This study included patients with unilateral TKA who were older than 18 years of age and classified as ASA I or II (American Society of Anesthesiologists physical status). The surgeries were performed at IOT HCFMUSP between February and December of 2018.
Patients were excluded if they were diagnosed with grade II obesity according to body mass index (BMI) higher than 35 kg/m2, had renal failure (serum creatinine > 1.4 mg/dL or on a dialysis program), myocardial infarction, unstable coronary disease in the six months before surgery, severe liver or gastrointestinal disorders, neuropathic diseases, diabetes, psychiatric disorders, were pregnant or lactating, or were smokers. Patients with hematocrit (Ht) levels below 30% or hemoglobin (Hb) levels below 10g/dL, with a history of coagulation disorders, or who used anticoagulants or antiplatelet agents in the five days before surgery were also excluded.
In this prospective, randomized study, we recorded patients’ age, BMI, sex, and ASA status. Subjects were assigned into one of two groups by a random number table. The control group did not receive any intervention as preconditioning, while the sevoflurane group participants received 2% sevoflurane for 15 minutes before limb ischemia by a pneumatic tourniquet. The primary outcome was the volume of blood drainage in the postoperative period.
Electrocardiography (ECG), oxygen saturation (SpO2), and noninvasive blood pressure measurements were recorded throughout the surgery. An 18-gauge intravenous catheter was inserted in the upper limb to administer a lactate solution (10 mL/kg) followed by midazolam (0.05 mg/kg) and prophylactic antibiotic therapy with cefoxitin (1.5g). Patients then received spinal anesthesia with a 27G Whitacre needle inserted through the L4-L5 intervertebral space. We injected 20 mg of 0.5% isobaric bupivacaine and 100 µg of morphine. After the spinal anesthesia, patients were placed in the supine position to receive general anesthesia with propofol (1.5 mg/kg to 2.5 mg/kg), fentanyl (2.5 µg/kg-5 µg/kg), and cisatracurium (0.1mg/kg) followed by an intratracheal tube insertion. Mechanical ventilation was instituted with FiO2 at 40%, PEEP at 5 cm H2O, RR at 10 rpm, tidal volume at 5 mL/kg-7 mL/kg, and new settings to preserve ETCO2 at 35-37 mmHg.
Right after mechanical ventilation was instituted, we administered 2% sevoflurane to the treatment group for 15 minutes, while the control group received a mixture of oxygen and compressed air with 40% FiO2. During this 15-minute interval, a Foley urinary catheter was inserted to quantify the urine output during surgery and for up to 24 hours afterward, and then removed. Volume replacement was maintained at a rate of 5mL/kg/hour, except in cases where there was a drop of 20% or more in baseline systolic blood pressure (SBP), the SBP was less than 90 mmHg, the heart rate (HR) greater than 100 bpm, or urine output was 0.5mL/Kg/h or lower.
All anesthetic procedures were performed by the same anesthesiologist up to discharge from the post-anesthesia care unit (PACU) and were not blinded to randomization. Neither the patient nor the surgical team knew which study group the participants were in (Consolidated Standards of Reporting Trials, CONSORT, Figure1). We exsanguinated limbs with an Esmarch bandage and installed a pneumatic tourniquet on the subjects’ thighs with a pressure of 200-300 mmHg after sevoflurane inhalation ended.
We prevented hypothermia with thermal blankets and intravenous heat. Cases of bradycardia [HR<50 bpm] were treated with atropine (0.5 mg- 1 mg in bolus) and hypotension (SBP< 90 mmHg or a decrease > 20% of the initial SBP) with ephedrine (5 mg-10 mg in bolus). Transfusion of blood components in the intraoperative period was indicated only when hemoglobin levels were < 7 mg/dL or in cases of persistent hemodynamic instability, even after volume expansion and use of the vasopressor ephedrine.
After the surgical procedure, patients were extubated, returned to consciousness, and referred to the PACU with the operative suction drain open. This was the milestone for the start of bleeding volume measurement. Prophylaxis for deep vein thrombosis was performed with 40 mg of subcutaneous enoxaparin 12 hours after the end of the surgical procedure. Early walking was also encouraged.
Blood samples were collected at the time of venipuncture in the operating room (LAB PRE), immediately after the tourniquet was released (LAB POS), and two hours (LAB2), 12 hours (LAB12), and twenty-four hours after the tourniquet was released (LAB24). The analysis included measurements of blood and platelet counts, hematocrit, creatinophosphokinase (CPK), urea, creatinine, sodium, potassium, calcium, chlorides, alanine aminotransferase, aspartate aminotransferase, D-dimer, lactate, fibrinogen, glycemia, prothrombin time (TP), international normalized ratio (INR), and activated partial thromboplastin time (APTT)
Postoperative blood loss was defined as the blood volume measured in the suction drain after the end of surgery. The volume of blood collected in the suction drain was measured and discarded at one hour (VOL1), two hours (VOL2), 12 hours (VOL12), and 24 hours (VOL24) after tourniquet release. PACU discharge was granted only after collection of the LAB2 sample, blood volume measurement VOL2, and a score of 10 in the modified Aldrete-Kroulik evaluation. Participants were followed up until the 30th postoperative day, and morbidity was registered by analyzing medical records and through telephone contact.
A previous study suggested a visible blood loss around 740 mL, while a meta-analysis showed numbers lower to a volume of 480 mL. [13,14] Upon these informations, we based our sample on an educated guess of a standard deviation of 200 mL to reach 12 patients required in each group for a power of 80% and an alpha error of 0.05. The analyses were conducted using SPSS software. The distribution of variables was analyzed using the Shapiro-Wilk test. Normally distributed data were reported as mean ± SD. Non-parametric distributions were reported as a median (minimum and maximum), whereas the categorical variables were represented as frequencies and percentages. A Fisher’s exact test was used for comparing categorical variables, and unpaired t-tests or Mann-Whitney tests were used for univariate analysis of continuous variables. The results at determined times, within and between groups, were evaluated using the generalized estimating equation (GEE) with Bonferroni correction.  A p value lower than 5% was considered statistically significant.