Safety of prehospital nitroglycerin

To define changes in vital signs and cardiac rhythm in prehospital patients given sublingual nitroglycerin.

A five-month prospective observational study with nitroglycerin administration as the independent variable.

Five independent advanced life support services.

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.

Nitroglycerin was administered by regional emergency medical services protocols or by the order of an on-line medical command physician.

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.

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.