Regional oxygenation in cardiac surgery. Influence of temperature, pump flow and insulin

Abstract

Surgical trauma triggers neural, endocrine and inflammatory reactions with subsequent alterations in systemic and regional blood flow, blood pressure and metabolism. These changes are detectable after all major surgical procedures but are often more pronounced after cardiac surgery, probably because of blood exposure to artificial surfaces of the heart lung machine, temperature modulation (e.g. cooling and rewarming) and systemic and/or regional hypoxia. Hypoperfusion may lead to dysfunction in vital organs after cardiac surgery. Regional venous oxygenation reflects oxygen supply/demand balance and marked regional deoxygenation occurs during cardiopulmonary bypass. This thesis addresses two important perspectives of cardiopulmonary bypass (CPB): 1. Central and regional oxygenation, and 2. The systemic inflammatory response.Ninety-three patients, undergoing elective cardiac surgery were included in four prospective, randomized and controlled studies. Three studies were performed during CPB (I-III) and one study (IV) was performed in the early postoperative phase. The relationship between central mixed and regional venous oxygenation was evaluated in Paper I. In Paper II it was investigated if a reduction in CPB flow, within the recommended range, affects central and regional oxygenation and if the degree of hypothermia affects central and regional venous oxygenation and inflammatory activation. In Paper III it was investigated if high dose insulin affects central mixed and hepatic venous oxygenation and inflammatory response and in Paper IV if skeletal muscle luxury perfusion is the sole effect of high dose insulin in cardiac surgery.Regional deoxygenation occurred during cardiopulmonary bypass, despite normal central mixed venous oxygenation. Reduction in pump flow, within the recommended range, reduced oxygenation in both central and regional venous blood. More pronounced hypothermia during CPB resulted in an improved oxygenation, but did not affect the inflammatory response. Insulin infusion improved oxygenation in both central mixed and hepatic venous blood, but did not affect the inflammatory response. The insulin-induced increase in cardiac output in the early phase after cardiac surgery could not be explained solely by a reduction of skeletal muscle vascular resistance.