Patent Publication Number: US-2021162110-A1

Title: Systems and methods for oxygenator performance evaluation

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application is a Continuation application of Ser. No. 15/805,896, filed on Nov. 7, 2017, entitled, “SYSTEMS AND METHODS FOR OXYGENATOR PERFORMANCE EVALUATION,” now allowed, which claims the benefit of the filing date of U.S. Provisional Patent Application Ser. No. 62/418,832, filed Nov. 8, 2016, entitled “SYSTEMS AND METHODS FOR OXYGENATOR PERFORMANCE EVALUATION,” the entire teachings of which are incorporated herein by reference. 
    
    
     BACKGROUND 
     The present disclosure relates to oxygenating blood in an extracorporeal circuit. More particularly, the disclosure relates to systems and methods for evaluating performance of an oxygenator operating in an extracorporeal circuit. 
     An extracorporeal circuit is commonly used during cardiopulmonary bypass to withdraw blood from the venous portion of the patient&#39;s circulation system (via a venous cannula) and return the blood to the arterial portion (via an arterial cannula). The extracorporeal circuit typically includes a venous drainage line, a venous blood reservoir, a blood pump, an oxygenator, a heat exchanger, one or more filters, and blood transporting tubing, ports, and connection pieces interconnecting the components. Oftentimes, an oxygenator and heat exchanger are combined into a single device. 
     Blood oxygenators are disposable components of extracorporeal circuits and are used to oxygenate blood. In general terms, the oxygenator takes over, either partially or completely, the normal gas exchange function of the patient&#39;s lungs. The oxygenator conventionally employs a microporous membrane or bundle comprised of thousands of microporous or semipermeable hollow fibers. Blood flow is directed around the outside surfaces of the hollow fibers. Concurrently, an oxygen-rich gas mixture is passed through the fiber lumens. Due to the relatively high concentration of carbon dioxide in the blood arriving from the patient, carbon dioxide is transferred from the blood, diffusing across the microporous fibers and into the passing stream of oxygenating gas. At the same time, oxygen is transferred from the oxygenating gas, diffusing across the fibers and into the blood. The oxygen content of the blood is thereby raised, and the carbon dioxide content is reduced. After the blood has flowed around the fibers of the oxygenator bundle it must be routed outside the oxygenator housing via a blood outlet port. 
     One of the most common failure modes of an extracorporeal circuit is when the oxygenator clogs. Extracorporeal life support cases are often conducted with minimal patient heparinization. This can lead to thrombus formation if heparin levels dip below levels that would control thrombus formation. Plugging or clogging of the oxygenator can also occur due to particulate matter or other mechanical issues. 
     In light of the above, a need exists for improved systems and methods for easy and reliable detection of oxygenator performance impairment. 
     SUMMARY 
     Some aspects in accordance with principles of the present disclosure relate to systems and methods for detecting detrimental oxygenator apparatus plugging or impedance in extracorporeal circuit systems or the like. One example oxygenator apparatus establishes a blood flow path from a blood inlet port, through an oxygenator fiber bundle and to a blood outlet port. During use of the oxygenator apparatus, the oxygenator fiber bundle can become clogged, thus reducing the flow of blood through the oxygenator and impairing its performance (i.e. the oxygenator&#39;s ability to oxygenate a sufficient amount of blood). Aspects of the disclosure provide systems and methods for measuring and monitoring oxygenator apparatus impedance to identify the progression of thrombus formation or other blockages in the oxygenator apparatus. 
     One example system includes an oxygenator apparatus having a first sensor for generating an inlet pressure measurement, a second for generating an outlet pressure measurement and a third sensor for generating a blood flow rate measurement. The inlet pressure measurement, outlet pressure measurement and blood flow rate measurement are used to calculate flow impedance and the systems disclosed herein communicate information relating to the same. 
     One method of monitoring oxygenator apparatus performance begins with fluidly connecting the blood inlet and outlet ports of the oxygenator apparatus into an extracorporeal circuit. Blood from the patient is delivered to the blood inlet port and is oxygenated when passing through the oxygenator fiber bundle. Blood flow impedance is calculated by a controller, as a function of a measured pressure differential divided by blood flow rate. In some embodiments, a baseline impedance is established. Blood from the patient is continually passed through the oxygenator apparatus and impedance measurements are repeatedly monitored to determine operational impedance. In situations where the difference between the baseline impedance and the operational impedance exceeds a predetermined threshold, an alert is communicated to the caregiver or clinician via a communication device to notify the caregiver that the oxygenator apparatus performance is impaired to the extent that the oxygenator apparatus should be replaced or heparin dosage should be reconsidered. In some disclosed systems and methods, the controller and communication device are provided by a standalone oxygenator apparatus used in a perfusion circuit and in other embodiments, systems and methods provide the controller and communication device apart from the oxygenator apparatus as provided to a user. With the disclosed methods, oxygenator apparatus impairment determinations are relatively effortless and oxygenator apparatus performance can be monitored by one having little training or experience. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic drawing of an extracorporeal circuit including an oxygenator apparatus for oxygenating patient blood. 
         FIG. 2  is a schematic drawing of an example oxygenator apparatus showing blood, fluid medium and gas medium flow through the oxygenator apparatus. 
         FIG. 3  is a cross-sectional, side view of the oxygenator apparatus schematically shown in  FIG. 2 . 
         FIG. 4  is a schematic diagram of one system for monitoring impairment of an oxygenator apparatus, such as the oxygenator apparatus of  FIGS. 2-3 . 
         FIG. 5  is a schematic diagram of an alternate system, similar to that of  FIG. 4 . 
         FIG. 6  is a flow chart generally illustrating one method of communicating information indicative of oxygenator apparatus performance. 
         FIG. 7  is a flow chart generally illustrating one example method of detecting oxygenator apparatus impairment. 
