Symposium on Surgical Techniques
Construction of Arteriovenous Fistulas for Hemodialysis
Edwin G. Beven, M.D., and Norman R. Hertzer, M.D.
The availability of blood vessels for chronic hemodialysis is essential to the preservation of life in patients with terminal renal failure. The exposed, Silastic arteriovenous shunt developed in 1960 by Quinton and associates11 permitted intermittent dialysis in the setting of expanding home dialysis programs as well as by expert technicians in major centers. In 1966, Brescia and associates2 first described the use of a subcutaneous arteriovenous fistula constructed at the wrist which allowed repeated percutaneous cannulation of the arterialized superficial veins of the forearm. Their technique eliminated the incidence of thrombosis, infection, and multiple revisions often associated with the extemal shunt, and provided the patient with freedom of activity not previously possible.4 • 6-9 • 12 Although the Brescia-Cimino fistula is feasible for the majority of patients, construction at the level of the wrist frequently is impossible in the presence of occlusive arterial disease, antecedent shunt failure, or superficial venous thrombosis. Accordingly, several alternative methods have been suggested. When the proximal cephalic vein is patent, an arteriovenous fistula may be established immediately above the antecubital crease.5 Other procedures involve the interposition of autogenous vein10 or bovine heterograffl between an appropriate distal artery and proximal deep vein, and dialysis is performed by puncturing the graft itself. Such bypassing techniques are adaptable to the anterior thigh when all upper extremity sites have been exhausted. The techniques for the construction of standard wrist arteriovenous fistulas, and the alternative methods necessary in selected cases to be described in this article, are based upon experience during the past 8 years with 242 patients comprising 346 fistulas. No attempt is made to describe all variations reported in the surgical literature, and discussion is limited only to those procedures which we have found dependable. The factors determining the type and site of arteriovenous fistula merit From the Department of Vascular Surgery, The Cleveland Clinic Foundation and the Cleveland Clinic Educational Foundation, Cleveland, Ohio I
I
Surgical Clinics of North America- Vol. 55, No.5, October 1975
1125
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BEVEN AND NORMAN
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HERTZER
particular emphasis, since these factors can determine the success or failure of the operation.
GENERAL CONSIDERATIONS Arteriovenous fistulas constructed originally at the wrist provide a long segment of arterialized cephalic vein within the relatively shallow subcutaneous tissue of the radial aspect of the forearm, which is cannulated easily by either technicians or family members. Moreover, eventual failure of a distal fistula usually does not complicate construction of another at a more proximal site, whereas thrombosis of a proximal fistula eliminates the cephalic vein in that extremity from further use. The preoperative evaluation should define the presence of functional arterial and venous segments throughout the extremity, but those near the wrist should be used as an initial procedure whenever possible.
Physical Examination Careful palpation of arterial pulses should be done throughout both arms. The Allen test is performed to assess individual patency of both the radial and ulnar arteries, particularly in older patients or those with prolonged renal failure in whom occlusive arterial disease is common. If the ulnar artery is occluded, thrombosis of the radial artery as either an operative complication or the result of late fistula failure could cause serious ischemia of the hand. In such cases, the contralateral extremity is preferable for distal fistula use. Examination of the superficial veins of the arm is equally important. Although a pliant, patent cephalic vein may be obvious, patients with chronic renal failure often have a frustratingly selective thrombosis of those veins most preferred for fistula construction. Because inspection and palpation at times are misleading, we routinely employ phlebography to assess the patency of the venous system (Fig. 1). The choice of which arm to use depends solely upon the quality of the vessels available for creation of the arteriovenous fistula. If both are equally suitable, we prefer the nondominant arm. The basilic vein should not be used for fistula construction, since its course is parallel to that of the brachial artery and repeated cannulation is difficult and risks arterial injury. The ulnar artery, usually small and without a usable adjacent vein, is employed only rarely.
