505 Electrical Impedance Tomography (EIT) Can Rapidly Detect Small Pneumothoraces

Background: Diagnosis of pneumothorax currently relies on clinical suspicion and chest radiography and is often delayed. Aims: To determine whether EIT can accurately identify the location of surgically created pneumothoraces of varying sizes. Methods: Six anaesthetised and muscle-relaxed piglets with saline lavaged surfactant-deficient lungs (AaDO2 >350mmHg in FIO2 1.0) were studied. A chest drain was inserted into the right ventral chest and increasing amounts of air (10 to 200 mL in 10-20mL aliquots) were instilled into the pleural space. At the end of these instillations, a Heimlich valve was attached to the chest drain. At each instillation, regional end-expiratory volumes (EELV) were measured using EIT concurrently with SpO2, heart rate and arterial blood pressure (BP). Results: At all volume instillations, mean impedance within the right ventral (RV) quadrant was significantly higher than all other quadrants (p< 0.0001 ANOVA). A significantly greater EIT timecourse signal was identified in the RV quadrant after as little as a 10 mL instillation (p< 0.0001; ANOVA). Impedance in the RV quadrant fell from mean (SD) 46 (39.5) c.u. to 18.3 (20.5) suggesting a 60.3% resolution of the pneumothorax within 60- secs following attachment of the Heimlich valve (p< 0.001; ANOVA). A deterioration in SpO2 to 89 (6)% did not occur until 100 mL instillation (p< 0.001; ANOVA) and tachycardia mean (SD) to 245 (44) bpm occurred at 140 mL instillation (p=0.001). Figure Conclusions: EIT accurately identified the location of even small volume pneumothoraces before physiological parameters changed.