Why some patients may be more prone to epidural hematoma than the normal population?

End-stage renal disease and uremia are risk factors for epidural hematoma. Moreover, this patient demonstrates the systemic ramifications of advanced renal disease in multi-organ dysfunction, including the coagulation system. Even though the patient may have a normal platelet count, uremia causes a qualitative platelet dysfunction. In fact, advanced renal disease disrupts normal platelet activation, aggregation, and adherence. The etiology of altered hemostasis is multifactorial, but includes a release in platelet-inhibitory factors as well as a disturbance in the platelet-vessel wall.

Early studies had made the observation that uremic platelets in normal plasma function normally. Consequently, uremic plasma mixed with normal platelets triggered platelet dysfunction. Thus, the hypothesis was made that platelet-inhibitory factors in the plasma of uremic patients led to impaired platelet function. However, in vitro studies could not replicate this effect with the known uremic toxins until the discovery of guanidinosuccinic acid. The formation of guanidinosuccinic acid occurs in the urea cycle when excess urea exerts an inhibitory effect on the cycle’s own enzymes. Therefore, the accumulation of L-arginine, an intermediate in the urea cycle, gets converted to guanidinosuccinic acid in an alternate pathway for ammonia detoxification. Interestingly, L-arginine is also a substrate for nitric oxide production. Excess nitric oxide production by the vascular endothelium and uremic platelets is implicated as the cause of bleeding by inhibiting platelet aggregation. Guanidinosuccinic acid is thought to be a precursor to nitric oxide production and may actually mimic the effects of nitric oxide as well.

The goal of treatment prior to surgery is to reduce platelet dysfunction in patients who are about to undergo an invasive procedure. In addition to the basic labs in the preoperative workup, the bleeding time is a nonspecific test that can be used to evaluate platelet and vascular wall function. Although uremic bleeding is associated with a prolonged bleeding time, it is controversial whether the test is a reliable predictor of clinical bleeding, such as an epidural hematoma. Unfortunately, there have been no large prospective studies that correlate prolonged bleeding time to risk of bleeding secondary to a procedure. The bleeding time can be used to evaluate the effectiveness of therapy. One such treatment is desmopressin (DDAVP) which is an analog of antidiuretic hormone. Desmopressin’s mechanism of action occurs at the endothelium where the drug increases the secretion of von Willebrand factor. Given at least one hour prior to any invasive procedure at a dose of 0.3 micrograms/kilogram intravenously, its duration of action persists for four to twenty-four hours. The advantage of desmopressin is that it can be used in an acute setting where the first dose can lower the bleeding time in half of the patients. Routine dialysis preoperatively has reduced the amount of uremic bleeding during surgery. Although dialysis has been shown to improve platelet function by eliminating circulating toxins, it may not effectively eliminate the risk of an epidural hematoma. Dialysis has been shown to partially reduce bleeding time in only two-thirds of uremic patients. Moreover, there have been case reports of spontaneous epidural hematomas during dialysis. In conclusion, even though these treatments can reduce the frequency of uremic bleeding, they won’t reliably normalize the risk of epidural hematoma equal to the general population.

End-stage renal disease patients under neuraxial anesthesia require close monitoring for any signs of spinal cord compression. The monitoring that was provided to the patient by the nursing staff and supervised by the acute pain service, provides the template for future protocols that may be implemented for other patients that have developed signs/symptoms of epidural hematoma. This protocol should include hourly neurological examination for 12 hours followed by exams every 2-4 hours for 24 hours consisting of lower extremity sensorimotor examination, assessment of bowel/bladder function, pre-anal pinprick sensory change (which may be the first sign of cauda equina syndrome), or exacerbation of back pain. Even though the outcome may be catastrophic with an epidural hematoma, the benefits of regional anesthesia greatly outweigh the risks for orthopedic procedures such as joint replacement surgery. The risk-to-benefit ratio must be formulated individually for each patient based on comorbidities as well as the surgical procedure.