What is the target cerebrospinal fluid (CSF) drainage rate after external ventricular drainage?

Target CSF Drainage After External Ventricular Drainage

The optimal target for cerebrospinal fluid (CSF) drainage after external ventricular drain (EVD) placement is 5-15 mL per hour, with the EVD system positioned to maintain intracranial pressure (ICP) between 10-20 mmHg.

Indications for EVD Placement and CSF Drainage

External ventricular drainage is indicated in several clinical scenarios:

• Hydrocephalus, especially in patients with decreased level of consciousness 1
• Intraventricular hemorrhage (IVH) 1
• Persistent intracranial hypertension despite sedation and correction of secondary brain insults 1
• Monitoring and treatment of elevated ICP in patients with:
  • Glasgow Coma Scale (GCS) score ≤8
  • Clinical evidence of transtentorial herniation
  • Significant IVH or hydrocephalus 1

CSF Drainage Targets and Technique

Volume-Based Approach

• Target drainage rate: 5-15 mL per hour 2
• This approach maintains adequate CSF flow while preventing overdrainage
• Drainage should be titrated based on clinical response and ICP values

Pressure-Based Approach

• Set EVD height to maintain ICP between 10-20 mmHg 1
• Cerebral Perfusion Pressure (CPP) should be maintained at 50-70 mmHg 1
• The drip chamber height determines the pressure threshold at which CSF will drain

Monitoring Considerations

When using an EVD for both drainage and ICP monitoring:

• Closed system monitoring: For accurate ICP readings, temporarily close the drainage system for at least 15 minutes before measurement 3
• Open system monitoring: Continuous ICP monitoring during drainage is possible but may underestimate true ICP by approximately 0.56-0.78 mmHg at physiological flow rates 4
• The Pressure Equalization (PE) ratio can help characterize response to CSF drainage:
  • Higher PE ratio (>0.8) suggests CSF outflow obstruction that responds well to drainage
  • Lower PE ratio (<0.5) suggests cerebral swelling as the predominant pathology 5

Special Clinical Scenarios

Traumatic Brain Injury

• TBI patients typically have higher baseline ICP (average 26 mmHg) but drain less CSF (average 4 mL) compared to non-TBI patients 5
• Lower PE ratios (average 0.43) indicate that cerebral swelling often predominates over CSF outflow obstruction 5
• Consider more aggressive management of ICP through additional measures beyond CSF drainage

Intraventricular Hemorrhage

• IVH occurs in approximately 45% of patients with spontaneous ICH 1
• EVD patency may be difficult to maintain due to blood clots
• More frequent catheter flushing or replacement may be necessary

Negative Pressure Hydrocephalus

• In rare cases of negative pressure hydrocephalus, CSF drainage at subatmospheric pressure may be required 2
• Target drainage remains 5-15 mL per hour, even when negative pressure is needed to achieve flow

Complications and Considerations

Risks of EVD

• Infection (ventriculitis): 2.9-9% incidence 1
• Intracranial hemorrhage: 2.1-3% incidence (higher in coagulopathies, up to 15.3%) 1
• Overdrainage leading to ventricular collapse or subdural hematoma
• Catheter obstruction

Precautions Before EVD Placement

• Evaluate coagulation status
• Consider platelet transfusion for patients on antiplatelet agents
• Reverse coagulopathy in patients on warfarin 1
• In ECMO patients, EVD placement carries higher bleeding risk and should be considered only when benefits outweigh risks 1

Practical Management Algorithm

1. Initial setup:

   • Position EVD system with collection chamber at prescribed height (typically 10-20 cm above the external auditory meatus)
   • Ensure system is properly zeroed at the level of the foramen of Monro

2. Drainage management:

   • Monitor hourly CSF output, targeting 5-15 mL/hour
   • Adjust drip chamber height to achieve target ICP (10-20 mmHg)
   • Document color, clarity, and amount of CSF

3. ICP monitoring:

   • For accurate readings, close the system for at least 15 minutes before measurement
   • Maintain CPP between 50-70 mmHg by adjusting mean arterial pressure as needed

4. Weaning protocol:

   • Gradually raise the height of the drainage system
   • Monitor for signs of increased ICP
   • Consider clamping trials before EVD removal

By following these guidelines for CSF drainage after EVD placement, clinicians can effectively manage intracranial hypertension while minimizing associated risks.