Abstract:
This invention is an air block for industrial, medical, and non-medical uses. For example, the air block is connected to the proximal end of a vascular access catheter. The air block is either removably connected to the proximal end of the catheter or it is integral to the proximal end of the catheter. The air block permits introduction of other catheters or instrumentation through its central lumen and on into a lumen of the catheter while minimizing fluid loss or gain into the catheter. The air block further prevents air from entering the catheter and provides for removal of the air or other gas from the central lumen before it can enter the catheter where it could cause harm to the patient. The air block can be attached to various standard proximal catheter terminations including Luer fittings and hemostasis valve outer barrels.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is the U.S. National Phase filing under 35 U.S.C. §371 of PCT/US2006/043149, filed Nov. 3, 2006, which designated the United States and was published in English, which claims priority to U.S. Provisional Patent Application No. 60/763,604, filed Jan. 30, 2006. The contents of these applications are incorporated herein by reference in their entireties. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention relates to devices and methods for blocking gases for industrial purposes such as during access to vessels, chambers, canals or containers, or for medical purposes such as during access to the cardiovascular system or other body vessels or lumens, especially procedures performed in the fields of cardiology, radiology, electrophysiology, and surgery. 
       BACKGROUND OF THE INVENTION 
       [0003]    During certain interventional procedures that require vascular access, the patient is catheterized through a vein or artery and a catheter is routed to the heart or other region of the cardiovascular system. The initial steps involve placement of a hollow tube within the blood vessel. The hollow tube can be a sheath or catheter. In many cases, these catheters or sheaths are fairly long. Catheters or other devices are routinely routed through these sheaths into the arterial side of the circulatory system where pulsatile blood pressure generally averages 100 mm Hg cycles and pulses at an average rate of approximately 1 to 3 beats per second. The peak systolic pressures in the arterial side in a normal patient are around 110 to 130 mm Hg and the lowest diastolic pressures are around 70 to 90 mm Hg. In a hypertensive patient experiencing what is known as high blood pressure, the peak systolic arterial pressure can exceed 250 mm Hg. A catheterization lab or operating room is typically a clean room, which is maintained at positive pressure ranging from 0 to 2 mm Hg. When a catheter is routed into the arterial system, the distal end of a through lumen will be exposed to these arterial blood pressures and a positive pressure gradient will exist between the distal end and the proximal end of the catheter can be such that, unless proper hemostasis is maintained, blood is forced out through the catheter into the ambient environment. 
         [0004]    There are an increasing number of cases where a sheath is routed to the venous side. Its distal end is exposed to central venous blood pressure, which cycles at the same rate as the arterial side, approximately 1 to 3 beats per second. The normal, healthy, pulsatile venous pressures are lower than those in the arterial side and can range between low values of around 3 to 5 mm Hg and peak values of around 15 to 20 mm Hg with an average of approximately 10 mm Hg. Patients with ectopic beats or premature ventricular contractions can achieve nearly zero central venous pressure during part of the cardiac cycle. Patients with tricuspid incompetence and conduction pathologies can experience right atrial pressures of −5 to −10 mm Hg. In the central venous circulation, for example, as measured in the right atrium of the heart, the distal end of the sheath can be exposed, during part or all of the cardiac cycle, to pressures equal to or below those to which the proximal end of the sheath is exposed. When the room or ambient pressure, to which the proximal end of the sheath is exposed, is above that of the distal end of the sheath, a negative pressure gradient or pressure drop can occur. Such a negative pressure drop allows air to be forced into the proximal end of the catheter. Should the air reach the distal end of the catheter by way of a through lumen, it could escape into the blood stream in the form of large or small bubbles, resulting an air embolism. Such air embolisms can cause harm to the health of the patient, or even death, and need to be avoided. This situation can be exacerbated by ambient room pressures often found in the cath lab. Under normal conditions, the environment of the clean room, operating theatre, or catheterization lab can be maintained at an elevated air pressure of around 5 to 10 mm Hg above exterior air pressure. Thus, a right atrial pressure, which momentarily dips to 2 mm Hg, can be overcome by a room air pressure of 2 to 3 mm Hg causing air to be forced retrograde through the catheter and into the circulatory system. 
         [0005]    Typical arterial catheter procedures include percutaneous transluminal coronary angioplasty, coronary stenting, aortic stent-graft procedures, endarterectomy, and the like. In the United States, more than 500,000 of these arterial procedures are performed each year. The number of venous procedures being performed each year is increasing as more endovascular therapies evolve or are developed for pathologies such as atrial fibrillation, mitral valve repair, mitral valve replacement, and the like. There are currently more than 200,000 electrophysiology procedures performed in the right and left atrium of the heart annually in the United States. During a venous procedure, a catheter is routed through the venous circulation where low instantaneous, or pulsatile, pressures can occur. During the approach to the heart and in preparation for a trans-septal puncture, the distal end of the catheter can reside in the vena cava or right atrium for a substantial amount of time. Such positioning renders the catheter at risk for being exposed to a negative pressure drop and the potentially catastrophic consequences of retrograde air flow. An air embolism or bubble escaping into the venous circulation can lodge in the lungs causing a pulmonary embolism. Pressures in the left atrium are similar to those in the right atrium. Left atrial pressure is pulsatile and can have peak values of around 10 to 20 mm Hg and minimum values of between −5 and 5 mm Hg. Negative minimum pressures are experienced in patients with certain pathophysiologies such as aortic stenosis. These types of patients are often the ones who undergo catheterization procedures. Left sided (arterial) procedures, which are accessed from the right (or venous) side present a further complication in that a gas bubble or embolism that escapes into the arterial side can be pumped by the heart to sensitive tissues where it can lodge, prevent distal blood flow, and thus cause ischemia. Such ischemia is potentially life threatening if it occurs in the cerebrovasculature or the coronary arteries. 
