OXYGEN-CONSUMPTION AND CARDIOVASCULAR FUNCTION IN CHILDREN DURING PROFOUND INTRAOPERATIVE NORMOVOLEMIC HEMODILUTION

The clinically acceptable limit of acute normovolemic, normothermic he modilution, a standard procedure in scoliosis surgery, is not yet well defined. Eight ASA class I patients undergoing idiopathic scoliosis c orrection were administered a standard anesthetic with 100% oxygen and controlled ventilation. Hemodilution was accomplished by exchanging w hole blood for 5% albumin in 0.9% saline. Blood gases, acid-base statu s, and circulatory variables were recorded prior to and after hemodilu tion, and every 30 min throughout surgery. The impact of hemodilution was judged by mixed venous oxygen saturation which was maintained at g reater than or equal to 60%, while intravascular volume was maintained with the 5% albumin solution. Reinfusion of the autologous blood was completed by the end of surgery. In the eight controlled cases in whic h normovolemic hemodilution was studied, hemoglobin levels decreased f rom 10.0 +/- 1.6 g/dL to 3.0 +/- 0.8 g/dL. Mixed venous oxygen saturat ion decreased from 90.8% +/- 5.4% to 72.3% +/- 7.8%. Oxygen extraction ratio increased from 17.3% +/- 6.2% to 44.4% +/- 5.9%. Oxygen deliver y decreased from 532.1 +/- 138.1 mL.min(-1).m(-2) to 260.2 +/- 57.1 mL .min(-1).m(-2), while global oxygen consumption did not decrease and p lasma lactate did not appreciably increase. Central venous pressure in creased and peripheral resistance decreased during hemodilution. Cardi ac index increased, heart rate remained essentially constant, and left ventricular stroke work index did not decrease significantly. No pati ents suffered clinically ad verse outcomes. Global oxygen transport an d myocardial work can be maintained at extreme normovolemic anemia. Ou r evidence suggests that stages of normovolemic hemodilution more seve re than previously reported map be clinically acceptable for young, he althy patients during normocarbic anesthesia.