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