         FIG. 8A  is a graph illustrating a first example of impedance trending information. 
         FIG. 8B  is a graph illustrating a second example of impedance trending information. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  schematically illustrates an exemplary extracorporeal circuit  10  that can be modified and used in accordance with the teachings of the present disclosure. The extracorporeal circuit  10  is a system or device in which blood is desired to be oxygenated (and, optionally, temperature controlled). One particular system is an electromechanical extracorporeal circulatory support system known as a cardiopulmonary bypass (CPB) system, commercially sold by Medtronic, Inc., of Minneapolis, Minn. under the trade name Performer-CPB System. Other systems are contemplated by the present disclosure. The exemplary extracorporeal circuit  10  includes an oxygenator apparatus  12  and generally draws blood of a patient  14  during cardiovascular surgery through a venous line  16 . Venous blood drawn from the patient  14  is discharged into a venous reservoir  18 . Cardiotomy blood and surgical field debris are aspirated by a suction device  20  and are pumped by a pump  22  into a cardiotomy reservoir  24 . Once de-foamed and filtered, the cardiotomy blood is also discharged into the venous reservoir  18 . Alternatively, the function of the cardiotomy reservoir  24  may be integrated into the venous reservoir  18 . In the venous reservoir  18 , air entrapped in the venous blood rises to the surface of the blood and is vented to the atmosphere. 
     A pump  26  draws blood from the venous reservoir  18  and pumps it through the oxygenator apparatus  12 . Some exemplary types of pumps  26  include, but are not limited to, roller pumps and centrifugal pumps. The pump  26  may be external to the oxygenator apparatus  12  as shown, or may alternatively be incorporated into the oxygenator apparatus  12 . As described above, the blood is de-aerated, optionally temperature controlled, and oxygenated by the oxygenator apparatus  12 , and then returned to the patient  14  via an arterial line  28 . 
     In one example embodiment, during operation of the oxygenator apparatus  12  as part of the circuit  10 , air is purged from oxygenator apparatus  12  via an air purge port  27  (referenced generally in  FIG. 1 ). In some embodiments, during normal operation this purge will consist solely of blood, which may detract from the total blood flow out of the oxygenator apparatus  12 . When air enters the oxygenator apparatus  12 , the inlet geometry forces the air out of the air purge port  27  and through an air purge line  29 . 
     One of the most common failure modes of an extracorporeal circuit is when a patient on extracorporeal life support or extracorporeal membrane oxygenation therapy is when the oxygenator apparatus  12  clogs. Extracorporeal life support cases are often conducted with minimal patient heparinization. This can lead to thrombus formation if heparin levels dip below levels that would control thrombus formation. Clogging of the oxygenator apparatus  12  can also occur due to particulate matter or other mechanical issues. Therefore, the present disclosure further includes methods of monitoring oxygenator apparatus performance and alerting a caregiver when the oxygenator performance is nearing an unacceptable threshold and/or when it is recommended that the oxygenator apparatus be replaced or patient heparin dosage can be revised to address thrombus formation. Further embodiments can include providing various stages of alert (e.g., green, yellow, red) for when the oxygenator is adequately performing (green), when the oxygenator apparatus is nearing inadequate performance (yellow) and when the oxygenator apparatus is insufficiently performing (red). The methods and systems disclosed herein make oxygenator apparatus monitoring and maintenance effortless and can be performed by one having little training or experience. 
     Components of one system  30 , including a non-limiting example of an oxygenator apparatus  32  useful for treating blood in an extracorporeal circuit, are shown in  FIGS. 2-3 . In general terms, the oxygenator apparatus  32  includes a housing  34  and an oxygenator  36 . The oxygenator  36  includes a plurality of gas exchange elements (referenced generally as oxygenator fiber bundle  38 ) that can be connected to a gas supply  40 . To effectuate temperature control of the blood, the oxygenator apparatus  32  can optionally include a heat exchanger  42  (a plurality of heat exchange elements are referenced generally) for connection to a fluid supply  44 . The housing  34  provides or maintains a blood inlet port  46  and a blood outlet port  48 . A blood flow path  50  is defined from the blood inlet port  46  to the blood outlet port  48 , with blood oxygenation occurring as the blood interfaces with an oxygenator fiber bundle  38 . Additionally disclosure regarding the example oxygenator  36  and heat exchanger  42  are provided in U.S. Pat. No. 8,545,754 (Carpenter et al.), the disclosure of which is hereby incorporated by reference in its entirety. 
     The system  30  further includes a first sensor  52  proximate the blood inlet port  46  for generating an inlet pressure measurement and a second sensor  54  proximate the blood outlet port  48  for generating an outlet pressure measurement. The system  30  further includes a third sensor  56  for generating a blood flow rate measurement. In various embodiments, the third sensor  56  is proximate the blood outlet port  48  or downstream of the blood outlet port  48  (see also,  FIG. 1 ). The disclosure is not intended to be limited to any specific placement of the first, second and third sensors  52 ,  54 ,  56 . Any placement of the first-third sensors  52 ,  54 ,  56  capable of determining a pressure differential and blood flow rate measurement are acceptable. 
     In this embodiment, the housing  34  further carries a controller  60  and/or communication device  62 . The controller  60  is electronically connected with the first, second and third sensors  52 ,  54 ,  56  as well as the communication device  62 . The controller  60  is programmed to determine flow impedance through the oxygenator fiber bundle  38  as a function of the inlet pressure measurement, the outlet pressure measurement and the blood flow rate measurement generated by the first, second and third sensors  52 ,  54 ,  56 . The controller  60  is further configured to prompt the communication device  62  to communicate information indicative of the determined oxygenator apparatus  32  performance, including, but not limited to blood flow impedance. In one embodiment, the blood flow impedance is defined as: 
       (inlet pressure measurement−outlet pressure measurement)/blood flow rate measurement  (1)
 
