Rapid Review·Cardiovascular
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PATHOLOGY
T1Must knowShock
FA P317
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Four shocks distinguished by four hemodynamic numbers.
Key takeaways
Reading the numbers
Shock
inadequate organ perfusion and nutrient delivery. Initially reversible, but life-threatening if not treated promptly.The unifying idea
CVP and PCWP give the filling pressures, SVR gives vessel tone, and SvO2 tells you whether tissue is extracting more oxygen than usual.| Type | Caused by | Skin | CVP | PCWP | CO | SVR | SvO2 |
|---|---|---|---|---|---|---|---|
| Hypovolemic | Hemorrhage, dehydration, burns | Cold, clammy | Low | Low | Low | High | Low |
| Cardiogenic | MI, heart failure, valvular disease, arrhythmia | Cold, clammy | High | High | Low | High | Low |
| Obstructive | PE, tension pneumothorax, tamponade | Cold, clammy | High | Low | Low | High | Low |
| Distributive | Sepsis (early), anaphylaxis, CNS injury | Warm, dry | Low | Low | High | Low | High |
| Feature | Cardiogenic | Obstructive |
|---|---|---|
| CVP | High | High |
| PCWP | High, the left heart is the problem | Low, blood cannot reach the left heart |
| Primary lesion | Pump failure | Mechanical obstruction to flow |
| Parameter | Distributive | All other shocks |
|---|---|---|
| Skin | WARM, dry | Cold, clammy |
| Cardiac output | High | Low |
| SVR | Low | High |
| SvO2 | High, from impaired extraction | Low |
Sepsis
Definitions
sepsis is organ dysfunction caused by infection; septic shock is sepsis with hemodynamic compromise and a lactate above 2 mmol/L despite adequate fluids. It can run hot or cold: a hypothermic presentation reflects cytokine disruption of hypothalamic temperature control and carries a worse prognosis.Why the tissue starves despite a high output
three failures stack.- Less oxygen delivered: capillary leak and vasodilation shrink the effective circulating volume, and ARDS lowers the PaO2.
- Less oxygen extracted: vasodilation shunts blood through organs too fast, edema widens the diffusion distance, and microthrombi block capillaries.
- Less oxygen used: reactive oxygen species damage mitochondria and the electron transport chain, so oxidative phosphorylation and ATP fall and lactate rises.
| System | What fails |
|---|---|
| CNS | Delirium ("septic encephalopathy") |
| Cardiovascular | Vasodilation and distributive shock, capillary leak, myocardial depression when severe |
| Pulmonary | Noncardiogenic pulmonary edema (ARDS) |
| Renal | Acute kidney injury (ATN) |
| Hematologic | DIC, acute marrow suppression (thrombocytopenia) |
| Endocrine | Glucose dysregulation, primary adrenal insufficiency |
| GI and hepatic | Cholestatic and hepatocellular injury, paralytic ileus |
| Neuromuscular | Polyneuropathy and myopathy |
A patient in shock has warm skin, a high cardiac output, and a low SVR. Which type, and why is the mixed venous oxygen high?
Distributive (early sepsis, anaphylaxis, CNS injury). Blood is shunted past the tissues and the mitochondria cannot use what arrives, so the oxygen comes back unextracted.
How it's tested
Distributive shock is the only one with warm skin, a high cardiac output, and a low systemic vascular resistance, while every other shock is cold and clammy with a low output, so the skin exam alone splits the table in two. When both cardiogenic and obstructive shock show a high central venous pressure, the wedge pressure separates them: high in cardiogenic because the left heart has failed, low in obstructive because blood never reaches it.
Go deeper
First Aid 2026 — CV/Pathology (p.317) · B&B — Shock · Mehlman — HY Cardio (shock hemodynamics, wedge pressure)
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