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.
Highlights
Electrical impedance tomography (EIT) of the lungs facilitates visualization of ventilation distribution during mechanical ventilation
EIT was performed using the EIT Evaluation Kit 2 (Dräger Medical GmbH, Lübeck, Germany) with a 32×32 pixel resolution (1024 pixel per image) in consecutive patients scheduled for major open upper abdominal surgery of at least 3 hours duration
Intraoperative use of EIT was initiated in 14 consecutive patients
Summary
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. We conducted a pilot-study and tested whether EIT is feasible in patients undergoing major open upper abdominal surgery. Electrical impedance tomography (EIT) of the lung is a relatively new on-site tool to visualize and quantify intrathoracic ventilation-dependent gas distribution [1]. In patients undergoing mechanical ventilation EIT can be used to monitor recruitment maneuvers, to detect individual optimal positive endexpiratory pressure levels and to improve tidal volume distribution [3,4,5]. In clinical practice EIT is mostly used in critically ill patients, like in patients with acute respiratory distress syndrome, in order to optimize ventilator settings with the aim to reduce ventilator-induced lung injury [6]
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