Although chronic hemodialysis (HD) is a life-saving maintenance therapy for end-stage renal disease (ESRD) patients, it is totally dependent on the availability of a functioning vascular access. Unfortunately, this interface between the patient and the dialysis machine is defective. The vascular access is associated with major complications, including infection, occlusion, increase in cardiac load, and quality-of-life impairments. These complications, among others, result in patient morbidity and mortality and add considerably to the cost of managing chronic renal failure.
The annual cost of maintaining vascular access in the United States is approaching $1 billion1. However, this represents only the tip of the iceberg. Problems that derive both directly and indirectly from these complications result in a major proportion of the hospitalizations required in this frequently hospitalized population of patients2.
Since its introduction 21 years ago3, the polytetrafluoroethylene (PTFE) graft has come to represent the primary means for delivering HD to patients in the United States. Unfortunately, PTFE grafts are particularly prone to problems, especially venous stenosis and thrombosis. These problems occur at a rate of approximately 1 to 1.5 times per patient per year4. Cumulative patency rates for these devices in most centers are only 55 to 75% at one year and 50 to 60% at two years4,5,6,7,8,9.
The obvious solution to the problem of vascular access in the chronic hemodialysis patient population is to increase the use of native arteriovenous fistulae. However, for a variety of reasons, universal usage of this means for accessing the patient's circulation is unlikely to be realized. There is a definite need for an improved implantable dialysis access system. Toward this goal, the Lifesite Dialysis System® (Vasca Inc., Tewksbury, MA, USA) has been developed.
METHODS
Description of the LifeSite® System
LifeSite® is a subcutaneous access system that provides immediate central venous access for ESRD patients. This system consists of an access valve and silicone cannula Figure 1, which is typically implanted below the clavicle and tunneled to the right internal jugular vein. The valve is designed so that a standard 14-gauge fistula needle actuates an internal pinch clamp as the needle enters and seals Figure 2. Upon removal of the needle, the pinch clamp closes and flow stops. The LifeSite System also employs two unique techniques for vascular access. The first is the repeated use of a single cannulation site in the patient's skin, which forms a pain-free tissue tract called a "buttonhole." The second is a prophylactic infection-control technique that involves the in vivo disinfection of the valve pocket and buttonhole tract by irrigation with an antimicrobial solution.
Figure 2.
(A) Appearance of 14-gauge fistula needle entering valve with pinch clamp closed. (B) Appearance as the fistula needle activates the internal pinch clamp as it enters valve. Upon removal of the needle, the pinch clamp closes and flow stops.
Full figure and legend (138K)Valve and cannula
The valve is approximately 2.48 cm in diameter and 0.68 cm in height and is constructed of stainless steel and titanium alloy. The valve has a dimpled entrance in the center of the domed top, which facilitates entry of a standard 14-gauge dialysis needle Figure 1. The circular ring surrounding the dimpled entrance at the top of the valve serves as a guide to the needle when the device is being cannulated. The valve's stem accepts a 12 French silicone cannula. The bottom plate of the valve has suture holes to allow for anchoring of the device at the time of implantation Figure 1.
The fact that the mechanical pinch clamp opens and closes when the dialysis needle is inserted or removed, respectively, prevents any leakage of blood when the dialysis needle is not seated in the valve and allows for maintaining the heparin lock within the cannula. Thus, there is no possibility for fluid flow when the dialysis needle is not in place.
Once the needle is seated in the metal taper seal, it is turned approximately one-quarter turn to provide a friction fit that keeps the needle securely in place. A slight twist and pull of the needle frees it to permit easy withdrawal. The channel for blood passage through the device is smooth without constrictions or dead space. There is therefore no opportunity for the creation of turbulence in blood flow. The valve was designed without a septum in order to avoid the failures associated with repetitive fistula needle punctures.
At the time of use, the LifeSite System is irrigated with an antimicrobial solution using a 25-gauge needle. This antimicrobial agent is used for localized prophylaxis of the LifeSite valve pocket and buttonhole tract prior to and following each dialysis treatment. The LifeSite System was designed to utilize an antimicrobial solution in order to help reduce the potential for infection. The 25-gauge needle cannot open or damage the internal pinch clamp, ensuring that the antimicrobial solution is prevented from entering the circulatory system.
The 12 French, single lumen, silicone cannula is 34.8 centimeters in length and can be cut to the desired length at the time of implantation. The distal tip is placed in the right atrium and has six side holes located radially around the axis. These side holes allow for an alternative flow path in the presence of fibrin sheathing or in case the cannula is positioned against the wall of the vein.
