Hypertension variability during cardiac surgery may increase risk of death

For patients with hypertension undergoing heart surgery, large variations in blood pressure before, during, and after the operation are associated with an increased risk of death, reports the July issue of Anesthesia & Analgesia, official journal of the International Anesthesia Research Society (IARS).

Although preliminary, the findings raise the possibility that anesthesiologists and surgeons may want to exercise tighter control over blood pressure during heart surgery in patients with hypertension. The study was led by Dr. Solomon Aronson of Duke University Medical Center, Durham, N.C.

Blood Pressure Variability Linked to One-Month Mortality Risk
The researchers analyzed data on 1,512 patients with hypertension (high blood pressure) undergoing cardiac surgery, drawn from a previous study. Most of the patients were undergoing coronary artery bypass graft (CABG) surgery for blocked coronary arteries.

Data on variations in blood pressure during surgery and in the pre- and postoperative period were analyzed in relation to the risk of death after surgery. One month after surgery, 3.2 percent of patients had died.

The results suggested that patients who spent more time with their systolic blood pressure outside a certain range were at increased risk of death. Systolic blood pressure is the first, or higher, number in the blood pressure reading. A systolic blood pressure of less than 120 millimeters of mercury (mm Hg) is considered normal.

The risk of death was higher for patients who spent more time with blood pressure outside the range of 75 to 135 mm Hg during surgery, and 85 to 145 mm Hg before and after surgery. For each systolic blood pressure swing of greater than 60 mm Hg, the risk of death was increased by 16 percent. Put another way, the risk of death increased by three percent for each minute spent outside a range of 105 to 130 mm Hg.

The impact of blood pressure variability was greater for patients at higher risk of death. For this group, the 30-day risk of death was 61 percent for those with wide swings in blood pressure versus 40 percent without such variability. For low-risk patients, the absolute difference was much smaller: 0.5 versus 0.2 percent.

More than two-thirds of patients undergoing cardiac surgery have hypertension, which is a major risk factor for death and other adverse outcomes. However, it's not a simple matter to establish the optimal blood pressure before, during, and after surgery. Because patients with hypertension have problems with blood pressure regulation, the range of "acceptable" blood pressures may be narrower than in patients with normal blood pressure.

The study provides new evidence linking wide variations in blood pressure to an increased risk of death after heart surgery in patients with hypertension. It's too early to draw any conclusions about proper blood pressure control, however—further studies will be needed to confirm the findings and to determine the reasons for the increased risk.

In an accompanying editorial, Dr. Martin J. London discusses the study implications, emphasizing the highly complex nature of the data and the difficulty of reaching definitive conclusions. Until such studies are available, Dr. London plans to continue following the "sage advice" of a respected mentor who advised letting the blood pressure drop…"but maybe not so much or so often."