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An experimental study of microvascular technique, patency rates and related factors
AN EXPERIMENTAL PATENCY
STUDY OF MICROVASCULAR TECHNIQUE, RATES AND RELATED FACTORS
By J. W. HAYHURST, M.D.l and B. McC. O’BRIEN,B.Sc., M.S., F.R.C.S., F.R.A.C.S., F.A.C.S. Microsurgery Project: St Vincent’s Hospital, Melbourne, Australia
THE ability to anastomose successfully and reliably vessels of I to 2 mm diameter has a number of current clincial applications in the replantation and transfer of tissues. The wide variation in the reported rates of patency following anastomosis in animals suggests variability in the technique and/or methods of assessing patency. It has become clear to us from the work reported here that improved patency rates can be achieved by refined technique alone, rather than by resorting to various anticoagulants (Kolar et al., 1973; Ketchum et al., 1974). MATERIALAND METHODS White English strain rabbits 2.0-3.3 kg (average 2.4) were given 30 mg/g of Nembutal intravenously and maintained on oxygen, nitrous oxide and halothane by mask. The femoral vessels were exposed with minimal handling to avoid spasm of the vein. Spasm may also be due to blood on the external surface of the vessels (Acland, 1973). The operative area is therefore frequently irrigated with normal saline at room temperature (22%) to remove blood and other vasoconstrictive substances. The temperature in the operative field was usually 34°C at the beginning of the operation and 28°C at the end. A radiant energy source to maintain the temperature of the operative field at a constant 38°C did not reduce vascular spasm significantly nor did warmed saline. A standard set of microvascular instruments was used including those developed in this centre previously (Henderson et al., 1970; O’Brien, 1973; O’Brien and Hayhurst, 1973) and the technique in general was that published by O’Brien et al. (1970). Arterial anastomosis. The needle should pass through the full thickness of the vessel wall and is inserted 60-80 p from the vessel edge. Such sutures cause minimal damage and are less likely to lead to thrombosis (Baxter et al., 1972). The vessel ends are just approximated and the tissue encompassed by the sutures must not be strangulated. When tied with correct tension, the suture may be seen through the translucent vessel wall forming a small circle with a diameter roughly equal to the thickness of the wall of the artery. So far as spacing of the sutures is concerned, the goal is the accurate apposition of the vessel edges with a minimum number of sutures; a 0.9 mm artery usually requires 8. Venous anastomosis. The vein walls are extremely thin and fragile, and tend to collapse against each other. To prevent this the sutures are inserted within a pool of normal saline which is removed before tying as the surface tension of the fluid causes the suture to stick to itself. Previous work has shown a high incidence of vein wall necrosis associated with suture crowding (Baxter et al., 1972). Because of this the first 50 veins were anastomosed 1 Formerly Research Fellow in Microsurgery and Clinical Assistant in Plastic Surgery, St Vincent’s Hospital, Melbourne. Now Resident in Plastic Surgery, Norfolk General Hospital, Virginia, USA. Address for reprints:
B. McC.
O’Brien,
82 Collins 128
Street,
Melbourne.
MICROVASCULAR
FIG.
TECHNIQUE,
PATENCY
RATES
AND
RELATED
FACTORS
129
I. Patency A, Blood emptied from “downstream” segment of _ -. check of completed anastomosis. artery. l3, Kelease of forceps nearest to the anastomosis, allowing blood to fill the emptied segment.
with a minimal number of sutures using approximately 6 for a 1.1 mm vein. Evaluation of the first 50 veins indicated however that patency results were improved where more sutures had been used. An additional 25 veins were therefore sutured more accurately with approximately 12 sutures for each anastomosis. Evaluation of patency. With completion of the anastomosis and removai of the plastic cuff, patency was checked thus. A number 2 jeweller’s forceps grasped the vessel immediately distal to the anastomosis with sufficient force to occlude the blood flow. A second jeweller’s forceps emptied the “downstream” side of the vessel of bIood (Fig. I). With the forceps most distant from the anastomosis still occluding the vessel, the forceps nearest to the anastomotic site was released. If the anastomosis was patent, blood rushed through the anastomosis to fill the empty segment of vessel. Beginning with the 3rd post-operative day, several rabbits were autopsied at I to 2 day intervals up to the 15th day. Thereafter, several rabbits were examined every few days up to 41 days. Each anastomosis with a small adjacent segment of the vessel was dissected free and tested for patency as described. Dissection of the vessel was tedious and often required as much time as the original anastomosis. After the 2nd post-operative week collateral vessels were frequently seen at the anastomotic site. Opening the vessel “downstream” from the anastomotic site and noting bleeding from the vessel is therefore not considered proof of patency as it may come from collateral vessels which must be coagulated to assess true patency. In 5 veins in this series, there was only a small or questionable flow of blood at the anastomotic site and these vessels were assessed as occluded. After determination of patency, a small segment of the vessel including the anastomosis was resected for histological examination. No anticoagulants were used at any time.
