To determine the validity of functional electric impedance tomography to monitor regional ventilation distribution in experimental acute lung injury, and to develop a simple electric impedance tomography index detecting alveolar recruitment. Randomized prospective experimental study. Academic research laboratory. Sixteen anesthetized, tracheotomized, and mechanically ventilated pigs. Acute lung injury was induced either by acid aspiration (direct acute lung injury) or by abdominal hypertension plus oleic acid injection (indirect acute lung injury) in ten pigs. Six pigs with normal lungs were studied as a control group and with endotracheal suction-related atelectasis. After 4 hrs of mechanical ventilation, a slow inflation was performed. During slow inflation, simultaneous measurements of regional ventilation by electric impedance tomography and dynamic computed tomography were highly correlated in quadrants of a transversal thoracic plane (r2 = .63-.88, p < .0001, bias <5%) in both direct and indirect acute lung injury. Variability between methods was lower in direct than indirect acute lung injury (11 +/- 2% vs. 18 +/- 3%, respectively, p < .05). Electric impedance tomography indexes to detect alveolar recruitment were determined by mathematical curve analysis of regional impedance time curves. Empirical tests of different methods revealed that regional ventilation delay, that is, time delay of regional impedance time curve to reach a threshold, correlated well with recruited volume as measured by CT (r2 = .63). Correlation coefficients in subgroups were r2 = .71 and r2 = .48 in pigs with normal lungs with and without closed suction related atelectasis and r2 = .79 in pigs subject to indirect acute lung injury, respectively, whereas no significant correlation was found in pigs undergoing direct acute lung injury. Electric impedance tomography allows assessment of regional ventilation distribution and recruitment in experimental models of direct and indirect acute lung injury as well as normal lungs. Except for pigs with direct acute lung injury, regional ventilation delay determined during a slow inflation from impedance time curves appears to be a simple index for clinical monitoring of alveolar recruitment.

Postoperative pulmonary complications (PPCs) increase the morbidity and mortality of surgery in obese patients. High levels of positive end-expiratory pressure (PEEP) with lung recruitment maneuvers may improve intraoperative respiratory function, but they can also compromise hemodynamics, and the effects on PPCs are uncertain. We hypothesized that intraoperative mechanical ventilation using high PEEP with periodic recruitment maneuvers, as compared with low PEEP without recruitment maneuvers, prevents PPCs in obese patients. The PRotective Ventilation with Higher versus Lower PEEP during General Anesthesia for Surgery in OBESE Patients (PROBESE) study is a multicenter, two-arm, international randomized controlled trial. In total, 2013 obese patients with body mass index ≥35 kg/m2 scheduled for at least 2 h of surgery under general anesthesia and at intermediate to high risk for PPCs will be included. Patients are ventilated intraoperatively with a low tidal volume of 7 ml/kg (predicted body weight) and randomly assigned to PEEP of 12 cmH2O with lung recruitment maneuvers (high PEEP) or PEEP of 4 cmH2O without recruitment maneuvers (low PEEP). The occurrence of PPCs will be recorded as collapsed composite of single adverse pulmonary events and represents the primary endpoint. To our knowledge, the PROBESE trial is the first multicenter, international randomized controlled trial to compare the effects of two different levels of intraoperative PEEP during protective low tidal volume ventilation on PPCs in obese patients. The results of the PROBESE trial will support anesthesiologists in their decision to choose a certain PEEP level during general anesthesia for surgery in obese patients in an attempt to prevent PPCs. ClinicalTrials.gov identifier: NCT02148692. Registered on 23 May 2014; last updated 7 June 2016.

Avoiding tidal recruitment and collapse during mechanical ventilation should reduce the risk of lung injury. Electrical impedance tomography (EIT) enables detection of tidal recruitment by measuring regional ventilation delay inhomogeneity (RVDI) during a slow inflation breath with a tidal volume (V_T) of 12 mL/kg body weight (BW). Clinical applicability might be limited by such high V_Ts resulting in high end-inspiratory pressures (P_EI) during positive end-expiratory pressure (PEEP) titration. We hypothesized that RVDI can be obtained with acceptable accuracy from reduced slow inflation V_Ts. In seven ventilated pigs with experimental lung injury, tidal recruitment was quantified by computed tomography at PEEP levels changed stepwise between 0 and 25 cmH₂O. RVDI was measured by EIT during slow inflation V_Ts of 12, 9, 7.5, and 6 mL/kg BW. Linear correlation of tidal recruitment and RVDI was excellent for V_Ts of 12 (R² = 0.83, p < 0.001) and 9 mL/kg BW (R² = 0.83, p < 0.001) but decreased for V_Ts of 7.5 (R² = 0.76, p < 0.001) and 6 mL/kg BW (R² = 0.71, p < 0.001). With any reduction in slow inflation V_T, P_EI decreased at all PEEP levels. Receiver-Operator-Characteristic curve analyses revealed that RVDI-thresholds to predict distinct amounts of tidal recruitment differ when obtained from different slow inflation V_Ts. In conclusion, tidal recruitment can sufficiently be monitored by EIT-based RVDI-calculation with a slow inflation of 9 mL/kg BW.