Patient Information

A common complication of many serious neurologic conditions is an elevation of the pressure within the skull, the intracranial pressure or ICP. In adults, the average ICP ranges from 0-10 mm Hg. 20 mm Hg is considered to be the maximal upper limit of desirable ICP and pressures exceeding 40 mm Hg are considered extremely elevated. Intracranial pressure may be high for several reasons. ICP can be elevated if there is a rise in the pressure of the fluid circulating around the brain (the cerebrospinal fluid). This condition is known as hydrocephalus. Alternatively, the blood vessels supplying the brain can leak fluid into the brain causing the brain to swell, a situation referred to as cerebral edema. Whatever the underlying cause an increase in intracranial pressure is extremely dangerous.

The type of monitor used is dependent on a number of clinical factors, not the least of which is the neurologic disease causing the pressure increase. The following is a list of the instruments commonly used:

• Intraventricular Catheters: These are the most widely used ICP monitoring devices. A catheter (a tubular instrument) is placed inside fluid filled cavities within the brain called ventricles. Cerebrospinal fluid is synthesized within these cavities and then flows out of the ventricles to circulate over the surface of the brain. Intraventricular catheters can be installed during brain surgery or in the ICU under local anesthesia. They are considered among the most accurate devices used to measure ICP. Intraventricular catheters also are unique in that they can simultaneously monitor and treat increased intracranial pressure. The catheter allows cerebrospinal fluid to be drained thus lowering the pressure within the skull.
• Fiberoptic Monitors: These are devices which employ fiberoptic technology to measure intracranial pressure. The fiber-optic probe has a transducer at the tip which can be inserted into the brain itself, the ventricles which it surrounds, or the subdural space. Fiber-optic monitors are easily inserted and their usage is increasing. At the Columbia Neuro-ICU, the Camino system of fiberoptic monitors is used.
• Subarachnoid Bolts: These are metallic cylindrical instruments which are inserted such that the tip protrudes into the subarachnoid space. The most common device used is the Becker bolt (also known as the Richmond screw). These devices have the advantage of being easy to instal. However, problems with accuracy have limited their use.
• Epidural Monitors: These are recording devices which are placed in the epidural space. This is a potential space between the inner surface of the skull and the dura mater.

Transcranial Doppler (TCD) monitoring devices are used to asses blood flow in vessels supplying blood to the brain. This technique is used to detect a blockage of blood flow to the brain (cerebral ischemia). Cerebral ischemia can result in a stroke. In this case blood flow is arrested by the presence of a clot in a blood vessel. Patients also can have cerebral ischemia as the result of vasospasm, the contraction of the blood vessels supplying the brain. Vasopasm of cerebral blood vessels is a common complication of a subarachnoid hemorrhage (a bleeding into the subarachnoid space between the brain and the skull). Blood vessel contraction can result in the obstruction of the lumen of the vessel, leading to cerebral ischemia and a subsequent number of disabilities. In a Neuro-ICU TCD can be used to detect vasospasm before it can give rise to deleterious effects of cerebral ischemia.

Transcranial Doppler ultrasonography operates in the following manner. TCD devices use an ultrasonic signal which penetrates areas of the skull where the bone is thinnest. Upon meeting flowing blood cells this signal is altered and reflected back to a recording device. When an artery within the skull contracts due to vasospasm the blood flow velocity within this vessel increases, an increase which can be recorded by a TCD instrument.

Unlike other techniques used to asses cerebral blood flow (CBF) a TCD monitor is non-invasive. It is completely painless, easily performed at the patient's bedside and it gives immediate results.

Single Photon Emission Computerized Tomography or SPECT is a method used to create a computer generated image of the brain in order to asses blood flow. The SPECT device generates a computer image of the brain based on its detection of photons emitted by radionuclides administered to the patient. SPECT images are of resolution comparable to that of Positron Emission Tomography (PET) scans. SPECT scans are cheaper, faster, and more accessable than PET scans.

