Postoperative acute respiratory distress syndrome (ARDS) is rare in patients undergoing low-risk surgery, but still carries a very high mortality rate, a large study shows.
The analysis also identifies several aspects of intraoperative management that may influence ARDS risk.
Just 0.2% of 50,367 patients developed the complication, report James Blum (University of Michigan Health System, Ann Arbor, USA) and team in Anesthesiology.
Most previous research has focused on high-risk surgical populations, whereas Blum et al excluded patients undergoing cardiac, thoracic, transplant, trauma, and vascular surgery. But despite the patients' relatively low risk for mortality, 27% of the 93 patients who developed ARDS died within 90 days, compared with 12% of 372 controls matched for preoperative ARDS risk.
In an editorial accompanying the study, Daryl Kor (Mayo Clinic, Rochester, Minnesota, USA) and Daniel Talmor (Beth Israel Deaconess Medical Center, Boston, Massachusetts, USA) say that such a mortality rate is "quite consistent with the available literature and is entirely unacceptable in a low-risk surgical population."
They add: "Indeed, it seems the ARDS-related risk of death is largely independent of the population's baseline surgery-related risk."
Within the matched groups, Blum et al identified several intraoperative management variables that were associated with risk for ARDS. The risk was increased more than fivefold if patients received an erythrocyte transfusion, and rose with increasing drive pressure, fraction inspired oxygen, and crystalloid administration.
Kor and Talmor note that the apparent effect of higher drive pressure could actually reflect the presence of lung disease in these patients, especially given the lack of association between tidal volume and ARDS.
"This dissonance suggests that lowering tidal volume, although important, is not always enough and that additional measures to reduce the ventilator driving pressure may be necessary in certain patients."
The editorialists stress that the study cannot establish cause and effect, as all data came from a review of procedures at a single institution. But they say: "If causal relationships are confirmed, the potential for mitigating the onset and severity of postoperative ARDS by the way we deliver care in the operating room may well exist. If true, how important this would be."
In the cohort as a whole, significant risk factors for ARDS included American Society of Anesthesiologists' status 3-5, emergent surgery, renal failure, chronic obstructive pulmonary disease, and number of anesthetics administered.
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