Plasma viscosity and cremophor-containing anaesthetics.

The cremophor-containing anaesthetic agents, Althesin, propanidid and diazepam, were added to plasma in vitro and administered to patients. In vitro these anaesthetics, and cremophor alone in concentrations equal to those obtained in vivo, decreased the viscosity of plasma 45% at shear rate 11.5 s-1. In 11 patients given cremophor-containing anaesthetics to induce anaesthesia, plasma samples obtained 5 min after injection showed a mean decrease in viscosity of 42% compared with the pre-induction values. The effect on viscosity after a single dose disappeared in 50 min. Triton x-100 added to plasma caused a decrease in viscosity similar to that of cremophor. The interaction in vitro of cremophor and Triton x-100 with concentrated urea was found to be identical both in plasma and dextran. This suggests that cremophor acts by increasing the sheet of structured water around the protein molecules, thereby preventing the aggregation of proteins.