Patent Publication Number: US-2020276378-A1

Title: Blood treatment air purging system and method

Description:
PRIORITY CLAIM 
     The present application is a continuation of U.S. application Ser. No. 15/789,535, entitled “Blood Treatment Air Purging Systems”, filed Oct. 20, 2017, which is a continuation of U.S. application Ser. No. 14/446,609, entitled “Blood Treatment Air Purging Methods”, filed Jul. 30, 2014, now U.S. Pat. No. 9,795,731, issued Oct. 24, 2017, which is a continuation of U.S. application Ser. No. 13/894,020, entitled “Fluid and Air Handling in Blood and Dialysis Circuits”, filed May 14, 2013, now U.S. Pat. No. 8,834,403, issued Sep. 16, 2014, which is a continuation of U.S. application Ser. No. 12/237,160, entitled “Fluid and Air Handling in Blood and Dialysis Circuits”, filed on Sep. 24, 2008, now U.S. Pat. No. 8,444,587, issued May 21, 2013, which claims priority to and the benefit of U.S. Provisional Patent Application Ser. No. 60/976,731, filed Oct. 1, 2007, entitled “Fluid And Air Handling In Dialysis Circuit Air Removal System”, the disclosure if each of which is incorporated herein by reference and relied upon. 
    
    
     BACKGROUND 
     The examples discussed below relate generally to medical fluid delivery. More particularly, the examples disclose systems, methods and apparatuses for dialysis, such as hemodialysis (“HD”), hemofiltration (“HF”) hemodiafiltration (“HDF”) automated peritoneal dialysis (“APD”). 
     Due to various causes, a person&#39;s kidneys can fail. Renal failure produces several physiological derangements. It is no longer possible to balance water and minerals or to excrete daily metabolic load. Toxic end products of nitrogen metabolism (urea, creatinine, uric acid, and others) can accumulate in blood and tissue. 
     Kidney failure and reduced kidney function have been treated with dialysis. Dialysis removes waste, toxins and excess water from the body that normal functioning kidneys would otherwise remove. Dialysis treatment for replacement of kidney functions is critical to many people because the treatment is life saving. 
     One type of kidney failure therapy is Hemodialysis (“HD”), which in general uses diffusion to remove waste products from a patient&#39;s blood. A diffusive gradient occurs across the semi-permeable dialyzer between the blood and an electrolyte solution called dialysate to cause diffusion. Hemofiltration (“HF”) is an alternative renal replacement therapy that relies on a convective transport of toxins from patient&#39;s blood. This therapy is accomplished by adding substitution or replacement fluid to the extracorporeal circuit during treatment (typically ten to ninety liters of such fluid). That substitution fluid and the fluid accumulated by the patient in between treatments is ultrafiltered over the course of the HF treatment, providing a convective transport mechanism that is particularly beneficial in removing middle and large molecules (in hemodialysis there is a small amount of waste removed along with the fluid gained between dialysis sessions, however, the solute drag from the removal of that ultrafiltrate is not enough to provide convective clearance). 
     Hemodiafiltration (“HDF”) is a treatment modality that combines convective and diffusive clearances. HDF uses dialysate flowing through a dialyzer, similar to standard hemodialysis, to provide diffusive clearance. In addition, substitution solution is provided directly to the extracorporeal circuit, providing convective clearance. 
     Most HD (HF, HDF) treatments occur in centers. A trend towards home hemodialysis (“HHD”) exists today in part because HHD can be performed daily, offering therapeutic benefits over in-center hemodialysis treatments, which occur typically bi- or tri-weekly. Studies have shown that a patient receiving more frequent treatments removes more toxins and waste products than a patient receiving less frequent but perhaps longer treatments. Studies on HHD have shown a reduction in anti-hypertensive medications while restoring normotension. Randomized trials on long daily dialysis have shown a reduction in left ventricular hypertrophy, which is a surrogate marker for improved patient survival. In addition a patient receiving more frequent treatments does not experience as much of a down cycle as does an in-center patient who has built-up two or three days worth of toxins prior to a treatment, providing much better quality of life. In certain areas, the closest dialysis center can be many miles from the patient&#39;s home causing door-to-door treatment time to consume a large portion of the day. HHD can take place overnight or during the day while the patient relaxes, works or is otherwise productive. 
     Another type of kidney failure therapy is peritoneal dialysis, which infuses a dialysis solution, also called dialysate, into a patient&#39;s peritoneal cavity via a catheter. The dialysate contacts the peritoneal membrane of the peritoneal cavity. Waste, toxins and excess water pass from the patient&#39;s bloodstream, through the peritoneal membrane and into the dialysate due to diffusion and osmosis, i.e., an osmotic gradient occurs across the membrane. Osmotic agent in dialysis provides the osmotic gradient. The spent dialysate is drained from the patient, removing waste, toxins and excess water from the patient. This cycle is repeated. 
