- Email: [email protected]
Microvascular anastomosis of arteries under tension
British Journal of Plastic Surgery (1982) 35, 82-81 0 1982 The Trustees of British Association of Plastic Surgeons
Microvascular
0007-I 226/X2/02744082
$02.00
anastomosis of arteries under tension
S. P. CHOW, C. D. HUANG and C. W. CHAN Departments Orthopaedics,
of Orthopaedics and Pathology, University of Hong Kong and Zhong Shan Medical College, Guangzhou, Peoples* Republic of China
the
Department
of
resected, the tension after approximating the cut ends together was so great that the two cut ends tended to slip out of the jaws of the Ikuta clamps. The clamps were therefore applied in the angle between the f&moral artery and the two branches (Fig. 3). Microvascular anastomosis was
One of the basic principles of microvascular surgery is that there should be no undue tension at the anastomosis site (O’Brien et al., 1979). Clinically, however, it may be difficult to decide what is “undue tension” or even “normal tension”. On restoration of blood flow, vein grafts which have been used to bridge a gap are often found to be too long and tortuous (Alpert et al., 1978). Other measures to overcome excessive tension such as bone shortening (Kleinert et al., 1977), fusion of the neighbouring joints, or rerouting of vessels (Pho et al., 1979) may lead to impairment of function. To determine how much tension an anastomosis can tolerate before its patency is affected, we have performed microvascular anastomosis of the rat femoral artery after resecting varying lengths of the vessel. The associated tissue changes were studied by scanning electron microscopy and histological sections.
Fig. 1 A segment of femoral artery (9mm long) between the superficial circumflex iliac (arrow on right) and the superficial epigastric branch (arrow on left). Each square on the grid measures 1 mm.
Materials and method
Healthy Sprague-Dawley rats, of approximately 400gm body weight were anaesthetised with intraperitoneal pentobarbitone (30 mg/kg body weight) and the femoral artery was exposed. A segment of the vessel between the superficial circumflex iliac and the superficial epigastric branch was freed and its distance measured (Fig. 1). An Ikuta arterial approximator with a clamping pressure of about 250gm/mm2 was applied at the site of the two branches. A segment of the femoral artery (40 %, 60x, or 80 % of the distance between the two branches, i.e. between the clamps) was resected according to a semirandomised plan (Fig. 2). The length of the resected segment at zero tension was measured at once so that its percentage contractility could be calculated. The blood vessels on each side of the resected segment were gently irrigated with 1 y0 heparinised saline before approximation. In those cases where 80% of the artery had been
Fig. 2 resected
82
60 % (5.4mm) segment shrank
of the vessel to 3.6mm.
was
resected
and
the
MICROVASCULAR
ANASTOMOSIS
OF ARTERIES
UNDER
then performed with 11-O suture (18 p suture, 50~ needle) using 8 to 10 sutures (Fig. 4). After completion of the anastomosis the clamps were removed (Fig. 5) and any bleeding noted and stopped by light pressure. The patency of the vessel was then checked by the double forcep patency test. Patency only in the antigrade direction, but not in the retrograde direction was labelled as “sluggish flow”. The femoral vessel on the opposite leg was also treated in the same way. In some of the vessels their external diameter was measured before and after the anastomosis. All the rats were re-operated upon one week later to re-check the patency rate of the anastomoses. The anastomosed segment was then removed for study with the scanning electron microscope and for histological examination.
83
TENSION
After 807: resection, the clamps were applied in the Fig. 3 angle between the femoral artery and its branches and brought together under great tension.
