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

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.

Determine the minimum blood discard volume to obtain samples through radial arterial catheter.

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.

We found values outside the Clinical Acceptance Interval (CAI) in sample A versus control in pCO₂ (47.42%), HCO₃ ^- (60.71%), Haemoglobin (67.85%), Na²⁺ (7.14%), K⁺ (71.42%) and glycaemia (21.42%). In the case of lactate, no values outside the Clinical Acceptance Interval were found. When comparing sample B versus control, we found significant differences in HCO₃ ^- (p = 0.027) and glycaemia (p = 0.001). However, none of the parameters studied presented values outside the Clinical Acceptance Interval. When the results were related to the Reference Value of Change (RVC), the pCO₂ 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.

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.

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.