Determination of the Minimum Discard Volume in the Extraction of Blood Samples Through Arterial Catheters in Critical Patients

BACKGROUND: The critically ill patient requires multiple extractions through catheters, implying a substantial blood loss. The discard method continues to be a commonly used method in Intensive Care Units. However, there is no homogeneity in practice. AIM: Determine the minimum blood discard volume to obtain samples through radial arterial catheter. STUDY DESIGN: Quasi-experimental, prospective, cross-sectional study employing the STOBE checklist. Four consecutive arterial blood gases were performed considering the flush volume (sample A with 1 dead space discarding 1 mL, sample B with 2 discard space [2 mL], sample C with 3 discard space [3 mL] and control with 4 discard space [4 mL]). The study was approved by the Ethics and Pharmacological Research Committee of the Research Institute of La paz Hospital (Law No. 2023.564). It was conducted in the Burn Intensive Care Unit and the Resuscitation and Critical Care Unit of La Paz Hospital from September 2023 to June 2024. RESULTS: and Haemoglobin values presented 3.57% of values outside the Clinical Acceptance Interval, respectively, although they did not present statistically significant differences (p > 0.05). When comparing sample C versus control, no significant differences were found in any parameter, nor values outside the Clinical Acceptance Interval. CONCLUSIONS: The volume of discard required to obtain valid values is twice the volume used to purge the arterial catheterization system (2 mL) for obtaining samples for clinical use. RELEVANCE TO CLINICAL PRACTICE: The calculation of the minimum amount of discard in the collection of blood samples through the arterial catheter is an intervention at no extra cost that will reduce iatrogenic anaemia, reducing the need for transfusions, the complications associated with this therapy and the reduction of costs in critically ill patients.