Research
Comparison of three methods of extravascular lung water volume measurement in patients after cardiac surgery
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* Corresponding author: Rupert M Pearse rupert.pearse@bartsandthelondon.nhs.uk
1 Barts and The London School of Medicine and Dentistry, Queen Mary's University of London, Royal London Hospital, London E1 1BB, UK
2 Intensive Care Unit, University Hospital Wales, Heath Park, Cardiff CF14 4XW, UK
3 Sektion Anästhesiologische Pathophysiologie und Verfahrensentwicklung, Universitätsklinikum, Ulm, Robert-Koch-Str. 8, 89081, Germany
Critical Care 2009, 13:R107 doi:10.1186/cc7948
Published: 6 July 2009Abstract
Introduction
Measurement of extravascular lung water (EVLW) by using the lithium-thermal (Li-thermal) and single-thermal indicator dilution methods was compared with the indocyanine green-thermal (ICG-thermal) method in humans.
Methods
Single-center observational study involving patients undergoing cardiac surgery with cardiopulmonary bypass. Paired measurements were taken 1, 2, 4, and 6 hours after surgery. Bland-Altman analysis was used to calculate bias and limits of agreement. Data are presented as mean (SD) or median (IQR).
Results
Seventeen patients were recruited (age, 69 years (54 to 87 years); Parsonnet score 10 (0 to 29)). Sixteen ICG-thermal measurements were excluded after blinded assessment because of poor-quality indicator dilution curves. EVLW volume as measured by the ICG-thermal technique was 4.6 (1.9) ml/kg, compared with 5.3 (1.4) ml/kg for the single-thermal method. Measurements taken with the Li-thermal method were clearly erroneous (-7.6 (7.4) ml/kg). In comparison with simultaneous measurements with the ICG-thermal method, single-thermal measurements had an acceptable degree of bias, but limits of agreement were poor (bias, -0.3 ml/kg (2.3)). Li-thermal measurements compared poorly with the ICG-thermal reference method (bias, 13.2 ml/kg (14.4)).
Conclusions
The principal finding of this study was that the prototype Li-thermal method did not provide reliable measurements of EVLW volume when compared with the ICG-thermal reference technique. Although minimal bias was associated with the single-thermal method, limits of agreement were approximately 45% of the normal value of EVLW volume. The Li-thermal method performed very poorly because of the overestimation of mean indicator transit time by using an external lithium ion electrode. These findings suggest that the assessment of lung water content by lithium-indicator dilution is not sufficiently reliable for clinical use in individual patients.