Central Blood Pooling as an Explanation for Lowered FRC during Anaesthesia? Thigh Volume Measurements by Plethysmography

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Abstract
Segmental volumes of the thigh and the upper arm were measured by means of an air-filled plethysmograph before and during various anaesthesias. A small but significant fall in segmental volume was seen with the induction of anaesthesia with thiopentone. A further fall was observed during neurolept anaesthesia but not with halothane. Epidural and spinal anaesthesias caused no change in segmental thigh volume. The results suggest a redistribution of 50-150 ml blood from the extremities to the trunk during general anaesthesia. This redistribution may contribute to the well-known fall in FRC with general anaesthesia.