There are specific medical conditions especially amenable to SPECT monitoring. Following stroke, SPECT can give an accurate assessment of the adequacy of blood flow to the brain and the presence of neurologic injury. SPECT can also accurately detect reductions in blood flow related to vasopasm, blood vessel contraction which is a common complication following subarachnoid hemorrhage. Lastly, SPECT is used to asses brain damage following head injury. Following head injury an area of the brain may become poorly perfused with blood. This area may not be visible on Magnetic Resonance Imaging (MRI) or Computed Tomography (CT) scans. Even subtle brain abnormalities can be picked up in head injury patients using SPECT.

There are a number of clinical situations in which the use of a SPECT machine is invaluable in assessing blood flow and associated brain damage. This makes SPECT a valued component of the Neuro-ICU's arsenal of monitoring techniques.

An electroencephalogram or EEG is a device used to measure electrical potentials in the brain by attaching electrodes to the scalp. An EEG is often employed to monitor brain wave patterns during seizures and to give critical information concerning the level of functioning of the central nervous system. A Neuro-ICU is specialized to take continuous EEG recordings. A single recording is a mere sampling and often does not accurately reflect the patient's overall condition. Continuous EEG monitoring has several advantages over a single EEG reading. A continuos EEG profile often leads the ICU staff to a correct diagnosis and gives a much better indication of the patient's prognosis. Furthermore, continuous recording allows physicians to monitor a patient's response to drug therapy as well as identify complications.

There are two clinical situations in which continuos EEG monitoring has proved especially useful. First, an EEG can accurately detect ongoing seizures in a patient with status epilepticus. Second, an EEG can provide important data on the flow of blood to the brain. Prolonged EEG recordings can detect a cessation of blood flow to part of the brain (a situation known as cerebral ischemia). Such ischemia commonly follows strokes and is extremely dangerous if not rapidly detected.

Therefore, continuos EEG monitoring is critical in establishing a correct diagnosis of the patient, predicting the outcome of the patient, assessing the patient's condition during drug therapy, and detecting problems early before they can lead to serious neurologic complications.

The Columbia-Presbyterian Neuro-ICU has available to it a group of consulting epileptologists. These are physicians who are specialized in monitoring EEGs and treating serious seizure disorders. The combination of epileptologists and continuos EEG monitoring allows the Neuro-ICU to rapidly and adeptly treat life-threatening seizure disorders.

Invasive hemodynamic monitoring refers to the assessment of blood flow and blood pressure via devices placed within blood vessels. In many medical settings these devices are used to measure circulatory function in the presence of heart or lung disease. A Neuro-ICU uses these techniques to ensure that the brain is being properly perfused with blood. The instruments used to measure circulatory function are known as catheters. Blood pressure is recorded by a fluid-filled catheter and this pressure is transmitted to a transducer which converts the information into an electrical signal visible on a monitor. There are two general techniques to monitor blood pressure:

• Arterial catheters: These are catheters placed into a major artery (such as the radial artery in the wrist or the femoral artery in the thigh) to measure blood pressure. Arterial catheterization is indicated in a Neuro-ICU setting when abnormal blood pressure threatens to compromise blood flow to the brain, exacerbate high pressure within the skull (intracranial pressure), or worsen bleeding within the skull. Low blood pressure (hypotension) can cause inadequate blood flow to the brain, especially if intracranial pressure is already elevated. High blood pressure (hypertension) can increase intracranial pressure and/or increase bleeding into the brain and surrounding compartments. Furthermore, arterial catheterization can be used in patients with neuromuscular respiratory failure, (due to myasthenia gravis or Guillain-Barré syndrome) in order to measure blood gases.
• Swann-Ganz catheters: These are catheters placed into the pulmonary artery which carries blood from the heart to the lungs to be oxygenated. A Swann-Ganz catheter has an inflatable balloon near its tip. The catheter is capable of measuring a number of clinical variables including pulmonary wedge pressure and cardiac output. Pulmonary wedge pressure is obtained when the balloon near the tip of the Swann-Ganz catheter is inflated thus "wedging" it into a branch of the artery entering the lungs. The resulting "wedge" pressure recorded is approximately equivalent to the pressure in the left atrium, that chamber of the heart into which blood flows after exiting the lungs. Cardiac output is the volume of blood ejected by the heart in a one minute period. The use of a Swann-Ganz catheter is mandated in the presence of shock due to low blood pressure. It is also recommended to asses cardiovascular status when the patient is on a mechanical ventilator. However, a Swann-Ganz is primarily used in a neuro-ICU to monitor a patient's condition during vasoactive drug therapy. Thus the Swann-Ganz catheter is used to ensure that drugs used to increase the brain's perfusion do not cause cardiovascular complications.

