To the Editor:—

Dual-lung capnography allows carbon dioxide to be monitored from each lung individually or from both lungs simultaneously without interrupting two-lung ventilation. Dual-lung capnography has helped to detect major unilateral ventilation/perfusion mismatching during anesthesia. 1Here we describe a situation wherein information obtained via  dual-lung capnography allowed the anesthesia team to render an informed opinion to the surgical team regarding the status of the flow in a major pulmonary artery after the surgeons expressed concern about accidentally stapling the vessel during a technically complex thoracic operation.

The case involved a 57-yr-old woman who had undergone a left upper lobectomy for adenocarcinoma 3 yr earlier and now presented with an anterior mediastinal mass (5 × 7 × 6 cm; adenocarcinoma). After induction of general anesthesia and placement of a left-sided double-lumen tube, we sampled end-tidal carbon dioxide partial pressure continuously using an adapter located between the double-lumen tube and the anesthesia circuit (standard approach). The surgical procedure was performed through a median sternotomy. Because the mass was adherent to the thymus and pericardium, the surgeons began their dissection from the right side of the thymus, excising the mass along with a portion of the thymus and a segment of pericardium. A wedge resection of the left lung was also required because the mass adhered tenaciously to portions of this lung. Despite our use of one-lung ventilation (right lung), the left pulmonary artery proved difficult to visualize, and the possibility arose that this vessel had been accidentally occluded (stapled) during the wedge resection.

We hypothesized that if such an occlusion had indeed occurred, it would produce a major unilateral perfusion deficit characterized by a marked decrease in carbon dioxide delivery to the left lung and a correspondingly low end-tidal carbon dioxide partial pressure from the left lung that could be detected using dual-lung capnography. We therefore commenced double-lung ventilation using the set-up described by us previously to measure and record carbon dioxide waveforms from each lung during two-lung ventilation. 1The end-tidal carbon dioxide partial pressure values of the individual lungs were found to be similar (36 mmHg on the left vs.  38 mmHg on the right), and the waveforms from the two lumens of the double-lumen tube were similar. We interpreted these findings as an indication that there was no major blood flow limitation in left main pulmonary artery. Confirming our hypothesis was a subsequent intraoperative Doppler study that showed that the left pulmonary artery was patent with normal flow velocity.

Bhavani Shankar K, Roger R, Aklog L, Mushlin PS: Dual capnography facilitates detection of a critical perfusion defect in an individual lung. A NESTHESIOLOGY 1999; 90:302–5