).Resuscitation principles
Access and oxygen
two large-bore intravenous lines (intraosseous if not obtainable) and oxygen.Fluid by mechanism (Approach to Fluid Replacement)
crystalloid boluses of 500 mL to 1 L, reassessed after each; blood for bleeding; small cautious boluses only in cardiogenic and obstructive shock.Drugs
norepinephrine is first line in most vasodilatory and undifferentiated shock; epinephrine for anaphylaxis and cardiac arrest; dobutamine or milrinone for low output with adequate pressure; vasopressin second in sepsis (Vasopressors & Inotropes).Targets
MAP of 65 or more, urine output of 0.5 mL/kg/h or more, clearing mentation, a falling lactate (recheck at 2 to 4 hours), capillary refill under 3 seconds.A hypotensive patient has warm, flushed skin, bounding pulses, flat neck veins and clear lungs; a catheter shows a high mixed venous saturation. What type of shock is this, and what are the first moves?
Distributive shock (warm skin, low SVR, high mixed venous saturation: the tissues cannot extract). Fluids, then norepinephrine (epinephrine if anaphylaxis), and treat the cause (antibiotics within the hour for sepsis).
How it's tested
A hypotensive trauma patient with cool skin and flat neck veins: hypovolemic until proven otherwise — find and stop the bleeding; a normal first hemoglobin means nothing.
Febrile patient with warm extremities, a wide pulse pressure and BP 80/40 after 2 L of crystalloid: septic shock — norepinephrine now, not more fluid.
Hypotension with distended neck veins: cardiogenic or obstructive. Crackles → LV failure; clear lungs → tamponade or PE; one silent hemithorax → tension pneumothorax.
Blood pressure now 100/60 after resuscitation but urine output 10 mL/h and lactate rising: still under-perfused — re-examine the mechanism and escalate.
Stem gives high CVP, low output, high SVR, low PCWP: obstruction before the left heart — PE or tension pneumothorax, not LV failure.
Go deeper
Guidelines: 2026 Surviving Sepsis Campaign Adult Guidelines · ACS Trauma Quality Programs Best Practices Guidelines
Related Step 2 pages: Hypovolemic & Hemorrhagic Shock, Cardiogenic Shock, Distributive Shock, Anaphylactic Shock, Obstructive Shock, Approach to Fluid Replacement, Vasopressors & Inotropes
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