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Pitfalls in the diagnosis and management of acid–base disorders in humans: a laboratory medicine perspective
  1. Henry Carlton1,
  2. Kate E Shipman1,2
  1. 1 Chemical Pathology, University Hospitals Sussex NHS Foundation Trust, Chichester, UK
  2. 2 Department of Medical Education, Brighton and Sussex Medical School, Brighton, UK
  1. Correspondence to Dr Kate E Shipman; kate.shipman{at}nhs.uk

Abstract

Diagnostic errors affect patient management, and as blood gas analysis is mainly performed without the laboratory, users must be aware of the potential pitfalls. The aim was to provide a summary of common issues users should be aware of.

A narrative review was performed using online databases such as PubMed, Google Scholar and reference lists of identified papers. Language was limited to English.

Errors can be pre-analytical, analytical or post-analytical. Samples should be analysed within 15 min and kept at room temperature and taken at least 15–30 min after changes to inspired oxygen and ventilator settings, for accurate oxygen measurement. Plastic syringes are more oxygen permeable if chilled. Currently, analysers run arterial, venous, capillary and intraosseous samples, but variations in reference intervals may not be appreciated or reported. Analytical issues can arise from interference secondary to drugs, such as spurious hyperchloraemia with salicylate and hyperlactataemia with ethylene glycol, or pathology, such as spurious hypoxaemia with leucocytosis and alkalosis in hypoalbuminaemia. Interpretation is complicated by result adjustment, for example, temperature (alpha-stat adjustment may overestimate partial pressure of carbon dioxide (pCO2) in hypothermia, for example), and inappropriate reference intervals, for example, in pregnancy bicarbonate, and pCO2 ranges should be lowered.

Lack of appreciation for patient-specific and circumstance-specific reference intervals, including extremes of age and altitude, and transformation of measurements to standard conditions can lead to inappropriate assumptions. It is vitally important for users to optimise specimen collection, appreciate the analytical methods and understand when reference intervals are applicable to their specimen type, clinical question or patient.

  • Diagnostic Techniques and Procedures
  • BIOCHEMISTRY
  • Chemistry, Clinical
  • Evidence-Based Practice

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Footnotes

  • Handling editor Patrick J Twomey.

  • X @Henry_C_Carlton

  • Contributors HC and KES were both involved in conception, design and acquisition/interpretation of data. HC did initial literature review. HC and KES were involved in preparing the manuscript. KES acted as the guarantor.

  • Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

  • Competing interests None declared.

  • Provenance and peer review Commissioned; externally peer reviewed.

  • Supplemental material This content has been supplied by the author(s). It has not been vetted by BMJ Publishing Group Limited (BMJ) and may not have been peer-reviewed. Any opinions or recommendations discussed are solely those of the author(s) and are not endorsed by BMJ. BMJ disclaims all liability and responsibility arising from any reliance placed on the content. Where the content includes any translated material, BMJ does not warrant the accuracy and reliability of the translations (including but not limited to local regulations, clinical guidelines, terminology, drug names and drug dosages), and is not responsible for any error and/or omissions arising from translation and adaptation or otherwise.