Abstract:
A method of diversion of an embolus during fluid circulation in an extracorporeal circuit which includes the steps of establishing a first circuit ( 100, 101   a,    101   b,    101   c,    102, 103, 104, 106   b,    106   a,    107 ) between an outlet of a vascular system and an inlet of said vascular system; establishing a 5 second circuit ( 101   b,    101   c,    102, 103, 104, 106   b,    108 ) configured to bypass said inlet and outlet; providing a fluid reservoir ( 102 ) a pumping means ( 103 ), and a bubble detector ( 105 ) in said circuits; detecting by means of said bubble detector ( 105 ) an embolus in said first circuit and sending a signal to an automatic embolus diversion supervisor ( 121 ) connected to said bubble detector ( 105 ); and controlling fluid flow direction means ( 110, 111 ) in dependence of the signal from said bubble detector ( 105 ); whereby said fluid flow direction means ( 110, 111 ) are controlled to redirect a detected embolus to said second circuit.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to diversion of an embolus during fluid circulation. More specifically the present invention relates to the separation of an embolus comprised in a flowing fluid before the flowing fluid reaches a target. 
       BACKGROUND OF THE INVENTION 
       [0002]    During extracorporeal circulation in e.g. heart surgery there is a risk to introduce detrimental matter into the circulation of the patient. The formation of blood clots and gas bubbles can occur unobtrusively despite rigorous routines to avoid the formation of these emboli, or it can occur from malpractice by the involved personnel. Gas emboli are formed in circulating blood due to cavitation, temperature gradients, and the surplus amount of gases dissolved in blood. In the case the extracorporeal circuit contains a gas-exchange device e.g. an oxygenator there is even a greater risk of gaseous emboli. 
         [0003]    Gas emboli can be detected by different techniques, and all modern heart-lung machines are equipped with a warning system to detect gas emboli. Typically the bubble sensor can discern bubbles with a diameter of approximately 0.3 mm, but the main pump is halted first when a bubble with a diameter of 3-5 mm is recognized, as reported in e.g. the manuals of Jostra HLM20 and Stockert S3 heart-lung machines. It is obvious for a person skilled in the art that bubbles or other emboli of millimeter-size may be harmful for the organism since capillaries are much smaller with diameters a hundred times less. Thus, the built-in security measures against bubble injection in heart-lung machines currently on the market seem inadequate. Besides, when an embolus halts the heart-lung machine the patient is deprived completely of circulation and a series of maneuvers has to be performed by the perfusionist and the surgeon to rid the tubing from the embolus. This may take some time and there is a great risk in misunderstandings and mishandling of the situation due to stress. Formerly, extracorporeal procedures were most often performed in hypothermia which increased the acceptable period of no-circulation, but nowadays most procedures are in normothermia, i.e. at normal temperatures, which adds to the stress. Thus, not only the adverse effects of bubbles per se, but also the cumbersome mandatory maneuvers to rid the device of sensed bubbles before their entry into the patient, may be deleterious. 
         [0004]    The symptoms in patients appearing after a heart operation with extracorporeal circulation has been termed “Pumphead” and include long lasting and possibly permanent cognitive decline, cf. Scientific American, 2003, (289) 68-73. Furthermore, symptoms also include personality changes, difficulties in concentration and emotional unstableness. Bearing in mind that more than a million extracorporeal procedures are performed in the world annually this is a formidable problem. Researchers in the field speculate that the cause of these adverse effects stems from microembolization and depositing gas or fat into the capillaries of the brain as well as activation of the inflammatory response, complement system etc. Focal neurological deficits also add to postpump complications, and these have been attributed to the manipulation of ascending aorta, letting free solid parts of ateheromatous plaques into the blood stream which subsequently obstruct cerebral vessels. 
