Severe Hemodilution - Clinical and Experimental Studies

Abstract: In children, it is often desirable to minimize allogenic blood transfusion, and this thesis explores the physiology of an alternative method of managing perioperative blood loss: hemodilution with Ringer´s dextran. Methods Clinical studies: Arterial pressure, superior caval venous oxygen saturation (ScvO2) and blood lactate concentration (L) were studied during bone marrow harvesting (BMH) on 23 occasions in 19 children, 1-17 years of age, with healthy hearts and lungs. Experimental studies - A. Shivering was induced by surface cooling and the hemodynamic and metabolic responses studied in hemodiluted (Hgb = circa 50 g/L), 12-14 weeks old anesthetized pigs and their normoemic controls. B. The tolerance to progressive isovolemic anemia was studied during hypothermia in anesthetized and paralyzed pigs (32 °C) and their normothermic controls (38.5 °C). Main findings Clinical studies: BMH caused a blood loss of 26 (17-42) ml per kg body weight, and decreased the blood hemoglobin concentration (Hgb) to 54 (47- 84) g/L. ScvO2 was 72 (61-88) % in the awake child, and increased to 82 (70 - 94) % after induction of general anesthesia. During hemodilution, it decreased to 76 (60-92) %. The lowest ScvO2: 66 (55-79) % was seen after awakening the child in spite of the fact that Hgb had now increased to 70 (58-95) g/L by transfusion of the child´s own, preoperatively collected, blood. There was an increase in mean heart rate from 89 to 108 bpm during BMH. Mean L increased from 1.0 to 1.5 mmol/L but was never above the normal limit. Experimental studies: A. During shivering, oxygen consumption (VO2) increased by a mean factor of 2.9 in the hemodiluted pigs, and 3.7 in the controls (P< 0.001). Two of the former exhibited signs of myocardial hypoxia. B. Hgb at death was 14 ± 4 g/L in cooled pigs and 19 ± 3 g/L in the controls (P=0.015). Clinical implications -The healthy child tolerates extreme hemodilution (Hgb 50-70 g/L) if suitably anesthetized. The strain on the organism is greater after awakening. -The findings cannot be extrapolated to children with compromised function of the heart or lungs, who the author believes will frequently benefit from a normal-high Hgb. -Extreme hemodilution reduces oxygen delivery to the body and will, hence, decrease the tolerance to challenges with increased oxygen demand such as shivering. -Cooling is modestly protective during severe anemia.