     There are various types of peritoneal dialysis therapies, including continuous ambulatory peritoneal dialysis (“CAPD”), automated peritoneal dialysis (“APD”), tidal flow dialysate and continuous flow peritoneal dialysis (“CFPD”). CAPD is a manual dialysis treatment. Here, the patient manually connects an implanted catheter to a drain to allow spent dialysate fluid to drain from the peritoneal cavity. The patient then connects the catheter to a bag of fresh dialysate to infuse fresh dialysate through the catheter and into the patient. The patient disconnects the catheter from the fresh dialysate bag and allows the dialysate to dwell within the peritoneal cavity, wherein the transfer of waste, toxins and excess water takes place. After a dwell period, the patient repeats the manual dialysis procedure, for example, four times per day, each treatment lasting about an hour. Manual peritoneal dialysis requires a significant amount of time and effort from the patient, leaving ample room for improvement. 
     Automated peritoneal dialysis (“APD”) is similar to CAPD in that the dialysis treatment includes drain, fill and dwell cycles. APD machines, however, perform the cycles automatically, typically while the patient sleeps. APD machines free patients from having to manually perform the treatment cycles and from having to transport supplies during the day. APD machines connect fluidly to an implanted catheter, to a source or bag of fresh dialysate and to a fluid drain. APD machines pump fresh dialysate from a dialysate source, through the catheter and into the patient&#39;s peritoneal cavity. APD machines also allow for the dialysate to dwell within the cavity and for the transfer of waste, toxins and excess water to take place. The source can include multiple sterile dialysate solution bags. 
     APD machines pump spent dialysate from the peritoneal cavity, though the catheter, and to the drain. As with the manual process, several drain, fill and dwell cycles occur during dialysis. A “last fill” occurs at the end of APD and remains in the peritoneal cavity of the patient until the next treatment. 
     In any of the above modalities, entrained air and other gases are a concern. Entrained air can cause inaccuracies when pumping dialysate for either PD or HD. Entrained air can cause a reduction in effective surface area in a hemodialysis filter when it accumulates on the filter fibers, leading to a reduction in the effectiveness of the therapy. Entrained air entering a patient&#39;s peritoneum during PD can cause discomfort. Entrained air entering a patient&#39;s bloodstream during HD can have severe consequences. Even though the patient may be protected from an air embolism in some HD equipment, there have been situations with removing the air from the blood in which the patient has had to throw away the extracorporeal circuit, resulting in blood loss and cost. Accordingly, a need exists to provide an apparatus that ensures that entrained air is removed from dialysate or blood prior to delivering such fluids to the patient. 
     SUMMARY 
     The present disclosure may employ level sensing and coordinated pumping and valving algorithms to control the fluid level in an air trap. In addition, the present disclosure allows the system to flow either gas or fluid (saline and/or heparin and/or priming solution and/or dialysis solution and/or blood and/or etc.) out of a fluid circuit directly to a fluid drain and/or fluid vessel (i.e. saline bag and/or priming bag and/or dialysis solution bag and/or container). Also, the present disclosure allows the system to flow gas out of a fluid circuit directly to atmosphere and fluid (saline and/or heparin and/or priming solution and/or dialysis solution and/or blood and/or etc.) out of a fluid circuit directly to a fluid drain and/or fluid vessel (i.e. saline bag and/or priming bag and/or dialysis solution bag and/or container). 
     The method of controlling level and removing air described above has advantages in the areas of priming and air trap level control. Currently air trap level control is a manual process. Prior to the therapy, the operator must connect a port on the air trap to a luer connection on the instrument. This port connects the air trap to a compressor on the instrument. This in turn allows for lowering or raising the air trap fluid level through level control switches on the instrument. If the operator does not make this connection securely, blood can flow up through this port and into the instrument during the therapy placing the patient at risk for blood loss and/or blood contamination. In other devices the patient attaches a syringe to the extracorporeal circuit to try to draw air out of the circuit. Because of the pressurization of the circuit blood loss can occur if the tubing is not closed properly after withdrawing air and there is also the risk of blood contamination during the manual procedure. The present disclosure eliminates these risks because the level control mechanism does not require the operator to make any connections. 
     During prime, the operator must monitor the fluid level in the air trap and manually raise this level to remove air from the extracorporeal circuit. During therapy, the operator must continue to monitor the fluid level in the air trap. If the operator fails to properly maintain the fluid level and lets this level drop to where air is able to pass through the air trap the patient is at risk for an air embolism. The air trap level changes with changes in fluid pressure, making frequent monitoring of the fluid level in the air trap important. The present disclosure removes both of those failure causes by using automatic level sensing to determine when action needs to be taken to raise the level and uses pump and valve configurations to automatically purge the air. 
     In addition, the present disclosure allows the priming solution from the extracorporeal circuit to be dumped to the drain. Currently the priming solution is either returned to the patient or purged to a waste container. Each of these methods have risks. If the priming solution is returned to the patient, it may return harmful substances that were released from the disposable kit and/or dialyzer during the prime, to the patient. If the priming solution is sent to a waste container, there is a risk that the patient may lose a significant amount of blood if the operator does not stop the purge at the appropriate time. With the current method of sending prime solution to a waste container, the operator connects the arterial bloodline to the patient&#39;s arterial access site. The venous line remains disconnected while the instrument draws blood from the patient and displaces priming fluid from the venous line into a waste container or rinse bucket. If the operator fails to stop the blood pump and connect the venous line to the patient when blood reaches the end of the venous bloodline, significant blood loss may result. 