     With the above in mind,  FIG. 4  schematically illustrates the system  30  of  FIGS. 2-3  for oxygenating blood in an extracorporeal circuit (e.g., circuit  10  of  FIG. 1 ). As previously indicated, the system  30  includes the oxygenator apparatus  32  having the housing  34  carrying the oxygenator  36  as well as the communication device  62  (e.g., display and/or speaker) and controller  60 . Alternatively, the controller  60  and communication device  62  can be provided elsewhere in the system  30 , separate from the housing  34 . 
       FIG. 5  schematically illustrates one such alternate system  130 . The system  130  differs from system  30  only in that the controller  60  and communication device  62  are not part of or carried by the housing  34 . In this embodiment, the controller  60  and communication device  62  are provided as separate parts of the system  130 . As indicated with reference numerals, it will be understood that all other aspects of the system  130  are configured and operate in ways previously disclosed with respect to system  30 . 
     Referring also to  FIG. 6 , one example method for automatically characterizing the performance of the oxygenator apparatus  100  includes directing patient blood flow through an oxygenator apparatus  102 , generating an inlet pressure measurement  104 , generating an outlet pressure measurement  106  and also sensing a blood flow rate measurement  108 . In certain embodiments, the inlet pressure measurement is generated at or adjacent the blood inlet port  46 , the outlet pressure measurement is generated proximate the blood outlet port  48  and the flow rate is generated proximate the blood outlet port  48  (as shown in  FIGS. 2-5 ). The method further comprises utilizing the controller  60  to automatically determine oxygenator apparatus  32  flow impedance as a function of the inlet pressure measurement, the outlet pressure measurement and blood flow rate measurement  110  to determine and communicate information indicative of the oxygenator apparatus flow impedance to a clinician. For example, Equation (1) is applied via the controller  60  and then the controller  60  sends a signal to the communication device  62  to communicate data  112  (e.g., via display and/or audio) regarding either oxygenator apparatus flow impedance and/or the measurements obtained in steps  104  through  108 . 
     In various embodiments, the controller  60  is further programmed to determine a baseline oxygenator apparatus  32  flow impedance at a first point in time and a second point in time, after the first point in time, and then also prompt the communication device  62  to communicate information indicative of a comparison between the baseline oxygenator apparatus flow impedance and the current oxygenator apparatus flow impedance. In even further embodiments, the controller  60  can be programmed to generate oxygenator apparatus flow impedance trending information based on a multiplicity of sequentially determined oxygenator apparatus flow impedances; and determine an end-of-life criteria for the oxygenator apparatus based upon the oxygenator apparatus flow impedance trending information. Alternatively, or in addition, the controller  60  can be programmed to prompt the communication device  62  to communicate an alert when the determined difference exceeds a predetermined value. In yet further embodiments, when significant impedance is identified, patient heparin dosage can be revised, which may reduce impedance due to blood clotting without the need for replacing the oxygenator apparatus. Further embodiments can include providing various stages of alert (e.g., green, yellow, red) for when the oxygenator is adequately performing (green), when the oxygenator apparatus is nearing inadequate performance (yellow) and when the oxygenator apparatus is insufficiently performing (red). Such a “yellow” stage of alert can also include a prediction when the oxygenator will transition to a “red” state of alert (i.e. when the oxygenator will need to be replaced). This would allow a nurse who notices rising oxygenator impedance the knowledge that they have time to allow specialists (perfusionists) to be available, potentially after one or more shifts. The nurse would be informed that the oxygenator is starting to clot, but it is not critical yet and can wait until other staffing is available. In one example, the green stage is when the transmembrane pressure range is between 150 mmHg-250 mmHg, the yellow stage is greater than 250 mmHg-350 mmHg and the red stage is when the transmembrane pressure range exceeds 350 mmHg. Such various stages of alert can be visual, audial or the like. 
     Reference is now also made to  FIG. 7 , which illustrates one such method of monitoring oxygenator apparatus performance  200 . The method can begin with providing an oxygenator apparatus incorporated into a system for oxygenating blood, such as the extracorporeal circuit  10  disclosed above. Before venous blood is drawn from the patient, a threshold variance establishing blood impedance within the oxygenator apparatus  32  is established  202 . This threshold can be established by the oxygenator apparatus manufacturer or, alternatively, selected or adjusted by the user. After the predetermined threshold is established  202 , venous blood is drawn from the patient and ultimately directed into the oxygenator apparatus  204  via the blood inlet port  46 . From the blood inlet port  46 , the venous blood is oxygenated, optionally heated via the heat exchanger  42 , and discharged out of the oxygenator apparatus  32  via the blood outlet port  48 . First, second and third sensors  52 ,  54 ,  56  are positioned to measure the blood flow rate and pressure differential across the oxygenator apparatus  32 . From this information, a normalized or baseline impedance is calculated  206 : 
       Impedance=(inlet pressure measurement−outlet pressure measurement)/blood flow rate measurement
 
