CHAPTER 28 Blood Pressure Disturbances
1 What is the significance of hypertension to the general patient population?
The prevalence of hypertension (HTN) is about 20% to 25% of the general population, making it a common preoperative comorbidity. It is a leading cause of death and disability in most Western societies. Long-standing HTN leads to atherosclerosis and chronic organ failure. It is a major risk factor for cardiac, vascular, cerebral, and renal disease.
2 What blood pressure value is considered hypertensive?
The numbers are somewhat arbitrary. Blood pressure (BP) changes throughout the day and can be affected by posture, exercise, medications, smoking, caffeine ingestion, and mood. HTN cannot be diagnosed on the basis of one abnormal BP reading but requires sustained elevations over multiple measurements on different days. Systemic hypertension is usually considered sustained elevations of diastolic BP greater than 90 to 95 mm Hg or a systolic BP greater than 140 to 160 mm Hg. Borderline HTN is defined as diastolic BP between 85 and 89 mm Hg or a systolic BP between 140 and 159 mm Hg. Diastolic pressures between 110 and 115 mm Hg define severe HTN, and malignant HTN is defined by BPs greater than 200/140mm Hg. Malignant HTN is a medical emergency.
3 What causes hypertension?
Endocrine: Cushing’s syndrome, hyperaldosteronism, pheochromocytoma, thyrotoxicosis, acromegaly, estrogen therapy
4 What are some of the physiologic processes that occur as a patient becomes hypertensive?
Often cardiac output temporarily increases, followed by sustained increases in systemic vascular resistance. Vascular smooth muscular hypertrophy is observed, and there is increased arteriolar tone. Extracellular fluid volume and renin activity have no consistent pattern, but usually intracellular sodium and calcium concentrations increase. Sustained HTN leads to concentric hypertrophy of the left ventricle and impaired ventricular relaxation, known as diastolic dysfunction. Diastolic dysfunction leads to increased end-diastolic pressures.
5 Identify current drug therapies for hypertensive patients
Single-agent therapy is usually initiated; if this is ineffective, multiple agents may be prescribed. Multiple factors determine which agents are used, including race, gender, age, and comorbidities. For instance, black patients respond better to calcium channel blockers, angiotensin-converting enzyme (ACE) inhibitors, and β-blockers. β-Blockers are relatively contraindicated in patients with reactive airway disease, and patients with renal artery stenosis should not receive ACE inhibitors. Diuretics produce hypokalemia and hyperglycemia. β-Blockers are not particularly effective in elderly patients. Table 28-1 reviews commonly prescribed antihypertensive medications.
TABLE 28-1 Commonly Prescribed Antihypertensive Medications
| Class | Examples | Side Effects |
|---|---|---|
| Thiazide diuretics | Hydrochlorothiazide | Hypokalemia, hyponatremia, hyperglycemia, hypomagnesemia, hypocalcemia |
| Loop diuretics | Furosemide | Hypokalemia, hypocalcemia, hyperglycemia, hypomagnesemia, metabolic alkalosis |
| β-Blockers | Propranolol, metoprolol, atenolol | Bradycardia, bronchospasm, conduction blockade, myocardial depression, fatigue |
| α-Blockers | Terazosin, prazosin | Postural hypotension, tachycardia, fluid retention |
| α2-Agonists | Clonidine | Postural hypotension, sedation, rebound hypertension, decreases MAC |
| Calcium channel blockers | Verapamil, diltiazem, nifedipine | Cardiac depression, conduction blockade, bradycardia |
| ACE inhibitors | Captopril, enalapril, lisinopril, ramipril | Cough, angioedema, fluid retention, reflex tachycardia, renal dysfunction, hyperkalemia |
| Angiotensin receptor antagonists | Losartan, irbesartan, candesartan | Hypotension, renal failure, hyperkalemia |
| Vascular smooth muscle relaxants | Hydralazine, minoxidil | Reflex tachycardia, fluid retention |
ACE, Angiotensin-converting enzyme; MAC, minimal alveolar concentration.
Adapted from Morgan GE, Mikhail MS, Murray MJ: Clinical anesthesiology, ed 4, New York, 2005, McGraw-Hill, Chapter 20.
6 What are the consequences of sustained hypertension?
Untreated hypertensive patients develop end-organ disease, including left ventricular hypertrophy, coronary artery disease, congestive heart failure, cardiomyopathy, renal failure, and cerebrovascular accidents. Hypertensive patients also demonstrate labile BPs intraoperatively.
Full access? Get Clinical Tree
