imageBy James E. Barone, MD

Cautious observation is likely safe but no better than tube thoracostomy for occult pneumothorax found on chest computed tomography (CT) scan, according to results from a randomized trial presented at the 2012 annual meeting of the American Association for the Surgery of Trauma.

With the liberal use of CT scanning for trauma patients, occult pneumothorax (a pneumothorax seen on CT scan but not on plain chest x-ray) is being discovered more frequently. Previous studies have reported conflicting results for the two management strategies.

A randomized multicenter, unblinded trial from four Canadian trauma centers included 52 patients in the observation group and 40 patients in the group treated with chest tubes after discovering their occult pneumothoraces. All patients enrolled in the study were adults. Baseline characteristics and injury severity scores of patients in both groups were similar. Patients who were randomized to observation were allowed to undergo tube thoracostomy at the discretion of the attending surgeon or for respiratory distress, difficulty weaning or increasing pleural fluid collections.

Andrew W. Kirkpatrick, MD, medical director of trauma services at the University of Calgary and lead author of the study commented by email to General Surgery News that it was hard to tell exactly what triggered the decision to place a tube.

“A conclusion that we are coming to with looking and relooking at all the data is that no patient got into trouble with just an elective operation and an occult pneumothorax, but about 25% of those needing prolonged positive pressure ventilation required a tube for some, often multifactorial reason,” Dr. Kirkpatrick said.

The primary outcome, which was the incidence of respiratory distress, and the secondary outcomes of mortality rate, number of ventilator days, ICU length of stay (LOS) and hospital LOS were not significantly different. Of the patients who were initially treated with chest tubes, 15% had complications related to the tubes and another 15% had tubes that were not optimally placed.

Regarding the malpositioned chest tubes, Dr. Kirkpatrick said, “Several required repositioning but none of these [required] replacement; otherwise, they would have been upgraded to a ‘major’ complication.”

One patient in the observation group suffered a tension pneumothorax that was successfully treated, and 21% of the observed patients eventually required insertion of a chest tube for such problems as progression of the pneumothorax, increased plural effusion size, pneumonia or acute respiratory distress syndrome.

The invited discussant of the paper, Raul Coimbra, MD, chief of trauma at the University of California San Diego Health System, was not involved with the study. He told General Surgery News that the authors should be applauded for performing a prospective, randomized multi-institutional study.

“This is the right methodology to answer critical questions related to a difficult clinical problem.”

Dr. Coimbra added, “Based on our own data which led to an [American Association for the Surgery of Trauma] multi-institutional study and the data presented in Dr. Kirkpatrick’s manuscript, we use chest tubes selectively.”

Dr. Coimbra feels that a period of observation is safe for patients with occult pneumothorax even when undergoing positive pressure ventilation. “The key here is awareness of the presence of the pneumothorax and close clinical observation and monitoring,” he said.

Dr. Kirkpatrick and his fellow researchers concluded that both treatments have distinct complications and “cautious routine observation with immediate on-demand pleural drainage seems safe but not proven better.” They plan to continue enrolling patients in the study.