Investigations

Initial bedside tests include:

• Capillary blood glucose
• Blood gases to determine pH, bicarbonate and potassium
• Urine dipstick for ketones and urinalysis
• ECG to investigate the possibility of a myocardial infarction, which may be silent
• Measure or calculate osmolality (2 sodium + glucose + urea) frequently to monitor the response to treatment.

The 2012 Joint British Diabetes Societies (JBDS) guideline recommends monitoring serum osmolality to measure the patient’s response to treatment as follows:

• Hourly for the first 6 hours
• 2 hourly from 6 to 12 hours as long as serum osmolality is falling at 3 to 8 mOsm/kg/hour (3-8 mmol/kg/hour)
• 4 hourly after 12 hours if serum osmolality continues to improve.

Learning bite

There is no need to take arterial blood routinely in suspected HHS. Venous blood can be used, as the mean difference between arterial and venous pH is 0.03. Arterial sampling should only be undertaken if there is a concern that there is respiratory failure.