CONTINUOUS BLOOD DENSITY-MEASUREMENTS AND VOLUME CHANGES DURING EXTRACORPOREAL-CIRCULATION IN PATIENTS UNDERGOING CARDIAC-SURGERY

The changes of blood volume and transcapillary fluid shifts during extracorporeal circulation (ECC) was examined using continuous measurements of blood density by the mechanical oscillator technique. Sixteen patients (1 female, 15 male) with a mean age of 61.4 years (+/-7.6 years, 47-70 years) undergoing coronary artery bypass surgery were included in this study. The equipment for continuous measurement of the blood density (DPRT by Paar/Austria) was installed at the arterial line of the heart-lung bypass. Higher-precision discrete measurements of some parameters used the DMA 55 equipment produced by the Paar company. Measurements were taken at 37 degrees C. In 11 patients the transcapillary volume loss (difference of total volume between beginning and end of ECC) during heart-lung bypass (mean observation period of 55 min (+/- 16 min, 28-82 min) was found to be 870 ml/m(2) body surface area (BSA) (+/- 360 ml, 290-1560 ml/m(2)) by the dilution method using the priming solution at the beginning and 500 mi lactated Ringer's solution added at the end of the ECC. The calculated volume shift using the ''double density method'', which takes into account blood density, plasma density, and hematocrit, amounted to 830 ml/m(2) BSA (+/- 200 ml, 450-1210 ml/m(2)). The density of the transcapillary volume loss into the interstitial layer was calculated and found to be 1.0026 g/ml (+/- 0.0017 g/ml, 1.0003-1.0063 g/ml). A significant difference of transcapillary volume shift correlated with the administered catecholamine (dopamine, dobutamine) dosage postoperatively. Without catecholamine this difference was 260 ml/m(2) BSA, with 3 mu m/kg/min dopamine it rose to > 500 ml/m(2) BSA. The mechanical oscillator technique allows the measurement of blood volume shifts during cardiopulmonary bypass in order to monitor the course of the ECC and the transcapillary volume shift without increasing the stress on the patient.