CONTENTS
- Introduction
- Indications
- Contraindications
- EVD settings
- Troubleshooting
- EVD weaning
- ICP interpretation 📖
- Complications
- Lumbar drain
- DVT prophylaxis
- Podcast
- Questions & discussion
- Pitfalls
basics of what an external ventricular drain (EVD) is
- A burr hole is used to penetrate the skull, after which a catheter is blindly advanced into the lateral ventricle using anatomic landmarks. Among critically ill patients, the procedure is usually performed at the bedside.
- An EVD is the gold standard approach to measurement of intracranial pressure, because it allows for rezeroing of the pressure transducer as needed. (Some other devices don't allow rezeroing, which may cause the pressure to “drift” out of calibration over time.)
advantages of an EVD
- (1) Accurate measurement of the intracranial pressure (ICP).
- (2) Therapeutic drainage of cerebrospinal fluid may be performed (especially in hydrocephalus).
- (3) Diagnostic sampling of CSF may be performed.
- (4) Intrathecal administration of medications is possible (e.g., chemotherapeutics or antibiotics).
disadvantages of an EVD
- An EVD is the most invasive strategy for measurement of ICP. This may carry a higher risk of infection compared to less invasive monitors.
- Communication with the ventricular system leads to a substantial risk of nosocomial ventriculitis.📖
- (More on different types of devices for ICP monitoring here: 📖)
hydrocephalus, for example due to:
- Intraventricular hemorrhage (IVH).
- Subarachnoid hemorrhage (SAH).
- Meningitis.
- Brain tumors.
- Failure of a ventriculoperitoneal shunt.
- (More on hydrocephalus here: 📖)
ICP monitoring & treatment, for example:
status post neurosurgery
- Promotes dural healing after skull base or posterior fossa surgery.
The following contraindications are not absolute. For example, in the context of life-threatening hydrocephalus, emergent CSF drainage may be necessary despite coagulopathy.
coagulopathy, for example:
- Platelet count <100,000/mm3.
- INR >1.4 (33497549)
- Antiplatelet or anticoagulant medication use.
trajectory limitations
- Overlying scalp cellulitis or osteomyelitis.
- Intracranial hematoma or infection (e.g., epidural hematoma or epidural empyema).
anatomic barriers
- Compressed, slit-like ventricles may make EVD placement difficult.
- Midline shift increases the risk of catheter misplacement, if placement is based on anatomic landmarks.(Kumar 2018)
- Most EVDs are placed blindly at the bedside. However, for patients with abnormal anatomy, an EVD may need to be inserted in the operating room using stereotactic guidance.(33497549)
clamped versus open
- Most EVDs have a relatively simple design. They cannot measure the intracranial pressure and drain fluid at the same time:
- Intracranial pressure can be measured accurately only when the EVD is clamped (with most devices). For some patients, the EVD will intermittently be clamped briefly to periodically check the intracranial pressure (e.g., every hour).
- ⚠️ When the EVD is open, it may display a pressure measurement – but this measurement is not accurate! (Albin 2022)
- Fluid can be drained only when the EVD is open (which places the catheter in continuity with the drainage apparatus).
- The EVD may be clamped or opened by rotating a stopcock 90 degrees, as shown below:
open to drain
- The EVD will be set to drain CSF when the CSF pressure exceeds a certain value equal to the height of the drainage apparatus (e.g., 5-15 cm H2O).
- Low pressure (e.g., ~5 cm H2O) will encourage fluid drainage. This may be useful initially, to encourage removal of blood or infected material.
- Higher pressure (e.g., ~15 cm H2O) will discourage fluid drainage. For example, patients with a normal intracranial pressure might not drain any fluid at these settings. However, if ICP increases >15 cm H2O then fluid would drain – thereby preventing dangerous pressure accumulation. Higher pressures may be appropriate in the following situations:
- Higher pressures may be utilized during weaning of the EVD (to try to remove less fluid).
- Higher pressures may be utilized if there is concern that excess fluid removal could cause dangerous tissue shifts (e.g., a posterior fossa mass with threatened upwards herniation).
- Evidence of overdrainage (more on this below 📖).
- Higher pressures are often used for patients with subarachnoid hemorrhage and an unsecured aneurysm, to avoid increasing a pressure gradient that could encourage aneurysmal rebleeding.(26069848)
clamped
- The EVD should always be clamped when adjusting the head of the bed (to avoid rapid fluctuations in pressure). Before unclamping the EVD, readjust the height of the EVD to match the patient's external auditory meatus.
- Following medication administration into the EVD, the EVD is generally clamped for an hour.(26069848)
- Clamping of the EVD will be performed prior to its removal, to simulate the effects of eliminating the EVD entirely (more on this below).