The brain is nourished by oxygen carried to it in the blood. Many imaging techniques can asses the blood supply to the brain but near infrared (NIR) spectroscopy is unique in being able to provide information about the amount of oxygen present in this blood supply, the cerebral oxygen saturation.

Cerebral oxygen saturation is measured by a device which emits light of a near infrared wavelength. Once in the blood the light is absorbed by the blood protein which carries oxygen, hemoglobin. The signal is then reflected back to two detectors. The signal will differ based on whether the light was absorbed by hemoglobin containing oxygen or by hemoglobin not carrying oxygen. As a result the machine is capable of determining the ratio of oxygen carrying hemoglobin to hemoglobin which is not bound to oxygen. It is this ratio which reveals the cerebral oxygen saturation.

NIR is a new technique with several technical pitfalls. NIR is currently under investigation as a potential monitoring technique for use in the neuro-ICU.

In order to understand this monitoring technique one must first have knowledge of the blood supply to the brain. The brain is supplied with oxygenated blood via the internal carotid arteries. Once blood from these vessels has perfused the brain the blood is drained back to the heart in the internal jugular veins. Jugular Venous Oxygen Saturation (SjvO2) Monitoring is the assessment of the amount of oxygen dissolved in the internal jugular vein. This is the amount of dissolved oxygen in the blood returning from the brain which was not used by the brain. As such SjvO2 monitoring records the balance of the supply of oxygen available to the brain and the brain's demand for oxygen. The knowledge of such a balance (sometimes referred to as the cerebral oxygen balance) is important as it indicates the brain's oxygen consumption. For example, a low SjvO2 value indicates that the brain needs more oxygen. This is a dangerous situation since without oxygen brain tissue dies.

Jugular venous oxygen saturation is monitored by the placement of a fiber-optic catheter into the internal jugular vein. This is a catheter (a tubular instrument) which employs fiber-optic technology to measure the amount of oxygen dissolved in a blood vessel.

Measuring SjvO2 is currently investigational but may be useful in certain clinical settings. For instance, studies have shown that during a cardiopulmonary bypass operation jugular venous oxygen saturation monitoring can be useful to detect cerebral oxygen deprivation. In addition SjvO2 monitoring can be used to detect cerebral oxygen deprivation following head injury. It is common for the brain to be deprived of oxygen following head injury. A SjvO2 monitoring device can detect such deprivation before it can give rise to permanent and severe neurological injury.

A form of stroke commonly managed in a Neuro-ICU is subarachnoid hemorrhage, a bleeding into the subarachnoid space between the brain and the skull. This bleeding usually occurs as the result of the rupture of a brain aneurysm. A brain aneurysm is a swelling or ballooning of a small segment of an artery in the brain. Unfortunately such aneurysms commonly rupture a second time, resulting in a dangerous rebleeding of the brain aneurysm. Endovascular GDC Coils are small, stainless steel platinum coils which are placed inside the lumen of a brain aneurysm. The coils are packed inside the swollen portion of the artery until the aneurysm sac is completely filled with coils. Essentially, these coils act as a blood clot (or thrombus) which prevents blood from flowing into the aneurysm. Also, the metallic coils are coated with thrombogenic fibers to aid in clot formation. The aneurysm is thus prevented from bursting a second time and causing a rebleed.

