Cardiovascular Disorders and Hemodynamic Monitoring
Core concepts
Understand shock physiology by category: hypovolemic, cardiogenic, distributive (septic, neurogenic, anaphylactic), and obstructive (tamponade, tension pneumothorax, massive PE). Integrate physical exam, lactate, central venous oxygen saturation, and bedside ultrasound. Know the four shock states on the Forrester and pressure-based frameworks: cardiac output and systemic vascular resistance distinguish them. Master vasopressors (norepinephrine first-line for septic and most vasodilatory shock), inotropes (dobutamine, milrinone), and fluid responsiveness assessment (passive leg raise, pulse pressure variation). Recognize ECG patterns of STEMI, tamponade (electrical alternans, low voltage), and PE (S1Q3T3).
Traps
Central venous pressure is a poor predictor of fluid responsiveness - do not rely on a single number. In cardiogenic shock, aggressive fluids worsen pulmonary edema. In obstructive shock, the answer is often a procedure (pericardiocentesis, needle decompression) rather than a drug. Watch for the hypotensive patient on high-dose norepinephrine who actually needs an inotrope because of poor contractility.
Worked example
A patient after a large MI has BP 78/50, cool extremities, elevated JVP, and clear lungs. Echocardiogram shows a dilated, poorly contracting left ventricle. This is cardiogenic shock: low output, high SVR. Start norepinephrine to maintain perfusion pressure and add dobutamine or milrinone for inotropy; avoid large fluid boluses. Rule of thumb: cold and wet = cardiogenic (diurese, inotrope); warm and wet = distributive with capillary leak (vasopressor, cautious fluids).