Low BP and pulse pressure during noncardiac surgery may increase postop mortality

Low blood pressure (BP) or mean arterial pressure (MAP) and pulse pressure (PP) is associated with increased postoperative mortality in patients undergoing major elective noncardiac surgery, revealed a database analysis presented at the 2018 annual meeting of the American Society of Anesthesiologists.

Blood pressure (BP) is routinely measured during preoperative evaluation for surgery. The association of preoperative Blood pressure(BP) profiles with mortality after major elective noncardiac surgery remains unclear.

The study was conducted by Ashwin Shankar and colleagues at the University of Toronto, Department of Anesthesia which aimed at ascertaining the association of preoperative Blood pressure(BP) profiles with mortality after major elective noncardiac surgery.

After institutional ethics approval, the team conducted a retrospective cohort study of consecutive patients undergoing major elective noncardiac surgery at University Health Network (Toronto, Canada) between 2008 and 2015. Institutional databases linked preoperative clinic assessments (patient characteristics) with the operating room registry (surgical details) and electronic inpatient records (outcomes). The primary exposure was the resting ambulatory BP measured in the preoperative clinic, characterized as the mean arterial pressure (MAP) and pulse pressure (PP). The primary outcome was 30-day in-hospital mortality.

A priori, the authors expected possible non-linear relationships between the exposures (i.e., MAP, PP) and outcome. The exposures were therefore expressed as 4-knot restricted cubic splines that allowed for flexible modeling of their relationship with outcome. In unadjusted analyses, the association of each of MAP and PP with 30-day mortality were graphically examined, and exposure thresholds associated with 30-day mortality were established. In adjusted analyses, a multivariable logistic regression model evaluating the association of MAP and PP with 30-day mortality was constructed that adjusted for demographics, body mass index, comorbidities, and surgical procedure.

The team verified underlying model assumptions and tested for statistical interaction between MAP and PP. Model validation was performed using the bootstrap resampling technique; 1,000 bootstrap samples were created and the optimism-corrected c-index was examined.

Key findings of the study

• The cohort included 40,289 patients, with a median MAP of 97 mm Hg and PP of 52 mm Hg.


• In total, 1.7% of patients died within 30-days of surgery.


• Non-linear relationships were observed between MAP, PP and mortality in unadjusted and adjusted analyses.


• In unadjusted analyses, a MAP less than 90 mm Hg, PP less than 40 mm Hg and PP greater than 60 mm Hg were associated with increased odds of mortality.


• A MAP less than 90 mm Hg and PP less than 40 mm Hg were associated with increased odds of mortality.


• There was no statistically significant interaction between MAP and PP.


• Model validation revealed an optimism-corrected c-index of 0.81.

To conclude the study the authors wrote "Low preoperative MAP and PP were associated with increased postoperative mortality in this large cohort of patients undergoing major elective noncardiac surgery. Future research is needed to explore mechanisms underlying this association, and to test interventions to mitigate risks in patients with low MAP and PP"

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