Should Rcpaqap Blood Gas Program Include Instrument Calculated Parameters?

A normal term baby girl was found to have low oxygen saturation on pulse oximeter (88–95%) on day 2 and did not respond to oxygen therapy. Cardio-pulmonary workup was uneventful. Arterial blood gas on room air revealed normal pH, pO2, pCO2, bicarbonate and sO2, but a high instrument-calculated p50 of 30–42 mmHg (RR 25–29) suggested a haemoglobin of low oxygen affinity. Haemoglobin HPLC analysis revealed an abnormal peak of 1.6% detected at RT 4.50 min which was shown by alkaline and acid electrophoresis, and subsequent DNA testing to be heterozygous HbA1:c.283G>A in the alpha1-globin gene (haemoglobin Titusville). This is a rare haemoglobinopathy involving a single nucleotide change from G to A at codon 94 of the alpha globin gene, and results in a lower oxygen affinity, indicated by oxygen dissociation curve right shift and high p50.1,2 While RCPAQAP Blood Gas program monitors key analyser measurements, there is no attempt to probe the performance of calculated parameters which may be determined by sophisticated hidden software, e.g., for p50. This case illustrates the importance of looking beyond the basic parameters of pH, pCO2, pO2 and bicarbonate and raises the desirability of RCPAQAP monitoring calculated parameters across various blood gas platforms which may be particularly vulnerable to haemoglobinopathies.3 References 1.Scaravilli V, Polli F, Mendogni P, et al. Oxygenation during general anesthesia and thoracic surgery in a patient with Titusville low-oxygen affinity hemoglobin. J Appl Physiol 2019; 126: 810–4.2.Mina M, James R, Gandhi S. Haemoglobin Titusville: A case study and review of the literature. J Paediatr Child Health 2018; 54: 449–52.3.King RI, George PM, Swanney MP, Stanton JD, Walmsley TA. Comparison of p50 determination by siemens and radiometer blood gas analysers with tonometry. Pathology 2010; 42: S62–3.