Recruitable alveolar collapse and overdistension during laparoscopic gynecological surgery and mechanical ventilation: a prospective clinical study.

BACKGROUND: Laparoscopic surgery in Trendelenburg position may impede mechanical ventilation (MV) due to positioning and high intra-abdominal pressure. We sought to identify the positive end-expiratory pressure (PEEP) levels necessary to counteract atelectasis formation ("Open-Lung-PEEP") and to provide an equal balance between overdistension and alveolar collapse ("Best-Compromise-PEEP"). METHODS: In 30 patients undergoing laparoscopic gynecological surgery, relative overdistension and alveolar collapse were assessed with electrical impedance tomography (EIT) during a decremental PEEP trial ranging from 20 to 4 cmH2O in supine position without capnoperitoneum and in Trendelenburg position with capnoperitoneum. RESULTS: In supine position, the median Open-Lung-PEEP was 12 (8-14) cmH2O with 8.7 (4.7-15.5)% of overdistension and 1.7 (0.4-2.2)% of collapse. Best-Compromise-PEEP was 8 (6.5-10) cmH2O with 4.2 (2.4-7.2)% of overdistension and 5.1 (3.9-6.5)% of collapse. In Trendelenburg position with capnoperitoneum, Open-Lung-PEEP was 18 (18-20) cmH 2 O (p < 0.0001 vs supine position) with 1.8 (0.5-3.9)% of overdistension and 0 (0-1.2)% of collapse and Best-Compromise-PEEP was 18 (16-20) cmH2O (p < 0.0001 vs supine position) with 1.5 (0.7-3.0)% of overdistension and 0.2 (0-2.7)% of collapse. Open-Lung-PEEP and Best-Compromise-PEEP were positively correlated with body mass index during MV in supine position but not in Trendelenburg position. CONCLUSION: The PEEP levels required for preventing alveolar collapse and for balancing collapse and overdistension in Trendelenburg position with capnoperitoneum were significantly higher than those required for achieving the same goals in supine position without capnoperitoneum. Even with high PEEP levels, alveolar overdistension was negligible during MV in Trendelenburg position with capnoperitoneum. TRIAL REGISTRATION: This study was prospectively registered at German Clinical Trials registry (DRKS00016974).

Regional ventilation distribution in healthy lungs: can reference values be established for electrical impedance tomography parameters?

BACKGROUND: Although electrical impedance tomography (EIT) is widely used for monitoring regional ventilation distribution, reference values have yet to be established for clinical use. The present study aimed to evaluate the feasibility of creating reference values for standard EIT parameters for potential clinical application. METHODS: A total of 75 participants with healthy lungs were included in this prospective study (male:female, 48:27; age, 34±14 years; height, 172±7 cm; weight, 73±12 kg). The subjects were examined during spontaneous breathing in the supine position. EIT measurements were performed at the level of the 4th intercostal space. Commonly used EIT-based parameters, including the center of ventilation (CoV), dorsal and most dorsal fractions of ventilation distribution (TVD and TVROI4 respectively), global inhomogeneity (GI) index, and standard deviation of regional ventilation delay index (RVDSD) were calculated. RESULTS: Following outlier detection, EIT data from 71 subjects were finally evaluated. The values of the evaluated parameters were: CoV, 48.7%±1.7%; TVD, 48.1%±5.4%; TVROI4, 7.1%±1.8%; GI, 0.49±0.04; and RVDSD, 7.0±2.0. The coefficients of variation for CoV and GI were low (0.03 and 0.07, respectively), but those for TVROI4 and RVDSD were comparatively high (0.26 and 0.28, respectively). None of the evaluated parameters showed a significant correlation with age. The GI index showed a weak but significant correlation with body mass index (R=0.29, P=0.01). The RVDSD was slightly higher in males than in females. CONCLUSIONS: Our study indicated that CoV and GI were stable parameters with small coefficients of variation in participants with healthy lungs. The creation of EIT parameter reference values for setting treatment targets may be feasible.