Marino The ICU Book 4e, IE

146 Hemodynamic Monitoring

be multiplied by 80 to obtain more conventional units of resistance (dynes•sec - 1 •cm -5 /m 2 ), but this conversion offers no advantage (18).

PulmonaryVascular Resistance Index The pulmonary vascular resistance (PVR) has the same limitations as mentioned for the systemic vascular resistance. The PVR is a global measure of the relationship between pressure and flow in the lungs, and is derived as the pressure drop from the pulmonary artery to the left atri- um, divided by the cardiac output. Because the pulmonary artery wedge pressure (PAWP) is equivalent to the left atrial pressure, the pressure gra- dient across the lungs can be expressed as the difference between the mean pulmonary artery pressure and the wedge pressure (PAP – PAWP). PVRI = (PAP – PAWP)/CI (8.9) Like the SVRI, the PVRI is expressed in Wood units (mm Hg/L/min/m 2 ), which can be multiplied by 80 to obtain more conventional units of resist- ance (dynes•sec -1 •cm - 5 /m 2 ). OxygenTransport Parameters The oxygen transport parameters provide a global (whole body) measure of oxygen supply and oxygen consumption. These parameters are de- scribed in detail in Chapter 10 and are presented only briefly here. Oxygen Delivery The rate of oxygen transport in arterial blood is called the oxygen delivery (DO 2 ), and is the product of the cardiac output (or CI) and the oxygen concentration in arterial blood (CaO 2 ). DO 2 = CI × CaO 2 (8.10) The O 2 concentration in arterial blood (CaO 2 ) is a function of the hemo- globin concentration (Hb) and the percent saturation of hemoglobin with oxygen (SaO 2 ): CaO 2 = 1.3 × Hb × SaO 2 . Therefore, the DO 2 equation can be rewritten as: DO 2 = CI × (1.3 × Hb × SaO 2 ) (8.11) DO 2 is expressed as mL/min/m 2 (if the cardiac index is used instead of the cardiac output), and the normal range is shown in table 8.1. ), also called oxygen consumption, is the rate at which oxygen is taken up from the systemic capillaries into the tissues. The VO 2 is calculated as the product of the cardiac output (or CI) and the difference in oxygen concentration between arterial and venous blood (CaO 2 – CvO 2 ). The venous blood in this instance is “mixed” venous blood in the pulmonary artery. Oxygen Uptake Oxygen uptake (VO 2