Results Thirty-six femoral arteries in eighteen rats were anastomosed according to the above protocol. In five of these vessels, there were found dehiscence or infection and they were excluded from analysis: five other anastomoses were carried out to provide a total of 36 anastomosed vessels for analysis. The vessels were divided into three groups of twelve each according to whether 407/,, 60:/, or 80% of the segment between the superficial circumflex iliac and the superficial epigastric branches had been resected. The distance between these two branches ranged from 8 mm to 13 mm with an average of 10.9mm. The average length of vessel removed was 4.28mm for the 407; group, 6.18mm for the 607: group and 8.60mm for the 80 % group. The number of sutures used for the anastomoses averaged 9.36 for the 407” group, 9.73 for the 600/d group, and 10.33 for the 80% group. The patency rate immediately after anastomosis was compared (Table 1). The group of vessels following an 80% resection showed a markedly reduced patency rate and even in those vessels that were patent, three showed a sluggish flow. The patency rate was checked one week later (Table 2). The amount of leakage immediately after the anastomosis was noted. Significant bleeding from the anastomotic junction occurred in two vessels but was controlled by light pressure. Leakage from the suture holes (the result of excessive
Fig. 4 Eight sutures were used for this anastomosis. Note that excessive tension in approximating the clamps has caused the two branches to stretch in an oblique fashion.
Fig. 5
Good
patency
after completion
of the anastomosis.
BRITISHJOURNALOF PLASTICSURGERY
84 Patency rates immediately after anastomosis
Table 1
Table 5
Average % shrinkage of the resected segment % Shrinkage
Patency Rate 100 % (12/12) with 1 sluggish flow 92 % (1 l/12) all with free flow 75 % (9/12) 3 with sluggish flow
40 % group 60 % group 80% group
Table
40 % group 60 % group 80 % group Overall
32.8 % 31.6% 34.4 % 32.9 %
2 Patency rate at one week after anastomosis Patency Rate
40% group 60 % group 80 % group
92 % (1l/12) all with free flow 75 % (9/12) all with free flow 67 % (8/12) 1 with sluggish flow
There were no differences between the different groups and it can be seen that a 1Omm segment of the rat femoral artery at zero tension should lengthen to about 10 x grnrn is
tension due to the suture cutting into the vessel wall) was frequently seen (Table 3). In the 60% and 80% resection group, the leakage frequently took the form of pulsatile squirts from multiple holes. However, all were stopped by light pressure except in three cases where bleeding was stopped by an additional suture. As a result of tension after anastomosis, the vessels became stretched and their diameters were reduced. Ten vessels had their external diameters measured before and after anastomosis and the average percentage narrowing was estimated (Table 4). To gain some idea of the elasticity of the femoral vessels, the resected segment of vessel was measured before and after removal (when it is at zero tension). The percentage shrinkage in length was then calculated (Table 5).
i.e. 14.9 mm if it
to be stitched under “normal tension”.
Scanning electron microscopy and light microscopy studies The most obvious lesions in the vessels were transverse cracks in the lumenal surface (Fig. 6). The severity varied with individual vessels, but as one might expect were generally less severe in the 40% group. These cracks represented disruption of the endothelial lining, often with rupture of the elastic lamina and sometimes even the muscle layer (Fig. 7). In most cases, thrombi were seen over these areas and, as expected, the greater the tension the greater the tendency to thrombosis. Despite these changes, endothelial cells were found over defective areas and even over exposed suture material (Fig. 8).
Discussion Table 3
Leakage
from suture holes Leakage
40 % group
60 % group 80 % group
Table 4
33% 100% 100%
seen
(4112)
Average narrowing of vessel after anastomosis y(, Narrowing
40 % group
60 % group 80 % group
16% 26% 52%
Although it is generally accepted that a microvascular anastomosis should not be done under excessive tension, our results show that a patency rate of 92% at one week post-operatively can be obtained when 40% (average 4.28 mm) of a mobilised segment of the rat femoral artery is resected and the two ends subsequently anastomosed. This patency rate is similar to that achieved following simple transection and reanastomosis of the same vessel by two of us (S.P.C. and C.D.H.) who had achieved an average patency rate of 95 y0 in several hundred anastomoses of this vessel. What is more surprising is that even with resection of 80% (average 8.60mm) of the mobilised segment, a patency rate as high as 67 y0 could be obtained.