         [0005]    During heart operations with extracorporeal circulation, the tube supplying oxygenated blood to the body is introduced into the circulation through an aortic cannula introduced into the ascending aorta. Thus large bubbles may enter the circulation at a location where they are immediately directed into the cerebral circulation. The jet of blood entering the ascending aorta is concentrated in size and of high speed and may therefore preferentially enter one of the carotid arteries. The capillary bed of the brain serves as a filter for the blood from the heart-lung machine, which is disadvantageous and at least in part may explain the frequent clinical neurological deficiencies encountered after heart surgery. 
         [0006]    In the prior art, several methods focus on eliminating bubbles from circulating fluids including blood. An example of how to divert bubbles from an extracorporeal circuit is presented in U.S. Pat. No. 6,478,962, wherein bubbles are separated by radial centrifugal forces in a chamber constructed for the purpose which is incorporated into the extracorporeal circuit. The U.S. Pat. No. 6,053,967 discloses a method based on a similar principle, and in the U.S. Pat. No. 6,328,789 bubbles are separated by gravitational force. Also the method presented in the international patent application WO 02/072236 relies on the differences in density of the liquid and comprising emboli. None of these methods have means to detect bubbles in the blood stream when they occur. They all separate emboli mechanically due the difference in density of the emboli and the surrounding liquid. Also, in catastrophic events, when large amounts of air enter the system, these methods easily get saturated, letting air through into the blood vessels of the patient. 
       PURPOSE OF THE INVENTION 
       [0007]    The purpose of the present invention is to provide a method, an apparatus and a system for the elimination of an embolus, such as a gas bubble, in blood in an extracorporeal circulation circuit. Also very large amounts of gas emboli will be able to be diverted from entering the circulation of the patient. The automatic embolus diversion design of the present invention enables the device to decrease the total embolic load during the procedure. This is accomplished by constantly choosing the smallest possible sensed embolus to be diverted from the patient without adversely interfering with the perfusion. Also, automation will accomplish that the surgeon will not be disturbed in situations where today his attention to help debubble the tubing system is needed. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0008]    The problem to avoid an inadvertent introduction of gas bubbles or other emboli into the organism is solved according to the invention by a method, an apparatus and a system according to the independent claims. Preferred embodiments of the invention are set out in the dependent claims. 
         [0009]    The invention utilizes the signal from a bubble detector to automatically activate or deactivate a system of clamps or valves attached to an arterial line used for the extracorporeal circulation. Thus, a gas bubble detected in the arterial line is directed away from the patient via an arterio-venous tubing to the venous line of the extracorporeal system. This is accomplished by the action of a control unit that has the ability to control and to calculate timing of the clamping and declamping of the arterio-venous connecting tube. This is performed concomitantly as the aortic cannula is clamped during the period of time that the bubble is redirected over to the venous line via the arterio-venous tubing. Immediately after the bubble has passed, the clamps are to be reset to resume blood flow into the patient again. This sequence of exactly timed actions of different parts of the automatic device will need a computer designed for the purpose. It may need inputs from the heart-lung machine regarding current delivery rate of blood and also size of current tube diameter and distance of the arterial line from the sensor to the diverting valve. Also time constants of all parts of the automatic device have to be accounted for by the computer. 
         [0010]    The present invention will be described with reference to extracorporeal circulation in for example heart surgery, but other embodiments are obvious for the person skilled in the art of perfusion and the invention can also be used in other clinical applications, such as in the clinical setup for dialysis. Also in industrial processes the design of this invention may be useful. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0011]    The present invention will be described in further detail below, with reference to the accompanying drawings, of which 
           [0012]      FIG. 1  illustrates the state of art for extracorporeal circulation in heart surgery.  FIG. 1   a  shows the tubing in a majority of cases.  FIG. 1   b  utilizes an additional arterio-venous tubing connection close to the patient, operated by the thoracic surgeon while initiating extracorporeal circulation and weaning from the pump. 
