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Carbon dioxide absorption is not linearly related to intraperitoneal carbon dioxide insufflation pressure in pigs
D R Lister1, B Rudston-Brown, C B Warriner
1Department of Anaesthesia, St. Paul's Hospital, University of British Columbia, Vancouver, Canada.
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 (VCO2) and intraperitoneal carbon dioxide insufflation pressure has not been well defined.
Methods:
In 12 anesthesized pigs instrumented for laparoscopic surgery, intraperitoneal carbon dioxide (n = 6) or helium (n = 6) insufflation pressure was increased in steps, and VCO2 (metabolic cart), dead space, and hemodynamics were measured during constant minute ventilation.
Results:
VCO2 increases rapidly as intraperitoneal insufflation pressure increases from 0 to 10 mmHg; but from 10 to 25 mmHg, VCO2 does not increase much further. PaCO2 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 VCO2 is likely accounted for by increasing peritoneal surface area exposed during insufflation. The continued increase in PaCO2 without a corresponding increase in VCO2 is accounted for by increasing respiratory dead space.