Lindegaard Index

V MCA : VICA ratio

Lindegaard Index: differentiates vasospasm vs hyperemia

  1. MCA
    1. ratio between intracranial velocity and external carotid artery flow velocity
    2. >3 = vasospasm, ❤ hyperemia
  2. Vertebrobasilar artery
    1. ratio between basilar artery and extracranial vertebral artery
    2. >2 with elevated velocity in basilar = vasospasm

Indications of severe narrowing in TCDs:

  1.  BFV >200 cm/s
  2. rapid rise in flow velicities (>50cm/sec/day)
  3. Lindegaard ratio (VMCA:VICA) >6 (severe)

Best Doppler parameter = peak systolic velocity – threshold of 182 cm/s corresponds to maximal diagnostic accuracy

Lindegaard: differentiate high intracranial flow velocities associated with hyperemia from those with BFV increase from VSP

overall accuracy better than velocity measurements alone

3.6 appears to be threshold to diagnose mild spasm (<25% narrowing) in M1 segment whereas 4.4 indicates moderate to severe spasm (>25% narrowing)



Sn 42% Sp 76% for ACA when 120 cm/sec used as threshold for ACA spasm

TCCS threshold of 75cm/s mean BFV associated with Sn 71% and Sp 85%

V ACA : V ICA ratio can be helpful to differentiate spasm from the normal artery; the ratio VACA : V ICA varies between 0.54 and 2.55


Other Vessels:

few published data on TCD diagnosis of ICA, PCA, VA, BA spasm

sensitivity = 25%, 48%, 44%, and 77%

specificity = 91%, 69%, 88%, and 79%

Sn / Sp greater for BA spasm when ratio  of mean BFV in BA vs extracranial VA is used, with threshold at >2; Sn 100% Sp 95%

Normal reference ranges V PCA : V VA (0.76-2.90)

TCD is not useful to detect VSP in more distal branches. Data lacking.



Le Roux, Peter D, Joshua M Levine, and W. Andrew Kofke. Monitoring In Neurocritical Care. 1st ed. Philadelphia, PA: Elsevier/Saunders, 2013. Print.

Miller, Ronald D. Miller’s Anesthesia. 8th ed. 2015. Print.

EVD Weaning Protocols

10cm H20 prior to weaning

Initiation of weaning left to discretion of attending neurosurgeon.


  1. raise drain height by 5 cm q24h to final level of 25 cm H20
  2. on Day 4, close the drain
  3. reopen if:
    1. ICP>20mm H20 x >5 minutes
    2. neurologic deterioration
    3. CT next day shows hydrocephalus

RAPID WEANING (within 24 hours)

  1. close drain immediately
  2. reopen if:
    1. ICP>20mm H20 x >5 minutes
    2. neurologic deterioration
    3. CT next day shows hydrocephalus

Failure of weaning = VP shunt insertion

**No differnece in incidence of HCP / need for VP shunting (62.5 vs 63.4% p=0.932)

**gradual weaning group spent 2.8 more days in the ICU (p=0.0002)

Neurocritical Care Society Guideline:

EVD weaning should be accomplished as quickly as is clinically feasible so as to minimize the total duration of EVD monitoring and VRI risk.

Two main methods to select those who will need permanent CSF diversion: clamping trial vs progressive wean.1. Clamping Trial: clamp EVD and monitor ICP, clinical status, ventricle size – determine whether VPS is required2. Progressive wean – progressively increase level of ventricular drainage (usually 5mm Hg/d) while monitoring ICP, clinical status, ventricular size, drainage volume Only 1 RCT (Klopfenstein, see reference listed) comparing the two methods. Clamping trial associated with shorter duration of EVD and ICU and hospital LOS with similar clinical outcomes.Currently decision to shunt is based on clinical deterioration. There is little information about the effects of subclinical hydrocephalus on cognitive function, chronic headache and fatigue. Studies have shown decrease in CBF in NPH, correlating with cognitive dysfunction.


Fried, Herbert I. et al. “The Insertion And Management Of External Ventricular Drains: An Evidence-Based Consensus Statement”. Neurocritical Care 24.1 (2016): 61-81. Web.

Klopfenstein, Jeffrey D. et al. “Comparison Of Rapid And Gradual Weaning From External Ventricular Drainage In Patients With Aneurysmal Subarachnoid Hemorrhage: A Prospective Randomized Trial”. Journal of Neurosurgery 100.2 (2004): 225-229. Web.

Rabinstein, A. and Lanzino, G. (2018). Aneurysmal Subarachnoid Hemorrhage. Neurosurgery Clinics of North America, 29(2), pp.255-262.