CARBON-DIOXIDE ABSORPTION IS NOT LINEARLY RELATED TO INTRAPERITONEAL CARBON-DIOXIDE INSUFFLATION PRESSURE IN PIGS

Background: Carbon dioxide absorption into the blood during laparoscop ic surgery using intraperitoneal carbon dioxide insufflation may lead to respiratory acidosis, increased ventilation requirements, and possi ble serious cardiovascular compromise. The relationship between increa sed carbon dioxide excretion (V-co2) and intraperitoneal carbon dioxid e insufflation pressure has not been well defined. Methods: In 12 anes thetized pigs instrumented for laparoscopic surgery, intraperitoneal c arbon dioxide (n=6) or helium (n=6) insufflation pressure was increase d in steps, and V-co2, (metabolic cart), dead space, and hemodynamics were measured during constant minute ventilation. Results: V-co2 incre ases rapidly as intraperitoneal insufflation pressure increases from 0 to 10 mmHg; but from 10 to 25 mmHg, V-co2 does not increase much furt her. Pa-co2 increases continuously as intraperitoneal insufflation pre ssure increases from 0 to 25 mmHg. Hemodynamic parameters remained sta ble. Conclusions: By considering Fick's law of diffusion, the initial increase in V-co2 is likely accounted for by increasing peritoneal sur face area exposed during insufflation. The continued increase in Pa-co 2 without a corresponding increase in V-co2 is accounted for by increa sing respiratory dead space.