Volumetric measurements in endotoxic shock using single photon emission tomography (SPET)

In 25 sheep organ volumes were determined using single photon emission tomography (SPET) prior to and during early endotoxic shock. The tracer used was in vitro 99Tcm-labelled red blood cells. The comparisons between the SPET volumes with the different lower threshold (LT) settings and the 'true' weighed organ volumes were done. The correlation coefficient of -0.87 was found between the LT and the 'true' liver volume and same for the spleen was -0.87. The LT-volume correction curves were used to determine the correct SPET volumes. Thus the accuracy of the liver volume lies within +/- 8%, the splenic volume within +/- 13% and that for the kidney volume +/- 19%. A highly significant decrease of the splenic volume was found 1 h after the induction of endotoxic shock, from 178 +/- 55 ml (mean +/- S.D.) to 101 +/- 25 ml. The kidney volume also decreased from 102 +/- 28 to 78 +/- 19 ml (p less than 0.05), whereas the liver volume remained nearly unchanged (796 +/- 219 versus 761 +/- 165 ml). The SPET study allows measurement of the organ volumes in vivo and the results are reliable when compared to the 'true' volumes. However, the proper LT-settings for organ contour are volume dependent and must be taken into account.