Journal of Clinical Monitoring and Computing

, Volume 21, Issue 1, pp 7–12 | Cite as

Conductivity-Based Hematocrit Measurement During Cardiopulmonary Bypass

  • Jacoline Steinfelder-Visscher
  • Patrick W. Weerwind
  • Steven Teerenstra
  • Gheorghe A. M. Pop
  • René M. H. J. Brouwer



In a recent clinical study on the reliability of a point-of-care (POC) analyzer, we described a downward bias in hematocrit measurement during cardiopulmonary bypass leading potentially to overtreatment with packed red cells. We hypothesized that the detected deviation is caused by variations in electrolyte concentration rather than by colloids used.


Blood was sampled from patients before cardiac surgery to obtain undiluted anticoagulated whole blood samples (n = 53). From each sample, four dilution series covering a hematocrit range of 15–30% were made using NaCl (0.9%), modified gelatine (4%), hydroxyethylstarch (6%), or a potassium-based (16 mEq/l) solution, respectively. In each dilution series, hematocrit was measured by POC and via the “golden standard” microcentrifugal method to determine whether the deviation of the POC-analyzer to the microcentrifuge was dependent on the type and dilution level of the solution used.


In contrast to the colloid-based dilution series, the crystalloids revealed a significant downward bias of the POC-analyzer with respect to the microcentrifuge (p < 0.05). Due to the correction algorithm for sodium in the POC-analyzer, this deviation was nearly constant for NaCl (mean of difference: −1.8 ± 0.1%), but increased significantly in case of the potassium-based solution (up to −8.2 ± 0.4% after 1.5-times dilution). The starch- and gelatine-based solutions led to a significant upward bias (p < 0.05) that increased with progressing dilution (up to 1.2 ± 0.1% for hydroxyethylstarch and up to 1.3 ± 0.1% for modified gelatine after 1.5-times dilution).


Conductivity-based POC hematocrit measurement suffers from biases due to changes of the plasma constituents. The downward bias in hematocrit as often seen during cardiopulmonary bypass is driven by changes of different electrolyte concentration rather than by colloids used per se.


hematocrit conductivity cardiopulmonary bypass 


Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.



The skilful assistance of Mrs. Honey Hashemi (Department of Extra-Corporeal Circulation, Radboud University Nijmegen Medical Centre, The Netherlands) in the preparation and analysis of the dilution series is highly appreciated.


  1. 1.
    Steinfelder-Visscher J, Weerwind PW, Teerenstra S, Brouwer MH (2006) Reliability of point-of-care hematocrit, blood gas, electrolyte, lactate and glucose measurement during cardiopulmonary bypass. Perfusion 21:33–37CrossRefPubMedGoogle Scholar
  2. 2.
    Stott RAW, Hortin GL, Wilhite TR, Miller SB, Smith CH, Landt M (1995) Analytical artifacts in hematocrit measurements by whole-blood chemistry analyzers. Clin Chem 41:306–311PubMedGoogle Scholar
  3. 3.
    Fuller HD (1991) The electrical impedance of plasma: a laboratory simulation of the effect of changes in chemistry. Ann Biomed Eng 19:123–129CrossRefPubMedGoogle Scholar
  4. 4.
    McNulty SE, Sharkey SJ, Asam B, Lee JH (1993) Evaluation of stat-crit(r) hematocrit determination in comparison to coulter and centrifuge – the effects of isotonic hemodilution and albumin administration. Anesth Analg 76:830–834CrossRefPubMedGoogle Scholar
  5. 5.
    Hopfer SM, Nadeau FL, Sundra M, Makowski GS (2004) Effect of protein on hemoglobin and hematocrit assays with a conductivity-based point-of-care testing device: Comparison with optical methods. Ann Clin Lab Sci 34:75–82PubMedGoogle Scholar
  6. 6.
    McNulty SE, Sharkey SJ, Schieren H (1994) Bedside hemoglobin measurements: sensitivity to changes in serum protein and electrolytes. J Clin Monit 10:377–381CrossRefPubMedGoogle Scholar
  7. 7.
    Vedrinne JM, Motin J (1991) Colloids and hematocrit measurement by conductivity. Anesth Analg 72:840CrossRefPubMedGoogle Scholar
  8. 8.
    Connelly NR, Magee M, Kiessling B (1996) The use of the iSTAT portable analyzer in patients undergoing cardiopulmonary bypass. J Clin Monit 12:311–315CrossRefPubMedGoogle Scholar
  9. 9.
    Beneteau-Burnat B, Bocque MC, Lorin A, Martin C, Vaubourdolle M (2004) Evaluation of the blood gas analyzer GEM (R) PREMIER 3000. Clin Chem Lab Med 42:96–101CrossRefPubMedGoogle Scholar
  10. 10.
    Visser KR (1992) Electric conductivity of stationary and flowing human blood at low frequencies. Med Biol Eng Comput 30:636–640CrossRefPubMedGoogle Scholar

Copyright information

© Springer Science+Business Media, Inc. 2006

Authors and Affiliations

  • Jacoline Steinfelder-Visscher
    • 1
  • Patrick W. Weerwind
    • 1
  • Steven Teerenstra
    • 2
  • Gheorghe A. M. Pop
    • 3
  • René M. H. J. Brouwer
    • 4
  1. 1.Department of Extra-Corporeal Circulation (677)Radboud University Nijmegen Medical CentreNijmegenThe Netherlands
  2. 2.Department of Epidemiology and BiostatisticsRadboud University Nijmegen Medical CentreNijmegenThe Netherlands
  3. 3.Department of CardiologyRadboud University Nijmegen Medical CentreNijmegenThe Netherlands
  4. 4.Department of Cardiothoracic SurgeryRadboud University Nijmegen Medical CentreNijmegenThe Netherlands

Personalised recommendations