Does End-tidal PCO2 Reflect Adequately Arterial PCO2 during One-lung Ventilation for Thoracoscopy?

Lee, Jong Seok; Han, Jeong Uk; Shin, Cheung Soo; Lim, Kwang Ho

Abstract

BACKGROUND: Maintenance of normal arterial carbon dioxide tension (PaCO2) is not generally a problem if the same tidal volume can be maintained when changing from two-lung(TLV) to one-lung ventilation(OLV). However, there have been a few studies on the use of capnography in monitoring the adequacy of ventilation during one-lung anesthesia. We have therefore studied how closely end-tidal PCO2 (PETCO2) values reflect changes in PaCO2 in patients undergoing thoracoscopic sympathectomy during TLV and after transition to OLV.
METHODS
We have measured arterial oxygen tension(PaO2), PaCO2, PETCO2, and (PaCO2-PETCO2) in 24 adult, either sex, patients by infra-red spectrometry. They were measured after induction of anesthesia, in supine position(TLVsup), after a lateral decubitus position(TLVlat), at 15 minutes after left OLV(OLVLt), after right OLV(OLVRt), and at 10 minutes in the supine position re-positioned at the end of the operation(TLVrep). Data were analyzed with a one-way analysis of variance with repeated measures followed by multiple comparision. The correlation between PaCO2 and PETCO2 were tested using linear regression.
RESULTS
PaCO2 did not significantly change, whereas PETCO2 significantly decreased at OLVLt, OLVRt compared with TLVsup value (OLVLt, 29.7 mmHg OLVRt, 30.5 mmHg and TLVsup, 33.6 mmHg; P< 0.05). Compared with TLVsup(0.2 mmHg), (PaCO2-PETCO2) significantly increased at OLVLt, OLVRt, TLVrep(3.7 mmHg, 2.3 mmHg, 3.5 mmHg). The correlation between PaCO2 and PETCO2 in these series is consistent. (r>0.65, P<0.0006)
CONCLUSIONS
In the patients undergoing thoracoscopic sympathectomy with TLV or OLV in the lateral decubitus position, PETCO2 is a reliable estimate of the PaCO2. However, when the operative time is prolonged the arterial PCO2 may be more reliable than PETCO2.