Effect of end-tidal carbon dioxide on prognosis in pneumothorax cases in emergency department

Introduction Pneumothorax is the presence of air between the pleural layers. End-tidal carbon dioxide pressure (ETCO2) can be measured by capnography. ETCO2 directly reflects the respiratory excretion of CO2 and indirectly reflects the gas exchange capacity of the lung and the exchange of CO2 in the pulmonary circulation. The use of capnography in the emergency department (ED) is routinely used primarily to measure the efficiency of cardiopulmonary resuscitation (CPR) and to determine return of spontaneous circulation (ROSC) and to verify endotracheal tube placement during intubation. Although there are several studies on the use of ETCO2 in patients with pneumothorax in ED, there is a lack of information on the prognostic and predictive value of ETCO2. The aim of our study is to analyze the relationship between ETCO2 and the severity of the disease, morbidity and mortality in patients admitted to ED with pneumothorax. Method This study was conducted at Pamukkale University, Faculty of Medicine, Department of Emergency Medicine. Of the 98 patients who agreed to participate in the study, 54 patients received conservative management and 44 patients underwent tube thoracostomy (TT) drainage with clinical evaluation independent of the study. The ETCO2 value was measured for 1 minute on admission and 45 minutes after tube thoracostomy procedure using the B40 Monitor and E-miniC CO2 Module (GE Healthcare, USA). Vital signs, laboratory data, radiological findings, hospitalization data and 30-day mortality were evaluated to assess prognostic prediction. Results At the end of the study, out of 98 patients admitted to the ED and diagnosed with pneumothorax, 9 (16.6%) of 54 patients who did not undergo TT were spontaneous pneumothorax (SP) and 45 (84.4%) were traumatic pneumothorax (TP). Of the 44 patients who underwent TT, 22 (50%) had SP and 22 (50%) had TP. There was a significant difference between the groups with pneumothorax defined as large in the study methodology in 11 (20.4%) of 54 patients without TT and 36 (81.8%) of 44 patients with TT (p=0.001). When ETCO2 values were compared in SP and TP groups at admission and after TT procedure in patients who underwent TT, it was found that ETCO2 value increased significantly in both groups (p=0.0001). In the group that underwent TT, the mean A-aCO2 gradient at admission and the mean ETCO2 change with the procedure were found to be significantly lower in the group that underwent ward hospitalization after TT compared to the group that underwent ICU hospitalization (p=0.007, p=0.02 respectively). A-aCO2 gradient (mmHg) after TT was correlated with ICU length of stay (days) [spearman correlation factor; 0.343 (p=0.023)]. The cut-off point for the need for TT procedure for ETCO2 values of 33 mmHg and below has a sensitivity of 72.7% and a specificity of 40.7%. There is no significant difference between the groups when differentiating between the TT and non-TT groups regarding the prognostic value of ETCO2. Conclusion In this study, we investigated the prognostic value of ETCO2, a non-invasive and easily measurable value, in patients diagnosed with pneumothorax in the emergency department. Despite its potential as a prognostic marker, no difference was found in ETCO2 levels in TT placement, when SP and TP subgroups were included in the evaluation, in emergency department outcome, and in thirty-day mortality when compared with their counterparts. The highest sensitivity (72.7%) was found when the cut-off point of ETCO2 was chosen as 33 mmHg and the highest selectivity (77.8%) was found when the cut-off point was chosen as 27 mmHg in differentiating placement of a tube. Keywords: Capnography, emergency department, end tidal carbon dioxide, pneumothorax, prognosis