MICROVASCULAR
ANASTOMOSIS
OF ARTERIES
UNDER
85
TENSION
Fig. 6 Scanning electron micrograph of a vessel re-anastomosed after 60% reduction of length. Note the transverse cracks, cqxially the one to the right not related to the suture. To the left of Ihe suture there is an ohviouh tear of the wall covered by a fibrin platelet clol.
c
Fig. 7 Longitudinal section of an artery anastomosed after a 40% resection. Several areas of elastic can be seen. The arrow indicates gross disruption at the site of a suture. Elastic stain x 48.
and muscle disruption
BRITISH
Fig. 8 suture.
S.E.M.
of a vessel re-anastomosed
after 60”” reduction
It may be argued that the vessels on both sides of the mobilised segment may move closer together after the anastomosis is completed and the clamps removed thus relieving the tension to a certain extent, and that the percentage resection (40 %, 60X, 80%) does not reflect the true gradation of tension proportionately. However, the very great tension produced by the 80% resection is shown by the fact that even with the high clamping pressure (250gm/mm’) of the Ikuta clamps, the approximated vessel ends frequently slipped out of the jaws which, consequently, had to be resited in the angle between the vessel branches. The excessive tension in the 60% and 80 % resection groups was also demonstrated by the squirting of blood from the suture holes. The change in diameter of the vessels before and after anastomosis was also remarkable in the 80% group where vessels on the average was stretched and the diameter reduced by nearly half (48 %).
showing
JOURNAL
one of the cracks
OF PLASTIC
endothelialised,
SURGERY
probably
over a
It is therefore clear that in this experimental model the margin of safety for tension in microvascular anastomoses is not as narrow as commonly believed. The critical point at which the patency rate falls below 90% is probably between 40% to 60% of resection (actual defect between 4.28mm to 6.18mm). The direct projection of the results of this experiment to clinical work in man is unrealistic. The vessels in human beings are different from those in the rat and a vessel which has been ischaemic for several hours (such as those encountered in replantation surgery) may withstand tension less favourably. It is probably still good practice to use vein grafts in cases of doubt. Nonetheless it may be comforting to remember that there is still some margin of safety. Certainly, performing one anastomosis rather than two saves time and has its own advantages over a vein graft, vessel transfer or bone shortening. Perhaps it may even be better to
MTCROVASCXJLAR
ANASTOMOSIS
OF ARTERIES
UNDER
design an approximator with a clamping pressure that will allow the two vessel ends to slip out if the tension is more than acceptable. In this rat model, this tension is reached when about 507, of the mobilised segment (actual length about 5.13 mm) was lost.
Acknowledgement The authors would like to express their gratitude to the staff of the research laboratory, Department of Orthopaedics, Umversity of Hong Kong for technical assistance in this study.
TENSION
87
Kleinert, H. E., Jubala, C. A. and Tsai, T. M. (1977). Digital replantation-selection, technique and results. Orthopaedic Clinics qf’ North America, 8, 309. Philadelphia: W. B. Saunders Company. Pho, R. W. H., Chacha, P. B. and Yeo, K. Q. (1979). Rerouting vessels and nerves from other digits in replanting an avulsed and degloved thumb. Plastic und Rwomtructive SurKerx. 64, 330. Havhurst. J. W. and O’Brien. B. McC. ( 1975). An exnerimen&I study of microvascular technique. patency rate, and related factors. British Journrtl of Plastic Sur,qerF. 28, 128.
The Authors S.
References O’Brien, B. McC., Haw, C., Kubo, T., Gilbert, A. and Hayhurst, J. W. (1979) Microvenous grafting of small vein defects. British Journal qf Plastic Surgery, 32, 164. Alpert, B. S., Buncke, H. J. and Brownstein, M. (1978). Replacement of damaged arteries and veins with vein grafts when replanting crushed, amputated fingers. Plastic and Reconstructive Surgery, 61, I I.
P. Chow, FRCSE, Senior Lecturer. Department of Orthopaedic Surgery, University of Hong Kong, Hong Kong. C. D. Huang, MD. Professor (Orthopaedic). Department of Zhong Shan Medical College, Guangzhou Surgery. (Canton). People’s Republic of China. C. W. Chan, MRC Path., Senior Lecturer, Department of Pathology, University of Hong Kong, Hong Kong. Requests for reprints to: Dr S. P. Chow, FRCSE. Senior Lecturer, Department of Orthopaedic Surgery. University of Hong Kong, Hong Kong.
