Osmotic Diuresis
When the concentration of glucose exceeds the maximum re-absorption capacity of the kidney, glucose remains in the filtrate. This causes an increase in osmotic pressure causing water and potassium to move out and into the urine.
Fluid and electrolyte losses in typical DKA
| Water ml/Kg | 100 |
| Sodium mmol/Kg | 7-10 |
| Potassium mmol/Kg | 3-5 |
| Chloride mmol/Kg | 3-5 |
| Phosphate mmol/Kg | 1-1.5 |
| Magnesium mmol/Kg | 1-2 |
| Calcium mmol/Kg | 1-2 |
Below are some of the main osmotic diuresis changes with severe fluid and electrolyte loss:
Sodium changes
Hyperglycaemia is restricted to the extra-cellular space, this leads to a shift in water from the intra-cellular to the extra-cellular space, initially diluting plasma sodium. The osmotic diuresis causes the water to be lost in excess of the sodium in the initial stages. This leads to an artificially lowered plasma sodium concentration that can be corrected by the following formula displayed [16].
Potassium changes
Potassium depletion is due to excessive urinary potassium loss secondary to the osmotic diuresis. The diuresis leads to an increased delivery of fluid and potassium to potassium secretory sites in the distal nephron. The plasma potassium levels are usually within the normal range or high despite the loss, as hyperglycaemia and acidosis causes the potassium ions to shift from the intra-cellular to the extra-cellular compartment [2,3,7,8].