Abstract:
A wearable EVD system having a ventricular catheter and transducer supported proximately to a patient&#39;s ear by a mount, such as supporting headband or ear clip. An adjustable orifice valve or a spring-loaded needle valve is used to control the amount of CSF that drains into a drip chamber suspended on the patient for periodic measurement and emptying into a similarly located drainage bag, thereby avoiding the need for an IV pole and allowing the patient more mobility without disrupting drainage of CSF.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to external ventricular drain systems and, more particularly, to a wearable external ventricular drain system. 
     2. Description of the Related Art 
     Hydrocephalus is a medical condition characterized by an excess accumulation of fluid in the brain. It results in increased intracranial pressure (“ICP”) and can cause severe brain damage or death if the pressure is not relieved. An external ventricular drain (“EVD”) is used to drain excess cerebrospinal fluid (“CSF”) in cases of temporary hydrocephalus such as brain hemorrhage and shunt malfunction in order to provide a therapeutic reduction in ICP. 
     The currently existing EVD system consists of a thin soft tube (ventricular catheter) that is inserted under sterile procedure into the ventricle of the brain. The distal end of the ventricular catheter is connected to the EVD tubing which leads to a drip chamber with an adjustable height that is mounted to a frame. This tubing is rigid in order to prevent damping of pressure pulsation coming from the brain. On the frame of the EVD are pressure markings and the system is leveled to the patient&#39;s ventricle at the level of zero pressure by adjusting the system height vertically to set the zero level of the system level with the patient&#39;s ventricles. 
     The drip chamber has volume markings to allow for recording of the amount of fluid collected per time increment (typically hourly) and is emptied into a larger bag using a three-way stopcock after the output has been recorded. The tubing between the ventricle and the drip chamber generally includes a port that can be used for sampling CSF. A three-way stopcock connects the tubing to the drip chamber so the drain can be closed off from draining entirely, or allow for pressure measurement without draining fluid. 
     A pressure transducer may be connected to the system before the drip chamber at the level of the patient&#39;s ventricle (zero pressure mark on the EVD) to measure the pressure in the brain when the drain is closed. The entire EVD system is mounted on an intravenous drip (“IV”) pole where the EVD system can be raised and lowered as needed to maintain level with the ventricle. The pressure transducer is kept at a position that is level with the patient&#39;s ventricle and is connected to one branch of a three way stopcock. The reason for this connection is that the true pressure in the brain can only be measured when CSF flow is stopped (valve closed to drainage). The rigid tubing between the patient&#39;s brain and the pressure transducer does not affect the pressure reading, as it is an extension of the rigid cranial compartment. The transducer connects wirelessly or via cable to a monitor. The monitor generally displays an average ICP along with a pressure waveform. In the ICU setting, the nurse on call must be able to view an ICP waveform while draining CSF (valve open to pressure transducer, and to flow), or while the drain is closed. 
     The greatest issue with the current EVD system is that the zero level of the drain must be level with the patient&#39;s ventricle at all times. If the drain is not level with the patient&#39;s ventricle, more or less back pressure will be applied to the brain, and thus more or less CSF than desired will flow into the drip chamber. This requirement causes decreased safety to the patient and increased nursing time necessary to level the drain, as patients are prone to frequently adjusting the positions and elevations of their heads. 
     For example, many ICU patients with hydrocephalus have neurological deficits and cannot always remember that they have an EVD. These patients are likely to sit up quickly, which results in over-drainage of CSF into the EVD. Over-drainage can be very hazardous to the patient, possibly causing increased headache, collapse of ventricles, decreased cerebral perfusion, hemorrhage, and death. In addition, if the patient adjusts his/her bed from an elevated position to a horizontal position, under-drainage of CSF would occur. Under-drainage of CSF can lead to a dangerous over-accumulation of fluid in the brain, possibly causing headaches, nausea, brain damage, brain herniation, and death. 
     Conventional EVD systems thus result in decreased mobility and independence for ICU patients, which lead to poorer outcomes and loss of function while the patients are hospitalized. Brain bleeds and shunt infections may require the patient to be tethered to an EVD for a period of weeks. Each EVD patient must be closely visually monitored so that that the nurse can intervene as soon as the patient moves. Mobile ICU patients must ring their call bells each time they want to move so that the nurses can close and readjust the height of their EVD systems in order to maintain the zero levels of their EVDs relative to the patients&#39; ventricles. Only properly trained nurses can adjust the EVD drain, so this requirement prevents other health care workers or family members from being able to assist the patients to reposition their heads, or move about the room or hospital. 
