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