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Tidal Volume and Positive End-expiratory Pressure and Postoperative Hypoxemia during General Anesthesia: A Single- center Multiple Crossover Factorial Cluster Trial

July 22, 2022

Intraoperative mechanical ventilation is a major component of general anesthesia. The extent to which various intraoperative tidal volumes and positive end-expiratory pressures (PEEP) effect on postoperative hypoxia and lung injury remains unclear. We hypothesized that adults having orthope- dic surgery, ventilation using different tidal volumes and PEEP levels affect the oxygenation within first hour in the postoperative care unit.
We conducted a two-by-two factorial crossover cluster trial at the Cleveland Clinic Main Campus. We enrolled patients having orthopedic sur- gery with general anesthesia who were assigned to factorial clusters with tidal volumes of 6 or 10 ml/kg of predicted body weight and to PEEP of 5 or 8 cm H 2 O in 1-week clusters. The primary outcome was the effect of tidal volume or PEEP on time-weighted average peripheral oxygen saturation measured by pulse oximetry divided by the fraction of inspired oxygen (Spo2 /Fio2 ratio) during the initial postoperative hour.
We enrolled 2,860 patients who had general anesthesia for ortho- pedic surgery from September 2018 through October 2020. The interaction between tidal volume and PEEP was not significant (P = 0.565). The mean ± SD time-weighted average of Spo2 /Fio2 ratio was 353 ± 47 and not different in patients assigned to high and low tidal volume (estimated effect, 3.5%; 97.5% CI, –0.4% to 7.3%; P = 0.042), for those assigned to high and low PEEP (estimated effect, –0.2%; 97.5% CI, –4.0% to 3.6%; P = 0.906). We did not find significant difference in ward Spo2 /Fio2 ratio, pulmonary complica- tions, and duration of hospitalization among patients assigned to various tidal volumes and PEEP levels.
Among adults having major orthopedic surgery, postoperative oxygenation is similar, with tidal volumes between 6 and 10 ml/kg and PEEP between 5 and 8 cm H 2 O. Our results suggest that any combination of tidal volumes between 6 and 10 ml/kg and PEEP between 5 versus 8 ml cm H 2 O can be used safely for orthopedic surgery.