Your home plumbing system works best at a specific water pressure. If it is designed to run at a pressure of 50 pounds per square inch (PSI) and you slowly or suddenly increase that pressure to 100 PSI, you would naturally expect busted pipes, leaky connections and malfunctioning appliances. That's hypertension. The principles are the same when applied to the human body; your arteries are the pipes, while your heart dictates the pressure.

Called the 'silent killer,' hypertension is on the rise and currently affects 25 to 30 percent of all adults in the U.S. Hypertension is a potent independent predictor of premature death and, as expected, hypertension-related mortality has increased significantly over the years (33 percent increase from 1980 to 1998). Hypertension has also been cited as one of the leading factors in a patient calling for emergency medical assistance. However, before discussing the proper approach to patient care, it is crucial to understand how hypertension is caused and how to accurately diagnose it.

So what causes high blood pressure? About 90 percent of the time we don't know for sure and use the terms 'primary' or 'essential' hypertension to describe it. Essentially, we don't have the specific cause of elevated blood pressure, but we do have recognizable contributing factors such as excessive alcohol use, high salt intake, obesity, insulin resistance and aging. The remaining 10 percent is called secondary hypertension; the onset of hypertension is secondary to potentially reversible causes. Three common etiologies include drugs (prescription, non-prescription, illegal), obstructive sleep apnea and kidney diseases. If we treat the underlying conditions, the secondary hypertension will improve or resolve.

How to measure hypertension
So, what level of blood pressure is too high? Blood pressure is measured in millimeters of mercury (mmHg) sometimes called "torr." One mmHg equals the pressure it takes to move the mercury in a tube (manometer) one millimeter in measure. Normal pressure is considered to be a systolic blood pressure (SBP) of 120 mmHg or less and a diastolic blood pressure (DBP) of 80 mmHg or less. Hypertension is a SBP of 140 or higher and/or a DBP of 90 or higher. Numbers that fall in between are considered pre-hypertension. Of course, these numbers need to be obtained accurately.

The most precise method of measuring blood pressure is to connect the inside of an artery directly to a pressure-measuring device. This isn’t very practical for field use. The most precise non-invasive method is using a mercury manometer, which has been the accepted standard device since its creation in 1896. But mercury is environmentally unfriendly and current blood pressure devices utilize mechanical or electronic means for measurement. Regardless of how the machine obtains the blood pressure, it must be calibrated to start at zero and validated to ensure accurate measurements over a range of pressures. Routine re-calibration and re-validation assures continued accuracy.

According to the World Hypertension League, to obtain an accurate blood pressure measurement from a reliable blood pressure machine, the patient should first be seated and at rest for 5 minutes. The cuff should encircle 80 percent of the arm and two readings should be obtained — separated by at least 2 minutes — and then averaged.

Severe hypertension and patient care
Now that we can define hypertension and accurately measure blood pressure, our clinical interest exists on two levels: patient care and personal relevance.

For most of our patients, hypertension is a chronic disease that slowly damages various organs over a prolonged period of time until normal functioning is deranged or destroyed. Less frequently, a patient may develop severe hypertension, defined as a SBP over 180 or DBP over 110. If there is no evidence of sudden (acute) organ damage, the severe blood pressure can be controlled over a period of several days. If the pressure is dropped too quickly, it can produce inadequate organ perfusion, which can lead to even further problems post-treatment.

On the other hand, if the severe hypertension is associated with the rapid onset of injury to the brain, heart or kidneys, then we have a hypertensive emergency which must be treated more aggressively. The majority of hypertensive emergencies occur at a DBP over 120. And a significant number of cases are simply due to patient’s non-compliance; they just stop taking their blood pressure medications.
 
Field recognition of a hypertensive emergency begins with an accurate determination of severe blood pressure and the recognition of acute end organ dysfunction or damage. These patients most commonly present signs and symptoms of an acute cerebral infarct, cerebral bleeding or altered brain function (encephalopathy). The next most common presenting signs are acute pulmonary edema, heart failure and/or unstable angina or infarct. Aortic dissection and eclampsia are present much less frequently.

So what do you do now? You have already accomplished the important first step: recognition of the hypertensive emergency. The rest is providing supportive care during transport to the closest appropriate receiving facility. This includes oxygen, intravenous access and continual reassessment; just the usual. You might ask, "But what about dropping the blood pressure?" Even though the pressure needs to come down sooner rather than later, hypoperfusion and/or rapid swings in blood pressure from antihypertensive therapy can result in even more damage. Sometimes the best treatment is no treatment at all. The decrease in blood pressure needs to occur in a controlled descent in an emergency department or intensive care environment. And levels should not be brought down to normal right away, but just enough to restore adequate organ perfusion, which is generally in the range of 10 to 20 percent off the top.

Now for that personal perspective, there's good news and bad news.

First the bad news: there is a one in four chance you will develop hypertension in your lifetime. It is the number one reported reason for a visit to the doctor’s office.

The good news is if you get it, it is highly treatable. Those patients with hypertension need to take their medication faithfully; the number one cause of a hypertensive emergency is non-compliance with blood pressure medication. Learning to maintain a normal blood pressure through a low-salt diet and an overall healthy lifestyle will prevent all of those bad things produced by over-pressurization, including being subjected to a hypertensive emergency.

References

• National Heart, Lung, and Blood Institute. The Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation and Treatment of High Blood Pressure. NIH Publication No. 04-5230, August 2004.
• Ayala C, Croft JB, Wattigney WA, Mensah GA. Trends in Hypertension-Related Death in the United States: 1980-1998. Journal of Clinical Hypertension. 2004;6(12):675-681.
• Carretero OA, Oparil S. Essential Hypertension : Part I: Definition and Etiology. Circulation. 2000;101:329-335.
• Jones DW, Appel LJ, Sheps SG, Roccella EJ, Lenfant C. Measuring Blood Pressure Accurately. JAMA. 2003;289:1027-1030.
• Measuring Your Blood Pressure. World Hypertension League. Retrieved September 23, 2007 from www.worldhypertenisonleague.org/Pages/MeasuringYourBloodPressure.aspx
• Flanigan JS, Vitberg D. Hypertensive Emergency and Severe Hypertension: What to Treat, Who to Treat, and How to Treat. Medical Clinics of North America. 2006;90:439-451.