Chapter 84: Hypertension: Preoperative Evaluation

DEFINING HYPERTENSION

Hypertension is defined as elevated arterial blood pressure. The Joint National Committee on Evaluation, Detection, and Prevention of High Blood Pressure defines the optimal blood pressure for adults less than 120/80.

Stage II hypertension is classified as urgent or emergent hypertension.

Stage II becomes emergent with signs of end organ damage including headache, blurred vision, stroke, congestive heart failure, myocardial ischemia, and acute kidney injury.

The normal blood pressure measurements for children increase with age:

PATHOPHYSIOLOGY

The pathophysiology of hypertension can best be explained by separating systolic, diastolic, and pulse pressure hypertension.

Systolic Hypertension

Systolic hypertension is a macrovascular disease. It is caused by atherosclerosis of the aorta and large arteries. The aorta becomes less compliant and less distensible in response to ventricular and aortic outflow from the heart. Decreased compliance of the arterial tree increases blood pressure and afterload. Risk factors for systolic hypertension include age more than 60 years, diabetes mellitus, hyperlipidemia, and smoking.

Diastolic Hypertension

Diastolic hypertension is a microvascular disease. It is caused by atherosclerosis of the small vessels more than 1 mm. Isolated diastolic hypertension often occurs in younger patients less than 50 years old. It is a marker for coronary artery disease and increased mortality.

Pulse Pressure Hypertension

In a normotensive patient, systole occurs as blood is ejected from the heart and travels to the periphery in a pulsatile wave. As the blood reaches the arterial bifurcations, the impedance causes a wave to return to the heart. This normally coincides with diastole, augmenting blood flow, and diastolic pressure. Normal pulse pressure is less than 40 mm Hg.

In patients with systolic hypertension, the systolic wave travels faster and returns faster. This augments systolic pressure rather than diastolic pressure.

Pulse pressure hypertension occurs in 50% of patients with isolated systolic hypertension. Increased pulse pressure occurs in normotensive patients as well as patients with systolic and diastolic hypertension. Hypertensive patients typically have increased systemic vascular resistance and normal cardiac output.

ETIOLOGY

The most common cause of hypertension is essential hypertension. The etiology is unknown.

Other causes include:

• Renal: Renal artery stenosis, polycystic kidney disease, diabetic nephropathy, glomerulonephritis

• Endocrine: Cushing’s disease, pheochromocytoma, hyperthyroidism, hyperaldosteronism, hyperparathyroidism

Risk factors for essential hypertension include:

• African American

• Family history of hypertension

• Excess alcohol consumption

• Obesity

• Dyslipidemia

PREOPERATIVE ASSESSMENT