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Caring for neurosurgical patients with external ventricular drains

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This article reviews the essentials of nursing care for patients with external ventricular drains. It comes with a self-assessment, enabling you to test your knowledge after reading it

Abstract

External ventricular drains are life-saving devices used in neurosurgical patients with hydrocephalus (excessive amounts of cerebrospinal fluid). The fluid is produced in the brain ventricles and circulates around the brain and spinal cord, protecting them from injury and supplying brain cells with nutrients. Hydrocephalus can occur due to impaired circulation or malabsorption and is a medical emergency, which can lead to raised intracranial pressure. Nurses are responsible for the care of patients who have external ventricular drains. This article explains how the drains work and discusses key nursing considerations for their management.

Citation: Humphrey E (2018) Caring for neurosurgical patients with external ventricular drains. Nursing Times [online]; 114: 4, 52-56.

Author: Emily Humphrey is staff nurse (mental health), neurosciences department, surgical division, Nottingham University Hospitals Trust.

Introduction

Hydrocephalus is a medical emergency and its treatment involves inserting an external ventricular drain (EVD) into one of the lateral ventricles of the brain to remove excess cerebrospinal fluid (CSF). This article discusses the essentials of nursing care for patients with EVDs.

CSF circulation

Cerebrospinal fluid is a clear, odourless liquid containing substances that bathes the brain and spinal cord, providing energy to the working brain cells (neurons), such as glucose, oxygen and electrolytes (Hickey, 2009). It travels around the brain and spinal cord within the subarachnoid space, an enclosed area that sits between two of the three outer protective layers (meninges) that envelop the brain and spinal cord (Fig 1).

fig 1 subarachnoid space ventricles and meninges

From outer to inner layers, the order of the meninges and subarachnoid space is:

  • Dura mater;
  • Arachnoid mater;
  • Subarachnoid space;
  • Pia mater.

Before entering the subarachnoid space, CSF travels through the ventricles (Waugh and Grant, 2014), four specialised cavities in the brain: one in each of the two cerebral hemispheres (left and right lateral ventricles) plus two additional ones. The fluid is constantly produced and reabsorbed, so while 500ml is produced daily, only around 150ml is in circulation at any one time in healthy patients (Hickey, 2009). On average, 125ml of CSF is present in the subarachnoid space and 25ml in the ventricles of the brain (Sakka et al, 2011).

The route of CSF circulation is as follows: most is produced in the blood vessels lining the two lateral ventricles (choroid plexus) (Sakka et al, 2011). The fluid passes from the lateral ventricles into the intraventricular foramina, a narrow descending passageway, before entering the third ventricle. It then passes into the cerebral aqueduct, a longer and narrower descending passageway, to reach the fourth ventricle, from where it enters the subarachnoid space through the median aperture (Sakka et al, 2011). While CSF moves in one direction when passing through the ventricles, it moves in several different directions within the subarachnoid space (Sakka et al, 2011). It is eventually absorbed by the arachnoid villi (protruding structures that line the subarachnoid space) and leaves the subarachnoid space to enter the venous bloodstream (Waugh and Grant, 2014).

CSF functions

The CSF cushions the brain and spinal cord, acting as a shock absorber and reducing the impact of outside knocks and jolts. It also keeps the brain buoyant by reducing its density, thereby preventing its circulation being cut off by the impact of its weight (Woodward and Mestecky, 2011). In addition, CSF enables homoeostasis by delivering important substances – such as hormones, oxygen and nutrients – to brain cells and removing waste (Waugh and Grant, 2014).

These functions rely on a constant flow of CSF being produced and absorbed in the correct amounts. However, sometimes there is excessive CSF in circulation: this is known as hydrocephalus.

Causes of hydrocephalus

Hydrocephalus is a broad term for any situation where there is too much CSF in circulation, for example because the choroid plexus secretes too much, there is an obstruction somewhere on its route, or there are problems with its absorption by the arachnoid villi. Secretion is not in equilibrium with absorption, and CSF builds up.

