Background: One population prone to aspiration pneumonia and impaired cough is the postoperative patient. Postoperative pneumonia is the third most common complication among surgical patients after urinary tract and wound infections (Wren, Martin, Yoon, & Bech, 2010). A patient who has their surgical course complicated by aspiration pneumonia has increased morbidity, increased length of hospital stay and places greater demands on the health system. Mortality rates are cited as high as 70% (Wren, et al., 2010). Despite the prevalence of postoperative pneumonia and the high morbidity and mortality rates, little is known about the effect of anaesthesia on swallowing and airway protection. This study investigated the effect of clinical doses of fentanyl on suppressed cough reflex in healthy participants.

Materials and Methods: After receiving ethical approval, 14 young, healthy participants gave informed written consent and completed the study protocol. Each participant received a total of 2 mcg/kg of fentanyl in four doses administered at five-minute intervals. Fentanyl effect site concentrations (ESC) were estimated using a standard pharmacokinetic model. During the administration period, suppressed cough response testing (SCR) with nebulised citric acid was performed after each fentanyl dose. Citric acid was presented in increments of 0.2M from each participant’s baseline cough response until a present-strong response was achieved. During the post-administration period, SCR was compared with reducing effect site concentrations to determine the time course for resolution of cough suppression.

Results: Suppressed cough threshold increased and decreased in parallel with modeled fentanyl effect site concentrations. Mean citric acid concentration increased from 0.5M at baseline to 0.6M after 0.5 mcg/kg of fentanyl, 0.7 M after 1 mcg/kg of fentanyl, 0.9M after 1.5 mcg/kg of fentanyl and 1.2M after 2 mcg/kg of fentanyl. Predicted effect site concentrations after final doses of fentanyl (2 mcg/kg) were 1.89 ng/mL (1.81-1.96), well within the range seen clinically in the postoperative period. After the final dose of fentanyl, participants had on average 3.4 increments of change in their cough response (at increments of 0.2M).

Conclusion: SCR testing with citric acid is sensitive enough to mirror changes in fentanyl ESC in healthy, young participants. The degree of reflex suppression seen has been associated with an 8-fold increase in aspiration risk in the general medical patient with dysphagia (Miles, Moore, McFarlane, Lee, Allen, Huckabee, 2013). Further research into the application of SCR in the postoperative period may help clinical decisions regarding safety to commence oral intake.