Post-Noncardiac Surgery, No Association Found Between Intra-op Hypertension and AKI Or Other Adverse Outcomes

Author: Michael Vlessides

Anesthesiology News

In a controversial finding, there was no apparent association noted between intraoperative hypertension and the risk for acute kidney injury (AKI), acute myocardial injury and mortality after noncardiac surgery.

The retrospective study found no obvious thresholds above which systolic blood pressure is related to postoperative acute myocardial injury/mortality or AKI. After adjusting for confounding, no apparent relationship was found between maximum cumulative systolic blood pressure and any of the postoperative adverse events.

To help test this theory, Dr. Shimada, Daniel Sessler, MD, the Michael Cudahy Professor and Chair of the Department of Outcomes Research, and their colleagues analyzed data from 76,042 patients who underwent noncardiac surgery at the institution between 2005 and 2018. Patients were excluded from the analysis if they had chronic kidney disease, underwent urologic procedures, or if their anesthesia lasted less than 60 minutes.

“We considered patients to have AKI if their peak creatinine concentration increased at least 1.5-fold or by more than 0.3 mg/dL within seven days of surgery,” Dr. Shimada explained. The composite of myocardial injury/mortality was defined by at least one fourth-generation postoperative troponin T concentration of at least 0.03 ng/L within seven days after surgery, and/or death within 30 postoperative days.

As Dr. Shimada reported at the 2019 annual meeting of the American Society of Anesthesiologists (abstract BOC09), the overall incidence of AKI was found to be 4.5%, while the overall rate of composite myocardial injury/mortality was 1.9%. Patients’ average baseline systolic blood pressure was 113±16 mm Hg, while the intraoperative time-weighted average of systolic blood pressure was 118±14 mm Hg.

“Unsurprisingly, people who experienced AKI were older and sicker than those who did not,” Dr. Shimada explained.

Univariable analyses revealed a steady linear increase over the entire range of systolic blood pressure, with no apparent threshold or change point. Indeed, individuals who suffered postoperative myocardial injury/AKI demonstrated a higher time-weighted average, area above threshold, and number of minutes above all thresholds compared with those with no evidence of the adverse events (P<0.001 for all).

“After adjusting for confounding variables, however, cumulative minutes at a patient’s highest blood pressure was no longer associated with either outcome,” Dr. Shimada said. “Additionally, the interaction between baseline blood pressure and each outcome showed no association on multivariable analysis.

“This contrasts starkly with low blood pressure, which is distinctly associated with acute kidney and myocardial injury,” he added.

Despite the strength of the findings, the researchers acknowledged that the investigation was limited by the fact that few patients demonstrated systolic blood pressure levels over 200 mm Hg, which precluded adequate analysis of higher pressures. Furthermore, only 16% of patients had postoperative troponin tests. The investigators assumed that patients with missing troponin tests were negative for negative outcomes, although they acknowledged that some myocardial injury was likely missed along the way.

“In summary,” Dr. Shimada said, “there was no clinically important association between systolic blood pressure and AKI or a composite of myocardial injury and mortality over the range of 120 to 200 mm Hg. We therefore recommend treating only extreme intraoperative hypertension while simultaneously working to prevent hypotension.”

The findings were met with surprise by the session’s co-moderator Martin London, MD, the professor emeritus of clinical anesthesia at the University of California, San Francisco. “This is a great study with fascinating data,” he said. “But I also think it’s very controversial.

“Unfortunately, we didn’t check the interaction between heart rate and the outcome,” Dr. Shimada replied. “However, our previous research has demonstrated that heart rates up to 100 beats per minute are not associated with adverse outcomes, including myocardial injury or mortality.”