     It is accordingly an advantage to provide improved systems and methods for the removal of air from dialysis systems. 
     Additional features and advantages are described herein, and will be apparent from, the following Detailed Description and the figures. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIGS. 1 to 5  illustrate various steps for a method and corresponding system for venting air to drain. 
         FIGS. 6 to 12  illustrate various steps for a method and corresponding system for venting air to atmosphere. 
         FIGS. 13 to 18  illustrate various steps for a method and corresponding system for venting air to a bag, such as a saline bag. 
     
    
    
     DETAILED DESCRIPTION 
     The systems described herein include common components (unless otherwise stated), such as the following dialysate valves: V-AVD-P, which is a primary dialysate air vent valve; V-AVD-S, which is a secondary air vent valve; V-B1, which is a balance chamber or balance tube inlet valve; V-B1-FI, which is a balance chamber 1 fresh inlet valve; V-B1-FO, which is a balance 1 fresh outlet valve; V-B1-SI, which is a balance chamber 1 spent inlet valve; V-B1-SO, which is a balance chamber 1 spent outlet valve; V-B2-FI, which is a balance chamber 2 fresh inlet valve; V-B2-FO, which is a balance chamber 2 fresh outlet valve; V-DD, which is a dialysate drain valve; V-DR, which is a dialysate recirculation valve; V-DBY, which is a dialyzer bypass valve; V-DI-PRE, which is a dialysate/infusate predilution hemofiltration or hemodialfiltration valve; V-DI-VEN, which is a dialysate/infusate postdilution hemofiltration or hemodialfiltration valve; V-DI-FIL, which is a dialysate/infusate inlet to the filter, and V-AV, which is an airline vent valve. 
     Common blood valves (unless otherwise stated) include V-AVB-P, which is a primary blood vent valve; V-AVB-S, which is a secondary blood vent valve; V-SA, which is a saline to arterial side of blood circuit valve; V-SV, which is a saline to venous side of blood circuit valve; and V-H, which is a heparin valve. 
     The above valves are all volcano or cassette type valves in one embodiment (pneumatically or electromechanically actuated). The following valves can instead be pinch valves or clamps: V-DB1 through V-DB6, which open and close supply lines to solution bags 1 to 6, respectively; V-ALC, which is an arterial Line clamp (fail safe); and V-VLC, which is a venous line clamp (fail safe). 
     The systems each include temperature sensors, such as: T-DC, which is a dialysis solution preheat temperature sensor; and T-DH, which is a dialysis solution heated temperature. The systems each include pressure sensors, such as: P-DO, which senses a pressure of fluid leaving the dialyzer or filter; P-AL, which is an arterial line pressure sensor; P-VL, which is a venous line pressure sensor; P-PPB, which is a post blood pump pressure sensor. 
     The systems each include optical sensors, such as: for balance chamber 1, O-B1-T1, transmitter 1 transmits to O-B1-R1, receiver 1 for end of travel; O-B1-T2, transmitter 2 transmits to O-B1-R2, receiver 2 for end of travel; O-B1-T3, transmitter 3 transmits to O-B1-R3, receiver 3 for end of travel; O-B1-T4, transmitter 4 transmits to O-B1-R4, receiver 4 for end of travel. Balance chamber 2 has the same set of end of travel optical sensors. O-HT1 is a heparin transmitter that transmits to O-HR1, heparin receiver to look for heparin instead of blood. 
     The systems each include other sensors, such as: CS 1 to 12, which are capacitive sensors for sensing the presence and/or orientation of the solution bags. AD-AL, which is an arterial line, e.g., ultrasonic, air detector. AD-VL, which is a venous line, e.g., ultrasonic, air detector. AD-HL, which is a heparin line, e.g., ultrasonic, air detector. BSD-VL, which is a venous line blood/saline, e.g., optical, detector. L-ATD, which is a dialysate air trap level sensor. L-ATB, which is a blood air trap level sensor. BLD, which is an e.g., optical, blood leak detector. ADS-A, which is an arterial line access disconnection sensor. ADS-V, which is a venous line access disconnection sensor. 
     The systems also include a drain relief valve RV-Drain and check valves CK-ATB for blood air trap, CK-PRE for prefilter infusate and CK-VEN for venous infusate. 
     The systems also include a filter, F-VL, which is a venous line macro-aggregate filter and other components such as ATD, which is a dialysate air trap and ATB, which is an air trap for blood. 
     The above valves and sensing areas for the above sensors can be placed in one or more disposable pumping cassette. For example, the systems can employ dedicated blood and dialysate cassettes with integrated air traps. Suitable configurations for cassettes with air traps are disclosed in co-pending patent application Ser. No. 11/865,577, entitled “Dialysis Systems Having Air Traps With Internal Structures To Enhance Air Removal”; Ser. No. 11/865,583, entitled “Dialysis Systems Having Air Separation Chambers With Internal Structures To Enhance Air Removal”; Ser. No. 11/865,552, entitled “Dialysis System Having Air Separation Chambers With Internal Structures To Enhance Air Removal”; and 60/976,731, entitled “Fluid And Air Handling In Dialysis Circuit Air Removal System”, each filed on Oct. 1, 2007, assigned to the eventual assignee of the present disclosure, the entire contents of each of which are incorporated expressly herein by reference. 
