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Postoperative lower extremity bypass surveillance: Beyond ankle arm blood pressures
Vol. XIII
No. 3
JOURNAL OF VASCULAR NURSING
PAGE 75
Postoperative lower extremity bypass surveillance: Beyond ankle arm b l o o d pressures Marcia S. F o l d e s , BSN, RVT Presented at the Twelfth Annual National Symposium, Society for Vascular Nursing, St. Louis, Mo., May 19-21, 1994. Surveillance is essential to the postoperative follow-up of lower extremity bypass grafts. Early, intermediate, and late thrombosis place the patient's limb at risk, so detection of problems before the graft fails is critical Because contrast angiography is not routinely performedfor surveillance, most vascular surgeons rely on history, physical examination, and noninvasive vascular studies (NVS) to assess perfusion to the lower extremity after bypass grafting. These NVS include ankle/brachial waveforms, blood pressures, and indexes before and after exercise. The purpose of this study is to report our findings with duplex color-flow ultrasonography (DCU) to examine lower extremity bypass grafts. According to our protocol, we monitor lower extremity grafts with ankle/brachial Doppler pressures, analogue waveforms, and lower extremity exercise when possible. These NVS areperformed by nurses in the vascular laboratory before the patient is discharged from the hospital, at least twice during the first year, and then annually. DCU is also performed at least two times during the first year and then annually. If the study results are abnormal or if the patient has symptoms, testing is usually repeated. When abnormalities persist contrast angiograpby may be warranted. We have detected anatomic and hemodynamic changes in lower extremity bypasses by use of our protocol By adding DCU to ankle/brachial bloodpressures, we have identified aneurysmal dilation, diffuse atherosclerosis, focal narrowing, arteriovenous fistulas caused by unligated venous branches, retained venous valves, and disease progression proximal or distal to the graft. For years nurses in the vascular laboratory have been able to assess the hemodynamics of lower extremity bypass grafts by use of history, physical examination, ankle and arm blood pressures, a n d waveforms. Now with DCU the vascular laboratory progresses beyond these methods to detect abnormalities in graft anatomy early, before the graft fails. Consequently tissue damage and limb loss of patients can potentially be minimized. (J Vasc SVRG1995;13: 75-8.)
The goal o f lower extremity arterial reconstruction is adequate tissue perfusion. This is accomplished by a patent bypass graft. Failure or occlusion o f the graft can lead to tissue loss. Vascular surgeons prefer to correct problems before the graft fails. 1 Therefore the follow-up of these patients to discern grafts at risk is crucial for long-term
Marcia Foldes is a Vascular Nurse Technologist at the Blood Flow Laboratory of St. John's Mercy Medical Center in St. Louis, Mo. Address reprint requests to Marcia Foides, BSN, RVZ, Blood Flow Laborator~ St. John's Mercy Medical Center, 615 S. New BaUas Raft., St. Louis, MO 63141. Copkmtgbt © 1995 by the Society for Vascular Nursing, Inc. 1062-0303/95/85.00 + 0 40/1/662"/0
patency. Methods of graft surveillance are the subject of this study; but first, general information about lower extremity bypasses will be reviewed. TYPES AND CHOICES OF GRAFT MATERIAL The surgeon's first choice for graft material is autologous vein. The greater saphenous, lesser saphenous, basilic, cephalic, or any o t h e r vein o f adequate diameter and length may be used. Polytetrafluoroethylene is a synthetic material used primarily for above-knee bypasses at this hospital. Preserved umbilical vein has b e e n used as a conduit. Sometimes synthetic materials are c o m b i n e d with autologous vein to form a composite bypass w h e n a sufficient length o f vein is not available for a distal bypass. The synthetic material is used in the proximal p o r t i o n o f the graft; it is sewn to the v e n o u s portion and t h e n anastomosed to the native artery at the distal e n d of the bypass. T h e r e are various techniques used in p e r f o r m i n g lower extremity bypass grafting. An in situ bypass is o n e in which the vein remains in place but is dissected free at the proximal and distal