         [0006]    Current devices and methods prevent air entrainment into a sheath or catheter or for preventing blood escape from these sheaths or catheters involve the use of valves such as stopcocks, hemostasis valves, adjustable Tuohy-Borst valves, and the like. These devices are adequate at preventing the loss of substantial amounts of blood during arterial procedures. The current devices, however, are less well suited to preventing air backflow into the sheath or catheter and possibly into the patient. Instances can arise where a hemostasis valve breaks or becomes disconnected from the sheath or catheter and a substantial bolus of air can enter the cardiovascular system with sometimes catastrophic consequences. Even without such equipment failure, operator error can result in air being pumped retrograde into the blood stream by ambient air pressure, if a Tuohy-Borst valve is not properly adjusted, a hemostasis valve becomes distorted, or too small a catheter is used for the type of hemostasis valve. 
         [0007]    There is a need for improved systems, devices, apparatus and methods for preventing air entrainment into a patient through catheters routed into the venous circulation. Such systems, devices, apparatus, and methods need to accept catheters or instrumentation through their central lumens and close the seal around those catheters better than current devices. The systems further need to close more quickly than the current systems when the inserted catheter is removed. The current systems need also to be improved to prevent air passage retrograde back into the catheter while still maintaining device operability. 
       SUMMARY OF THE INVENTION 
       [0008]    An embodiment of this invention allow work in a medical environment wherein a pressure-differential is expected. Certain embodiments of the invention will prevent air from entering and/or the escape of blood or other body fluids when a high pressure system (defined as above atmospheric) is accessed by interventional techniques. 
         [0009]    For example, disclosed in one embodiment is an air block, or air trap, module that is affixed to the proximal end of a primary sheath, said primary sheath intended for vascular access. The module is generally disposable and can be provided integral to the primary sheath, permanently attached to the primary sheath, or removably attached to the primary sheath. The module permits introduction of catheters or other instrumentation through the central lumen of the primary sheath. In one embodiment, the module further substantially prevents the loss of blood when the distal end of the catheter is exposed to circulating blood, either in the arterial or venous system. The module traps substantially any air entrained into its interior lumen, prevents the air from entering the through lumen of the primary catheter, and shunts the air out of the interior lumen of the module through an air exit port. 
         [0010]    In other embodiments, the invention is applicable to industrial uses where the blocking of gasses is desired. For example, an embodiment of the invention prevents gas from entering and/or the escape of gas of other materials from a vessel when a high pressure system is accessed. 
         [0011]    The air block comprises a main housing or shell, a catheter entry port, a catheter exit port, an inner channel further comprising perforations in its wall, a fluid inlet port, and a gas, or air, exit port. The catheter entry port further comprises a hemostasis valve such as, but not limited to, a slit valve, duckbill valve, Tuohy-Borst valve, or the like. The catheter exit port further comprises a hemostasis valve such as, but not limited to, a slit valve, a duckbill valve, a Tuohy-Borst valve, or the like. The catheter exit port also comprises a docking mechanism capable of securely affixing the air block to the proximal end of the primary sheath such that the catheter exit port and the inlet port of the primary catheter are concentric and aligned. 
         [0012]    In other embodiments directed to industrial or non-medical uses, the catheter ports are replaced with a wide variety of different types of ports. Also, instead of a catheter, an embodiment of the invention can be adapted to receive a variety of devices such as tubular devices for insertion into containers, canals, vessels, passageways, or the like. Such devices can be designed, for example, to permit injection or withdrawal of fluids or to keep a passage open. For example, an embodiment of the invention directed to industrial uses prevents gas from entering and/or the escape of gas of other materials from a vessel when a device is inserted into the vessel. 
         [0013]    Thus, while certain embodiments are described with respect to endovascular uses or a catheter, the invention is not so limited and can be configured for use in a variety of medical, non-medical and industrial uses where the blocking of gas is desired. 
         [0014]    The air block, or air removal system, can be operably connected to an external subsystem that provides a reservoir of liquid such as water, saline, Ringers solution, or the like pressurized to a level above that of the venous pressure. The fluid delivery subsystem is operably connected to the fluid inlet port of the air block by way of a tube, manifold, or the like. The air block can also be operably connected to an external subsystem that withdraws or removes gas, specifically air, which can collect within the shell of the air block. The gas removal subsystem is operably connected to the shell of the air block by the gas removal port. Although the subsystems are referred to as being external, they can also be internal, integral to, or affixed to the air block module. In an embodiment, the gas removal subsystem can comprise a gas permeable membrane that permits gas such as air to pass but substantially prevents the loss of liquids such as water, saline, or blood. In this embodiment, a pump is operably connected to withdraw the air out of the trap through the as permeable membrane by generating a pressure drop within a range that facilitates such air passage. 
         [0015]    The air block, in an embodiment, can comprise one way valves at the fluid inlet port and at the gas outlet port. These one-way valves permit flow only in a single direction and make sure that fluid can only flow into the air block from the fluid inlet port and that gas can only flow out of the gas outlet port. In another embodiment, the air block comprises an outer shell and a core tube, the core tube having either a straight tubular configuration or a central bulge directed radially outward from the axis of the tube. The core tube can further comprise perforations large enough to cause gas collected within the core tube to pass out into the surrounding area within the air block shell. 
         [0016]    Another aspect of the invention is the method of use of the bubble, gas, or air block apparatus. The air block is affixed to the proximal end of the primary catheter, cannula, introducer, or sheath. The primary catheter is flushed with saline and purged of air. The primary catheter is introduced into the vascular system, generally after first placing a guidewire, which is routed through the central lumen of the air block. The fluid inlet port of the air block is connected to a source of normal saline. The gas outlet port of the air block can be connected to a fluid removal system. The primary catheter is routed to its target location. The secondary catheter, or catheters, can be inserted through the proximal most hemostasis valve of the air block, through the central lumen of the core tube of the air block, through the secondary air block hemostasis valve, through the catheter lumen and into the vascular system at the target site. Any air that becomes entrained into the core tube of the air escapes through perforations in the core tube and migrates into the larger diameter shell. The trapped air either remains within the larger diameter shell or it is drawn off by the fluid removal system either into the air or into an air reservoir. The fluid removal system can be optimized to selectively withdraw only gasses such as air. This selective withdrawal of air can be performed using a microporous membrane fabricated from materials such as, but not limited to, polypropylene, polyethylene, polytetraflouoroethylene, other polyolefin, polyester, or the like. The membrane can have porous structures that penetrate from one side of the membrane to the other and with a size of about 100 microns with a range of 50 microns to 1000 microns. The pore density and pore size can be selected to be compatible with a pressure drop across the membrane, as generated by a pump or other suction (vacuum) or pressure generating device so as to remove a given volume of air over a specified length of time without the loss of a substantial amount of liquid such as blood. 