Microvascular
0007-I 226/X2/02744082
$02.00
anastomosis of arteries under tension
S. P. CHOW, C. D. HUANG and C. W. CHAN Departments Orthopaedics,
of Orthopaedics and Pathology, University of Hong Kong and Zhong Shan Medical College, Guangzhou, Peoples* Republic of China
the
Department
of
resected, the tension after approximating the cut ends together was so great that the two cut ends tended to slip out of the jaws of the Ikuta clamps. The clamps were therefore applied in the angle between the f&moral artery and the two branches (Fig. 3). Microvascular anastomosis was
One of the basic principles of microvascular surgery is that there should be no undue tension at the anastomosis site (O’Brien et al., 1979). Clinically, however, it may be difficult to decide what is “undue tension” or even “normal tension”. On restoration of blood flow, vein grafts which have been used to bridge a gap are often found to be too long and tortuous (Alpert et al., 1978). Other measures to overcome excessive tension such as bone shortening (Kleinert et al., 1977), fusion of the neighbouring joints, or rerouting of vessels (Pho et al., 1979) may lead to impairment of function. To determine how much tension an anastomosis can tolerate before its patency is affected, we have performed microvascular anastomosis of the rat femoral artery after resecting varying lengths of the vessel. The associated tissue changes were studied by scanning electron microscopy and histological sections.
Fig. 1 A segment of femoral artery (9mm long) between the superficial circumflex iliac (arrow on right) and the superficial epigastric branch (arrow on left). Each square on the grid measures 1 mm.
Materials and method
Healthy Sprague-Dawley rats, of approximately 400gm body weight were anaesthetised with intraperitoneal pentobarbitone (30 mg/kg body weight) and the femoral artery was exposed. A segment of the vessel between the superficial circumflex iliac and the superficial epigastric branch was freed and its distance measured (Fig. 1). An Ikuta arterial approximator with a clamping pressure of about 250gm/mm2 was applied at the site of the two branches. A segment of the femoral artery (40 %, 60x, or 80 % of the distance between the two branches, i.e. between the clamps) was resected according to a semirandomised plan (Fig. 2). The length of the resected segment at zero tension was measured at once so that its percentage contractility could be calculated. The blood vessels on each side of the resected segment were gently irrigated with 1 y0 heparinised saline before approximation. In those cases where 80% of the artery had been
Fig. 2 resected
82
60 % (5.4mm) segment shrank
of the vessel to 3.6mm.
was
resected
and
the
MICROVASCULAR
ANASTOMOSIS
OF ARTERIES
UNDER
then performed with 11-O suture (18 p suture, 50~ needle) using 8 to 10 sutures (Fig. 4). After completion of the anastomosis the clamps were removed (Fig. 5) and any bleeding noted and stopped by light pressure. The patency of the vessel was then checked by the double forcep patency test. Patency only in the antigrade direction, but not in the retrograde direction was labelled as “sluggish flow”. The femoral vessel on the opposite leg was also treated in the same way. In some of the vessels their external diameter was measured before and after the anastomosis. All the rats were re-operated upon one week later to re-check the patency rate of the anastomoses. The anastomosed segment was then removed for study with the scanning electron microscope and for histological examination.
83
TENSION
After 807: resection, the clamps were applied in the Fig. 3 angle between the femoral artery and its branches and brought together under great tension.