Implantation
Implantation of the LifeSite System is relatively simple and can be performed in a radiological or surgical suite. It is important that precautions providing maximum barrier protection be followed at the time of implantation.
The design of the LifeSite Hemodialysis Access System requires that two separate valves be implanted for HD. The device was designed in this manner to permit the flexibility of using two separate implantation sites if needed and to permit the replacement of only half of the assembly if a problem occurs. Separate valve devices also allow the access system to be used for single needle dialysis as well as for peritoneal dialysis.
Implantation of the LifeSite System consists of two stages: the subcutaneous implantation of the two valves and the insertion of the two silicone cannulas. The time required for implantation is in the range of 1 to 1.5 hours. Local anesthesia and conscious sedation are used for patient comfort.
The cannulas are inserted into a central vein, typically the right internal jugular, although other approaches are available (left internal jugular, bilateral approach, external jugular, or subclavian). The cannulas are inserted using the Seldinger technique for central vein cannulation and catheter insertion. Then two subcutaneous valve pockets are created side by side about 2 to 4 cm below the clavicle. These pockets are created beneath the subcutaneous tissue so that the fascia of the muscle forms their floor. The cannulas are then tunneled subcutaneously to the pockets and cut to the proper length to allow for their tips to be located within the right atrium with the return cannula being approximately 2 cm longer than the draw cannula. The final length of the cannulas is dependent on the individual characteristics of the patient's body habitus and the exact placement of the valves. By convention, the medial valve and cannula are typically used for draw and the lateral for the return.
After each of the cannulas is attached to the appropriate valve, the valve is placed into its pocket and anchored to the muscle fascia of the pocket floor with sutures passed through the holes in the base plate. The incisions are closed. After placement of the devices is complete, the initial cannulation is made utilizing 14-gauge dialysis fistula needles. They can be used immediately for dialysis.
Use of the LifeSite System for HD
Proper technique for site cleansing, pocket sterilization, and needle cannulation and removal is very important in ensuring the occurrence of minimal complications.
At the time of dialysis, the skin over each of the valves is first cleansed with a 4% chlorhexidine solution. The LifeSite valve and pocket as well as the buttonhole tract are then sterilized using 1 to 3 mL of 0.2% sodium oxychlorosene antimicrobial irrigation solution with a 25-gauge needle Figure 3.
Figure 3.
Appearance of 25-gauge needle entering valve without disturbing the pinch clamp.
Full figure and legend (140K)After the valve is irrigated, it is cannulated using a standard 14-gauge dialysis needle Figure 4. A buttonhole technique is used for this purpose. This involves accessing the valve through the same skin site and tissue tract each time the device is cannulated.
Once the needle is seated in the metal taper seal, it is turned approximately one-quarter turn. The friction fit of the needle within this taper seal keeps the needle in the valve securely. With the needle in place, 5 mL of blood are aspirated to remove the heparin lock and any blood clots from inside the cannula. The valve is then flushed with saline and connected to the bloodlines for the dialysis session.
At the end of the dialysis session, the LifeSite valves are flushed with 10 mL of saline to remove any blood that is remaining within the system. A heparin lock is instilled into each of the cannulas. The needles are then removed with a twist-and-pull motion. After the dialysis needle has been removed, the valve is again irrigated with 1 to 3 mL of 0.2% sodium oxychlorosene solution using a 25-gauge needle. The cannulation site is then scrubbed with 4% chlorhexidine solution, and a nonocclusive gauze dressing is applied.
In vitro studies
The LifeSite valve was tested for mechanical durability by exposing it to the equivalent of 6000 dialysis treatments (or 38 years of use) using a standard 14-gauge dialysis needle. The device was also tested with a pressure of 2000 mm Hg to determine the force required to disconnect the cannula from the valve. This was compared with a standard chemotherapy port.
Tests for hemolysis were conducted using fresh bovine blood. Forty hours of simulated dialysis was conducted using the LifeSite System consisting of a valve, a cannula, and a 14-gauge dialysis needle. A 15-gauge dialysis needle and a 10 French dialysis catheter (Tesio; MedComp, Harleysville, PA, USA) were used as controls. Hemolysis was measured using a test that is very similar to the Normalized Index of Hemolysis that is widely applied for hemolysis evaluation during in vitro testing of heart-assist devices10. Tests were performed at two blood flow rates: 300 mL/min and 450 mL/min.
Patient studies
Two pilot clinical studies have been completed, one in Canada consisting of 13 patients and one in the United States consisting of 10 patients.
