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

Abstract

BackgroundElectrical 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.MethodsFollowing 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.ResultsA 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 2nd and 4th 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.ConclusionsDespite 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.

Assessment of Ventilation Distribution during Laparoscopic Bariatric Surgery: An Electrical Impedance Tomography Study

“…The same was observed by Karsten et al [12] and He et al [13] at the 5th and by Schaefer et al [8] between the 2nd and 4th intercostal space.…”

“…Reports on intraoperative use of EIT for ventilation assessment are scarce [8, 12–15]. Schaefer et al [8] pointed out that EIT monitoring during abdominal surgery has significant limitations.…”

“…Schaefer et al [8] pointed out that EIT monitoring during abdominal surgery has significant limitations. These are loss of high impedance signal quality and close proximity to the surgical site if the belt is positioned between the 5th and 6th intercostal space.…”

“…In collaboration with the surgeons Schaefer et al [8] placed the belt between the 2nd and 3rd intercostal space and obtained 93% of valid measurements. It should be noted that the studies by Karsten et al [12] and He et al [13] which were also conducted during abdominal laparoscopic surgery did not report on any technical problems even though the belt was placed between the 5th and 6th intercostal space.…”

“…However, EIT monitoring at this level in abdominal surgery may not be feasible [8]. Close proximity to the surgical site and change of patient positioning make access to the electrodes difficult and may preclude the examination.…”