Evaluation of the effects of helmet continuous positive airway pressure on laryngeal size in dogs anesthetized with propofol and fentanyl using computed tomography.

Objective To evaluate the effect of 5 cm H2O of continuous positive airway pressure (CPAP) on laryngeal size in spontaneously breathing anesthetized dogs via computed tomography (CT). Design Prospective, randomized, cross-over clinical study. Setting University teaching hospital and referral private practice. Animals Eight healthy client-owned dogs undergoing CT. Interventions Dogs were sedated with acepromazine 20 mu g/kg IM and induced with fentanyl 2 mu g/kg and propofol 3-5 mg/kg IV before being maintained on fentanyl (5 mu g/kg/h) and propofol (0.3 mg/kg/min) constant rate infusion. Dogs received an air/oxygen mixture with (CPAP) and without (NO-CPAP) 5 cm H2O of CPAP in a random order. Each study step lasted 15 minutes. Measurements and Main Results Ten minutes after the beginning of each study period, a CT scan of the laryngeal region was obtained at end-expiration. CT images were analyzed to determine the laryngeal cross-sectional area (CSA; cm(2)), total volume (V-TOT; cm(3)), and laterolateral and dorsoventral diameters (D(LL)andD(DV), respectively; cm). Differences between the 2 treatments were analyzed witht-test for paired data (P < 0.05). Compared to the NO-CPAP, during CPAP the CSA increased by 53.3 +/- 23.1% (ie, from 3.3 +/- 0.8 to 5.1 +/- 1.3 cm(2),P = 0.0004),V(TOT)increased by 52.4 +/- 13.6% (from 6.2 +/- 1.7 to 9.4 +/- 2.4 cm(3),P < 0.0001), andD(LL)andD(DV)were 55.5 +/- 13.3% (3.6 +/- 0.8 vs 2.4 +/- 0.5 cm,P = 0.006) and 20.3 +/- 8.8% larger (3.2 +/- 0.7 vs 2.7 +/- 0.6 cm,P = 0.0002), respectively. Conclusions Laryngeal volume and cross sectional area increased during the application of 5 cm H2O of helmet CPAP in spontaneously breathing anesthetized dogs.