Background: One of the factors that can modify the serum potassium concentration level is a change in extracellular fluid osmolality. The aim of this study was to investigate the influence of 20% mannitol infusion on the serum potassium level in humans during general anesthesia.
Methods: The study group comprised forty patients who underwent intervertebral disc removal under general anesthesia. Patients were randomly divided into two groups. Twenty group I patients received a bolus (0.7g/kg) of a 20% mannitol solution. Twenty group II subjects received an equivalent volume of 0.9% NaCl. The effect of the infused fluid on the changes in serum potassium, sodium bicarbonate and serum pH was measured. Statistical analysis was done by t-tests for independent groups.
Results: Following the infusion of 20% mannitol, the pH decreased by 0.0378±0.0212 and the serum K+ concentration level increased by 0.20±0.084 mmol/l (average). These changes were statistically significant at a=0.05. Following the infusion of the saline solution, a statistically insignificant increase in the serum pH of 0.0224±0.0115 and a statistically significant decrease in the serum K+ concentration level of 0.14±0.042 mmol/l were obtained.
Conclusions: Intravenous administration of a 20% mannitol solution at a dose of 0.7 g/kg increases the serum potassium level and decreases the serum pH in humans during general anesthesia.
key words: general anesthesia, potassium, mannitol

Keywords: general anesthesia, Potassium, Mannitol