Extravascular Lung Water Volume Measurement After Cardiac Surgery
Extravascular Lung Water Volume Measurement After Cardiac Surgery
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.
Increased extravascular lung water (EVLW) volume during critical illness is associated with prolonged mechanical ventilation and increased mortality rates. Quantification of EVLW volume may allow the use of therapeutic interventions to regulate lung water content, perhaps resulting in improved clinical outcomes. Neither assessment of oxygenation nor chest radiography provides a reliable indication of EVLW volume. No ideal method exists for measuring EVLW volume at the bedside.
In a previous laboratory study, we explored the use of indicator-dilution techniques to measure intrathoracic blood volume (ITBV) and EVLW volume. The objective of this research was to develop a more convenient method of EVLW volume measurement by using lithium-thermal indicator dilution. Lithium chloride satisfies many of the criteria for an ideal indicator, including a good safety profile, small displacement volume, and minimal indicator loss. However, in a recent laboratory investigation in porcine models of acute lung injury, both the existing indicator-dilution methods of EVLW volume measurement and our prototype Li-thermal method compared poorly with postmortem gravimetric measurements. Given that each of these technologies was developed for use in humans, it is possible that measurements of EVLW volume would prove more reliable in humans. It is, therefore, necessary to compare indocyanine green-thermal indicator dilution, single-thermal indicator dilution, and the prototype lithium-thermal methods in humans. The aim of this study was to compare measurements of ITBV and EVLW volume made by using the indocyanine green-thermal (ICG-thermal), lithium-thermal (Li-thermal), and single-thermal indicator dilution techniques in patients after elective cardiac surgery with cardiopulmonary bypass.
Abstract and Introduction
Abstract
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.
Introduction
Increased extravascular lung water (EVLW) volume during critical illness is associated with prolonged mechanical ventilation and increased mortality rates. Quantification of EVLW volume may allow the use of therapeutic interventions to regulate lung water content, perhaps resulting in improved clinical outcomes. Neither assessment of oxygenation nor chest radiography provides a reliable indication of EVLW volume. No ideal method exists for measuring EVLW volume at the bedside.
In a previous laboratory study, we explored the use of indicator-dilution techniques to measure intrathoracic blood volume (ITBV) and EVLW volume. The objective of this research was to develop a more convenient method of EVLW volume measurement by using lithium-thermal indicator dilution. Lithium chloride satisfies many of the criteria for an ideal indicator, including a good safety profile, small displacement volume, and minimal indicator loss. However, in a recent laboratory investigation in porcine models of acute lung injury, both the existing indicator-dilution methods of EVLW volume measurement and our prototype Li-thermal method compared poorly with postmortem gravimetric measurements. Given that each of these technologies was developed for use in humans, it is possible that measurements of EVLW volume would prove more reliable in humans. It is, therefore, necessary to compare indocyanine green-thermal indicator dilution, single-thermal indicator dilution, and the prototype lithium-thermal methods in humans. The aim of this study was to compare measurements of ITBV and EVLW volume made by using the indocyanine green-thermal (ICG-thermal), lithium-thermal (Li-thermal), and single-thermal indicator dilution techniques in patients after elective cardiac surgery with cardiopulmonary bypass.
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