Is minimising waste volume for drawing blood samples in critically ill patients feasible?

INTRODUCTION: Drawing blood samples through a central venous catheter (CVC) is a customary practice in Intensive Care Units (ICUs). It is indicated to discard a volume of waste blood to avoid interference in the results. AIM: To determine whether a lower discard volume for obtaining blood samples from temporary CVCs placed into the internal jugular, femoral or subclavian vein offers valid results. METHOD: A quasi-experimental prospective cross-sectional study for which sixty-five patients of over 18 years of age in ICUs, who had been fitted with a triple lumen central venous catheter, were recruited over a period of eight months. Two consecutive blood samples were extracted with tubes for biochemistry, coagulation and hemogram from each patient from the distal lumen. The first sample was obtained with a discarded waste of 1.5 ml from a total extracted volume of 10.2 ml, similar to the usual waste in our ambit (10 ml). Subsequently the second sample was obtained. The paired t-test was used to analyse the data. The Bland-Altman plot and intraclass correlation coefficient (ICC) were used to measure the agreement between methods. The reference change value (RCV) was established as the admissible limit of variation between the pairs of samples. RESULTS: A total of 65 sample pairs were drawn (intervention-control). The paired t-test found statistically significant differences with a significance level of α = .05 for chlorine (-.536; .012); prothrombin time (-.092; .019) and prothrombin activity (.284; 1.375).The ICC was greater than .9 in all the variables and the limit determined for the RCV was not surpassed by any value. CONCLUSIONS: The results show the reliability of the blood samples drawn with a discard volume of 1.5 ml.

Minimizar el volumen de descarte para la extracción de muestras sanguíneas en los pacientes críticos: ¿es factible? / Is minimising waste volume for drawing blood samples in critically ill patients feasible?

Introducción: La extracción de muestras sanguíneas a través de un catéter venoso central es una práctica habitual en las unidades de cuidados intensivos. Está indicado desechar un volumen de sangre, denominado volumen de descarte, con la finalidad de evitar que los resultados puedan verse alterados. Objetivo: Determinar si un menor volumen de descarte para la obtención de analíticas procedentes de catéter venoso central temporales alojados en la vena yugular interna, femoral o subclavia ofrece resultados válidos. Método: Estudio cuasiexperimental, prospectivo, transversal donde se seleccionaron 65 pacientes críticos mayores de 18 años portadores de catéter venoso central temporal de 3 luces durante un período de 8 meses. Para cada paciente se extrajeron 2 analíticas consecutivas de la luz distal con los valores de hemograma, bioquímica y coagulación comúnmente analizados en el paciente crítico. Se obtuvieron 2 muestras consecutivas: la primera, con un descarte de 1,5ml y un volumen extraído total de 10,2ml, similar al desecho habitual en nuestro medio (10 ml). Seguidamente se obtuvo la segunda muestra. Para el análisis de datos se utilizó la prueba t pareada; para medir la concordancia entre métodos, la representación de Bland-Altman y el coeficiente de correlación intraclase. Se estableció el valor de referencia del cambio como límite admisible de variación entre los pares de muestras. Resultados: Se extrajeron un total de 65 pares de muestras (intervención-control). El contraste de medias encontró diferencias estadísticamente significativas con α=0,05 para cloro (−0,536; 0,012), tiempo de protrombina (−0,092; 0,019) y actividad de protrombina (0,284; 1,375). El coeficiente de correlación intraclase resultó mayor de 0,9 en todas las variables y el valor de referencia del cambio no fue superado por ningún valor. Conclusiones: Los resultados muestran la validez de los análisis de las muestras de sangre extraídas con un volumen de descarte de 1,5ml.(AU)

Introduction: Drawing blood samples through a central venous catheter is a customary practice in intensive care units. It is indicated to discard a volume of waste blood to avoid interference in the results. Aim: To determine whether a lower discard volume for obtaining blood samples from temporary central venous catheters placed into the internal jugular, femoral or subclavian vein offers valid results. Method: A quasi-experimental prospective cross-sectional study for which 65 patients of over 18 years of age in intensive care units, who had been fitted with a triple lumen central venous catheter, were recruited over a period of 8 months. Two consecutive blood samples were extracted with tubes for biochemistry, coagulation and haemogram from each patient from the distal lumen. The first sample was obtained with a discarded waste of 1.5ml from a total extracted volume of 10.2ml, similar to the usual waste in our ambit (10ml). Subsequently the second sample was obtained. The paired t-test was used to analyse the data. The Bland-Altman plot and intraclass correlation coefficient were used to measure the agreement between methods. The reference change value was established as the admissible limit of variation between the pairs of samples. Results: A total of 65 sample pairs were drawn (intervention-control). The paired t-test found statistically significant differences with a significance level of α=0.05 for chlorine (−0.536; 0.012); prothrombin time (−0.092; 0.019) and prothrombin activity (0.284; 1.375). The intraclass correlation coefficient was greater than 0.9 in all the variables and the limit determined for the reference change value was not surpassed by any value. Conclusions: The results show the reliability of the blood samples drawn with a discard volume of 1.5ml.(AU)