anastomosis sites. Branches are ligated, and the valves are r e n d e r e d i n c o m p e t e n t by use o f a valvulotome. Reversed vein grafts are those in which the vein is harvested, r e m o v e d from the leg, reversed, and t u n n e l e d back into the leg at the site of the bypass. The venous valves remain intact because, after reversing the vein, the valves will allow the flow o f b l o o d from proximal to distal in the bypass. Venous branches are ligated with this type of vein graft as well. Translocated vein grafts are those in which any vein is harvested, branches ligated, and t h e n t u n n e l e d into the leg as a bypass conduit. Examples o f these veins include the greater s a p h e n o u s or lesser saphenous vein (ipsilateral or contralateral) or the basilic or cephalic vein from either arm. CAUSES OF GRAFT FAILURE The three basic causes o f graft failure include thrombosis, h e m o d y n a m i c failure, and structural failure.1 The causes for graft failure vary d e p e n d i n g o n length o f time after the bypass was p e r f o r m e d . In the early postoperative period, graft failure is most often caused by technical errors during the o p e r a t i o n (retained venous valves, kinks in the conduit), decreased outflow (significant atherosclerotic disease in the vessels d o w n s t r e a m from the distal anastomosis), infection, or the patient's hypercoagulable state. From 1 m o n t h to 2 years after operation, graft failure usually occurs because o f occlusive lesions (neointimal fibroplasia) within the graft itself, in the inflow, or outflow vessels. If the graft fails after 2 years, it is most likely caused by atherosclerotic disease progression, either within the graft or in the native vessels proximally o r distally. 1
PAGE 76
JOURNAL OF VASCULAR NURSING
A B N O R M A L I T I E S F O U N D BY D C U
Stenosis Aneurysmal dilation Pseudoaneurysm Retained valve leaflets Arteriovenous fistula Plaque Thrombosis
METHODS OF SURVEILLANCE An accurate history and physical examination begin the postoperative assessment of lower extremity grafts. The date of surgery and exact location of the d o n o r vessel at the proximal anastomosis and the runoff vessel at the distal anastomosis should be d o c u m e n t e d . Recurrent symptoms such as claudication o r rest pain, limb pallor, numbness or tingling, d e v e l o p m e n t o f n e w ulcers, or improvement of preoperative lesions should be noted. Cessation of smoking should be strongly encouraged, with the packs smoked per day recorded. I m p r o v e m e n t in walking tolerance and distance is also noteworthy. The graft should be palpated at the proximal anastomosis, as well as at various locations t h r o u g h o u t its length. Contrast angiography is not routinely p e r f o r m e d for surveillance but may be p e r f o r m e d to confirm the results of noninvasive vascular studies w h e n an abnormality is d e t e c t e d and d e t e r m i n e the type of subseq u e n t intervention required. Noninvasive vascular studies are the mainstay of most lower extremity bypass graft surveillance protocols. At this institution, analogue waveforms are obtained from the foot arteries: dorsalis pedis, posterior tibial, and peroneal. Bilateral Doppler blood pressures are also obtained at these arteries, as well as bilateral brachial artery blood pressures. These are obtained with the patient at rest and after the patient exercises, if possible. Exercise is p e r f o r m e d by having the patient walk o n the treadmill (at a constant speed and elevation) or by stationary toe raises. The highest D o p p l e r pressure at the ankle is divided by the highest D o p p l e r pressure obtained in the brachial artery to obtain the ankle/brachial index (ABI). A normal ABI is 0.9 to 1.0 or more; an abnormal ABI is less than 0.9. Duplex color ultrasonography (DCU) or color-flow Doppler imaging (CDI) has b e e n a d d e d to surveillance protocols to assess the anatomy and flow in the bypass graft. The p u r p o s e of DCU is to assess graft patency by determining the p r e s e n c e of blood flow in the graft. CDI expedites the process of graft assessment and can alert the examiner to areas of color flow disturbance or abnormality by changes in the color displayed. Spectral analysis is then used to obtain a peak systolic velocity (PSV) in p r e d e t e r m i n e d areas o f the graft, as well as in areas of disturbed color flow. These p r e d e t e r m i n e d areas include the proximal and distal
