Patent Publication Number: US-2020276377-A1

Title: Blood gas exchanger with restriction element or elements to reduce gas exchange

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. patent application Ser. No. 15/571,548, filed Nov. 3, 2017, which is a national stage application of PCT/IB62015/053493, filed May 12, 2015, which is herein incorporated by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates generally to extracorporeal fluid circuits. More specifically, the disclosure relates to an oxygenator, or gas exchanger, used in such circuits having at least one restriction element that allows for a reduction in gas exchange to avoid hypo-capnia and hyper-oxygenation in small patients. 
     BACKGROUND 
     The disclosure pertains generally to blood processing units used in blood perfusion systems. Blood perfusion entails encouraging blood through the vessels of the body. For such purposes, blood perfusion systems typically entail the use of one or more pumps in an extracorporeal circuit that is interconnected with the vascular system of a patient. Cardiopulmonary bypass surgery typically requires a perfusion system that provides for the temporary cessation of the heart to create a still operating field by replacing the function of the heart and lungs. Such isolation allows for the surgical correction of vascular stenosis, valvular disorders, and congenital heart defects. In perfusion systems used for cardiopulmonary bypass surgery, an extracorporeal blood circuit is established that includes at least one pump and an oxygenation device to replace the functions of the heart and lungs. 
     More specifically, in cardiopulmonary bypass procedures oxygen-poor blood, i.e., venous blood, is gravity-drained or vacuum suctioned from a large vein entering the heart or other veins in the body (e.g., femoral) and is transferred through a venous line in the extracorporeal circuit. The venous blood is pumped to an oxygenator that provides for oxygen transfer to the blood. Oxygen may be introduced into the blood by transfer across a membrane or, less frequently, by bubbling oxygen through the blood. Concurrently, carbon dioxide is removed across the membrane. The oxygenated blood is filtered and then returned through an arterial line to the aorta, femoral artery, or other artery. 
     In small patients, particularly neonatal patients, with low blood volumes, if a standard sized oxygenator is used during cardiopulmonary bypass, excessive carbon dioxide removal and excessive oxygen delivery can result. Excessive carbon dioxide removal can lead to a deleterious change of pH of the blood out of the physiological levels. Avoiding excessive carbon dioxide removal and excessive oxygen delivery is, therefore, desired. 
     SUMMARY 
     Example 1 of the present disclosure is a gas exchanger comprising: a gas exchanger housing including an outer wall and a core which defines an inner wall and having a blood inlet for receiving a blood supply and a blood outlet, the gas exchanger housing defining a gas exchanger volume; a hollow fiber bundle disposed within the housing between the core and the outer wall, the hollow fiber bundle comprising hollow gas permeable fibers, each fiber having first and second ends and a hollow interior; and a gas inlet compartment for receiving an oxygen supply and directing the oxygen supply to the first ends of the hollow gas permeable fibers; wherein the gas inlet compartment includes at least one restriction element configured to allow the oxygen supply to reach only a portion of the hollow gas permeable fibers. 
     Example 2 is the gas exchanger of Example 1, wherein the at least one restriction element comprises a gasket. 
     Example 3 is the gas exchanger of Example 1, wherein the at least one restriction element is moveable such that the at least one restriction element can assume a first position that is opened in order to allow the oxygen supply to reach all of the hollow gas permeable fibers and a second position that is closed such that the oxygen supply only reaches a portion of the hollow gas permeable fibers. 
     Example 4 is the gas exchanger of Example 1, wherein the gas exchanger includes at least two restriction elements and the at least two restriction elements are concentrically arranged. 
     Example 5 is the gas exchanger of Example 1, wherein the gas exchanger housing is tubular in shape, the gas inlet compartment includes a gas inlet that is located at or near the center of the lid, and the at least one restriction element concentrically surrounds the gas inlet. 
     Example 6 is the gas exchanger of Example 1, wherein 50% of the fiber bundle is provided with oxygen supply for a small, neonatal patient. 
