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

Background: Carbon dioxide absorption into the blood during laparoscopic surgery using intraperitoneal carbon dioxide insufflation may lead to respiratory acidosis, increased ventilation requirements, and possible serious cardiovascular compromise. The relationship between increased carbon dioxide excretion (V-co2) and intraperitoneal carbon dioxide insufflation pressure has not been well defined. Methods: In 12 anesthetized pigs instrumented for laparoscopic surgery, intraperitoneal carbon dioxide (n=6) or helium (n=6) insufflation pressure was increased in steps, and V-co2, (metabolic cart), dead space, and hemodynamics were measured during constant minute ventilation. Results: V-co2 increases rapidly as intraperitoneal insufflation pressure increases from 0 to 10 mmHg; but from 10 to 25 mmHg, V-co2 does not increase much further. Pa-co2 increases continuously as intraperitoneal insufflation pressure increases from 0 to 25 mmHg. Hemodynamic parameters remained stable. Conclusions: By considering Fick's law of diffusion, the initial increase in V-co2 is likely accounted for by increasing peritoneal surface area exposed during insufflation. The continued increase in Pa-co2 without a corresponding increase in V-co2 is accounted for by increasing respiratory dead space.