A new system for assessing atelectasis on chest x-ray after sternotomy for cardiac surgery

Abstract

Rationale Pulmonary atelectasis is common following sternotomy for cardiac surgery and has been associated with post-operative complications. A number of studies have used the degree of atelctasis present on chest X-rays(CXR) to assess the efficacy of interventions designed to reduce atelectasis. Unfortunately the CXR scoring systems used often exaggerate the clinical effect of atelectasis in these patients. One of the reasons for this is that they tend to over state the clinical importance of the basal atelectatic changes that are present in the majority of patients who have had a sternotomy for cardiac surgery, resulting in a reduced specificity and thus decreasing the validity of such a surrogate outcome in clinical trials. We have produced an alternative scoring system that seeks to correct this problem and this study is an initial attempt to validate this system. Methods We retrospectively selected 50 consecutive patients who met the inclusion criteria; Median sternotomy for cardiac surgery (using cardiopulmonary bypass) Weaned from mechanical ventilation and extubated within the first 8 hrs. Only required nasal prong or facemask oxygen following extubation. Clinical details of oxygenation on post-operative day 1 and 3 were collected from the patients records and electronic copies of CXR taken on return to ICU, on D1 and on D3. The x-rays were scored using both the old and new scoring system by a single radiologist who was blinded to the oxygenation data. One patient had incomplete clinical records so was excluded from analysis. The Day 1 and Day 3 CXR scores were compared with oxygenation indices(P/F or S/F ratio) at the time of CXR. Day 1 scores were also assessed for their ability to predict Day 3 oxygenation indices or supplemental oxygen requirement. Results The new score demonstrated similar sensitivity but better specificity than the old score when comparing the CXR findings with the clinical oxygenation status of the patients (Table 1). ROC analysis demonstrated a greater AUC for the new score vs the old score(table 2). The new score also performed better than the old score at predicting day3 clinical status from the day1 CXR. (Table presented) Conclusions This new scoring method is probably better suited as an outcome measure for atelectasis in studies of patients following cardiac surgery. It may also have some utility in predicting patients who require ongoing supplemental oxygen on postoperative Day 3, however further prospective studies are required.