Hartmann's Solution - osmolality and lactate

Compound sodium lactate, Hartmann's Solution (Baxter Healthcare, Sydney, NSW), is a commonly used intravenous fluid treatment during anaesthesia. We investigated two poorly understood characteristics of this solution.

First, the solution is considered isotonic. The reported osmolality on the bag is a calculation derived by summing the nominal electrolyte concentrations and is 278 mOsmol/kg. We measured the osmolality using freezing point depression on the Advanced Instruments model 3320 osmometer. The measured osmolality of two different batches of Hartmann's was 257.7±0.6 mOsmol/kg (mean ± SD); 20 mOsmol/ kg less than indicated on the bag. It represents a significant free water load which may not be easily cleared in the presence...