     I. Vent to Drain 
     Referring now to the drawings and in particular to  FIGS. 1 to 5 , in one primary embodiment a dialysis system  10  and corresponding method vents air to drain. System  10  can accomplish at least two tasks with the vent to drain option: (i) venting air that accumulates in an air trap ATD (air trap for dialysate) or ATB (air trap for blood) during prime or throughout the course of a therapy and (ii) purging extracorporeal circuit priming solution, e.g., saline, to drain (as opposed to returning to the solution to the patient). 
     Vent to Drain—Purging Air that Accumulates During Therapy 
     The air purging method of system  10  determines in one embodiment when it is necessary to remove air from the air trap, e.g., via an automatic level sensor L-ATD or L-ATB associated with air trap ATD and ATB, respectively, or via operator intervention. System  10  begins the air removal process by establishing an appropriate flow path from air trap ATD or ATB. The flow path from air trap ATD to drain  12  will be via dialysate circuit  20 . The flow path from air trap ATB to drain  12  will be via blood circuit  30 . Once the relevant flow path is open, system  10  displaces air from the air trap ATD or ATB, generating a pressure in the air trap that is higher than the pressure of drain  12 . System  10  continues to displace air from the air trap ATD or ATB until automatic level sensor L-ATD or L-ATB, respectively, senses that it is no longer necessary to do so. Or, an operator visually determines that enough air has been removed from system  10 . 
     One example of purging air from blood circuit  30  to drain  12  is illustrated in  FIG. 1 . Here the extracorporeal circuit level detector L-ATB detects a low fluid level. System  10  stops blood pump (PUMP-Blood) and dialysis solution pumps (PUMP-DF, PUMP-DS). System  10  closes venous patient line clamp V-VLC, saline valves V-SV, V-SA, heparin valve V-H, and extracorporeal air vent valves V-AVB-S, V-AVB-P in extracorporeal circuit  30 . System  10  opens air vent valve V-AV and drain valve V-DD near drain  12 . 
     System  10  then begins running PUMP-Blood clockwise, while metering air through the air vent valves V-AVB-S and V-AVB-P. Air vent valves V-AVB-S and V-AVB-P alternate in a chamber-lock type manner. First, vent valve V-AVB-P is opened allowing air to pressurize the line up to vent valve V-AVB-S. Then, the valve states are reversed, allowing pressurized air trapped between the vent valves V-AVB-S and V-AVB-P to be released to drain  12  via air vent line  14 . One of the vent valves is thus closed at all times, and the valves alternate at a rate related to the rate of PUMP-Blood. 
     The extracorporeal circuit level detector L-ATB may be used in combination with a blood leak detector BLD (see  FIG. 5 ) to ensure that the blood level does not fall too low and to detect when the blood level has overfilled blood air trap ATB. When blood leak detector BLD detects an overfill, system  10  stops PUMP-Blood and closes extracorporeal air vent valves V-AVB-S and V-AVB-P, closes air vent valve V-AV, and closes drain valve V-DD. System  10  then opens venous patient line clamp V-VLC and saline valves V-SV, V-SA or heparin valve V-H if appropriate and restarts PUMP-Blood to push an appropriate amount of blood from air trap ATB to the patient, lowering the level in the air trap, and allowing fluid in vent line  14  sensed at BLD to fall back into blood from air trap ATB. Dialysis solution pumps DF and DS are also run at the same rates they were running before the air vent to dialyze blood that is being pushed through dialyzer  16  during the level lowering process within air trap ATB. 
     Vent to Drain—Purging Extracorporeal Priming Solution to Drain 
     System  10  begins a blood prime process after extracorporeal circuit  30  has been primed with priming fluid (saline, heparin, dialysis solution etc.). For blood prime, system  10  assures that the patient has been connected to the system or accessed. First, system  10  communicates circuit  30  with patient  18  flow path. System  10  then flows blood from patient  18 , through the circuit  30 , including air trap ATB, to displace priming fluid out of system  10  to the fluid drain  12 , until the extracorporeal circuit is sufficiently primed with blood, e.g., using a blood detector BLD and/or flow sensing and/or a recorded number of pump rotations sufficient to completely remove priming fluid and/or a total time spent pumping sufficient to completely purge circuit  30  of priming fluid. 
       FIGS. 1 to 4  illustrate in detail how system  10  performs blood prime venting. In  FIG. 1 , system  10  performs a first step in which it is in a safe state following extracorporeal circuit prime with all valves and patient line clamps closed and all pumps stopped. 
     At step 2 in  FIG. 2 : (a) an operator establishes vascular access with a venous patient line  32  of blood circuit  30 ; (b) the operator establishes vascular access with the arterial patient line  34  of blood circuit  30 ; (c) system  10  prepares for blood prime by opening extracorporeal circuit air vent valves V-AVB-S and V-AVB-P, dialysate circuit air vent valves V-AVD-S and V-AVD-P, and drain valves V-DD and V-DR; (d) system  10  runs fresh dialysate pump DF in the clockwise direction as shown in  FIG. 2  until the blood saline detector BSD-VL detects blood. System  10  can also run fresh dialysate pump DF longer, so blood moves beyond the blood saline detector, e.g., using a total number pump strokes as the indicator to finally stop dialysate pump DF. This operation pulls blood from patient  18 , through venous or return line  32 , to blood saline detector BSD-VL, displacing priming fluid in venous line  32  with the patient&#39;s blood. Negative pressure is applied by priming fluid being pulled through air vent line  14  and blood air trap ATB. Any air is pushed to drain via open valve V-DD. 
