What You Should Know About Hypertension and Surgery

Hypertension Monitoring During Surgery
Anesthesiologist Monitors During Surgery. Thierry Dosogne

Immediately upon arrival to the operating room, your blood pressure will be checked, to establish your "baseline" measurement, a measurement that will be used throughout the procedure to gauge your response to the surgery and to the medications used for anesthesia.  However, a recent study showed that the blood pressure measurement before you enter the operating room (OR) is more accurate, and it is that blood pressure that your doctor should use to determine your baseline.

The study, which was presented at the Anesthesiology 2015 annual meeting, found that when blood pressure was measured in the OR, it was usually significantly higher than blood pressure measurements taken before the day of surgery, or even blood pressure measurements taken on the day of surgery in the "holding area," before entering the OR. Blood pressure control is critical in surgery. Maintenance of the correct blood pressure can help prevent strokes and heart attacks in the perioperative period.

Generally, the anesthesiologist monitors blood pressure in the OR. Blood pressure management in the operating room has been considered adequate when it is within 20 percent of the patient's baseline blood pressure. However, the patient's baseline blood pressure can be significantly elevated as the result of anxiety in the OR, or it may be significantly reduced as the result of preoperative sedatives.

Other changes in blood pressure can result from withdrawal of normal blood pressure medications before surgery; pain or illness can raise blood pressure to higher than normal levels; and pain medications can also effect your blood pressure. Patients who are under anesthesia may not receive as much oxygen as they need and this can result in additional blood pressure increases.

In a study of over 2,000 patients, researchers found an increase in blood pressure in most patients when their blood pressure was measured in the operating room, compared to measurement in the clinic before surgery or in the preoperative holding area. 

One recent study with data from over 250,000 patients showed a greater association between low blood pressure and death than between high blood pressure and death during surgery.The researchers concluded the study by stating that while high blood pressure control is important for long-term health, it is not by itself a significant risk factor for postoperative death.

Drugs that are used for general anesthesia can affect your  blood pressure, particularly when you are initially being put to sleep and once again when you are beginning to wake up. Some people experience a large drop in blood pressure after they receive medications to put them to sleep, which is why the job of the anesthesiologist is to critical to successful surgery. The medications used for anesthesia have a common effect of dilating your blood vessels, or expanding them.

This results in an increased flow of blood to some organs, but the overall effect is a reduction in blood pressure. The anesthesiologist will carefully monitor your blood pressure and other vital signs during surgery. The anesthesiologist will check your blood pressure every five minutes at least during your surgery, and after surgery, as you recover in the recovery room, and until the medication effects wear off. If your blood pressure becomes too low, you will be at risk of a stroke or other complication, so the anesthesiologist will add medications through your intravenous (IV) line to return your blood pressure to normal. As surgical cutting and stimulation of your internal organs occur, your body will produce substances like epinephrine that will raise your blood pressure independent of medication.  


Even someone with high blood pressure can experience low blood pressure and shock if a lot of blood is lost during surgery. Although younger patients may be able to tolerate lower blood pressures during surgery, older people do not have as many compensatory mechanisms to keep adequate blood flow to vital organs when blood pressure drops. In cases of large amounts of blood loss, transfusion of blood products may be required to restore blood pressure high enough to adequately supply the body's critical cells and organs. 


During anesthesia, the anesthesiologist will balance all of the effects of surgery with available techniques to maintain a healthy blood pressure. Anesthesiologists undergo extensive specialty training, so you can be confident that they have encountered many different types of blood pressure changes. Finally, a single abnormal blood pressure during surgery may only be a machine error or an error by the person reading the machine. That's why anesthesiologist rarely acts on a single abnormal value. They monitor the progression of your blood pressure as carefully as they monitor the medications you receive for anesthesia.

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