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 patients without spontaneous breathing or arrhythmias). Frank-Starling mechanism describes the relationship between preload (ventricular end-diastolic volume) and stroke volume: on the steep portion of the curve, volume administration increases SV (fluid responsive); on the flat portion, additional volume provides no SV benefit and causes pulmonary/peripheral edema. Central venous pressure (CVP) via central venous catheter reflects right atrial pressure and is a poor predictor of fluid responsiveness as a static value, but CVP waveform analysis and trending provides useful clinical information.