Pathophysiology
Clinical meaning
Hemodynamic monitoring encompasses the assessment of cardiovascular function through measurement of pressures, flows, and oxygen transport. The cardiovascular system maintains tissue perfusion through the interaction of cardiac output (CO = SV x HR), vascular resistance (MAP = CO x SVR + CVP), and oxygen delivery (DO2 = CO x CaO2 x 10, where CaO2 = [Hgb x 1.34 x SaO2] + [PaO2 x 0.003]). Oxygen consumption (VO2) is normally 200-250 mL/min. The oxygen extraction ratio (O2ER = VO2/DO2) is normally 25-30%, meaning significant reserve exists before tissue hypoxia develops. When DO2 falls below a critical threshold (DO2crit, approximately 300-330 mL/min/m2), VO2 becomes supply-dependent and anaerobic metabolism produces lactate. Arterial blood pressure monitoring via indwelling arterial catheter provides continuous, beat-to-beat measurement and allows arterial blood gas sampling. The arterial waveform provides additional information: the systolic upstroke reflects LV contractility, the dicrotic notch represents aortic valve closure, the area under the curve correlates with stroke volume, and pulse pressure variation (PPV) during mechanical ventilation predicts fluid responsiveness (PPV >13% predicts positive fluid response with >90% sensitivity and specificity in fully mechanically ventilated...