An external ventricular drain (EVD), also known as a ventriculostomy or extraventricular drain, is a device used in

neurosurgery Neurosurgery or neurological surgery, known in common parlance as brain surgery, is the specialty (medicine), medical specialty that focuses on the surgical treatment or rehabilitation of disorders which affect any portion of the nervous system ...

to treat

hydrocephalus Hydrocephalus is a condition in which cerebrospinal fluid (CSF) builds up within the brain, which can cause pressure to increase in the skull. Symptoms may vary according to age. Headaches and double vision are common. Elderly adults with n ...

and relieve elevated

intracranial pressure Intracranial pressure (ICP) is the pressure exerted by fluids such as cerebrospinal fluid (CSF) inside the skull and on the brain tissue. ICP is measured in millimeters of mercury ( mmHg) and at rest, is normally 7–15 mmHg for a supine adu ...

when the normal flow of

cerebrospinal fluid Cerebrospinal fluid (CSF) is a clear, colorless Extracellular fluid#Transcellular fluid, transcellular body fluid found within the meninges, meningeal tissue that surrounds the vertebrate brain and spinal cord, and in the ventricular system, ven ...

(CSF) inside the

brain The brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It consists of nervous tissue and is typically located in the head (cephalization), usually near organs for ...

is obstructed. An EVD is a flexible plastic catheter placed by a

neurosurgeon Neurosurgery or neurological surgery, known in common parlance as brain surgery, is the medical specialty that focuses on the surgical treatment or rehabilitation of disorders which affect any portion of the nervous system including the brain, ...

or neurointensivist and managed by

intensive care unit An intensive care unit (ICU), also known as an intensive therapy unit or intensive treatment unit (ITU) or critical care unit (CCU), is a special department of a hospital or health care facility that provides intensive care medicine. An inten ...

(ICU) physicians and nurses. The purpose of external ventricular drainage is to divert fluid from the ventricles of the brain and allow for monitoring of

. An EVD must be placed in a center with full neurosurgical capabilities, because immediate neurosurgical intervention can be needed if a complication of EVD placement, such as bleeding, is encountered. EVDs are a short-term solution to hydrocephalus, and if the underlying hydrocephalus does not eventually resolve, it may be necessary to convert the EVD to a cerebral shunt, which is a fully internalized, long-term treatment for hydrocephalus.

EVD placement

The EVD catheter is most frequently placed by way of a twist-drill craniostomy placed at Kocher's point, a location in the

frontal bone In the human skull, the frontal bone or sincipital bone is an unpaired bone which consists of two portions.'' Gray's Anatomy'' (1918) These are the vertically oriented squamous part, and the horizontally oriented orbital part, making up the bo ...

of the skull, with the goal of placing the catheter tip in the frontal horn of the

lateral ventricle The lateral ventricles are the two largest ventricular system, ventricles of the brain and contain cerebrospinal fluid. Each cerebral hemisphere contains a lateral ventricle, known as the left or right lateral ventricle, respectively. Each later ...

or in the

third ventricle The third ventricle is one of the four connected cerebral ventricles of the ventricular system within the mammalian brain. It is a slit-like cavity formed in the diencephalon between the two thalami, in the midline between the right and lef ...

. The catheter is typically inserted on the right side of the brain, but in some cases a left-sided approach is used, and in other situations catheters are needed on both sides. EVDs can be used to monitor intracranial pressure in patients with

traumatic brain injury A traumatic brain injury (TBI), also known as an intracranial injury, is an injury to the brain caused by an external force. TBI can be classified based on severity ranging from mild traumatic brain injury (mTBI/concussion) to severe traumati ...

(TBI),

subarachnoid hemorrhage Subarachnoid hemorrhage (SAH) is bleeding into the subarachnoid space—the area between the arachnoid (brain), arachnoid membrane and the pia mater surrounding the human brain, brain. Symptoms may include a thunderclap headache, severe heada ...

(SAH),

intracerebral hemorrhage Intracerebral hemorrhage (ICH), also known as hemorrhagic stroke, is a sudden bleeding into Intraparenchymal hemorrhage, the tissues of the brain (i.e. the parenchyma), into its Intraventricular hemorrhage, ventricles, or into both. An ICH is ...

(ICH), or other brain abnormalities that lead to increased CSF build-up. In draining the ventricle, the EVD can also remove blood products from the ventricular spaces. This is important because blood is an irritant to brain tissue and can cause complications such as

vasospasm Vasospasm refers to a condition in which an arterial spasm leads to vasoconstriction. This can lead to tissue ischemia (insufficient blood flow) and tissue death (necrosis). Along with physical resistance, vasospasm is a main cause of ischemi ...

Ongoing care

The EVD is leveled to a common reference point that corresponds to the skull base, usually the tragus or

external auditory meatus The ear canal (external acoustic meatus, external auditory meatus, EAM) is a pathway running from the outer ear to the middle ear. The adult human ear canal extends from the auricle to the eardrum and is about in length and in diameter. Str ...

