Haemodynamic and haematologic alterations with protamine reversal of anticoagulation: comparison of standard heparin and a low molecular weight heparin fragment.

Reversal of anticoagulation with protamine sulfate causes many adverse haemodynamic and haematologic effects which could be due to differences in the mechanism of action of standard and low molecular weight heparin. Three groups of dogs were investigated: one group received normal saline pretreatment followed by heparinisation with standard heparin 150 IU/kg followed by protamine sulfate reversal 1.5 mg/kg after aortic interposition grafting: the second group were given normal saline pretreatment followed by heparinisation with low molecular weight heparin 150 U antiXa/kg and after grafting protamine sulfate reversal 1.5 mg/kg. The third group were given protamine sulfate pretreatment 2.25 mg/kg followed by low molecular weight heparin 150 U antiXa/kg and later protamine sulfate reversal 1.5 mg/kg after grafting. The same haemodynamic changes were seen regardless of the type of heparin or pretreatment with protamine given along with low molecular weight heparin. There was a suggestion that regular heparin cause a more pronounced increase in pulmonary artery pressure and a decrease in heart rate. On the other hand the systemic hypotension and reduction of cardiac output seemed more pronounced in the low molecular weight heparin group. Platelet count decreased less in the low molecular weight heparin group, but white blood cell count was equally reduced. Pretreatment with protamine did not abolish the adverse effects of protamine when reversing anticoagulation achieved with low molecular weight heparin, a finding not shared with standard heparin-protamine interactions.