Sensitivity of chest ultrasound for postoperative pneumothorax in comparison to chest X-ray after lung resecting surgery

Abstract

OBJECTIVES Thoracic ultrasound is superior to chest X-ray for the detection of a pneumothorax in trauma and intensive care medicine. Data regarding its use in non-cardiac thoracic surgery are scarce and contradictory. Previous studies are heterogeneous regarding sonographic methodology and patient selection. This study aimed to evaluate the accuracy of thoracic ultrasound for pneumothorax assessment after lung resecting surgery in unselected patients. METHODS SONOR (SONOgraphy vs x-Ray) is a prospective observational trial (registry-ID DRKS00014557). A total of 123 consecutive patients with lung resecting surgery received a standardized thoracic ultrasound the same day and in addition to routine chest X-rays in erect position after removal of the chest tube. The sonographer was blinded to radiological findings and vice versa. RESULTS Sensitivity, specificity, positive and negative predictive values of ultrasound after removing the chest tube were 0.32, 0.85, 0.54, 0.69 for any pneumothorax and 1.0, 0.82, 0.19, 1.0 for pneumothorax ≥3 cm. No clinically relevant pneumothorax was missed. The agreement between sonography- and routine-based therapeutic decisions was 97%. Lung pulse was the most frequently detected sign to sonographically rule out a pneumothorax. CONCLUSIONS Postoperative thoracic ultrasound in unselected patients has a low overall sensitivity to detect a residual pneumothorax; however, its sensitivity and negative predictive values regarding clinically relevant pneumothorax are high. Test quality depends on the distinct sonographic methodology and patient selection. Anatomic differences in postsurgical and medical patients may be responsible for the contradictory results of previous trials. Studies with a larger population size are required to validate the accuracy of relevant pneumothoraces and identify appropriate selection criteria. Clinical trial registration number DRKS—German Clinical Trials Register, www.drks.de, registry-ID DRKS00014557.

Most patient conditions do not a priori debilitate the sensitivity of thoracic ultrasound in thoracic surgery-a prospective comparative study

“…The role of lung ultrasound as an alternative to routine chest roentgenograms for the detection of a pneumothorax after thoracic surgery is under discussion. Two large studies, which were performed under routine [ 16 ] or near-routine conditions [ 23 ], exhibited a low sensitivity (0.32, 0.19, respectively), whereas two smaller studies with rather artificial conditions (restrictive inclusion criteria [ 24 ], small sample size with very high pneumothorax rate [ 21 ]) revealed a 1.0 sensitivity. The reasons for this discrepancy are not clear; different sonographic examination techniques and inclusion criteria are suspected to be the cause.…”

“…Second, a pneumothorax on the first day after surgery will be larger than later, otherwise one would not have decided to remove the chest tube. We have demonstrated that the sensitivity of ultrasound is dependent on the pneumothorax size [ 16 ]. Third, the examiner who – consciously or not – perceives an air leakage through a chest tube will probably expect a pneumothorax and examine more accurately (examiner bias / diagnostic suspicion bias [ 30 , 31 ]).…”

“…Lung pulse is a powerful, but often neglected artefact to rule out pneumothorax in difficult situations [ 16 , 33 ].…”

“…Two studies have reported the usefulness of lung ultrasound despite its low sensitivity [ 22 , 37 ]. For instance, the negative predictive value for relevant pneumothorax sizes is clinically more important after chest tube removal, since small apical pneumothoraces are usually not of clinical interest [ 16 , 22 ].…”

“…Therefore, we have recently conducted a prospective observational trial which compared a standardised lung ultrasound with p.a. upright chest X-ray after chest tube removal following thoracic surgery [ 16 , 17 ]. We have refrained from excluding the “difficult” patients to evaluate a pragmatic, real-life accuracy of chest ultrasound.…”