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Erschienen in:
30.09.2019 | Images in Anesthesia
Understanding an unusual capnography waveform using electrical impedance tomography
Erschienen in: Canadian Journal of Anesthesia/Journal canadien d'anesthésie | Ausgabe 1/2020
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An unusual capnography waveform with a descending “reverse” phase III (Figure, panel A) was observed in an intubated, mechanically ventilated, postoperative patient. Although air leaks and pneumothorax were excluded, a preoperative computed tomography (CT) scan showed severe chronic changes in the lung parenchyma (Figure, panel B). Heterogeneously distributed, the lesions included bronchiectasis and thickening of the bronchial walls in the right lung and large sub-pleural areas of abnormally low attenuation and destruction of alveolar septa (i.e., bullae) in the left lung. Thus, we reasoned that the altered waveform could be due to heterogeneous regional ventilation.
Figure
Electrical impedance tomography (EIT) monitoring of a postoperative subject with an unusual descending capnography waveform (panel A) and heterogeneous distribution of emphysematous lung changes seen on chest computed tomography (CT) scans (panel B). EIT showed that the ventilation was characterized by temporal ventilation heterogeneity, as filling and emptying of different regions of interest (ROIs) in the lung (e.g., ROI-1 to ROI-4, panels C to F) were out of phase. Images in panels C to F were obtained during a single breath, with each corresponding to the start of deflation (red vertical lines). The ventral right ROI-1 exhibited the fastest inflation and deflation (i.e., shortest time constant), as indicated by the red line positioned first (panel C). The dorsal left ROI-4, occupied by the large bullae on the preoperative CT scan, was the last to start deflating (red line, Figure panel F), likely due to a longer time constant
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