     Example 7 is a gas exchanger comprising: a gas exchanger housing including an outer wall, at least one lid, and a core which defines an inner wall and having a blood inlet for receiving a blood supply and a blood outlet, the gas exchanger housing defining a gas exchanger volume; a hollow fiber bundle disposed within the housing between the core and the outer wall, the hollow fiber bundle comprising hollow gas permeable fibers, each fiber having first and second ends and a hollow interior, wherein the first ends of the hollow gas permeable fibers are located in a first potting that is located at or near the lid; and a gas inlet compartment including a gas inlet for receiving an oxygen supply and directing the oxygen supply to the first ends of the hollow gas permeable fibers; wherein the gas inlet compartment includes at least one restriction element that concentrically surrounds the gas inlet, wherein the one or more restriction elements are moveable such that the one or more restriction elements can assume a first position that is open in order to allow the oxygen supply to reach all of the first ends of the hollow gas permeable fibers and a second position that is compressed against the potting such that the oxygen supply only reaches a portion of the hollow gas permeable fibers. 
     Example 8 is the gas exchanger of Example 7, further comprising at least one rigid lever that is connected to the at least one restriction element and that is configured to move the at least one restriction element between the first and second positions. 
     Example 9 is the gas exchanger of Example 7, wherein the gas inlet compartment is located within the at least one lid. 
     Example 10 is the gas exchanger of Example 7, wherein the oxygenator includes at least two restriction elements and the at least two restriction elements are concentrically arranged. 
     Example 11 is the gas exchanger of Example 7 wherein the at least one restriction element comprises a gasket. 
     Example 12 is the gas exchanger of Example 7, wherein 50% of the fiber bundle is provided with oxygen supply for a small, neonatal patient. 
     Example 13 is a method of oxygenation comprising: providing a gas exchanger comprising: a gas exchanger housing including an outer wall and a core which defines an inner wall and having a blood inlet for receiving a blood supply and a blood outlet, the gas exchanger housing defining a gas exchanger volume; a gas inlet compartment for receiving an oxygen supply and directing the oxygen supply to the first ends of the hollow gas permeable fibers; wherein the gas inlet compartment includes at least one restriction element configured to allow the oxygen supply to reach only a portion of the hollow gas permeable fibers; activating the at least one restriction element; causing the oxygen supply to flow through the hollow interior of the portion of the hollow gas permeable fibers; delivering blood to the gas exchanger through the blood inlet; causing the blood to flow through the gas exchanger housing over the exterior of the hollow gas permeable fibers; and discharging the blood through the blood outlet. 
     Example 14 is the method of Example 13, wherein the at least one restriction element comprises a gasket. 
     Example 15 is the method of Example 13, wherein the at least one restriction element is moveable such that the at least one restriction element can assume a first position that is open in order to allow the oxygen supply to reach all of the hollow gas permeable fibers and a second position that is closed such that the oxygen supply only reaches a portion of the hollow gas permeable fibers. 
     Example 16 is the method of Example 15, wherein activating the at least one restriction element comprises moving the at least one restriction element to the second position. 
     Example 17 is the method of Example 13, wherein the gas exchanger includes at least two restriction elements and the at least two restriction elements are concentrically arranged. 
     Example 18 is the method of Example 13, wherein the gas exchanger housing is tubular in shape, the gas inlet compartment includes a gas inlet that is located at or near the center of the lid, and the at least one restriction element concentrically surrounds the gas inlet. 
     Example 19 is the method of Example 13, wherein the at least one restriction element concentrically surrounds the gas inlet, wherein the one or more restriction elements are moveable such that the one or more restriction elements can assume a first position that is open in order to allow the oxygen supply to reach all of the first ends of the hollow gas permeable fibers and a second position that is compressed against the potting such that the oxygen supply only reaches a portion of the hollow gas permeable fibers. 
     Example 20 is the method of Example 13, wherein 50% of the fiber bundle is provided with oxygen supply for a small, neonatal patient. 
     While multiple embodiments are disclosed, still other embodiments of the present disclosure will become apparent to those skilled in the art from the following detailed description, which shows and describes illustrative embodiments of the disclosure. Accordingly, the drawings and detailed description are to be regarded as illustrative in nature and not restrictive. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an oxygenator, or gas exchanger, in accordance with embodiments of the disclosure. 
