Selective brain and spinal cord hypothermia method and apparatus

[0002] This application claims priority from U.S. Provisional Patent Application No. 60/287,299 filed Apr. 30, 2001, the entire disclosures of which are incorporated herein by reference.

[0003] The current invention relates to treatment of cerebral swelling as well as regulation of the temperature in the brain and spinal cord. The invention relates to a method and apparatus for altering the temperature of the brain surface and/or the cerebrospinal fluid in the ventricles of the brain and surrounding the spinal cord.

[0004] Hypothermia has been shown to provide cerebral and spinal cord injury protection from either trauma, ischemia, or hypoxia. Ischemia may occur from cardiac arrest, cardiac failure, stroke, head or spinal cord injury, aneurysm surgery, cardiac surgery, and aortic or carotid surgery. Hypothermia is also effective in reducing increased intracranial pressure from cerebral swelling. The mechanisms involved in hypothermic cerebral protection are several-fold and include 1) reduction in cerebral glucose and oxygen metabolism and decreasing lactate content following injury, 2) preventing disruption of the blood brain barrier and consequently reducing cerebral edema, 3) reduction of endogenously toxic neurotransmitters like glutamate, glycine, aspartate, acetylcholine, and norepinephrine into the brain after injury, 4) inhibit excessive calcium entry and intracellular calcium overload into neurons, 5) protecting membrane structural proteins like microtubule-associated protein-2, and 6) preventing diffuse axonal injury following brain trauma.

[0005] In general, the human brain and spinal cord are maintained at a constant temperature of approximately 37 to 38 degrees celsius. Hypothermia is considered mild when the body temperature is 33 to 35 degrees celsius, moderate between the temperatures of 28 to 32 degrees, and severe in the temperature range of 24 to 28 degrees celsius. Most studies in humans have involved mild to moderate systemic hypothermia mainly because of the significant side effects that occur from induced systemic hypothermia. These include infection, cardiac arrhythmias, coagulopathy, renal failure, as well as rewarming shock. In order to avoid these complications the degree and duration of hypothermia has been shortened thereby limiting its effectiveness.

[0006] Generally, cooling of the brain has been accomplished through whole body cooling with use of a cooling blanket, immersing the patient in ice, or cooling the blood through a cardiopulmonary bypass machine. A few methods have been described regarding selective brain and spinal cord hypothermia. These involve cooling the arterial vessel or blood supply to the brain or external cooling helmets, each with its own significant limitations.

[0007] Several catheters have been developed to induce systemic hypothermia by inserting them into the bloodstream. More recently catheters have been developed that can be inserted into the arterial vessels to the brain to induce selective brain hypothermia. These catheters are limited in their size and functionality by the small vessel lumen as well the inability to cool all the four major arterial vessels supplying blood to the brain and are unable to cool the spinal cord via this methodology. They also carry the risk of ischemic and thromboembolic stroke by either impairing the blood flow to the brain or dislodging clots that can develop in intra-arterial catheters.

[0008] External cooling helmets have limited effectiveness since the blood to the cooled scalp does not circulate into the brain and returns systemically which along with the thick skull dilutes the hypothermic effect to the brain.

[0009] Selective brain and spinal cord cooling with insertion of catheters or templates into the ventricular, subdural or epidural space is a novel concept. This avoids the side effects and complications seen from other methods of cooling.

[0010] The invention provides a method and apparatus for performing selective hypothermia to the brain and/or the spinal cord for injury protection without the need for systemic cooling.

[0011] For selective brain cooling, in one embodiment of the present invention, a flexible catheter is inserted into the cerebral lateral ventricle to cool the cerebrospinal fluid and henceforth the brain. The catheter has three lumens with a distal heat conductive element which also has holes to allow for drainage of cerebrospinal fluid. The inner-most lumen is connected with the outer-most lumen at the tip of the catheter and allows for circulation of a coolant. The intermediate lumen has holes at the distal end that allows for drainage of cerebrospinal fluid as well as intracranial pressure monitoring similar to a ventriculostomy. An occipital approach to the placement of the catheter is preferred to allow for a longer catheter with more surface area for heat exchange. In another embodiment of this catheter, the inner-most lumen allows for drainage and the intermediate lumen is connected with the outer lumen for circulation of the coolant.

[0012] For selective spinal cord cooling, in another embodiment of the catheter described above, a catheter with a longer distal heat conductive element is inserted into the lumbar subdural or epidural space to allow for cooling around the spinal cord. This catheter may or may not have a lumen for drainage of cerebrospinal fluid.

[0013] In another embodiment for selective brain cooling, a larger surface area template is inserted into the subdural space either through a burr-hole or following a craniotomy. These templates have variable sizes with small thickness and circulate a coolant with a wider surface area to allow placement in the subdural space to directly cool the brain surface. These templates can also be placed in the epidural space of the spine for selective spinal cord cooling.

[0014] The catheters and templates are designed to allow an inert coolant to circulate in the lumens without direct exposure to the brain or spinal cord and thereby altering the brain or spinal cord temperature. This allows for selective cooling of the brain and spinal cord for treatment of injury from trauma, ischemia, hypoxia and/or cerebral swelling. The length and size of the catheters and templates is variable to allow for a wide selection and patient individuality.

