Tissue Perfusion and Oxygenation Evaluated by Measurements of Tissue Gases and pH. An Experiemental Study

University dissertation from Åke Mellström, Dept of Anaesthesiology, Malmö Univesity Hospital, S-205 02 Malmö, Sweden

Abstract: Optimum peripheral perfusion, oxygenation and oxygen utilization is a prerequisite for normal wound healing, resistance to infection and cardiac function. The purpose of this study was to evaluate peripheral oxygen utilization by measurements of subcutaneous tissue gases and pH (PscO2, PscCO2 and pHsc) in comparison to established techniques for measurements of periph-eral tissue oxygenation and oxygen utilization in experimental animal models with hyperoxia-hypoxia, acidosis-alkalosis and haemorrhage-resuscitation. The oxygen electrode of polarographic type, Paratrend 7™ was compared with established electrodes of the same type, Biogenesis™ and Continucath 1000™ in an in vitro and an in vivo model. The Paratrend 7 and the Biogenesis sensors generated almost equal tissue oxygen ten-sion values in response to changes in arterial oxygen tension. The Continucath sensor gener-ated 50 % higher tissue oxygen tension values compared with the Paratrend 7 and Biogenesis sensors, both with and without tonometer. During hyperoxia and hypoxia measurements of sub-cutaneous tissue gases and pH are indicators of oxygen utilization. Correction of oxygen utiliza-tion in the subcutaneous tissue as measured by subcutaneous carbon dioxide tension and pH is slower than indicated by changes in subcutaneous oxygen tension, blood gases and pH. Over-compensation of acidosis with bicarbonate resulting in alkalosis impairs oxygenation. Subcuta-neous oxygen tension was an early indicator of changes in peripheral tissue perfusion and oxy-genation during hypovolemia and resuscitation. Measurements of subcutaneous carbon dioxide tension and pH verified inadequate tissue oxygen utilization during shock and recovery from tissue acidosis after resuscitation in contrast to the corresponding measurements in arterial blood. Measurements of subcutaneous tissue gases and pH, to a large extent reflect similar changes in splanchnic perfusion, oxygenation and tissue oxygen utilisation during hemorrhage and resuscitation. Additional measurements of PscCO2 and pHsc in combination with PscO2 generate relevant infor-mation on tissue oxygen utilization in a variety of clinical conditions.

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