Effects of 12 and 17 cmH2O positive end-expiratory pressure applied after alveolar recruitment maneuver on pulmonary gas exchange and compliance in isoflurane-anesthetized horses

Objective To compare static compliance (Cst) and alveolarearterial oxygen tension difference [P(Aea) O-2] between positive end-expiratory pressures (PEEP) of 7, 12 and 17 cmH(2)O applied after an alveolar recruitment maneuver (RM) in isoflurane-anesthetized horses. Study design Prospective, randomized, clinical study. Animals A group of 30 healthy adult horses undergoing arthroscopic surgery. Methods Animals in dorsal recumbency and mechanically ventilated with a tidal volume of 14 mL kg(-1) and 7 cmH(2)O PEEP (control; n = 6) were subjected to an RM by increasing PEEP from 7 to 22 cmH(2)O in 5 cmH(2)O increments at 5 minute intervals, and then decreased similarly to PEEP of 17 (RM17; n = 8), 12 (RM12; n = 8) or 7 cmH(2)O (RM7; n = 8). Cst and P(Aea) O-2 were assessed prior to (baseline) and after the RM at 5, 10, 15, 20, 40, 60 and 80 minutes after achieving each target PEEP, and during recovery from anesthesia. Results Post-RM improvements on P(Aea) O-2 were maintained (baseline versus 80 minutes) in RM12 [216 +/- 77 mmHg (28.8 +/- 10.3 kPa) versus 194 +/- 39 mmHg (25.9 +/- 5.2 kPa)] and RM17 [180 +/- 86 mmHg (24.0 +/- 11.6 kPa) versus 136 +/- 75 mmHg [18.2 +/- 10.0 kPa]). The improvements on Cst were maintained only in RM12 (0.80 +/- 0.13 versus 0.98 +/- 0.13 mL cmH(2)O(-1) kg(-1)). No such improvements were observed in RM7 and control. No significant differences were observed between groups during recovery from anesthesia. Conclusions and clinical relevance The 12 and 17 cmH(2)O PEEP can be used to maintain the improvements on P(Aea) O-2 obtained after an RM. Only 12 cmH(2)O PEEP maintained the post-RM increase on Cst. Such variables were not influenced by the 7 cmH(2)O PEEP.