[0015] A better understanding of the present invention will be had after a reading of the following detailed description taken in conjunction with the accompanying drawings wherein:

[0016] FIG. 1 is a top view of one embodiment of the catheter

[0017] FIG. 2 is a cross-sectional side view of the catheter taken along line A in FIG. 1

[0018] FIG. 3 is a cross-sectional view of the catheter taken along line B in FIG. 1

[0019] FIG. 4 is a cross-sectional side view of another embodiment of the catheter

[0020] FIG. 5 is a cross-sectional view of the catheter in FIG. 4

[0021] FIG. 6 is a cross-sectional side view of another embodiment of the catheter

[0022] FIG. 7 is a cross-sectional view of the catheter in FIG. 6

[0023] FIG. 8 is a cross-sectional side view of another embodiment of the catheter

[0024] FIG. 9 is a top view of various sized templates

[0025] FIG. 10 is a cross-sectional top view of a template

[0026] FIG. 11 is a cross-sectional view of the template taken along line C in FIG. 10

[0027] FIG. 12 is a cross-sectional top view of another embodiment of the template

[0028] FIG. 13 is a cross-sectional view of the template taken along line D in FIG. 12

[0029] FIG. 14 is a cross-sectional top view of another embodiment of the template

[0030] FIG. 15 is a cross-sectional top view of another embodiment of the template

[0031] FIG. 16 is a cross-sectional top view of another embodiment of the template

[0032] FIG. 17 is a cross-sectional top view of another embodiment of the template

[0033] FIG. 18 is a cross-sectional top view of another embodiment of the template

[0034] FIG. 19 is a cross-sectional top view of another embodiment of the template

[0035] FIG. 20 is a cross-sectional side view of the template taken along line E in FIG. 19

[0036] FIG. 21 is a cross-sectional view of the template taken along line F in FIG. 19

[0037] FIG. 22 is a cross-sectional view of the template conduit taken along line G in FIG. 19

[0038] In one method of selective brain and/or spinal cooling, a catheter as shown in FIG. 1, can be placed into the ventricle of the brain or the subdural space of the spine. This allows for cooling of the cerebrospinal fluid and hence the brain and/or spinal cord selectively. The catheter 1 has a proximal portion 2 and a distal heat transfer element 3. The distal heat transfer element 3 has several circumferential holes 4 that allow drainage of cerebrospinal fluid.

[0039] In one embodiment of the cooling catheter as shown in FIGS. 2 & 3, the heat exchange fluid or compressed refrigerant enters through the central lumen 9 into the distal end of the heat transfer element 7. The coolant or the gaseous refrigerant returns through the outer lumen 6. The circulation of the coolant through the catheter cools the distal heat transfer element, thereby allowing the cerebrospinal fluid surrounding the catheter to be cooled. The middle lumen 8 provides for drainage of the cerebrospinal fluid through the holes 5.

[0040] In another embodiment of the cooling catheter as shown in FIGS. 4 & 5, a coolant enters through the middle lumen 13 into the distal end of the heat transfer element 12 and returns through the outer lumen 11. The central lumen 14 allows drainage of the cerebrospinal fluid through the holes 10.

[0041] In another embodiment of the cooling catheter, as shown in FIGS. 6 & 7, a coolant enters through the central lumen 16 into the elongated distal heat transfer element 19. The central lumen has holes in the sides 18 that create some turbulence in the heat transfer element 19, thereby facilitating the transfer of heat. The coolant returns through the outer lumen 15. In a modification of this embodiment as shown in FIG. 8, the outer lumen 15 can expand with increased pressure from the circulating coolant, thereby increasing the outer surface area of the heat transfer element to allow rapid heat exchange.

[0042] For more selected cooling of the brain or spinal cord, a template of varying sizes can be used overlying the area of the central nervous system in need of hypothermia. FIG. 9 is an illustration of some of the various sizes of the templates. The length and width may vary but the thickness is uniform to allow for a low profile in the subdural or epidural space of the brain or spine. The cooling templates consist of a proximal conduit 21 and a template 20.

[0043] In one embodiment of the cooling template as shown in FIGS. 10 & 11, the proximal conduit has two lumens 25 & 26. One of the conduit lumens 26 supplies the cooled heat exchange fluid or compressed refrigerant to the template lumen 22. The template has internal conduits 23 & 24 which introduce the coolant into the lumen 22 through which the heat exchange fluid circulates and is returned through the other conduit lumen 25 for external cooling.

[0044] In another embodiment of the cooling template as shown in FIGS. 12 & 13, the proximal conduit has two lumens 31 & 32. One of the conduit lumens 32 supplies the cooled heat exchange fluid or compressed refrigerant to the template lumen 29. The template has internal conduits 28 with holes on the sides 30 which introduce the coolant into the lumen 29 through which the coolant circulates and is returned through the conduit lumen 31 for external cooling. FIG. 14 illustrates another embodiment of the template with a shorter central internal conduit 33. FIG. 15 illustrates yet another embodiment of the template with shorter outermost internal conduits 34.

[0045] In another embodiment of the cooling template as illustrated in FIG. 16, there is a single internal conduit 35 in the template lumen 36 with side holes 37.

[0046] FIG. 17 illustrates another embodiment of the cooling template with two internal conduits without side holes 38 in the template lumen 39. In another embodiment illustrated in FIG. 18, the internal conduits 40 have a curved tip at the distal ends 41. This allows the coolant to flow in the template lumen 42 from the distal end to the proximal end where it is returned to an external cooler through the conduit lumen 43.

[0047] In yet another embodiment of the cooling template as shown in FIGS. 19 to 22, the proximal conduit 45 has a lumen 50 through which the coolant enters the template 44. The template has two lumens 46 & 47 separated by a membrane 49. The two template lumens 46 & 47 communicate at the distal end 48. The coolant enters the template lumen 46 and is returned through template lumen 47 and conduit lumen 51 to an external cooler.

[0048] While the present invention has been described in conjunction with preferred embodiments and methods, it is intended that the description and accompanying drawings shall be interpreted as only illustrative of the invention. It is evident that those skilled in the art may make numerous uses and modifications of and departures from the specific embodiments described herein without departing from the inventive concept.

[0049] U.S. Patent Documents