[Effects of equiosmolar load of 20% mannitol, 7.5% saline and 0.9% saline on plasma osmolarity, haemodynamics and plasma concentrations of electrolytes].

OBJECTIVES: Mannitol 20% (M) and NaCl 7.5% (H) are hypertonic solutions used in-patient in hypovolaemic shock and in case of increased ICP. To our knowledge no study in humans compared them in an equiosmolar load. The objectives of this study were to compare the pharmacokinetics of both solutions in an equiosmolar load with an isotonic solution (NaCl 0.9% (C)) in terms of osmolarity, electrolytes and haemodynamic parameters over time.

STUDY DESIGN: Prospective, randomized, controlled study.

PATIENTS: Thirty ASA I and II patients undergoing non haemorrhagic surgery under general anesthesia.

METHODS: Three groups were studied (groups M, H and C), each receiving an equiosmolar load (4.95 mOsm kg(-1)) of solutions of mannitol 20%, saline 7.5% and saline 0.9% over ten minutes. Vital parameters (non invasive blood pressure, heart rate, oesophageal temperature) were monitored and blood samples (hemoglobin, hematocrit, K(+), Na(+), Cl(-), urea, creatinine, glucose, mannitolemia, osmolarity) were assessed preoperatively and intraoperatively at times 0, 3, 5, 10, 15, 30, 45, 60, 90, 120, 150 min of perfusion.

RESULTS: In both hypertonic groups, osmolarity was maximal at the end of infusion (group M: 329 +/- 7 mOsm l(-1); group H: 321 +/- 11 mOsm l(-1)); at the same time, Na(+) value was lowest in group M: 129 +/- 3 mmol l(-1) and highest in group H: 151 +/- 5 mmol l(-1), P < 0.001) with normalisation at 60 min. These results were also statistically significant when compared to the isotonic group (group C: osmolarity: 296 +/- 3 mOsm l(-1), P < 0.001; Na(+): 140 +/- 2 mmol l(-1), P < 0.001). Plasma volume expansion was statistically significantly larger in-group C between 10 and 15 min compared to both hypertonic groups (haematocrit: group C: 35 +/- 4%, group M: 39 +/- 5%; group H: 41 +/- 3%, P < 0.004). Haemodynamic parameters were similar in the 3 groups with however a trend towards lowers HR in the mannitol group, particularly at T10. Temperature was lower in the control group because of the volume infused. Cl(-) was higher in the H group.

CONCLUSION: A single infusion of 4.95 mOsm kg(-1) of mannitol 20% or NaCl 7.5% induces a similar osmolar variation over time with a maximal effect after 10 min.