     Additionally, as a patient recovers, the patient&#39;s treatment may include physical therapy, which requires the patient to leave the bed. The patient or nurse then must bring the EVD, which is attached to an IV pole, and its lengthy tubing along with the patient. This procedure adds the risk of the patient tripping, and limits the amount of time that the patient can be out of the bed, since the EVD must be adjusted or turned off and closely monitored in order for the patient to stand. 
     BRIEF SUMMARY OF THE INVENTION 
     It is therefore a principal object and advantage of the present invention to provide an EVD system that results in increased mobility and independence for ICU patients, thus leading to better outcomes and increases of function while the patients are hospitalized. 
     In accordance with the foregoing objects and advantages, the present invention comprises a wearable EVD system having a ventricular catheter that is placed in the ventricle of the brain to drain CSF and a valve located in line with the patient&#39;s ear. A transducer may be also provided level with the patient&#39;s ventricle and connected to a monitor that continuously or periodically measures the intracranial pressure. The valve and transducer are firmly secured at the level of the ventricle with a support headband and/or ear clip. The valve may be either an adjustable orifice valve or a spring-loaded needle valve or any other adjustable valve. CSF that drains through the valve is collected in the drip chamber for periodic measurement and then emptied into the drainage bag. In a simpler embodiment, the CSF can collect directly into the drainage bag and the drip chamber may be left out. The drip chamber and drainage may be attached to the patient inferior to the cranium via securement straps. As a result, no IV pole is needed and a patient is free to sit up or move about while the EVD system is in place without disrupting drainage of CSF, eliminating the potential for patient harm. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S) 
       The present invention will be more fully understood and appreciated by reading the following Detailed Description in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a schematic of a wearable external ventricular drain system according to the present invention; 
         FIG. 2  is a schematic of an adjustable needle valve for a wearable external ventricular drain system according to the present invention; and 
         FIG. 3  is a schematic of an adjustable orifice valve for a wearable external ventricular drain system according to the present invention. 
         FIG. 4  illustrates a cylinder of an exemplary orifice valve. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings, wherein like reference numbers refer to like parts throughout, there is seen in  FIG. 1  a wearable EVD system  10  comprising a ventricular catheter  12  that is placed in the ventricle of the brain to drain CSF. The amount of CSF drained is determined by a valve  14  which must be located at the level of the patient&#39;s ventricle. A transducer  16  may also be provided in this location and connected to a monitor that continuously measures the intracranial pressure. Alternatively, various other sensors may be used, such as a flow sensor or a glucose sensor, and or combinations thereof. Valve  14  and transducer  16  are firmly secured at the level of the ventricle with a support headband  18  and/or an ear clip  20 . The headband and ear clip can be used independently, though used together provide the most secure fastening device. Head band  18  and/or ear clip  20 , which may be flexible, hold the valve  14 , and optionally, pressure transducer  16  and an array of sensors conducting measurements on the CSF at the level of the patient&#39;s ventricle. 
     Valve  14  is preferably an adjustable orifice valve or a spring-loaded needle valve as exampled in more detail below. CSF that drains through valve  14  is passed through drain tubing  22  and optionally collected in a drip chamber  24  which is attached via a removable connector (such as hook and loop, or a pocket) to the front of a securement strap  26 . The collection of fluid in drip chamber  24  may be periodically measured and then emptied into a drainage bag  28  via a three-way stopcock (not shown). Drainage bag  28  is attached to a horizontal portion of securement strap  26  also using a removable connection so that the drainage bag can be changed when full. The securement strap  26  is adjustable and can be easily removed or adjusted to fit patients of any size. Drainage bag  28  can optionally be hung on the side of a bed when the patient is in bed or it may be attached to a patient, such as by a securement strap, when the patient is mobile. 
     Proposed wearable EVD system  10  thus relocates the system from the IV pole and attaches the system to the patient. Transducer  16  and drain tubing  22  is attached to the head of a patient at the same level as the ventricles within the brain. System  10  thus allows the patient to move as he/she pleases (within the constraint placed by the length of the cable extending from the pressure transducer, if used) without the risk of over or under draining CSF through system  10 . Transducer  16  may be provided with wireless capabilities to interface with a remote monitoring system or attached via a data line. For example, some existing ICU monitors are wireless and thus transducer  16  could be wireless to interface with this system. Regardless, a patient may be untethered from a monitor. 
