Hypertension is the fourth most prevalent chronic medical condition in the United States. According to "Tintinalli's Emergency Medicine," up to 24 percent of the adult population and 32 percent of African Americans are affected. Many patients present to the emergency room from clinics, health fairs or their homes with potentially dangerously elevated blood pressures. Most of these patients are undergoing what is called an acute hypertensive episode with pressures higher than 180/110. "Current Diagnosis and Treatment Emergency Medicine" says that treating a complication-free acute hypertensive episode can lead to low blood pressures and a drop in oxygen delivery to the brain. However, when hypertension is complicated by evidence of organ damage--for example, altered mental status, kidney failure, or chest pain--the diagnosis changes to hypertensive emergency, and urgent intravenous medications are necessary before irreversible damage occurs.
Sodium Nitroprusside
This is the drug of choice for hypertension emergencies because it takes effect rapidly, lowers blood pressure in a controlled manner, and lasts only a short time so the effects can be reversed quickly if the blood pressure is inadvertently dropped too low. It acts by dilating--or widening--both veins and arteries throughout the body. This reduces the pressure the heart has to work against to pump blood. The main disadvantages to nitroprusside are that it needs to be protected from light at all times .necessitating wrapping the IV tubing in tin foil, and prolonged use may result in the buildup of cyanide in the blood.
Labetalol
Labetalol is a popular antihypertensive that can be given both orally--for example, during acute hypertensive episodes with no evidence of organ damage--or intravenously. It acts by blocking receptors in the blood vessels and the heart. This causes the heart to beat with less force and the blood vessels to dilate. The main disadvantage of labetalol is a prolonged duration of action. It takes longer for labetalol to be cleared from the system than nitroprusside. Therefore, if too much is given, it can lead to prolonged hypotension. "Tintinalli's Emergency Medicine" says that it should also be avoided in patients with asthma or COPD because it can cause constriction of the airways in the lungs.
Intravenous Nitrogylcerin
Nitroglycerin is the same medication given beneath the tongue in tablet form during attacks of angina or myocardial infarctions. It can also be given intravenously during hypertensive emergencies to dilate blood vessels. The main indication for the use of intravenous nitroglycerin is when the acutely elevated blood pressure causes chest pain or a drop in oxygen delivery to the heart. This is because nitroglycerin dilates the blood vessels that supply blood to the heart more than the other vessels in the body.
Hydralazine
Hydralazine acts directly upon the smooth muscle tissue that constricts to narrow the arteries. It causes these muscles to relax, dilating vessels and allowing the blood to flow more freely. It's not used as often as the other medications because it takes an average of 10 minutes to begin working and, according to "Tintinalli's Emergency Medicine," it can last from four to six hours. However, unlike many of the other IV antihypertensives it's safe to use in pregnancy and is often given during cases of eclampsia for this reason.
References
- "Tintinalli's Emergency Medicine: A Comprehensive Study Guide, 6e"; Judith E. Tintinalli, MD, MS, Gabor D. Kelen, MD, J. Stephan Stapczynski, MD, O. John Ma, MD and David M. Cline, MD; 2004
- "Tintinalli's Emergency Medicine: A Comprehensive Study Guide, 6e"; Judith E. Tintinalli, MD, MS, Gabor D. Kelen, MD, J. Stephan Stapczynski, MD, O. John Ma, MD and David M. Cline, MD; 2004
