Deep vein thrombosis (DVT) is a result of disturbed balances in blood flow patterns, blood clotting factors promoting coagulation and vessel wall endothelial injury. The subsequent disruption of coagulation and fibrinolysis mechanisms lead to venous clot formation and propagation. The neurosurgical procedure performed increases the risk of DVT; cranial procedures have a higher risk (3.4%) compared to spinal surgery (1.1%). DVT is the underlying cause of PE in approximately 36-45% of cases. PE is associated with a high rate of morbidity and mortality. Estimates using pooled study data and national databases determine the rate of PE to be approximately half of symptomatic DVT, ranging 0.4-1.2%. The most commonly used prophylactic measures are mechanical and pharmacologic or a combination of the two. Mechanical prophylaxis includes compression stockings and intermittent pneumatic compression. Pharmacological includes low-dose unfractionated heparin and low-molecular-weight heparin. The two different forms of prophylaxis inhibit clot formation by different pathways. Meta-analyses of the topic have been limited by study heterogeneity and no high-quality large randomised studies have been performed. Recent meta-analyses of nine studies comparing pharmacological prophylaxis versus control show absolute risk reduction of 9% for DVT formation and a relative risk reduction of 42%. They found no significant difference in intracranial haemorrhage rates in cranial surgery patients (2.7% in pharmacological prophylaxis versus 1.6% in control). In summary, there is a lack of high-quality studies to help guide decision-making regarding the best DVT prophylaxis strategy that balances the risk-reward ratio of lowering DVT/PE without increasing catastrophic haemorrhage. However, the addition of pharmacologic prophylaxis to mechanical prophylaxis in cranial procedures results in a decrease in the rate of DVTs along with a possible increase in incidence of haemorrhage. 

Deep vein thrombosis prophylaxis in the neurosurgical patient.
Shaikhouni A, Baum J, Lonser RR.
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Aaron SJ Ferguson

Department of Otolaryngology, Ninewells Hospital, UK.

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