130
BRITISH JOURNAL OF PLASTIC SURGERY RESULTS
The 50 arteries averaged approximately 0.9 mm in diameter and immediate patency was achieved in IOOper cent of these vessels with long-term patency in 98 per cent. The cause of the single occlusion was not evident. The initial 50 veins averaged approximately I .I mm in diameter and immediate patency was obtained in 98 per cent with a long-term patency in 80 per cent (3-41 days). The percentage of veins occluded at various times is shown in the Table. Though the numbers involved were too small to be statistically significant, it appears that an apparent improvement in results occurs after the 2nd post-operative week. TABLE Relationship
of the time of examination
to the percentage of veins occluded
Days after operation
Veins examined
Veins c ccluded
Percentage occluded
3-7
I.5
3
20.0
5 I
29’4 16.6
I
8.5
8-14 15-26 35-41
17 6 I2
To avoid falsely high patency rates the second group of 25 veins of similar diameter was evaluated during the 2nd post-operative week. Immediate patency was IOO per cent and 92 per cent were found patent during the 2nd week. One occluded vein examined on the 12th day was exposed in a large, open, infected wound. The other had no distinguishing characteristics. In the first 50 veins the relationship of the surgeon’s judgment of the technical adequacy of the anastomosis, the amount of spasm and the amount of blood coming in contact with the external wall of the vessel was recorded. The numbers involved are too small to be statistically significant but it is our impression that the technical adequacy of the anastomosis is the most important factor in assuring the ultimate patency of the vein with spasm and bleeding being relatively less so. As only 3 vessels were occluded in 50 arteries and the final 25 veins, evaluation of these factors in these 75 vessels yielded no further useful information. In the initial 50 operative sites in 27 rabbits, 7 wounds showed clinical signs of wound infection: an open wound or excessive collection of turbid fluid or pus. Only one however contained an occluded vein. DISCUSSION In microarterial anastomosis, the surgeon should endeavour to achieve an ultimately leak-free anastomosis with as few sutures as possible to avoid medial necrosis and arterial occlusion. The cuffing technique allows the surgeon to achieve this with fewer sutures than would otherwise be necessary (McLean and Buncke, 1972). Sutures which pass through the full thickness of the vessel wall probably cause less medial disruption than sutures which pick up only part of the wall. Most human arteries of this size have a consistency similar to rabbits’ arteries and require approximately the same number of sutures. In micro-venous anastomoses accurate approximation should take precedence over fear of suture crowding. The latter is frequently associated with vein wall necrosis, but in contrast to arteries does not usually lead to occlusion. On the other hand, poor apposition of the vein edges has been shown to be one of the most frequent accompaniments of venous occlusion (Baxter et al.). Human veins of this size generally have a more sub-
MICROVASCULARTECHNIQUE, PATENCY RATES AND RELATED FACTORS
131
stantial consistency of their walls and require fewer sutures than the rabbit’s femoral vein. The apparent improvement in vein patency after the 2nd post-operative week is probably due to a dissolution or dislodgement of a small occluding plug at the anastomotic site and is to be differentiated from recanalisation which takes place more slowly. Flow may also be established around the anastomosis by collateral vessels and patency rates after 2 weeks in vessels of this size may be falsely high. This confirms the findings of other series that patency rates after the 2nd post-operative week have been consistently higher than those before (DeWeese and Niguidiia, 1960; Chase and Schwartz, 1963; Collins and Douglas, 1964; Ts’ui et al., 1966; Hattori et al., 1970; O’Brien et al., 1970; Baxter et al., 1972; Tamai et al., 1972; Kolar et al., 1973; Ketchum et ul., 1974). With very small vessels of about 0.5 mm diameter Acland (1972) found that many occluding thrombi plugs had dissolved before 2 weeks. We found that occlusion occurred mostly within the first 72 hours as did Ketchum er al. (1974). Our experience with replantation has shown that few are lost from vascular failure after the first week (O’Brien et al., 1973) and in microvascular free flap transfers no losses have occurred after 3 days (O’Brien et al., 1974). Therefore the patency rate of vessels approximately I mm in diameter can be accurately determined immediately after the 1st week. While no anticoagulants were used in this series, experience with experimental digital replantations after 24 hours cold storage (Hayhurst et al., 1974) and clinical repiantations (O’Brien et al., 1974) have demonstrated the advisability of anticoagulants where vascular damage has occurred from trauma or long periods of ischaemia. SUMMARY Microvascular repairs of 50 rabbits’ femoral arteries averaging 0.9 mm in diameter gave an immediate patency rate of IOO per cent and a follow-up patency rate of 98 per cent after 3-41 days. The patency rate of 50 veins averaging 1.1 mm in diameter was 98 per cent immediately after surgery and 80 per cent after 3-41 days. No anticoagulants or antispasmodics were used. An additional 25 vein repairs with sufficient additional sutures to ensure more accurate apposition of the vein edges resulted in IOO per cent immediate patency and 92 per cent patency when examined during the 2nd week, the period which reveals the truest patency rate. Technical adequacy of the microvascular repair is the most important factor in ensuring final patency. This work was carried out in part under grants from the National Health and Medical Research Council of Australia, the Ramaciotti Foundation and the Nu$ield Foundation. Grateful appreciation is expressed to LIr Thelma Baxter for the histopathology and to Miss Madeleine McEniry, Miss Sue Askew and Mr Tom Elezovic for their excellent technical assistance.
