ABSTRACT
OBJECTIVE: Arterial catheters are used to extract blood samples. To maintain its permeability we use heparin solution, which may contaminate and alter the desired results. Our aim was to determine the volume of the minimum discards during blood extractions to avoid results that might be altered in the analysis of biochemistry. MATERIAL AND METHODS: A prospective study was carried out in 18 beds intensive care unit. Patients with arterial catheter (Seldicath) were included, maintaining 500 UI of heparin in saline of 500 ml, at a pressure of 300 mmHg through pressurizer (Tycos). The dead space (DS) in the radial arterial system is 0.8 ml and 1 ml in the femoral. We analyzed the reliability of different discards comparing the following: 3 ml + DS, 7.5 ml + DS, 12 ml + DS and 16.5 ml + DS. The statistical analysis was carried out through ANOVA and t Student. RESULTS: In biochemistry, significant differences were not found except for potasium (p< 0.001) with 3 ml+DS during control, although it is not clinically relevant [difference through = 0.1 mEq/l (DS 0.2)]. Significant differences in prothrombina (p = 0.004) were found in coagulation, comparing 3 ml+DS and 16.5 ml + DS and in cefaline, comparing 7.5 ml + DS (p< 0.0001) and 16.5 ml + DS. There were not significant differences in the studies of gases. CONCLUSIONS: Our study shows that to reach a reliable analytical results, it is not necessary to discard more than 3 ml+DS in biochemistry and in blood gases, and to determine cefalina time would necessary to discard a minimum of 7.5 ml+DS.
