Cardiovascular Disorders and Hemodynamic Monitoring
Shock framework
Classify shock as distributive, hypovolemic, cardiogenic, or obstructive, then confirm with bedside echocardiography: LV and RV size and function, pericardial effusion, IVC caliber, and lung B-lines. Norepinephrine is first-line for vasodilatory shock; target MAP ≥65 mmHg, individualizing upward in chronic hypertension or known cerebrovascular disease.
Monitoring
Static pressures - CVP and pulmonary artery occlusion pressure - correlate poorly with volume responsiveness, though extreme values retain meaning. Dynamic indices are better: pulse pressure variation and stroke volume variation, passive leg raise, and IVC respiratory variation. PPV is valid only with controlled ventilation at ≥8 mL/kg, sinus rhythm, no spontaneous effort, closed chest, and no significant RV failure. Lactate and capillary refill track resuscitation but clear slowly.
Tamponade and constriction
Tamponade shows a circumferential effusion, right atrial systolic collapse, RV diastolic collapse, respiratory variation in mitral and tricuspid inflow, and equalization of diastolic pressures. Constrictive pericarditis also equalizes pressures but produces a prominent y-descent and pericardial thickening without a large effusion.
Exam traps
- Treating a CVP number instead of the patient.
- Trusting PPV in atrial fibrillation or spontaneous breathing.
- Missing large v-waves from acute mitral regurgitation and misreading the wedge pressure.
- Attributing hypotension to hypovolemia in a patient with RV failure after cardiac surgery.
- Forgetting that high PEEP and auto-PEEP inflate wedge pressure.
Worked example
A ventilated patient with MAP 58, lactate 3.2, and PPV 18%: a 250–500 mL crystalloid challenge with reassessment is reasonable. If PPV is 6% and the LV is dilated and hypokinetic, fluid will harm - start norepinephrine and consider inotropy.
Rule of thumb: in undifferentiated shock, the first test is an echocardiogram, not a fluid bolus.