The criteria for entry into the study were the need for dialysis and the absence of an adequately functioning vascular access, whether a catheter or a peripheral access. Patients with active infection and those who were positive for hepatitis were excluded. The patients all signed informed consent, and the appropriate Institutional Review Boards approved the studies. Data on the two studies have been combined.
Measurements of maximum blood flow were made on each patient using the HT110 Bypass Flow Meter (Transonic Systems, Inc., Ithaca, NY, USA). Recirculation was determined by saline dilution using the same device. The dose of dialysis delivered using the LifeSite System was determined by calculating the patient's Kt/V. Life table analysis data were calculated using the Kaplan–Meier method.
Bacteremia was determined by blood cultures drawn from the arterial bloodline port during dialysis at the blood flow rate that was being used for the treatment. Device-related infection was defined as bacteremia in the absence of any other obvious cause. The incidence of device-related infection was expressed as infections per 1000 patient days and was calculated using the total number of days that the devices were in place and the total number of device-related infections.
Patients and staff were interviewed to determine their attitude and impressions of the use of the device.
RESULTS
In vitro studies
There was no malfunction or degradation in function with repetitive cannulation up to 6000 times using a standard 14-gauge dialysis needle. The cannula disconnect force was determined to be 8.4 versus 4.6 pounds for a standard chemotherapy port (data on file; Vasca, Inc., Tewksbury, MA, USA).
Tests for hemolysis showed that the LifeSite System produced less blood damage than either the 15-gauge dialysis needle or the 10 French dialysis catheter (P < 0.005 to 0.05) and was deemed to be clinically insignificant (data on file; Vasca, Inc.).
Patient studies
The mean age of the patients in this study was 60.78 years, with a range of 20 to 82. Thirteen of the patients were male, and 10 were female. Of the 23 patients, 47.8% (11 out of 23) had diabetes, and 30.4% (7 out of 23) had hypertension as the cause of the ESRD.
The surgical implantation procedures were accomplished without difficulty. The time required for implantation was 60 to 90 minutes. There were no surgical failures; implantation was accomplished in all cases. The LifeSite Systems were used for dialysis immediately following surgery. Because of the freshness of the surgical site, some patients did report discomfort at the time of needle cannulation at initial dialysis treatments. Because of this, oral pain medication was generally given 30 to 45 minutes prior to the start of dialysis. After 10 to 14 days, the cannulation process was no longer uncomfortable, and the use of local or topical anesthesia was not required.
The Kaplan–Meier survival data are shown in Figure 5. The mean duration of device survival of the LifeSite System was 6.8 
0.97 months (median survival was 5.9 months; range 0.2 to 16.7 months). Although three patients died during the course of this study, none of these deaths were related to the study or the LifeSite System. In two cases, the patients elected to discontinue dialysis because of severe symptoms from comorbid conditions. One of these patients had scleroderma; the other had intractable pain related to multiple collapsed vertebrae.
The incidence of device-related infection was 2.5 infections per 1000 patient-days. Device-related infection occurred in 52.2% of the cases (12 out of 23), resulting in valve removal in all cases. These infections occurred at intervals ranging from 1.8 to 16.7 months. The mean time from implantation to infection was 7.7 1.6 months, with a median time of 5.9 months. In two patients, the episode of device-related bacteremia occurred following the development of a contact dermatitis related to the use of the chlorhexidine solution. In three instances, the infection was traced to a break in the protocol established for site preparation and needle cannulation. Seven episodes of non-device–related bacteremia were seen in six patients. The LifeSite Systems were removed because of non-device–related bacteremia in six instances. In four cases, the cannulas were exchanged because of the presence of bacteremia; one of these was device related. The valves were not disturbed in this process. The causes of valve loss are listed in Table 1.
![Table 1 - Reasons for LifeSite[reg] valve loss - Unfortunately we are unable to provide accessible alternative text for this. If you require assistance to access this image, please contact help@nature.com or the author](/common/images/table_thumb.gif)
The LifeSite System achieved prescription HD blood flow rates averaging 384.7 78.5 mL/min with a venous pressure of 223.2 60.3 mm Hg Figure 6. No recirculation was present even at maximum flow rates. Although flow problems did occur occasionally, there were no device removals because of occlusion. The cannulas were treated with intraluminal instillation of urokinase if a flow greater than 300 mL/min could not be achieved for a dialysis treatment during the course of the study. In one case, the cannulas were exchanged because of poor flow. Occasionally, blood clots 3 to 4 cm in length were aspirated when the nurses were withdrawing heparin from the cannulas at the initiation of dialysis. These clots did not occlude the cannulas and were of no consequence.