Choice of Anesthesia Anemia and serum electrolyte derangement are common among patients with chronic renal disease and tend to increase the risk of general inhalation anesthesia. Local infiltration anesthesia has proved quite satisfactory for the construction of arteriovenous fistulas at the wrist and antecubital fossa, as well as for interposition of saphenous vein or bovine heterografts in many cases. We currently restrict the use of general anesthesia to children and especially uncooperative adults.
ARTERIOVENOUS FISTULAS FOR HEMODIALYSIS
1127
Figure 1. Operative phlebograms performed by injection of 15 cc of contrast media into a dorsal hand vein. A, Normal study, showing a patent cephalic vein throughout the length of the arm. B, The cephalic vein is absent within the forearm, but is patent proximal to the antecubital fossa and available for anastomosis to the brachial artery. C, The cephalic vein is completely occluded.
SURGICAL TECHNIQUES Standard Side-to-Side Radiocephalic Arteriovenous Fistula The arm is draped free and the hand is wrapped in a sterile towel. A longitudinal incision is placed between the cephalic vein and the radial artery, slightly to the arterial side of the radius. The vein is located, and a segment measuring 3 to 4 em in length is isolated from surrounding subcutaneous and areolar tissue. Small venous branches, which if torn can bleed briskly after the fistula is completed, are ligated with fine nonabsorbable vascular suture and divided to improve mobility. The adventitia is removed during the dissection to avoid later kinking and segmental stenosis. The radial artery is similarly isolated and tiny muscular branches are controlled with fine suture ligatures. The superficial
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branch of the radial nerve lies immediately superficial and lateral to the artery and is preserved. Both the vein and the artery are handled gently to minimize vasospasm, using small angled instruments to elevate the vessels rather than direct application of forceps. Sufficient length is isolated until the two vessels rest side by side without tension. If tension cannot be corrected, the distal cephalic vein can be divided and ligated, and the proximal segment brought to the radial artery in an end-to-side fashion. This maneuver is rarely necessary at the wrist. A longitudinal venotomy measuring about 8 mm in length is made, and fine traction sutures are inserted to eliminate subsequent intimal damage from forceps. If venous valves are competent, the proximal vein may not require clamp control. A 3 French embolectomy catheter is inserted well into the proximal vein to confirm patency, then withdrawn without balloon inflation. The radial artery is controlled with atraumatic bulldog clamps, and an arteriotomy is made equal in length to the venotomy. Traction sutures are inserted. The distal and proximal artery is gently dilated with graduated sounds and infused with dilute heparin solution. The venotomy and arteriotomy should be planned in such a way that their approximation does not result in spiral rotation of either vessel (Fig. 2). The side-to-side anastomosis is performed with 6-0 vascular suture, although 7-0 material may be more appropriate with small vessels, especially in children. The assistance of magnification loupes also
Cephalic vein
Radial
artery Cephalic vein
B Figure 2. A, Sketch illustrating placement of a standard radiocephalic fistula. The vessels are under no tension. B, View of the anastomosis prior to its completion. The continuous suture is interrupted twice to prevent a pursestring effect.
A
ARTERIOVENOUS FISTULAS FOR HEMODIALYSIS
Figure 3.
1129
Photograph of a completed radiocephalic fistula.