GDC coils are placed within an aneurysm via an endovascular route, i.e. by passing a catheter (a tubular instrument) into certain blood vessels until the vessel containing the aneurysm is reached. The coils themselves are situated at the tip of the catheter. Once the coils have reached the aneurysm an electrical current is sent along a wire within the catheter causing the coils to detach from the rest of the instrument, thus packing them inside the aneurysm. The size and the shape of brain aneurysms vary; accordingly there are different coil shapes and sizes. In addition, the safety and efficacy of these devices is augmented by the fact that the coils easily deform to the shape of the aneurysm. This procedure can be complicated by the blockage a healthy blood vessel. To prevent this the anticoagulant heparin is given while the coils are installed.

The alternative to endovascular coil treatment is the surgical "clipping" of brain aneurysms. Such surgical resection of the aneurysm is very effective. However, surgery may be dangerous in certain patients. A patient may not be in a good enough condition to withstand the operation. Also, the size and location of the aneurysm may make it surgically inaccessible. Therefore, the occlusion of a brain aneurysm with endovascular GDC coils is a safe and efficient way of preventing a rebleeding of the aneurysm when surgical removal of the aneurysm is not advised.

Over the past twenty years, elevation of blood pressure with intravenous medications and administration of large volumes of intravenous fluids (a.k.a. hypertensive hypervolemic hemodilution or "triple-H therapy") has become the principle method for treating ischemic neurologic deficits from vasospasm after subarachnoid hemorrhage. This treatment improves cerebral blood flow in regions of ischemia by three mechanisms: (a) elevation of blood pressure, (b) elevation of cardiac output and total blood volume, and (c) reduction of blood viscosity. All three of these factors serve to "drive" blood flow through and around blocked arteries, which in turn can lead to immediate reversal of symptoms. Application of triple-H therapy has also been described for patients with ischemic stroke, and may be particularly useful in patients with high-grade stenosis or occlusion of the carotid artery and distal perfusion failure. Familiarity with application of this technique in a neuro-ICU setting is essential, as is invasive hemodynamic monitoring of blood pressure and cardiac output, which serves to guide treatment and minimize complications. Dopamine, phenylephrine or norepinephrine is most often used to raise blood pressure, and protein-rich fluid (colloid) is often used to increase the patients blood volume. Excessive strain on the heart (myocardial ischemia) or fluid overload (pulmonary edema), the most important potential complications, can be avoided with careful hemodynamic monitoring.

A stroke is commonly the result of a blockage of blood flow to the brain, a condition known as cerebral ischemia. Blood flow is interrupted in a vessel by the presence of a blood clot (or thrombus) in that vessel. Such clots can cause an ischemic stroke (if the clot occludes an artery in the brain) or a deep venous thrombosis (if a vessel draining blood from the brain is blocked). Thrombolysis is the use of drugs to restore proper flow in an artery by disrupting a clot (thrombo= clot; lysis= breaking).

There are two general categories of medications used in thrombolysis: those injected into the arterial circulation (intraarterial agents) and those injected into the venous circulation (intravenous agents). The intraarterial agents include the drugs urokinase (an enzyme produced by the kidney) and streptokinase (produced by bacteria). These agents work by activating the protein plasmin. Plasmin then serves to degrade the protein which comprises blood clots - fibrin. The intravenous thrombolytic agents include a recently developed drug known as tissue plasminogen activator (t-PA). Like streptokinase and urokinase, t-PA works by promoting the formation of plasmin, thereby disrupting fibrin clots. Once a clot is so degraded blood flow can be restored and the brain can once more be adequately perfused.

It is important that thrombolytic therapy begin within three hours of the onset of a stroke. Studies have shown that when administered in that "therapeutic window" t-PA can be extremely efficient at restoring blood flow. If delayed, however, such treatment can result in dangerous hemorrhaging. Therefore, the rapid administration of t-PA and related thrombolytics can vastly improve outcome following stroke by disrupting blood clots and thereby reperfusing the brain with blood, but only if given within a narrow timeframe. The one exception to this rule may be administration of intra-arterial thrombolytics for treatment of an evolving basilar artery occlusion.

