Due to the publication of significant literature in this area since commencement of the project which has now rendered the project unnecessary.

The study hypothesis is that in critically ill patients there is significant differences between electrolyte levels measured using blood gas analysers and by laboratory techniques, and between levels measured on arterial and venous blood samples.

The sudy hypothesis is that in critically ill patients there is a significant difference between electrolyte levels measured using blood gas analysers and by laboratory techniques, and between levels measured on arterial and venous blood samples.

The study aim is determine the agreement between electrolyte levels measure by formal laboratory serum analysis and point-of-care blood gas analysis.

Also, to determine the agreement between electrolyte levels measured on simultaneous arterial and venous blood samples, using both serum and whole blood samples.

Inclusion Criteria:

1. Adult patients 18 years or older admitted to the intensive care unit
2. Patients who have arterial and central venous access insitu for clinical management purposes.
3. Patients who consent to inclusion in the study, or if the patient is not competent, the next of kins' consent.

Exclusion Criteria:

Nil-