Anesthetics and Cerebral Oxygenation in LSG

Obesity is a global health issue that affects different organ systems and may cause severe health issues. Patients with a BMI \> 40 kg/m2 or those with a BMI \> 35 kg/m2 with accompanying comorbidities are candidates for weight loss surgeries, which are generally referred to as bariatric surgeries. Laparoscopic sleeve gastrectomy (LSG) is a restrictive bariatric surgery procedure gaining increased popularity in the surgical treatment of morbid obesity. However, LSG requires a reverse-Trendelenburg position and prolonged pneumoperitoneum. Carbon dioxide pneumoperitoneum increases intracranial pressure (ICP) by increasing intra-abdominal pressure and by causing dilation of cerebral vessels through carbon dioxide reabsorption. Also, the reverse-Trendelenburg position decreases cardiac output and mean arterial pressure (MAP) by reducing cardiac venous return. A Near-infrared spectroscopy (NIRS) is a non-invasive technique and provides continuous monitoring of regional cerebral tissue oxygen saturation (rSO2).

Sevoflurane and propofol are widely used for the maintenance of general anesthesia during bariatric surgery. Sevoflurane is an efficacious halogenated inhalational anesthetic for bariatric surgery because of its rapid and consistent recovery and because it does not cause hemodynamic instability because of its low blood solubility. Moreover, it increases global CBF through a direct intrinsic cerebral vasodilatory action and, in addition, it might improve cerebral oxygenation by decreasing the cerebral metabolic rate of oxygen (CMRO2) (luxury perfusion). Propofol can also be a suitable option for the maintenance of anesthesia in bariatric surgery. Propofol is a short-acting intravenous anesthetic agent with a very good recovery profile, and its elimination half-life and duration of action do not change in obese individuals. However, it has been reported that propofol may significantly decrease CBF by both suppressing CMRO2 and through a direct vasoconstrictive action. The impact of propofol on global CBF is more salient than that on CMRO2, resulting in a decrease in rSO2. The aim of the present study was to test the hypothesis that rSO2 is better preserved with sevoflurane than propofol in morbidly obese patients who have undergone LSG.

All patients were administered 300 mg of oral ranitidine the night before the surgery and 10 mg intravenous (IV) metoclopramide in combination with 150 mg ranitidine one hour before arrival to the operating room. Upon the arrival to the operating room, an electrocardiogram, noninvasive blood pressure, SpO2, rSO2 (INVOSTM 5100C oximeter; Covidien, Massachusetts, USA) and neuromuscular monitorization (TOF-WatchTM SX, Organon, Dublin, Ireland) were performed on the patients. Afterwards, preoxygenation was performed with 4 L/min oxygen (80%) for three minutes by using facemasks, and anesthesia was induced with an IV propofol injection (1.5-2.5 mg/kg of ideal body weight) and an IV bolus administration of remifentanil \[1 mcg/kg of lean body weight (LBW)\] for 30-60 s, and then switched to infusion at 0.25 mcg/kg of LBW/min. After the eyelid reflex disappeared, a neuromuscular blockade was performed using rocuronium (1.2 mg/kg of LBW), ensuring that the train-of-four count and the post-tetanic count (PTC) were both zero, and performed tracheal intubation. Mechanical ventilation was performed with a Draeger FabiusTM Plus anesthesia workstation (Draeger Medical, Lübeck, Germany), and volume-controlled mechanical ventilation was applied. Breathing gases (oxygen, carbon dioxide, sevoflurane) were measured using Draeger ScioTM gas measurement module (Draeger Medical, Lübeck, Germany). The tidal volume was set as 7-8 mL/kg of LBW, inspiratory: expiratory ratio as 1:2, positive end-expiratory pressure as 5-8 cmH2O, and the respiratory rate was determined to obtain an end-tidal carbon dioxide partial pressure (PETCO2) of 32-37 mmHg. These ventilator settings were not changed throughout the operation. Furthermore, after the induction of anesthesia, a radial arterial line was placed in all patients for the continuous measurement of mean arterial pressure and intermittent arterial blood gas analysis.

Oxygen/air (fraction of inspired oxygen (FiO2) of 0.40), inspiratory fresh gas flow of 2 L/min), sevoflurane (1 minimum alveolar concentration \[MAC\]) and remifentanil IV infusion (0.1-0.25 mcg/kg of LBW/min) were used in the Inhalation group for the maintenance of anesthesia. Propofol infusion (4-8 mg/kg of total body weight/h), oxygen/air (FiO2 of 0.40; inspiratory fresh gas flow of 2 L/min) and remifentanil IV infusion (0.1-0.25 μg/kg of LBW/min) were used in the TIVA group. Neuromuscular blockade was performed during the operation by rocuronium infusion (0.3-0.7 mg/kg of LBW/h), ensuring that PTC was zero. IV normal saline or lactated Ringer's solution at 5-7 mL/kg of LBW was also used for perioperative fluid maintenance. Nasopharyngeal temperature was monitored throughout the surgery, and the patient temperature (36-37°C) was ensured by using a forced-air warming system for the maintenance of intraoperative normothermia during the procedure.

After anesthesia induction, a neutral head position of the patients was preserved to prevent alteration of cerebral venous drainage. Carbon dioxide insufflation was performed with an electronic laparoflator using a closed Veress needle technique, and intra-abdominal pressure was automatically kept at the desired level (14-16 mmHg) during the surgery. After the insufflation of carbon dioxide, the patients were positioned in a 30° reverse-Trendelenburg and at a 10° right lateral position.

At the end of the surgery, the blockade was reversed by administering 4 mg/kg of adjusted body weight sugammadex with a PTC of 1-2. All patients were extubated in the beach chair position when fully awake. The patients were referred to the recovery unit and monitored for 50 minutes for complications. In cases where no complications were apparent, the recovery was evaluated using the modified Aldrete scoring system. Once the score was ≥9, the patients were taken to unit. For postoperative nausea and vomiting, 4-5 mg dexamethasone was used (except for diabetic patients on insulin) 90 min before anesthesia induction and 4-8 mg IV ondansetron 20-30 min before the end of the operation. For postoperative pain management, 1 g IV acetaminophen was administered 20 min after induction and 30 mg IV ketorolac 20 min before onset. Then, 1 g IV acetaminophen was administered every 6 h + 50 mg IV dexketoprofen every 8 h for the first 48 hours. In addition, morphine was administered using a patient-controlled analgesia delivery system (demand dose, 20 µg/kg of ideal body weight; lockout time, 6-10 min; 4 h limit, 80% of the total calculated dosage) for 48 h postoperatively.

Eligibility Criteria:
Inclusion Criteria:

* The American Society of Anaesthesiologists (ASA) physical status class II-III
* BMI of ≥ 35 kg/m2
* Patients were planning on undergoing an elective laparoscopic sleeve gastrectomy (LSG)

Exclusion Criteria:

* Patients with preexisting cerebrovascular diseases, overt neurological signs, alcohol or psychoactive drug addiction
* Uncontrolled diabetes or hypertension
* Advanced organ failure
* Preoperative peripheral oxygen saturation (SpO2) less than 96%
* Hemoglobin \<9 g/dL .