Neuromuscular diseases are characterized by muscle weakness and fatigability. If this weakness affects the muscles of respiration then a patient's breathing can be dangerously compromised. Myasthenia Gravis and Guillain-Barré syndrome are the two most common neuromuscular diseases. Both disorders are caused by the presence of antibodies in the bloodstream which are directed against part of the neuromuscular system. In the case of myasthenia gravis the antibodies are directed against the nerve-muscle junction, and in Guillain-Barré syndrome antibodies become directed against the lipid (myelin) sheath which insulates nerves.

To treat these illnesses a Neuro-ICU employs the technology of plasmaphoresis. Plasmaphoresis is the process of removing blood from the body, separating out the cellular elements of the blood, resuspending these cellular elements in a plasma substitute, and then reinfusing this mixture into the body. Most plasmaphoresis machines are continuous flow devices. This means blood continuously flows into the machine and the cellular elements are separated from the plasma by centrifugation and resuspended in a plasma substitute. This mixture is reinfused into the patient at a rate that equals that at which blood is removed. The purpose of this technique is to "cleanse" the blood of the antibodies which are responsible for the muscle fatigue. Thus plasmaphoresis is an effective technique of relieving the symptoms of muscle weakness and fatigue which accompany certain neuromuscular disorders.

Lowering of brain temperature is an effective method for "protecting" brain cells from death due to trauma or lack of blood flow and oxygen. The application of therapeutic hypothermia has recently been rediscovered as a method for improving outcome after severe traumatic brain injury, and is currently under investigation as a treatment for severe ischemic stroke or brain hemorrhage.

Most studies have shown that lowering of brain temperature to a safe level (approximately 32 to 33 degrees centigrade) requires cooling of the entire body with cooling blankets and iced saline lavaged into the stomach. The patient must be paralyzed to prevent shivering, which counteracts the cooling process and leads to metabolic complications. Since paralysis leads to loss of the ability to perform neurologic examinations, most patients require placement of a fiberoptic intracranial pressure monitor that has been configured to simultaneously measure brain temperature.

Hypothermia was tested and abonded as a treatment for severe brain injury in the 1940's and 1950's because it was felt to be unsafe. Complications of hypothermia can include cardiac arrythmia, increased susceptibility to infections, thinning of the blood, and a variety of metabolic disturbances (e.g. low potassium, high glucose). However, with present technology and careful application and monitoring in a Neuro-ICU, moderate systemic hypothermia can be safely administered. In one recent study, hypothermia was reported to be the first direct treatment to improve outcome after severe traumatic brain injury. Further studies are required to establish the efficacy of this treatment for severe stroke.

A Neuro-ICU employs a variety of innovative drug therapies which have proven useful in treating serious neurological illness. Pentobarbital and Propofol are two medications which are specialized for the management of patients in a neurological critical care unit:

Pentobarbital. This drug is one member of a group of agents known as barbiturates. Like other barbiturates, pentobarbital acts to depress functioning of the central nervous system. It can thus act to alter mood, to sedate, or even to induce coma. Pentobarbital is used in two separate situations in a neuro-ICU setting. The first situation is to treat a severe seizure disorder known as status epilepticus. Status epilepticus is defined as a seizure disorder lasting over thirty minutes. Longer lasting seizures are treated with a variety of medications. If the seizure is prolonged for over thirty minutes barbiturate therapy is instituted. First the barbiturate phenobarbital is used. If this proves ineffectual the patient is considered to be in "refractory status epilepticus" and pentobarbital treatment is employed.

