Background: In the morbidly obese patient undergoing laparoscopic gastric bypass (LGBP), insufflation with carbon dioxide to 20 mmHg for prolonged periods may induce significant hypercarbia and acidosis with attendant sequelae. We hypothesize that the use of helium as an insufflating agent results in less hypercarbia and acidosis.Methods: The study was performed between May and November 2002. A Paratrend 7 fiberoptic probe was placed via a carotid artery catheter in 5 adult Yorkshire swine as continuous pH and pCO2 levels were measured. Animals were ventilated to a constant pCO2, after which LGBP was performed. Blood gas values were measured during the procedure and for 1 hour after release of pneumoperitoneum. Helium was used for insufflation in 3 of the pigs and CO2 in 2. Comparison of arterial pH and pCO2 were made between groups.Results: Mean maximum pCO2 for the control group (CO2 insufflation) was 99.75 +/- 22.98 mmHg, while for the experimental group (helium insufflation) was 52.86 +/- 6.27 mmHg (P=.036). Mean low pH for the groups were 7.10 +/-.056 and 7.36 +/-.015 (P =.004) respectively. Normalization of pCO2 in the helium group occurred at a mean of 14.58 min (SD 13.3 min) after release of pneumoperitoneum, while in the control group levels did not normalize (mean final pCO2= 71.5 mmHg).Conclusions: Helium pneumoperitoneum in LGBP is associated with less intraoperative hypercarbia and acidosis than is the use of CO2. In addition, pCO2 returns to normal more rapidly postoperatively with the use of helium insufflation. Study of helium insufflation in humans undergoing LGBP is needed to prove its benefits in the clinical setting.