Reliability of blood test results in samples obtained using a 2-mL discard volume from the proximal lumen of a triple-lumen central venous catheter in the critically ill patient

BackgroundIntensive care patients require a high frequency of blood testing, which results in a significant amount of blood loss. When blood is obtained from a central venous catheter (CVC), a large volume is usually discarded to obtain an unaltered sample for testing. AimTo determine the reliability of complete blood test results in blood samples obtained from the proximal lumen of a triple-lumen CVC using a 2-mL discard volume DesignObservational study with the prospective collection of data MethodsThe subjects enrolled were all patients with a subclavian triple-lumen CVC, older than 17 years and consecutively admitted to intensive care over a 2-year period. In each of the 54 participants, one blood sample was drawn from the proximal lumen of the catheter, discarding 161 mL of blood plus 039 mL of catheter deadspace (2 mL) and without interrupting infusion in the middle and distal lumens. A second sample was then obtained by direct venous puncture. The reliability of blood test results was determined by comparing sets of variables recorded for the two sampling methods through intraclass correlation coefficients in the Bland-Altman method. ResultsInter-method reliability for the variables examined was excellent, >075; range (0868-0998). Mean differences between the two sample types for the variables most often determined in critically ill patients were leukocytes: 0200x10(3)/mu L, 95% confidence interval (CI) (0025 to 0375); erythrocytes: 0045x10(6)/uL, 95% CI (-0003 to 0094); sodium: 0074mEq/L, 95% CI (-0369 to 0517); potassium: -0002mEq/L, 95% CI (-0065 to 0061) and glucose: 2426mg/dL, 95% CI (0498-4354). ConclusionsThe sampling method proposed minimizes blood loss while offering reliable blood test results. Relevance to clinical practiceThe main benefit of the method proposed is reduced blood loss, improving the care of a critically ill patient.