• Pentobarbital is also used to treat an increase in the pressure within the skull, the intracranial pressure. Increased intracranial pressure is a common and very dangerous complication of many neurological conditions. Most commonly pentobarbital is used to decrease high intracranial pressure following head trauma. Pentobarbital lowers intracranial pressure by decreasing brain metabolism, the brain's use of oxygen, and the amount of blood perfusing the brain. Pentobarbital has the side effect of markedly reducing blood pressure. As a result medications which increase blood pressure (known as pressors) are often required when pentobarbital is used.
• Propofol. This drug is an intravenously administered anesthetic which is used in the operating room or intensive care unit setting. It is used to continuously sedate patients who are agitated following stroke or head trauma. To administer this drug the expertise of individuals skilled in the use of anesthetics is required. It is also required that a patient given this drug be on a mechanical ventilator to ensure proper breathing. Propofol has several advantages over conventionally used sedatives. It is rapidly acting, and smoothly induces hypnotic states with minimal excitation. Furthermore, patients wake up immediately after the use of propofol is discontinued. Therefore, propofol can quickly and efficiently sedate agitated critically ill patients in a Neuro-ICU, setting, making these patients more manageable and thus facilitating their treatment.

A stroke is commonly the result of a blockage of blood flow to the brain, a condition known as cerebral ischemia. If the blood flow is stopped temporarily a patient experiences a transient ischemic attack or TIA. Cerebral ischemia can be due to a narrowing (stenosis) of a blood vessel supplying the brain. Stenosis is commonly the result of atherosclerotic plaque building up on the walls of a vessel. If a vessel is narrowed by the presence of plaque a blot clot (or thrombus) can become lodged in that vessel, halting blood flow.

An operation known as percutaneous cerebral angioplasty can be performed to dilate the lumen of stenotic blood vessels. This operation is usually performed on the internal carotid artery, an artery in the neck which supplies blood to the brain. This procedure, performed by an interventional neuroradiologist, involves the placement of a small balloon in the area where the blood vessel is narrowed. The balloon is introduced on the tip of an angiographic catheter (a tubular instrument), which is passed through the circulatory tree until the stenotic region of the internal carotid artery is reached. Once there the balloon is inflated, thereby causing the vessel to dilate and improving blood flow to the brain.

In most cases, angioplasty is reserved for patients with multiple TIAs or small strokes related to stenosis of a cerebral blood vessel who have not responded completely to maximal medical therapy with blood thinners.

A common complication of many serious neurological conditions is an elevation of the pressure within the skull, the intracranial pressure or ICP. High intracranial pressure can accompany stroke, head injury, brain infections, and brain tumors. Intracranial pressure may be high for several reasons. ICP can be elevated if there is a rise in the pressure of the fluid circulating around the brain (the cerebrospinal fluid)-this condition is known as hydrocephalus. Alternatively, the blood vessels supplying the brain can leak fluid into the brain substance. This can cause the brain to swell with fluid, a situation referred to as cerebral edema. Whatever the underlying cause, however, an increase in intracranial pressure is extremely dangerous. High intracranial pressure can cause the compression of blood vessels supplying the brain resulting in a cessation of blood flow to the brain (cerebral ischemia). If blood flow to part of the brain is interrupted that part of the brain can die. In addition, increased intracranial pressure can cause the compression of the brain stem by the overlying brain hemispheres. Since the brain stem controls such basic body functions as respiration, heart rate, and arousal this compression can cause a loss of consciousness or even death.

A Neuro-ICU is highly specialized for the treatment of high ICP. The mainstay of such treatment is the installment of intraventricular catheters. A catheter (a tubular instrument) is placed inside fluid filled cavities within the brain called ventricles. Cerebrospinal fluid is synthesized within these cavities and then flows out of the ventricles to circulate over the surface of the brain. Intraventricular catheters allow cerebrospinal fluid to be drained from the ventricles, thus lowering the pressure within the skull. These instruments can be installed during brain surgery or in the Neuro-ICU under local anesthesia.

Intraventricular catheters are ideal treatment devices for increased intracranial pressure. Because they drain cerebrospinal fluid this fluid can be analyzed for the presence of blood or infectious agents. Also, these catheters can measure intracranial pressure, in addition to being able to reduce it. In fact, the intraventricular catheter is the device most commonly used to measure intracranial pressure. Therefore intraventricular catheters, unique to a Neuro-ICU environment, are safe and efficient instruments that can both monitor and reduce intracranial pressure.