Comparison of Cardiac Output and Circulatory Blood Volumes by Transpulmonary Thermo-Dye Dilution and Transcutaneous Indocyanine Green Measurement in Critically Ill Patients

Objective We prospectively studied the agreement between transpulmonary aortic fiberoptic-based and pulse dye densitometry (PDD) measurements of cardiac output and circulatory blood volumes. Design Prospective clinical study. Setting Operative ICU of a university hospital. Patients Sixteen critically ill, deeply sedated patients receiving mechanical ventilation with ARDS (n = 8), sepsis/septic shock (n = 6), subarachnoid hemorrhage (n = 1), and severe head injury (n = 1). Measurements and results Each patient received a 4F aortic catheter with an integrated fiberoptic and thermistor that was connected to a computer system for automatic calculation of the transpulmonary indicator dilution (TPID) technique for the measurement of cardiac output (CO tpid ), intrathoracic blood volume (ITBV), and total blood volume measured by TPID technique (TBV tpid ). In each patient, an indocyanine green sensor was attached to one nasal wing and connected to an analyzer for the PDD measurement of cardiac output (CO pdd ), central blood volume (CBV), and TBV measured by PDD (TBV pdd ). For all first measurements, linear regression analysis between CO tpid and CO pdd revealed that CO pdd = 0.63 × CO tpid + 3.69 (L/min)[ r = 0.64, p = 0.008]. Mean bias between both techniques was − 0.8 L/min (SD, 1.7 L/min). Correlations between ITBV/CBV ( r = 0.52) and TBV tpid /TBV pdd were only moderate: TBV pdd = 0.74 × TBV tpid + 2,362 (mL)[ r = 0.60, p = 0.015; mean bias, − 999 mL; SD, 1,353 mL]. Over all 55 measurements, TPID measurements were on average 11.5% (cardiac output) and 17.6% (TBV) higher than PDD measurements. The differences between both measurements ranged from − 58 to 81% (cardiac output) and from − 47 to 82% (TBV; 95% reference ranges). The main source of variation were the intraindividual differences, resulting in different peaks and trends in the patients' time courses depending on which measurement method was used. Conclusion PDD measurement of cardiac output and circulatory blood volumes agrees moderately with transpulmonary thermo-dye dilution technique in critically ill patients.