SEPTEMBER 1995
PATIENT PREPARATION FOR L)~U
Procedure explained Head of bed elevated slightly Patient in supine position with knee flexed and hip externally rotated
anastomoses, the proximal, mid, and distal portion of the thigh, the b e n d o f the knee, and the proximal, mid, and distal portion of the lower leg. When DCU is p e r f o r m e d early in the postoperative period, it can provide the baseline evaluation for subsequent studies. If abnormalities are detected such as those listed in Table I, grafts at risk of failure can be identified. The mechanism of graft failure can also be d e t e r m i n e d with DCU after the onset of ischemic symptoms. SURVEILLANCE PROTOCOL AT ST, J O H N ' S MERCY MEDICAL CENTER The surveillance protocol for lower extremity bypass grafts begins while the patient is still in the hospital. Nurses from the vascular laboratory obtain ankle/brachial Doppler pressures and analogue waveforms at the patient's bedside within the first 3 postoperative days. During the first postoperative year, this is d o n e two times, including exercise testing if the patient is able to tolerate walking on the treadmill. Yearly testing is t h e n performed. DCU is p e r f o r m e d twice in the first year, t h e n once a year if no symptoms or physical findings occur. Often, the ankle/brachial blood pressures, exercise, and DCU are p e r f o r m e d during the same outpatient visit. If the ABI decreases by 15% from the previous examination result and is confirmed by repeat testing, then DCU may be performed. Each noninvasive study is compared with the previous examination results to detect n e w disease or progression of previous abnormalities. Patient preparation for DCU is minimal. The salient points are s h o w n in Table II. Images of the graft are obtained along its entire length in transverse view with CDI to locate proximal and distal anastomosis and also any retained venous branches. Then, from proximal to distal, imaging is p e r f o r m e d in longitudinal view; PSV is obtained from the inflow vessel, at p r e d e t e r m i n e d areas m e n t i o n e d above, and in the outflow artery. If possible, PSV is also obtained in the native artery proximal to t h e distal anastomosis. PSV is o b t a i n e d at any areas of color flow disturbance and just proximal to this disturbed flow. Figure 1 is an example of a normal distal anastomosis in a c o m m o n femoral a r t e r y - t o - a n t e r i o r tibial artery vein graft as shown by DCU and contrast angiography. Abnormalities d e t e c t e d by DCU are outlined in Table I. Stenosis may b e f o u n d at any site in the graft o r native artery at the anastomatic site. Figure 2 shows an isolated stenosis with increased PSV in the mid thigh portion of a vein graft
Vol. XIII
No. 3
JOURNAL OF VASCULAR NURSING
PAGE 77
Figure 1. Photograph of distal anastomosis by DCU and contrast angiography of common femoral artery to anterior tibial artery vein graft.
Figure 2. Photograph of DCU and contrast angiogram show vein graft stenosis with increased PSV in mid thigh region.
with c o r r e s p o n d i n g angiogram. Aneurysmal dilation can o c c u r within the graft, especially in umbilical vein grafts, A p s e u d o a n e u r y s m can o c c u r at the anastomotic sites. Retained valve leaflets are those that were inadvertently missed with the valvulotome in in situ bypass grafts. Arteriovenous fistulas may result from unligated v e n o u s branches. Atherosclerotic plaque may be visualized within the graft itself, or in the native arteries proximal and distal
to the anastomoses. When thrombosis occurs within the graft, n o color flow is seen. DISCUSSION/INTERPRETATION Various criteria have b e e n r e p o r t e d to interpret PSV obtained with DCU. Bandyk 2 has f o u n d that PSV less than or equal to 45 cm/sec anywhere in the graft may be a preocclusive sign. Polak 3 reports that a PSV at a stenosis, which is
PAGE 78
JOURNAL OF VASCULAR NURSING
