Fluids

Intravenous fluids (0.9% saline) in IV line 1
(Caution in HF / CKD / BW< 50 kg)

The key parameter is osmolality to which glucose and sodium are the main contributors and that too rapid changes are dangerous. Although for practical and safety reasons an infusion of insulin is often commenced simultaneously, rapid falls in blood glucose are not desirable (see below).

Isotonic versus hypotonic fluid replacement

• Rapid changes in osmolality may be harmful. Use 0.9% sodium chloride solution as the principal fluid to restore circulating volume and reverse dehydration.
• Measurement or calculation of osmolality should be undertaken every hour initially and the rate of fluid replacement adjusted to ensure a positive fluid balance sufficient to promote a gradual decline in osmolality.
• Fluid replacement alone (without insulin) will lower blood glucose which will reduce osmolality causing a shift of water into the intracellular space. This inevitably results in a rise in serum sodium (a fall in blood glucose of 5.5 mmol/L will result in a 2.4 mmol/L rise in sodium). This is not necessarily an indication to give hypotonic solutions.
• Isotonic 0.9% sodium chloride solution is already relatively hypotonic compared to the serum in someone with HHS.
• Rising sodium is only a concern if the osmolality is NOT declining concurrently. Rapid changes must be avoided a safe rate of fall of plasma glucose of between 4 and 6 mmol/hr is recommended (Kitabachi 2009). If the inevitable rise in serum Na+ is much greater than 2.4 mmol/L for each 5.5 mmol/L fall in blood glucose (Katz 1973) this would suggest insufficient fluid replacement. Thereafter, the rate of fall of plasma sodium should not exceed 10 mmol/L in 24 hours (Adrogue 2000).
• The aim of treatment should be to replace approximately 50% of estimated fluid loss within the first 12 hours and the remainder in the following 12 hours though this will in part be determined by the initial severity, degree of renal impairment and co-morbidities such as heart failure, which may limit the speed of correction.
• A target blood glucose of between 10 and 15 mmol/L is a reasonable goal. Complete normalisation of electrolytes and osmolality may take up to 72 hours.

Water replacement and hypotonic (0.45% sodium chloride solution) fluid

Ideally patients will recover quickly enough to replace the water deficit themselves by taking fluids orally. There is no experimental evidence to justify using hypotonic fluids less than 0.45% sodium chloride solution. However, if the osmolality is no longer declining despite adequate fluid replacement with 0.9% sodium chloride solution AND an adequate rate of fall of plasma glucose is not being achieved then 0.45% sodium chloride solution should be substituted.