Lung Recruitment Manoeuvre in Morbidly Obese Patients Underdoing Laparoscopic Bariatric Surgery

• This prospective randomized clinical double-blinded study will be carried out at Anesthesiology Department in Tanta University Hospitals for one year from August 2023 to August 2024 after approval from our institutional ethical committee. All enrolled patients will sign an informed written consent to participate in the study.

• Every patient will receive an explanation of the purpose of the study and have secret code number to ensure privacy and confidentiality, all given data will be used for scientific purposes only.

• Any unexpected risks encountered during the research will be cleared to the participants, as well as to the Ethical Committee on time. The risk at the study includes increased risk of bradycardia and hypotension that will be managed by adequate monitoring, atropine, IV fluids, and ephedrine.

-Patients will be randomly allocated in one of the two equal groups using a computer-generated table of random numbers to :-

• Conventional group (group C); 30 patients: Patients will be shifted to 100% Oxygen then; the recruitment maneuver will be performed by manual inflation with a pressure of 30 cmH2O for 30 seconds.

• Ultrasound-guided group (group US); 30 patients: Patients will be shifted to 100% Oxygen then; the recruitment maneuver will be performed under the direct real-time guidance of ultrasound if atelectasis (defined as LUS of ≥ 2 for any of the 12 regions) is present. This will be done by manual inflation with a pressure of 10 cmH2O for 10 seconds, increased 10 cmH2O every 10 seconds until no collapsed areas are visible on the ultrasound, the maximum airway pressure will be limited to 40 cmH2O. This could be repeated if needed.

-Anesthesia technique

I-Preoperative assessment:

▪ All patients will be assessed preoperatively at the Anesthesia Clinic through history, physical examination and requesting the appropriate investigations.

II-In the Holding Area:

• Patient counselling regarding anesthesia technique and surgery.

• Secured IV line.

III- In the Operation Room:

• Standard Monitoring: On arrival of the patient to the operating theater and before induction of anesthesia, all standard monitors will be applied, including heart rate (HR), ECG, oxygen saturation (SpO2), end-tidal CO2, non-invasive blood pressure, and temperature.

• Induction of anesthesia: all patients will be pre-oxygenated with 80% oxygen for 3 minutes before induction. Anesthesia will be induced by slowly titrating doses of intravenous fentanyl (2 ug/kg of lean body weight) and propofol (1 mg/kg of lean body weight). Intubation will be facilitated with atracurium (0.5 mg/kg of lean body weight). Anesthesia will be maintained with atracurium, isoflurane of 1 MAC and fraction inspired Oxygen of 0.5 for each patient.

• Mechanical ventilation protocol: patients will receive the standard ventilation protocol as follows: volume-controlled ventilation mode, with a tidal volume of 4-6 mL/kg of predicted body weight, inspiratory: expiratory ratio 1: 2, PEEP 5 cmH2O, initial respiratory rate is 12/m then adjusted to keep end-tidal carbon dioxide tension (EtCO2) between 35- and 40-mm Hg, and inspired oxygen fraction of 0.5 with total gas flow 1L/m. The patients and investigators who will be responsible for assessing the primary outcomes will be blinded to study group assignment. However, the attending anesthesiologists, intraoperative nursing staff, and intraoperative assessors will not be blinded to study group assignment.

• Positioning and pneumoperitoneum: the patients will be put in reverse trendelenburg position, 30°C head-up position slowly, the position will be kept until the end of surgery.

Intraabdominal pressure will be maintained between 12 ± 3 cmH2O during surgery.

▪ Lung ultrasound examination: will be done: After the induction of anaesthesia (time point T1). After pneumoperitoneum (time point T2). At the end of surgery (before administrating reversal agents for neuromuscular blockade; (time point T3).

• Lung recruitment: recruitment maneuver will be performed in each group as described before after every intraoperative lung ultrasound examination. Intra-abdominal pressure will be recorded. If hypotension (MAP<65mmhg), bradycardia (heart rate<50/m.) or oxygen desaturation (spO2<95%) has been occurred, rescue strategy will be applied as described later.

• Rescue strategy for oxygen desaturation: In both groups, when SpO2 decreased to 95% or lower, the following rescue ventilation strategies will be performed in a stepwise manner (i.e., if SpO2 did not increase after a step, then the following step was applied; otherwise, no further steps were applied).

Steps were performed according to the following order:

• Step (1), three rounds of recruitment maneuvers with a pressure of 30 cmH2O for 10 s.

• Step (2), three rounds of recruitment maneuvers with a pressure of 35 cmH2O for 10 s.

• Step (3), increase FIO2 to 1.0. If SpO2 did not increase after all three rescue strategies, the ventilation strategies could be modified according to the attending anesthesiologist's judgement.