Evaluating tissue perfusion using labelled water indicator microdialysis in a rat model of haemorrhagic shock

The indicator microdialysis technique with (3)H(2)O was evaluated as a method for assessing local blood flow in skeletal muscle and liver in a rat model of haemorrhagic shock. Microdialysis probes were inserted into the hind limb muscle and liver of 12 rats and perfused with a solution containing (3)H(2)O. Haemorrhagic shock was induced in eight rats by repeated blood withdrawals; four rats were used as a control group. The outflow to inflow (O/I) ratio of water activity, lactate and pyruvate contents in the dialysate were repeatedly measured. The ratio of lactate to pyruvate (L/P) was calculated. There was no correlation between blood loss and O/I ratio (r = 0.323 for liver, r = 0.300 for muscle), between the mean arterial pressure and O/I ratio (r = 0.460 for liver, r = -0.301 for muscle) or between the concentration of lactate and O/I ratio (r = -0.237 for liver, r = 0.454 for muscle). A significant correlation was found between blood loss and lactate concentration in muscle (r = 0.619, p < 0.0001). We suppose that microdialysis with (3)H(2)O cannot be used as a sensitive method to estimate regional blood flow changes during haemorrhagic shock in rats. Measuring lactate, pyruvate and L/P ratio in the microdialysate seems to be a superior method to assess tissue hypoperfusion caused by haemorrhagic shock in rats.