Normovolemic induced hemodilution. Behavior of various hemodynamic indices

: Changes in mixed venous oxygen saturation of hemoglobin (SvO2), heart rate (HR), cardiac index, (SI) were measured in 20 patients undergoing major orthopedic surgery (rachis and pelvis bone resections for tumours: mean-lasting 8 hours), to estimate the safety limits during isovolemic hemodilution. Up to Hb 8 g%, in all patients, a cardiac index improvement (+41%) was found, and this was mainly caused by an increase in stroke index (+31%). For 16 patients at Hb 6 g%, this improvement was present only in 44% and declined during further hemodilution. In all cases, CI was moderately lower than baseline value (-18%) this was caused by an important increase in HR (= 55%) partially compensating for by the fall in SI (-57%). The Authors conclude that, in patients under general anaesthesia, isovolemic hemodilution is safe up to Hb 8 g%. Below this value the left ventricular performance rapidly declines.