           [0013]      FIG. 2  shows schematically a first embodiment of the inventive system; 
           [0014]      FIG. 3  shows schematically a detailed illustration of the extracorporeal tubing system close to the patient in accordance with the first embodiment of the invention as depicted in  FIG. 2 ; 
           [0015]      FIG. 4  is a schematic illustration of how a method for in vitro testing of the system can be performed before initiation of extracorporeal circulation; 
           [0016]      FIG. 5  shows schematically an alternatively constructed extracorporeal part of the first embodiment of the present invention; 
           [0017]      FIG. 6  shows schematically a second embodiment of the inventive system; 
           [0018]      FIG. 7  shows schematically an enlarged view of the automatic embolus diversion supervisor according to the invention; and 
           [0019]      FIG. 8  depicts schematically a third embodiment of the inventive system, intended for dialysis. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0020]    The present invention relates to control and diversion of bubbles in tubings where liquid is propelled. More specifically the present invention refers to simple, quick and efficient avoidance of bubbles entering into the circulation of a living being. This is accomplished by the construction of extracorporeal tubings equipped with devices intended to make it possible to momentarily divert bubbles or emboli, and which is controlled automatically by signals from one or more bubble/emboli sensors. The signals can be analyzed and processed in a computerized device having a central processor. The analyzed and/or processed information can then be utilized for diverting detected emboli and thereby avoiding infusion of hazardous emboli in a patient. The computer can also get input data from a heart-lung machine. 
         [0021]    The present invention relates to a system, an apparatus, and a method for controlling the bubbles in an extracorporeal circulatory procedure. It is intended for heart surgery, but can also be employed in a multitude of clinical applications, e.g. dialysis, in which it is desirable to extracorporeally circulate a body fluid. 
         [0022]      FIG. 1  illustrates schematically the current state of art for the setup of the tubing of the main pump in extracorporeal circulation during open heart surgery. In  FIG. 1   a  venous blood is diverted from vena cava through a venous cannula  100  to a venous tubing or line  101  and enters a venous blood reservoir  102 . Here it is filtered and large bubbles may be eliminated by gravitational force. A main pump  103 , here shown of a roller pump model, subsequently generates movement energy to the blood which then enters an oxygenator  104  where gas exchange occurs. A bubble detector  105  is attached to an arterial tubing or line  106 . In some cases this is done after an optional embolus filter. Blood then enters the blood vessels of the patient through an arterial cannula  107  which in the exemplifying embodiment is introduced into the ascending aorta. 
         [0023]      FIG. 1   b  shows a slightly different setup with an arterio-venous connection  108  of the tubing close to the patient, which is manipulated by the surgeon during the operation. This can be used for the continuous circulation of priming fluid and bubble elimination after cannulation but before the initiation of extracorporeal circulation. Also, during extracorporeal assist, in case an air embolus has halted the main pump  103  by the bubble sensing device  105 , the embolus can be diverted from entering into the patient by alerting the surgeon to momentarily open the arterio-venous connection and concomitantly clamp the arterial and venous cannula. 
         [0024]    The present invention will now be described in more detail. In the figures the same reference numerals is used for the same or similar features. 
         [0025]      FIG. 2  shows schematically a first embodiment of the present invention. A first fluid circuit  100 ,  101   a ,  101   b ,  101   c ,  102 ,  103 ,  104 ,  106   a ,  106   b ,  107 ,  109  is established between an outlet from a vascular system of a living being and an inlet into said vascular system. As exemplified in  FIG. 2 , the outlet is realized as an outlet from the vena cava and the heart and the inlet is realized as an inlet into ascending aorta of the patient. Blood can be extracted from the outlet by means of a extraction means, e.g. a cannula,  100  and extracorporeally circulated in said fluid circuit between the outlet and the inlet. 
