Magnesium sulphate suppresses fentanyl-induced cough during general anesthesia induction: a double-blind, randomized, and placebo-controlled study.

Fentanyl-induced cough is a common phenomenon during anesthesia induction. Magnesium sulphate (MgSO4) is reported to have a powerful relaxation of airway smooth muscle. This study is to investigate the effects of prophylactic MgSO4 on the incidence and severity of fentanyl-induced cough. A total of 120 patients, scheduled for elective surgery under general anesthesia, were randomly allocated into three groups (n = 40, each group) and injected with 50 ml normal saline, 30 mg/kg and 50 mg/kg of MgSO4 (diluted with normal saline into 50 ml) in groups I, II and III, respectively. One minute later all patients were injected with 5.0 μg/kg of fentanyl within 5 s. The incidence and severity of cough were recorded 30 s after fentanyl injection. Hemodynamic parameters and plasma magnesium concentration of the patients were also noted. Three patients dropped off the study due to obvious burning sense during injection of 50 mg/kg of MgSO4. Injection with 50 mg/kg of MgSO4 increased plasma magnesium level at the end of its infusion, but the latter still remained within therapeutic range (2-4 mmol/L). The incidence of cough in group I was much higher than those in groups II and III (45.0% vs. 15.0% and 8.1%, P < 0.05). Compared with the group I, both the groups II and III had lower incidence of moderate cough (P < 0.05). There were no differences in the hemodynamic data at three timepoints among the three groups. In conclusion, fentanyl-induced cough may be suppressed effectively and safely by prophylactic 30 mg/kg of MgSO4 during anesthetic induction.