double the PSV just proximal to it. usually means that a 50% stenosis is present. Sladen~ uses a velocity ratio (VR) to categorize the degree of stenosis. The VR is the PSV at the stenosis divided by the PSV just proximal to it. A VR of 2 to 3 shows a 40% to 59% stenosis; VR 3 to 6 equals 60% to 79% stenosis; and a VR greater than 6 reveals a 80% to 99% stenosis. The results of DCU combined with ankle/brachial Doppler pressures, the ABIs, and the patient's symptoms will determine the necessity for intervention. The role of the vascular nurse is crucial in this surveillance protocol. Expertise in the performance of the noninvasive vascular studies is an essential component of surveillance. In addition, the nurse's assessment skills are required to document the patient's symptoms and physical findings. Discussing the patients feelings related to their present status, as well as reassuring the patients may help our patients deal with their peripheral arterial occlusive disease. 5 The patient needs to be a part of this follow-up process, so therefore the nurse can help the patient understand the potential symptoms, can encourage the patient in an exercise program, and can strongly urge the patient to stop smoking. If results are abnormal, the nurse should reassure the patient about the intervention options and support the patient in decision,making efforts. CONCLUSION DCU technology can be used in combination with history, physical examination, and ankle/brachial Doppler pressures to detect abnormalities in the lower extremity bypass graft early, before the graft fails. Consequently, tissue damage and limb loss can be averted. The vascular nurse with expertise in the performance of noninvasive vascular studies is in a unique position to assess, teach, and reassure the patient with a patent or at-risk lower extremity bypass graft. This article was reviewed by Donna Blackburn, RN,, RVI;, Technical Director of the Blood Flow Laboratory, Northwestern Memorial Hospital, Chicago, Illinois. REFERENCES
1. Rutherford RB. Prevention and management of graft thrombosis. In: Kempczinski RF, ed. The ischemic leg. Chicago: Yearbook Medical Publishers, 1985:495-508. 2. Bandyk DF. Postoperative surveillance of infrainguinal bypass. Surg Clin North Am 1990;70:71-85. 3. Polak JF, Donaldson MC, Dobkin GR. Early detection of saphenous vein arterial bypass graft stenosis by colorassisted duplex sonography: a prospective study. Am J Radiol 1990; 154:857-61.
SEPTEMBER 1995
4. Sladen JG. Color flow duplex screening of infrainguinal grafts combining low and high velocity criteria. Am J Surg 1989:158:107-12. 5. Crosby FE, Ventura MR, Frainier MA, Wu YB~ Well-being and concerns of patients with peripheral arterial occlusive disease. J VAsc NuRs 1993;11:5-11. SUGGESTED READINGS 1. Bergamini TM, Towne JB, Bandyk DF, Seabrook GR, Schmitt DD. Experience with in situ saphenous vein bypasses during 1981-1989: determinant factors of long term patency. J Vasc Surg 1991;13:137-49. 2. Bourke BM. Duplex scan surveillance of infrainguinal bypass grafts: the case for selectivity. Aust N Z J Surg 1992;62:611-7. 3. Dzieciuch JM. Decision making of patients with arterial occlusive disease who are threatened with limb loss. J VASCNURS1994;12:6-9. 4. Edwards J, Kato R, Bandyk D. Vascular laboratory surveillance of infrainguinal vein bypass: the role of early post operative duplex scanning. J Vasc Technol 1991;15:24i-4. 5. Green RM, McNamara J, Ouriel K, DeWeese JA. Comparison of infrainguinal graft surveillance techniques. J Vasc Surg 1990;11:207-15. 6. Grigg MJ, Nicolaides AN, Wolfe JHN. Detection and grading of femorodistal vein graft stenoses: duplex velocity measurements compared with angiography. J Vasc Surg 1988;8:661-6. 7. Harris JP, Kidd JF, Waugh RC. Color enhanced duplex detection of vein graft stenoses after lower extremity arterial reconstruction. J Vasc Technol 1992; 16:129-32. 8. Hart BP. Vascular consequences of smoking and benefits of smoking cessation. J VASCNURS 1993;11:48-51. 9. Londrey GL, Hodgson KJ, Spadone DP. Initial experience with color flow duplex scanning of infrainguinal bypass grafts. J Vasc Surg 1990;12:284-90. 10. Luscombe J, Moneta GL, Cummings CA, Taylor LM, Porter JM. Postoperative surveillance of infrainguinal reverse vein grafts: an hypothesis for improving examination efficiency. J Vasc Technol 1993;17:291-4. 11. Maune J. Therapeutic walking program: an alternative to a formal vascular rehabilitation program. J VASCNURS 1994; 12:80-4. 12. Towne JB, Schmitt DD, Seabrook GR, Bandyk DF. The effect of vein diameter on patency of in situ graftS. J Cardiovasc Surg 1991;32:192-6.
