A description of intraoperative ventilator management and ventilation strategies in hypoxic patients

Hypoxia is a common finding in the anesthetized patient. Although there are a variety of methods to address hypoxia, it is not well documented what strategies are used by anesthesiologists when faced with a hypoxic patient. Studies have identified that lung protective ventilation strategies have beneficial effects in both oxygenation and mortality in acute respiratory distress syndrome. We sought to describe the ventilation strategies in anesthetized patients with varying degrees of hypoxemia as defined by the Pao(2) to fraction of inspired oxygen (Fio(2)) (P/F) ratio.

We conducted a review of all operations performed between January 1, 2005, and July 31, 2009, using a general anesthetic, excluding cardiac and thoracic procedures, to assess the ventilation settings that were used in patients with different P/F ratios. Patients older than 18 years who received a general anesthetic were included. Four cohorts of arterial blood gases (ABGs) were identified with P/F >300, 300 > or = P/F > 200, 200 > or = P/F > 100, 100 > or = P/F. Using the standard predicted body weight (PBW) equation, we calculated the milliliters per kilogram (mL/kg PBW) with which the patient's lungs were being ventilated. Positive end-expiratory pressure (PEEP), peak inspiratory pressures (PIPs), Fio(2), oxygen saturation (Sao(2)), and tidal volume in mL/kg PBW were compared.

A total of 28,706 ABGs from 11,445 operative cases met criteria for inclusion. There were 19,679 ABGs from the P/F >300 group, 5364 ABGs from the 300 > or = P/F > 200 group, 3101 ABGs from the 200 > or = P/F > 100 group, and 562 ABGs from the 100 > or = P/F group identified. A comparison of ventilation strategies found statistical significance but clinically irrelevant differences. Tidal volumes ranged between 8.64 and 9.16 and the average PEEP varied from 2.5 to 5.5 cm H(2)O. There were substantial differences in the average Fio(2) and PIP among the groups, 59% to 91% and 22 to 29 cm H(2)O, respectively.

Similar ventilation strategies in mL/kg PBW and PEEP were used among patients regardless of P/F ratio. The results of this study suggest that anesthesiologists, in general, are treating hypoxemia with higher Fio(2) and PIP. The average Fio(2) and PIP were significantly escalated depending on the P/F ratio.