The use of intranasal nitroglycerin to prevent pressor responses during intubation in general anesthesia--a comparison of various doses.

BACKGROUND: Intranasal nitroglycerin (NTG) was first reported to successfully prevent an increase in arterial blood pressure following laryngoscopy and tracheal intubation by Hill et al. Various different effective dosages of NTG have been reported. Grover et al. indicated 0.75 mg of intranasal NTG to be the most suitable dose. However, no definite conclusion has yet been made. This study was designed to compare the efficacy of four different dosages of intranasal NTG (0.3, 0.5, 0.75, and 1.0 mg) in preventing pressor responses to laryngoscopy and tracheal intubation during the induction of general anesthesia.

METHODS: One hundred patients (ASA I or II) scheduled for elective surgery were included. These study subjects were divided into five groups and randomly assigned to four different dosages of intranasal NTG and a placebo. Each group consisted of 20 patients. The NTG solution was administered 1 min before the injection of thiopental. Systolic arterial pressure (SAP), diastolic arterial pressure (DAP), mean arterial pressure (MAP) and heart rate (HR) were recorded before the induction of anesthesia (T1), before laryngoscopy (T2), and at 0, 3, and 5 min after tracheal intubation (T3, T4, and T5 respectively).

RESULTS: In patients who received a placebo (control group), there were significant increases in SAP, MAP, HR and rate-pressure-product (RPP) associated with tracheal intubation. Tachycardia was noted in all experimental groups. The increases in MAP associated with tracheal intubation were significantly less in patients who received NTG of 0.5 mg or more but not 0.3 mg. Although 0.5 mg of NTG did attenuate the increases in SAP after tracheal intubation, the increases in SAP of the other three experimental groups were no less than that of the control group. Rate-pressure-product (RPP) values of the experimental groups were noted to be equal to or higher than those of the control group during the period of study. Contrary to the results of the study conducted by Grover et al., 0.75 mg of NTG did not attenuate the pressor responses.

CONCLUSIONS: Intranasal NTG does not attenuate the pressor responses to laryngoscopy and tracheal intubation.