The Effect of Cigarette Smoking on Propofol EC50 of Airway Obstruction during Target Controlled Infusion of Propofol

Kim, Ki Seok; Kim, Kyemin; Lee, Sang Seok; Yoo, Byung Hoon; Lee, Younsuk; Yon, Jun Heum; Hong, Ki Hyuk

Abstract

BACKGROUND: Airway obstruction is a main cause of respiratory complications during sedation. The aim of this study was to identify the effect of smoking on the target plasma concentration of propofol (EC50) of airway obstruction during target controlled infusion (TCI) of propofol.
METHODS
Thirty healthy male adults scheduled for lower extremity surgery under regional anesthesia were randomly allocated to one of five target plasma concentrations (CP) of propofol: 1.0, 2.0, 3.0, 4.0, 5.0microgram/ml (n = 6 for each concentration). After performing regional anesthesia, oxygen was supplied and ETCO2 was measured. All patients received propofol TCI with the assigned CP. The occurrence of airway obstruction was observed until 5 minutes after effect site concentration (CE) reached CP. When hypoxemia, apnea or total airway obstruction was observed, ventilation was assisted with 100% oxygen. The CP, smoking history, snoring history, age, body mass index, Mallampati's classification and thyromental distance were regarded as independent variables. The relationship of airway obstruction and the variables was analyzed with logistic regression with Wald-forward method. By the equation of the probability of airway obstruction 'P = 1/(1 + e-z)', we estimated the propofol EC50 of airway obstruction in smokers and nonsmokers.
RESULTS
The result of logistic regression was as following: z (airway obstruction) = -5.557 + 2.128 x CP [microgram/ml] + 3.625 x smoking (CP: P = 0.007, smoking: P = 0.047). The propofol EC50 of airway obstruction of non-smokers and smokers was 2.6 (1.5-9.4)microgram/ml and 0.9 (-9.3)microgram/ml, respectively.
CONCLUSIONS
The propofol EC50 of airway obstruction of smokers was lower than that of nonsmokers.