Results Thirty-six femoral arteries in eighteen rats were anastomosed according to the above protocol. In five of these vessels, there were found dehiscence or infection and they were excluded from analysis: five other anastomoses were carried out to provide a total of 36 anastomosed vessels for analysis. The vessels were divided into three groups of twelve each according to whether 407/,, 60:/, or 80% of the segment between the superficial circumflex iliac and the superficial epigastric branches had been resected. The distance between these two branches ranged from 8 mm to 13 mm with an average of 10.9mm. The average length of vessel removed was 4.28mm for the 407; group, 6.18mm for the 607: group and 8.60mm for the 80 % group. The number of sutures used for the anastomoses averaged 9.36 for the 407” group, 9.73 for the 600/d group, and 10.33 for the 80% group. The patency rate immediately after anastomosis was compared (Table 1). The group of vessels following an 80% resection showed a markedly reduced patency rate and even in those vessels that were patent, three showed a sluggish flow. The patency rate was checked one week later (Table 2). The amount of leakage immediately after the anastomosis was noted. Significant bleeding from the anastomotic junction occurred in two vessels but was controlled by light pressure. Leakage from the suture holes (the result of excessive
Fig. 4 Eight sutures were used for this anastomosis. Note that excessive tension in approximating the clamps has caused the two branches to stretch in an oblique fashion.
Fig. 5
Good
patency
after completion
of the anastomosis.
BRITISHJOURNALOF PLASTICSURGERY
84 Patency rates immediately after anastomosis
Table 1
Table 5
Average % shrinkage of the resected segment % Shrinkage
Patency Rate 100 % (12/12) with 1 sluggish flow 92 % (1 l/12) all with free flow 75 % (9/12) 3 with sluggish flow
40 % group 60 % group 80% group
Table
40 % group 60 % group 80 % group Overall
32.8 % 31.6% 34.4 % 32.9 %
2 Patency rate at one week after anastomosis Patency Rate
40% group 60 % group 80 % group
92 % (1l/12) all with free flow 75 % (9/12) all with free flow 67 % (8/12) 1 with sluggish flow
There were no differences between the different groups and it can be seen that a 1Omm segment of the rat femoral artery at zero tension should lengthen to about 10 x grnrn is
tension due to the suture cutting into the vessel wall) was frequently seen (Table 3). In the 60% and 80% resection group, the leakage frequently took the form of pulsatile squirts from multiple holes. However, all were stopped by light pressure except in three cases where bleeding was stopped by an additional suture. As a result of tension after anastomosis, the vessels became stretched and their diameters were reduced. Ten vessels had their external diameters measured before and after anastomosis and the average percentage narrowing was estimated (Table 4). To gain some idea of the elasticity of the femoral vessels, the resected segment of vessel was measured before and after removal (when it is at zero tension). The percentage shrinkage in length was then calculated (Table 5).
i.e. 14.9 mm if it
to be stitched under “normal tension”.
Scanning electron microscopy and light microscopy studies The most obvious lesions in the vessels were transverse cracks in the lumenal surface (Fig. 6). The severity varied with individual vessels, but as one might expect were generally less severe in the 40% group. These cracks represented disruption of the endothelial lining, often with rupture of the elastic lamina and sometimes even the muscle layer (Fig. 7). In most cases, thrombi were seen over these areas and, as expected, the greater the tension the greater the tendency to thrombosis. Despite these changes, endothelial cells were found over defective areas and even over exposed suture material (Fig. 8).
Discussion Table 3
Leakage
from suture holes Leakage
40 % group
60 % group 80 % group
Table 4
33% 100% 100%
seen
(4112)
Average narrowing of vessel after anastomosis y(, Narrowing
40 % group
60 % group 80 % group
16% 26% 52%
Although it is generally accepted that a microvascular anastomosis should not be done under excessive tension, our results show that a patency rate of 92% at one week post-operatively can be obtained when 40% (average 4.28 mm) of a mobilised segment of the rat femoral artery is resected and the two ends subsequently anastomosed. This patency rate is similar to that achieved following simple transection and reanastomosis of the same vessel by two of us (S.P.C. and C.D.H.) who had achieved an average patency rate of 95 y0 in several hundred anastomoses of this vessel. What is more surprising is that even with resection of 80% (average 8.60mm) of the mobilised segment, a patency rate as high as 67 y0 could be obtained.
MICROVASCULAR
ANASTOMOSIS
OF ARTERIES
UNDER
85
TENSION
Fig. 6 Scanning electron micrograph of a vessel re-anastomosed after 60% reduction of length. Note the transverse cracks, cqxially the one to the right not related to the suture. To the left of Ihe suture there is an ohviouh tear of the wall covered by a fibrin platelet clol.
c
Fig. 7 Longitudinal section of an artery anastomosed after a 40% resection. Several areas of elastic can be seen. The arrow indicates gross disruption at the site of a suture. Elastic stain x 48.
and muscle disruption
BRITISH
Fig. 8 suture.
