Low-molecular-weight heparin [Neurosurgery Wiki]

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====== Low-molecular-weight heparin ======

Low molecular weight [[heparin]] (LMWH) is a class of [[anticoagulant]] medication.

These drugs are used for treating [[Deep-Vein Thrombosis]], [[pulmonary embolism]] when it is located in the veins, or heart attacks and [[stroke]]s when located in the arteries.

LMWHs, consist of only short chains of polysaccharide. LMWHs are defined as heparin salts having an average [[molecular weight]] of less than 8000 Da and for which at least 60% of all chains have a molecular weight less than 8000 Da. These are obtained by various methods of fractionation or depolymerization of polymeric heparin.

Heparin derived from natural sources, mainly porcine intestine or bovine lung, can be administered therapeutically to prevent thrombosis. However, the effects of natural, or unfractionated heparin are more unpredictable than LMWH.
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For emergencies: can be reversed with [[protamine]]
Non-emergencies: Longer times are needed in renal failure. A factor Xa level can be used to check anticoagulation status, but this usually must be sent out, making it unsuitable for acute management.
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LMWH prophylaxis in pediatric TBI appears to be more effective than UH in preventing VTE. Large, multicenter prospective studies are warranted to confirm the superiority of LMWH over UH in pediatric patients with TBI. Moreover, outcomes of VTE prophylaxis in the very young remain understudied; therefore, dedicated studies to evaluate this population are needed.
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Evidence suggests that it reduces [[cerebral edema]] and improves neurological recovery following [[stroke]] and [[traumatic brain injury]] (TBI), through blunting of cerebral [[leukocyte]] (LEU) recruitment. It remains unknown if unfractionated heparin (UFH) similarly affects brain inflammation and neurological recovery post TBI.

Prophylaxis was associated with decreased risk of pulmonary embolism and Deep-Vein Thrombosis, but no increase in risk of late neurosurgical intervention or death. Early prophylaxis may be safe and should be the goal for each patient in the context of appropriate risk stratification
((Byrne JP, Mason SA, Gomez D, Hoeft C, Subacius H, Xiong W, Neal M, Pirouzmand 
F, Nathens AB. Timing of Pharmacologic Venous Thromboembolism Prophylaxis in
Severe Traumatic Brain Injury: A Propensity-Matched Cohort Study. J Am Coll Surg.
2016 Jul 21. pii: S1072-7515(16)30651-2. doi: 10.1016/j.jamcollsurg.2016.06.382. 
[Epub ahead of print] PubMed PMID: 27453296.
)).

Unfractionated heparin (UFH)  after TBI reduces LEU recruitment, microvascular permeability and brain edema to injured brain. Lower UFH doses concurrently improve neurological recovery while higher UFH may worsen functional recovery. Further study is needed to determine if this is due to increased bleeding from injured brain with higher UFH doses
((Nagata K, Kumasaka K, Browne KD, Li S, St-Pierre J, Cognetti J, Marks J,
Johnson VE, Smith DH, Pascual JL. Unfractionated heparin after TBI reduces in
vivo cerebrovascular inflammation, brain edema and accelerates cognitive
recovery. J Trauma Acute Care Surg. 2016 Aug 16. [Epub ahead of print] PubMed
PMID: 27533909.
)).
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Low-dose heparin pretreatment may decrease the development of post-SAH early brain injury (EBI)
((Altay O, Suzuki H, Hasegawa Y, Sorar M, Chen H, Tang J, Zhang JH. Effects of
Low-Dose Unfractionated Heparin Pretreatment on Early Brain Injury after
Subarachnoid Hemorrhage in Mice. Acta Neurochir Suppl. 2016;121:127-30. doi:
10.1007/978-3-319-18497-5_22. PubMed PMID: 26463935.
)).