may be necessary. A pursestring effect is avoided by interrupting the continuous suture at least twice. A graduated sound inserted occasionally into the proximal and distal lumens during approximation of the anastomotic corners prevents narrowing. Since both vessels are small, suture placement must be precise. Both distal and proximal arterial segments are flushed free of debris before completion of the anastomosis. Once the fistula is complete, the distal venous and proximal arterial clamps are first removed to divert any remaining thrombus into the distal vein, and all other clamps are then removed. Light compression with hemostatic pledgets is usually sufficient to stop immediate anastomotic bleeding, but additional interrupted sutures may be necessary under temporary proximal arterial control. When flow is restored, a thrill should be palpable within the fistula and the central venous limb. Spasm of the proximal vein may be reduced by "milking" the vein distally against arterial perfusion. Pulsation of the central vein without a thrill may indicate proximal thrombus and. obstruction, and exploration of the venous segment with a small catheter should be considered. Failure of the distal radial pulse to reappear can be caused by either distal thrombosis or diversion of a critical volume of blood into the venous side of the fistula. If the distal arterial pulse is not restored by manual compression of the venous limbs, the embolectomy catheter is used to explore the distal artery through a short transverse incision in the proximal vein, passing the catheter through the anastomosis. Since we have encountered a symptomatic steal syndrome only once in 346 fistula constructions, loss of the distal arterial pulse caused by high fistula flow alone requires no immediate revision if the anastomosis otherwise is technically satisfactory (Fig. 3). The incision is closed in two layers. Sound approximation of subcutaneous tissue is important, since the pulsating fistula occasionally can
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erode the skin. The incision is covered with light gauze, and circumferential, constricting tape is avoided. Palpation and auscultation is performed again before the patient leaves the operating room to confirm continued patency after closure of the incision. Postoperative heparin therapy may be indicated if the vessels are particularly small and flow is sluggish.
Side-to-Side Brachiocephalic Arteriovenous Fistula The standard arteriovenous fistula at wrist level may be impossible for patients who have had previous failure of fistulas or shunts, or whose distal cephalic vein or radial artery is otherwise inadequate. In such cases, anastomosis of the cephalic vein and brachial artery immediately proximal to the antecubital crease provides a satisfactory alternative means of venous access. Except in the obese patient, the proximal cephalic vein is clearly available for cannulation between the level of the fistula and the deltoid groove. A transverse incision immediately proximal to the antecubital skin crease extends between the palpable brachial artery and the cephalic vein located by preoperative phlebography. Generous mobilization of both vessels with ligation and division of tethering branches is required, since the fistula must be constructed without tension anterior to the distal biceps muscle. Transverse sectioning of the bicipital aponeurosis often improves approximation of the vessels. The median nerve lies medial and posterior to the artery and should be protected. The anastomosis is virtually identical to that described for the radiocephalic fistula, but should be limited to a length of 7 mm to minimize the incidence of symptomatic distal arterial steal (Fig. 4A). Sufficient mobility may not be possible in obese or muscular patients to allow a side-to-side anastomosis. In such cases the distal cephalic vein is transected, and an end-to-side fistula is constructed. This alternative is necessary more frequently for the brachiocephalic fistula than for those performed at the wrist (Fig. 4B). If the brachial artery is calcified, a small oval of the arterial wall may be excised to provide a widely patent anastomosis. The central venous limb of arteriovenous fistulas placed at either the wrist or the antecubital area dilate with time because of greatly increased pressure and flow. A period of 3 weeks is generally sufficient to produce a venous segment which is easily cannulated for dialysis, although patients with initially large veins may use their fistulas almost immediately. Bypass Techniques Patients who have had previous unsuccessful arteriovenous fistulas or shunts, or who have had bilateral thrombophlebitis from repeated venipunctures often lack a suitable site for fistula construction. Such patients may be managed by interposition of segments of autogenous saphenous vein or bovine heterograft between a distal artery and proximal deep vein. Dialysis is performed by cannulation of the bypass graft itself. Provided phlebography had demonstrated patent deep veins
1131
ARTERIOVENOUS FISTULAS FOR HEMODIALYSIS
Brachial artery
Cephalic vein
A
B
Figure 4. A, Sketch of a side-to-side brachiocephalic arteriovenous fistula. The fistula must be constructed proximal to the antecubital crease to avoid kinking when the elbow is flexed. B, The alternative end-to-side fistula performed when tension prevents side-to-side anastomosis.
