Delayed surgery for thoracic and lumbar spine fractures raises respiratory failure risk

Low-risk patients treated within two days after admission have 0.021% probability of respiratory failure.

CHICAGO — In the first multivariate study on the issue, investigators confirmed that delayed stabilization in thoracic and lumbar spine fracture patients increases their risk for postoperative respiratory failure. In fact, these latest study results showed that delaying surgery by more than two days triples that risk.

LTC Timothy Patrick McHenry, MD, of Brooke Army Medical Center in Fort Sam Houston, Texas, and his colleagues conducted the retrospective cohort study of 1032 patients treated for thoracic and lumbar spine fractures over a 19-year period at Harborview Medical Center in Seattle.

“In the absence of any risk factors and early surgery less than two days after admission, the probability of respiratory failure was 0.021%,” McHenry said at the American Academy of Orthopaedic Surgeons 73rd Annual Meeting. “[In] the presence of all the risk factors and delayed surgery [patients] had a 36.2 times relative risk [over] patients with no risk factors and early surgery.”

A multivariate analysis identified five independent risk factors: age >35 years, injury severity score (ISS) >25, Glasgow Coma Score (GCS) <13, presence of blunt chest injury and surgery delayed more than two days after fracture.

Developing a prediction model

McHenry and his colleagues evaluated data from Harborview’s Trauma Registry and Acute Respiratory Distress Syndrome (ARDS) Registry, which includes patients with ARDS or acute lung injury (ALI).

They identified 1209 patients with thoracic and lumbar fractures who underwent surgical stabilization, but excluded 177 patients with incomplete data. Of the remaining 1032 patients, researchers found a 5% incidence of acute lung injury and a 9% incidence of ARDS.

“Looking at the incidence of respiratory failure vs. time of surgery in days, the significant difference (P<.0001) by chi-squared analysis was between two and three days after the admission or incidence of respiratory failure,” McHenry said.

In the univariate analysis, researchers found multiple significant risk factors for respiratory failure, including: age, ISS, GCS, pneumothorax, lung contusion, Charlson Comorbidity Score, thoracic spine level of injury, time to surgery and posterior surgical approach.

But they developed the final prediction model based on a logistic regression step-wise selection method using the five independent variants, McHenry said.

Patients with all risk factors treated within the two-day timeframe were 24.3 times more likely to develop respiratory failure, compared to the patients with all risk factors — including delayed surgery — who were 36.2 times more at risk.

Propensity analysis confirms findings

To rule out any selection bias between early surgery patients and delayed surgery patients, the researchers also performed a propensity analysis. They matched 301 patients who underwent early surgery to 301 who underwent surgery more than two days after fracture.

“We did a regression analysis of this matched cohort of 602 patients and found that again, age, ISS, GCS, blunt lung injury and time of surgery were all still significant (P<.002) and the prediction model was accurate with only slight degradation in the area of the Receiver Operating Characteristic (ROC) curve and the goodness-of-fit test,” McHenry said.

He noted that the study included some limitations. It was retrospective in nature and other variables that can cause respiratory failure were not considered: blood transfusion, metabolic acidosis and hypotension upon entering the emergency room. Also, the outcomes may only reflect the treatment philosophy of a few surgeons at one institution.

But McHenry said: “Within the limitations of this study, it appears that the incidence of respiratory failure is decreased if surgeons perform early — less than two days from initial indications of thoracic and spine fractures.”

For more information:
McHenry T, Mirza S, Wang J, et al. Risk factors for respiratory failure following operative stabilization of thoracolumbar fractures. #190. Presented at the American Academy of Orthopaedic Surgeons 73rd Annual Meeting. March 22-26, 2006. Chicago.