A study to assess the correlation of electrolyte values in the intensive care unit: Correlation of arterial and venous blood gas analysis and formal laboratory testing

Patients will be studied on their first routine morning bloods taken during their ICU stay. Serum electrolyte levels to be analysed will include sodium, potassium, chloride and lactate.Blood samples will be taken simultaneously as follows: 1.Arterial blood 1ml for point-of-care blood gas analysis. 2.Arterial blood 7ml for laboratory electrolyte analysis. 3.Venous blood 1ml for point-of-care blood gas analysis. 4.Venous blood 7ml for laboratory electrolyte analysis. The timing of specimen collection will coincide with routine blood testing that occurs each morning in ICU patients, and samples 1 and 2 (above) will be those taken for routine patient assessment. Samples 3 and 4 (above) will be additional to the routine blood tests, and will be taken at the same time to ensure comparison is valid. This will involve taking an extra 8ml of blood from each participant in the study, and will occur only once for each participant. The blood samples will be taken from intravenous and arterial cannulae already in situ, and the participants will be exposed to no addition punctures, discomfort or inconvenience. Blood electrolyte analysis will occur via two methods: 1.Blood gas analysis will be performed within the ICU by trained nursing staff. The Radiometer ABL 725 machine is located within the ICU and is maintained by the Biochemistry Department. This machine has daily quality assurance measures performed by biochemistry laboratory staff and complies with national standards for pathology testing. 2.Serum electrolyte analysis will be performed within the Biochemistry Department, in keeping with standard blood testing arrangements within The Royal Melbourne Hospital.