         [0026]    A second fluid circuit  101   b ,  101   c ,  102 ,  103 ,  104 ,  106   b ,  108 ,  109  is configured to bypass the inlet and the outlet of the vascular system. As shown in  FIG. 2 , the body will thus be bypassed by the second fluid circuit. However, it should be understood that the inlet and outlet do not have to be an inlet and an outlet of the same organ or body part, but they can be an inlet and an outlet of different organs or body parts. 
         [0027]    A fluid reservoir  102 , a pumping means  103 , and a bubble detector  105  is arranged at the first and second fluid circuits. The fluid reservoir  102  is also configured to filter the fluid and to, by means of gravitational force, eliminate or reduce large bubbles. The pumping means  103 , e.g. a roller pump, is configured to generate movement energy to the fluid in the fluid circuit. The bubble detector  105  is configured to detect an embolus in the first fluid circuit and to send a signal to an automatic embolus diversion supervisor  121  connected to the bubble detector  105 . By means of the signal, the automatic embolus diversion supervisor  121  is informed that an embolus is detected. Based on the signal, the automatic embolus diversion supervisor  121  can determine when the fluid flow is to be redirected from the first fluid circuit to the second fluid circuit in order to divert said detected embolus from the inlet, i.e. in order not to introduce the detected embolus into the body part of the living being. When the embolus has passed by a branching element  109  of the fluid circuit, the fluid flow is redirected from the second fluid circuit back to the first fluid circuit. 
         [0028]    The automatic embolus diversion supervisor  121  is connected to the extracorporeal tubings  106   a ,  106   b ,  108 , and to the bubble detector or sensor  105 . Further, the automatic embolus diversion supervisor  121  is attached with hydraulic/pneumatic tubes  135 ,  136 ,  137 ,  138  or electric cables (not shown) to the fluid flow redirection means  110 ,  111 . The fluid flow redirection means  110 ,  111  can be realized as automatic clamping devices  110 ,  111 . Signals from the bubble sensor  105  to the automatic embolus diversion supervisor  121  are transmitted by means of the cable  133  and inputs from and outputs to a heart-lung machine can be transmitted by means of cables  132  and  134 . The automatic embolus diversion system  121  is thus configured to control the redirectional valves or clamping devices, to sense and ascertain that redirection of an embolus has occurred, and possibly also to control the pumping means. Further, the automatic embolus diversion system  121  can be configured to display the amount of emboli sensed and redirected. 
         [0029]      FIG. 3  depicts a part of the extracorporeal tubing system of the first embodiment of the inventive system. In this embodiment the controlling of flow throw the tubing is performed by hydraulic or pneumatic forces working on pistons in cylinders. A vital part of the tubing is the branching element, y-piece,  109  inserted into the arterial line  106   a ,  106   b . Here is where the embolus shall be directed from entering the vascular system of the patient and redirected into the extracorporeal arterio-venous tubing  108 . These parts of the tubing are close to the operating field and consequently sterile. The cylinders and pistons  110 ,  111  are intended for use a multitude of times and therefore not sterile. To be able to attach them to the tubing close to the y-piece  109 , this has to be performed while protecting the sterile vicinity from contamination. Therefore the single-use set of tubing could be equipped with a sterile protective shield  112  covering the arterial line  106 , the y-piece  109  and a further distance of the connecting arterio-venous tubing  108  so that the cylinders and pistons with their tubing can be attached properly, leaving so much space that in case of malfunction of the device its detaching and the manual clamping and declamping necessary for a safe extracorporeal procedure can easily be performed. 
         [0030]    A signal generated by the bubble sensor pumps fluid/gas in the tubes  113 ,  114  into the device  110  so that the arterio-venous tube  108  is opened for the passage of the embolus. Concomitantly, or shortly afterwards, the arterial flow into the patient through the arterial cannula  107  is halted in a similar but opposite way by pumping fluid/gas in the tubes  115 ,  116  into the device  111 . After an appropriate time period to let the embolus pass into the venous system, the tubing into the patient is reopened and the arterio-venous connection closed. 
