01Core principlesThe concepts and mechanisms needed to understand the subject.
An EVD enters a lateral ventricle through the skull and connects to external tubing, a pressure-transduction pathway and a collection chamber. It provides temporary CSF diversion in acute hydrocephalus and can provide ventricular ICP measurement. Common indications include subarachnoid or intraventricular haemorrhage, intraparenchymal haemorrhage with hydrocephalus, tumour-related obstruction, infection and shunt failure. The device is often lifesaving, but its benefits coexist with tract haemorrhage, catheter malposition, obstruction, overdrainage, disconnection and ventriculostomy-related infection.
Drainage is governed by a hydrostatic relationship between the ventricular reference point and the prescribed collection-system threshold. Raising, lowering or tilting the patient without the authorised re-level process changes that relationship. A system prescribed open to drainage behaves differently from one temporarily configured for an authorised pressure reading. Because manufacturers and units differ, the safe learning point is conceptual: know whether the system is open or clamped, know the prescribed reference and order, and involve trained staff for every change. A numerical height or “always clamp for transfer” rule is not universal.
Sudden lack of drainage has several explanations: the ventricle may no longer generate flow above the prescribed threshold, the catheter or tubing may be obstructed, a clamp may be closed, the system may be malpositioned relative to the patient, or the catheter may have migrated. Excess drainage can follow an unrecognised lowering of the collection system or changed patient position and may contribute to ventricular collapse or subdural bleeding. Neither problem should trigger unsupervised flushing, tubing milking or setting changes. Assess the patient first and escalate through the protocol.
Infection risk grows with duration and breaches of the closed system. The NCS consensus suggests avoiding routine CSF sampling and limiting manipulation; its sampling recommendation is conditional and based on low-quality evidence. IDSA recommends periprocedural prophylaxis and antimicrobial-impregnated drains, but not prolonged systemic prophylaxis throughout EVD duration or fixed-interval exchange. A standard insertion and maintenance bundle is central. Removing or weaning the EVD as soon as clinically feasible reduces exposure, but the strategy and trial criteria remain disease- and service-specific.
Ventriculitis can be difficult to diagnose because fever, altered consciousness and abnormal CSF may also reflect the original haemorrhage or surgery. IDSA states that CSF cell count, glucose and protein may be unreliable and that normal values do not reliably exclude infection; culture is the most important test. Sampling itself must be clinically justified and performed through the authorised sterile method. If a drain is being used to treat an established CSF infection, culture monitoring differs from routine surveillance of a non-infected drain.
Key points
- An EVD is a temporary ventricular catheter connected to a closed collection and pressure system; it can drain CSF, monitor ventricular pressure, or do both.
- The prescribed drain reference and height create a hydrostatic threshold. Patient position and reference level therefore affect drainage and the displayed pressure.
- Pressure cannot generally be interpreted while the system is freely draining in the same way as when the transducer is exposed to the ventricle; follow the device protocol for a valid reading.
- Never improvise drain height, clamping, zeroing, sampling, flushing or transport practice. Confirm the written order and use the named local/device protocol.
- Keep the system closed and minimise manipulation. NCS suggests CSF sampling only when clinically indicated; IDSA advises against daily cultures for drains not being used to treat infection.
- Prevent infection with a standardised insertion and maintenance bundle, periprocedural antibiotics and an antimicrobial-impregnated catheter where used; prolonged antibiotics for the entire EVD duration and fixed-interval exchange are not recommended by IDSA.
02Mechanisms and patternsImportant relationships and how to distinguish them.
At every handover identify the indication, whether the system is for drainage, monitoring or both, prescribed reference and state, relevant limits, and exactly which team may alter it. Never infer a setting from another patient.
New headache, vomiting, drowsiness or pupil change with unexpectedly absent drainage or an altered waveform raises recurrent hydrocephalus or device obstruction. Verify only permitted external observations and escalate immediately.
A new postural or severe headache, unexpected high output, neurological change or new subdural collection may reflect excessive drainage. Position and reference errors are preventable causes; respond through the current protocol.
Inspect for catheter migration, pulled sutures, leakage, cracked tubing, loose connections and a contaminated field. Protect the system as trained and call the responsible team; do not reconnect an exposed circuit ad hoc.
New fever, worsening neurological state, wound erythema, tenderness, drainage or unexplained inflammatory change raises infection. Meningism may be absent and postoperative or bloody CSF can obscure routine indices.
Interpret ICP only when the system configuration permits a valid measurement and with the examination and waveform. A normal displayed number does not exclude focal herniation, drain failure or intermittent obstruction.
03Interpreting evidenceInformation, measurements and their limitations.
Consider the information, its meaning and its limitations before deciding what follows.
- 01
Structured bedside system check - Why
- Identify an obvious external cause of changed drainage or invalid monitoring without breaching the system.
- Interpretation and limitations
- Under the named protocol confirm patient position, prescribed reference, documented order, clamp state visible to authorised staff, tubing course, connections, collection and waveform. Do not manipulate or flush beyond competency.
- 02
Serial neurological observations - Why
- Detect recurrent hydrocephalus, overdrainage, haemorrhage, infection or a new neurological event.
- Interpretation and limitations
- Trend GCS components, pupils, limb response and vital signs. Patient deterioration overrides a reassuring drain output or single ICP value.