throughout the extremity, either the saphenous vein or bovine graft may be interposed between the radial artery and a deep antecubital vein, or between the brachial artery and an axillary vein. The upper arm is preferable for slender patients in whom the taut skin of the forearm makes difficult the construction of a slack, yielding subcutaneous tunnel which will not compress the graft or ulcerate with repeated trauma. Otherwise, location of the bypass is limited only by the availability of arterial inflow. It is especially important that the bovine heterograft should not cross a point of flexion, such as the elbow, because the heterograft kinks easily and could thrombose. After experience with both saphenous vein and bovine grafts for purposes of hemodialysis, we currently prefer the bovine heterograft. Produced from tanned bovine carotid arteries, the heterografts consist almost solely of antigenetically neutral collagen tissue and produce no clinical rejection effects. Their use eliminates the need for additional thigh incisions required to harvest the saphenous vein, and makes unnecessary the inconvenience of such procedures as the saphenous loop fistula. The diameter of the bovine carotid, measuring 7 mm or more,
1132
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permits almost immediate cannulation for dialysis. Conversely, the size of the heterograft limits its use in small children in whom the diameter of autogenous vein is more appropriate. The arm is draped free, including the axilla if the upper arm is to be used. The bovine heterograft is placed in sterile saline to rinse any remaining preservative while dissection is in progress. The recipient vein is exposed first to assess its size and patency. In the forearm, a transverse incision distal to the antecubital crease is used. In the upper arm, the axillary vein is isolated from the axillary artery and distal brachial plexus through a transverse incision at the level of the humoral insertion of the deltoid muscle. The radial or brachial artery, respectively, is mobilized, opened with a longitudinal arteriotomy, dilated with graduated sounds, and infused with heparin solution just as is done during construction of an arteriovenous fistula. The bovine graft is trimmed at one end at an angle that will allow it to lie in its subcutaneous position without kinking. The arterial anastomosis is then performed using a continuous 6-0 vascular suture. The graft is flushed with proximal arterial blood, occluded near the anastomosis with an atraumatic vascular clamp, and flow is restored through the donor artery. The subcutaneous tunnel is developed using a long instrument with a rounded tip. If the procedure is performed under local anesthesia, additional anesthesia along the projected course of the tunnel is necessary. The tunnel should follow a gentle curve if the arm is short, so that a longer segment of graft is available for cannulation. The gr
Construction of Arteriovenous Fistulas for Hemodialysis
Edwin G. Beven, M.D., and Norman R. Hertzer, M.D.
The availability of blood vessels for chronic hemodialysis is essential to the preservation of life in patients with terminal renal failure. The exposed, Silastic arteriovenous shunt developed in 1960 by Quinton and associates11 permitted intermittent dialysis in the setting of expanding home dialysis programs as well as by expert technicians in major centers. In 1966, Brescia and associates2 first described the use of a subcutaneous arteriovenous fistula constructed at the wrist which allowed repeated percutaneous cannulation of the arterialized superficial veins of the forearm. Their technique eliminated the incidence of thrombosis, infection, and multiple revisions often associated with the extemal shunt, and provided the patient with freedom of activity not previously possible.4 • 6-9 • 12 Although the Brescia-Cimino fistula is feasible for the majority of patients, construction at the level of the wrist frequently is impossible in the presence of occlusive arterial disease, antecedent shunt failure, or superficial venous thrombosis. Accordingly, several alternative methods have been suggested. When the proximal cephalic vein is patent, an arteriovenous fistula may be established immediately above the antecubital crease.5 Other procedures involve the interposition of autogenous vein10 or bovine heterograffl between an appropriate distal artery and proximal deep vein, and dialysis is performed by puncturing the graft itself. Such bypassing techniques are adaptable to the anterior thigh when all upper extremity sites have been exhausted. The techniques for the construction of standard wrist arteriovenous fistulas, and the alternative methods necessary in selected cases to be described in this article, are based upon experience during the past 8 years with 242 patients comprising 346 fistulas. No attempt is made to describe all variations reported in the surgical literature, and discussion is limited only to those procedures which we have found dependable. The factors determining the type and site of arteriovenous fistula merit From the Department of Vascular Surgery, The Cleveland Clinic Foundation and the Cleveland Clinic Educational Foundation, Cleveland, Ohio I
I
Surgical Clinics of North America- Vol. 55, No.5, October 1975
1125
1126
EDWIN
G.
BEVEN AND NORMAN
R.
