Chapter 76

### INTRODUCTION

Venous thromboembolism is an important health-care problem and the source of significant morbidity and mortality. Nearly all hospitalized patients have at least one risk factor for thromboembolism, with 40% having three or more risk factors. Therefore, many hospitalized patients are candidates for thromboembolism and receive thromboprophylaxis.

The estimated incidence of neurologic dysfunction resulting from bleeding complications associated with neuraxial blockade has been reported as less than 1/150 000 for epidurals and less than 1/220 000 for spinal anesthetics. However, some studies show that the incidence may be as high as 1/3000 in some patient populations. The risk of clinically significant bleeding increases with age, existing problems with the spinal cord or vertebral column, underlying coagulopathy, difficulty with needle placement, and sustained anticoagulation with indwelling epidural catheter.

Bleeding is the major complication of anticoagulant and thrombolytic therapy, and is classified as major if it is intracranial, intraspinal, intraocular, mediastinal, retroperitoneal, or results in hospitalization or death. The most dreaded complication for patients with indwelling epidural catheter is a spinal hematoma. The term spinal hematoma is defined as bleeding within the spinal neuraxis and it most commonly occurs in the epidural space because of the prominent epidural venous plexus. Neurologic compromise presents as progression of sensory or motor block or bowel/bladder dysfunction and not as severe radicular back pain. Spinal cord ischemia tends to be reversible if patients undergo laminectomy within 8 hours of onset of neurologic dysfunction, with 38% of patients having partial or complete neurologic recovery in one study.

### UNFRACTIONATED HEPARIN (UFH)

The mechanism of action of heparin is to bind to antithrombin with high affinity and subsequently inactivate thrombin (IIa), factor Xa, and factor IXa. IV injection of heparin results in immediate anticoagulant activity compared to subcutaneous injection which results in a delay of effect for 1-2 hours. Administration of small dose (5000 U) of subcutaneous heparin does not prolong activated partial thromboplastin time (aPTT), however, it can result in unpredictable blood concentrations in some patients 2 hours after administration. Heparin is rapidly revered by protamine and each milligram of protamine can neutralize 100 U of heparin.

#### Intravenous Unfractionated Heparin

Intraoperative heparin doses range from 5000 to 10 000 U IV, especially during vascular surgery to prevent coagulation during cross clamping. The use of neuraxial procedures after administration of IV heparin may be associated with an increased risk of epidural hematoma. As a result, performance of neuraxial procedures should take place at least 1 hour before the administration of heparin and removal of the epidural catheter should take place 2-4 hours after the last heparin dose. Careful assessment of the patient's neurologic status in the lower extremities should take place for at least 12 hours after catheter removal.

#### Subcutaneous Unfractionated Heparin

The administration of 5000 U subcutaneous unfractionated heparin (SCUFH) every 12 hours is ...

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