     As will be understood, the baseline impedance can vary greatly on a number of factors particular to the electromechanical extracorporeal circulatory support system, blood characteristic, etc. After the baseline impedance is determined  206 , venous blood flow through the oxygenator apparatus  32  continues  208  and operational impedance is repeatedly measured  210 . With at least some of the operational impedance measurements, the operational impedance measurements are compared to the baseline impedance measurement via the controller  60  to determine if a variance, if any, between the baseline impedance and the operational impedance measurement meets or exceeds the predetermined threshold  212 . If the threshold variance is not met, operation of the oxygenator apparatus  32  continues and venous blood continues to flow through the oxygenator apparatus  208 . If the threshold variance is met and/or exceeded, an alert or communication  214  is provided (e.g., via communication device  62 ) to the clinician that oxygenator apparatus  32  performance is impaired to the extent that the oxygenator apparatus should be replaced or heparin dosage should be revised  216  to maintain adequate oxygenator apparatus performance. The alert can be a visual, audial or both, for example. 
     Example A 
       FIG. 8A  a graph illustrating generated impedance values of an oxygenator apparatus (i.e. generated impedance trending information). Such impedance trending information can be used by the controller to monitor oxygenator performance. In Example A, the oxygenator apparatus flow impedance trending information is generated based on a multiplicity of sequentially determined oxygenator apparatus flow impedances in accordance with Equation (1). The data generated in this Example is provided in Table 1. In this Example, the predetermined threshold variance is 35 mmHG*min/L. Therefore, should the calculated impedance exceed 35 mmHG*min/L, the controller is configured to prompt the communication device to provide an alert, as discussed above. In the present Example, throughout the test period the oxygenator apparatus is sufficiently operational and the measured oxygenator apparatus impedance does not reach a value great enough to trigger an alert. 
     