Hydrocephalus can have many causes:

  • Following subarachnoid haemorrhage, blood in the subarachnoid space makes it harder for the CSF to reach the arachnoid villi and slows down or prevents its absorption (Bowles, 2014);
  • Following intraventricular haemorrhage, blood in the ventricles can enter the subarachnoid space and impair CSF absorption (Muralidharan, 2015);
  • Tumours near the third and fourth ventricles can obstruct CSF flow (Woodward and Waterhouse, 2009);
  • Exudate from infection (such as meningitis or encephalitis) can block the cerebral aqueduct and therefore obstruct CSF flow (Woodward and Waterhouse, 2009);
  • Genetic disorders, such as: aqueduct stenosis (abnormally narrow cerebral aqueduct); Dandy-Walker malformation (several abnormal brain structures including a dilated fourth ventricle); and Arnold Chiari malformation (where the base of the brain pushes through the opening of the skull and protrudes into the spinal canal) can impair CSF circulation (Woodward and Waterhouse, 2009);
  • Tumours of the choroid plexus, which are rare, can cause overproduction of CSF (Woodward and Mestecky, 2011).

A medical emergency

Hydrocephalus, from any cause, needs to be treated urgently as it can cause increased pressure in the ventricles (either by build-up of CSF around an obstruction or by blood increasing the overall circulating volume in the ventricles and subarachnoid space). Increased ventricular pressure equates to increased intracranial pressure (ICP) in the skull overall (Sakka et al, 2011).

Raised ICP is critical because it reduces blood flow to the brain, starving it of oxygen, glucose and other vital substances. Due to the limited space in the skull, untreated ICP will eventually lead to brain herniation, a medical emergency in which the brain shifts into any available space – usually downwards. It descends into the opening at the base of the skull, crushing the structures of the brain stem and impeding the vital functions they control, such as respiration and heart rate (Woodward and Mestecky, 2011).

EVD insertion

Hydrocephalus is temporarily treated by insertion of an EVD. Also known as an external ventriculostomy (Hammer et al, 2016), the EVD is a small soft catheter inserted directly into one of the lateral ventricles (Hickey, 2009), usually of the right hemisphere, to drain excess CSF (Fig 2). The right hemisphere is the non-dominant hemisphere for language (Grandhi et al, 2015), so insertion into the right lateral ventricle reduces the risk of language dysfunction. Box 1 lists the clinical indications for EVD insertion

fig 2 external ventricular drain

Box 1. Indicators for external ventricular drain insertion

  • Monitoring intracranial pressure
  • Treating hydrocephalus, including negative-pressure hydrocephalus, where pressure level is set below zero, correcting intracranial hypertension
  • Administering medication for intraventricular haemorrhage or ventriculitis
  • Diverting infected or bloodstained cerebrospinal fluid, preventing its absorption by the arachnoid villi
  • Treating hydrocephalus secondary to aneurysmal subarachnoid haemorrhage or a tumour

To reduce the risk of infection, the catheter is initially tunnelled a few centimetres under the scalp before entering the skull. It is then inserted into the anterior horn of the ventricle (the large C-shaped structure at the front) by drilling a small hole in the skull (burr hole) and incising the meninges. The skin incision is then sutured, the catheter is sutured to the scalp and the wound covered with a sterile occlusive dressing (Woodward et al, 2002).

Patients requiring ongoing CSF drainage will have a cerebral shunt surgically inserted. Shunts are thin tubes that drain CSF to other parts of the body such as the abdomen, heart or lung for absorption. A valve can be set at the desired pressure to allow CSF to escape whenever the pressure level is exceeded.

Monitoring CSF drainage

Outside the skull, the catheter is connected to a drainage system consisting of a collection chamber hanging from an intravenous (IV) pole attached to the bed, a pressure scale (also hanging from the IV pole) and a drainage bag (Fig 2). Stopcocks between the collection chamber and drainage bag allow control of the entry of CSF and its drainage (Fig 3).

fig 3 stopcoack positioning

The collection chamber and pressure scale hang side by side. Pressure is measured in millimetres of water pressure (cmH20). The scale includes both positive and negative measurements; zero corresponds to the pressure where the catheter enters the ventricle, and should always be horizontally level with the tragus of the patient’s ear (Fig 4) (Woodward and Waterhouse, 2009).

fig 4 ear pierced at the tragus

When the patient is lying on one side, this anatomical reference point becomes the bridge of the nose (Woodward and Mestecky, 2011). It is a key nursing responsibility to ensure that zero on the pressure scale is level with the patient’s tragus at all times (Woodward et al, 2002).

