The use of pneumatic tourniquet allows a clear surgical field by restricting blood flow to the area to be operated, which implies at least intraoperative bleeding, but with a high risk of postoperative bleeding.
The late bleeding associated with tourniquet use appears to be due to the imbalance between coagulation and fibrinolysis. The use of antifibrinolytics, such as tranexamic acid and epsilon aminocaproic acid, has been shown to reduce postoperative bleeding, reducing the need for transfusion of blood components postoperatively, without increasing the risk of thromboembolism. The effects of tourniquet, which can be maintained at intervals of 75 to 100 minutes, include elevation in blood pressure while it is insuflated, cardiac index elevation during ischemia and its subsequent elevation at the moment of release to the circulation, at which time there is also an increase in oxygen consumption as well as the release of CO2. This increase in oxygen consumption is directly related to the time of ischemia.
Skeletal muscles's ischemia is accompanied by anaerobic glycolysis, formation of reactive oxygen species, and release of vasoactive factors. Inhaled anesthetics, such as isoflurane and sevoflurane, have been described as possible protective factors for both cardiac and skeletal muscles, although the literature still suggests the need for additional studies. Its use in the period before the onset of ischemia is called "ischemic preconditioning".
The objective of this investigation will be to observe the effects of an inhalational anesthetic, commonly used in anesthesia on bleeding, in the results of coagulation tests and in the consumption of blood components in the postoperative period of knee arthroplasty surgery.
Goals
To compare the effects of preconditioning with sevoflurane in total knee arthroplasty surgery by:
1. Coagulogram for coagulation times;
2. Volume of blood drainage in the postoperative period;
3. Need and volume of blood transfusion;
4. Dosage of arterial pH, lactate and CPK enzyme;
5. Immediate postoperative morbidity and up to 30 days postoperatively.
Statistic
Data will be presented by descriptive tables and frequency, mean and standard deviation, or medians and distribution in 25-75% percentiles for data that do not find a normal distribution. The Kolmogorov-Smirnov test will determine if there is a normal distribution.
Values for hemoglobin, hematocrit, platelet count, arterial blood gas values, electrolytes, creatinine, CPK, lactate, blood glucose and coagulogram will be compared by analysis of variance (ANOVA).
The intragroup analyzes will use repeated measures ANOVA and the Dunnett test if there is a significant difference between the moments of the same group, since the test may be better considered for comparison with a control (preoperative) time. Between the groups, the values will be compared moment by moment with Student's t-test.
The need for transfusion, considering the number of CC bags, will be compared by Fisher's exact test and its volume by Student's t-test. Pain intensity in the postoperative period will be evaluated by visual analogue scale and compared by Wilcoxon's test for non-parametric data between the time of entry and discharge of RPA. A commercially available statistical package - SPSS version 15.0 (SPSS Inc.) will be used. A value of P \<0.05 will be considered statistically significant.
Patients will be allocated to the study groups by random number table. Briefly, generating a list of two-digit numbers determines the order of entry of patients into the study groups. A minimum expected difference between the means of the treatments (groups) established at 500 ml for the required volume of postoperative transfusion, standard deviation at 400 ml, with test power at 80% and significance level in 5% suggesting a distribution of 15 patients in each group, considering losses in 50%.
