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)

Mujer de 18 años con metahemoglobinemia tras utilización de crema anestésica tópica / An 18 year old female with methaemoglinaemia after using EMLA(R) topical anaesthetic cream

La metahemoglobinemia es una entidad poco frecuente, cuyo diagnóstico se basa en la aparición de niveles elevados de metahemoglobina en sangre, tanto en adultos como en niños. Es una de las causas importantes de cianosis, y en ocasiones la severidad de su presentación puede requerir el ingreso en Unidades de Cuidado Intensivo. Las causas pueden ser adquiridas o congénitas, siendo ésta última debida a mutación en el gen de la hemoglobina reductasa dependiente de NADPH. La forma adquirida o metahemoglobinemia tóxica se produce cuando los hematíes son expuestos a sustancias químicas oxidantes que aumentan la producción de metahemoglobina, sobrepasando los mecanismos reductores de protección que actúan normalmente. Se presenta el caso de una mujer de 18 años, con cuadro de cianosis de aparición súbita diagnosticada de metahemoglobinemia tóxica tras utilización de crema anestésica tópica EMLA(R) (mezcla de anestésicos locales, lidocaína y prilocaína(AU)

Methaemoglobinaemia is a very uncommon disorder, with its diagnosis being based on the appearance of high levels of methaemoglobin in the blood, both in adults and children. It is an important cause of cyanosis, and occasionally its severity of its presentation may require admission to an Intensive Care Unit. It may be acquired or hereditary; the latter being due to a mutation of the NADPH-dependent haemoglobin reductase gene. The acquired form or toxic methaemoglobinaemia is produced when red cells are exposed to oxidising chemicals that increase methaemoglobin production, overwhelming the regulatory mechanisms that function normally (AU)

[Nocturnal drop of arterial blood pressure: determinant factors and relationship with organic damage secondary to hypertension]. / Descenso nocturno de la presión arterial: factores determinantes y relación con daño orgánico secundario a hipertensión.

OBJECTIVES: To evaluate the night-time drop in blood pressure in patients with light hypertension and to determine its possible relationship with damage in key organs. DESIGN: Cross-sectional study. SETTING: Eight urban health centres. PATIENTS: Four hundred and eighteen adults with light-moderate hypertension. INTERVENTIONS: a) Blood pressure reading on three visits; b) ambulatory monitoring of pressure for 24 hours; c) echocardiograph (in 219 patients); d) albuminuria determination (in 134 patients). A night-time drop in blood pressure was defined as the difference between day and night ambulatory pressures; and relative drop, as the night-time pressure drop as a percentage of the day-time pressure. RESULTS: Night-time drop in systolic and diastolic pressures was 13.6 (10.7) and 12.1 (8.6) mmHg, respectively. The predictive factors of night-time drop in blood pressure were, directly, daily ambulatory blood pressure (p < 0.05) and female gender (p < 0.05) and, inversely, age (p < 0.05). No association was observed between night-time drop in blood pressure and left ventricular mass. Only in women was an independent relationship found, inversely, between night-time drop in blood pressure and urinary excretion of albumin (p < 0.05). CONCLUSIONS: Relative night-time drop in blood pressure is greater in women than in men, diminishes with age and depends on the day-time ambulatory pressure. In women a minor night-time drop in blood pressure is associated with greater organic damage.