         [0031]      FIG. 4  illustrates the function test of the method. This can be performed in vitro before the commencement of the in vivo procedure. The cannula loop  117 , equivalent to  101   a  and  106   a , of the tubing is kept undivided and the automatic embolus diversion system  121  is mounted and activated while the heart-lung machine circulates the priming fluid through  108 . A syringe  118  filled with air is attached to the tubing through a conventional Luer-Lock  119  before the embolus sensor  105 . Coordinated in time with the surgeon, the perfusionist injects an air embolus from the syringe and the surgeon confirms that the mechanism of the pistons and cylinders are functioning so that the bubble is redirected from the cannula loop  117  into the arterio-venous tubing  108 . The testing can be performed at different pump-flows to check for proper calculation algorithm of the automatic embolus diversion supervisor  121 . 
         [0032]    Another embodiment of a part of the extracorporeal tubings is depicted in  FIG. 5 . In this embodiment, the branching element is realized as a circular, three-ways, valve  109 ′ which can be controlled by a valve control means  120 , e.g. by the position of a piston in a cylinder  120 . The cylinder  120  is connected to the valve  109 ′ and to the automatic embolus diversion supervisor  121 . 
         [0033]    It is obvious to a person skilled in the art that the invention may be modified in other ways within the scope of the appended claims, thus the mechanism for redirection of emboli may rest upon e.g. mechanic, hydraulic, pneumatic or electromagnetic force. 
         [0034]    A second embodiment for the additional safety of the inventive system is depicted in  FIG. 6  and includes two or more embolus sensors. One of these bubble detectors  105  is attached to the arterial line  106   b  as shown in the first embodiment. Another detector  139  may be attached to the arterio-venous tubing  108  as shown in  FIG. 6 . By this arrangement it is possible to ascertain that an embolus in the arterial line  106   b , detected by the first sensor  105 , indeed has been redirected by the embolus diversion system  121 , since, if the embolus has been correctly redirected the second bubble detector  139  will subsequently detect the diverted embolus. Another bubble detector (not shown) may be attached to the arterial line  106   a . This arrangement may even be deemed mandatory, since an embolus that ordinarily should halt the main pump, by the present invention does not halt the pump but is redirected. Thus, it is desirable, or mandatory, to ascertain, closer to the patient, the absence of the embolus detected by the first sensor  105 , signifying adequate function of the embolus diversion system  121 . And, in case the embolus again appears at the sensor closer to the patient, there is still time and space to halt the pump and avoid embolus entry into the vascular system. 
         [0035]    This embodiment may need an additional length of the arterial line  106   b , since the automatic embolus diversion system  121  will need time, firstly for the redirectional valves or clamping devices to react, secondly for the sensing and ascertaining that redirection of an embolus has occurred, and thirdly, in case of malfunction, for calculation and for the signal to be conveyed to halt the main pump. In  FIG. 6  therefore, both the proximal  106   a  and distal  106   b  part of the arterial line are shown with increased lengths. In this embodiment the branching element  109 ,  109 ′ may need to be incorporated into the tubing so close to the oxygenator  104  that there will be no need for keeping it sterile during the extracorporeal circulatory procedure. With the extra tubing needed for this embodiment extra priming volume may be needed to add. However, if the arterial tubing is of dimension ⅜″, less than 100 ml extra priming volume per meter tube will be satisfactory. 
         [0036]    In the case that the automatic embolus diversion system  121  is activated for a prolonged period there may be a need for the temporary closure of the venous line in order not to let an unnecessary amount of blood out from the patient into the venous reservoir. For this purpose, the invention also may include a third automatically controlled cylinder with piston (not shown) attached to the venous cannula  100  or tubing  101   a  in a similar way as the arterial counterpart  111 . However, the necessity to clamp the venous line during a main pump halt is basic to any perfusionist—who is obliged to act in accordance. 