HERTZER
particular emphasis, since these factors can determine the success or failure of the operation.
GENERAL CONSIDERATIONS Arteriovenous fistulas constructed originally at the wrist provide a long segment of arterialized cephalic vein within the relatively shallow subcutaneous tissue of the radial aspect of the forearm, which is cannulated easily by either technicians or family members. Moreover, eventual failure of a distal fistula usually does not complicate construction of another at a more proximal site, whereas thrombosis of a proximal fistula eliminates the cephalic vein in that extremity from further use. The preoperative evaluation should define the presence of functional arterial and venous segments throughout the extremity, but those near the wrist should be used as an initial procedure whenever possible.
Physical Examination Careful palpation of arterial pulses should be done throughout both arms. The Allen test is performed to assess individual patency of both the radial and ulnar arteries, particularly in older patients or those with prolonged renal failure in whom occlusive arterial disease is common. If the ulnar artery is occluded, thrombosis of the radial artery as either an operative complication or the result of late fistula failure could cause serious ischemia of the hand. In such cases, the contralateral extremity is preferable for distal fistula use. Examination of the superficial veins of the arm is equally important. Although a pliant, patent cephalic vein may be obvious, patients with chronic renal failure often have a frustratingly selective thrombosis of those veins most preferred for fistula construction. Because inspection and palpation at times are misleading, we routinely employ phlebography to assess the patency of the venous system (Fig. 1). The choice of which arm to use depends solely upon the quality of the vessels available for creation of the arteriovenous fistula. If both are equally suitable, we prefer the nondominant arm. The basilic vein should not be used for fistula construction, since its course is parallel to that of the brachial artery and repeated cannulation is difficult and risks arterial injury. The ulnar artery, usually small and without a usable adjacent vein, is employed only rarely.
Choice of Anesthesia Anemia and serum electrolyte derangement are common among patients with chronic renal disease and tend to increase the risk of general inhalation anesthesia. Local infiltration anesthesia has proved quite satisfactory for the construction of arteriovenous fistulas at the wrist and antecubital fossa, as well as for interposition of saphenous vein or bovine heterografts in many cases. We currently restrict the use of general anesthesia to children and especially uncooperative adults.
ARTERIOVENOUS FISTULAS FOR HEMODIALYSIS
1127
Figure 1. Operative phlebograms performed by injection of 15 cc of contrast media into a dorsal hand vein. A, Normal study, showing a patent cephalic vein throughout the length of the arm. B, The cephalic vein is absent within the forearm, but is patent proximal to the antecubital fossa and available for anastomosis to the brachial artery. C, The cephalic vein is completely occluded.
SURGICAL TECHNIQUES Standard Side-to-Side Radiocephalic Arteriovenous Fistula The arm is draped free and the hand is wrapped in a sterile towel. A longitudinal incision is placed between the cephalic vein and the radial artery, slightly to the arterial side of the radius. The vein is located, and a segment measuring 3 to 4 em in length is isolated from surrounding subcutaneous and areolar tissue. Small venous branches, which if torn can bleed briskly after the fistula is completed, are ligated with fine nonabsorbable vascular suture and divided to improve mobility. The adventitia is removed during the dissection to avoid later kinking and segmental stenosis. The radial artery is similarly isolated and tiny muscular branches are controlled with fine suture ligatures. The superficial
1128
EDWIN
G.
BEVEN AND NORMAN
R.
