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30-day mortality

BMI is a significant predictor of mortality following surgery

Data from ACS National Surgical Quality Improvement Program show low-BMI patients at greatest risk of death
Data included almost 200,000 cases of general and vascular operations from 2005-2006

A study examining the relationship between BMI and 30-day mortality risk has reported that BMI is a ‘significant predictor’ of mortality within 30 days of surgery, even after adjusting for the contribution to mortality risk made by type of surgery and for a specific patient's overall expected risk of death.

The researchers from the University of Virginia, Charlottesville, also noted that patients with a BMI of less than 23.1 appear to be at highest risk of death with 40% higher odds compared with patients in the middle range for BMI (26.3 to <29.7).

To examine the relationship BMI and 30-day mortality risk among patients, the investigators utilised the database of the American College of Surgeons National Surgical Quality Improvement Program.

A multi-variable logistic regression analysis was used to assess the statistical significance of the relationship between BMI and mortality, with adjustments for patient-level differences in overall mortality risk and principal operating procedures.

Odds ratios with 95% CIs were calculated to measure the relative difference in mortality by BMI quintile, with reference to the middle quintile of the BMI. The overall significance of the BMI and of the other covariates was measured using the Wald 2 test statistic.

A separate multivariable logistic regression model was developed to assess the significance of the interaction between BMI and primary procedure.

The data included 189,533 cases of general and vascular surgical procedures reported in 2005 and 2006 for patients with known overall probabilities of death. Among these, 3,245 patients died within 30 days of their surgery (1.7%). The authors found that the percentage of deaths (2.8%) among patients with a BMI less than 23.1 was over twice that of the percentage of deaths (1%) among patients with a BMI of 35.3 or higher.

Additionally, patients with a BMI of less than 23.1 had statistically significant increased risk of death, with 40 per cent higher odds of death than patients with mid-range BMI (between 26.3 and 29.6). 

When examining data by procedure category, the authors also found that patients who underwent exploratory laparotomy had the highest percentage of death (13.9 per cent) compared with patients in all other categories of principal surgery, and patients who underwent breast lumpectomy had one of the lowest overall mortality percentages (0.1 per cent). 

The researchers also noted a statistically significant interaction between BMI and procedure category, indicating that the association between BMI and mortality was statistically different for patients who underwent these procedures (including colostomy, wound debridement, musculoskeletal system procedures, upper gastrointestinal procedures, colorectal resection, hernia repair, among others), compared with patients who underwent laparoscopy.

“These results indicate that BMI is a significant predictor of mortality within 30 days of surgery, even after adjusting for the contribution to mortality risk made by type of surgery and for a specific patient's overall expected risk of death," the authors said.

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