     Valve  14  is preferably adjustable to control the flow of CSF from the patient&#39;s ventricles, which is a departure from conventional EVD systems that use hydrostatic pressure to create back pressure on the flow of the CSF from the ventricle so that when the drain is raised, the ICP must overcome the hydrostatic pressure of the drain before CSF flow will occur. System  10  includes an adjustable valve  14  that may be located on or near the ear piece and/or headband to provide the necessary back pressure, which may be adjusted based on a physician&#39;s orders. Valve  14  thus provides the necessary back pressure to the patient&#39;s ventricles, which will properly regulate drainage. Valve  14  may include a check valve portion, in the needle valve embodiment discussed below, to prevent retrograde flow into the brain. By contrast, an orifice type version of valve  14  would provide restriction to retrograde flow based on its setting and would minimize the effect of retrograde flow of CSF to the ventricles. 
     The present invention encompasses at least three embodiments for valve  14 , although one or more alternative valves may be employed instead. As seen in  FIG. 2 , the first embodiment of valve  14  is an adjustable, spring-loaded needle valve. Needle valves are capable of sensitive adjustments and high degrees of attainable resolution. This high resolution is critical, since using the device necessitates operating within a small pressure range. A needle valve according to the present invention is preferably adjustable from 0-30 mmHg in increments of 1 mmHg. Needle valve  30  comprises an adjustment knob  32  having advancement threads  34  for advancing or retracting a needle in the flow path having a fluid inlet  38  and a fluid outlet  40 . As further seen in  FIG. 2 , needle  36  is adapted to engage a needle seat  42  positioned between fluid inlet  38  and fluid outlet  40 , thereby adjusting the amount of fluid that can flow from fluid inlet  38  to fluid outlet  40 . When needle  36  is positioned far away from needle seat  42 , there will be little to no back pressure toward fluid inlet  38 . As needle  36  approaches needle seat  42 , there will be greater back pressure created by the flow restriction. Once the needle is in contact with the seat, the ICP must overcome the adjustable spring force in order to open the valve. Needle  26  can have either a flat, rounded, or a tapered bottom, although a tapered bottom allows for more surface area and provides for a finer adjustment due to increased surface area. 
     In a further embodiment of a needle style valve, needle  36  may comprise an adjustment rod  43  that is interconnected to needle  36  via a retainer clip  44  and retainer screw  46 . Adjustment rod  43  is further interconnected to needle  36  and a spring  48  positioned within a housing  49  that abuts against a compression plate  47  positioned along rod  43 . By rotating adjustment knob  32 , needle  36  is advanced or retracted and held in position by needle advancement threads  34 . Needle  36  may be advanced toward needle seat  42  in order to provide some back pressure toward fluid inlet  38 . When engaged, spring  48  makes adjustment of the back pressure more sensitive by exerting a known force on the needle toward the needle seat. Any fluid passing into the inlet will have to overcome this force to lift needle  36  against the bias of spring  48  in order to pass through the fluid outlet. 
     The second embodiment of valve  14  comprises an orifice valve  50  that is adjustable both in diameter and length. The back pressure provided by an orifice is provided by both its diameter and its length according to the Hagen-Poiseuille equation: 
               Δ   ⁢           ⁢   P     =       8   ⁢   μ   ⁢           ⁢   LQ       π   ⁢           ⁢     r   4               
As seen in  FIG. 3 , a series of rotating cylinders  52 , each having multiple orifices of varying diameters, are aligned along a common axis X-X. Orifices are preferably offset from the axis of rotation and positioned to align with a fluid pathway by a fluid input tube  56  to a fluid outlet  58 . As seen in  FIG. 4 , each cylinder  52  has a small orifice  60  and large orifice  62  that may be selectively aligned along fluid pathway and configures to provide a certain back pressure according to the Hagen-Poiseuille equation. For example, aligning the small orifices  62  of four cylinders  52 , each providing 1 mmHg back pressure, with the large orifices  62  of four remaining cylinders  52 , will provide a total of 4 mmHg back pressure. Each cylinder  52  may be sealed against adjacent cylinders  52  to provide a continuous, leak proof fluid path. For example, o-rings or gaskets may be used provided that they are employed in a manner that would not obstruct fluid flow or disengage within the fluid path.
 
     In a third embodiment, valve  14  may comprise an array of orifices of various specific diameters and lengths that provide a range of back pressures according to the Hagen-Poiseuille equation. A moveable shutter that selectively exposes a predetermined single orifice or array of orifices may be used to allow a user to adjust the specific amount of back pressure for system  10 .