Question: 

To which extent do abdominal insufflation of CO₂ and elevation of the intra-abdominal pressure (IAP) influence hemodynamic parameters derived from different methods of cardiac output (CO) measurement?

Methodology: 

In eight piglets (I, mean 11.14kg) atrial septal puncture was performed under fluoroscopic guidance and a 12mm balloon catheter was inflated (4 atm). Nine piglets (II, mean 11.07kg) served as the control group. The IAP was elevated to 8 and 16 mmHg, followed by desufflation after each IAP-step (each 20 min). Indirect calorimetric measurements (V'_O2, V'_CO2, RQ) were performed by the Deltatrac. A pulmonary artery catheter was used for measurement of CO by the thermodilution method (CO_TD) and of the temperature. P_O2, P_CO2, S_O2, pH and Hb of carotid and pulmonary artery blood were determined to calculate O₂ and CO₂ blood content (C_O2, C_CO2) and CO as a function of V'_O2 and of V'_CO2 (CO_V'O2=V'_O2/C_O2,a-pa, CO_V'CO2=V'_CO2/C_CO2,pa-a). (approved study 1.5177-07-04/G07-1-014).

Results: 

CO₂ uptake was significantly greater at an IAP of 8 mmHg (+25%) compared to that at an IAP of 16 mmHg (+13%). V'_O2 remained nearly unchanged. Decreases in S_O2,a (-6 - -10%) at elevated IAPs indicated right-to-left shunting (I), without recovery after desufflation. CO_TD was significantly lower than CO_V'O2 in the ASD-group (-15 - -23%) and higher than CO_V'CO2 in the Control-group (22–34%) due to greater decreases in P_O2,a compared to P_O2,pa (I) and increases in P_CO2,pa (II).

Conclusion: 

CO₂ uptake occurs mainly at low IAP-levels caused by greater peritoneal perfusion. Calorimetric measurements ensure assessment of hemodynamics independent of right-to-left shunting.