         FIG. 2  is a cross-sectional view of the oxygenator of  FIG. 1  taken at  2 - 2 . 
         FIG. 3  is a partial cross-sectional view of an oxygenator in accordance with embodiments of the disclosure. 
         FIG. 4  is a partial cross-sectional view of an oxygenator in accordance with embodiments of the disclosure. 
         FIG. 5  is a partial cross-sectional view of an oxygenator in accordance with embodiments of the disclosure. 
         FIG. 6  is a schematic cross-sectional view of an oxygenator in accordance with embodiments of the disclosure. 
         FIG. 7  is a cross-sectional view of an embodiment of an oxygenator in accordance with embodiments of the disclosure. 
         FIG. 8A  is a partial cross-sectional view of an oxygenator in accordance with embodiments of the disclosure. 
         FIG. 8B  is a cross-sectional view of the oxygenator of  FIG. 8A  taken at B-B. 
     
    
    
     While the disclosure is amenable to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and are described in detail below. The intention, however, is not to limit the disclosure to the particular embodiments described. On the contrary, the disclosure is intended to cover all modifications, equivalents, and alternatives falling within the scope of the disclosure. 
     DETAILED DESCRIPTION 
     The disclosure pertains to an oxygenator (also commonly referred to as a gas exchanger). In some embodiments, an oxygenator may be used in an extracorporeal blood circuit. An extracorporeal blood circuit, such as may be used in a bypass procedure, may include several different elements such as a heart-lung machine, a blood reservoir, a heat exchanger, as well as an oxygenator. In various embodiments, the gas exchanger, or oxygenator, includes one or more restriction elements that allow for a reduction in gas transfer performance of the oxygenator in order to avoid hypo-capnia and hyper-oxygenation in patients, particularly small or neonatal patients. In various embodiments, one or more restriction elements are configured to be activated to allow an oxygen supply to reach only a portion of hollow gas permeable fibers, thereby reducing the amount of gas exchange performed by the oxygenator. 
       FIG. 1  is a schematic illustration of an oxygenator  10  (or “gas exchanger”). While the internal components are not visible in the illustration, the oxygenator  10  will include a fiber bundle inside where gas exchange takes place. The oxygenator  10  includes a housing  12 , a first end cap  14  that is secured to the housing  12  and a second end cap  16  that is secured to the housing  12 . In some embodiments, the housing  12  may include other structures that enable attachment of the housing  12  to other devices. While the housing  12  is largely cylindrical in shape, in some embodiments, the housing  12  may have a triangular, rectangular or other parallelogram cross-sectional shape, for example. The fiber bundle inside may have generally the same sectional shape as the housing  12  or may have a different sectional shape. 
     In some embodiments, a blood inlet  18  extends into the housing  12  and a blood outlet  20  exits the housing  12 . As noted, the oxygenator  10  includes a fiber bundle inside where gas exchange takes place, and thus includes a gas inlet  22  and a gas outlet  24 . In some embodiments, the oxygenator  10  may include one or more purge ports  30  that may be used for purging air bubbles from the interior of the oxygenator  10 . 
     The positions of the blood and gas inlets and outlets, and the purge port  30  in  FIG. 1  are merely illustrative, as other arrangements and configurations are also contemplated. The purge port  30  may include a valve or a threaded cap. The purge port  30  operates to permit gases (e.g., air bubbles) that exit the blood to be vented or aspirated and removed from the oxygenator  10 . 
     The housing  12  is preferably made of a rigid plastic in order for the oxygenator  10  to be sturdy yet lightweight. The oxygenator is also preferably mainly transparent, in order to allow the user to see through the oxygenator. Therefore, a preferred material for the oxygenator is a transparent, amorphous polymer. One exemplary type of such a material is a polycarbonate, an ABS (Acrylonitrile Butadiene Styrene), or a co-polyester. Other suitable materials for the housing are also contemplated. 
