Real-time detection of pneumothorax using electrical impedance tomography.

OBJECTIVES: Pneumothorax is a frequent complication during mechanical ventilation. Electrical impedance tomography (EIT) is a noninvasive tool that allows real-time imaging of regional ventilation. The purpose of this study was to 1) identify characteristic changes in the EIT signals associated with pneumothoraces; 2) develop and fine-tune an algorithm for their automatic detection; and 3) prospectively evaluate this algorithm for its sensitivity and specificity in detecting pneumothoraces in real time. DESIGN: Prospective controlled laboratory animal investigation. SETTING: Experimental Pulmonology Laboratory of the University of São Paulo. SUBJECTS: Thirty-nine anesthetized mechanically ventilated supine pigs (31.0 +/- 3.2 kg, mean +/- SD). INTERVENTIONS: In a first group of 18 animals monitored by EIT, we either injected progressive amounts of air (from 20 to 500 mL) through chest tubes or applied large positive end-expiratory pressure (PEEP) increments to simulate extreme lung overdistension. This first data set was used to calibrate an EIT-based pneumothorax detection algorithm. Subsequently, we evaluated the real-time performance of the detection algorithm in 21 additional animals (with normal or preinjured lungs), submitted to multiple ventilatory interventions or traumatic punctures of the lung. MEASUREMENTS AND MAIN RESULTS: Primary EIT relative images were acquired online (50 images/sec) and processed according to a few imaging-analysis routines running automatically and in parallel. Pneumothoraces as small as 20 mL could be detected with a sensitivity of 100% and specificity 95% and could be easily distinguished from parenchymal overdistension induced by PEEP or recruiting maneuvers. Their location was correctly identified in all cases, with a total delay of only three respiratory cycles. CONCLUSIONS: We created an EIT-based algorithm capable of detecting early signs of pneumothoraces in high-risk situations, which also identifies its location. It requires that the pneumothorax occurs or enlarges at least minimally during the monitoring period. Such detection was operator-free and in quasi real-time, opening opportunities for improving patient safety during mechanical ventilation.

Accuracy of high resolution CT in assessing idiopathic pulmonary fibrosis histology by objective morphometric index.

To determine the accuracy of HRCT in assessing histology by objective morphometric index, twenty-five biopsy specimen-proved UIP were correlated with high-resolution CT (HRCT) by morphometric analysis. The scans were evaluated for the presence and extent of normal parenchyma, ground-glass attenuation, linear opacities, consolidation, honeycombing, vessels and bronchiectasis, and overall extent of histology involvement for normal parenchyma, honeycombing, alveolar septal inflammation, fibrosis, vessels, and bronchiectasis/bronchiolectasis. The comparison between morphometric measurements showed a strong correlation between HRCT and histologic parameters for extension (%) of normal tissue (p = 5 x 10(-5)), honeycombing (p = 6 x 10(-5)), and vessels (p = 0.0047). HRCT consolidation strongly correlated with alveolar septal inflammation (p = 0.015), whereas HRCT linear opacities had the highest correlation with histology for bronchiectasis or bronchiolectasis (p = 0.03). These associations also demonstrated that there was considerable residual scatter about the linear relationships found. By contrast, neither the ground glass patterns nor the bronchioectatic patterns determined by CT were associated with any histologic observation (p < 0.1). There was a borderline negative relationship between vessels determined by CT and histologic fibrosis (p = 0.069), i.e., the percentage of vessel patterns determined by CT was found to be lower when fibrosis was prominent histologically. Our results showed that HRCT patterns, usually employed to provide information about activity (ground glass) and fibrosis (consolidation) in IPF, failed to correlate with histology. On the other hand, chronic cystic lesions had a good correlation with histology. This finding suggests that in patients without a diffuse honeycomb pattern on HRCT, a lung biopsy may provide additional information. The more important limitation of our study was the lack of correlation related to the proximity of the biopsy site to the HRCT location evaluated by morphometry.