INTRODUCTION AND EPIDEMIOLOGY
Key Clinical Questions
What is hypertension?
What is the prevalence of hypertensive crises?
What causes hypertensive crises?
What are key differences between a hypertensive urgency and emergency?
How can one diagnose a hypertensive crisis?
What is the treatment for a hypertensive crisis?
Hypertension remains the most common reason for patients to seek medical attention in the United States. It affects over 75 million people in the United States, with global numbers approaching one billion. The annual costs of chronic hypertension, both direct and indirect, are estimated to be $50 billion in the United States alone.
The most popular classification of hypertension is that of the Seventh Report of The Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure (JNC VII). Blood pressure is classified as normal, prehypertension, stage 1 hypertension, and stage 2 hypertension (Table 91-1). The newer JNC VIII deals mostly with chronic hypertension, with less emphasis on the management of urgent and emergent situations.
TABLE 91-1Blood Pressure Classification Based on Guidelines from the Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure ||Download (.pdf) TABLE 91-1 Blood Pressure Classification Based on Guidelines from the Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure
| ||Normal ||Prehypertension ||Stage I ||Stage II |
|Systolic blood pressure (in mm Hg) ||<120 ||120-139 ||140-159 ||>160 |
|Diastolic blood pressure (in mm Hg) ||<80 ||80-89 ||90-99 ||>100 |
Patients with untreated or inadequately treated hypertension are prone to sudden elevations in blood pressure and the development of hypertensive crises. Up to 1% of all hypertensive patients will have a hypertensive crisis in their lifetime. Hypertensive crises come in two forms. In a hypertensive emergency, a surge in blood pressure is accompanied by end-organ damage. Hypertensive urgency is an acute elevation in blood pressure without evidence of end-organ damage. There is no blood pressure threshold that defines a hypertensive crisis, although most patients with pressures exceeding 180/120 mm Hg can be considered to be in hypertensive crisis, with diastolic blood pressures over 120 mm Hg being most strongly associated with end-organ damage. Patients who develop a hypertensive crisis in settings other than chronic essential hypertension may develop end-organ damage at lesser degrees of blood pressure elevation, as they lack the vascular smooth muscle hypertrophy that provides some protection against uncontrolled hypertension.
NORMAL BLOOD PRESSURE CONTROL
Many elements are involved in blood pressure regulation, such as the renin-angiotensin-aldosterone system (RAAS) of the kidney. Renin is released by the juxtaglomerular apparatus ...