Bleeding in Knee Arthroplasty After Preconditioning With Sevoflurane

Knee arthroplasty is performed with restriction of blood flow by use of the pressure tourniquet. Ischemia of skeletal musculature is accompanied by the formation of reactive oxygen species and release of vasoactive factors. Inhaled anesthetics were described as possible protective factors, termed "ischemic preconditioning". The objective of this investigation is to observe the effects of preconditioning with inhaled anesthetic on bleeding in the postoperative period of knee arthroplasty surgery. The study will be prospective and randomized. Patients will be allocated by means of a randomized table in two groups: Group Preconditioning (GP) - subarachnoid and general anesthesia with preconditioning with 1 minimal alveolar concentration (MAC) for 15 minutes before the installation of the ischemia by tourniquet; Group control (GC) - subarachnoid and general anesthesia with sevoflurane without preconditioning. Will be evaluated: hemoglobin and hematocrit, platelet count and coagulogram, electrolytes and creatinine, lactate and glycemia. Volume of drainage will be evaluated until drainage is withdrawn and need for transfusion measuring the number of bags of blood concentrate and volume transfused. Pain assessment will be done by means of visual analog scale. Morbidity will be recorded up to the 30th postoperative day by chart analysis. Patients will be allocated to the study groups by random number table. Data will be presented descriptively, frequently, mean and standard deviation, or medians and distribution in 25-75% percentiles. The comparison between continuous measurements will be made by means of repeated measures intra-group analysis of variance (ANOVA) and Student's t-test for evaluation between groups. The need for transfusion will be compared by Fisher's exact test. Pain intensity will be compared by Wilcoxon test for non-parametric data. A commercially available statistical package - SPSS version 15.0 (SPSS Inc.) will be used. A value of P \<0.05 will be consi