Measurement of extravascular renal water by the thermal dye indicator dilution technique.

Simple mechanical swelling of the renal parenchyma against an unyielding renal capsule may be responsible in part for the development of oliguria and acute tubular necrosis. However, until now, renal swelling was difficult to measure, except by postmortem gravimetric techniques. A new in vivo technique, the thermal dye double indicator dilution technique, was used to assess renal swelling by measuring extravascular renal water. Ice cold indocyanine green dye solution was injected rapidly into the renal artery of 5 mongrel dogs, and the thermal dilution and dye dilution curves were recorded simultaneously by means of a thermistor catheter in the renal vein. The curves were corrected for the response time of the measuring systems, then the extravascular renal water was compared (renal blood flow multiplied by the difference in mean transit times of the thermal dilution and dye dilution curves). The results were compared to the gravimetrically determined extravascular renal water. A high correlation was found to exist between the thermal dye dilution method and the gravimetric method (r = 0.92, X = 0.65 Y + 19.8, p less than 0.05). These preliminary results are encouraging and warrant further trials, inasmuch as this technique would allow the sequential in vivo measurement of renal edema. It is therefore feasible to quantitate the effect of clinical insults, such as hypovolemic shock or sepsis, on the kidney, and to assess the value of different therapeutic interventions. A small body of evidence attempts to relate the role of simple mechanical swelling of the kidney to the pathogenesis of acute renal failure.