     At step 3 in  FIG. 12 , system  10  returns to a safe state by closing all blood and dialysate valves and patient line clamps and stopping all pumps. 
     At step 4 in  FIG. 3 , system  10  prepares for completion of blood prime by opening extracorporeal circuit air vent valves V-AVB-S and V-AVB-P, dialysate circuit air vent valves V-AVD-S and V-AVD-P, arterial patient line clamp V-ALC, and drain valve V-DD. System  10  starts PUMP-Blood in the clockwise direction as shown in  FIG. 3  and runs the pump for a specific number of pump strokes or a specific period of time until blood travels from patient  18 , through arterial line  34 , dialyzer  16 , and a portion of venous line  32  to blood air trap ATB. System  10  can also run PUMP-Blood longer so blood moves into the air trap ATB, provided system  10  can verify that blood does not leave blood air trap ATB during the rest of the priming process. 
     At step 5 in  FIG. 1 , system  10  returns to a safe state by closing all valves and patient line clamps and stopping all pumps. All saline has been removed from blood circuit  30  except perhaps for a small amount between blood air trap ATB and blood saline detector BSD-VL. Again, any air is pushed to drain via valve V-DD. 
     Vent to Drain—Alternative Vent Valving 
     Referring now to  FIG. 4 , secondary air vent valves V-AVD-S and V-AVB-S for the dialysate circuit  20  and extracorporeal circuit  30 , respectively, have been removed to reduce hardware. The vent to drain and priming fluid to drain sequences above may be performed using the reduced vent valve arrangement of  FIG. 4 . To increase safety, a blood leak detector BLD may be added to vent line  14  upstream of the singly used air vent valves V-AVD-P and V-AVB-P. Since system  10  is closed to drain, it may be possible to eliminate both the primary and secondary vent valves. 
     Vent to Drain—Extra Blood Detector 
     Referring now to  FIG. 5 , to prime the extracorporeal circuit  30  to a greater extent, a blood detector BLD can be placed in the post-air trap air vent line, between trap ATB and vent valve V-AVB-P or alternatively between valves V-AVB-P and V-AVB-S. In  FIG. 5 , dialysate pump DF is shown pulling saline, as described shown in  FIG. 2 , in turn pulling blood to the added detector BLD. Blood could be drawn alternatively to detector BLD via PUMP-Blood via the process of  FIG. 3 . An advantage in either case is that more of the air trap priming volume or saline is sent via drain line  14  to drain  12 . 
     Vent to Drain—Fluid Use Efficiency 
     It is also possible in the vent to drain system  10  embodiments to maximize fluid use efficiently by pumping dialysis solution to prime the extracorporeal circuit. Here, a suitable path of valves is opened to allow fresh dialysate pump DF to pump fresh dialysate into dialyzer  16 , and through the hollow fiber membranes of the dialyzer, into extracorporeal circuit  30 . In this manner, system  10  can remove air from circuit  30  to drain using dialysate instead of requiring an extra priming fluid, such as saline. The dialysate can then be replaced with blood as shown above, so that the dialysate volume is not delivered to the patient. 
     II. Vent to Atmosphere 
     In another primary embodiment shown in  FIGS. 6 to 12 , the system  10  vents air to atmosphere. System  10  can accomplish at least two tasks using the vent to atmosphere option: (i) venting air that accumulates in the blood air trap during prime or throughout the course of a therapy and (ii) purging the extracorporeal circuit priming solution to drain (as opposed to returning the priming solution to the patient). 
     Vent to Atmosphere—Purging Air that Accumulates During Therapy 
     In the vent to atmosphere embodiment, system  110  determines when it is necessary to remove air from the extracorporeal or dialysate side air traps ATD and ATB via automatic level sensors L-ATD and L-ATB and/or operator intervention as discussed above. System  110  begins the air removal process by establishing an appropriate flow path from the air trap ATD or ATB to atmosphere. Once the flow path is open, system  110  displaces air from the relevant air trap ATB, generating a higher than atmospheric pressure in the associated air trap and/or generating a lower than air trap pressure in the atmosphere, e.g., drawing a vacuum on the air trap. System  110  continues to displace air from the air trap until it is no longer necessary to do so (as determined by automatic level sensors L-ATD or L-ATB and/or via operator intervention. 
       FIG. 6  illustrates an embodiment of system  110  in which venting to atmosphere can be accomplished. System  110  differs form system  10  primarily in that system  110  has connected drain vent valve V-AV to atmosphere through a 0.2 micron filter instead of connecting it to the drain lines as in system  10 . All air is vented through dialysate vent valve V-AV to atmosphere through this filter. 
