6.6 Perioperative Hypertension

If BP is well controlled, and history and physical examination are unremarkable, further testing may be unnecessary for uncomplicated surgery or procedures, but is appropriate if history or physical are concerning, and for larger and invasive surgeries. Electrocardiography (ECG) and transthoracic echocardiography (TTE) detect the presence of LVH.

Echocardiography can also measure its severity. Wall motion abnormalities and left ventricular ejection fraction (LVEF) can be detected with TTE. Referral to a cardiologist may be advisable to determine appropriate preoperative tests, assess perioperative risk, and make focused recommendations for perioperative care. Cardiac catheterization is usually only performed when indicated by symptoms, and the cardiologist believes preoperative intervention may be indicated, such as percutaneous coronary intervention in a patient with worsening angina. A neurologist should assess neurologic signs or symptoms before elective surgery. Serum creatinine can indicate impaired renal function, though it needs to be appreciated that approximately 50% of kidney function may be lost before creatinine begins to rise. Electrolytes should be performed if patients are on antihypertensives that impact electrolytes, such as diuretics. Complete blood count and platelet count are indicated if the procedure is likely to be associated with significant blood loss. Still, many preoperative clinics will perform a complete blood count prior to all but minor procedures. In patients with HTN, a basic metabolic panel should be performed to document the preoperative state of kidney function with serum creatinine.

In general, patients should be instructed to take their oral antihypertensive medications the day of surgery, with a sip of water. It is widely accepted to withhold diuretics, due to the overnight fast. Still, in patients with severe CHF, a reduced dose of diuretic, or even the usual dose, might be considered. Perhaps this decision should be made by the anesthesiologist in the preoperative area, after measurement of BP and auscultation of the lungs. Patients on chronic beta-blocker therapy should receive their beta-blocker on the day of surgery. However, beta-blockade therapy should not be initiated immediately before surgery, for although it has been shown to decrease the incidence of cardiac events, it also increases the risk of bradycardia, stroke, and death.

Preoperative Evaluation on the Day of Surgery (DOS)

Patients who present for anesthesia should have normal BP on the DOS, although it may be somewhat increased above their usual level due to anxiety. Once SBP reaches 170 mm Hg or DBP reaches 100 mm Hg, it is likely the patient will manifest BP gyrations in the perioperative period. These can usually be managed safely with appropriate administration of anesthetics, analgesics, and antihypertensives. If a patient presents with SBP of 180 or DBP of 110 and has no prior history of HTN or manifests these BP measurements despite having taken their BP medications the DOS, elective surgery should be postponed until BP is better controlled. If SBP is 180 or DBP is 110 and the patient has not taken their antihypertensives that morning, they should be given with a small dose of an anxiolytic such as midazolam with a sip of water, or a comparable intravenous antihypertensive administered.

If surgery is emergent and must proceed despite poorly controlled BP, precautions should be taken. A recent ECG and echocardiogram should be reviewed. In patients in whom such information is not available, a brief delay to obtain a STAT ECG and echocardiogram may be appropriate.

If surgery is of an emergent nature, careful monitoring of BP with an arterial line is advised, and pharmacologic therapies should be immediately available to treat HTN. Such treatment may need to be continued into the post-anesthesia care unit (PACU) and/or intensive care unit (ICU).

Anesthesiologist’s primary responsibility is to ensure safe levels of BP. This may be achieved with anesthetics, analgesics, and antihypertensive agents, with the choice of specific techniques and drugs tailored to the specific patient’s comorbidities. Poor management of BP in the perioperative period may cause end-organ complications. However, assuming BP is carefully managed during anesthesia, it is more likely that the anesthesiologist will be tailoring management of the patient based upon preexisting end-organ complications of HTN, or the measured BP on the DOS.

In 80%-90% of surgical patients, the standard intermittent non-invasive blood pressure (BP) that is obtained using oscillometry with a brachial cuff has been shown to have only poor agreement with IBP in critically ill patients. Invasive blood pressure (IBP) is the gold standard of arterial pressure measurement in 10-20% of high-risk patients.

Regional nerve blocks provide surgical anesthesia with minimal hemodynamic changes. Spinal and epidural techniques similarly permit maintenance of spontaneous ventilation, but BP may drop significantly. Such decreases may be ameliorated with volume infusion and/or vasoconstrictors. Rigid adherence to certain anesthetics for specific procedures is not recommended, as each patient’s comorbidities need to be considered. Still, the application of regional techniques and patient-controlled analgesia help minimize postoperative pain and the stress response. In addition, postoperative mobilization may be more rapid after regional techniques.

Poorly controlled HTN may lead to large reductions in BP during the administration of anesthesia, and both treated and untreated hypertensive patients often display a lower BP nadir than normotensive patients. Severe HTN and significant hypotension are both associated with increased risk of perioperative complications. Maintenance of appropriate intraoperative BP targets is important to minimize the risk of CHF.