         [0017]    For purposes of summarizing the invention, certain aspects, advantages and novel features of the invention are described herein. It is to be understood that not necessarily all such advantages may be achieved in accordance with any particular embodiment of the invention. Thus, for example, those skilled in the art will recognize that the invention may be embodied or carried out in a manner that achieves one advantage or group of advantages as taught herein without necessarily achieving other advantages as may be taught or suggested herein. These and other objects and advantages of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]    A general architecture that implements the various features of the invention will now be described with reference to the drawings. The drawings and the associated descriptions are provided to illustrate embodiments of the invention and not to limit the scope of the invention. Throughout the drawings, reference numbers are re-used to indicate correspondence between referenced elements. 
           [0019]      FIG. 1  illustrates a schematic view of the cardiovascular system of the human; 
           [0020]      FIG. 2  illustrates a graph of the blood pressure within the arterial system at a location near the heart plotted against time; 
           [0021]      FIG. 3  illustrates a graph of the blood pressure within the venous system in the region of the right atrium, plotted against time; 
           [0022]      FIG. 4  illustrates a graph of the blood pressure within the left atrium of the heart, as it varies with time; 
           [0023]      FIG. 5  illustrates a schematic diagram of an embodiment of the air block system; 
           [0024]      FIG. 6  illustrates an embodiment of the air block without subsystems or catheters; 
           [0025]      FIG. 7  illustrates an embodiment of the air block connected to a primary catheter; 
           [0026]      FIG. 8  illustrates an embodiment of the air block connected to a primary catheter with fluid input and gas withdrawal subsystems attached; 
           [0027]      FIG. 9  illustrates an embodiment of the air block connected to a primary catheter with a secondary catheter inserted therethrough; 
           [0028]      FIG. 10  illustrates a close up view of an embodiment of the air block showing a catheter inserted therethrough and a bolus of air being drawn out of the core tube into the lumen of the outer shell; and 
           [0029]      FIG. 11  illustrates a side view of an embodiment of an air block or air block that utilizes a dual chamber design. 
           [0030]      FIG. 12  illustrates an embodiment of an air embolism prevention device. 
           [0031]      FIG. 13  illustrates an embodiment of a system of preventing air embolism during vascular procedures. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0032]    In accordance with current terminology pertaining to medical devices, the proximal direction will be that direction on the device that is furthest from the patient and closest to the user, while the distal direction is that direction closest to the patient and furthest from the user. These directions are applied along the longitudinal axis of the device, which is generally an axially elongate structure having one or more lumens or channels extending through the proximal end to the distal end and running substantially the entire length of the device. As defined herein, a sheath is an axially elongate tube that can also be termed a catheter, a cannula, an introducer, or the like. 
         [0033]    The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is therefore indicated by the appended claims rather than the foregoing description. All changes that come within the meaning and range of equivalency of the claims are to be embraced within their scope. 
         [0034]      FIG. 1  illustrates a schematic diagram of a part of the circulatory system  102  of a human  100 . The circulatory system  102  comprises a heart  112 , an inferior vena cava  104 , a superior vena cava  106 , an iliac vein  108 , and a femoral vein  110 . The heart  112  further comprises a left ventricle  114 , a right ventricle  116 , a left atrium  118 , a right atrium  120 . The circulatory system  102  also comprises the aorta  122 . 
         [0035]    Referring to  FIG. 1 , all the functional components are operably connected to each other. The left ventricle  114  of the heart  112  pumps blood into the aorta  122  by muscular contraction of the myocardium. Blood enters the left ventricle  114  through the mitral valve from the left atrium  118 . Blood is pumped from the right ventricle  116 , through the pulmonary valve into the pulmonary artery. Blood enters the right ventricle  116  from the right atrium  120  through the tricuspid valve. All parts of the heart  112  and circulatory system  102  are integral to each other, although they are comprised of various types of tissue. 
         [0036]      FIG. 2  illustrates a plot of arterial pressure  200  as a function of time. The arterial pressure  200  is pulsatile and the waveform generally repeats itself each cardiac cycle. The end of the first cardiac cycle  202  is approximately 0.8 seconds following the beginning of the cycle. The arterial pressure waveform  200  has a maximum value  204 , a minimum value  206 , and a dicrotic notch  208 . 
         [0037]    Referring to  FIG. 2 , typical arterial or systemic pressure within the human circulatory system is a time varying value that appears somewhat like a triangle wave, having rounded peak and minimum curvature, with a maximum value  204  called the peak systolic pressure and the minimum value  206  called the minimum diastolic pressure. A small feature in the downsloping part of the wave is called the dicrotic notch  208  and is the hemodynamic remnant of the closure of the aortic valve. 
         [0038]      FIG. 3  illustrates a plot of the right atrial pressure  300  as a function of time. The right atrial pressure  300  is pulsatile and the waveform generally repeats itself each cardiac cycle. The end of the first cardiac cycle  302  is approximately 0.74 seconds following the beginning of the cycle. The following partial cycle  304  illustrates a right atrial pressure tracing in a patient with an arrhythmia causing the minimum pressure to drop as low as 0 mm Hg. 
         [0039]    Referring to  FIG. 3 , the right atrial pressure has a much lower mean value than that in the systemic circulation. The larger, first pressure pulse, within the right atrium, is generated by the contraction of the right atrium which increases pressure within the right atrium. A smaller, second pressure pulse is generated when the right ventricle contracts and causes the tricuspid valve to balloon backward into the right atrium. A third pressure pulse is caused by muscular or myocardial contraction of the heart. A second beat  304  begins at the end  302  of the first recorded cycle  300 . The second beat  304  is the result of a heart experiencing electrical disturbances and the beat results in a higher peak of around 11 or 12 mm Hg and a minimum value of 0 mm Hg. 
