Assessment of the cough reflex after propofol anaesthesia for colonoscopy

Abstract

Background. Dysfunction of the cough reflex as a result of the lingering effects of anaesthetics may lead to aspiration pneumonia or retained secretions after general anaesthesia. It is unknown whether low concentrations of propofol alter the cough reflex in the early period after anaesthesia. The objective of this study was to investigate the effect of low concentrations of propofol on the cough reflex sensitivity as assessed by the cough reflex threshold to an inhaled irritant. Methods. Fifteen, ASA I-II, non-smoking patients undergoing elective colonoscopy were studied. Anaesthesia was induced and maintained with a blood target-controlled propofol infusion. Cough reflex threshold was measured with citric acid. Increasing concentrations of nebulized citric acid (2.5, 5, 10, 20, 40, 80, 160, 320, and 640 mg ml-1) were delivered during inspiration until a cough was evoked. The citric acid concentration eliciting one cough (C1) was defined as the cough reflex threshold. C1 was log transformed for statistical analysis (Log C1). Log C1 was measured before anaesthesia and during the recovery period with estimated decreasing propofol concentrations of 1.2, 0.9, 0.6, and 0.3 μg ml-1. Results. Log C1 (median; interquartile range) measured with propofol concentrations of 1.2, 0.9, 0.6, 0.3, and 0 μg ml-1 were 1.9 (0.6), 1.9 (1.0), 1.9 (1.1), 1.9 (0.6), and 1.9 (0.7) mg ml-1 (NS), respectively. However, light sedation was observed with propofol concentrations of 1.2 and 0.9 μg ml-1. Conclusion. This study indicates that residual sedation after propofol anaesthesia for colonoscopy does not adversely affect the cough reflex. © The Board of Management and Trustees of the British Journal of Anaesthesia 2005. All rights reserved.