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 H 2 O 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 μg/kg IM and induced with fentanyl 2 μg/kg and propofol 3–5 mg/kg IV before being maintained on fentanyl (5 μg/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 H 2 O 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 and D DV , respectively; cm). Differences between the 2 treatments were analyzed with t ‐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), and D LL and D 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 H 2 O of helmet CPAP in spontaneously breathing anesthetized dogs.