Airway Pressure Changes Using Esophageal Balloon Catheter (OBC) in Laparoscopic Surgery

General anaesthesia: Patients will be induced and intubated as per the choice of consultant anaesthetist. Anaesthesia will be maintained with inhalational agent and paralysis maintained with atracurium infusion or bolus so as to keep train of four counts <2 twitches using peripheral nerve stimulator throughout surgery. Conventional ventilation was standardised with mode as pressure control ventilation, pressure inspired targeted to either tidal ventilation of 6-8 ml/kg or end tidal carbon di oxide concentration of 40-50 mmHg and positive end expiratory pressure limited to 5 cm of water. Fraction of inspiratory oxygen was adjusted to keep oxygen saturation > 95%. No recruitment manoeuvres were permitted unless, patient is desaturating actively, and in which case patient will be excluded from the study. Abdominal cavity was insufflated with carbon dioxide with initial high flow and pressure, but later the pressure was maintained at 15cm water.

Esophageal balloon catheter insertion, placement and removal: After applying topical anaesthetic (10% lidocaine spray) to patient's nasopharynx and water-soluble lubricant jelly to distal end of esophageal catheter, it is inserted into patient's esophagus via nasal cavity or oropharyngeal cavity. Estimated depth of catheter insertion is calculated as: patient's height (in cm) X 0.288. Once the esophageal balloon catheter is inserted to estimated depth, balloon is inflated with 4 ml of air and pressure on the stomach is applied to look for positive deflection of oesophageal pressure reading. Once convinced, 2 ml air was taken out and catheter was slowly withdrawn till cardiac oscillations are visible. Occlusion test is performed to confirm the placement of catheter in lower thoracic region. In occlusion test, patient is briefly disconnected from ventilator, endotracheal tube is blocked and pressure is applied on to chest wall. Simultaneous increase in oesophageal balloon pressure and airway pressure is noted. (Change is oesophageal pressure/ change in airway pressure on application of external pressure should be close to 1). Stylet is removed and Oesophageal balloon catheter is secured at this position on nostril or angle of mouth similar to nasogastric tube and connected to pressure transducer to do necessary measurements. Catheter is removed at the end of surgery before extubation after complete deflation of cuff.

Measurements: Soon after confirmation of position, patient is subjected to end inspiratory hold to record the end inspiratory pleural pressure and plateau airway pressure. Patient is then subjected to end expiratory hold to record end expiratory pleural pressure and positive end expiratory pressure. Similar steps are repeated once pneumoperitoneum is achieved and patient is placed in trendelenburg or reverse trendelenburg position and once pneumoperitoneum deflated. Problems encountered during insertion and measurement of esophageal balloon catheter will be resolved using manufacturer's recommendation.