REFERENCES ACLAND, R. (1972). Prevention of thrombosis in microvascular surgery by the use of magnesium sulphate. British Journal of Plastic Surgery, 25, 292. ACLAND, R. (1973). Personal communication. BAXTER, T. J., O’BRIEN, B. McC., HENDERSON,P. N. and BENNETT, R. C. (1972). The histopathology of small vessels following microvascular repair. British journal of Surgery, 59, 617. CHASE,M. D. and SCHWARTZ,S. L. (1963). Suture anastomosis of small arteries. Surger_y, Gynecology and Obstetrics, 117, 44. COLLINS, R. E. and DOUGLAS, F. M. (1964). Small vein anastomosis with and without operative microscope. Archives of Surgery, 88, 740.
132
BRITISH
JOURNAL
OF PLASTIC
SURGERY
DEWEESE, J. H. and NIGUIDIIA, F. (1960). The replacement of short segments of vein with functional autogenous venous grafts. Surgery, Gynecology and Obstetrics, IIO, 303. HATTORI, H., KILLEN, D. A. and GREEN, J. W. (1970). Suture materials and technique on patency of anastomosed arteries of less than 1.5 mm in diameter. American Journal qf Surgery, 36, 352. HAYHURST, J. W., O’BRIEN, B. McC., ISHIDA, H. and BAXTER, THELMA J. (1974). Experimental digital replantations after prolonged cooling. The Hand (in press). HENDERSON, P. N., O’BRIEN, B. McC. and PAREL, J. M. (1970). An adjustable double microvascular clamp. Medical Journal of Australia, I, 715. KETCHUM. L. D.. WENNEN, W. W., MASTERS, F. W. and ROBINSON, A. W. (1974). Esverimen&l use -of Pluronic F68. in micro;ascular surgery. Plastic and iie’construYtive Surgery, 53 288. KOLAR, L., WIEBERDINK, J. and RENEMAN, R. S. (1973). Anticoagulation in microvascular surgery. European Surgical Research, 5, 52. MCLEAN, D. H. and BUNCKE, H. J. (1973). Use of the Saran Wrap cuff in microsurgical arterial repairs. Plastic and Reconstructive Surgery, 51, 624. O’BRIEN, B. McC,., HENDERSON, I’. N., BENNETT, R. C. and CROCK, G. W. (1970). Microvascular surgical technique. Medical Journal of Australia, I, 722. O’BRIEN, B. McC. (1973). A modified triploscope. British Journal of Plastic Surgeq, 26, 301. O’BRIEN, B. McC., MACLEOD, A. M., MILLER, G. D. H., NEWING, R. K., HAYHURST, J. W. and MORRISON, W. A. (1973). Clinical replantation of digits. Plastic and Reconstructive Surgery, 52, 490. O’BRIEN, B. McC. and HAYHURST, J. W. (1973). A new metallized microsuture and micraneedle holder. Plastic and Reconstructive Sureerv. ~2. 677. O’BRIEN, B. McC., MORRISON, W. A., ISHIDA, H., MACLEOD, A. M. and GILBERT, A. (1974). Free flap transfers with microvascular anastomoses. British Journal of Plastic Surgery, 27, 220. TAMAI, S., SAROUCHI, N,, HORI, Y., TATSUMI, Y. and OKUDA, H. (1972). Microvascular surgery in orthopaedlcs and traumatology. Journal of Bone andJoint Surgery, 54B, 637. TS’UI, C. Y., FENG, Y. H., K’ANG, C. Y., :I, C. M., UYU, Y. C., CH’EN, C. C., SHIH, Y. F., WANG, W. H., CHIANG, L. I?., CH’IU, H. I’., MA, S. C., LIN, P. L. and CH’EN, C. (1966‘). Microvascular anastomosis and transplantation. Chinese Medical 3ourna1, 85, 610.
