Extreme hemodilution: Effects of inhalation anesthetics, hypoxia, and blood loss. An Experimental study in pigs.

Hemodilution reduces the need for blood transfusion and hereby the risk for transmission of infectious agents. The present study investigated effects on systemic and myocardial circulation and oxygenation, and blood lactate concentrations; induced by nitrous oxide, isoflurane, hypoxia, and uncompensated blood loss, in pigs hemodiluted to a hematocrit of 11%. In addition, indicators of hypovolemia and insufficient oxygen delivery, as well as the correlation between mixed and central venous blood oxygen were studied. It was found that nitrous oxide had insignificant circulatory effects, but oxygen delivery decreased during isoflurane administration, hypoxia or uncompensated blood loss, and delivery dependent oxygen uptake and hyperlactemia was observed when systemic oxygen delivery decreased below 10 ml x kg-1 x min-1. The heart was more tolerant to the reduced oxygen delivery than were other organs, when judged by arterial lactate concentration and myocardial lactate uptake. The decrease in mixed venous oxygen saturation and systemic oxygen delivery correlated well with the increase in arterial lactate concentration. There was a close relation between central and mixed venous oxygen saturation. A decrease in arterial blood pressure was the first sign of hypovolemia during hemodilution, wheras central venous and pulmonary capillary wedge pressures were insensitive indicators of hypovolemia. It is concluded that the risk of compromising cardiovascular function and inducing severe tissue hypoxia is high during extreme acute normovolemic hemodilution. Nevertheless our findings suggest that in young individuals a hematocrit as low as 11% can be accepted temporarily providing adequate monitoring is available, and if caution is taken to avoid further decrease in systemic oxygen delivery.