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INTRODUCTION: Obesity is associated with increased risk of hypercapnic respiratory failure, prolonged duration on mechanical ventilation, and extended weaning periods. OBJECTIVE: Pilot study to determine whether morbidly obese adult tracheotomized subjects (body mass index [BMI] ⩾ 40) can be more efficiently weaned from the ventilator by optimizing their positive end-expiratory pressure (PEEP) using either an esophageal balloon or the best achieved static effective compliance. METHODS: We randomly assigned 25 morbidly obese adult tracheotomized subjects (median [interquartile range] BMI 53.4 [26.4]; range 40.4-113.8) to 1 of 2 methods of setting PEEP; using either titration guided by esophageal balloon to overcome negative transpulmonary pressure (Ptp) (goal Ptp 0-5 cmH2O) (ESO group) or titration to maximize static effective lung compliance (Cstat group). Our outcomes of interest were number of subjects weaned by day 30 and time to wean. RESULTS: At day 30, there was no significant difference in percentage of subjects weaned. 8/13 subjects (62%) in the ESO Group were weaned vs. 9/12(75%) in the Cstat Group (P = 0.67). Among the 17 subjects who weaned, median time to ventilator liberation was significantly shorter in the ESO group: 3.5 days vs Cstat group 14 days (P = .01). Optimal PEEP in the ESO and Cstat groups was similar (ESO mean ± SD = 26.5 ± 5.7 cmH2O and Cstat 24.2 ± 7 cmH2O (P = .38). CONCLUSIONS: Optimization of PEEP using esophageal balloon to achieve positive transpulmonary pressure did not change the proportion of patients weaned. Among patients who weaned, use of the esophageal balloon resulted in faster liberation from mechanical ventilation. There were no adverse consequences of the high PEEP (mean 25.4; range 13-37 cmH2O) used in our study. The study was approved by the Institutional Review Board at our institution (UMCIRB#10-0343) and registered with clinicaltrials.gov (NCT02323009).
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BACKGROUND: Concomitant lung/brain traumatic injury results in significant morbidity and mortality. Lung protective ventilation (Acute Respiratory Distress Syndrome Network [ARDSNet]) has become the standard for managing adult respiratory distress syndrome; however, the resulting permissive hypercapnea may compound traumatic brain injury. Airway pressure release ventilation (APRV) offers an alternative strategy for the management of this patient population. APRV was hypothesized to retard the progression of acute lung/brain injury to a degree greater than ARDSNet in a swine model. METHODS: Yorkshire swine were randomized to ARDSNet, APRV, or sham. Ventilatory settings and pulmonary parameters, vitals, blood gases, quantitative histopathology, and cerebral microdialysis were compared between groups using χ2, Fisher's exact, Student's t test, Wilcoxon rank-sum, and mixed-effects repeated-measures modeling. RESULTS: Twenty-two swine (17 male, 5 female), weighing a mean (SD) of 25 (6.0) kg, were randomized to APRV (n = 9), ARDSNet (n = 12), or sham (n = 1). PaO2/FIO2 ratio dropped significantly, while intracranial pressure increased significantly for all three groups immediately following lung and brain injury. Over time, peak inspiratory pressure, mean airway pressure, and PaO2/FIO2 ratio significantly increased, while total respiratory rate significantly decreased within the APRV group compared with the ARDSNet group. Histopathology did not show significant differences between groups in overall brain or lung tissue injury; however, cerebral microdialysis trends suggested increased ischemia within the APRV group compared with ARDSNet over time. CONCLUSION: Previous studies have not evaluated the effects of APRV in this population. While our macroscopic parameters and histopathology did not observe a significant difference between groups, microdialysis data suggest a trend toward increased cerebral ischemia associated with APRV over time. Additional and future studies should focus on extending the time interval for observation to further delineate differences between groups.