         [0037]    The automatic embolus diversion supervisor  121 , see  FIG. 7 , is the computerized control unit of this invention. The automatic embolus diversion supervisor  121  contains means for proper handling of the system, i.e. interactive means such as displays, knobs, keyboard. The size of the arterial line  106   a ,  106   b  diameter can be set by the perfusionist with a knob  122 . The sensitivity of the embolus sensor can be chosen with the knob  123 , i.e. by means of the knob  123  the diameter of an embolus to be diverted can be set. The knob  123  may also have a position with no sensitivity at all, which position gives that the automatic embolus diversion system is not in operation. The test switch  124  in the on-position makes the automatic embolus diversion supervisor to be activated but not to document an embolus sensed. The screen  125  shows the size and frequency distribution of small emboli that have been sensed but not redirected by the automatic embolus diversion system  121 . Thus no emboli larger than the size chosen by the sensitivity knob  123  should be possible to document on the screen  125 . Before extracorporeal circulation is commenced, the priming fluid is circulated through the arterio-venous tube  108 . Then, when bypass starts the arterio-venous tube  108  is clamped and the arterial  107  and venous  100  cannulae declamped. This maneuver can be performed by the surgeon and perfusionist in concert—the surgeon manually declamps the venous cannula  100  and the perfusionist clamps the arterio-venous tube  108  and declamps the arterial cannula  107  by turning the switch  126  on the display. This may also start the timing of extracorporeal procedure and the documentation of emboli sensing by  105 , so that the frequency of operation of the automatic embolus diversion system  121  can be displayed  127  and the sensitivity knob  124  be adjusted in order to achieve optimal performance of the system. Instead of the total number of occasions the automatic embolus diversion system  121  has been activated, the total active time can be shown in this display  127 . In this embodiment of the automatic embolus diversion supervisor  121 , the displays  128 ,  129 ,  130 , and  131  show the present setting for some operation parameters, such as arterial line diameter, main pump output, the distance between the sensor  105  and the branching element  109 ,  109 ′, and hydraulic pressure, respectively. 
         [0038]    The distance between the sensor  105  and the branching element  109 ,  109 ′, and the flow rate in the arterial line  106  are important parameters to know in order for the system to bypass a detected embolus optimally in time and thus minimize the amount of blood that is diverted and not reinfused to the patient by means of the arterial cannula  107 . During extracorporeal circulation it is desirable to open the flow in the arterio-venous line  108  and to close the flow in the arterial cannula  107  just as a detected embolus enters the branching element  109 ,  109 ′ and then, reversely, closing the arterio-venous line  108  and opening the flow towards the arterial cannula  107  just as the entire embolus has passed into the arterio-venous line  108 . 
         [0039]    Signals of interest from a connected heart-lung machine such as perfusion flow (l/min), bubble detection can be conveyed to the automatic embolus diversion supervisor through the cable  132 . Signals from high quality sensor(s)  105  and  139  for emboli detection are transmitted in cable  133 . Information and demands from the automatic embolus diversion supervisor  121  to the heart-lung machine are conveyed by the cable  134 . Tubes or cables  135 ,  136 ,  137 , and  138  are for controlling clamping devices. 
         [0040]    A third embodiment of the inventive system is depicted in  FIG. 8 . In this application the invention is modified to be used in dialysis. The oxygenator is in this situation not needed and a dialysis membrane  140  is added. In dialysis, the venous reservoir may be of a smaller size as compared to the size of the venous reservoir in the previously described embodiments. However, in case a large bubble has been detected and is redirected according to the method of the invention, the venous reservoir should contain enough volume to minimize operational arrests. In  FIG. 8  the dialysis catheter  141  entering the body is depicted as a two-lumen veno-venous dialysis catheter, but other arrangements of cannulation the vascular system for dialysis are feasible. 
         [0041]    The present invention has been described above with reference to exemplifying embodiments, and it is obvious to a person skilled in the art that the invention may be modified in other ways within the scope of the appended claims.