     In one sequence, the extracorporeal circuit level detector L-ATB detects a low fluid level. System  110  stops PUMP-Blood and dialysis solution pumps DF and DS. System  110  closes venous patient line clamp V-VLC, saline valves V-SV and V-SA, heparin valve V-H, and extracorporeal air vent valves V-AVB-S, V-AVB-P and opens saline valve V-SA. System  110  then slowly runs PUMP-Blood clockwise (as oriented in  FIG. 6 ), drawing in blood while metering air through the air vent valves V-AVB-S and V-AVB-P and through open valve V-AV and out the 0.2 micron filter. One of the vent valves is closed at all times as described above to ensure that no outside air contacts blood. 
     The extracorporeal circuit level detector L-ATB may be used in combination with a blood leak detector BLD (see  FIG. 5 ) to ensure that the blood level does not fall too low and to detect when the blood level has overfilled blood air trap ATB. When blood leak detector BLD detects an overfill, system  110  closes extracorporeal air vent valves V-AVB-S and V-AVB-P, opens venous patient line clamp V-VLC and saline valves V-SV, V-SA or heparin valve V-H if appropriate and restarts dialysis solution pumps DF and DS and Pump-Blood at the same rates that they were running before the venting of air through trap ATB, vent valve V-AV, and 0.2 micron filter. 
     Vent to Atmosphere—Purging Extracorporeal Priming Solution to Drain 
     System  110  begins a blood prime process after extracorporeal circuit  30  has been primed with priming fluid (saline, heparin, dialysis solution etc.). For blood prime, system  110  assures that the patient has been connected to the system or accessed. First, system  110  communicates circuit  30  with patient  18 . System  110  then flows blood from patient  18  through the circuit  30 , including air trap ATB to displace priming fluid out of system  110  to the fluid drain  12  until the extracorporeal circuit is sufficiently primed with blood, e.g., using a blood detector BLD and/or flow sensing and/or a recorded number of pump rotations sufficient to completely remove priming fluid and/or a total time spent pumping sufficient to purge circuit  30  of priming fluid. 
       FIGS. 6 to 10  illustrate in detail how system  110  accomplishes blood prime venting to atmosphere. 
     In step 1 at  FIG. 6 , system  110  is in a safe state following extracorporeal circuit prime with all valves and patient line clamps closed and all pumps stopped. 
     In step 2 at  FIG. 7 : (a) an operator establishes vascular access with the venous patient line  32 ; (b) system  110  prepares for blood prime by opening extracorporeal circuit air vent valves V-AVB-S and V-AVB-P, dialysate circuit air vent valves V-AVD-S and V-AVD-P, and drain valves V-DD and V-DR; and (c) system  110  runs fresh dialysate pump PUMP-DF in the clockwise direction as seen in  FIG. 7  and until the blood saline detector BSD-VL detects blood. It is also be possible to run the fresh dialysate pump DF longer, so blood moves beyond the blood saline detector BSD-VL using total pump strokes as the indicator to stop, for example. 
     In step 3 at  FIG. 6 , system  110 : (a) returns to safe state by closing all valves and patient line clamps and stopping all pumps; and (b) the operator establishes vascular access with the arterial patient line  34 . 
     In step 4 at  FIG. 8 : (a) system  110  prepares for blood prime by opening extracorporeal circuit air vent valves V-AVB-S and V-AVB-P, dialysate circuit air vent valves V-AVD-S and V-AVD-P, and drain valves V-DD and V-DR; (b) system  110  runs PUMP-Blood in the clockwise direction, and the fresh dialysate pump DF in the clockwise direction as shown in  FIG. 8  at the same flow rate for a specific number of pump strokes or period of time until blood flows through arterial line  34 , dialyzer  16 , and a portion of venous line  32  until reaching air trap ATB. Pressure sensor P-PPB can be used to indicate when one pump is running at a higher flow rate than the other. It is also possible to run the pumps longer, so blood moves into the air trap, provided that system  110  can verify that blood never leaves the air trap during the rest of the priming process. A blood-saline-air detector can be installed between V-AVB-P and V-AVB-S to further optimize priming solution removal. 
     In step 5 at  FIG. 6 , system  110  returns to the safe state by closing all valves and patient line clamps and stopping all pumps. 
     In step 6 at  FIG. 9 , system  110  prepares to clear the dialysate circuit side of the air vent by opening the air vent valve V-AV, dialysate circuit air vent valves V-AVD-S and V-AVD-P, and drain valves V-DD and V-DR. 
     In step 7 at  FIG. 10 , system  110  runs the fresh dialysate pump L-ATB-DF in the clockwise direction, pumping fresh fluid from air trap ATB and pulling air into the trap via air vent line  14  and vent valves V-AVD-S and V-AVD-P until level detector L-ATD in the dialysate circuit air trap ATD indicates a certain level. System  110  can alternatively accomplish this step by running dialysate pump DF for a specific number of pump strokes or period of time until fluid is completely removed from the dialysate circuit air vent line  14 . 
     In step 7 at  FIG. 10 , system  110  runs the fresh dialysate pump L-ATB-DF in the clockwise direction, pumping fresh fluid from line  14  and pulling air into the trap ATD via air vent line  14  and vent valves V-AVD-S and V-AVD-P until level detector L-ATD in the dialysate circuit air trap ATD indicates that there is no fluid in air trap ATD. System  110  can alternatively accomplish this step by running dialysate pump DF for a specific number of pump strokes or period of time until fluid is completely removed from the dialysate circuit air vent line  14 . 
