Anesthesia for Patients with Hypertension

Introduction

• Globally, chronic hypertension is the leading modifiable risk factor for heart disease and stroke.
• Hypertension is defined as an average BP of more than 130 mmHg systolic (sBP) and/or more than 80 mmHg diastolic (dBP)¹ (Table 1).

• Patients with an average BP greater than 140/90 or greater than 130/80 with another comorbidity (diabetes mellitus, cerebrovascular disease, coronary artery disease, or chronic kidney disease) should be on prescribed antihypertensive therapy.

Outpatient Management

• Chronic hypertension should be addressed in the outpatient setting so that an appropriate treatment regimen can be initiated with a goal of a BP less than 130/80.¹
• Undiagnosed or untreated obstructive sleep apnea, noncompliance with medical therapy, subtherapeutic antihypertensive regimens, pain, anxiety, tobacco use, and/or illicit drug use can be addressed during an outpatient preoperative visit to optimize hypertensive patients prior to surgery.²
• In patients with persistent hypertension despite compliance with three or more medications, secondary causes of hypertension should be considered (primary aldosteronism, renal artery stenosis, pheochromocytoma).¹
• Antihypertensive medications may be started or escalated in the outpatient setting if there is adequate time before surgery to do so (weeks to months).²

Medication Management

• Alpha, beta-, and calcium channel blocker therapy should be continued preoperatively.
• Interruption of beta- or calcium channel blocker therapy increases perioperative risk of major adverse cardiac events. For this reason, missed doses should be administered in the preoperative period.
• Interruption of clonidine therapy can result in severe rebound hypertension. It should be continued and can be administered orally or transdermally.
• Loop diuretics are commonly held to avoid hypovolemia, but may be continued in patients with severe heart failure.
• Thiazide and potassium-sparing diuretics can be continued
• RAASi have historically been held prior to surgery, but this management strategy is currently under scrutiny and an area of active research.
• There is an increased incidence of intraoperative hypotension in patients who continue RAASi. Conversely, patients who hold RAASi have significantly higher rates of postoperative hypertension.²
• Neither strategy (interrupting or continuing RAASi) is associated with better outcomes; therefore, at this time, either approach is acceptable.
• Stop-or-Not trial: continuing versus stopping RAAS inhibitors before major noncardiac surgery:³
  • Randomized clinical trial of 2,222 patients being treated with a RAASi for at least 3 months scheduled to undergo a major noncardiac surgery between January 2018 and April 2023 at 40 hospitals in France
  • Patients were randomized to continue use of RAASIs (n = 1107) until the day of surgery or to discontinue use of RAASIs 48 hours prior to surgery (n = 1115).
  • No difference in mortality or postoperative complications between groups

Preoperative Management

• Hypertension on the day of surgery is a common occurrence. Preoperative BP readings are often much higher than home values due to anxiety, pain, or medication interruption. Repeating the measurement when a patient is more relaxed, allowed to empty their bladder, or after treating pain or anxiety often results in improvement in these numbers.
• As mentioned, missed doses of beta-blockers, calcium channel blockers, and/or clonidine should be administered in the preoperative area.
• A patient with an elevated BP (>180/120) experiencing any of the following symptoms meets the diagnostic criteria for hypertensive emergency: headache, blurred vision, chest pain, focal neurologic signs, or dyspnea.
• Patients meeting criteria for hypertensive emergency should be treated prior to emergency surgery and should not proceed to the operating room if not emergently necessary.
• Current guidelines suggest that there is no benefit to delaying elective surgery in an asymptomatic hypertensive patient if dBP is <110mmHg and sBP is <180mmHg.
• Initiating new therapy in the immediate preoperative period to rapidly achieve normotensive BP values in an asymptomatic patient is not recommended.

Intraoperative BP Management

• The most commonly accepted strategies for maintaining BP intraoperatively are:
  • Absolute: maintaining a BP above a specific mean arterial pressure (MAP)
  • Relative: maintaining a BP within a range of baseline
• For absolute BP management, sBP greater than 90mmHg and a MAP greater than 65mmHg were associated with reduced risk of overall mortality, acute kidney injury, myocardial injury, and stroke in multiple studies.
• For chronically hypertensive patients with high baseline BPs (MAP >100mmHg), MAP targets should be higher to avoid myocardial injury and kidney injury.
• For a relative BP control strategy, home BP readings are considered the most accurate measure of baseline when available. BPs obtained in the preoperative area are commonly higher than home values.
• Most evidence supports a goal of BP within 20% of baseline.
• One study showed that attempting to maintain sBP within 10% of baseline led to fewer complications (composite of systemic inflammatory response syndrome with renal, respiratory, cardiovascular, or neurologic dysfunction).
• Profound hypotension after induction of anesthesia in a chronically hypertensive patient occurs frequently. Relative to normotensive patients, patients with systemic hypertension have a reduced intravascular volume due to chronic vasoconstriction. The vasodilatory effects of induction medications in the setting of relative hypovolemia leads to an abrupt drop in preload. Gentle hydration with ~250mL of crystalloid just prior to induction can help blunt this response.
• Euvolemia should be maintained and vasoactive medications should be administered as needed to achieve target BPs.

Intraoperative Hypertension

• Clinicians should consider and treat reversible causes of hypertension.
• If acute hypertension is severe or persists for longer than several minutes, use IV antihypertensive medications.
  • Start with short-acting agents to avoid overtreatment and persistent hypotension (for example, esmolol, hydralazine, or nicardipine)
  • Longer-acting agents such as labetalol or metoprolol can be given, especially in the setting of concomitant tachycardia.
  • Infusions may be necessary to achieve BP control in patients with persistent hypertension.
• Typical causes of intraoperative hypertension include:
  • Laryngoscopy and endotracheal intubation
  • Surgical stimulation
  • Hypoxemia and hypercarbia (can cause hypertension and tachycardia due to sympathetic stimulation)
  • Hypervolemia
  • Antihypertensive medication withdrawal
  • Emergence and tracheal extubation
  • Bladder distention
  • Elevated intracranial pressure
  • Alcohol or benzodiazepine withdrawal
  • Recent cocaine or methamphetamine use

Postoperative Hypertension

• Hypertension in the postanesthesia care unit is typically treated if sBP is greater than 180mmHg or dBP is greater than 110mmHg in similar ways as stated above.
• Common causes of postoperative hypertension include:
  • Pain
  • Nausea/vomiting
  • Hypoxemia
  • Hypercarbia
  • Delirium/agitation
  • Hypothermia with shivering
  • Bladder distension
  • Hypervolemia
  • Withdrawal from alcohol or opioids
  • Recent cocaine/methamphetamine/phencyclidine use
• Treat reversible causes as appropriate: analgesics, antiemetics, benzodiazepines, noninvasive ventilatory support, and/or catheterization for bladder emptying
• Clinicians should reinstate preoperative oral antihypertensive therapy as soon as possible or use an IV alternative if the patient remains nil per os in the acute postoperative setting.
• Postoperative BPs within 20% of baseline are typically acceptable for discharge from the postanesthesia care unit.