Lactic Acidosis : A Poorly Understood Concept - Lactic Acidosis : A Poorly Understood Concept - Open Access Pub

Lactic acidosis is a condition commonly encountered in the hospital setting particularly in critically ill patients and is very often used as a diagnostic adjunct when encountering cases of ischaemia or other hypoperfusion states. Despite its use many clinicians have long forgotten the biochemical mechanisms that give rise to hyperlactataemia. One reason for this is because the basic science regarding lactate metabolism is taught in the early years of the medical undergraduate course, and unless one specialises in metabolic medicine, is unlikely to encounter it again. In this article we aim to elucidate the basic mechanisms of lactate metabolism and the accompanying acidosis, and illustrate various clinical settings that give rise to this biochemical abnormality. DOI10.14302/issn.2572-5424.jgm-16-1066 Lactic acidosis is a condition commonly encountered in the hospital setting particularly in critically ill patients and is very often used as a diagnostic adjunct when encountering cases of ischaemia or other hypoperfusion states. Despite its use many clinicians have long forgotten the biochemical mechanisms that give rise to hyperlactataemia. One reason for this is because the basic science regarding lactate metabolism is taught in the early years of the medical undergraduate course, and unless one specialises in metabolic medicine, is unlikely to encounter it again. In this article we aim to elucidate the basic mechanisms of lactate metabolism and the accompanying acidosis, and illustrate various clinical settings that give rise to this biochemical abnormality. Types of Lactic Acidosis Lactic acidosis has traditionally been accepted to be defined as serum lactate concentration of 5 mmol/L with a pH of 7.35 or less. Cohen and Woods have divided lactic acidosis into type A and type B which differ with respect to the presence or absence of hypoperfusion and poor tissue oxygenation (table 1).1 A more recent review by Kruse et al characterise normal lactate levels as less than 2 mmol/L, intermediate lactate levels as between 2 mmol/L and 4 mmol/L and high levels as being 4 mmol/L or more.2 Table 1. The classification of lactic acidosis according to the underlying etiolog Type Features Aetiology A Hypoperfusion Increase in production or decrease in excretion of lactate e.g. shock, ischaemia and liver disease B No hypoperfusion B1 Systemic disease e.g. diabetes, renal failure, some malignancies B2 Medications e.g. biguanides, isoniazid, salicylates and ethanol B3 In-born errors of metabolism e.g. pyruvate dehyrogenase deficiency, pyruvate carboxylase deficiency