     In step 8 at  FIG. 6 , system  110  returns to safe state by closing all valves and patient line clamps and stopping all pumps. 
     During the therapy, if air gathers in the top of air trap ATB, valves V-AVB-P and V-AVB-S are alternately opened so that air is shuttled out of the air trap without allowing any blood to escape and vented through valve V-AV and the 0.2 micron vent filter. 
     Vent to Atmosphere—Alternative Vent Valving 
     Just like with  FIG. 4  for venting to drain, system  110  can be modified to remove secondary air vent valve V-AVB-S from blood circuit  30  and V-AVD-S from dialysate circuit  20  to reduce hardware, which can also be performed by adding a blood leak detector BLD in vent line  14  upstream of the primary vent valves V-AVB-P and V-AVD-P to sense any blood that may enter vent line  14 . Since venting is done to atmosphere, at least a primary vent valve should be provided at the blood and dialysate air traps ATB and ATD. 
     Vent to Atmosphere—Extra Drain/Air Vent Lines 
       FIG. 11  illustrates that system  110  can alternatively connect air vent line  14  running from air traps ATB and ATD directly to drain line  12 , similar to the vent to drain system  10 . Unlike system  10 , which provides an extra vent to drain valve V-AV for both air traps, system  110  uses vent valves V-AVD-S and V-AVD-P to control flow from dialysate air trap ATD to drain  12 . Valve V-AC is provided as a vent valve for blood air trap ATB, which provides a second vent to atmosphere option using vent valves V-AVB-S and V-AVB-P and a 0.2 micron filter. 
       FIG. 12  illustrates that system  110  can alternatively have separate air vent lines for the dialysate and extracorporeal circuits, allowing the circuits to both vent at the same time. In  FIG. 12 , dialysate air vent line  14   a  runs to drain  12 , while blood air trap ATB vents directly to atmosphere via vent line  14   b , valves V-AVB-S And V-AVB-P and a 0.2 micron filter. 
     Vent to Atmosphere—Extra Blood Detector 
     In an alternative vent air to atmosphere embodiment, to prime the extracorporeal circuit to a greater extent, a blood detector BLD (see  FIG. 5 ) can alternatively be placed in the post air-trap air vent line  14 . An advantage here is that more of the air trap fluid priming volume can be replaced with blood before treatment. 
     Vent to Atmosphere—Alternative Method 
     Referring again to  FIG. 6 , in a further alternative embodiment, vent to atmosphere system  110  maximizes fluid use efficiently by pumping dialysis solution to prime the extracorporeal circuit  30 . Here, a suitable path of valves is opened to allow fresh dialysate pump DF to pump fresh dialysate into dialyzer  16 , and through the hollow fiber membranes of the dialyzer, into extracorporeal circuit  30 . In this manner, system  110  can remove air from circuit  30  to drain using dialysate instead of requiring an extra priming fluid, such as saline. The dialysate can then be replaced with blood as discussed above, so that the dialysate volume is not delivered to the patient. 
     Vent to Atmosphere—Fluid Use Efficiency 
     It is also possible in the vent to atmosphere system  110  to use dialysis solution to prime extracorporeal circuit  30  as discussed above with vent to drain system  10 . 
     III. Vent to Saline Bag 
     In a further alternative primary embodiment shown in  FIGS. 13 to 18 , system  210  vents to a bag such as a saline bag  36 . Here again, system  210  can accomplish at least two tasks: (i) venting air that accumulates in air traps ATB and ATD during prime or throughout the course of a therapy and (ii) purging the extracorporeal circuit priming solution to saline bag  36  as opposed to returning the solution to patient  18 . 
     Vent to Saline Bag—Purging Air that Accumulates During Therapy 
     System  210  determines when it is necessary to remove air from air trap ATB and ATD (via e.g., automatic level sensors L-ATB and L-ATD and/or operator intervention). System  210  begins the air removal process to by establishing an appropriate flow path from the air trap (extracorporeal ATB, dialysate ATD) to the saline bag  36 . Once the flow path is open, system  210  displaces air from the air trap ATB or ATD by generating a higher than saline bag pressure in the air trap ATB or ATD and/or generating a lower than air trap pressure in the saline bag  36 . System  210  continues to displace air from the air trap ATB or ATD until it is no longer necessary to do so, for example as determined by automatic level sensors L-ATB or L-ATD and/or operator intervention. 
       FIG. 13  illustrates system  210 , which vents air to saline bag  36 . When extracorporeal circuit level detector L-ATB detects a low fluid level of fluid within trap ATB, system  210  stops PUMP-Blood and dialysis solution pumps DF and DS. System  210  closes venous patient line clamp V-VLC, saline valves V-SV, V-SA, heparin valve V-H and extracorporeal air vent valves V-AVB-S and V-AVB-P. 
     System  210  then runs Pump-Blood clockwise, while metering air through the air vent valves V-AVB-S or V-AVB-P. Either valve V-AVB-S or V-AVB-P is closed at all times for safety. The valves alternate in a chamber lock manner, which can be cycled at a rate related to the blood pump rate. This action pushes air to saline bag  36 . 
