Abstract:
Preservation of blood pH within a narrow range is essential to optimal physiological function. This narrow pH range is maintained
via the interactions of various buffer systems. Blood gas analysis is thus essential in the diagnosis and management of disorders
affecting blood pH. Common methods of acid-base interpretation in veterinary science are the traditional approach, the
physicochemical approach and the semiquantitative approach. However, blood gas analysis is prone to error during the preanalytical,
analytical and post-analytical phases of the laboratory process. The pre-analytical phase incorporates steps in obtaining
the sample, thus sources of pre-analytical error are related to operator technique. Most errors occur during the pre-analytical
phase. Pre-analytical errors include entrainment of air bubbles into the sample and delays between sampling and analysis, both
of which cause inaccurate measurement of oxygen and carbon dioxide tensions. The analytical phase outlines processes within
the analyser. Common analytical errors are related to substances confounding analyte measurements. The post-analytical phase
mainly describes interpretation of the results. Some of the approaches to acid-base interpretation require extensive post-analytical
calculations, thus lending themselves to error. Errors occurring during the prior phases will be amplified. Errors in the measurement
of the carbon dioxide tension (from which bicarbonate concentration and base excess are calculated) will introduce error into all
three methods of acid-base interpretation. Furthermore, errors occurring in the measurements of electrolytes and lactate will
result in incorrect interpretations if the physicochemical and semiquantitative approaches are applied. The potential sources of
error during the various phases are reviewed.
