To evaluate the minimal dose of lidocaine required for suppression of fentanyl-induced cough. 320 ASA I and II patients, non-smokers of both sexes scheduled for elective surgery between the ages of 18 to 60 yr were randomly allocated into four equal groups. The patients were assigned to receive lidocaine 0.5 mg.kg(-1) (Group I), 1.0 mg.kg(-1)(Group II), 1.5 mg.kg(-1) (Group III) or placebo (Group IV) over five seconds, one minute prior to the administration of fentanyl 3 microg.kg(-1) in a randomized and double-blind fashion. Any episode of cough was classified as coughing and graded as mild (1-2) moderate (3-4) or severe (5 or more). The data were analyzed by test of proportion. Eleven, 12, 11 and 28 patients (13.75%, 15%, 13.75% and 35%) had cough in Groups I, II, III and IV respectively (P < 0.05 Groups I, II, III vs IV). There was no significant difference in the incidence and severity of cough among the lidocaine pretreated groups (P > 0.05). The results of our study suggest that iv lidocaine 0.5 mg.kg(-1) is the minimal dose required to suppress fentanyl-induced cough when administered one minute prior to fentanyl. Any further increase in the lidocaine dose does not reduce the incidence or severity of fentanyl-induced cough.
