Figure 4.

ICG clearance as a function of core body temperature in pigs. Twelve female landrace pigs (mean weight 49 ± 2 kg) were anesthetized (ketamine 5–10 mg/kg/h, sufentanil 5–10 μg/kg/h, isoflurane 0–2%) and subjected to two ICG clearance tests: one at baseline and one after 4 h of passive ambient (20.7 ± 0.6°C) cooling. To that end, 25 mg ICG (PULSION Medical Systems) was administered in 5 mL of 0.9% NaCl via an ear vein catheter. The ICG plasma disappearance rate (PDR) was measured using tail pulse-oximetry. Body temperature, mean arterial pressure and cardiac output were measured with a Swan-Ganz thermodilution catheter placed in the jugular vein. All animal experiments were approved by the institute’s animal ethics committee. (A) ICG PDR (y axis) plotted as a function of pig core body temperature (x axis), which revealed a strong correlation between these parameters (Pearson r = 0.8635, p < 0.0001; the dashed lines indicate the 95% confidence interval). Corroboratively, linear regression of ICG PDR data yielded a regression equation of y = −0.376 + 0.016x and a goodness of fit (R²) of 0.7456, which equates to a 0.91-fold increase in ICG clearance for every 1°C drop in core body temperature, thereby approximating the Arrhenius equation. (B) Cardiac output of the pigs remained stable throughout the experiment and was not affected by core body temperature (Pearson r = 0.1893, p = 0.3758; the dashed lines indicate the 95% confidence interval). Combined with the findings that the pH and mean arterial pressure of the pigs were maintained at physiological levels (data not shown), this indicates that the drop in ICG PDR at lower temperatures is explained by a decrease in basolateral transporter function and is not caused by hypothermia-induced alterations in hepatic perfusion dynamics.