How External Ventricular Drains and Intraparenchymal ICP Monitors Are Placed
Both external ventricular drains (EVDs) and intraparenchymal ICP monitors are placed at the bedside in the ICU using sterile technique, with the patient already intubated, sedated, and arterially monitored—no additional preparation beyond ensuring adequate sedation and hemodynamic stability is required.
Pre-Procedure Setup
The patient should already have:
- Endotracheal intubation with adequate sedation (typically propofol or midazolam with fentanyl)
- Arterial line functioning for continuous blood pressure monitoring to calculate CPP
- Head of bed elevated to 30 degrees
- Hemodynamic stability confirmed
Standard insertion protocols must be followed to ensure safety and reliability 1. The arterial line is critical because cerebral perfusion pressure (CPP) calculation requires simultaneous ICP and mean arterial pressure (MAP) monitoring.
Device Selection Algorithm
Choose EVD when:
- Hydrocephalus is present on imaging (EVD is preferred over parenchymal monitoring when safe and practical) 1
- CSF diversion is needed in addition to ICP monitoring
- Ventricular size allows safe cannulation
Choose intraparenchymal monitor when:
- Ventricles are compressed or shifted
- Rapid placement is needed
- Uninterrupted ICP monitoring during CSF drainage is required (parenchymal monitors remain accurate during drainage, while intraventricular measurements become unreliable) 2
Both devices provide equally reliable and accurate ICP data 1, and recent multicenter data shows no difference in 6-month functional outcomes between device types 3.
Placement Technique
Standard Freehand Approach
- Sterile field preparation with chlorhexidine
- Local anesthetic infiltration at Kocher's point (11 cm posterior from nasion, 3 cm lateral from midline, typically right side)
- Twist drill or burr hole creation
- Dural puncture with cautery
- For EVD: Catheter advanced perpendicular to skull surface, aimed toward ipsilateral medial canthus in coronal plane and external auditory meatus in sagittal plane, typically 5-7 cm depth until CSF flows
- For parenchymal monitor: Bolt system placed, then fiberoptic or strain gauge transducer advanced 1-2 cm into brain parenchyma
Emerging Guidance Technologies
While freehand placement remains standard, ultrasound, electromagnetic navigation, and augmented reality platforms can improve first-pass success rates, particularly when anatomy is distorted 4. However, these are not required for safe placement.
Critical Safety Points
Neurointensivists can safely place these devices with complication rates comparable to neurosurgeons (infection rate 0-3.4%, hemorrhage rate approximately 20% but typically small tract hematomas <5 cm³) 5.
Common pitfalls to avoid:
- Inadequate sedation during placement can cause patient movement and increase hemorrhage risk
- Failure to confirm hemodynamic stability before starting—maintain MAP >65 mmHg to preserve CPP during the procedure
- Not zeroing the arterial line transducer at the same reference point (tragus) as the ICP monitor leads to inaccurate CPP calculations
- Multiple passes increase hemorrhage risk—consider guidance technology if first attempt fails
Post-Placement Protocol
Immediately after placement:
- Connect ICP monitor to bedside display
- Zero both arterial line and ICP transducer at the tragus (external auditory meatus)
- Confirm CPP calculation is automated (CPP = MAP - ICP)
- Obtain head CT to confirm placement and rule out hemorrhage
- Continuously monitor ICP waveform quality—instantaneous values must be interpreted with trends, CPP, and clinical evaluation 1
The target ICP threshold is generally >20-25 mmHg, though this remains somewhat uncertain in the literature 1. The arterial line enables real-time CPP optimization, which is fundamental to preventing secondary brain injury.