The effect of mannitol on reperfusion injury and postischaemic compartment pressure in skeletal muscle.

Mannitol has previously been shown to reduce skeletal muscle reperfusion injury and postischaemic compartment pressure. The present study was designed to evaluate whether these effects result from hyperosmolarity or free radical scavenging. A rabbit hindlimb perfusion model was used to compare the effects of mannitol (n = 6), glucose (n = 6)--an isomer of mannitol without scavenging effect--and fasciotomy (n = 6) on oedema, compartment pressure, energy charge, and muscle injury after 4 hours of ischaemia and 2 hours of reperfusion. One limb from each animal received treatment, while the other limb served as an untreated control. Mannitol and glucose reduced (p < 0.05) muscle water content and decreased (p < 0.01) the compartment pressure. Fasciotomy had no effect on muscle water content but normalised compartment pressure. The increase in energy charge following reperfusion was improved (p < 0.05) and uptake of [Tc99]methylenediphosphonate--an indicator of muscle injury--was reduced (p < 0.05) by mannitol only. In conclusion, mannitol reduces postischaemic oedema mainly by its hyperosmolar property whereas restitution of energy production and reduction of muscle necrosis seem to be an effect of free radical scavenging. The compartment pressure is reduced by hyperosmolarity and free radical scavenging.