Although there is a significant association between elevated baseline pulse pressure and acute kidney injury (AKI) after coronary artery bypass graft (CABG) surgery, no association exists with the weighted duration of intraoperative hemodynamic perturbations, such as hypotension or hypertension.
“It’s known that elevated pulse pressure is a predictor of acute kidney injury after CABG surgery,” said Miklos Kertai, MD, PhD, associate professor of anesthesiology at Duke University Medical School, in Durham, N.C. “But we were also interested in seeing whether these patients could be at higher risk for intraoperative hemodynamic instability, and whether this instability put them at increased risk of postoperative AKI after CABG surgery. So that’s the new thing here: trying to see whether pulse pressure alone or in combination with intraoperative hemodynamic perturbations were also predictors of AKI after CABG.”
To shed light on this question, Dr. Kertai and his co-investigators evaluated data from 5,799 patients who underwent CABG surgery with cardiopulmonary bypass at Duke University Medical Center between January 2001 and June 2015. Baseline arterial blood pressure was defined as the mean of the first five measurements recorded by the automated record-keeping system before induction of anesthesia. The weighted durations of intraoperative hypotension and hypertension were defined, respectively, as the area (minutes × mm Hg) below either a mean arterial pressure of 55 mm Hg or above a mean arterial pressure of 100 mm Hg.
In presenting the study at the 39th annual meeting of the Society of Cardiovascular Anesthesiologists (abstract SCA15), Dr. Kertai reported that baseline pulse pressure was less than 40 mm Hg in 90 patients (1.6%), 40 to 80 mm Hg in 2,458 patients (42.4%), and more than 80 mm Hg in 3,251 patients (56.1%). Postoperative AKI was found to occur in 3,348 patients (57.7%). This group included 249 patients (7.4%) who experienced stage II AKI and 93 patients (2.8%) who experienced stage III AKI.
The researchers also created a risk-adjusted model for postoperative AKI. This analysis revealed that elevated baseline pulse pressure was significantly associated with higher odds for postoperative AKI, with every 20-mm Hg increase in pulse pressure having an adjusted odds ratio (OR) of 1.16 (95% CI, 1.10-1.21; P<0.0001). Elevated baseline pulse pressure was also significantly associated with greater severity of postoperative AKI (adjusted proportional OR, 1.13; 95% CI, 1.03-1.23; P=0.01).
Risk Factors for Post-op AKI
“We found that although patients with elevated pulse pressure were at higher risk for postoperative AKI after CABG surgery, it was independent of intraoperative hypotension and hypertension,” Dr. Kertai said. “Interestingly, we also identified other modifiable risk factors for postoperative AKI.” These included postoperative anemia and blood transfusion.
The weighted durations of intraoperative hypotension and hypertension were not independently associated with postoperative AKI. “So the interesting part of our findings is that we truly expected to see that the duration of hypotension and hypertension would be predictors of postoperative acute kidney injury,” he said. “[We] tried to manage these patients by keeping them between a certain blood pressure range. But clearly, going above or below the blood pressure range made no difference in terms of the risk of acute kidney injury, at least in this study.”
Applying these findings to real-life situations should not be particularly challenging, Dr. Kertai noted. “We are trying to look into how patients with elevated pulse pressure can be preemptively treated, so their risk of acute kidney injury after CABG could be minimized,” he told Anesthesiology News. “You can exercise the concept of the perioperative surgical home and help prepare these patients for the surgical procedure by taking steps that can reduce pulse pressure, postoperative anemia or the risk of blood transfusion. These are all factors that anesthesiologists can actually intervene on, thereby reducing the risk for acute kidney injury.” Future research, he added, may try to address these factors in prospectively.
Andrew Shaw, MB, said AKI after heart surgery is a significant clinical problem, as this data set confirms. “Their overall incidence of 57% is a little higher than in most series, reflecting the complexity of cases done in tertiary institutions like Duke,” said Dr. Shaw, professor and executive vice chair of anesthesiology at Vanderbilt University Medical Center, in Nashville, Tenn. “The Duke group has published an association between pulse pressure and AKI before, so the fact that it is still associated is not surprising.
“What is interesting about these new data is that there appears to be little effect of intraoperative hemodynamic upset on the incidence of AKI,” Dr. Shaw pointed out. “That finding clearly requires further confirmation since it challenges conventional dogma that blood pressure management in the OR is a modifiable risk factor for AKI. These data are drawn over a 15-year period during which there have been several changes in the field, so it would be interesting to see if there is an interaction with year of surgery.
“In summary, these data raise questions about intraoperative blood pressure management,” Dr. Shaw said, “and if confirmed by other groups, suggest we may need to rethink the way we plan our perioperative care for on-pump CABG patients.”