The number above (or below) the zero point is the prescribed pressure level of the EVD determined by the neurosurgical team (Woodward et al, 2002). In the patient’s brain, this pressure level corresponds to the amount of pressure that must be inside the ventricles before the CSF drains into the catheter. In the

external drainage system, it corresponds to the height at which the collection chamber hangs.

If the collection chamber hangs from a higher point, it will drain CSF from a higher pressure in the ventricles than one hanging from a lower point. The prescribed pressure level must be documented, and the collection chamber must be checked frequently to ensure it is neither too high (which would cause under-drainage of CSF) nor too low (which would cause over-drainage) (Woodward and Waterhouse, 2009).

Problems associated with EVDs

Infection

The insertion of an EVD is a highly invasive procedure and carries a significant risk of infection (Muralidharan, 2015; Chatzi et al, 2014; Wong, 2011); this risk increases the more frequently it is accessed by health professionals to obtain CSF samples (Jamjoom et al, 2017), and the longer the EVD is kept in situ (Camacho et al, 2010). Touching EVD components, such as the stopcock or drainage bag, must be an aseptic procedure and handling must be kept to a minimum (Woodward and Waterhouse, 2009).

A sterile, closed drainage system should be maintained and the entry site dressing should only be changed if it becomes soiled or loose. The neurosurgical team should be informed as soon as possible if the dressing may be wet from CSF leakage (Woodward et al, 2002) as this poses an infection risk. The drainage bag should be changed when it is three-quarters full, as too much weight could disrupt drainage (Woodward et al, 2002).

The integrity of the entire EVD system must be checked at a minimum of every four hours, and damage or disconnection of any of the components reported as an emergency. Patients must also be checked every four hours for early signs of infection such as an increase in temperature, pulse and respirations; cloudiness or debris in previously clear CSF indicates infection and should be reported to the neurosurgical team (Woodward and Waterhouse, 2009). Patients might need to be monitored more frequently depending on the stability and status of their neurological and vital observations, so this requires clinical judgement.

Over- and under-drainage

It is crucial to monitor EVDs meticulously, ensuring the zero point on the scale is horizontally level with the patient’s tragus and that the prescribed pressure level is correct. If CSF drains at a higher pressure it will cause under-drainage and lead to raised ICP, signs of which include:

  • Reduced level of consciousness indicated by a decline in Glasgow Coma Scale score;
  • New weakness in any of the limbs;
  • Headache;
  • Changes in pupil size and equality;
  • Vision changes (including double or blurred vision);
  • Oedema of the optic disc (papilloedema);
  • Changes in vital signs (Woodward and Mestecky, 2011).

Neurological and vital signs should be observed at least every four hours as above and CSF output documented hourly on a fluid balance chart (Woodward et al, 2002). Signs of under-drainage should be reported immediately to the neurosurgical team.

Equally damaging for the patient is over-drainage, which can collapse the ventricle, pulling the brain tissue away from the dura, tearing cortical veins and leading to subdural haematoma (Woodward and Waterhouse, 2009). Over-drainage can be prevented by ensuring that the CSF is not draining at a lower pressure than that set by the neurosurgeon.

Over-drainage of CSF can be caused by increased pressure inside the ventricles. Straining to pass faeces can increase intraventricular pressure, so it is important to ensure patients with EVDs maintain regular bowel habits using stool softeners. Drainage should be turned off at the collection chamber before any intervention involving patient movement, such as suctioning, walking, physiotherapy and repositioning in bed – all of which can increase intraventricular pressure.

Drainage at the collection chamber is turned off by turning the stopcock so that it points ‘north’ (upwards). It can be helpful to visualise the stopcock as obstructing CSF flow into the drainage bag when it is pointing north and associate ‘off’ with the stopcock pointing north. As soon as the intervention is finished, the stopcock should be turned to point ‘west’, turning the drainage system back on again (Fig 3). Drainage should not be turned off for longer than needed, as this can cause the catheter to block.

