Risks of anticoagulation therapy after experimental corticectomy in the rat

To determine the optimal postoperative interval after which heparin therapy can be safely initiated, a rat model for experimental craniotomy and corticectomy was developed. In 50 rats (100 lesions), heparin therapy was initiated 1, 2, 3, 5, or 7 days after standardized bilateral frontal corticectomy and was continued for 7 days. Intraperitoneally administered heparin, 75 to 100 U/kg.h, was continuously given to maintain the activated partial thromboplastin time in one of two ranges: therapeutic (1.5-3 times control) or supratherapeutic (> 3 times control). The size of intracranial hemorrhage was determined from coronal brain sections by automated image analysis. No significant hemorrhage was observed in control (saline infusion) animals or in rats receiving therapeutic doses of heparin beginning more than 24 hours after surgery. Small (10-50 mm3) and large (> 50 mm3) hemorrhages were frequent at all intervals up to 5 days in animals with supratherapeutic activated partial thromboplastin time (P < 0.01). Judicious heparin therapy may be safely initiated at 48 hours after craniotomy and corticectomy in rats, whereas supratherapeutic anticoagulation is associated with intracranial hemorrhage at intervals of up to 5 days.