Measurement of intrathoracic blood volume by lithium dilution: comparison with thermodilution

Introduction

The intrathoracic blood volume is usually measured clinically by transpulmonary thermodilution (PiCCO system; Pulsion Ltd). New software also allows measurement at the bedside by lithium dilution (LiDCO system; LiDCO Ltd). We sought to compare the new lithium dilution method with the existing method.

Methods

Ethics approval was obtained. Nonpregnant adult patients on the ICU with PiCCO monitoring were recruited. Consent was given by patients' representatives. Simultaneous calibration of PiCCO and LiDCO systems with one lithium dilution curve and the average of three thermal dilution curves allowed comparison of results.

Results

Six patients were studied (five males, one female). All were intubated but none were receiving muscle relaxation. Mean age was 60.6 ± 21.8 years. The mean APACHE II score was 20.8 ± 2.3. Ten paired results were obtained (see Table 1). The mean difference of LiDCO from PiCCO overall was -5.49 ± 21.3%. The correlation coefficient r = 0.73 (P = 0.0166).

Table 1 abstract

Conclusion

There was general agreement between LiDCO and PiCCO. There were significant differences (>30%) in only three out of 10 measurements. Combining the results of >1 lithium calibration may improve accuracy. These results are promising but a larger trial will be required.