     The fiber bundle (not shown in  FIG. 1 ) inside housing  12  may include a number or plurality of microporous hollow fibers through which a gas such as oxygen may flow. The blood may flow around and past the hollow fibers. Due to concentration gradients, oxygen may diffuse through the microporous, semi-permeable hollow fibers into the blood while carbon dioxide may diffuse into the hollow fibers and out of the blood. 
     In some embodiments, the hollow fibers are made of semi-permeable membrane including micropores. Preferably, the fibers comprise polypropylene, polyester, or any other suitable polymer or plastic material. According to various embodiments, the hollow fibers may have an outer diameter of about 0.25 to about 0.3 millimeters. According to other embodiments, the microporous hollow fibers may have a diameter of between about 0.2 and 1.0 millimeters, or more specifically, between about 0.25 and 0.5 millimeters. The hollow fibers may be woven into mats that can range from about 50 to about 200 millimeters in width. In some embodiments, the mats are in a criss-cross configuration. The fiber bundle may be formed of hollow fibers in a variety of winding patterns or structures. 
     The hollow fibers are embedded, or sealed, at their ends, in rings of polyurethane resin, for example, which is known as “potting.” The fiber bundle of hollow fibers is preferably in a cylindrical shape, but other shapes are also contemplated. The hollow fibers, at first ends, are connected to the first end cap  14  through the potting, with the gas inlet  22  being located in the first end cap  14 . At second ends, the hollow fibers are connected to the second end cap  16  through the potting with the gas outlet  24  being located in the second end cap  16 . The internal lumens of the fibers are part of the gas pathway that is determined by the fist end cap  14 , the potting at the first end, the fibers, the second potting and the second end cap  16 . The oxygenator chamber is thus defined by the housing as an outer wall and an inner wall or core, together with the pottings at each end of the hollow fibers. 
     Oxygen, or a mixture of oxygen and air, known as an oxygen supply, enters through gas inlet  22 , passes through the microporous hollow fibers within the fiber bundle, and exits the oxygenator  10  through the gas outlet  24 . In some embodiments, the pressure or flow rate of oxygen through the oxygenator may be varied in order to achieve a desired diffusion rate of, for example, carbon dioxide diffusing out of the blood and oxygen diffusing into the blood. In some embodiments, as illustrated, the oxygen flows through the hollow fibers while the blood flows around and over the hollow fibers. 
     Differences in concentration of gases between the blood and the oxygen supply produce a diffusive flow of oxygen toward the blood and of carbon dioxide from the blood in the opposite direction. The carbon dioxide reaches the gas outlet  24  and is discharged from the oxygenator  10 . 
     Any suitable gas supply (or oxygen supply) system may be used with the oxygenator  10  of the disclosure, in order to deliver an oxygen supply to the fiber bundle or hollow fibers of oxygenator  10 . Such a gas supply system may also include, for example, flow regulators, flow meters, a gas blender, an oxygen analyzer, a gas filter, and a moisture trap. Other alternative or additional components in the gas supply system are also contemplated. 
     As shown in  FIG. 1 , in some embodiments, structural features may be included within oxygenator  10 , and specifically within the first end cap  14  in the figure, that allow an oxygen supply delivered to the oxygenator  10  to reach only a portion of the hollow fibers in the fiber bundle where gas exchange takes place. The restriction elements are configured to be either in an open/inactivated position or a closed/activated position. Moving the at least one restriction element to a closed or activated position will result in an oxygen supply being delivered to only a portion of the hollow fibers in the fiber bundle, and thereby will reduce gas transfer performance. The disclosure provides a way to decrease gas exchange efficiency of the oxygenator  10  in order to avoid excessive carbon dioxide removal and excessive oxygen delivery to small patients, including neonatal patients. 
       FIG. 1  shows two restriction elements, first restriction element  32  and second restriction element  34 , extending from or within first end cap  14 . Although two restriction elements are shown, it is contemplated that any number of restriction elements may be included, such that the size of the first end cap  14  may accommodate the restriction elements. The figure also shows two levers or arms  36  and  38  that extend from or that are coupled or attached to the restriction elements  32 , which are used to move the restriction elements between a restricted or closed configuration and an unrestricted or open configuration. Levers or arms  36 ,  38  are exemplary structural features used to move the restriction elements  32 ,  34 , but other suitable features are also contemplated by the disclosure. 
