Excessive clotting can also be serious problem, as it can lead to deep venous thromboses (DVTs) or pulmonary emboli. Neurosurgery patients are particularly prone to developing abnormal blood clots because they are frequently bed-bound while in the ICU, they may have a tumor or spinal cord damage, or they may have had surgery, all of which predispose to blood clot formation.

To prevent this from happening, patients are instructed to wear SCDs (sequential compression devices), which are boots that intermittently inflate with air to compress the patient's calf muscles to promote blood flow and to inhibit blood clotting on a systemic level; patients are encouraged to ambulate as early as possible after surgery to prevent venous stasis; and patients are given daily medications to prevent DVTs (Heparin, Lovenox, etc.).

If a patient is suspected of developing a blood clot, different tests can be done to detect the clot, including an ultrasound (Venous Duplex Scan) or Spiral CT scan of the lungs.