         [0040]      FIG. 4  illustrates a plot of the left atrial pressure  400  as a function of time. The left atrial pressure  400  is pulsatile and the waveform generally repeats itself each cardiac cycle. The end of the first cardiac cycle  402  is approximately 0.7 seconds following the beginning of the cycle. 
         [0041]    Referring to  FIG. 4 , the left atrial pressure  400 , in the illustrated tracing reaches a maximum of 7.5 mm Hg and a minimum of 5 mm Hg. The left atrial pressure  400  pulsatile waveform comprises a larger peak  404  followed by a smaller peak  406  during the course of a single cardiac cycle. The first, larger peak  404  is generated by contraction of the left atrium and the second, smaller peak  406  is generated by contraction of the left ventricle causing retrograde flow into the left atrium and ballooning of the mitral valve into the left atrium. 
         [0042]      FIG. 5  illustrates a gas block system  500  comprising a core tube  502 , an outer shell  504 , a proximal hemostasis valve  506 , a distal hemostasis valve  508 , a distal connector  510 , a reverse flow one way check valve  512 , a forward flow one way check valve  514 , a fluid inlet line  516 , a fluid outlet line  518 , an optional fluid withdrawal pump  520 , a liquid reservoir  522 , an outer shell lumen  524 , and a volume of liquid  526 . The core tube  502  further comprises a plurality of fenestrations  528 . The outer shell  504  further comprises an outlet port  530  and an inlet port  532 . 
         [0043]    Referring to  FIG. 5 , the core tube  502  is affixed concentrically within the outer shell  504  at both ends. Both ends of the outer shell  504  where the core tube  502  penetrates are sealed against the passage of fluids from the outer shell lumen  524 . The proximal hemostasis valve  506  is affixed to the proximal end of the core tube  502  and the central flow lumen of the proximal hemostasis valve  506  is operably connected to the central lumen of the core tube  502 . The distal hemostasis  508  valve is affixed to the distal end of the core tube  502  and the central flow lumen of the distal hemostasis valve  508  is operably connected to the central lumen of the core tube  502 . The distal connector  510  is affixed to the distal end of the distal hemostasis valve  508  and the central through lumen of the distal connector  510  is operably connected to the central lumen of the distal hemostasis valve  508 . The distal end of the distal connector  510  is reversibly, or permanently, affixed to the proximal end of a catheter hub (not shown). The reverse flow one way check valve  512  is affixed to, and operably connected to, the outlet port  530 , which is operably connected to the outer shell  504  and the central lumen of the reverse flow one way check valve  512  is operably connected to the inner lumen  524  of the outer shell  504 . The forward flow one way check valve  514  is affixed to and operably connected to the inlet port  532 , which is affixed to and operably connected to the outer shell  504 . The central lumen of the forward flow one way check valve  514  is operably connected to the inner lumen  524  of the outer shell  504 . The fluid inlet line  516  is affixed and operably connected to the central lumen of the forward flow check valve  514  at one end and affixed to and operably connected to the liquid reservoir  522  at the other end. The fluid outlet line  518  is affixed and operably connected to the central lumen of the reverse flow check valve  512  at one end and affixed to and operably connected to the optional fluid withdrawal pump  520  or a reservoir (not shown) at the other end. The volume of liquid  526  fills at least a portion of the liquid reservoir  522 , the fluid inlet line  516 , the forward flow check valve  514 , and the outer shell  504 . In one embodiment, the fenestrations  528  are integral to the core tube  502  and are generally breaks or holes in the outer wall of the core tube  502 . 
         [0044]    The outer shell  504  and the core tube  502  can be fabricated from glass or polymers such as, but not limited to, polycarbonate, polysulfone, polypropylene, polyethylene, polyurethane, polyvinyl chloride, acrylic, polystyrene, or the like. The outer shell  504  and the core tube  502  are preferably fabricated from materials that are transparent and optically clear with a minimum of defects or blemishes. The outer shell  504  and the core tube  502  should be transparent so that bubbles can be visualized or identified by the user such that they can be removed or guided out of the outer shell  504 . Some small amount of colorant is acceptable such that a slight blue, violet, green, or yellow tint is present. The outer shell  504  and the core tube  502  can have wall thicknesses that range from 0.020 inches to 0.50 inches, and preferably between 0.040 and 0.250 inches. The reverse flow check valve  512  and the forward flow check valve  514 , as well as the proximal hemostasis valve  506 , the distal hemostasis valve  508 , and the distal connector  510  can be fabricated from the same materials as those used for the outer shell  504 . In addition, the valves  512 ,  514 ,  506 , and  508  can comprise internal seals (not shown) fabricated from flexible or elastomeric polymers such as, but not limited to, polyurethane, silicone elastomer, thermoplastic elastomer, latex rubber, or the like. The fluid inlet line  516  and the fluid outlet line  518  can be fabricated from materials such as, but not limited to, polyvinyl chloride, polyurethane, silicone elastomer, polypropylene, polyethylene, or the like. The fluid reservoir  522  can be a bag or a container such as a bottle, box, or tub fabricated from the same materials as the fluid inlet line  516 . The gas removal pump  520  can be a syringe that is manually or mechanically operated or it can be a pump such as a roller pump, a diaphragm pump, a centrifugal pump, a piston pump, or the like. The pump  520  can be manually, electrically, or fluidically powered. In another embodiment, the pump  520  can be a simple fluid reservoir with no active means of pulling a vacuum on the outlet of the reverse flow check valve  512 . The pump  520  is advantageously oriented higher than the outer shell  504 . The outlet port  530  and the inlet port  532  can be integral to the outer shell  504  or they can be bonded or welded thereto. The outlet port  530  and the inlet port  532  can be perforations in the wall of the outer shell  504 . 
