Discussion: You assess the patient carefully. A review of his chart shows he’s been taking anti-hypertensive oral medications for ten years. His current regimen includes daily atenolol and lisinopril, with his most recent doses taken this morning with a sip of water. He was seen in his internist’s office one week ago, and at that time his blood pressure was 140/88. He has no other medical comorbidities. His cardiac, renal, and neurologic histories are negative. He does not have diabetes. His BMI (Body Mass Index) is normal at 25. He walks three miles per day. His resting EKG and his BUN and creatinine are normal.
The patient’s physical exam is unremarkable except that he appears nervous. Should you cancel the case and send him back to his internist to adjust the blood pressure medical therapy regimen? Should you lower his blood pressure acutely with intravenous antihypertensive drugs, and then proceed with the surgery?
Hypertension, defined as two or more blood pressure readings greater than 140/90 mm Hg, is a common affliction found in 25% of adults and 70% of adults over the age of 70 (Miller’s Anesthesia, 7th Edition, Chapter 34, Preoperative Evaluation). Over time, hypertension can cause end-organ damage to the heart, arterial system, and kidneys. Hypertensive and ischemic heart disease are the most common types of organ damage associated with hypertension. Anesthesiologists are always wary of cardiac complications in hypertensive patients.
Chronic hypertension is a serious health hazard. But what about a single, markedly-elevated blood pressure value prior to elective surgery? Are there any data to guide our decision about whether to proceed with surgery? There are. A 2004 publication by Howell is a meta-analysis of 30 studies examining the relationship between hypertensive disease, elevated admission arterial pressure, and perioperative cardiac outcome. This paper found little evidence for perioperative complications in patients with admission arterial pressures of less than 180 mm Hg systolic or 110 mm Hg diastolic. This paper recommends that anesthesia and surgery not be cancelled for blood pressures lower than 180/110 mm Hg.
Based on the Howell study, Miller’s Anesthesia recommends that elective surgery be delayed for hypertension, until the blood pressure is less than 180/110 mm Hg.
In my prior career as an internal medicine doctor, I saw many hypertensive patients who’d presented for surgery with elevated blood pressures, yet whose blood pressure was adequately controlled in clinic. The anxiety and stress of anticipated surgery can elevate blood pressure acutely. If surgery is cancelled because of this hypertension and the patient is referred back to the primary care internist, the blood pressure is often well-controlled in the office setting on the same drug regimen that gave poor blood pressure control on admission to surgery. A primary care provider will be reluctant to add further medications in the office setting if the blood pressure is not elevated in clinic.
What about emergency surgery? What if a patient presents for urgent surgery for acute cholecystitis, and his blood pressure is 190/118 mm Hg? For urgent or emergent surgery, consider titrating intravenous antihypertensive drugs such as labetolol (5–10 mg q 5–10 minutes prn) or hydralazine (5–10 mg q 5–10 minutes prn) to decrease blood pressure prior to initiating anesthesia. Because the eventual induction of general anesthesia with intravenous and volatile anesthetics will lower blood pressure by vasodilation and cardiac depression, any pre-induction antihypertensives must be titrated with great care. Once doses of labetolol or hydralazine are injected, there is no way to remove the effect of that drug. For critically ill patients, consider monitoring with an arterial line and infusing a more titratable and short-acting drug such as nitroprusside for blood pressure control.
Let’s return to the anesthetic for your elective shoulder surgery patient with the blood pressure of 170/99 mmHg. You begin by administering 2 mg of midazolam IV. Three minutes later his blood pressure decreases to 160/90. You anesthetize him with 50 micrograms of fentanyl, 140 mg of propofol IV, and 30 mg of rocuronium, and intubate the trachea. In the next 20 minutes, while the patient is moved into a lateral position for the surgery, his blood pressure drops to 95/58. Because most anesthetics depress blood pressure by vasodilation or cardiac depression, it’s common for patients such as this one to require intermittent vasopressors to avoid hypotension, especially at moments when surgical stimulus is minimal. One of the recommendations of the Howell study is that intraoperative arterial pressure be maintained within 20% of the preoperative arterial pressure. This recommendation can be a challenge, especially if the preoperative blood pressure was elevated. A 20% reduction from 170/99 (mean pressure = 122 mm Hg) would be 136/79. A 20% reduction from the mean pressure of 122 mm Hg would be a mean pressure of 98 mm Hg. You choose to treat the patient’s hypotension with 10 mg of IV ephedrine, which raises the blood pressure to 140/85. Fifteen minutes later, the surgeon makes his incision, and the blood pressure escalates to 180/100. You treat this by deepening anesthesia with small, incremental doses of fentanyl and propofol. The surgery concludes, you awaken the patient without complications, and his blood pressure in the Post Anesthesia Care Unit is 150/88 mm Hg.
This pattern of perioperative blood pressure lability is common in hypertensive patients, and will require your vigilance to avoid extremes of hypotension or hypertension. Remember that based on the Howell study, Miller’s Anesthesia recommends elective surgery be delayed for hypertension until the blood pressure is less than 180/110 mm Hg. Armed with this information, you’ll cancel fewer patients for preoperative hypertension.