Haemorrhage during anaesthesia and surgery: continuous measurement of microcirculatory blood flow in the kidney, liver, skin and skeletal muscle.

Multichannel laser Doppler flowmeters allow continuous, simultaneous measurement of perfusion in several organs. We measured microcirculatory blood flow in the kidney, liver, skin and skeletal muscle in 10 anaesthetized rats subjected to abdominal surgery and graded haemorrhage (withdrawal of 5% total blood volume every 10 min). Mean arterial blood pressure, heart rate and haemoglobin concentrations were also measured. Muscle blood flow decreased after only 10% blood loss, but without significant changes in the other organs. At this time the perfusion signal from the muscle was cycling 2-3 times per min (slow wave flowmotion) which was never seen in any other organ. After 35% blood loss, all organs monitored maintained approximately 70% of initial flow, despite a 45% decrease in mean arterial pressure from 104 +/- 12 to 55 +/- 9 mmHg (mean +/- SD). After 40% blood loss there was a sharp decrease in blood flow in all organs. Haemoglobin concentration decreased from 14.4 +/- 0.8 to 10.8 +/- 1.3 mg dL-1 after 45% blood loss. We conclude that laser Doppler flowmetry is useful for continuous measurement of microcirculatory blood flow in several organs simultaneously during haemorrhagic hypovolaemia. It showed that microcirculatory blood flow in skeletal muscle is particularly sensitive to lesser degrees of blood loss during anaesthesia. Hypovolaemia-induced slow wave flowmotion occurred only in skeletal muscle, which may be linked to fluid mobilization during haemorrhage.