         [0045]      FIG. 6  illustrates an air block subassembly  600  comprising the core tube  502 , the outer shell  504 , a proximal hemostasis valve  506 , the distal hemostasis valve  508 , a distal connector  510 , the reverse flow one way check valve  512 , the forward flow one way check valve  514 , and an outer shell lumen  524 . The one way check valves  512  and  514  each further comprise an internal connector  602 , and an external connector  604 . 
         [0046]    Referring to  FIG. 6 , the internal connector  602  is affixed to the outer shell  504  and the central lumen of the internal connector is operably connected to the central lumen  524  of the outer shell  504  by way of holes in the outer shell  504 . In one embodiment, the external connectors  604  are permanently affixed to the outermost edges of the reverse flow check valve  512  and the forward flow check valve  514 . The internal connectors  602  and the external connectors  604  can be Luer type connectors, or other bayonet mount or screw mount with a tapered sealing port, for example, suitable for attachment to medical fluid lines and connectors. Referring to  FIG. 5 , the internal connectors  602  and the external connectors  604  can be fabricated from the same materials as those used to fabricate the outer shell  504 . 
         [0047]      FIG. 7  illustrates an air block subassembly  600  affixed to a primary catheter  700 . The primary catheter  700  comprises a hub  702 , a main tube  704 , and a hub connector  706 . The air block subassembly  600  further comprises the proximal hemostasis valve  506 , the distal hemostasis valve  508 , and the distal connector  510 . 
         [0048]    Referring to  FIG. 7 , the hub  702  is affixed to the main tube  704 . In one embodiment, the hub  702  has an integral or attached hub connector  706 . The hub connector  706  is permanently or releasably affixed to the distal connector  510  of the air block system  600 . The distal connector  510  can be configured to be a device such as, but not limited to, a luer lock, a bayonet mount, a collar with a set screw, an adhesively coupled connector, a threaded connector, or the like. 
         [0049]      FIG. 8  illustrates the air block system  500  affixed to the primary catheter  700 . The primary catheter  700  comprises the hub  702  and the main tube  704 . The air block system  500  comprises the outer shell  504 , the proximal hemostasis valve  506 , the distal hemostasis valve  508 , the distal connector  510 , the reverse flow check valve  512 , the forward flow check valve  514 , the liquid inlet line  516 , the fluid outlet line  518 , the fluid withdrawal pump  520 , and the liquid reservoir  522 . The air block system  500  further comprises an air reservoir  802 , a power supply  804 , a plurality of power lines  806 , a gas permeable membrane  810 , and a power switch  808 . 
         [0050]    Referring to  FIG. 8 , the air reservoir  802  is affixed to the end of the fluid outlet line  518  that is opposite the end of the fluid outlet line  518  that is connected to the reverse flow one way check valve  512 . In an embodiment, the air reservoir  802  can be affixed to the reverse flow one way check valve  512  directly without the intervening fluid outlet line  518 . The fluid withdrawal pump  520  is affixed to the air reservoir  802  with or without an intervening fluid line (not shown). The power supply  804  is operably connected to the fluid withdrawal pump  520  using power lines  806 . In the illustrated embodiment, there are two power lines  806 . A power switch  808  can be operably connected to at least one power line  806  and used to enable power delivery to the fluid withdrawal pump  520  through the power lines  806 . In an embodiment, the power supply  804  can be a battery system and the fluid withdrawal pump  520  can be electrically powered. 
         [0051]    The fluid removal system can be optimized to selectively withdraw only gasses such as air while leaving liquids behind, within the outer shell  504 . In an embodiment, a gas permeable membrane  810  can be operably connected within or about the outlet line  518 . The gas permeable membrane  810  is a filter comprising, for example, a microporous membrane fabricated from materials such as, but not limited to, polypropylene, polyethylene, polytetraflouoroethylene, other polyolefin, polyester, or the like. The membrane can have porous structures that penetrate from one side of the membrane to the other. The size of the pores can be about 100 microns with a range of about 50 microns to about 1000 microns. The pore density and pore size can be selected to be compatible with a pressure drop across the membrane, as generated by the pump  520  or other suction (vacuum) or pressure generating device, so as to remove a given volume of air over a reasonable length of time, for example 1-cc in 5 minutes, while preventing the loss of blood or other liquids from the system. 
         [0052]      FIG. 9  illustrates the air block subassembly  600  comprising the proximal hemostasis valve  506 , the distal hemostasis valve  508 , and the distal connector  510  affixed to the primary catheter  700 . The air block subassembly  600  comprises the perforated core tube  502  which further comprises an interior distal surface  910  that is smooth and gently sloped. A secondary catheter  900  is inserted through the air block subassembly  600  and the primary catheter  700 . The secondary catheter  900  comprises a hub  902  and a main tube  904 . 
         [0053]    Referring to  FIG. 9 , the main tube  904  of the secondary catheter  900  is affixed to the hub  902  and one or more lumens within the main tube  904  are operably connected to one or more lumens in the hub  902 . The main tube  904  of the secondary catheter  900  is slidably inserted through the proximal hemostasis valve  506 , the air block system  600 , and the central lumen of the primary catheter  700 . The proximal hemostasis valve  506  and the distal hemostasis valve  508  operably seal against the passage of fluids around the exterior surface of the main tube  904 . The inner surfaces of the core tube  502  are smooth and without bumps, especially on the distal end  910  of the core tube, so that the secondary catheter  900 , when inserted in the distal direction, does not hang up or catch on ridges, bumps, or ledges. The interior surface of the distal end  910  of the core tube  502 , when tapering from a larger to a smaller diameter when moving in the distal direction, beneficially has a relatively gentle angle of 1 to 45 degrees to facilitate advancement of the secondary catheter  900 , especially if the secondary catheter  900  comprises radial enlargements or a curvature or bend at right angles to the longitudinal axis. Such gentle tapering and lack of bumps or ridges can also be present on the proximal end of the core tube  502  inner surface, and can reduce friction on a secondary catheter  900  which has radial enlargements while it is being withdrawn proximally through the core tube  502 . 
