Contamination of arterial blood samples by flushing solution

Drs Gupta and Cook are to be congratulated on their honest, open and expertly analysed case 1. I was also interested to read the accompanying article by Smith 2 and the related article by Leslie et al. 3. A major issue of sampling from any line attached to a flushing solution is the potential for contamination by that flush. During my training, I have witnessed several occurrences whereby, with a saline flush, postoperative patients have received both a blood transfusion and potassium infusions unnecessarily, the latter with near fatal consequences. As a result of this, I always teach trainees to know the composition of the flush so that, in the case of saline 0.9%, any unexplained hypernatraemia, hypokalaemia or acidosis may be related to the sample's being contaminated by the flush, and thereby alert the clinician to this possibility. Given the biochemical composition of the flush used (as shown in Fig. 1b of Gupta and Cook's article), I wonder whether or not there was any acidosis, hypernatraemia, hyperchloraemia or hypokalaemia measured in any of the samples, as the flush was potassium-free, had a pH of 3.5–6.5, and a sodium and chloride concentration of 154 mmol.l−1? Whilst I accept that glucose may contaminate a blood sample even after large amounts of deadspace have been discarded, the importance of knowing the composition of the flush cannot be overemphasised.