The Hemodynamic and Metabolic Effects of Tourniquet Application During Knee Surgery

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Abstract
We evaluated the effects of tourniquet application on the cardiovascular system and metabolism in 10 young men undergoing knee surgery with general anesthesia. The duration of inflation was from 75 to 108 min. Heart rate, mean arterial pressure, cardiac index (CI) by pulse contour method, and systemic vascular resistance were measured before, during, and after tourniquet inflation. pH, Pao2, Paco2, and lactate blood concentrations were also measured. V̇o2 and V̇co2 were assessed every minute from tracheal intubation up to 15 min after tourniquet deflation and V̇o2 in excess of the basal value over the 15 min after deflation (V̇o2exc) was calculated. Mean arterial pressure increased 26% (P < 0.05) during inflation and returned to basal values after deflation. CI did not change immediately after inflation; although, thereafter, it increased 18% (P < 0.05). Five minutes after deflation, CI further increased to a value 40% higher than the basal value. Therefore, systemic vascular resistance increased 20% suddenly after inflation (P < 0.05) and decreased 18% after deflation (P < 0.05). V̇o2 and V̇co2 remained stable during inflation and increased (P < 0.05) after deflation. V̇o2exc depended on duration of tourniquet inflation time (Tisch) (P < 0.05). After deflation, Paco2 and lactate increased (P < 0.05) while Tisch increased. We conclude that tourniquet application induces modifications of the cardiovascular system and metabolism, which depend on tourniquet phase and on Tisch. Whether these modifications could be relevant in patients with poor physical conditions is not known. Implications The clinical effects of tourniquet application were evaluated in 10 young men undergoing knee surgery. Our data indicate that tourniquet application causes hemodynamic and metabolic changes which may become clinically relevant after a long period of tourniquet inflation, particularly in patients with concomitant cardiovascular diseases.