- If the EVD is clamped for a prolonged period of time, be sure to monitor the intracranial pressure carefully (as displayed on the monitor). Also look for any clinical signs of intracranial pressure elevation (e.g., emesis, headache, altered mental status).
risk factors for overdrainage
- Consistently draining >15-20 ml/hr suggests the possibility of overdrainage. CSF shouldn't generally be drained faster than 20 ml/hour. (Naidech 2022)
- Noncommunicating hydrocephalus may increase the risk of overdrainage.(28169966)
- ⚠️ Overdrainage may occurs if the patient's head is raised without simultaneously adjusting the height of the EVD. This inadvertently drops the effective level of the EVD.
potential consequences of overdrainage
- Intracranial hypotension, with temporary cessation of CSF drainage.
- Ventricular collapse causing malfunctioning/occlusion of the ventricular drain. (Naidech 2022)
- Tissue shifts (e.g., upwards herniation of a posterior fossa mass).
- Subdural hematoma or hygroma (fluid/blood accumulation in the subdural space, due to negative pressure).
- Rebleeding from a ruptured aneurysm.
- Pneumocephalus.
management of overdrainage
- Raise the pressure of the EVD, to reduce the amount of CSF drainage.
causes of cessation of CSF drainage
- Intracranial hypotension (note: in this scenario the ICP waveform should look normal).
- Disconnection of the catheter.
- Obstruction of the catheter due to debris or kinking (note: ICP waveform may be dampened or absent).
- Ventricular wall is collapsed around the catheter.
troubleshooting
- Ensure that all stopcocks are in the proper (“open”) position.
- Inspect tubing and drain for kinks, disconnection, or occluding material.
- Attempt lowering the EVD pressure gradually. Even a small amount of fluid return indicates that the catheter is patent.
- CT scan may help evaluate for catheter misplacement, hematoma formation, and/or worsening hydrocephalus (which may result from catheter malfunction).(Shutter 2019)
- Attempt to gently flush the catheter (should be performed only by neurosurgery). If the catheter doesn't flush properly, it may need to be replaced.
- If occluding material is seen in the tubing, the tubing may be flushed away from the patient to remove the debris (if possible).(28169966)
overall strategy
- It is controversial whether to gradually increase the pressure or to progress more aggressively to clamping trials.(31773310) The optimal strategy may depend on the specific patient and underlying pathology.
- Slow weans don't generally appear to have an advantage over more rapid weaning (e.g., immediate clamping trial).(Kumar 2018)
- Nonetheless, a common approach involves gradually increasing the pressure (e.g., 5 cm/day), followed by clamping for 24 hours and subsequent removal.(Shutter 2019)
- DVT prophylaxis should be held prior to removal to reduce the risk of a tract hemorrhage (more on DVT prophylaxis below 📖).(Demetriades 2018)
clamping trial
- Carefully supervised clamping trials have been shown to be safe. These may accelerate weaning off the EVD (for example, in the context of subarachnoid hemorrhage). (28929378)
- During the clamping trial, the intracranial pressure should be continuously monitored. If the pressure increases in a sustained fashion, then the EVD should be unclamped (e.g., >~22 cm for >~10 minutes 📖).
- Criteria for a successful clamping trial include: (Louis 2021)
- (1) ICP remains <20 mm Hg.
- (2) Patient remains neurologically stable.
- (3) CT scan shows no ventricular enlargement (CT scan before/after clamping may help provide reassurance that EVD removal is safe).
- A 24-hour clamping trial is generally sufficient.(Louis 2021) If there is concern for gradually developing hydrocephalus, a longer clamp trial may be performed.(Albin 2022)
causes of ventriculitis
- External ventricular drain insertion (ventriculitis occurs in ~10%).(Torbey, 2019) Risk factors for ventriculitis include:
- The primary risk factor is duration of insertion (with a risk of infection of roughly ~1 per 100 catheter-days, although this daily risk increment decreases over time).(28203777)
- Intraventricular or subarachnoid hemorrhage.(30241709)
- Systemic infection.
- Numerous insertion attempts.
- Frequent sampling or irrigation.(Torbey, 2019)
- Ventricular shunt infection (e.g., ventriculoperitoneal shunt).
- Rupture of an abscess in to the ventricular system.
- Retrograde spread of meningitis into the ventricular system (ventriculitis occurs in about a third of meningitis patients).
microbiology of ventriculitis in general
- Bacteria:
- Gram-positives, gram-negatives, or anaerobes (depending on the context; for example, Staph. spp are commonly involved in nosocomial ventriculitis).
- Listeria monocytogenes.
- Nocardia spp.
- Viral: CMV, VZV.
- Fungal: Candida species, Cryptococcus neoformans, Coccidioides immitis, Mucor spp.
- Parasites: Toxoplasmosis gondii, neurocysticercosis.