HERTZER
branch of the radial nerve lies immediately superficial and lateral to the artery and is preserved. Both the vein and the artery are handled gently to minimize vasospasm, using small angled instruments to elevate the vessels rather than direct application of forceps. Sufficient length is isolated until the two vessels rest side by side without tension. If tension cannot be corrected, the distal cephalic vein can be divided and ligated, and the proximal segment brought to the radial artery in an end-to-side fashion. This maneuver is rarely necessary at the wrist. A longitudinal venotomy measuring about 8 mm in length is made, and fine traction sutures are inserted to eliminate subsequent intimal damage from forceps. If venous valves are competent, the proximal vein may not require clamp control. A 3 French embolectomy catheter is inserted well into the proximal vein to confirm patency, then withdrawn without balloon inflation. The radial artery is controlled with atraumatic bulldog clamps, and an arteriotomy is made equal in length to the venotomy. Traction sutures are inserted. The distal and proximal artery is gently dilated with graduated sounds and infused with dilute heparin solution. The venotomy and arteriotomy should be planned in such a way that their approximation does not result in spiral rotation of either vessel (Fig. 2). The side-to-side anastomosis is performed with 6-0 vascular suture, although 7-0 material may be more appropriate with small vessels, especially in children. The assistance of magnification loupes also
Cephalic vein
Radial
artery Cephalic vein
B Figure 2. A, Sketch illustrating placement of a standard radiocephalic fistula. The vessels are under no tension. B, View of the anastomosis prior to its completion. The continuous suture is interrupted twice to prevent a pursestring effect.
A
ARTERIOVENOUS FISTULAS FOR HEMODIALYSIS
Figure 3.
1129
Photograph of a completed radiocephalic fistula.
may be necessary. A pursestring effect is avoided by interrupting the continuous suture at least twice. A graduated sound inserted occasionally into the proximal and distal lumens during approximation of the anastomotic corners prevents narrowing. Since both vessels are small, suture placement must be precise. Both distal and proximal arterial segments are flushed free of debris before completion of the anastomosis. Once the fistula is complete, the distal venous and proximal arterial clamps are first removed to divert any remaining thrombus into the distal vein, and all other clamps are then removed. Light compression with hemostatic pledgets is usually sufficient to stop immediate anastomotic bleeding, but additional interrupted sutures may be necessary under temporary proximal arterial control. When flow is restored, a thrill should be palpable within the fistula and the central venous limb. Spasm of the proximal vein may be reduced by "milking" the vein distally against arterial perfusion. Pulsation of the central vein without a thrill may indicate proximal thrombus and. obstruction, and exploration of the venous segment with a small catheter should be considered. Failure of the distal radial pulse to reappear can be caused by either distal thrombosis or diversion of a critical volume of blood into the venous side of the fistula. If the distal arterial pulse is not restored by manual compression of the venous limbs, the embolectomy catheter is used to explore the distal artery through a short transverse incision in the proximal vein, passing the catheter through the anastomosis. Since we have encountered a symptomatic steal syndrome only once in 346 fistula constructions, loss of the distal arterial pulse caused by high fistula flow alone requires no immediate revision if the anastomosis otherwise is technically satisfactory (Fig. 3). The incision is closed in two layers. Sound approximation of subcutaneous tissue is important, since the pulsating fistula occasionally can
1130
EDWIN
G.
BEVEN AND NORMAN
R.
HERTZER
erode the skin. The incision is covered with light gauze, and circumferential, constricting tape is avoided. Palpation and auscultation is performed again before the patient leaves the operating room to confirm continued patency after closure of the incision. Postoperative heparin therapy may be indicated if the vessels are particularly small and flow is sluggish.