     The extracorporeal circuit level detector L-ATB may be used in combination with a blood leak detector BLD (see  FIG. 5 ) to ensure that the blood level does not fall too low and to detect when the blood level has overfilled blood air trap ATB. When blood leak detector BLD detects an overfill, system  210  stops PUMP-Blood, closes extracorporeal air vent valves V-AVB-S and V-AVB-P, opens venous patient line clamp V-VLC and saline valves V-SV, V-SA or heparin valve (V-H) if appropriate; and runs Pump-Blood and dialysis solution pumps DS and DF at the same rates they were running before the air vent action. Such action pulls air saline from bag  36  into trap ATB, which pushes blood from the trap ATB. 
     Vent to Saline Bag—Purging Extracorporeal Priming Solution to Drain 
     The blood prime process of system  210  begins after the extracorporeal circuit has been primed with priming fluid (saline, heparin, dialysis solution etc.). Blood prime assumes that the patient&#39;s blood access has been connected to the system. First, system  210  establishes the appropriate flow paths accomplished with the illustrated ( FIG. 13 ) system of valves and clamps. System  210  then flows blood from patient  18  through the appropriate flow path (which includes air trap ATB) to displace priming fluid saline bag  36  to other containers. System  210  then switches the flow path to continue to displace priming fluid until extracorporeal circuit  30  is sufficiently primed with blood. System  210  can determine if the blood prime is complete using a blood detector, flow sensing, or a recorded number pump rotations and/or a total time spent pumping. As with system  110 , vent to bag system  210  does not need an extra vent valve V-AV provided with system  210 . System  210  replaces vent line  14  with saline vent line  44 . 
       FIGS. 13 to 16  illustrate in detail how blood prime venting to saline bag  36  or other bag can be accomplished. 
     In step 1 at  FIG. 13 , system  210  is placed in a safe state following extracorporeal circuit prime with all valves and patient line clamps closed and all pumps stopped. 
     In step 2 at  FIG. 14 : (a) the operator establishes vascular access with the venous patient line  32 ; (b) the operator establishes vascular access with the arterial patient line  34 ; (c) system  210  prepares for blood prime by opening venous patient line clamp V-VLC and saline valve V-SA; and (d) system  210  runs PUMP-Blood in the counterclockwise direction as seen in  FIG. 17 , pumping blood from patient  18 , through venous line  32  until the blood saline detector BSD-VL detects blood. System  210  can alternatively run the PUMP-Blood longer so blood moves beyond the blood saline detector BSD, e.g., using total pump strokes as the indicator to stop. 
     In step 3 at  FIG. 13 , system  210  returns to the safe state by closing all valves and patient line clamps and stopping all pumps. 
     In step 4 at  FIG. 15 , system  210  prepares for blood prime by opening extracorporeal circuit air vent valves V-AVB-S and V-AVB-P, dialysate circuit air vent valves V-AVD-S and V-AVD-P, arterial patient line clamp V-ALC, and drain valve V-DD. 
     In step 5 at  FIG. 16 , system  210  runs PUMP-Blood in the clockwise direction for a specific number of pump strokes or period of time pulling blood from patient  18 , through arterial line  34 , dialyzer  16  and a portion of venous line  32  until blood reaches the beginning of the air trap ATB. System  210  can alternatively run the PUMP-Blood longer so blood moves into the air trap ATB, provided that system  210  can verify that blood does not escape air trap ATB during the blood priming process. The addition of a blood saline detector BSD as illustrated in  FIG. 5  would facilitate this process. 
     In step 6 at  FIG. 13 , the system returns to safe state by closing all valves and patient line clamps and stopping all pumps. 
     Vent to Saline Bag—Fewer Air Vent Valves 
     Referring to  FIG. 17 , secondary air vent valves for the dialysate circuit V-AVD-S and extracorporeal circuit V-AVB-S have been removed. Primary vent vales V-AVD-P and V-AVB-P function primarily to maintain safety and may be used in combination with blood leak detectors BLD&#39;s as has been described herein. Since system  210  is closed to saline bag, however, it may be possible to use no vent valves. 
     Vent to Saline Bag—No Post-Pump Line 
     Referring again to  FIG. 13 , system  210  does not need separate pre- and post-blood pump saline lines (holding V-SV and V-SA) to the saline bag, so the post-pump saline line (holding V-SV) can be removed. Here system  210  uses the air trap fluid line  44  to also function as the post-pump fluid line. 
     Vent to Saline Bag—Extra Blood Detector 
     As with system  10  in  FIG. 5 , to prime the extracorporeal circuit  30  to a greater extent, system  210  can add a blood detector BLD in the post air-trap air vent line running to saline bag  36 . An advantage here is that more of the air trap priming volume can be sent to the saline or other container. 
     Vent to Saline Bag—Other Container 
     Referring to  FIG. 18 , the vent container does not have to be a saline bag  36 . Vent line  44  can run instead to a different container, such as a used supply bag or a dedicated vent container. 
     It should be understood that various changes and modifications to the presently preferred embodiments described herein will be apparent to those skilled in the art. Such changes and modifications can be made without departing from the spirit and scope of the present subject matter and without diminishing its intended advantages. It is therefore intended that such changes and modifications be covered by the appended claims.