- 03
Urgent CT head - Why
- Assess catheter position, ventricular size, tract or new haemorrhage, ventricular collapse, subdural collection and the original lesion.
- Interpretation and limitations
- Compare with previous imaging. A correctly positioned tip does not alone prove patency, and stable ventricular size does not explain away a declining examination.
- 04
Clinically indicated CSF culture - Why
- Establish healthcare-associated ventriculitis when clinical features justify sampling.
- Interpretation and limitations
- Culture is the most important diagnostic test; normal cell count, glucose or protein and a negative Gram stain do not reliably exclude infection. Prior antibiotics can make culture negative, and slow-growing organisms may require prolonged incubation.
- 05
Blood cultures and cause-directed tests - Why
- Investigate systemic infection and competing causes of fever or deterioration.
- Interpretation and limitations
- Obtain cultures before antibiotics when clinically safe and appropriate, but do not delay treatment of sepsis. Interpret results with the device type, clinical syndrome and antimicrobial exposure.
04Applied reasoningWorked examples connecting principles to decisions.
01Worked case: stopped drainageNeurological decline with an EVD in situA patient with an EVD becomes drowsier and the recorded CSF drainage has unexpectedly stopped.+
- 1Assess airway, breathing and circulation, repeat GCS components, pupils and limb responses, and call the responsible neurosurgical and critical-care team immediately.
- 2Using only the authorised bedside checklist, compare the written drain order with patient position, reference level, visible clamp state, tubing course, connections and collection chamber.
- 3Do not flush, milk, aspirate, alter the prescribed height or open a closed connection unless specifically trained and instructed within the named protocol.
- 4Arrange urgent CT and specialist device assessment to distinguish obstruction, migration, recurrent hydrocephalus, haemorrhage or another cause of deterioration.
- 5After correction or replacement, verify clinical response, ventricular imaging and valid pressure or drainage observations; document the event and configuration clearly.
02Infection pathwayFever with an EVDA patient develops fever, neurological change or insertion-site abnormality while an EVD is present.+
- 1Assess for sepsis and neurological deterioration, examine the insertion site and search for respiratory, urinary, line, wound and other infection sources.
- 2Discuss clinically indicated CSF sampling with the responsible team and use the sterile sampling route specified by the device and unit protocol; avoid routine surveillance sampling.
- 3Interpret culture as central evidence while recognising that CSF cell count, glucose, protein and Gram stain can be falsely reassuring after surgery, haemorrhage or antibiotics.
- 4If device infection is established, coordinate antimicrobial therapy and removal or replacement strategy with neurosurgery, microbiology and infection specialists; IDSA recommends removal of an infected CSF drain.
03Transfer pathwayPosition change or transportAn EVD patient requires mobilisation, turning, CT transfer or inter-hospital movement.+
- 1Before moving, identify the written order, responsible clinician, drain purpose and the exact local/device instruction for clamp state and reference management.
- 2Use trained staff to maintain the system, prevent traction and preserve sterility during movement; never rely on a universal remembered transfer rule.
- 3After positioning, re-establish the prescribed reference and configuration before interpreting drainage or pressure, then repeat the neurological assessment.
05Checking understandingVerify the reasoning, revisit uncertainties and apply feedback.
- At every handover record indication, prescribed configuration, reference, observed drainage, valid pressure context, waveform when relevant and the named escalation thresholds.
- Trend neurological observations and drain behaviour together; neither output nor ICP should be interpreted without the patient examination.
- Inspect insertion site, dressing integrity, tubing, connections and securement at the frequency set by the unit protocol while minimising system manipulation.
- Record temperature and infection features, but do not obtain daily CSF cultures from a drain not being used to treat infection unless clinically indicated.
- Review daily whether the EVD remains necessary and pursue the disease-specific weaning or removal plan as soon as clinically feasible.
06Special situationsVariants, exceptions and circumstances that change the usual approach.
Geometry governs flow
The drain is a hydrostatic system. Changing bed height or patient position without re-referencing can change drainage even when no control knob was touched.
Open is not measuring
Free drainage alters ventricular pressure and system configuration; a displayed number is interpretable only according to the validated device protocol.
Less access, less risk
Closed-system integrity and minimal manipulation are central infection-prevention principles; routine sampling and routine component changes add breaches without established benefit.
Culture carries weight
Postoperative inflammation and intraventricular blood make routine CSF indices unreliable. Culture is the most important test when infection is genuinely suspected.
Remove when feasible
Longer device duration adds infection exposure. NCS supports weaning and removal as quickly as clinically feasible, while the exact method remains disease- and service-specific.
07Common pitfallsFrequent interpretation and management errors.
- 01
Treating a sudden change in drain output as a tubing problem before assessing the patient for neurological deterioration.
- 02
Moving or sitting up a patient without following the prescribed clamp and re-level sequence for that device and unit.
- 03
Flushing, aspirating, milking or reconnecting the system without explicit competence, sterile conditions and specialist direction.
- 04
Interpreting an ICP value obtained while the system configuration does not permit a valid ventricular pressure reading.
- 05
Sending routine daily CSF cultures or extending systemic antibiotic prophylaxis for the entire drain duration.
- 06
Changing a catheter at fixed intervals rather than reviewing ongoing need and using the infection or malfunction pathway when indicated.