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Carbon dioxide elimination during continuous venovenous hemodiafiltration (CVVHD)-laboratory experiment

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In a previous experiment with crystalloid solution we have shown that during CVVH(D) CO2 losses are proportional to the fractional ultrafiltration (UF) rate of circulating solution, with only a marginal impact of dialysis and temperature [1]. We report here results of a similar experiment with packed RBC.


Packed RBC were heparinized, diluted with crystalloid solution with bicarbonate to hematocrit of 0.35 and continuously saturated in a special mixing chamber to targeted pCO2value of 5 kPa. After equilibration, the mixing chamber was connected to a PRISMA monitor (Prisma, Hospal, France) at a blood rate (Qb) of 150 mlhr-1and different CVVH(D) settings were tested for CO2 elimination at two temperature levels (37 and 40°C). Blood samples were drawn in triplicate at each setting before and after the filter for blood gases analysis (ABL 520, Radiometer, Denmark). CO2 content was calculated using standard formula [2] and CO2 removal was expressed as pre-postfilter CO2 content difference.


CO2 removal values (in % of prefilter CO2content) are summarised in Table 1 (means).


The often used CVVH setting (UF 1000 ml/hr, Qb 150 ml/min) leads to CO2 elimination at about 5 ml/min, i.e. a negligible part of the whole body CO2 production (VCO2). A significant CO2 loss (about 15% ofVCO2) can be expected using high volume ultrafiltration techniques.

Table 1


  1. Ruzicka J, Šrámek V, Novák I, Hadravský M, Rokyta R, Hora P, Mate-jovic M, Nalos M: Gas exchange during continuous extracorporeal elimination techniques (CRRT). In Anaesthesia, Pain, Intensive Care and Emergency Medicine Selected Papers. Edited by Gullo A 1998, p409.

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  2. Giovannini I, Chiarla C, Boldrini G, Castagneto M: Calculation of venoarterial CO 2 difference. J Appl Physiol 1993, 74: 959-964.

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This paper was supported by GAUK, Czech Republic.

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Ruzicka, J., Novak, I., Rokyta, R. et al. Carbon dioxide elimination during continuous venovenous hemodiafiltration (CVVHD)-laboratory experiment. Crit Care 4 (Suppl 1), P40 (2000).

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