       FIG. 2  is a cross-sectional view of the first end cap  14  shown in the embodiments of the disclosure in  FIG. 1  taken at line  2 - 2 .  FIG. 2  shows that restriction elements  32  and  34  are circular in shape and are concentrically arranged and surrounding gas inlet  22 . The circular shape is one exemplary cross-sectional shape of the restriction elements  32  and  34 , but other shapes are also contemplated by the disclosure. The restriction elements  32 ,  34  may be gaskets, for example, although other options are also contemplated. Preferably, such gaskets may be made from a silicone or any soft rubber-like material that is able to provide an airtight seal with the polymeric wall of the end cap  14 . The silicone or rubber-like material of the restriction elements may also be supported by a rigid material in order to provide rigidity to the gasket and allow it to open and close. 
       FIGS. 3, 4 and 5  are partial cross-sectional perspective views of oxygenator  10 .  FIG. 3  shows the oxygenator  10  with both restriction elements  32 ,  34 , in an open or inactivated configuration.  FIG. 4  shows the same view as in  FIG. 3 , but with restriction element  32  being in a closed or activated configuration.  FIG. 5  shows the same view again as in  FIGS. 3 and 4 , but with restriction element  34  being in a closed or activated configuration. 
       FIGS. 3, 4 and 5  show cross-sectional views of circular-shaped, restriction elements  32 ,  34 , with rigid levers  36 ,  38  attached, respectively. The levers  36 ,  38  that are attached to or an extension of restriction elements  32 ,  34  are one example of a feature that may be used to move the restriction elements between an inactivated configuration and an activated configuration or vice versa. Other methods or structural features that would allow the restriction elements to be moveable between the two configurations are also contemplated by the disclosure. For example, a pre-loaded spring (not shown) may be provided in order to move the restriction elements between an open and a closed position. Alternatively, a snap (not shown) may be used to fix the restriction elements in an open or a closed position. Another alternative restriction element is shown in  FIGS. 8A and 8B , and is described in detail below. 
     Fiber bundle  40 , made up of a plurality of hollow fibers (not shown individually), is shown with a potting  42  on first ends of the hollow fibers. A gas inlet compartment  44  is formed within first end cap  14  between the gas inlet  22  and potting  42 . The gas-holding capacity or size of the gas inlet compartment  44  is determined by whether the restriction elements  32 ,  34  are activated or not. 
       FIG. 4  shows restriction element  32  in the closed or activated configuration. In order to activate the restriction elements  32 ,  34 , the levers  36 ,  38  may be pushed, which moves the restriction elements  32 ,  34  inward through the gas inlet compartment  44  and towards potting  42 . Once the restriction elements  32 ,  34  are in contact with potting  42 , the portion of the gas inlet compartment  44  that is capable of filling with the gas or oxygen supply is reduced. Also, the portion of the hollow fibers in fiber bundle  40  that are able to be reached by the oxygen supply is reduced. Oxygen supply coming in through gas inlet  22  is only able to reach the portion of the hollow fibers in fiber bundle  40  with first end openings that are located between gas inlet  22  and the activated restriction element  32  or  34 .  FIG. 5  shows restriction element  34  in an activated configuration. Compared to  FIG. 4 , where restriction element  32  is activated, a greater number of hollow fibers would be able to receive oxygen supply in the fiber bundle in  FIG. 5 ; however it would still only be only a portion of the hollow fibers in the whole fiber bundle  40 . Any number and locations of restriction elements may be included in embodiments of the disclosure, as can be accommodated by the size of the oxygenator  10 . 