Side-to-Side Brachiocephalic Arteriovenous Fistula The standard arteriovenous fistula at wrist level may be impossible for patients who have had previous failure of fistulas or shunts, or whose distal cephalic vein or radial artery is otherwise inadequate. In such cases, anastomosis of the cephalic vein and brachial artery immediately proximal to the antecubital crease provides a satisfactory alternative means of venous access. Except in the obese patient, the proximal cephalic vein is clearly available for cannulation between the level of the fistula and the deltoid groove. A transverse incision immediately proximal to the antecubital skin crease extends between the palpable brachial artery and the cephalic vein located by preoperative phlebography. Generous mobilization of both vessels with ligation and division of tethering branches is required, since the fistula must be constructed without tension anterior to the distal biceps muscle. Transverse sectioning of the bicipital aponeurosis often improves approximation of the vessels. The median nerve lies medial and posterior to the artery and should be protected. The anastomosis is virtually identical to that described for the radiocephalic fistula, but should be limited to a length of 7 mm to minimize the incidence of symptomatic distal arterial steal (Fig. 4A). Sufficient mobility may not be possible in obese or muscular patients to allow a side-to-side anastomosis. In such cases the distal cephalic vein is transected, and an end-to-side fistula is constructed. This alternative is necessary more frequently for the brachiocephalic fistula than for those performed at the wrist (Fig. 4B). If the brachial artery is calcified, a small oval of the arterial wall may be excised to provide a widely patent anastomosis. The central venous limb of arteriovenous fistulas placed at either the wrist or the antecubital area dilate with time because of greatly increased pressure and flow. A period of 3 weeks is generally sufficient to produce a venous segment which is easily cannulated for dialysis, although patients with initially large veins may use their fistulas almost immediately. Bypass Techniques Patients who have had previous unsuccessful arteriovenous fistulas or shunts, or who have had bilateral thrombophlebitis from repeated venipunctures often lack a suitable site for fistula construction. Such patients may be managed by interposition of segments of autogenous saphenous vein or bovine heterograft between a distal artery and proximal deep vein. Dialysis is performed by cannulation of the bypass graft itself. Provided phlebography had demonstrated patent deep veins
1131
ARTERIOVENOUS FISTULAS FOR HEMODIALYSIS
Brachial artery
Cephalic vein
A
B
Figure 4. A, Sketch of a side-to-side brachiocephalic arteriovenous fistula. The fistula must be constructed proximal to the antecubital crease to avoid kinking when the elbow is flexed. B, The alternative end-to-side fistula performed when tension prevents side-to-side anastomosis.
throughout the extremity, either the saphenous vein or bovine graft may be interposed between the radial artery and a deep antecubital vein, or between the brachial artery and an axillary vein. The upper arm is preferable for slender patients in whom the taut skin of the forearm makes difficult the construction of a slack, yielding subcutaneous tunnel which will not compress the graft or ulcerate with repeated trauma. Otherwise, location of the bypass is limited only by the availability of arterial inflow. It is especially important that the bovine heterograft should not cross a point of flexion, such as the elbow, because the heterograft kinks easily and could thrombose. After experience with both saphenous vein and bovine grafts for purposes of hemodialysis, we currently prefer the bovine heterograft. Produced from tanned bovine carotid arteries, the heterografts consist almost solely of antigenetically neutral collagen tissue and produce no clinical rejection effects. Their use eliminates the need for additional thigh incisions required to harvest the saphenous vein, and makes unnecessary the inconvenience of such procedures as the saphenous loop fistula. The diameter of the bovine carotid, measuring 7 mm or more,
1132
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G.
'BEVEN AND NORMAN
R.
HERTZER
permits almost immediate cannulation for dialysis. Conversely, the size of the heterograft limits its use in small children in whom the diameter of autogenous vein is more appropriate. The arm is draped free, including the axilla if the upper arm is to be used. The bovine heterograft is placed in sterile saline to rinse any remaining preservative while dissection is in progress. The recipient vein is exposed first to assess its size and patency. In the forearm, a transverse incision distal to the antecubital crease is used. In the upper arm, the axillary vein is isolated from the axillary artery and distal brachial plexus through a transverse incision at the level of the humoral insertion of the deltoid muscle. The radial or brachial artery, respectively, is mobilized, opened with a longitudinal arteriotomy, dilated with graduated sounds, and infused with heparin solution just as is done during construction of an arteriovenous fistula. The bovine graft is trimmed at one end at an angle that will allow it to lie in its subcutaneous position without kinking. The arterial anastomosis is then performed using a continuous 6-0 vascular suture. The graft is flushed with proximal arterial blood, occluded near the anastomosis with an atraumatic vascular clamp, and flow is restored through the donor artery. The subcutaneous tunnel is developed using a long instrument with a rounded tip. If the procedure is performed under local anesthesia, additional anesthesia along the projected course of the tunnel is necessary. The tunnel should follow a gentle curve if the arm is short, so that a longer segment of graft is available for cannulation. The gr
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