Risk Calculator Predicts Postoperative Respiratory Failure

Ricki Lewis, PhD

November 08, 2011

November 8, 2011 — Postoperative respiratory failure (PRF) is defined as mechanical ventilation required more than 48 hours after surgery, or unplanned intubation within 30 days of surgery. A report published in the November issue of Chest analyzes the association of PRF with several clinical outcomes and applies the data in a logistic regression model to generate and validate an interactive risk calculator for postoperative morbidity and mortality. The instrument can help to guide surgical decision-making and informed consent.

PRF develops in approximately 3% of patients, and more than 25% of them die within 30 days. Up to 40% of postoperative complications after abdominal and vascular surgeries are pulmonary in nature.

The study, from Himani Gupta, MD and colleagues from the University of Pittsburgh in Pennsylvania and Creighton University in Omaha, Nebraska, considers all surgeries and distinguishes PRF from other pulmonary complications. Data are from the American College of Surgeons' National Surgical Quality Improvement Program, which represents more than 180 hospitals. The investigation goes beyond past studies that considered only men, represented only a single institution, or considered only cardiac complications.

Surgical nurses entered the data and did not include intubation after patient removal of the tube or necessity for return to surgery for reoperation. The researchers used data from 2007 (n = 211,410) to identify risk factors and validated the findings against 2008 data (n = 257,385). The data from both years were consistent with rates of PRF seen in previous investigations: 3.1% (6531/211,410) from 2007 and 2.6% (6590/257,385) from 2008. Death rates seen in this study population were also consistent with earlier studies; namely, 25.62% of those with PRF died within 30 days, which was significantly higher than the percentage of those without PRF who died within 30 days (0.98%; P < .001).

Five strong predictors for PRF emerged from evaluation of the data:

  • surgery type,

  • emergency case,

  • dependent functional status,

  • preoperative sepsis,

  • higher American Society of Anesthesiologists class.

The riskiest surgeries were those of the brain, aorta, and foregut/hepatopancreatobiliary region.

The risk calculator is an interactive spreadsheet. "When the required input is entered into this calculator for a given patient, it returns a model-based percent estimate of PRF," the investigators write.

The calculator is more precise than a point system, the researchers claim, and is amenable to use on a handheld device. Limitations of the study include the fact that it was retrospective, did not account for certain comorbid conditions (such as obstructive sleep apnea and venous thromboembolism), and did not include pulmonary function test results.

There has been no decline in rates of either PRF or its associated death in the last decade, the authors explain. "The high association of PRF with mortality emphasizes the importance of risk estimation and preoperative optimization. This risk calculator, with its high discriminative/predictive ability for PRF, is a step in that direction," they conclude.

No support was received for this study. The authors have disclosed no relevant financial relationships.

Chest. 2011;140:1207-1215. Abstract

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