SAFETY OF PREHOSPITAL NITROGLYCERIN

Study objective: To define changes in vital signs and cardiac rhythm in prehospital patients given sublingual nitroglycerin. Design: A five-month prospective observational study with nitroglycerin administration as the independent variable. Setting: Five independent advanced life support services. Type of participant: Three hundred prehospital patients who were given nitroglycerin by advanced life support personnel for presumed myocardial ischemia or congestive heart failure; excluded were those without repeat vital signs or ECG monitoring and those given additional medications. Intervention: Nitroglycerin was administered by regional emergency medical services protocols or by the order of an on-line medical command physician. Results: Four study patients (1.3%) had adverse effects: One became asystolic and apneic for two minutes, two experienced profound bradycardia with hypotension, and one became hypotensive while tachycardic. All recovered. The 95% confidence interval for adverse effects was 0.5% to 3.4%. Mean fall in systolic blood pressure for the other 296 patients was 14 mm Hg for one dose (confidence interval, 11 to 16 mm Hg) and 8 mm Hg (confidence interval, 2 to 13 mm Hg) for a second dose. Heart rate changed minimally with nitroglycerin administration. The blood pressure drop was linearly correlated with initial systolic pressure (r= -.44; P< .001) but not correlated with number of prior doses of nitroglycerin, initial heart rate, advanced life support time interval, age, or sex. Conclusion: Nitroglycerin seems to be a relatively safe advanced life support drug; however, a few patients experience serious adverse effects. Most of the adverse effects we observed were bradycardic-hypotensive reactions, which appeared to be unpredictable by pretreatment characteristics. Emergency personnel should have an increased awareness of this danger when considering the use of prehospital nitroglycerin.