No. 3
JOURNAL OF VASCULAR NURSING
PAGE 75
Postoperative lower extremity bypass surveillance: Beyond ankle arm b l o o d pressures Marcia S. F o l d e s , BSN, RVT Presented at the Twelfth Annual National Symposium, Society for Vascular Nursing, St. Louis, Mo., May 19-21, 1994. Surveillance is essential to the postoperative follow-up of lower extremity bypass grafts. Early, intermediate, and late thrombosis place the patient's limb at risk, so detection of problems before the graft fails is critical Because contrast angiography is not routinely performedfor surveillance, most vascular surgeons rely on history, physical examination, and noninvasive vascular studies (NVS) to assess perfusion to the lower extremity after bypass grafting. These NVS include ankle/brachial waveforms, blood pressures, and indexes before and after exercise. The purpose of this study is to report our findings with duplex color-flow ultrasonography (DCU) to examine lower extremity bypass grafts. According to our protocol, we monitor lower extremity grafts with ankle/brachial Doppler pressures, analogue waveforms, and lower extremity exercise when possible. These NVS areperformed by nurses in the vascular laboratory before the patient is discharged from the hospital, at least twice during the first year, and then annually. DCU is also performed at least two times during the first year and then annually. If the study results are abnormal or if the patient has symptoms, testing is usually repeated. When abnormalities persist contrast angiograpby may be warranted. We have detected anatomic and hemodynamic changes in lower extremity bypasses by use of our protocol By adding DCU to ankle/brachial bloodpressures, we have identified aneurysmal dilation, diffuse atherosclerosis, focal narrowing, arteriovenous fistulas caused by unligated venous branches, retained venous valves, and disease progression proximal or distal to the graft. For years nurses in the vascular laboratory have been able to assess the hemodynamics of lower extremity bypass grafts by use of history, physical examination, ankle and arm blood pressures, a n d waveforms. Now with DCU the vascular laboratory progresses beyond these methods to detect abnormalities in graft anatomy early, before the graft fails. Consequently tissue damage and limb loss of patients can potentially be minimized. (J Vasc SVRG1995;13: 75-8.)
The goal o f lower extremity arterial reconstruction is adequate tissue perfusion. This is accomplished by a patent bypass graft. Failure or occlusion o f the graft can lead to tissue loss. Vascular surgeons prefer to correct problems before the graft fails. 1 Therefore the follow-up of these patients to discern grafts at risk is crucial for long-term
Marcia Foldes is a Vascular Nurse Technologist at the Blood Flow Laboratory of St. John's Mercy Medical Center in St. Louis, Mo. Address reprint requests to Marcia Foides, BSN, RVZ, Blood Flow Laborator~ St. John's Mercy Medical Center, 615 S. New BaUas Raft., St. Louis, MO 63141. Copkmtgbt © 1995 by the Society for Vascular Nursing, Inc. 1062-0303/95/85.00 + 0 40/1/662"/0
patency. Methods of graft surveillance are the subject of this study; but first, general information about lower extremity bypasses will be reviewed. TYPES AND CHOICES OF GRAFT MATERIAL The surgeon's first choice for graft material is autologous vein. The greater saphenous, lesser saphenous, basilic, cephalic, or any o t h e r vein o f adequate diameter and length may be used. Polytetrafluoroethylene is a synthetic material used primarily for above-knee bypasses at this hospital. Preserved umbilical vein has b e e n used as a conduit. Sometimes synthetic materials are c o m b i n e d with autologous vein to form a composite bypass w h e n a sufficient length o f vein is not available for a distal bypass. The synthetic material is used in the proximal p o r t i o n o f the graft; it is sewn to the v e n o u s portion and t h e n anastomosed to the native artery at the distal e n d of the bypass. T h e r e are various techniques used in p e r f o r m i n g lower extremity bypass grafting. An in situ bypass is o n e in which the vein remains in place but is dissected free at the proximal and distal anastomosis sites. Branches are ligated, and the valves are r e n d e r e d i n c o m p e t e n t by use o f a