Early signs of over-drainage include headaches, and the neurosurgical team should be notified urgently if the rate of drainage exceeds 10ml per hour or a total of more than 30ml drains in one hour (Woodward et al, 2002).

When the patient is being transferred, the EVD system must remain in an upright position and not be left lying flat on the bed, as this will impair drainage (Woodward and Waterhouse, 2009).

Trauma and haemorrhage

Although they are life-saving devices, EVDs are not without risk. Lewis et al (2015) suggest there is a link between EVDs and delayed hydrocephalus in patients with subarachnoid haemorrhage, arguing that the drain may interrupt CSF flow and slow down clearance of debris from bleeding, which can impair CSF absorption by the arachnoid villi.

EVDs themselves can cause trauma and therefore lead to haemorrhage in the ventricles (intraventricular haemorrhage), or in functioning brain tissue (parenchymal haemorrhage) (Dash et al, 2016), as well as to aneurysm rupture (when a weakened part of a cerebral blood vessel bursts) (Muralidharan, 2015).

Placement of the drain can cause the dura mater to pull away from the overlapping skull bones and Dash et al (2016) report the case of a patient developing a haematoma above the dura (epidural haematoma) after EVD placement. Grandhi et al (2015) report a case of EVD placement causing a pseudoaneurysm (where blood collects between the two outer layers of an artery) of a major cerebral artery; they also cite evidence that EVDs can cause arteriovenous malformations (AVMs), which are abnormal connections between arteries and veins. Aneurysms and AVMs carry a major risk of rupture and bleeding.

Nurses need to be vigilant for signs of trauma, which is another reason why neurological and vital observations should be performed frequently. They also need to:

  • Alert the neurosurgical team immediately if previously clear CSF is blood-stained;
  • Cohort or provide one-to-one care to confused or agitated patients to prevent accidental removal of the EVD;
  • Regularly check that the catheter is swinging: a patent catheter will gently swing but a catheter that is not swinging at all could indicate that it is blocked by clotted blood or tissue debris;
  • Regularly check that the catheter is not kinked: this can cause a blockage.

A blocked catheter needs immediate medical attention; the neurosurgical team may need to irrigate it, remove any haematoma or remove the EVD altogether.

Due to the risks of intracranial haemorrhage (haemorrhage anywhere in the brain), prophylactic anticoagulants prescribed for deep vein thrombosis may be contraindicated in patients with an EVD in situ. Nurses must check the local policy and raise any concerns with the neurosurgical team.

Conclusion

Box 2 lists what to monitor and document, while Box 3 features a range of competencies relating to the safe care and management of patients with an EVD in situ. Although these drains can appear daunting, with an understanding of their key elements and functioning they are a rewarding aspect of patient care. 

Box 2. Monitoring and documentation

  • On pressure scale, check prescribed pressure level is correct and zero is in line with tragus
  • Document amount of cerebrospinal fluid (CSF) drained per hour on fluid balance chart
  • Check catheter is oscillating and not kinked
  • Monitor colour of CSF and alert the neurosurgical team immediately if it changes
  • Monitor clarity of CSF and alert the neurosurgical team immediately if cloudiness and/or debris appear
  • Check dressing is intact, clean and dry

Box 3. Competencies for managing patients with external ventricular drains

  • Know infection control policies about handling, monitoring and cleaning medical devices
  • Know how to assess patients for infection
  • Be able to apply principles of asepsis
  • Understand how external ventricular drains (EVDs) work and appreciate importance of maintaining alignment with tragus
  • Know the ‘on’ and ‘off’ positions of stopcock
  • Be able to identify indications for and complications of EVDs
  • Know how to manage complications
  • Be able to use the Glasgow Coma Scale to detect early neurological deterioration

Key points

  • Hydrocephalus, an excess of cerebrospinal fluid, is a medical emergency as it raises intracranial pressure
  • Excess fluid can be removed from the brain by an external ventricular drain
  • Patients with EVDs need to have cerebrospinal output monitored hourly
  • EVDs carry a high risk of infection, so nurses need to maintain asepsis and regularly assess patients
  • Assessing patients’ consciousness is crucial to identify neurological deterioration early

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