Lesson 5. CARDIOLOGY EMERGENCY

HYPERTENSIVE EMERGENCY

Approximately 10 million people in the Ukraine are affected by hypertension (HTN).

New data show an increased lifetime risk of developing HTN and an increased risk of cardiovascular complications associated with blood pressures (BPs) previously considered to be normal. Given this information, the Joint National Committee (JNC-7) has introduced a new classification system for HTN.²

• Prehypertension - Systolic blood pressure (SBP) 120-139 mm Hg or diastolic blood pressure (DBP) 80-89 mm Hg
• Stage I HTN - SBP 140-159 mm Hg or DBP 90-99 mm Hg
• Stage II HTN - SBP >160 mm Hg or DBP >100 mm Hg

Hypertensive crises encompass a spectrum of clinical presentations where uncontrolled BPs lead to progressive or impending target organ dysfunction (TOD). The clinical distinction between hypertensive emergencies and hypertensive urgencies depends on the presence of acute TOD and not on the absolute level of the BP.

Hypertensive emergency

Hypertensive emergencies represent severe HTN with acute impairment of an organ system (eg, central nervous system [CNS], cardiovascular, renal). In these conditions, the BP should be lowered aggressively over minutes to hours.

Hypertensive urgency

Hypertensive urgency is defined as a severe elevation of BP, without evidence of progressive TOD. These patients require BP control over several days to weeks.

Emergency department considerations

Optimal control of hypertensive situations balances the benefits of immediate decreases in BP against the risk of a significant decrease in target organ perfusion. The emergency physician must be capable of the following:

• Appropriately evaluating patients with an elevated BP
• Correctly classifying the HTN
• Determining the aggressiveness and timing of therapeutic interventions
• Making disposition decisions

An important point to remember in the management of the patient with any degree of BP elevation is to "treat the patient and not the number."

The most common clinical presentations of hypertensive emergencies are cerebral infarction (24.5%), pulmonary edema (22.5%), hypertensive encephalopathy (16.3%), and congestive heart failure (12.0%). Less common presentations include intracranial hemorrhage, aortic dissection, and eclampsia.

Central nervous system

Cerebral autoregulation is the inherent ability of the cerebral vasculature to maintain a constant cerebral blood flow (CBF) despite changes in blood pressure. As mean arterial pressure (MAP) increases, the cerebral endothelium is disrupted and the blood-brain barrier can become interrupted. Fibrinoid material deposits in the cerebral vasculature and causes narrowing of the vascular lumen. The cerebral vasculature then attempts to vasodilate around the narrowed lumen. This leads to cerebral edema and microhemorrhages. Patients with chronic HTN can tolerate higher MAPs before they have disruption of their autoregulation system. However, such patients also have increased cerebrovascular resistance and are more prone to cerebral ischemia when flow decreases.

Hypertensive encephalopathy is one of the clinical manifestations of cerebral edema and microhemorrhages seen with dysfunction of cerebral autoregulation. Without treatment, hypertensive encephalopathy can lead to cerebral hemorrhage, coma, and death.

Cardiovascular system

HTN affects the structure and function of the coronary vasculature and left ventricle. HTN also activates the renin-angiotensin-aldosterone system, causing systemic vasculature constriction. This results in increasing myocardial oxygen demand by increasing the left ventricular wall tension and leads to left ventricular hypertrophy and coronary compression. During hypertensive emergencies, the left ventricle cannot overcome systemic vascular resistance. This leads to left ventricular failure and pulmonary edema or myocardial ischemia.

Renal system

Chronic HTN causes pathologic changes to the small arteries of the kidney. The arteries develop endothelial dysfunction and impaired vasodilation, which alter renal autoregulation. When the renal autoregulatory system is disrupted, the intraglomerular pressure starts to vary directly with the systemic arterial pressure, thus offering no protection to the kidney during BP fluctuations. During a hypertensive crisis, this can lead to acute renal ischemia.

Date: 2015-01-12; view: 671