The study was approved by the Ethics Committee for Human Research of the Civil Hospital of Guadalajara “Dr. Juan I Menchaca” (Registration number: 17CI14 039 116 COFEPRIS). Written informed consent was obtained from all subjects after they were informed about the research procedures. The trial was retrospectively registered prior to patient enrollment at clinicaltrial.gov (NCT04854252, Martínez-López E, PhD, 22/04/2021). Besides, the study was conducted in accordance with the Declaration of Helsinki (2013) guidelines. This manuscript adheres to the applicable Enhancing the quality and Transparency of Health Research (EQUATOR) guidelines.
Sample size and randomization
The sample size was determined by using the formula for estimating the difference in effect using preliminary data obtained in our hospital and reported previously in literature  with the following assumptions: α of 0.05 (two-tailed), power of 90%, Zα of 1.96 (according to the normal distribution at a confidence level of 95), and Zβ of1.282 (value equivalent to β=0.10 with a power of 90%). Therefore, a minimum of 15 patients per group was calculated. However, a formula for the correction for losses or abandonments was used, then a minimum of 19 patients per group was considered. Patients who met the inclusion criteria were recruited and simple 1:1 randomized by L.R.P.
In this randomized cross-sectional study, a total of 40 unrelated adults aged 18 -65 years from western Mexico who were scheduled for bypass surgery at the Service of Anesthesiology and Bariatric Surgery of the Civil Hospital of Guadalajara “Dr. Juan I Menchaca”, Jalisco, Mexico, were recruited. The past medical history of study subjects was assessed. The inclusion criteria were: patients aged 18 to 60 years, with a BMI > 30 kg/m2, who were scheduled to undergo a gastric bypass, have undergone an integrated preoperative evaluation and who have signed the informed consent. The exclusion criteria were: patients with a history of ischemic heart disease, history of drug abuse, and with any known allergy to any of the drugs used during anesthesia. Elimination criteria were: patients who withdrew their consent or with insufficient and poor quality blood samples (coagulated) or other reasons that did not allow sample processing.
Anthropometric parameters were measured after an 8-10 hour overnight fast. Measurements were performed with light clothes and without shoes. Height measurement was determined using a stadiometer with a precision of 1 mm (Rochester Clinical Research, Inc., Rochester, NY, USA). Body mass was determined to the nearest 0.05 kg using a balance scale (Seca 703; Seca, Hamburg, Germany) with subjects in underwear. Body mass index (BMI) was calculated as kg/m2 and interpreted according to WHO specifications where subjects with a BMI of 30-34.9 kg/m2 were considered as type I obesity, a BMI of 35-39.9 kg/m2 as type II obesity, and ≥ 40 kg/m2 as obesity type III .
TIVA opioid-containing anesthesia
Before the laparoscopic Roux-en-Y gastric bypass (LRYGB), as a bariatric procedure, subjects were randomly assigned to the study groups of anesthesia with or without an opioid. The general anesthesia technique was defined as a combination of medications administered intravenously in the absence of any inhaled anesthetic agent. Patients undergoing OCA received the following medication schedule:
Loading dose: fentanyl in a bolus dose of 3 mcg/kg (corrected weight), propofol 2-2.5 Cp by target-controlled infusion (TCI) with the Cortínez-Sepúlveda pharmacokinetic model (real weight), ketamine 0.15 mg/kg (corrected weight), lidocaine 2% 1 mg/kg (corrected weight), magnesium sulfate 30-50 mg / kg (corrected weight), and rocuronium bromide in a bolus dose of 0.6/kg (real weight).
Maintenance dose: fentanyl 0.003-0.006 mcg/kg/minute (corrected weight), propofol 2-2.5 Cp with the Cortínez-Sepúlveda pharmacokinetic model (real weight), ketamine 0.15 mg/kg/ minute (corrected weight), lidocaine 2% 1mg/kg (corrected weight), magnesium sulfate 10 mg/kg/minute (corrected weight), and rocuronium bromide 1.25 mcg/ Kg/minute (corrected weight).
TIVA opioid-free anesthesia
TIVA opioid-free anesthesia technique is defined as a combination of medications administered intravenously in which no intraoperative systemic, neuraxial or intracavitary opioid is administered during anesthesia and it also avoids opioids in the perioperative period. Patients undergoing OFA received the following medication schedule:
Loading dose: dexmedetomidine 1-1.5 mcg/kg (corrected weight) for 40 minutes, propofol 2.5-3.5 Cp with the Cortínez-Sepúlveda pharmacokinetic model (real weight), ketamine 0.15 mg/kg (corrected weight), lidocaine 2% 1mg/kg (corrected weight), magnesium sulfate 30-50 mg/kg (corrected weight), and rocuronium bromide in a bolus dose of 0.6/kg (real weight).
Maintenance dose: dexmedetomidine 0.3- 0.7 mcg/kg/minute (corrected weight), propofol 2-4 Cp with the Cortínez-Sepúlveda pharmacokinetic model (real weight), ketamine 0.15 mg/kg/ minute (corrected weight), lidocaine 2% 1mg/kg (corrected weight), magnesium sulfate 10 mg/kg/minute (corrected weight), and rocuronium bromide 1.25 mcg/kg/minute (corrected weight).
All patients were reverted from deep rocuronium-induced neuromuscular blockade with sugammadex at a dose of 2-4 mg / kg (corrected weight) in train-of-four (TOF) monitoring.
Besides, TCI calculated with the Cortínez-Sepúlveda pharmacokinetic model was performed with Syramed® SP6000 Premium Syringe Pump (Arcomed AG, Switzerland).
Depth of anesthesia monitoring
To assess the depth of anesthesia and state of consciousness, indicators of hypoxia and brain death, the Spectral Edge Frequency (SEF) of processed real-time electroencephalography (EEG) was used during surgery.
Basal and post-surgery serum levels of IL-1β, IL-6 and TNF-α.
Post-surgery pain estimation.
Post-surgery Adverse effects.
Blood samples were taken before and immediately after surgery in a Vacutainer® tube and then centrifuged for 15 minutes at 3500 rpm at 4°C to obtain the serum, then, samples were stored at -80°C until analysis. Cytokine serum levels were measured with an enzyme-linked immunosorbent (ELISA) assay. LEGEND MAX™ Human IL-1β (cat # 437007), LEGEND MAX™ Human IL-6 (cat # 430507) and LEGEND MAX™ Human TNF-α (cat # 430207) ELISA kits were used according to the supplier’s instructions.
After 24h of surgery and with a numerical pain rating scale (NPRS), patients were asked to circle the number between 0 and 10 that best fits their pain intensity where 0 represented “no pain at all” and 10 “the worst pain ever” . Therefore, there were 11 possible answers between 0–10.
Regarding adverse effects, nausea and vomiting were reported after 24h after surgery.
The Shapiro Wilk test was used to analyze normal distribution of quantitative variables. Crude means or medians between groups were compared using Student’s t-test or a Mann-Whitney U test, respectively. The general univariate linear model adjusted for other quantitative variables was used to compare differences between the two study groups. Moreover, a chi-square test was used to compare two categorical variables. To determine if the presence of one of the variables behaves as a risk factor for higher cytokine levels, an odds ratio (OR) test was performed. Regarding the evaluation of the individual and joint effect of two or more factors on a quantitative dependent variable, a linear regression model was carried out. The analysis plan was developed before accessing the data.
Statistical analyses were performed using the Statistical Package for the Social Sciences (SPSS), version 20.0 software (IBM Corp., Armonk, NY, USA). A confidence interval of 95% was set and a p<0.05 was considered statistically significant.