Plasma volume measurement in septic patients using an albumin dilution technique: comparison with the standard radio-labelled albumin method

Abstract

Objective

To investigate a technique using 20% albumin for measurement of plasma volume in critically ill patients.

Design and setting

Laboratory and clinical investigation in the adult intensive care unit and anaesthetic laboratories of a university hospital.

Patients

12 patients fulfilling ACCP/SCCM criteria for septic shock.

Interventions and measurements

Each patient received ¹²⁵I-labelled albumin, and the volume of distribution was measured at 1 and 10 min. The accepted standard plasma volume measurement (98% of the 10-min volume of distribution) was calculated. Immediately thereafter 200 ml 20% human albumin was given. Albumin concentrations were measured before and 1 min after this 40-g bolus, and the volume of distribution calculated using a formula that corrected for the 200 ml fluid in which the albumin was dissolved.

Results

Plasma volumes measured using the albumin dilution technique at 1 min were smaller than the standard technique by 110±280 ml; limits of agreement were from −660 to +440 ml (−16% to +11%). Plasma volumes measured by ¹²⁵I-albumin at 1 min were smaller than the standard by 120±110 ml; limits of agreement were from −330 to +100 ml (−8 to +2%).

Conclusions

Non-labelled albumin can be used easily and quickly to measure a plasma volume in ICU patients and gives a moderately accurate estimate when compared with the ¹²⁵I-labelled albumin methods. The normal isotope method over-estimates plasma volumes in septic patients because excessive transcapillary escape of albumin is inadequately compensated for by the standard correction factor.