The hemodynamic and metabolic effects of tourniquet application during knee surgery

We evaluated the effects of tourniquet application on the cardiovascular sy stem and metabolism in 10 young men undergoing knee surgery with general an esthesia. The duration of inflation was from 75 to 108 min. Heart rate, mea n arterial pressure, cardiac index (CI) by pulse contour method, and system ic vascular resistance were measured before, during, and after tourniquet i nflation. pH, PaO2, PaCO2, and lactate blood concentrations were also measu red. (V) over dot O-2 and (V) over dot CO2 were assessed every minute from tracheal intubation up to 15 min after tourniquet deflation and ire, in exc ess of the basal value over the 15 min after deflation and ((V) over dot O( 2)exc) was calculated. Mean arterial pressure increased 26% (P < 0.05) duri ng inflation and returned to basal values after deflation. CI did not chang e immediately after inflation; although, thereafter, it increased 18% (P < 0.05). Five minutes after deflation, CI further increased to a value 40% hi gher than the basal value. Therefore, systemic vascular resistance increase d 20% suddenly after inflation (P < 0.05) and decreased 18% after deflation (P < 0.05). (V) over dot O-2 and (V) over dot CO2 remained stable during i nflation and increased (P < 0.05) after deflation, (V) over dot O(2)exc dep ended on duration of tourniquet inflation time (Tisch) (P < 0.05). After de flation, Pace, and lactate increased (P < 0.05) while Tisch increased. We c onclude that tourniquet application induces modifications of the cardiovasc ular system and metabolism, which depend on tourniquet phase and on Tisch. Whether these modifications could be relevant in patients with poor physica l conditions is not known.