The effect of nitroglycerin on response to tracheal intubation. Assessment by radionuclide angiography

The effect of intravenous (IV) nitroglycerin (NTG) on perioperative myocardial ischemia as detected by single pass radionuclide angiocardiography was studied in 20 patients scheduled for elective coronary artery bypass grafting (CABG). Ten patients, selected at random, received IV NTG 1 microgram.kg-1.min-1 (NTG group) and 10 others, IV saline (control group). Anesthetic induction consisted of midazolam 0.2 mg.kg-1, vecuronium 0.1 mg.kg-1, and 50% N2O in O2. ECG leads I, II, and V5 were monitored for ST segment changes. Single pass radionuclide angiocardiography (RNA) was performed at 5 times: prior to induction, prior to tracheal intubation, and at 1, 3.5, and 6 min following intubation. The presence of new regional wall motion abnormalities (RWMA) was determined from each RNA study as compared with the preinduction measurement. Apart from one patient in the control group who developed a new "v" wave after intubation, there was no evidence of ischemia by pulmonary capillary wedge pressure. No ECG evidence of ischemia was detected in any patient. Despite this, new regional wall motion abnormalities were observed in 3 patients in the control group and 1 patient in the NTG group. Blood pressure and heart rate responses of patients with new RWMA were not significantly different from other patients. The low incidence of ischemia in this population precludes a definitive statement regarding the efficacy of IV NTG, but the lower incidence of RWMA in the NTG group suggests a protective effect.