. The EVD is set to drain into a closed, graduated burette at a height corresponding to a particular pressure level, as prescribed by a healthcare professional, usually a

or neurointensivist. Leveling the EVD to a set pressure level is the basis for

(CSF) drainage;

hydrostatic pressure Hydrostatics is the branch of fluid mechanics that studies fluids at hydrostatic equilibrium and "the pressure in a fluid or exerted by a fluid on an immersed body". The word "hydrostatics" is sometimes used to refer specifically to water and o ...

dictates CSF drainage. The fluid column pressure must be greater than the weight of the CSF in the system before drainage occurs. It is therefore important that family members and visitors understand the patient's head of bed position cannot be changed without assistance. An example of a healthcare provider order regarding an EVD is: set EVD to drain CSF for ICP > 15 mm Hg, check and record cerebrospinal fluid drainage and

at least hourly. Continuous CSF drainage is associated with a higher risk of complications. The cerebral perfusion pressure (CPP) can be calculated from data obtained from the EVD and systemic blood pressure. In order to calculate the CPP the

and

mean arterial pressure In medicine, the mean arterial pressure (MAP) is an average calculated blood pressure in an individual during a single cardiac cycle. Although methods of estimating MAP vary, a common calculation is to take one-third of the pulse pressure (the d ...

(MAP) must be available.

CPP=MAP-ICP

Other areas that should be monitored are: signs and symptoms of intracranial hypertension, looking for any leaks in the EVD system to prevent infection from entering the brain, and changes in the amount and color of the CSF. A sudden increase in hourly output of CSF may indicate intracranial hypertension, bloody CSF may indicate recurrent aneurysm rupture, and cloudy CSF may indicate brain infection.

Complications

EVD placement is an invasive procedure. It is associated with several potential complications:

Bleeding

Bleeding can occur along the EVD insertion tract or in the several layers of the meninges that prohibit passage into the brain. If drilling or dural puncture is not successful, the surgeon may dissect away dura and create a secondary bleed known as an epidural or subdural hemorrhage. Bleeding from EVD placement can be life-threatening and can require neurosurgical intervention in some cases. The risk of hemorrhage with EVD placement is increased if the patient suffers from

coagulopathy Coagulopathy (also called a bleeding disorder) is a condition in which the blood's ability to coagulate (form clots) is impaired. This condition can cause a tendency toward prolonged or excessive bleeding ( bleeding diathesis), which may occur s ...

Mechanical

Mechanical complications from EVD placement can be categorized into: *Malplacement Malplacement of the EVD tube into the brain tissue instead of ventricles can occur in 10 to 40% of the cases. Therefore, computed tomography (CT), ultrasound, endoscopy, and stereotactic neuronavigation are used to minimize placement errors of EVD tubes. *Obstruction Obstruction/occlusion of EVD commonly due to fibrinous/clot like material or kinking of the tube. The brain can swell due to pressure build up in the ventricles and permanent brain damage can occur. Physicians or nurses may have to adjust or flush these small diameter catheters to manage medical tube obstructions and occlusions at the intensive-care bedside. *Migration After EVD placement, the drain is tunneled subcutaneously and secured with

surgical suture A surgical suture, also known as a stitch or stitches, is a medical device used to hold Tissue (biology), body tissues together and approximate wound edges after an injury or surgery. Application generally involves using a Sewing needle, needle w ...

s and/or

surgical staple Surgical staples are specialized Staple (fastener), staples used in surgery in place of surgical suture, sutures to close skin wounds or to resection (surgery), resect and/or anastomosis, connect parts of an Organ (biology), organ (e.g. bowels, ...

s. However, it is possible for the EVD to dislodge or migrate. This will cause the tip of the drain to migrate away from its intended position and provide inaccurate ICP measurement or lead to occlusion of the drain.

Infection

The EVD is a foreign body inserted into the brain, and as such it represents a potential portal for serious infection. Historically, the rate of infections associated with EVDs has been very high, ranging from 5% to > 20%. Infections associated with EVDs can progress to become a severe form of brain infection known as

ventriculitis Ventriculitis, also known as ependymitis, ventricular empyema, pyocephalus, and pyogenic ventriculitis, is the inflammation of the ventricles in the brain. The ventricles are responsible for containing and circulating cerebrospinal fluid through ...

. Protocols designed to reduce the rate of EVD infections have been successful, applying

infection control Infection prevention and control (IPC) is the discipline concerned with preventing healthcare-associated infections; a practical rather than academic sub-discipline of epidemiology. In Northern Europe, infection prevention and control is expande ...

'bundle' approaches to reduce the rate of infection to well less than 1%.

Neurological

Although neurological deficits from passing the EVD catheter across the brain are uncommon, there can be an association of a patient's poor neurological status with EVD malplacement. In one report, the EVD was inserted too deeply into the fourth ventricle; the authors hypothesized that the patient's coma was due to irritation of the recticular activating system. The patient's level of consciousness improved after the EVD was adjusted.

References

{{reflist Medical drains Neurosurgery