Clinical Hemodynamic Parameters Do Not Accurately Reflect Systemic Oxygen Transport in Neonates after the Norwood Procedure.

Abstract

Clinical hemodynamic parameters (heart rate, systolic arterial pressure [SAP], and arterial and venous oxygen saturation saturations [SaO2 and SvO2 ]) are commonly used to guide management to optimize oxygen transport after the Norwood procedure. The adequacy of this practice has not been demonstrated. We examined the correlations between these clinical parameters and direct measurements of oxygen transport in these patients. Oxygen consumption (VO2 ) was measured using respiratory mass spectrometry for 72 hours in 17 neonates after the Norwood procedure. Arterial, superior vena caval, and pulmonary venous blood gases and pressures were measured at intervals of 2-4 hours to calculate cardiac output (CO), systemic and pulmonary blood flows (Qs , Qp), systemic vascular resistance (SVR), total pulmonary vascular resistance including the Blalock-Taussig shunt (tPVR), oxygen delivery (DO2), and extraction ratio (ERO2 ). Heart rate and SAP were also recorded. Heart rate was positively correlated with VO2 (P = .004) and ERO2 (P = .005). SAP was positively correlated with CO (P = .006), VO2 (P = .02), ERO2 (P = .01), and SVR (P = .08). SaO2 was negatively correlated with tPVR, Qs, and DO2 but positively with Qp and SVR (P < .05 for all). SvO2 was positively correlated with CO, Qs , and DO2 (P < .0001 for all) and negatively correlated with SVR, VO2, and ERO2 (P < .05 for all). Routine clinical hemodynamic parameters do not accurately reflect oxygen transport after the Norwood procedure, except for SvO2, which does not differentiate between VO2 and DO2. Higher heart rate and SAP are correlated with a worse balance of oxygen transport. The results of clinical hemodynamic monitoring should be interpreted with caution. Direct measurements of oxygen transport parameters are important in the care of neonates after the Norwood procedure.