RESUMEN
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.
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Procedimientos Quirúrgicos Cardíacos , Agua Pulmonar Extravascular , Anciano , Anciano de 80 o más Años , Femenino , Humanos , Verde de Indocianina , Masculino , Persona de Mediana EdadRESUMEN
OBJECTIVE: To compare the lithium-thermal double indicator dilution (Li-thermal), indocyanine green-thermal double indicator dilution (ICG-thermal), single thermal indicator dilution (single-thermal) and gravimetric techniques of extravascular lung water volume (EVLW) measurement in porcine models of acute lung injury. DESIGN: Two animal models designed to invoke a systemic inflammatory response. SETTING: Laboratory study. SUBJECTS: A total of 12 immature Deutsches Landschwein pigs. INTERVENTIONS: Extravascular lung water volume was measured at four time points using Li-thermal, ICG-thermal and single-thermal techniques. Measurements were performed using existing technology according to manufacturer's instructions. Post-mortem gravimetric EVLW measurements were performed by measuring wet and dry mass of lung tissue. Measurements were compared using the Bland-Altman method. Data are presented as mean (SD). MEASUREMENTS AND MAIN RESULTS: Data were collected in 12 animals and comparison between all 4 techniques was possible in 10 animals. EVLW measured by gravimetry was 9.2 (+/-3.0)ml kg(-1). When compared to gravimetry, both Li-thermal and ICG-thermal techniques showed minimal bias but wide limits of agreement (LOA) [Li-thermal: bias -1.8 ml kg(-1) (LOA +/- 13.1); ICG-thermal bias -1.0 ml kg(-1) (LOA +/- 6.6)]. Comparison between the single-thermal and gravimetric methods identified both considerable bias and wide LOA [+8.5 ml kg(-1) (LOA +/- 14.5)]. CONCLUSION: Clinically significant differences between EVLW measurements obtained with the gravimetric method and three in vivo indicator dilution techniques were identified. While none of the techniques could be considered ideal, the ICG-thermal method appeared more reliable than either the Li-thermal or single thermal techniques. Further research is required to determine whether the accuracy of the prototype Li-thermal technique can be improved.