Intravenous agents that may be used to treat severe intraoperative HTN under anesthesia include sodium nitroprusside, nicardipine, and nitroglycerin. Infusion of these agents, with appropriate adjustments, can provide control of even severely elevated BP. Rapid dose adjustments can be facilitated with beat-to-beat arterial line monitoring. Once a steady state is reached, hydralazine. may be used to provide longer-term control, and to facilitate weaning from such infusions.
In summary, in patients with HTN and/or significant cardiovascular disease, overall appropriate targets for intraoperative BP can be summarized as SBP approximately 130 mm Hg, MAP 60 to 65 mm Hg, and DBP 70 to 90 mm Hg.

It is understood that young, healthy patients, such as those with baseline BP of 110/65 mmHg, can tolerate lower values than the recommendations above for patients with HTN or cardiovascular disease (CVD). Still, even in healthy patients, a prolonged period of hypotension may increase morbidity and mortality.

Even patients with baseline BP of 150/90 mm Hg may demonstrate significant fluctuations in BP during the perioperative period. If the planned procedure is intracranial, intrathoracic, or major abdominal, insertion of an arterial line for beat-to-beat measurement of BP may be advisable. For less invasive procedures, an arterial line may not be necessary but, as the risk/benefit ratio of an arterial line is low, any significant fluctuations in BP should result in arterial line placement. If perioperative BP fluctuations are significant, hospitalization for 24 to 48 hours postoperatively may be necessary to begin an antihypertensive regimen to control BP prior to hospital discharge.

In critically ill patients in whom invasive blood pressure monitoring is not immediately available, non-invasive BP should be repeated every one to two minutes. Still, in patients who are severely hypertensive, hypotensive, receiving drugs that rapidly change blood pressure, or are undergoing surgical procedures that may result in significant fluctuations in BP or bleeding, invasive measurement of BP via an arterial catheter should be initiated as soon as possible. The radial artery is the most common location where arterial catheters are inserted, but other possible sites include the femoral, axillary, brachial, and dorsal pedis arteries. In neonates, the umbilical artery may be the easiest artery to cannulate.

If surgery is performed in the sitting position, as is sometimes done during neurosurgery and shoulder surgery, it should be appreciated that non-invasive BP measured at the level of the brachial artery does not reflect BP perfusing the brain. Therefore, cuff BP goals should be maintained higher than normal. If an arterial line is inserted, the transducer should be placed and zeroed at the level of the ear. Placement of the arterial line transducer at the level of the operating room table, and management of BP to that arterial line, has resulted in brain injury in a patient undergoing neurosurgery in the sitting position.

In Pheochromocytoma preoperative preparation includes alpha blockade, followed by the addition of CCB or beta-blockers as needed to control BP. Several measurements of SBP should be less than 160 mm Hg before surgery. As alpha blockade takes effect, patients are advised to increase liquid and salt intake orally. Beta-blockade should never be initiated before alpha-blockade in patients with pheochromocytoma, as the unopposed alpha effect can result in severe HTN.

Postoperative hypertension is an acute, transient increase in blood pressure that develops within 30 to 90 minutes following a surgical procedure and typically lasts for 4 to 8 hours after surgery. It is defined as a systolic blood pressure greater than 160 mm Hg or a diastolic blood pressure greater than 90 mm Hg.

Reversible or treatable causes of hypertension, including pain, anxiety, hypothermia, and hypoxemia, should be considered and treated before the implementation of antihypertensive therapy. The ideal agent for treating APH is intravenously administered, is fast acting, and has a short duration of action, allowing the rapid and safe adjustment of therapy to achieve a targeted BP range. Sodium nitroprusside has long been considered the standard therapy and has many of the ideal characteristics. However, because of the need for invasive hemodynamic monitoring and concerns about toxicity in patients given sodium nitroprusside, several newer agents may be preferable in routine clinical practice. Labetalol, nicardipine, and nitroglycerin have been widely studied or used. Hydralazine, esmolol, fenoldopam, angiotensin-converting-enzyme inhibitors, and clonidine may also be useful treatment options.

The perioperative period is unique in that multiple healthcare providers contribute to the care of the patient. Communication between these providers will ensure patient safety preoperatively. Referral to existing or new providers if perioperative BP values are concerning is emphasized. This will ensure that an antihypertensive regimen is initiated and follow up visits are scheduled to optimize the antihypertensive regimen. When treatment of APH is necessary, therapy should be individualized for the patient.

In general, the treatment goal should be based on the patient’s preoperative BP. A conservative target would be approximately 10% above that baseline; however, a more aggressive approach to lowering BP may be warranted for patients at very high risk of bleeding or with severe heart failure who would benefit from after load reduction. Careful monitoring of patient response to therapy, and adjustment of treatment, are paramount to safe and effective treatment of perioperative hypertension. After surgery, the clinician can safely transition the patient to an effective oral antihypertensive regimen to manage the long-term risks of hypertension and cardiovascular diseases.