- Tuberculosis.
clinical findings of ventriculitis due to a ventricular drain
- Unlike community-acquired meningitis, ventriculitis may be due to indolent organisms with relatively low pathogenicity. These organisms may only be pathogenic in the presence of prosthetic material (e.g., coagulase-negative staphylococci or Propionibacterium acnes). These pathogens may cause subtle symptoms.(28203777)
- Manifestations can include:
- Fever might be the most reliable indicator of infection (although this remains nonspecific).
- Altered mental status.
- New headache.
- Intraventricular deris may cause ventricular outflow obstruction that causes acute hydrocephalus.
- Local signs related to the drain: (Jally 2021)
- Erythema, tenderness, or purulent drainage at the drain site.(28203777)
- Ventriculoperitoneal shunt infection may cause abdominal pain, peritonitis, or abdominal fluid collections.
- Ventriculopleural shunt infection may cause pleuritis.
- Ventriculoatrial shunt infection may cause bloodstream infection.
sampling CSF in efforts to diagnose ventriculitis in a patient with a ventricular drain
- CSF sampling should generally be obtained from the proximal port of the EVD, rather than the collection chamber (to avoid rapid degradation of cellular components).(26069848) Aspiration should be very slow (no more than 1 ml/min).
- CSF interpretation is very challenging:
- CSF is often abnormal at baseline (due to underlying brain pathology or simply irritation from the drain).
- Normal CSF cell count, glucose, and protein may not reliably exclude infection.(28203777)
- Interpretation of CSF results:
- CSF cultures are the most important test.(28203777) Note that Candida or skin organisms (such as coagulase negative staphylococcus) may cause ventriculitis – so a positive culture with these organisms should be taken seriously.
- If seen, CSF hypoglycemia strongly signals infection (<50 mg/dL or <40-50% of serum glucose).(Torbey, 2019)
- CSF pleocytosis is not a reliable parameter. However, a dramatic increase from baseline may signal infection (trends in CSF parameters over time may be more useful than absolute values).
- Elevated CSF lactate may be useful.📖 (28203777) Lactate values >4.15 mM appear to have good performance, although lactate can also be elevated by intraventricular hemorrhage.(34680826)
imaging findings in bacterial ventriculitis
- Neuroimaging is recommended in patients with suspected ventriculitis, ideally a contrast-enhanced MRI.(28203777)
- CT findings may include:(31964490)
- Layering debris may be seen in the ventricles, which is the most specific finding.(Torbey, 2019)
- The ependyma may enhance with contrast.
- Ventricular dilation (which may be segmental, due to adhesions).
- MRI may reveal:(30761443)
- Ventricular debris:
- Enhancement of the ventricles, meninges, and choroid plexus.
- Periventricular diffusion restriction and increased brightness on FLAIR.
differential diagnosis of ependymal enhancement (aka, periventricular enhancement)
- Neoplastic
- Primary CNS lymphoma (enhancement may be thick, irregular, and more focal).
- Primary glial neoplasms.
- Ependymoma
- Infection (enhancement is typically thin, <2 mm):(17374867)
- Viral infection (e.g., CMV, VZV).
- Bacterial ventriculitis:
- (1) Infection of an external ventricular drain (EVD).
- (2) Rupture of a brain abscess into the ventricular system.
- (3) Meningitis with extension of infection in a retrograde fashion into the ventricular system (against the normal direction of CSF flow).
- Fungal, toxoplasmosis, tuberculosis.
- Inflammatory (e.g., sarcoidosis, histiocytosis, neuromyelitis optica).
- AVM (arteriovenous malformation).
prevention of ventriculitis due to EVD
- A single dose of antibiotic prior to EVD insertion is recommended.(26738503) However, antibiotic prophylaxis should not be continued for the duration of EVD placement.(Demetriades 2018; 28203777)
- The EVD should be removed as soon as it is safe to do so.
- Meticulous sterile technique during insertion has been shown to reduce infection rate.
management of nosocomial ventriculitis
- Empiric therapy should cover the possibilities of MRSA and pseudomonas (e.g., vancomycin + cefepime; or vancomycin + meropenem). Note that agents with good CSF penetration should be utilized (more on meningeal penetration here: 📖).
- The infected catheter should be removed. If an EVD is still necessary, a new catheter should be inserted at a fresh site.(26069848; 28203777)
- If there is an indwelling catheter, repeat CSF sampling may be considered after 2-4 days. Ideally this should demonstrate sterilization of the CSF.
- Intrathecal instillation of antibiotics may be considered for patients who continue to have an indwelling ventricular catheter, in the following situations:
- Failure of the CSF to sterilize by day ~5-7.
- Highly drug-resistant organisms.
- Situation which prevents removal of the infected ventricular drain.
- For more information, see the IDSA 2017 guidelines for healthcare-associated ventriculitis and meningitis. 📄
- Tract hemorrhage is common (~~20%), but usually clinically insignificant.
