Exposure to high environmental temperature in the sauna does not change plasma indocyanine green (ICG) clearance in healthy subjects.

Indocyanine green (ICG) was given intravenously (0.5 mg kg-1) to seven healthy male volunteers in random order during a control session and a session in the sauna bath. The sauna bathing session consisted of three 10 min. stays in the sauna (temperature 85-95 degrees, relative humidity 25-30%), separated by two 5-min. periods of resting at 22 degrees. Blood samples were taken for 60 min. in order to calculate ICG plasma clearance (CI), volume of distribution (Vss) and elimination half-life (t1/2 beta). The mean +/- S.E.M. values of ICG plasma clearance, Vss and t1/2 beta for the control session and the sauna bathing session were 0.47 +/- 0.08 1 min.-1 versus 0.39 +/- 0.04 1 min.-1, 2.4 +/- 0.4 1 versus 2.3 +/- 0.2 1 and 3.9 +/- 0.3 min. versus 4.4 +/- 0.3 min., respectively. No statistically significant differences in the CI, t1/2 beta or Vss of ICG were detected between the control and sauna bathing sessions. The results suggest that short-term exposure to high ambient temperatures during sauna bathing does not affect hepatic blood flow. Consequently, short-term hyperthermia and associated changes in hepatic blood flow are assumed to have little, if any, effect on the hepatic clearance of drugs.