Variations in superficial renal cortical blood flow and tissue oxygenation: an experimental porcine model.

Renal cortical microcirculation and its relation to inulin clearance, central haemodynamics and pulmonary gas exchange were studied in eight pigs under continuous intravenous chlormethiazole-pancuronium anaesthesia. The animals were studied during six consecutive 30-min periods. Four of the animals were also studied 19 h after the first period. In the superficial renal cortex, regional blood flow (Q) was measured by laser Doppler flowmetry (LDF) and tissue oxygenation (P1o2) by surface microelectrode technique. Central haemodynamics and pulmonary gas exchange values were distributed within normal ranges. The importance of stable central haemodynamics in order to perform accurate microcirculatory measurements in the renal cortex was documented. A significant relation between Q and pulmonary capillary wedge pressure (PCWP) was found (P <0.0001) despite the fact that PCWP was distributed within a range of only 0.7 kPa (all values were well within the normal range for pigs). No other relationships were found between central haemodynamics or pulmonary gas exchange variables and renal microcirculatory parameters. Concerning renal microcirculation and inulin clearance, at least 2–3 h may be required for stabilization after surgery. The average temporal variability between measurements performed every 30 min in each animal was 6 ± 7% (s.d.) in the LDF values and 21 ± 21% in the P1o2, values (mean P1o2,). No correlations were found between Q or P1o2, and inulin clearance. Since the haemodynamic parameters, pulmonary gas exchange variables and haematocrit were distributed within narrow ranges, we regard the temporal microcirculatory variability obtained here as normal in this experimental situation, and consider the porcine model well suited for further studies concerning renal microcirculation.