         [0054]      FIG. 10  illustrates the air block subassembly  600  affixed to the primary catheter  700  with the main tube  904  of the secondary catheter  900  inserted through both the air block subassembly  600  and the primary catheter  700 . The air block subassembly  600  comprises the core tube  502  further comprising the plurality of fenestrations  528 , the outer shell  504 , the proximal hemostasis valve  506 , the distal hemostasis valve  508 , and the distal connector  510 . A bolus of air  1000  has escaped into the air block assembly  600  and is being removed from the lumen of the core tube  502 , through the fenestrations  528 , into the lumen of the outer shell  504 . 
         [0055]    Referring to  FIG. 10 , an air bubble  1000  is shown trapped within the lumen of the core tube  502 . The air bubble  1000  is shown moving upward toward the reverse flow check valve  512  due to buoyancy forces generated by gravity acting on the bubble  1000  and the liquid within the air block system  600 . The air bubble  1000  will ultimately move out of the core tube  502  altogether where it will reside within the outer shell  502  prior to being withdrawn out through the reverse flow check valve  512  and away from the blood path. 
         [0056]      FIG. 11  illustrates a side cross-sectional view of a dual chamber air block  1100 . The dual chamber air block  1100  comprises the first outer shell  504 , the first core tube  502 , the distal hemostasis valve  508 , the proximal hemostasis valve  506 , the reverse flow check valve  512 , the forward flow check valve  514 , the distal coupler  510 , the primary catheter  700 , and the secondary catheter  900  further comprising the secondary catheter hub  902  and the secondary catheter tube  904 . The dual chamber air block  1100  further comprises a second outer shell  1104 , a second core tube  1102 , a second reverse flow check valve  1112 , and a second proximal hemostasis valve  1130 . 
         [0057]    Referring to  FIG. 11 , the distal end of the second core tube  1102  is affixed to and its central lumen is operably connected to the proximal end of the proximal hemostasis valve  506 . The second proximal hemostasis valve  1130  is affixed to and its through lumen is operably connected to the central lumen of the second core tube  1102 . The second reverse flow check valve  1112  is affixed to the second outer shell  1104  and its central lumen operably connected to the internal lumen of the second outer shell  1104  by way of a fenestration or outlet port in the second outer shell  1102 . A pressurized liquid source is operably connected to the forward flow check valve  514  or it is directly connected to the interior volume of the first outer shell  504 . 
         [0058]    Referring to  FIGS. 11 and 5 , the sizes of the two chambers of the dual chamber air block  1100  can be approximately the same, or they can vary by as much as 80% in volume. The forward flow check valve  514  can be operably connected to the pressurized source  522  of liquid  526 . The liquid  526  can be delivered at pressures of between 20 and 300 mm Hg. It is preferable that the liquid  526  be biologically compatible fluid such as, but not limited to, ringers solution, isotonic saline, heparinized saline, or the like. The liquid  526  can be sterilized and delivered through a sterile system to prevent infection to a patient. The liquid  526 , delivered at a pressure higher than that of the central venous circulation, will flow both distally and proximally, if allowed, within the first outer shell  504  and the second outer shell  1104 . The movement of the liquid  526  is controlled by the distal hemostasis valve  508 , the proximal hemostasis valve  506 , and the second proximal hemostasis valve  1130 . Should air be entrained into the second outer shell  1104  through the second proximal hemostasis valve  1130 , the high pressure within the first outer shell  504  will prevent entrance of the air into the first outer shell through any potential opening or defect in the proximal hemostasis valve  506 . A leak or defect in the distal hemostasis valve  508  could result in the flow of the liquid  526  through the first catheter  700  and into the patient, but since the liquid  526  is biocompatible, this event will have no adverse clinical effect. Any air that does become trapped within the system can be drawn out through the reverse flow check valve  512  or the second reverse flow check valve  1112 . In other embodiments, the forward flow check valve  514  can be eliminated and the line  516  can be directly connected to the outer shell  504 . In another embodiment, one or more of the reverse flow check valves  512  or  1112  can be eliminated and replaced by gas permeable membranes, or simply be connected to the fluid withdrawal line  518 . 
         [0059]    Referring to  FIGS. 5 ,  6 ,  7 , and  11 , the volume of the outer shell  504  or  1104  can vary between 0.5 cubic centimeter (cc) and 100-cc. The size of the system is beneficially reduced to allow the system  500 ,  600 , or  1100  to be connected to a primary catheter  700  and still be maneuvered without encumbering the user or hindering manipulation. The air block system  500  is beneficially sterilized prior to use to prevent infection to a patient. 
         [0060]    Referring to  FIG. 5 , an air block apparatus  500  is disclosed herein, which prevents air from passing through a catheter, cannula, or sheath into a patient&#39;s cardiovascular system, wherein the air block  500  comprises an outer shell  500 , further comprising a wall and an inner lumen  524  having a proximal end and a distal end, a core tube  502  comprising an axially elongate wall, an inner lumen, and a plurality of fenestrations  528 , wherein the core tube  502  resides within the outer shell  504  and is sealed to the outer shell  504  at its proximal end and its distal end, a first hemostasis valve  506  affixed to the core tube  502  at the proximal end of the core tube, a second hemostasis valve  508  affixed to the core tube  502  at the distal end of the core tube  502 , and an outlet port  530  affixed to the wall of the outer shell  504 , wherein the outlet port  530  is operably connected to the inner lumen  524  of the outer shell  504 , wherein the fenestrations  528  in the wall of the core tube  502  are large enough to permit air or other gas to pass out of the core tube  502  and into the inner lumen  524  of the outer shell. 
         [0061]    In another embodiment, the air block apparatus can further comprise an inlet port  532  affixed to the wall of the outer shell  504 , wherein the inlet port  532  is operably connected to the inner lumen  524  of the outer shell  504 . 