       
         
           
               
               
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                 Inlet 
                 Outlet 
                 Inlet 
                 Blood 
                   
                 Predetermined 
               
               
                   
                 pressure 
                 pressure 
                 pressure − 
                 Flow 
                   
                 Threshold of 
               
               
                 Time 
                 measurement 
                 measurement 
                 outlet 
                 Rate 
                 Impedance 
                 Impedance 
               
               
                 (mins) 
                 (mmHG) 
                 (mmHG) 
                 pressure 
                 (L/min) 
                 (mmHG * min/L) 
                 (mmHG * min/L) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 10 
                 337 
                 163 
                 174 
                 7 
                 24.9 
                 35 
               
               
                 30 
                 368 
                 167 
                 201 
                 7 
                 28.7 
                 35 
               
               
                 90 
                 358 
                 167 
                 191 
                 7 
                 27.3 
                 35 
               
               
                 180 
                 361 
                 169 
                 192 
                 7 
                 27.4 
                 35 
               
               
                 270 
                 362 
                 167 
                 195 
                 7 
                 27.9 
                 35 
               
               
                 360 
                 367 
                 168 
                 199 
                 7 
                 28.4 
                 35 
               
               
                 450 
                 372 
                 168 
                 204 
                 7 
                 29.1 
                 35 
               
               
                 540 
                 377 
                 168 
                 209 
                 7 
                 29.9 
                 35 
               
               
                 630 
                 382 
                 168 
                 214 
                 7 
                 30.6 
                 35 
               
               
                 720 
                 387 
                 168 
                 219 
                 7 
                 31.3 
                 35 
               
               
                 810 
                 392 
                 168 
                 224 
                 7 
                 32.0 
                 35 
               
               
                 900 
                 397 
                 168 
                 229 
                 7 
                 32.7 
                 35 
               
               
                   
               
            
           
         
       
     
     Example B 
       FIG. 8B  graph illustrating a second example showing impedance values of an oxygenator apparatus (i.e. generated impedance trending information). In Example B, the oxygenator apparatus flow impedance trending information is generated based on a multiplicity of sequentially determined oxygenator apparatus flow impedances in accordance with Equation (1). The data generated in this Example is provided in Table 2 below. In this Example, the predetermined threshold for impedance is also set at 35 mmHG*min/L. In the present Example, the oxygenator apparatus performance is sufficiently compromised at minute  630  when the generated impedance reaches 37.1 mmHG*min/L. In this Example, the controller would prompt the communication device to provide an alert indicative of the inadequate oxygenator apparatus performance due to blood flow impedance at minute  630 . 
     
       
         
           
               
               
               
               
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                   
                 Inlet 
                 Outlet 
                 Inlet 
                 Blood 
                   
                 Predetermined 
               
               
                   
                 pressure 
                 pressure 
                 pressure − 
                 Flow 
                   
                 Threshold of 
               
               
                 Time 
                 measurement 
                 measurement 
                 outlet 
                 Rate 
                 Impedance 
                 Impedance 
               
               
                 (mins) 
                 (mmHG) 
                 (mmHG) 
                 pressure 
                 (L/min) 
                 (mmHG * min/L) 
                 (mmHG * min/L) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 10 
                 337 
                 163 
                 174 
                 7 
                 24.9 
                 35 
               
               
                 30 
                 368 
                 167 
                 201 
                 7 
                 28.7 
                 35 
               
               
                 90 
                 358 
                 167 
                 191 
                 7 
                 27.3 
                 35 
               
               
                 180 
                 361 
                 169 
                 192 
                 7 
                 27.4 
                 35 
               
               
                 270 
                 362 
                 167 
                 195 
                 7 
                 27.9 
                 35 
               
               
                 360 
                 367 
                 168 
                 199 
                 7 
                 28.4 
                 35 
               
               
                 450 
                 372 
                 168 
                 204 
                 7 
                 29.1 
                 35 
               
               
                 540 
                 400 
                 168 
                 232 
                 7 
                 33.1 
                 35 
               
               
                 630 
                 428 
                 168 
                 260 
                 7 
                 37.1 
                 35 
               
               
                 720 
                 456 
                 168 
                 288 
                 7 
                 41.1 
                 35 
               
               
                 810 
                 484 
                 168 
                 316 
                 7 
                 45.1 
                 35 
               
               
                 900 
                 512 
                 168 
                 344 
                 7 
                 49.1 
                 35 
               
               
                   
               
            
           
         
       
     
     Examples A and B are hypothetical scenarios and do not represent actual test data. 
     Although the present disclosure has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes can be made in form and detail without departing from the spirit and scope of the present disclosure.