Perioperative Hypertension

Philip G. Boysen

CASE SUMMARY

A 41-year-old woman, weighing 135 kg and a body mass index of 42 is referred for surgery due to inflammatory bowel disease and chronic gastrointestinal bleeding, leading to anemia. She has a history of hypertension and type II diabetes. Her blood pressure (BP) and glucose have been poorly controlled, and she is referred for further evaluation and treatment before surgery. Her preoperative BP was 180/90 mm Hg despite therapy with fosinopril and verapamil. A β-blocker was added to the regimen about a week before surgery. The patient had a full cardiac evaluation within the last 6 months, including coronary angiography, which revealed nonobstructive coronary disease and a left ventricular ejection fraction of 55%. She denied orthopnea, and exercise was limited by body weight. Her preoperative hematocrit is 24%. Her electrocardiogram (ECG) shows left ventricular hypertrophy with strain pattern, unchanged from previous studies. On the morning of surgery, her BP was 190/100 mm Hg in the sitting position, with no orthostatic changes. Her heart rate is 80 bpm, and a fingerstick shows a blood sugar of 120 mg per dL. Owing to poor peripheral intravenous access, a preoperative central venous catheter is placed in the right internal jugular vein under ultrasound guidance. Two units of packed red blood cells were transfused, and metoprolol was administered and titrated to achieve a heart rate under 70 bpm. Following a successful induction of general anesthesia, a small bowel resection and anastamosis proceeded without incident, with the BP maintained at approximately 140/80 mm Hg. During emergence and following extubation, her BP rose steadily to 200/100 mmHg, and the patient complained of pain. While in the postanesthesia care unit (PACU), she remained hypertensive despite the administration of intravenous narcotics and labetalol. The patient also began to complain of obstruction to the upper airway, resulting in oxygen desaturation to 85%. Therapy with bi-level positive airway pressure (BiPAP) was instituted, and intravenous nitroglycerin was initiated for control of her hypertension. The patient was then transferred to the intensive care unit for further management. During the next 3 days, the patient was weaned from nitroglycerin, and trandolapril, amiodipine, metoprolol, and hydrochlorthiazide were given for BP control. Upper airway obstruction cleared, and she was discharged home on the fifth postoperative day without incident.

INTRODUCTION

Hypertension has become a global health care issue, crossing all geographic boundaries.¹ Economic globalization has led to an increasingly sedentary lifestyle, a highcalorie and high-fat diet, and an increased incidence of comorbidities, such as obesity and diabetes mellitus.² Even with such negative influences, longevity is increasing, and an older population also has a higher incidence of hypertension. BP and BP patterns increase with age. Systolic blood pressure (SBP) increases throughout a life-time. Diastolic blood pressure (DBP) increases with age, but plateaus between the age of 50 and 60, and then begins to decline. Therefore at approximately the same age, the pulse pressure begins to increase. In patients older than 50 years, isolated systolic hypertension is the most common presentation of hypertension.³

How Has the Definition and Parameters of Hypertension Changed?

For many years, the major concern to avoid complications due to hypertension was focused on diastolic hypertension. ⁴ However, recent data from large observational studies indicate a closer association between isolated systolic hypertension and coronary artery disease and stroke. Often, isolated systolic hypertension is also associated with an increased pulse pressure. Both systolic hypertension and increased pulse pressure are now a focus of much more aggressive treatment.⁵ Whereas tight control of BP in the outpatient setting is thought to improve
outcome, the need for tight control in the perioperative setting is unclear, making the challenge to the anesthesiologist even greater in terms of assessing and managing the hypertensive patient.⁶,⁷

TABLE 20.1 Clinical Classification of Hypertension

Category	SBP (mm Hg)	DBP (mm Hg)
Optimal	<120	<80
Normal	<130	<85
Prehypertension	130-139	85-89
Mild hypertension	140-159	90-99
Moderate hypertension	160-179	100-109
Severe hypertension	>180	>110
Isolated systolic hypertension	>140	>90
Pulse pressure hypertension	>60	—
SBP, systolic blood pressure; DBP, diastolic blood pressure.

In the general population, the association of hypertension and increased cardiovascular risk is well established. ⁸,⁹ Studies involving more than 1 million human subjects indicate that death from ischemic heart disease and stroke increases from an SBP as low as 115 mm Hg and a DBP as low as 75 mmHg. This has led epidemiologists to examine the assertion that the upper limit of a “normal” BP reading is 140/90 mmHg. Moreover, it has prompted the need to reevaluate the target BP levels for treatment, because the risk of cardiovascular complications increases at BP readings previously thought to be “normal.”¹⁰ The current classification of hypertension based on severity is listed in Table 20.1.

For the anesthesiologist, the problem is even more complex. First, there is an increased number of patients with diagnosed hypertension undergoing surgical procedures. Second, a large number of patients undergoing preoperative evaluation lack the diagnosis of hypertension and are clearly unaware, despite sustained BP readings in excess of 140/90 mmHg.¹¹ Third, a subset of treated patients have abnormally high preoperative BP readings either due to noncompliance or ineffective therapy.¹²

What Type of Decisions Face the Anesthesiologist in the Operating Room?

