Minimum Volume of Discard for Valid Blood Sampling From Indwelling Arterial Cannulae

Abstract

The volume of discard for valid blood sampling from indwelling femoral (leader cath) and radial (Venflon) arterial cannulae (with internal volume of cannula plus connecting tubing of approximately 2 ml) was investigated by analysing sequential 2-ml aliquots of 10-ml samples. The aliquots were analysed for pH, carbon dioxide tension, oxygen tension, standard bicarbonate, haemoglobin concentration, haemoglobin oxygen saturation and potassium concentration. Analysis of variance showed that, for these variables and these catheters, a valid blood sample was obtained after discarding 4 ml, but not after only 2 ml. The haemoglobin concentration, as measured by a Corning oximeter, provided good warning of inadequate discard.

A snapshot of guideline compliance reveals room for improvement: A survey of peripheral arterial catheter practices in Australian operating theatres

“…Practice was compared with evidence-based practice recommendations for minimal discard volume for ABG sampling (Dennis et al 1985, Clapham et al 1987, Preusser et al 1989, Fowler & Berenson 2003, Rickard et al 2003 (Clapham et al 1987) and dead space volume is the volume from the peripheral arterial catheter tip to the sampling port (Dennis et al 1985).…”

“…Practice was compared with evidence-based practice recommendations for minimal discard volume for ABG sampling (Dennis et al 1985, Clapham et al 1987, Preusser et al 1989, Fowler & Berenson 2003, Rickard et al 2003. Practice was also considered in relation to the Centers for Disease Control Guidelines for the Prevention of Intravascular Catheter-Related Infections (O'Grady et al 2002) and the PS28 Australian and New Zealand College of Anaesthetists' (ANZCA) Guidelines on Infection Prevention in Anaesthesia in Australia and New Zealand (Australian & New Zealand College of Anaesthetists 2005).…”

“…Discard volumes were investigated in relation to the arterial line dead space, using the dead space of the volume from the peripheral arterial catheter tip to the sampling port. A further study (Clapham et al 1987) investigated the minimum discard volume required for accuracy. A discard volume of 4 mL was found to be sufficient with a dead space of approximately 2 mL.…”

Practical points in the application of oxygen transport principles

“…Accurate blood gas and hemoglobin measurements require removal of all the dead space from the system, which is at least 4 ml for an arterial line [5]. From the distal lumen of the pulmonary artery flotation catheter (PAFC) at least 6 ml should be removed by gentle aspiration over a minimum of 30 s to avoid contamination with arterialized blood.…”

Methods to identify saline-contaminated electrolyte profiles

“…Saline-contaminated samples represent a specific example of inaccurate measurements. While serum is usually discarded prior to sample collection, samples contaminated with saline during collection can still occur and lead to inaccurate measurement of electrolytes, inappropriate electrolyte replacement, unnecessary additional testing, and misinterpretation of a patient’s true clinical status [13–14]. The contamination of blood samples with saline is of particular concern given the high prevalence of venous access devices during patient hospitalization, the frequency with which chemistry panels are ordered, and the practical difficulty of estimating deadspace volume when discarding initial sample [13, 15–25].…”