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.

[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.