       FIG. 6  is a schematic view of a portion of a cross-section of the oxygenator  10  shown in  FIG. 1 . The portion shown includes core  50  of the housing  12 , which is not shown in previous figures. In  FIG. 6 , restriction element  34  is activated and in contact with potting  42 . Only hollow fibers making up the fiber bundle  40  that are to the interior of the restriction element  34  are active or effective and able to receive oxygen supply. The dotted lines mark the outer perimeter of the active or effective fibers, which are bracketed and marked as  60  in the figure. This configuration is possible if a gas inlet connector (not shown) is to the interior of restriction element  34 . If, however, the gas inlet connector (not shown) is to the exterior of the restriction element  34 , then the hollow fibers of the fiber bundle that are to the exterior of the restriction element  34  would be active or effective and able to receive oxygen supply. 
       FIG. 7  is a cross-sectional view of another embodiment of an oxygenator  100  of the present disclosure. The oxygenator of the present disclosure can stand alone or, as shown, oxygenator  100  can include an integrated heat exchanger  118 . In the particular embodiment shown, blood flow through the heat exchanger portion  118  is circumferential, while blood flow though the gas exchanger portion is longitudinal. Other arrangements are contemplated, however. As shown in  FIG. 7 , the oxygenator  100  includes a housing  102 , a first end cap  104 , and a second end cap  106 . The oxygenator  100  includes a blood inlet  108  and a blood outlet  110 . A gas inlet  112  permits oxygen to be provided to the gas exchanger portion, while a gas outlet  114  permits gases to exit the oxygenator  100 . 
     The oxygenator  100  includes a heat exchanger core  116 , a heat exchanger element  118  disposed about the heat exchanger core  116 , a cylindrical shell  120  disposed about the heat exchanger element  118  and a gas exchanger element  122 , all disposed inside the outer shell or housing  102 . The heat exchanger element  118  and the gas exchanger element  122  may each include a number of hollow fibers as discussed with respect to oxygenator  10  ( FIGS. 1-6 ). In some embodiments, the housing  102  includes an annular portion  124  that is in fluid communication with the blood outlet  110 . 
     In use, blood enters the blood processing apparatus or oxygenator  100  through the blood inlet  108  and passes into the heat exchanger core  116 . The blood fills the heat exchanger core  116  and exits through an elongate core aperture  126  and thus enters the heat exchanger element  118 . In some embodiments, the heat exchanger core  116  includes a single elongate core aperture  126 , while in other embodiments, the heat exchanger core  116  may include two or more elongate core apertures  126 . In some embodiments, the elongate aperture  126  allows or directs blood to flow through the heat exchanger element  118  in a circumferential direction. 
     As shown in  FIG. 7 , according to some embodiments, the cylindrical shell  120  includes an elongate collector or channel  127 . The channel  127  may be disposed at a location substantially diametrically opposed to the location of the elongate core aperture  126 . Locating the channel  127  substantially opposite the location of the core aperture  126  causes blood to flow in a generally circumferential flow pattern within the heat exchanger element  118 . The channel  127  may extend from between about 1 and about 15 degrees about the circumference of the cylindrical shell  120 . In one exemplary embodiment, the channel  127  extends about 5 degrees about the circumference. The blood flow path can be circumferential, as described. Some other alternatives to the blood flow path, however, include radial or longitudinal flow or combinations of circumferential, radial and/or longitudinal flow. 
     After blood passes through the heat exchanger element  118 , it collects in the channel  127  and flows into an annular shell aperture  128 . The shell aperture  128 , in various embodiments, extends entirely or substantially around the circumference of the cylindrical shell  120 , such that blood exits the inner cylindrical shell  120  around the entire or substantially the entire circumference of the cylindrical shell  120 . In some embodiments, the radially disposed shell aperture  128  may be located near an end of the oxygenator  100  that is opposite the blood outlet  110 , thereby causing the blood to flow through the heat exchanger element  118  in a longitudinal direction. Blood then collects in the annular portion  124  before exiting the oxygenator  100  through the blood outlet  110 . 
     At least one restriction element  132 , as in the embodiment shown in  FIG. 7 , would be located radially outward from, and circumferentially surround, the gas inlet  112 . Restriction element  132  would include a lever or another activation member  136  that would allow the restriction element  132  to be moved to contact the potting of the fiber bundle in order to reduce the number of hollow fibers in the fiber bundle of the gas exchanger element  122  that receive oxygen supply. 
