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Clinical Case for Discussion: This month’s question is on hypertension and anesthesia. You are scheduled to anesthetize a 71-year-old male for an arthroscopic rotator cuff repair. His blood pressure when you meet him in pre-op is 170/99 mmHg. The nurses and the surgeon are alarmed. What would you do? Should you cancel surgery for a blood pressure of 170/99?
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 the internist’s preoperative clearance note documents that 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 without shortness of breath. His resting EKG and his BUN and creatinine are normal. In short, he has no signs that hypertension has caused end-organ damage to his heart, kidneys, or brain.
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, 9th Edition, Chapter 31, 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 elevated blood pressure value prior to elective surgery?
Per Miller’s Anesthesia, “while preoperative hypertension is associated with an increased risk of cardiovascular complication, this association is generally not evident for systolic blood pressure values less than 180 mm Hg or diastolic blood pressure values less than 110 mm Hg. Additionally, there is no compelling data that delaying surgery to optimize blood pressure control will result in improved outcomes.”
Note that this is in the setting of elective surgery in a patient who has no end-organ damage to his or her heart, kidneys, or brain. A patient with shortness of breath, angina, elevated BUN/Creatine, decreased glomerular filtration rate, or symptoms of a cerebral vascular accident, would pose a significant risk during the elective induction of general anesthesia.
For emergency or urgent surgery, per Miller’s Anesthesia, “anesthesiologists should weigh the potential benefits of delaying surgery to optimize antihypertensive treatment against the risks of delaying the procedure.” 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, and can destabilize the patient, 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 a preoperative arterial line and infusing a more titratable and short-acting drug such as nitroprusside or nitroglycerine 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. A common recommendation is to maintain intraoperative arterial pressure 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.
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Unstable BP often seen during anesthesia with wide swings from high to low is mostly the effect of low intra vascular volume secondary to chronic peripheral vaso constriction. Early administration of 500cc full strength solution helps mitigate the problem. In the ideal wold one can be flexible with the acceptable numbers of BP because there are othe variables from the type and place of surgery to prior treatment, age and medical history. In the real world you need limits because of the practice of writing incident reports on cancellations should a BP continue to climb, and not many chances can be taken in ambulatory surgery. 180/100 sounds right and nurses like fixed numbers and guidelines.