Simply adding positive end-expiratory pressure has limited effects on oxygenation in obese dogs.

Positive end-expiratory pressure (PEEP) can be used to prevent atelectasis during anesthesia. We evaluated the effect of PEEP on intra- and postoperative oxygenation on obese dogs admitted for stifle surgery. Dogs received no PEEP (ZEEP; n = 10) or 7 cmH2O PEEP (n = 9) at random during general anesthesia. The partial pressure of arterial oxygen (PaO2) and its ratio to inspired fractional oxygen (PaO2:FiO2) were measured at start and end of surgery (FiO2 1.0), and 20, 120, and 240 minutes after extubation (FiO2 0.2). Cases of hypoxemia (PaO2 < 80 mmHg) were identified. There were no differences between treatment for either variable (P > 0.1 for treatment and P > 0.6 for treatment*time, for both variables). There were three cases of postoperative hypoxemia in the ZEEP treatment (P = 0.21). No significant improvement was achieved when PEEP 7 cmH2O was applied in isolation. Successful use of PEEP may require additional maneuvers.