SAFETY OF PREHOSPITAL NITROGLYCERIN

Study objective: To define changes in vital signs and cardiac rhythm i n prehospital patients given sublingual nitroglycerin. Design: A five- month prospective observational study with nitroglycerin administratio n as the independent variable. Setting: Five independent advanced life support services. Type of participant: Three hundred prehospital pati ents who were given nitroglycerin by advanced life support personnel f or presumed myocardial ischemia or congestive heart failure; excluded were those without repeat vital signs or ECG monitoring and those give n additional medications. Intervention: Nitroglycerin was administered by regional emergency medical services protocols or by the order of a n on-line medical command physician. Results: Four study patients (1.3 %) had adverse effects: One became asystolic and apneic for two minute s, two experienced profound bradycardia with hypotension, and one beca me hypotensive while tachycardic. All recovered. The 95% confidence in terval for adverse effects was 0.5% to 3.4%. Mean fall in systolic blo od pressure for the other 296 patients was 14 mm Hg for one dose (conf idence interval, 11 to 16 mm Hg) and 8 mm Hg (confidence interval, 2 t o 13 mm Hg) for a second dose. Heart rate changed minimally with nitro glycerin administration. The blood pressure drop was linearly correlat ed with initial systolic pressure (r= -.44; P< .001) but not correlate d with number of prior doses of nitroglycerin, initial heart rate, adv anced life support time interval, age, or sex. Conclusion: Nitroglycer in 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 app eared to be unpredictable by pretreatment characteristics. Emergency p ersonnel should have an increased awareness of this danger when consid ering the use of prehospital nitroglycerin.