Intraoperative mechanical ventilation is a major component of general anesthesia. The extent to which various intraoperative tidal volumes and positive end-expiratory pressures (PEEP) on postoperative hypoxia and lung injury remains unclear. We hypothesized that adult patients having orthopedic surgery, ventilation using different tidal volumes and PEEP levels affects the oxygenation within first hour in the postoperative care unit.


We conducted a 2 by 2 factorial cross-over cluster trial at the Cleveland Clinic Main Campus. We enrolled patients having orthopedic surgery 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 H20 in one-week clusters The primary outcome was the effect of tidal volume or PEEP on time-weighted average peripheral oxygen saturation divided by the fraction of inspired oxygen (SpO2/FiO2 ratio) during the initial postoperative hour.


We enrolled 2860 patients who had general anesthesia for orthopedic 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%,7.3%;P=0.042), and for those assigned to high and low PEEP (-0.2% (97.5%CI: ‐4.0%,3.6%;P=0.906). We did not find significant difference in ward SpO2/FiO2 ratio, pulmonary complications, and duration of hospitalization among patients assigned to various tidal volumes and PEEP levels.


Among adults having major orthopedic surgery, pulse oximetry oxygenation is similar with tidal volumes between 6 and 10 ml/kg and PEEP between 5 and 8 cm H20. Our results suggest that any combination of tidal volumes between 6 and 10 ml/kg and PEEP between 5 vs. 8 mL cmH20 can be used safely for orthopedic surgery.