Ventilation with high versus low peep levels during general anaesthesia for open abdominal surgery does not affect postoperative spirometry: A randomised clinical trial.

BACKGROUND: Invasive mechanical ventilation during general anaesthesia for surgery typically causes atelectasis and impairs postoperative lung function. OBJECTIVE: We investigated the effect of intraoperative ventilation with high positive end-expiratory pressure (PEEP) and recruitment manoeuvres (RMs) on postoperative spirometry. DESIGN: This was a preplanned, single-centre substudy of an international multicentre randomised controlled trial, the PROVHILO trial. SETTING: University hospital from November 2011 to January 2013. PATIENTS: Nonobese patients scheduled for major abdominal surgery at a high risk of postoperative pulmonary complications (PPCs). INTERVENTION: Intraoperative low tidal volume ventilation with PEEP levels of 12 cmH2O and RM (the high PEEP group) or with PEEP levels of 2 cmH2O or less without RM (the low PEEP group). MAIN OUTCOME MEASURES: Time-weighted averages (TWAs) of the forced expiratory volume in 1 s (FEV1) and the forced vital capacity (FVC) up to postoperative day five. RESULTS: Thirty-one patients were allocated to the high PEEP group and 32 to the low PEEP group. No postoperative spirometry test results were available for 6 patients. In both groups, TWA of FEV1 and FVC until postoperative day five were lower than preoperative values. Postoperative spirometry test results were not different between the high and low PEEP group; Data are median [interquartile range], TWA FVC 1.8 [1.6 to 2.4] versus 1.7 [1.2 to 2.4] l (P = NS) and TWA FEV1 1.2 [1.1 to 2.5] versus 1.2 [0.9 to 1.9] l (P = NS). Patients who developed PPCs had lower FEV1 and FVC on postoperative day five; 1.1 [0.9 to 1.6] versus 1.6 [1.4 to 1.9] l (P = 0.001) and 1.6 [1.2 to 2.6] versus 2.3 [1.7 to 2.6] l (P = 0.036), respectively. CONCLUSION: Postoperative spirometry is not affected by PEEP and RM during intraoperative ventilation for open abdominal surgery in nonobese patients at a high risk of PPCs, but rather is associated with the development of PPCs. TRIAL REGISTRATION: ClinicalTrials.gov NCT01441791.

Electrical impedance tomography during major open upper abdominal surgery: a pilot-study.

BACKGROUND: Electrical impedance tomography (EIT) of the lungs facilitates visualization of ventilation distribution during mechanical ventilation. Its intraoperative use could provide the basis for individual optimization of ventilator settings, especially in patients at risk for ventilation-perfusion mismatch and impaired gas exchange, such as patients undergoing major open upper abdominal surgery. EIT throughout major open upper abdominal surgery could encounter difficulties in belt positioning and signal quality. Thus, we conducted a pilot-study and tested whether EIT is feasible in patients undergoing major open upper abdominal surgery. METHODS: Following institutional review board's approval and written informed consent, we included patients scheduled for major open upper abdominal surgery of at least 3 hours duration. EIT measurements were conducted prior to intubation, at the time of skin incision, then hourly during surgery until shortly prior to extubation and after extubation. Number of successful intraoperative EIT measurements and reasons for failures were documented. From the valid measurements, a functional EIT image of changes in tidal impedance was generated for every time point. Regions of interest were defined as horizontal halves of the picture. Monitoring of ventilation distribution was assessed using the center of ventilation index, and also using the total and dorsal ventilated lung area. All parameter values prior to and post intubation as well as extubation were compared. A p < 0.05 was considered statistically significant. RESULTS: A total of 120 intraoperative EIT measurements during major abdominal surgery lasting 4-13 hours were planned in 14 patients. The electrode belt was attached between the 2(nd) and 4(th) intercostal space. Consecutive valid measurements could be acquired in 13 patients (93%). 111 intraoperative measurements could be retrieved as planned (93%). Main obstacle was the contact of skin electrodes. Despite the high belt position, distribution of tidal volume showed a significant shift of ventilation towards ventral lung regions after intubation. This was reversed after weaning from mechanical ventilation. CONCLUSIONS: Despite a high belt position, monitoring of ventilation distribution is feasible in patients undergoing major open upper abdominal surgery lasting from 4 to 13 hours. Therefore, further interventional trials in order to optimize ventilatory management should be initiated.