         [0062]    In another embodiment, the air block apparatus can further comprise an inlet port  530  operably connecting the inner lumen  524  of the outer shell with a source  522  of liquid  526 . The apparatus can also comprise a vacuum source  520  operably connected to the outlet port  530 , wherein the vacuum source  520  removes gas from the inner lumen  524  of the outer shell  504 . Referring to  FIGS. 5 and 8 , the air block apparatus  500  can comprise a gas permeable membrane  810  operably connected between the vacuum source  520  and the outlet port  530 , wherein the gas permeable membrane  810  permits the removal of gas from the inner lumen  524  of the outer shell  504  while substantially preventing the removal of liquid from the inner lumen  524  of the outer shell  504 . Referring to  FIG. 6 , the air block apparatus  500  can also have a core tube  502  that further comprises a central bulge  610  extending radially outward such that when the inner lumen  524  is oriented perpendicular to the line of gravity, gas moves radially away from the central axis of the core tube  502  toward the outer wall, where it is able to pass into the inner lumen of the outer shell through fenestrations  528  in the wall of the core tube  502 . 
         [0063]    The core tube  502  of the air block  600  can comprise a central bulge  610  extending radially outward, wherein said central bulge  610  is gently tapered along the inner distal surface  612  of the outer wall of the core tube  502  such that a catheter inserted therethrough, from the proximal end, does not catch, but is guided into the smaller diameter regions of the core tube without catching or hanging up as it is advanced distally. In another embodiment, the first, proximal hemostasis valve  506  of the apparatus is configured to receive a catheter and seal around said catheter when the catheter is inserted therethrough and further wherein the proximal hemostasis valve  506  is configured to seal substantially against the flow or air or liquid when nothing is inserted therethrough. The second hemostasis valve  508  can be configured to receive a catheter and seal around said catheter when the catheter is inserted therethrough and further wherein the distal, or second hemostasis valve  508  is configured to seal substantially against the flow or air or liquid when nothing is inserted therethrough. Referring to  FIGS. 6 and 7 , the air block apparatus  600  can further comprise an adapter  510  to permit attachment of the distal end of the second hemostasis valve  508  to a hub  702  of a catheter  700  such that the central lumen of the core tube  502  is operably connected to the inner lumen of the hub  702  of the catheter or sheath  700  as permitted by the second hemostasis valve  508 . The adapter  510  can be configured to permit removable attachment of the air block apparatus  600  to the hub of the catheter  700 . 
         [0064]    Referring to  FIGS. 5 ,  6 ,  7 , and  9 , in another embodiment, a method of preventing substantial infusion of air into the proximal end of a first catheter  700  is disclosed, the method comprising the steps of affixing an air block  600  having a longitudinal axis to the proximal end of a first catheter  700 , wherein the air block comprises an outer shell  504 , a fenestrated core tube  502 , a first hemostasis valve  506 , a second hemostasis valve  508 , an inlet port  532 , and an outlet port  530 , affixing a source  522  of sterile liquid  526  to the inlet port, affixing a gas withdrawal system  520  to the outlet port, inserting a secondary catheter  900  through the air block into the first catheter or sheath  700 , wherein the first and second hemostasis valves  506  and  508  prevent air from entering or escaping the air block  600 , orienting the air block  600  such that its longitudinal axis is substantially horizontal relative to the pull of gravity; and removing gas bubbles that collect between the outer shell  504  and the fenestrated core tube  502  such that the gas bubbles no longer reside within the outer shell  504 . 
         [0065]    The method can further comprise the step of elevating the source  522  of sterile liquid  526  above the level of the outer shell  504 . The method can also comprise the step of activating a pump  520  to remove the gas from the outer shell  504  through the outlet port  530 . In another embodiment, the method can further comprise the step of removing the gas from the outer shell  504  through a gas permeable membrane  810  which is operably connected to the outlet port  530 . The method can involve replacement of the secondary catheter  900  with a guidewire at one or more points in the procedure. The method can further comprise the step of collecting the removed gas in a holding chamber  802 , which can be a separate structure or integral to the block  500 . In another embodiment, the method can comprise the step of returning any liquid, which was unintentionally removed from the system, back into the outer shell  504  through the inlet port  532 . 
         [0066]    The method can comprise the step of sterilizing the air block  500  or  600  prior to attaching it to the first catheter, sheath, or introducer  700 . The method can also comprising the step of packaging the air block  500  or  600  within a kit, wherein the kit comprises at least the first catheter or sheath  700  and the air block  500 ,  600 . The method can comprise pre-affixing the air block to the hub  702  of the first catheter, sheath, introducer, or cannula  700 . The method of can comprise the step or steps of providing therapeutic intervention within the cardiovascular system wherein the instrumentation is placed through the air block apparatus  500 ,  600  into the sheath or first catheter  700 . The method can comprise the step or steps of providing diagnostic intervention within the cardiovascular system through the air block apparatus  500 ,  600 . The method can comprise routing the first catheter or sheath  700  to the right atrium of the heart through the venous system. Subsequent steps can involve passing the first catheter or sheath  700  through the interatrial septum and resides, at its distal end, within the left atrium of the heart. 
         [0067]    In another embodiment, an apparatus  1100  is disclosed, which is adapted for preventing substantial infusion of air into the proximal end of a first catheter  700  comprising means for collecting air within a primary inner chamber  502 , means for collecting air within a primary outer chamber  504 , means for permitting the air to move from the primary inner chamber  502  to the primary outer chamber  504 , means for inserting a catheter  900  through the inner chamber  502 , means  506  for preventing substantial air from entering the primary inner chamber  502  from the proximal end of the primary inner chamber  502 , means  508  for preventing substantial air from leaving the primary inner chamber  502  at its distal end while still permitting passage of a catheter  900  therethrough, means for infusion of liquid into the primary outer chamber  504 , and means for removal of gas from the primary outer chamber  504 . The apparatus  1100  can further comprise a secondary, perforated, inner chamber  1102  surrounded by a secondary outer chamber  1104 , a means  1112  for removing air from the secondary outer chamber  1104 , and a secondary proximal hemostasis valve  1130 , wherein said secondary, or second, inner and outer chambers  1102  and  1104 , respectively, positioned proximally to the primary inner chamber  502  and operably separated from the primary outer chamber  504  by a means  506  to permit catheter passage between the primary  502  and secondary  1102  inner chambers while substantially prohibiting the flow of fluids between said primary  502  and secondary  1102  inner chambers. 
