External ventricular drain
An external ventricular drain (EVD), also known as an extraventricular drain or ventriculostomy, is a device used in neurosurgery that relieves elevated intracranial pressure and hydrocephalus when the normal flow of cerebrospinal fluid around the brain is obstructed. This is a plastic tube placed by neurosurgeons, neurologists or neurointensivists and managed by ICU nurses and Critical Care Paramedics to drain fluid from the ventricles of the brain and thus keep them decompressed, as well as to monitor intracranial pressure.
The tube is most frequently placed in Kocher's point with the goal of having the catheter tip in the frontal horn of a lateral ventricle. The catheter is normally inserted on the right side of the brain. An EVD (also called an intraventricular catheter, or IVC) is used to monitor pressure in patients with brain injuries, intracranial bleeds or other brain abnormalities that lead to increased fluid build-up. In draining the ventricle it can also remove blood from the ventricular spaces. This is important because blood is an irritant to brain tissue and can cause complications such as vasospasm.
Care of the Patient with an External Ventricular Drain
The external ventricular drain (EVD) is leveled to a common reference point, usually the tragus. The external ventricular drain is set on a graduated burette the pressure level of the EVD is prescribed by a healthcare professional, usually a neurosurgeon. Leveling the EVD to a set pressure level is the basis for cerebrospinal fluid (CSF) drainage, hydrostatic pressure dictates CSF drainage. The fluid column pressure must be greater than the weight of the CSF in the system before drainage occurs. It is 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: Level external ventricular drain to 15 cmH20 above midbrain, open to drain continuously, check and record cerebrospinal fluid drainage and intracranial pressure every hour.
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 intracranial pressure and mean arterial pressure (MAP) must be available.
If the EVD becomes occluded, clogged, or obstructed, as it often does with fibrinous or clot like material, the brain can swell due to pressure build up in the ventricles and permanent brain damage can occur. Physicians, nurses, and Critical Care Paramedics often have to adjust or flush these small diameter catheters to manage medical tube obstructions and occlusions at the intensive-care bedside. Pressure settings are generally measured in cmH2O. The equilibrium pressure of the EVD apparatus is adjusted based on cerebrospinal fluid output, ICP waveform, imaging including CT or MRI of the brain, and clinical response.
- "Care of the Patient Undergoing Intracranial Pressure Monitoring/ External Ventricular Drainage or Lumbar Drainage". AANN Clinical Practice Guideline Series. American Association of Neuroscience Nurses. Retrieved 23 October 2012.
- Kakarla UK, Kim LJ, Chang SW, Theodore N, Spetzler RF (2008). "Safety and accuracy of bedside external ventricular drain placement.". Neurosurgery 63 (1 Suppl 1): ONS162–6; discussion ONS166–7. doi:10.1227/01.neu.0000335031.23521.d0. PMID 18728595.