- Symptomatic hemorrhage may occur in <2% of placements.(Torbey, 2019)
- Potential consequences of hemorrhage:
- EVD dysfunction.
- Mass effect exerted on surrounding tissue.
indications include:
- CSF leak (e.g., due to trauma or surgery). Lumbar drain may be used to treat an active CSF leak, or to prevent development of a postoperative CSF leak. (Albin 2022)
- Communicating hydrocephalus (e.g., subarachnoid hemorrhage).
- Assessment for shunt responsiveness in normal pressure hydrocephalus.(Kumar 2018)
- Surgery involving the aorta, with possible damage to the spinal cord (CSF diversion is thought to promote spinal cord perfusion).
drain management
- Volume-driven drainage is typical (e.g., 10 ml removed every 2 hours). However, pressure-driven drainage can be used in a manner similar to an EVD.
potential complications (32979671)
- Infection (e.g., meningitis, spinal epidural abscess).
- Brain herniation (e.g., due to obstructive hydrocephalus).
- Intracranial hemorrhage (roughly ~1% risk of subdural hematoma formation, due to shifts in pressure which place tension on bridging veins).(Kumar 2018)
- Overdrainage:
- This is a common problem, with complications ranging from positional headaches to severe sequelae (subdural/epidural hematoma, rebleeding from a ruptured aneurysm, cranial neuropathies, cerebellar tonsillar herniation, pneumocephalus).(32979671)
- Overdrainage may be managed by reducing the drainage rate and temporarily placing the patient in Trendelenburg position. In the context of herniation, injection of isotonic saline into the lumbar drain to replace the lost CSF may be attempted as an emergency intervention.(28169966)
- Immobility (which may promote DVT/PE, atelectasis, ileus).
- Nerve root irritation.
- Hematoma.
- Retained catheter (due to catheter fracture).
Deep vein thrombosis (DVT) prophylaxis may be complicated, as patients often have numerous risk factors for thrombosis and bleeding (e.g., EVD plus intracranial hemorrhage). Decisions regarding DVT prophylaxis should be made in conjunction with the neurosurgical team, but here are some useful concepts:
EVD insertion or removal
- Both EVD insertion and removal carry significant risks of bleeding.(28169966)
- Chemical DVT prophylaxis (i.e., s.q. heparin) should be held prior to insertion or removal. Patients should be managed with intermittent pneumatic compression devices when chemical DVT prophylaxis isn't possible.
- Chemical DVT prophylaxis can generally be resumed >24 hours afterwards (unless placement or removal was complicated by bleeding).(Kumar 2018, 23991846)
- According to 2017 guidelines from the Society for Neuroscience in Anesthesiology and Critical Care, “Contrary to popular concern, chemical prophylaxis against venous thromboembolism started within 24 hours of admission and therapeutic heparinization initiated within 24 hours of placement of the EVD does not increase bleeding risk.”(28169966)
lumbar drain
- Lumbar drain placement has a lower risk of hemorrhage compared to EVD placement. Thus, a similar or more aggressive strategy towards chemical DVT prophylaxis might be reasonable.
- DVT prophylaxis is generally held prior to lumbar drain insertion or removal. Subsequently, DVT prophylaxis may often be resumed without delay.(32979671) However, if bloody CSF or aspiration of blood occurs during placement, anticoagulation should be avoided for 24 hours.(28169966)
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- 🛑 Always be sure to clamp the EVD when adjusting bed position. Prior to unclamping the EVD, make sure it's aligned correctly with the patient. If in doubt about how to do this, ask the patient's nurse for help.
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References
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- 26738503 Fried HI, Nathan BR, Rowe AS, Zabramski JM, Andaluz N, Bhimraj A, Guanci MM, Seder DB, Singh JM. The Insertion and Management of External Ventricular Drains: An Evidence-Based Consensus Statement : A Statement for Healthcare Professionals from the Neurocritical Care Society. Neurocrit Care. 2016 Feb;24(1):61-81. doi: 10.1007/s12028-015-0224-8 [PubMed]
- Greenberg, M. S. (2016). Handbook of Neurosurgery (8th ed.). Thieme.
- 28169966 Lele AV, Hoefnagel AL, Schloemerkemper N, Wyler DA, Chaikittisilpa N, Vavilala MS, Naik BI, Williams JH, Venkat Raghavan L, Koerner IP; Representing SNACC Task Force for Developing Guidelines for Perioperative Management of External Ventricular and Lumbar Drains. Perioperative Management of Adult Patients With External Ventricular and Lumbar Drains: Guidelines From the Society for Neuroscience in Anesthesiology and Critical Care. J Neurosurg Anesthesiol. 2017 Jul;29(3):191-210. doi: 10.1097/ANA.0000000000000407 [PubMed]
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