LAUSR

Learning Objectives: Pulmonary embolism (PE) causes 100,000 deaths and contributes to over 4 billion dollars of annual healthcare costs. Acute PE is a diagnostic challenge as symptoms vary widely and are nonspecific. Definitive diagnosis requires computed tomography (CT) scanning of the lungs, exposing patients to radiation and intravenous contrast. This study examined the accuracy and harm avoidance of adding end tidal carbon dioxide (EtCO ... 2) measurement to the PE diagnostic process in hospitalized adults without shock or hypotension. Methods: This study used a single center, prospective, descriptive, correlational design. Hospitalized adults (SBP ≥ 90mmHg) with an order for CT scan to rule out PE were identified and consented. Within 24 hours of CT, EtCO ... 2 was obtained with a microstream assessment by nasal cannula or with an airway adaptor connected to the breathing circuit in mechanically ventilated patients. Radiologist and PI were blinded to the EtCO ... 2 or CT result, respectively. Demographic and clinical variables were collected from the electronic medical record. Sensitivity, specificity, and negative predictive value (NPV) were calculated using SPSS. Results: The typical subject was a 59-year-old, Caucasian female on the general medicine service. Definitive CT results were obtained from 111 of 112 subjects. PE prevalence was 18.9%. Mean±SD EtCO ... 2 was lower for PE+ (28 ± 7.8 mmHg) than PE(33 ± 8.1 mmHg, P=.01) subjects. The EtCO ... 2 ROC curve had an area of .674 (95% CI .542 .805). For PE exclusion, an EtCO ... 2 cutoff value of ≥42mmHg yielded 100% sensitivity, 12.2% specificity, and 100% NPV. Use of this EtCO ... 2 cutoff score could have safely eliminated 11 subjects (9.9%) from receiving an unnecessary CT scan. Mean±SD radiation exposure was not different for PE+ (5.5 ± 2.5 mSv) than PE(6.4 ± 4.0 mSv) subjects (P=.32). Frequency of contrast induced nephropathy also was not different for PE+ (11%) and PE(7.5%) subjects (P=.86). No allergic reactions were noted. Conclusions: Bedside EtCO ... 2 assessment is a low cost, non-invasive test that could be used to help exclude a PE diagnosis. Our data suggest an absolute EtCO ... 2 cutoff value of ≥42mmHg could decrease the need for CT scans in up to 10% of hospitalized adult patients suspected of having a PE; thus, decreasing healthcare costs and risk of iatrogenic injury.