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Abstract

Introduction: Perioperative ventilation may impact the development of ARDS. However, the effect of the type of ventilator on intraoperative ventilation has not been extensively studied. This study compares the intraoperative positive pressure ventilation characteristics of patients undergoing general anesthesia (GA) before (pre) and after (post) updating OR ventilators. Hypothesis: A change in OR ventilator will result in different intraoperative ventilator management. Methods: In Feburary and March of 2007, existing anesthesia machines (Narkomed, IIb) at the University of Michigan Medical Center were replaced with new devices (General Electric, Aisys). Utilizing data electronically collected in an anesthesia information system (AIMS,) we compared the median positive pressure ventilation characteristics of patients anesthetized between 11/1/06 and 1/31/07 (pre) with those of patients anesthetized between 4/1/07 and 6/30/07 (post). All adult (age >18 years) patients receiving GA for non-cardiothoracic surgery were included in the dataset. Using the standard predicted body weight (PBW), we compared the median tidal volume (Total Vt and mL/kg PBW) as well as positive end-expiratory pressure (PEEP), peak inspiratory pressure (PIP), Delta P (PIP-PEEP), and FiO2 of the groups. Results: A total of 4,484 operative cases were included in the study with 2,303 patients included in the pre group and 2,581 patients included in the post group. A comparison of ventilation characteristics found statistically significant differences in medians (pre v post): PIP (25.4 ± 5.7 v 20.5 ± 6.3 cmH2O,p<.001), Delta P (23.5 ± 5.5 v 18.8 ± 5.7 cmH2O,p<.001), Vt (586 ± 139 v 555 ± 124 ml,p<.001; 9.3 ± 2.2 v 8.8 ± 1.9 ml/kg,p<.001), FiO2 (58 ± 17 v 52 ± 18%, p<.001) Groups did not differ in age, ASA category, PBW or BMI. The pre group received slightly more crystalloids (2.5 ± 4.4 v 2.2 ± 3.5 L,p=.027). Conclusions: In this study, we observed different ventilator settings depending on the type of anesthesia machine utilized. The settings in new, electronically controlled machines seem more consistent with lung protective ventilation (smaller Vt and lower PIP) and may imply a lower risk of volutrauma and barotrauma; which may be significant in at-risk populations.