INTERSTITIAL FLUID VOLUME DURING CARDIAC-SURGERY MEASURED BY MEANS OFA NONINVASIVE CONDUCTIVITY TECHNIQUE

Fluid accumulation in the interstitium is frequently found after cardi ac surgery. In extreme this can lead to pulmonary and myocardial oedem a. The origin of this accumulation is not exactly known and may be two fold. It is probably a combination of the noninfectious whole body inf lammatory response and a change in Starling forces due to a decrease i n colloid osmotic pressure (COP) which is caused by the primed extraco rporeal circuit. To study the changes in interstitial fluid volume (IS FV) a non-invasive conductivity technique was used. The relationship b etween temperature and conductivity was first investigated in vitro. A linear relationship was found between conductivity and different sali ne solutions and temperature. From the in vitro experiments it can be concluded that temperature corrected conductivity does not depend on h aematocrit. After the in vitro experiments eleven patients undergoing cardiac surgery were studied. During the first minutes of cardiopulmon ary bypass (CPB) a steep significant decrease in COP to 61.4+/-6.9% (f rom 19.6+/-1.1 to 12.0+/-1.2 mmHg), and a rise in ISFV to 105.5+/-2.8% (from 12.3+/-1.4 mS to 14.0+/-1.3 mS) was noticed. After this decreas e COP increased significantly, till the end of the operation, but did not reach the pre-operative level. An increase in ISFV was noticed til l the rewarming point. After this point no significant change in ISFV was noticed. Furthermore, a significant correlation was found between the fluid balance and the ISFV increase at the start, at the end of CP B, and at the end of the operation. From the in vivo experiments it ca n be concluded that the non-invasive conductivity technique in a valua ble acquisition for the investigation of ISFV changes during cardiac s urgery. It shows that the changes in ISFV are mainly disturbed during the first part of CPB probably due to a marked decrease in COP.