valvulotome. Reversed vein grafts are those in which the vein is harvested, r e m o v e d from the leg, reversed, and t u n n e l e d back into the leg at the site of the bypass. The venous valves remain intact because, after reversing the vein, the valves will allow the flow o f b l o o d from proximal to distal in the bypass. Venous branches are ligated with this type of vein graft as well. Translocated vein grafts are those in which any vein is harvested, branches ligated, and t h e n t u n n e l e d into the leg as a bypass conduit. Examples o f these veins include the greater s a p h e n o u s or lesser saphenous vein (ipsilateral or contralateral) or the basilic or cephalic vein from either arm. CAUSES OF GRAFT FAILURE The three basic causes o f graft failure include thrombosis, h e m o d y n a m i c failure, and structural failure.1 The causes for graft failure vary d e p e n d i n g o n length o f time after the bypass was p e r f o r m e d . In the early postoperative period, graft failure is most often caused by technical errors during the o p e r a t i o n (retained venous valves, kinks in the conduit), decreased outflow (significant atherosclerotic disease in the vessels d o w n s t r e a m from the distal anastomosis), infection, or the patient's hypercoagulable state. From 1 m o n t h to 2 years after operation, graft failure usually occurs because o f occlusive lesions (neointimal fibroplasia) within the graft itself, in the inflow, or outflow vessels. If the graft fails after 2 years, it is most likely caused by atherosclerotic disease progression, either within the graft or in the native vessels proximally o r distally. 1
PAGE 76
JOURNAL OF VASCULAR NURSING
A B N O R M A L I T I E S F O U N D BY D C U
Stenosis Aneurysmal dilation Pseudoaneurysm Retained valve leaflets Arteriovenous fistula Plaque Thrombosis
METHODS OF SURVEILLANCE An accurate history and physical examination begin the postoperative assessment of lower extremity grafts. The date of surgery and exact location of the d o n o r vessel at the proximal anastomosis and the runoff vessel at the distal anastomosis should be d o c u m e n t e d . Recurrent symptoms such as claudication o r rest pain, limb pallor, numbness or tingling, d e v e l o p m e n t o f n e w ulcers, or improvement of preoperative lesions should be noted. Cessation of smoking should be strongly encouraged, with the packs smoked per day recorded. I m p r o v e m e n t in walking tolerance and distance is also noteworthy. The graft should be palpated at the proximal anastomosis, as well as at various locations t h r o u g h o u t its length. Contrast angiography is not routinely p e r f o r m e d for surveillance but may be p e r f o r m e d to confirm the results of noninvasive vascular studies w h e n an abnormality is d e t e c t e d and d e t e r m i n e the type of subseq u e n t intervention required. Noninvasive vascular studies are the mainstay of most lower extremity bypass graft surveillance protocols. At this institution, analogue waveforms are obtained from the foot arteries: dorsalis pedis, posterior tibial, and peroneal. Bilateral Doppler blood pressures are also obtained at these arteries, as well as bilateral brachial artery blood pressures. These are obtained with the patient at rest and after the patient exercises, if possible. Exercise is p e r f o r m e d by having the patient walk o n the treadmill (at a constant speed and elevation) or by stationary toe raises. The highest D o p p l e r pressure at the ankle is divided by the highest D o p p l e r pressure obtained in the brachial artery to obtain the ankle/brachial index (ABI). A normal ABI is 0.9 to 1.0 or more; an abnormal ABI is less than 0.9. Duplex color ultrasonography (DCU) or color-flow Doppler imaging (CDI) has b e e n a d d e d to surveillance protocols to assess the anatomy and flow in the bypass graft. The p u r p o s e of DCU is to assess graft patency by determining the p r e s e n c e of blood flow in the graft. CDI expedites the process of graft assessment and can alert the examiner to areas of color flow disturbance or abnormality by changes in the color displayed. Spectral analysis is then used to obtain a peak systolic velocity (PSV) in p r e d e t e r m i n e d areas o f the graft, as well as in areas of disturbed color flow. These p r e d e t e r m i n e d areas include the proximal and distal