Figure 6.
Average blood flow. The line (A) represents the line of identity; the line (B) is the actual flow rate. Abbreviations are: Qb-actual, blood flow measured with Transonic HD Monitor; Qb-RPM, blood flow as indicated on the dialysis machine (r.p.m. meter).
Full figure and legend (27K)The mean Kt/V was 1.51. No postdialysis bleeding problems were encountered. No difficulties were experienced in using the buttonhole technique for needle cannulation. Patient acceptance of the device was favorable, citing a perception of pain-free cannulations, improved body image, and improved quality of life. Dialysis facility staff expressed a strong acceptance of the device once they had learned to use it. They cited ease of cannulation and immediate hemostasis following dialysis as positive points.
DISCUSSION
This study serves to validate the use of the LifeSite System as an alternative HD access device for chronic use as a HD access system. These devices were easily placed without complication. They were easily cannulated using a standard 14-gauge dialysis needle and could be used immediately after placement. The LifeSite System had excellent flow characteristics. With flow being proportional to the diameter of the catheter raised to the fourth power, good flow should be expected with a 12 French cannula. Flows in excess of 400 mL/min were routinely obtained without recirculation. This enabled the patients in the study to receive very effective dialysis, obtaining a mean Kt/V of 1.51. This Kt/V was the result of high flow rates plus the fact that patients were dialyzed for a minimum time of four hours.
In 1995, the mean age of the United States dialysis population was 60 years, and the incidence of diabetes was 37.4%. In our study, the mean age was 60.87, and the incidence of diabetes was 47.8%. Because of this increased incidence of diabetes, these patients would be expected to represent a higher than average risk group. Nevertheless, the patency and infection rates observed in this series were better than has been reported in some of the studies with tunneled chronic dialysis catheters.
The mean patency rate for tunneled catheters has been reported to range from 73 to 84 days11,12. The mean patency rate in this series was 174 days (5.8 months). Reported device-related infection in association with tunneled chronic dialysis catheters has ranged from 0.7 to 5.5 per 1000 patient-days13,14,15,16,17,18. The device-related infection rate of 2.5 infections per 1000 patient-days noted with the LifeSite System falls about midway within this reported range. Although this is a preliminary study, these observations suggest that the LifeSite System has an improved patency rate and at least a comparable infection risk profile when compared with tunneled chronic dialysis catheters.
Unfortunately, infection was not eliminated with the LifeSite System. Good technique at the time of valve cannulation and needle removal are important. We have found that it is possible to exchange the cannulas attached to the valves without disturbing the valves themselves. This is analogous to exchanging a chronic dialysis catheter in the management of catheter-related bacteremia17,18,19. Whether this is appropriate in association with the LifeSite System has not been validated.
Although flow problems occurred infrequently and no device was lost because of this complication, blood clots 3 to 4 cm in length were frequently aspirated from the cannulas at the initiation of a dialysis treatment. The ability to aspirate these clots was attributed to the large diameter of the cannula (12 French).
The buttonhole technique used for cannulating the valves offered several advantages. This technique made cannulation easier and was performed faster because the site was constant and easily recognized. After a short period, cannulation of the valve was also painless, a very welcome feature for these patients who have to undergo a needle stick so frequently. Using the same site repetitively also reduces scarring and may eliminate the need of needle reinsertion because of "bad sticks." After 156.9 patient-months of using the buttonhole technique, no problems have been encountered.
Acceptance of the LifeSite System among patients and dialysis center staff members has been excellent. Patients especially favored the pain-free cannulations, improved body image, and resulting improved quality of life. This latter benefit was attributed at least in part to an ability to achieve effective dialysis in a population of patients that had not had adequate dialysis because of access problems prior to entering the study.
In summary, this clinical study validates the applicability of the LifeSite Hemodialysis Access System as a vascular access for chronic HD. The results of this study suggest that it has several advantages over tunneled chronic dialysis catheters. The exact place of this device in the armamentarium of the nephrologist dealing with vascular access will depend on further study and experience. However, these data suggest that it can play an important role as a bridge to allow for maturation of a peripheral access and as an alternative for long-term use when a peripheral access is not feasible. The LifeSite System may also be ideal as an alternative for patients whose comorbidities would not tolerate the strain of shunt systems as well as patients whose quality-of-life needs demand the discreetness of a subcutaneous system.
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