In each of these cases, the anesthesiologist is faced with a decision—either to proceed with the surgery and the anesthetic, or to cancel or delay the surgery while waiting for better control of the BP through more aggressive therapy. Although there are no data to indicate that isolated hypertension alters anesthetic risk, most patients have hypertension in combination with multiple comorbidities.¹³,¹⁴,¹⁵

The issue of increased pulse pressure hypertension and perioperative outcome deserves special mention. This phenomenon occurs when the SBP is >140 mmHg, and the DBP is <90 mm Hg.³ When the difference between the SBP and the DBP is >90 mmHg, there is an increased risk of stroke, coronary artery disease, and preeclampsia. The pulse pressure provides information concerning the coupling between the left ventricle and the arterial tree. An elevation of the pulse pressure >65 mm Hg reflects the stiffness and loss of elasticity of the conduit vessels, that is, the aorta, and the reflection of the energy wave propagated during ventricular ejection. With vessel stiffening and lack of compliance, failure of the vasculature to relax and accommodate ejected volume results in early reflection of the pulse wave, which augments systole rather than resulting in diastolic augmentation of blood flow to vital organs.¹⁶ In turn, the constant and increased stress imposed on the vascular system is exposed and breaks down the elastic elements of the vascular wall, causing further changes in time varying elastance of the vascular anatomy. Other factors that contribute to loss of vessel distensibility are age, glucose tolerance, coronary artery disease, hyperlipidemia, and inflammatory responses. This progressive deterioration is the final common pathway for multiple risk factors. Increased pulse pressure is also significantly associated with postoperative cardiac, renal, and cerebral events, whereas neither systolic nor diastolic hypertension showed a similar relation.¹⁷,¹⁸,¹⁹

How Is the Diagnosis of Hypertension Made?

▪ MEASUREMENTS DURING SLEEP

BP values tend to fluctuate during the waking hours, depending on activity and sympathetic state. There are also major changes in BP and heart rate during physiologic sleep.²⁰ Light sleep, or REM sleep, is associated with increased sympathetic tone, resulting in tachycardia and elevated BP. Deep sleep is characterized by parasympathetic dominance, with low BP and heart rate. Although these fluctuations in BP may be in the range of 40 to 50 mmHg, they are not always innocuous. Myocardial ischemia, infarction, and sudden death often occur at the end of the 90-minute cycle leading to light sleep, and dreaming with rapid eye movement.

▪ MEASUREMENTS IN THE SITTING POSITION

For the reasons elucidated in the preceding text, the standards for making the diagnosis of hypertension have recently been closely examined.²¹,²² Sustained hypertension is diagnosed only after multiple readings on separate occasions. The BP is to be measured in the sitting position, with a cuff that is appropriately sized to the arm
circumference, and positioned at the level of the right atrium. The cuff is inflated well in excess of the anticipated SBP and slowly deflated (no more than a 10 mm Hg decrease per three heart beats), and the examiner listens carefully for the Korotkoff sounds, with the bell of the stethoscope positioned close to the cuff over the brachial artery. A minimum of two readings are taken per session and the results are averaged. If the “white coat” phenomenon is suspected (i.e., anxiety and elevated BP in the presence of a physician), paramedical personnel can take the BP with the physician absent. This alternative, however, brings into question the training and monitoring of office personnel to ensure that the measurements are appropriately made. With tight control of measuring devices and personnel, even a 2-mmHg rise in the BP is deemed significant.

▪ MONITORING DEVICES

The gold standard for BP measurement continues to be the mercury manometer. Aneroid sphygmomanometers are more typically used but are not as accurate. Given the concerns of maintaining devices that contain elemental mercury, many facilities are replacing these measuring devices with automated BP devices; most of these are oscillometric devices that keep a constant pressure in the cuff to establish a mean BP, then “search” for the SBP and the DBP. Because these are now the standard of care for intraoperative readings, they are preferred in preanesthesia evaluation clinics.

The use of devices to continuously measure BP for 24 hours, much like the monitoring used to detect cardiac arrhythmias, are available but have not been widely employed. However, there is every reason to recommend that patients learn to monitor their own BP at home.²² Wrist devices are easy to use and inexpensive, and can provide valuable information as to variation in BP during wakefulness.

▪ CURRENT DEFINITIONS

Whereas in the past, “normal” BP was considered to be 120/80 mmHg, and the cut-off for treatment 140/90 mmHg, current definitions include a diagnosis of “prehypertension.” This state is characterized by an SBP between 120 and 139 mm Hg, and a DBP of 80 to 89 mmHg. For this group of patients, the recommended treatment is lifestyle modification, emphasizing weight loss, diet low in sodium, and frequent aerobic exercise.²¹

How Can Hypertension Be Treated in the Preoperative Period?

No absolute cut-off for either the SBP or DBP values have been established.⁶,⁸,¹² The presence of comorbidities that must also be addressed complicates the approach to an individual patient. Also, the perioperative period is a time of increased surgical stress and altered physiology. There is often an excessive release of catecholamines despite adequate management of pain and anxiety.²³ Many surgical procedures and techniques result in ischemia-reperfusion, with the release of mediators and tissue injury.²⁴ There can be an increased cellular and immune response, platelet activation, and a compromise in microvasular blood flow.²⁵ In the presence of hypertension and other comorbidities, this constellation of physiologic changes can result in a higher risk for stroke, myocardial infarction, or decompensated heart failure.²⁶,²⁷,²⁸

Only gold members can continue reading. Log In or Register to continue