SEPTEMBER 1995
PATIENT PREPARATION FOR L)~U
Procedure explained Head of bed elevated slightly Patient in supine position with knee flexed and hip externally rotated
anastomoses, the proximal, mid, and distal portion of the thigh, the b e n d o f the knee, and the proximal, mid, and distal portion of the lower leg. When DCU is p e r f o r m e d early in the postoperative period, it can provide the baseline evaluation for subsequent studies. If abnormalities are detected such as those listed in Table I, grafts at risk of failure can be identified. The mechanism of graft failure can also be d e t e r m i n e d with DCU after the onset of ischemic symptoms. SURVEILLANCE PROTOCOL AT ST, J O H N ' S MERCY MEDICAL CENTER The surveillance protocol for lower extremity bypass grafts begins while the patient is still in the hospital. Nurses from the vascular laboratory obtain ankle/brachial Doppler pressures and analogue waveforms at the patient's bedside within the first 3 postoperative days. During the first postoperative year, this is d o n e two times, including exercise testing if the patient is able to tolerate walking on the treadmill. Yearly testing is t h e n performed. DCU is p e r f o r m e d twice in the first year, t h e n once a year if no symptoms or physical findings occur. Often, the ankle/brachial blood pressures, exercise, and DCU are p e r f o r m e d during the same outpatient visit. If the ABI decreases by 15% from the previous examination result and is confirmed by repeat testing, then DCU may be performed. Each noninvasive study is compared with the previous examination results to detect n e w disease or progression of previous abnormalities. Patient preparation for DCU is minimal. The salient points are s h o w n in Table II. Images of the graft are obtained along its entire length in transverse view with CDI to locate proximal and distal anastomosis and also any retained venous branches. Then, from proximal to distal, imaging is p e r f o r m e d in longitudinal view; PSV is obtained from the inflow vessel, at p r e d e t e r m i n e d areas m e n t i o n e d above, and in the outflow artery. If possible, PSV is also obtained in the native artery proximal to t h e distal anastomosis. PSV is o b t a i n e d at any areas of color flow disturbance and just proximal to this disturbed flow. Figure 1 is an example of a normal distal anastomosis in a c o m m o n femoral a r t e r y - t o - a n t e r i o r tibial artery vein graft as shown by DCU and contrast angiography. Abnormalities d e t e c t e d by DCU are outlined in Table I. Stenosis may b e f o u n d at any site in the graft o r native artery at the anastomatic site. Figure 2 shows an isolated stenosis with increased PSV in the mid thigh portion of a vein graft
Vol. XIII
No. 3
JOURNAL OF VASCULAR NURSING
PAGE 77
Figure 1. Photograph of distal anastomosis by DCU and contrast angiography of common femoral artery to anterior tibial artery vein graft.
Figure 2. Photograph of DCU and contrast angiogram show vein graft stenosis with increased PSV in mid thigh region.
with c o r r e s p o n d i n g angiogram. Aneurysmal dilation can o c c u r within the graft, especially in umbilical vein grafts, A p s e u d o a n e u r y s m can o c c u r at the anastomotic sites. Retained valve leaflets are those that were inadvertently missed with the valvulotome in in situ bypass grafts. Arteriovenous fistulas may result from unligated v e n o u s branches. Atherosclerotic plaque may be visualized within the graft itself, or in the native arteries proximal and distal
to the anastomoses. When thrombosis occurs within the graft, n o color flow is seen. DISCUSSION/INTERPRETATION Various criteria have b e e n r e p o r t e d to interpret PSV obtained with DCU. Bandyk 2 has f o u n d that PSV less than or equal to 45 cm/sec anywhere in the graft may be a preocclusive sign. Polak 3 reports that a PSV at a stenosis, which is
PAGE 78
JOURNAL OF VASCULAR NURSING
