Arterial to end-tidal carbon dioxide tension difference during laparoscopic colorectal surgery

BACKGROUND: Determination of end-tidal carbon dioxide pressure (PET(CO2)) is effective to confirm adequate ventilation, because arterial to end-tidal carbon dioxide tension difference (deltaa-ET(CO2)) does not change normally during operation. But deltaa-ET(CO2) may change during laparoscopic surgery, because peritoneal insufflation of CO2 will increase CO2 production and reduce functional residual volume. Changes in deltaa-ET(CO2) were reported in laparoscopic cholecystectomy with cardiovascular complication, but there is controversy about how deltaaET(CO2) will change in more complicated and long laparoscopic surgery. In this prospective study, we examined changes in deltaa- ET(CO2) during laparoscopic colorectal surgery. METHODS: Fifty patients received combined general and epidural anesthesia. CO2 pneumoperitoneum was initiated after obtaining arterial blood for gas analysis. Mechanical ventilation was used to maintain PET(CO2) at a stable value between 30 and 40 mmHg during the procedure. Arterial blood gas analysis was performed 10, 60, 120 minutes after CO2 insufflation, and 10 minutes after the termination of insufflation. RESULTS: The mean +/- SD for deltaa-ET(CO2) was 5.8 +/- 4.1 before pneumoperitoneum, 7.1 +/- 4.8, 8.1 +/- 5.4, 6. 4 +/- 4.9 in 10, 60, 120 minutes after pneumoperitoneum, and 6.4 +/- 4.9 in 10 minutes after the termination of pneumoperitoneum. deltaa-ET(CO2) increased significantly during pneumoperitoneum, but did not increase further even if CO2 insufflation was longer than 60 minutes. CONCLUSIONS: In laparoscopic colorectal surgery, Pa(CO2) should be checked for at least the first 60 minutes to confirm adequate ventilation.