     The embodiment shown in  FIG. 7  is one exemplary integrated oxygenator and heat exchanger. The oxygenator of the present disclosure may or may not include a heat exchanger component. Also, other embodiments of integrated oxygenators and heat exchangers are contemplated by the disclosure that may include other configurations and blood flow patterns. The embodiment shown in  FIG. 7  is one example. 
       FIGS. 8A and 8B  show two different cross-sections of another embodiment of the gas exchanger, or oxygenator, of the present disclosure.  FIG. 8A  is a partial cross-section of the gas exchanger  200  taken longitudinally, and  FIG. 8B  is a cross-section taken at line B-B from  FIG. 8A . The oxygenator  200  has a housing  212  surrounding a plurality of hollow fibers  240  (not shown individually). A potting is shown by  210 . One end cap  214  is shown that includes a gas inlet  222 . A generally circular-shaped restriction element  250  is included in the end cap  214 . The restriction element  250  is able to be rotated in two directions as shown by the arrow on  FIG. 8B . Restriction element  250  includes a plurality of holes  243  or passages that may be lined up or not lined up with holes or passages  233  in stationary element  232  that may be located either radially inward or outward from restriction element  250 . Depending on whether or not the whole fiber bundle or only a portion of the fiber bundle is desired to be used for a particular patient, the holes  243  and  233  may or may not be lined up. If the holes  243  and  233  are lined up then gas will flow through the whole fiber bundle. If the holes  233  and  243  are not lined up, then the gas may only reach the fibers in the portion of the fiber bundle that is located radially outward from the restriction element  250 . This is one more exemplary embodiment of the gas exchanger of the present disclosure. 
     The present disclosure allows the use of one device for a range of sizes of neonatal patients. The device allows for ease in setting appropriate gas exchange performances based on specific patient dimensions, thereby avoiding excess carbon dioxide removal, particularly for very small patients (size 5 kg or less, for example). Gas exchange may be set based on the amount of fiber bundle that is active or used, based on whether or not a restriction element is activated or not. With no restriction elements activated, the percentage of the fiber bundle that is active or used is about 100%. If one restriction element is activated, the percentage of the fiber bundle that is active or used is about 50%,for example. If there are two restriction elements included in the device, then the percentage of active fiber bundle could be either about 33% or about 66%, for example, depending on which restriction element is activated. The percentages of fiber bundle that may be active or used may be varied as well as the number and location of the restriction element or elements. 
     Another embodiment of the disclosure is a method of oxygenation or oxygenating blood. The steps may comprise providing an oxygenator comprising: an oxygenator housing including an outer wall and a core which defines an inner wall and having a blood inlet for receiving a blood supply and a blood outlet, the oxygenator housing defining an oxygenator volume; a hollow fiber bundle disposed within the housing between the core and the outer wall, the hollow fiber bundle comprising hollow gas permeable fibers, each fiber having first and second ends and a hollow interior; a gas inlet compartment for receiving an oxygen supply and directing the oxygen supply to the first ends of the hollow gas permeable fibers; wherein the gas inlet compartment includes at least one restriction element configured to allow the oxygen supply to reach only a portion of the hollow gas permeable fibers. The oxygenator may alternatively be any embodiment as described, suggested or shown herein, or any other suitable oxygenator. The method may further comprise: activating at least one restriction element; causing an oxygen supply to flow through the hollow interior of the portion of the hollow gas permeable fibers; delivering blood to the oxygenator through the blood inlet; causing the blood to flow through the oxygenation housing over the exterior of the hollow gas permeable fibers; and discharging the blood through the blood outlet. Other methods of oxygenation are also contemplated by the disclosure. 
     Various modifications and additions can be made to the exemplary embodiments discussed without departing from the scope of the present disclosure. For example, while the embodiments described above refer to particular features, the scope of this disclosure also includes embodiments having different combinations of features and embodiments that do not include all of the described features. Accordingly, the scope of the present disclosure is intended to embrace all such alternatives, modifications, and variations as fall within the scope of the claims, together with all equivalents thereof.