According to the Joint National Committee's 2003 report, hypertension is defined as a systolic blood pressure (BP) >140 mm Hg or a diastolic BP >90 mm Hg.

• Essential (primary) hypertension describes high BP when no cause has been identified. Associated factors include obesity, excess dietary sodium intake, reduced physical activity, inadequate intake of fruits, vegetables and potassium, and excess alcohol intake.
• Secondary hypertension (<5%) is due to identifiable causes such as sleep apnea, drug-induced or related causes, chronic kidney disease, primary aldosteronism, renovascular disease, chronic steroid therapy, Cushing's syndrome, pheochromocytoma, coarctation of the aorta, thyroid, or parathyroid disease.

• The pathogenesis of essential hypertension is not completely understood. Studies have suggested that it may result from impaired sodium excretion by the kidneys, or an overactive renin-angiotensin or sympathetic nervous system. During the early stages, an increase in cardiac output and normal total peripheral resistance is seen. Over time, the cardiac output returns to normal levels, but the total peripheral resistance increases and intravascular volume decreases
• The relative intravascular volume depletion can become unmasked with sympatholysis from anesthetic medications and neuraxial techniques.

• Perioperative anesthetic management aims to maintain hypertensives within a range of 10–20% of preoperative values. However, increased vascular stiffness and decreased vascular filling predispose patients to greater swings in BP. Thus, tight control may require the use of antihypertensives, vasopressors, and invasive monitoring.
• There is conflicting evidence that mild-to-moderate preoperative hypertension in the absence of target organ damage is an independent predictor of postoperative cardiac complications of cardiac death, postoperative myocardial infarction (MI), heart failure, or arrhythmias.
• Cardiac events in hypertensives occur at a higher frequency in the perioperative period for cardiac surgery, carotid artery surgery, peripheral vascular surgery, abdominal aortic surgery, and thoracoabdominal surgery.
• Severe hypertension or crisis in the perioperative period (diastolic BP >120 mm Hg) or impending organ damage poses definite risks of cardiac complications such as myocardial ischemia, MI, or stroke. Causes may include abrupt withdrawal of clonidine or beta-blockers, interaction of monoamine oxidase inhibitors (MAO) with sympathomimetic agents, pheochromocytoma, preeclampsia, or eclampsia.
• Preoperative BP medications should be continued in the preoperative as well as perioperative period. ACE inhibitors and ARBs may cause profound and refractory hypotension when taken on the morning of surgery; however there are no guidelines at this time on how to manage.

Usually asymptomatic

This may include adoption of healthy lifestyles that reduce, prevent or delay hypertension, and increase the efficacy of antihypertensive medications. Lifestyle modifications include adoption of dietary changes that are low in salt and rich in fruits and vegetables, limitation of alcohol intake, regular exercise, and weight loss.

• Drug type, recent changes, and compliance should be reviewed. Over 40% of patients with hypertension do not take medications and 2/3^rd are not optimally controlled. Furthermore, most patients are on more than one antihypertensive.
• Diuretics. Thiazide-type diuretics are first-line treatment for most patients with uncomplicated hypertension, either alone or in combination with other classes.
• Beta-blockers
• Calcium channel blockers
• Alpha-adrenergic blockers
• ACE inhibitors/angiotensin receptor blockers (ARBs)
• Central sympatholytics
• Direct vasodilators
• Hypertensive patients with diabetes mellitus (DM), chronic kidney disease, heart failure, post-MI, high coronary disease risk, and recurrent stroke prevention are compelling indications for treatment with a certain, specific class of antihypertensives.

• Cardiovascular, cerebrovascular, renovascular, and peripheral vascular disease
• Obesity, sleep apnea, DM
• Untreated hypertension can lead to target organ damage of the heart (LVH, angina, and heart failure), brain (stroke or transient ischemic attack, dementia), chronic kidney disease, peripheral arterial disease, and retinopathy.

• Preoperative diastolic blood pressure (DBP) <110 mm Hg. Studies have suggested that patients can safely undergo elective surgery.
• Hypertensive urgency describes a severe elevation in BP without progressive end-organ dysfunction. Preoperative DBP >110 mm Hg have been associated with an increased risk of cardiac and vascular morbidity; thus elective surgery may be postponed until good antihypertensive control has been achieved. However, there is increasing evidence that in the absence of cardiac, vascular, or renal complications in this population, immediate control of hypertension prior to surgery may be effective in preventing complications.
• Hypertensive emergencies describe a DBP >120 mm Hg and accompanying end-organ dysfunction. Surgery should be delayed for emergent treatment.

• BP readings are the average of two or more seated checks on each of two or more separate office visits.
• Prehypertension: Systolic blood pressure (SBP) 120–139 mm Hg, DBP 80–89 mm Hg
• Stage 1: SBP 140–159 mm Hg, DBP 90–99 mm Hg
• Stage 2: SBP >160 mm Hg, DBP >100 mm Hg.
• Hypertensive urgency: Severe elevation without progressive end-organ dysfunction.
• Hypertensive crisis/emergency: SBP >180 mm Hg, DBP >120 mm Hg and accompanying end-organ damage (hypertensive encephalopathy, intracerebral hemorrhage, subarachnoid hemorrhage, acute stroke, unstable angina, acute MI, congestive heart failure, acute renal dysfunction, and acute aortic dissection)

Uncontrolled hypertension requires a higher level of care and monitoring.

Resume antihypertensive medications as soon as possible after surgery. If oral intake is not possible, the drug should be administered via the nasogastric tube or IV route (equivalent doses, preferably same class).

• Hypertension may result from pain or a full bladder. Other causes include hypoxia, hypercarbia, fluid overload, drugs, and cerebrovascular accident.
• Unexpected severe hypertension in the intraoperative or perioperative setting should lead to suspicion of undiagnosed pheochromocytoma.

• Perioperative Hypertension
• Pregnancy-Induced Hypertension
• Geriatric Physiology
• ACE Inhibitors and Hypotension

401.9 Unspecified essential hypertension

I10 Essential (primary) hypertension

Gundappa Neelakanta , MD