S.E.M.
of a vessel re-anastomosed
after 60”” reduction
It may be argued that the vessels on both sides of the mobilised segment may move closer together after the anastomosis is completed and the clamps removed thus relieving the tension to a certain extent, and that the percentage resection (40 %, 60X, 80%) does not reflect the true gradation of tension proportionately. However, the very great tension produced by the 80% resection is shown by the fact that even with the high clamping pressure (250gm/mm’) of the Ikuta clamps, the approximated vessel ends frequently slipped out of the jaws which, consequently, had to be resited in the angle between the vessel branches. The excessive tension in the 60% and 80 % resection groups was also demonstrated by the squirting of blood from the suture holes. The change in diameter of the vessels before and after anastomosis was also remarkable in the 80% group where vessels on the average was stretched and the diameter reduced by nearly half (48 %).
showing
JOURNAL
one of the cracks
OF PLASTIC
endothelialised,
SURGERY
probably
over a
It is therefore clear that in this experimental model the margin of safety for tension in microvascular anastomoses is not as narrow as commonly believed. The critical point at which the patency rate falls below 90% is probably between 40% to 60% of resection (actual defect between 4.28mm to 6.18mm). The direct projection of the results of this experiment to clinical work in man is unrealistic. The vessels in human beings are different from those in the rat and a vessel which has been ischaemic for several hours (such as those encountered in replantation surgery) may withstand tension less favourably. It is probably still good practice to use vein grafts in cases of doubt. Nonetheless it may be comforting to remember that there is still some margin of safety. Certainly, performing one anastomosis rather than two saves time and has its own advantages over a vein graft, vessel transfer or bone shortening. Perhaps it may even be better to
MTCROVASCXJLAR
ANASTOMOSIS
OF ARTERIES
UNDER
design an approximator with a clamping pressure that will allow the two vessel ends to slip out if the tension is more than acceptable. In this rat model, this tension is reached when about 507, of the mobilised segment (actual length about 5.13 mm) was lost.
Acknowledgement The authors would like to express their gratitude to the staff of the research laboratory, Department of Orthopaedics, Umversity of Hong Kong for technical assistance in this study.
TENSION
87
Kleinert, H. E., Jubala, C. A. and Tsai, T. M. (1977). Digital replantation-selection, technique and results. Orthopaedic Clinics qf’ North America, 8, 309. Philadelphia: W. B. Saunders Company. Pho, R. W. H., Chacha, P. B. and Yeo, K. Q. (1979). Rerouting vessels and nerves from other digits in replanting an avulsed and degloved thumb. Plastic und Rwomtructive SurKerx. 64, 330. Havhurst. J. W. and O’Brien. B. McC. ( 1975). An exnerimen&I study of microvascular technique. patency rate, and related factors. British Journrtl of Plastic Sur,qerF. 28, 128.
The Authors S.
References O’Brien, B. McC., Haw, C., Kubo, T., Gilbert, A. and Hayhurst, J. W. (1979) Microvenous grafting of small vein defects. British Journal qf Plastic Surgery, 32, 164. Alpert, B. S., Buncke, H. J. and Brownstein, M. (1978). Replacement of damaged arteries and veins with vein grafts when replanting crushed, amputated fingers. Plastic and Reconstructive Surgery, 61, I I.
P. Chow, FRCSE, Senior Lecturer. Department of Orthopaedic Surgery, University of Hong Kong, Hong Kong. C. D. Huang, MD. Professor (Orthopaedic). Department of Zhong Shan Medical College, Guangzhou Surgery. (Canton). People’s Republic of China. C. W. Chan, MRC Path., Senior Lecturer, Department of Pathology, University of Hong Kong, Hong Kong. Requests for reprints to: Dr S. P. Chow, FRCSE. Senior Lecturer, Department of Orthopaedic Surgery. University of Hong Kong, Hong Kong.