Reperfusion injury in skeletal muscle: interaction of osmotic and colloid-osmotic pressure in the initial reperfusate for oedema prevention.

Previous studies from the authors' laboratory have shown that controlled limb perfusion after prolonged, acute ischaemia minimizes reperfusion injury. The present study was performed to investigate the role of osmotic and colloid-osmotic pressure in the initial reperfusate in order to reduce postischaemic limb oedema and subsequent reperfusion injury. A total of 96 isolated rat hindlimbs were used: 18 were perfused immediately after amputation (no ischaemia; untreated) and 78 limbs were subjected to 4 h of warm ischaemia in a moist chamber. Thereafter eight limbs were used to investigate the effects of the addition of mannitol to the initial reperfusate. The remaining 70 limbs received controlled reperfusion (modified reperfusate with various osmotic (315-580 mosmol/l) and colloid-osmotic pressure (0-50 mmHg. perfusion pressure 50 mmHg) during the first 30 min after ischaemia. Controlled reperfusion was always followed by uncontrolled reperfusion (30 min. perfusion pressure 100 mmHg) to simulate the clinical condition where normal blood perfusion at systemic pressure will follow controlled reperfusion. Functional recovery, limb weight, water content of the soleus muscle, limb flow and tissue high-energy phosphates were assessed at the end of the experiment. Results show that a reperfusate without colloid-osmotic pressure (i.e. without macromolecules) produces severe limb oedema (84.6(2.0)% water content) and allows no functional recovery after prolonged warm ischaemia. Addition of mannitol to the initial reperfusate does not prevent severe reperfusion injury. In contrast, a hyperosmotic reperfusate with a colloid-osmotic pressure of 26 mmHg effectively prevents limb oedema (78.6(0.9)% water content, 110.8(2.4)% of control weight). Physiological osmotic pressure (315 mosmol/l), however, will not reduce oedema formation (82.7(0.4)% water content). Furthermore, colloid-osmotic pressure > 26 mmHg increases the viscosity of the reperfusate (flow decreases to < 50% of control) and does not allow an optimal functional recovery. Macromolecules used to create the colloid-osmotic pressure should be of similar molecular weight to albumin (69,000 Da); those with a smaller molecular weight (e.g. hydroxyethyl starch40,000/0.5) produce excessive limb oedema (184.9(13.5)% control weight; 85.7(1.4)% water content) without functional recovery (0% control contractions). The present data suggest that after prolonged limb ischaemia: (1) addition of mannitol to a crystalloid solution does not prevent oedema; (2) hyperosmotic reperfusates (380-480 mosmol/l) with a colloid-osmotic pressure of 26 mmHg are most effective in preventing limb oedema; and (3) macromolecules used to achieve colloid-osmotic pressure should have a molecular weight similar to albumin.