This study examined the effects of diameter discrepancy between interpositional vein grafts within a range of 0.25to 2 mm. One hundred rats underwent isolation of a 10 mm segment of the femoral artery, from which a 4 mm segment was removed. Venous grafts measuring 8 2 mm were interposed. The rats were categorized by their graft to artery diameter ratios. Patency was assessed upon completion and 4-6 days postoperatively. All surgical specimens were submitted to the pathology department for microscopic evaluation. Results showed Group I: graft to artery ratio 1:1, patency rate 90% (18/20); Group II: ratio 0.751,patency rate 80% (16/20); Group Ill: ratio 0.51, patency rate 60% (12/20), Group IV: ratio 0.253,patency rate 20% (4/20); Group V: ratio 2:1,patency rate 60% (12/20). It is concluded that 1:l venous graft to artery ratios are optimal. When this is impossible, diameter discrepancies should be at least 0.75:l for acceptable patency rates to be attained in microvascular grafting.
MICROVASCULAR GRAFTS: EFFECT OF DIAMETER DISCREPANCY ON PATENCY RATES JOSE J. MONSIVAIS. M.D.
Microvascular anastomosis is the mainstay of revascularization, reimplantation, and free tissue transfers. Although great progress has been made over the past 25 years in discovering factors that affect the patency of microscopically anastomosed vessels, much is in need of elucidation. Literature available on experimental anastomosis frequently mentions such factors as suture materials, needle size and contour, and the expertise and technique of the surgeon in determining successful outcome. However, little discussion of vessel diameter discrepancy in vein grafting as a factor possibly influencing patency is available. One of the few articles addressing the topic is by Seidenberg et aL5 from 1958. They state that smooth approximation of vessels is important in preventing thrombosis and that incidence of failure increases with increased discrepancy in vessel size. In 1972, Baxter et al.’ showed the most important requirement for successful anastomosis to be correct apposition of cut vessel edges. Hay-
From the Microsurgical Unit, Vista Hills Medical Center; Texas Tech. School of Medicine; and William Beaumont Army Medical Center, El Paso, TX. Acknowledgments: The author thanks the following individuals; their expertise and assistance made this study possible: Thomas J. Scully, Col. M.C., Department of Orthopedics. William Beaumont Army Medical Center, and Leo L. Hise, Cpt. M.C., Department of Orthopedics, William Beaumont Army Medical Center. This study was performed at The Biological Research Service, William Beaumont Army Medical Center, El Paso, TX. Address reprint requests to Dr. Jose J. Monsivais, 10201 Gateway West, Room 220, El Paso, TX 79925. Received for publication January 28, 1987; revision accepted November 30, 1989.
0 1990 Wiley-Liss. Inc.
hurst and O’Brien* supported this finding with a 1975 study showing that vein repairs done with special attention to the apposition of vein edges yielded higher patency rates than those done with a standard method. O’Brien et al.9 in 1974 discussed flap loss when diameter discrepancy existed at the junction of the lower end of a vein graft and flap artery. Literature surveys covering the mid- 1970s to the present yielded no further studies delineating the effects of vessel diameter discrepancy in microvascular anastomosis. The purpose of this study was to examine the effects of such diameter discrepancies between interpositional vein grafts within a 0.25-2 mm range. MATERIALS AND METHODS
One hundred Sprague-Dawley rats of approximately 300 g were divided into five groups of 20. The National Research Council guide for the care of laboratory animals was followed. The rats were anesthetized with intraperitoneal sodium pentobarbital and placed in the supine position. An incision was made from the inguinal region to the knee, and the femoral artery was exposed. The artery was measured, and a 10 mm segment was freed from adventitial tissue. A vein graft measuring 8 mm -1-2 mm in length was dissected from the ipsilateral side of each animal. The grafts were obtained from five different areas. The proximal femoral vein was used for Group I (1 :1 ratio), the distal femoral vein for Group I1 (0.75:l ratio), the superficial epigastric vein for Group I11 (0.5:l ratio), the saphenous vein for Group IV (0.25:1), and the external iliac vein for Group V (2:l). The vein graft was measured after dissection using
Figure 1. Patency rates.
Table 1. Patency Rate Among 100 Test Rats.
(1:l) 18/20 (90%)
(0.751) 16/20 (80%)
Group V (2:l)
the scale included in the 10-0 nylon suture material by Ethicon. The graft was then harvested. A 4 mm segment of the femoral artery was removed from each rat, and the venous grafts were interposed. Grafts were sutured in place using 10-0 nylon on a 75 pm needle. Patency was assessed after grafting by observing for antegrade flow distal to the anastomosis for a 20-minute period. All grafts were patent at the time of wound closure. The incision was closed with 5-0 Dexon in interrupted stitches, and the animals were observed for 4-6 days. At the end of this period, the animals were reexplored, and the microsurgical anastomosis was assessed for patency by occluding the femoral artery distal to the anastomosis with the vascular clamp. The artery was transected proximally to the clamp and observed for antegrade blood flow. At this time the grafts were removed, allowing a segment of normal artery to remain on both ends. The specimens were then submitted to the pathology department for microscopic evaluation. RESULTS
The data are presented in Table 1. In Group I, a venous graft to artery ratio of 1:l was created. Eighteen of 20 rats (90%) were patent at the end of the study period. In Group 11, a venous graft to artery ratio of 0.75: 1 was created. At the end of the study period, 16 of 20 grafts (80%) were patent. In Group III, a venous graft to artery ratio of 0 3 1 was made. Twelve of 20 grafts (60%)were patent at the end of the study period. In Group IV, a venous graft to artery ratio of 0.25: 1 was
made. Four of 20 grafts (20%) were patent at the end of the study period. In Group V, a venous graft to artery ratio of 2:l was made. Twelve of the 20 grafts (60%) remained patent at the end of the study period. Microscopic evaluation showed granulomas at the suture sites. A 2 X 2 contingency table was utilized in assessing further statistical differences for comparing the patency rates among groups, creating a sampling population of 40 trials per comparison. Based on highest success rate, Group I was used as a standard to which all other groups were compared. There was no significant difference in success rates when comparison was made between Groups I and 11. However, the values for statistical comparisons between Group I and Groups 111, IV, and V provided sufficient evidence to accept the hypothesis that statistically lower success rates were obtained in Groups 111-V. DISCUSSION
Safe limits for vessel diameter discrepancy in end-toend microsurgical anastomosis have not been clearly delineated. With this experiment, we hope to establish some guidelines so that a microsurgeon confronted with vessel diameter discrepancy while performing a vascular reconstruction using a reverse venous graft will have some information about how discrepancy ratios relate to patency rates, Our results indicate that graft to artery ratios of 0.751 and 1:l yielded the highest patency rates. Figure 1 illustrates a comparison of patency and occluded rates. An important element of thrombus formation in small vessels may be turbulence of blood flow as blood passes through different size vessel lumens. CONCLUSIONS
Since patency rates were highest with a 1: 1 venous graft to artery ratio, prudence would dictate a match as close to
1:l as possible when interposing vein grafts. When a 1:l match is not possible, discrepancies in diameter should fall within a range of 0.75:l to 1:l. Alternatives would include end-to-side anastomosis (alternative graft selection) or dilatation (spatulation, etc.) to result in a tapered, presumably less turbulent interface. The potential improvement in vessel graft diameter discrepancy in microsurgery with pharmacologic agents remains to be explored.
5. 6. 7. 8.
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