[Changes in plasma volume during and after middle-ear procedures (author's transl)]

We observed 20 patients undergoing middle-ear surgery under NLA in combination with halothane for controlled hypotension in respect to haematocrit, plasma protein concentration, plasma volume (Evans Blue) and intravascular protein mass during and after anaesthesia and surgery. As surgical bleeding was almost nil and infusion therapy was not necessary, patients behaved as a "closed system". With the start of anaesthesia we found a significant decrease of haematocrit and plasma protein concentration, being complete after 45-60 min, and unchanged thereafter until the end of anaesthesia. Suspicion of an increase in plasma volume could not yet be verified by a measurement of this parameter after 30 min of anaesthesia. Just after termination of anaesthesia we observed a significant increase in haematocrit and plasma protein concentration compared to control values with a downward trend over the next hour. At that point we also measured a decrease in plasma volume by 10% and in plasma protein mass by 6% compared to controls. These findings are interpreted as part of an "arousal reaction" with a temporary disequilibrium between transcapillary filtration rate of water and proteins and back transport of these substances via lymph flow.