Changes in Oxygen Consumption and Carbon Dioxide Elimination After Tourniquet Release in Patients Breathing Spontaneously Under Epidural Anesthesia

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Abstract
To examine whether the degree of the changes in metabolic variables correlates with the duration of tourniquet inflation or other factors in spontaneously breathing patients undergoing unilateral lower-limb surgery under epidural anesthesia, we measured changes in metabolic variables. Metabolic variables consisted of oxygen consumption (VO2), carbon dioxide elimination (VCO2), and respiratory quotient (RQ). The patients (n = 30) received continuous epidural anesthesia with 1.5% lidocaine with epinephrine solution (5 micro g/mL). The averaged values of VO2 and VCO (2) for 10 min after tourniquet release increased significantly from 171.2 +/- 34.5 mL/min to 262.7 +/- 90.0 mL/min and from 202.0 +/- 33.1 mL/min to 250.5 +/- 64.2 mL/min, respectively. They returned to the baseline values within 10 min after deflation. Therefore, rapid response to changes in metabolic condition can be anticipated after tourniquet release in patients breathing spontaneously under epidural anesthesia. The percent increases in the averaged values of VO2 and VCO2 for 10 min after tourniquet release were correlated with body surface area but not with tourniquet inflation time. We conclude that the changes in metabolic variables after tourniquet release are dependent on body size, i.e., muscle mass, but not on the duration of tourniquet inflation. Implications: We measured changes in metabolic variables, i.e., oxygen consumption and carbon dioxide elimination, after tourniquet release in patients undergoing lower-limb surgery under epidural anesthesia. We found that the extent of changes in these variables was dependent on body size but not on the duration of inflation. These results have implications as to how long a tourniquet can be inflated during surgery.