double the PSV just proximal to it. usually means that a 50% stenosis is present. Sladen~ uses a velocity ratio (VR) to categorize the degree of stenosis. The VR is the PSV at the stenosis divided by the PSV just proximal to it. A VR of 2 to 3 shows a 40% to 59% stenosis; VR 3 to 6 equals 60% to 79% stenosis; and a VR greater than 6 reveals a 80% to 99% stenosis. The results of DCU combined with ankle/brachial Doppler pressures, the ABIs, and the patient's symptoms will determine the necessity for intervention. The role of the vascular nurse is crucial in this surveillance protocol. Expertise in the performance of the noninvasive vascular studies is an essential component of surveillance. In addition, the nurse's assessment skills are required to document the patient's symptoms and physical findings. Discussing the patients feelings related to their present status, as well as reassuring the patients may help our patients deal with their peripheral arterial occlusive disease. 5 The patient needs to be a part of this follow-up process, so therefore the nurse can help the patient understand the potential symptoms, can encourage the patient in an exercise program, and can strongly urge the patient to stop smoking. If results are abnormal, the nurse should reassure the patient about the intervention options and support the patient in decision,making efforts. CONCLUSION DCU technology can be used in combination with history, physical examination, and ankle/brachial Doppler pressures to detect abnormalities in the lower extremity bypass graft early, before the graft fails. Consequently, tissue damage and limb loss can be averted. The vascular nurse with expertise in the performance of noninvasive vascular studies is in a unique position to assess, teach, and reassure the patient with a patent or at-risk lower extremity bypass graft. This article was reviewed by Donna Blackburn, RN,, RVI;, Technical Director of the Blood Flow Laboratory, Northwestern Memorial Hospital, Chicago, Illinois. REFERENCES
1. Rutherford RB. Prevention and management of graft thrombosis. In: Kempczinski RF, ed. The ischemic leg. Chicago: Yearbook Medical Publishers, 1985:495-508. 2. Bandyk DF. Postoperative surveillance of infrainguinal bypass. Surg Clin North Am 1990;70:71-85. 3. Polak JF, Donaldson MC, Dobkin GR. Early detection of saphenous vein arterial bypass graft stenosis by colorassisted duplex sonography: a prospective study. Am J Radiol 1990; 154:857-61.
SEPTEMBER 1995
4. Sladen JG. Color flow duplex screening of infrainguinal grafts combining low and high velocity criteria. Am J Surg 1989:158:107-12. 5. Crosby FE, Ventura MR, Frainier MA, Wu YB~ Well-being and concerns of patients with peripheral arterial occlusive disease. J VAsc NuRs 1993;11:5-11. SUGGESTED READINGS 1. Bergamini TM, Towne JB, Bandyk DF, Seabrook GR, Schmitt DD. Experience with in situ saphenous vein bypasses during 1981-1989: determinant factors of long term patency. J Vasc Surg 1991;13:137-49. 2. Bourke BM. Duplex scan surveillance of infrainguinal bypass grafts: the case for selectivity. Aust N Z J Surg 1992;62:611-7. 3. Dzieciuch JM. Decision making of patients with arterial occlusive disease who are threatened with limb loss. J VASCNURS1994;12:6-9. 4. Edwards J, Kato R, Bandyk D. Vascular laboratory surveillance of infrainguinal vein bypass: the role of early post operative duplex scanning. J Vasc Technol 1991;15:24i-4. 5. Green RM, McNamara J, Ouriel K, DeWeese JA. Comparison of infrainguinal graft surveillance techniques. J Vasc Surg 1990;11:207-15. 6. Grigg MJ, Nicolaides AN, Wolfe JHN. Detection and grading of femorodistal vein graft stenoses: duplex velocity measurements compared with angiography. J Vasc Surg 1988;8:661-6. 7. Harris JP, Kidd JF, Waugh RC. Color enhanced duplex detection of vein graft stenoses after lower extremity arterial reconstruction. J Vasc Technol 1992; 16:129-32. 8. Hart BP. Vascular consequences of smoking and benefits of smoking cessation. J VASCNURS 1993;11:48-51. 9. Londrey GL, Hodgson KJ, Spadone DP. Initial experience with color flow duplex scanning of infrainguinal bypass grafts. J Vasc Surg 1990;12:284-90. 10. Luscombe J, Moneta GL, Cummings CA, Taylor LM, Porter JM. Postoperative surveillance of infrainguinal reverse vein grafts: an hypothesis for improving examination efficiency. J Vasc Technol 1993;17:291-4. 11. Maune J. Therapeutic walking program: an alternative to a formal vascular rehabilitation program. J VASCNURS 1994; 12:80-4. 12. Towne JB, Schmitt DD, Seabrook GR, Bandyk DF. The effect of vein diameter on patency of in situ graftS. J Cardiovasc Surg 1991;32:192-6.