‘Triple low’ predicts postoperative mortality
MedWire News: Patients who, during surgery, develop the "triple low" of low blood pressure, low minimum alveolar concentration (MAC) of volatile anesthetic, and low bispectral index (BIS) are at increased risk for dying within 30 days, research suggests.
Having any two of these factors doubled a patient's risk for dying, while all three simultaneously quadrupled their risk, show the findings published in Anesthesiology.
However, editorialists Sachin Kheterpal (University of Michigan Medical School, Ann Arbor, USA) and Michael Avidan (Washington University School of Medicine, St Louis, Missouri, USA) stress that such intraoperative events may not themselves raise patients' mortality risk.
"Triple low may simply be an intraoperative stress test," they say. "It is also conceivable that a hybrid of the two concepts is at play: for a given patient, triple low may serve as a marker of disease, but allowing the patient to remain hypotensive may cause end organ hypoperfusion."
In the current study, the triple low occurred in 6% of 24,120 patients undergoing elective noncardiac surgery. The researchers defined low values according to the averages in the overall population; thus low values were less than 87 mmHg for mean arterial pressure (MAP), 46 for BIS, and 0.56 for MAC fraction.
Low MAP and BIS would be expected in patients with a high MAC fraction, which indicates a high anesthetic concentration. By contrast, "low MAP and/or BIS in patients receiving low anesthetic MAC fractions is atypical and may help identify patients who are unusually sensitive to anesthesia and at risk for complications," say the researchers, led by Daniel Sessler (Cleveland Clinic, Ohio, USA).
Indeed, 2.9% of patients with the triple low died within 30 days of surgery, compared with 0.5% of patients with no low values. Mortality rates in patients with low values for any two of the three factors ranged from 1.0% to 1.6%. The only factor to increase mortality rates in isolation was low MAC; patients with this had a mortality rate of 1.1%.
The effect of the triple low on mortality persisted after accounting for confounders, and it also significantly increased patients' lengths of hospital stay. The duration of the triple low was also important, with the adverse effects becoming apparent only if the state persisted for more than 30 minutes.
In their editorial, Kheterpal and Avidan concluded: "This impressive study demonstrates that the era of anesthesiology insularism is coming to a close. What we observe, and possibly what we do, during our brief intraoperative relationship with the patient probably is relevant to long-term patient outcomes."
MedWire (www.medwire-news.md) is an independent clinical news service provided by Springer Healthcare Limited. © Springer Healthcare Ltd; 2012
By Eleanor McDermid