         [0068]    An air block apparatus  500 ,  600 ,  1100  is disclosed herein, which is adapted for preventing air from passing from a room through a catheter, sheath, cannula, or introducer  700  into a patient&#39;s cardiovascular system comprising an outer shell  504  comprising a wall and an inner lumen having a proximal end and a distal end, a core tube  502  comprising an axially elongate wall, an inner lumen, and a plurality of fenestrations  528 , wherein the core tube  502  resides within the outer shell  504  and is sealed to the outer shell  504  at its proximal end and its distal end, a first valve  506  affixed to the inner lumen of the core tube  502  at the proximal end of the core tube  502 , wherein said first valve  506  permits the passage of a catheter  900  but substantially prohibits the flow of fluids, either liquid or room air, therethrough, a second valve  508  affixed to the inner lumen of the core tube  502  at the distal end of the core tube  502 , wherein said second valve  508  permits the passage of a catheter  900  but substantially prohibits the flow of fluids, either liquid or room air therethrough, an outlet port  530  for withdrawing any gas, including room air, collected in the outer shell  504 , away from the outer shell  504 , and a source  522  of sterile, biocompatible liquid  526  delivered at a pressure greater than central venous pressure, wherein the source  522  of sterile, biocompatible liquid  526  is operably connected to the inner lumen  524  of the outer shell  504 , wherein the sterile biocompatible liquid  526  is delivered at a pressure higher than that of the room air and substantially prevents the flow of room air from the first valve  506  into the inner lumen of the core tube  502 . 
         [0069]    An air block apparatus  500 ,  600 ,  1100  is disclosed, which is adapted for preventing gas from passing from a room environment through a catheter  700  into a patient&#39;s cardiovascular system comprising a chamber  504  affixed to the proximal end of a first catheter  700 , wherein the chamber  504  is operably connected to a source  522  of liquid  526  which is pressurized to a level above that of the pressure within the cardiovascular system, a first valve  506  affixed to the proximal end of the chamber  504 , wherein said first valve  506  permits insertion of a second catheter  900  from a room environment through the first valve  506  and into the chamber  504 , and a second valve  508  affixed to the distal end of the chamber  504 , wherein said second valve  508  permits insertion of the second catheter  900  from the chamber  504 , through the second valve  508 , into the proximal end the first catheter  700 , wherein the first valve  506  and the second valve  508  are configured to permit catheter  900  passage but substantially prohibit the passage of air, from the room environment, therethrough. 
         [0070]    In one embodiment, the cross-sectional area of the outer shell  504  is substantially larger than the cross-sectional area of the catheter  700 . In one embodiment, the cross-sectional area of the outer shell  504  is at least three times greater than the cross-sectional area of the catheter  700 . In yet other embodiments, the cross-sectional area of the outer shell  504  is at least two times greater than the cross-sectional area of the catheter  700 . 
         [0071]    In another embodiment, the diameter of the outer shell  504  is substantially larger than the diameter of the catheter  700 . In one embodiment, the diameter of the outer shell  504  is at least three times greater than the diameter area of the catheter  700 . In yet other embodiments, the diameter of the outer shell  504  is at least two times greater than the diameter of the catheter  700 . 
         [0072]      FIG. 12  illustrates an air embolism prevention device, or air block  1200 , comprising a shell  1202 , an exit valve  1204 , an intravascular sheath  1206 , and a catheter insert port  1208 . The air embolism prevention device  1200  prevents air bubbles from entering the intravascular sheath  1206  during any heart procedure, left-sided or right-sided. Air bubbles that get introduced into the vasculature could cause stroke, myocardial infarct, or other ischemic event. The shell  1202  is affixed to the intravascular sheath  1206  by a coupler (not shown) or it is permanently attached by bonding, welding, or the like. The catheter insert port  1208  is affixed to the proximal end of the shell  1202 . The exit valve  1204  is affixed to the distal end of the shell  1202  and is coupled, at or near its distal end, to a point substantially near the proximal end of the intravascular sheath  1206 . The exit valve  1204  is operably connects the through lumen of the intravascular sheath  1206  to the internal volume of the shell  1202  under control of the valving mechanism within the exit valve  1204 . The insert port  1208  operably connects the external environment with the interior volume of the shell  1202 . 
         [0073]      FIG. 13  illustrates a system and method of preventing air embolism during vascular procedures. The system, an air block or trap  1250 , comprises a case  1252 , a perforated cylindrical track  1254  further comprising fenestrations or perforations  1270 , an inlet valve  1256 , an outlet valve  1258 , an infusion port  1260  for a volume of pressurized liquid  1262 , an air escape valve  1264 , the volume of liquid  1262 , a volume of collected air  1266 , and a medical introducer sheath  1268 . The perforated cylindrical track  1254  allows catheter (not shown) passage and guide catheter (not shown) use when guidewires (not shown) have been introduced through the medical introducer sheath  1268 . The perforated cylindrical track  1254  further allows any air collected  1266  within its lumen to escape through the perforations  1270  into the surrounding chamber defined by annulus between the shell or case  1252  and the perforated cylindrical track  1254 . The pressurized infusion port  1260  prevents bleed out and air entry, maintaining a fluid (saline) interface at all times when the medical introducer sheath  1268  is used. The entire air block  1250  can be attached or affixed to a medical introducer sheath  1268 , catheter, cannula, or the like by way of a coupler (not shown) which engages, either permanently or removably, at or near the proximal end of the sheath  1268  hub (not shown). The inlet valve  1256  and the outlet valve  1258  are preferably hemostasis type valves, such as those known in the art of medical devices. 
         [0074]    The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. For example, the gas withdrawal system can be powered by an external power source or it can be powered manually. The scope of the invention is therefore indicated by the appended claims rather than the foregoing description. All changes that come within the meaning and range of equivalency of the claims are to be embraced within their scope.