EFFECTS OF VARIOUS INTRAVENOUS VOLUME LOA DING SOLUTIONS ON PLASMA OSMOLALITY

Objective: As hydratation of the normal brain is much more dictated by osmotic gradients than by hydrostatic or oncotic pressures, this stud y aimed to compare the effect of the infusion of currently used volume loading solutions on plasma osmolality. Study design: Randomized, com parative trial. Patients: Thirty ASA 1-2 patients, scheduled for lumba r intervertebral disc surgery were randomly allocated to three groups receiving either 2,000 mL of lactated Ringer's solution (RL, n = 10), 750 mL of hydroxyethylstarch 6% (HEA, n = 10) or 2,000 mi of normal sa line (NaCl, n = 10). Methods: Baseline osmolality, natraemia, glycaemi a and protidaemia were measured before induction of anaesthesia (T1), after the infusion of 375 mL of hydroxyethylstarch or 1,000 mL of cris talloids (T2) and at the end of the infusion (T3). Results: The three groups were identical for age, weight, initial plasma osmolality and n atraemia. However, osmolality in the RL group was decreased at T2 and T3 compared to T1 (respectively: 299 +/- 5 mOsm . kg(-1), 295 +/- 4 mO sm . kg(-1) and 292 +/- 5 mOsm . kg-1. Osmolality at T2 and T3 was als o lower in the RL group compared to the HEA and NaCl groups (respectiv ely: 301 +/- 6 mOsm . kg(-1) and 304 +/- 13 mOsm . kg(-1) for T2 and T 3 in the HEA group, and 299 +/- 5 mOsm . kg(-1) and 298 +/- 5 mOsm . k g(-1) in the NaCl group). In the HEA and NaCl groups, osmolality was u nchanged at T2 and T3 compared to T1. Conclusion: Both normal saline a nd hydroxyethylstarch 6% maintain plasma osmolality, whereas Ringer la ctate tends to decrease it. For that reason normal saline and hetastar ch 6%, but not lactated Ringer's solution, may be administered in pati ents experiencing blood-brain barrier damage.