Potential role of transcutaneous carbon dioxide monitoring in nonintubated video-assisted thoracic surgery

Dear Editor,

We read Dr. Ke and colleagues’ article published in the October issue of the Journal of the Chinese Medical Association with interest.¹ In their retrospective study, the authors demonstrated that patients who received nonintubated video-assisted thoracic surgery (VATS) lung wedge resection had benefits of shorter anesthesia induction and operative times, shorter postoperative hospital stays, and reduced chest tube retention compared with traditional wedge resection with double-lumen endotracheal tube. However, the nonintubated patients had a higher partial pressure of carbon dioxide (PaCO₂) levels in both the pre-one-lung and during one-lung ventilation periods and a lower serum pH levels during one-lung ventilation period as measured in arterial blood gas (ABG). The authors mentioned the technical difficulties in continuous end tidal carbon dioxide (ETCO₂) measurement in nonintubated patients because of the obstruction of ETCO₂ detector by transnasal humidified rapid-insufflation ventilatory exchange cannula in the nostril. Since ABG could only provide intermittent analysis, the lack of a continuous ETCO₂ monitoring could result in undetected hypercapnia. We congratulate the success of the authors’ publication, and we would like to suggest using transcutaneous carbon dioxide (TCCO₂) monitoring to overcome such difficulties.

TCCO₂ monitor provides continuous noninvasive monitoring of PaCO₂. The device involves a sensor attached to the earlobe which warms the skin to 42 to 43°C to provide vasodilatation of the capillary bed. This facilitates the diffusion of carbon dioxide from the capillary to the membrane of the detector. TCCO₂ readings have been found to correlate well with PaCO₂ obtained through ABG.² The first commercially available monitor was introduced into clinical practice in 1980. This technology is used commonly in the neonatal intensive care unit population.² Even though the use of TCCO₂ monitor is currently not a standard of care in the perioperative setting, TCCO₂ was found to be an accurate and reliable measurement of PaCO₂ during general anesthesia in adults.^3,4 The study of Tobias⁵ found that TCCO₂ provides good correlation to PaCO₂ during one-lung ventilation in thoracic surgery with a difference of 2.7 ± 1.4 mmHg. The use of TCCO₂ monitoring in nonintubated VATS has been reported once. Gravino et al studied VATS talc pleurodesis performed under monitored anesthesia care. They used TCCO₂ device to monitor efficiency and adequacy of spontaneous ventilation. However, the exact value and trend of TCCO₂ data was not reported.⁶

TCCO₂ monitoring has particular benefit when ETCO₂ monitoring is not applicable. As a result, we believe that its usage may have a potential role in nonintubated VATS. We are looking forward to learning the authors’ kind response.