STUDY OF MICROVASCULAR TECHNIQUE, RATES AND RELATED FACTORS
By J. W. HAYHURST, M.D.l and B. McC. O’BRIEN,B.Sc., M.S., F.R.C.S., F.R.A.C.S., F.A.C.S. Microsurgery Project: St Vincent’s Hospital, Melbourne, Australia
THE ability to anastomose successfully and reliably vessels of I to 2 mm diameter has a number of current clincial applications in the replantation and transfer of tissues. The wide variation in the reported rates of patency following anastomosis in animals suggests variability in the technique and/or methods of assessing patency. It has become clear to us from the work reported here that improved patency rates can be achieved by refined technique alone, rather than by resorting to various anticoagulants (Kolar et al., 1973; Ketchum et al., 1974). MATERIALAND METHODS White English strain rabbits 2.0-3.3 kg (average 2.4) were given 30 mg/g of Nembutal intravenously and maintained on oxygen, nitrous oxide and halothane by mask. The femoral vessels were exposed with minimal handling to avoid spasm of the vein. Spasm may also be due to blood on the external surface of the vessels (Acland, 1973). The operative area is therefore frequently irrigated with normal saline at room temperature (22%) to remove blood and other vasoconstrictive substances. The temperature in the operative field was usually 34°C at the beginning of the operation and 28°C at the end. A radiant energy source to maintain the temperature of the operative field at a constant 38°C did not reduce vascular spasm significantly nor did warmed saline. A standard set of microvascular instruments was used including those developed in this centre previously (Henderson et al., 1970; O’Brien, 1973; O’Brien and Hayhurst, 1973) and the technique in general was that published by O’Brien et al. (1970). Arterial anastomosis. The needle should pass through the full thickness of the vessel wall and is inserted 60-80 p from the vessel edge. Such sutures cause minimal damage and are less likely to lead to thrombosis (Baxter et al., 1972). The vessel ends are just approximated and the tissue encompassed by the sutures must not be strangulated. When tied with correct tension, the suture may be seen through the translucent vessel wall forming a small circle with a diameter roughly equal to the thickness of the wall of the artery. So far as spacing of the sutures is concerned, the goal is the accurate apposition of the vessel edges with a minimum number of sutures; a 0.9 mm artery usually requires 8. Venous anastomosis. The vein walls are extremely thin and fragile, and tend to collapse against each other. To prevent this the sutures are inserted within a pool of normal saline which is removed before tying as the surface tension of the fluid causes the suture to stick to itself. Previous work has shown a high incidence of vein wall necrosis associated with suture crowding (Baxter et al., 1972). Because of this the first 50 veins were anastomosed 1 Formerly Research Fellow in Microsurgery and Clinical Assistant in Plastic Surgery, St Vincent’s Hospital, Melbourne. Now Resident in Plastic Surgery, Norfolk General Hospital, Virginia, USA. Address for reprints:
B. McC.
O’Brien,
82 Collins 128
Street,
Melbourne.
MICROVASCULAR
FIG.
TECHNIQUE,
PATENCY
RATES
AND
RELATED
FACTORS
129
I. Patency A, Blood emptied from “downstream” segment of _ -. check of completed anastomosis. artery. l3, Kelease of forceps nearest to the anastomosis, allowing blood to fill the emptied segment.
with a minimal number of sutures using approximately 6 for a 1.1 mm vein. Evaluation of the first 50 veins indicated however that patency results were improved where more sutures had been used. An additional 25 veins were therefore sutured more accurately with approximately 12 sutures for each anastomosis. Evaluation of patency. With completion of the anastomosis and removai of the plastic cuff, patency was checked thus. A number 2 jeweller’s forceps grasped the vessel immediately distal to the anastomosis with sufficient force to occlude the blood flow. A second jeweller’s forceps emptied the “downstream” side of the vessel of bIood (Fig. I). With the forceps most distant from the anastomosis still occluding the vessel, the forceps nearest to the anastomotic site was released. If the anastomosis was patent, blood rushed through the anastomosis to fill the empty segment of vessel. Beginning with the 3rd post-operative day, several rabbits were autopsied at I to 2 day intervals up to the 15th day. Thereafter, several rabbits were examined every few days up to 41 days. Each anastomosis with a small adjacent segment of the vessel was dissected free and tested for patency as described. Dissection of the vessel was tedious and often required as much time as the original anastomosis. After the 2nd post-operative week collateral vessels were frequently seen at the anastomotic site. Opening the vessel “downstream” from the anastomotic site and noting bleeding from the vessel is therefore not considered proof of patency as it may come from collateral vessels which must be coagulated to assess true patency. In 5 veins in this series, there was only a small or questionable flow of blood at the anastomotic site and these vessels were assessed as occluded. After determination of patency, a small segment of the vessel including the anastomosis was resected for histological examination. No anticoagulants were used at any time.
130
BRITISH JOURNAL OF PLASTIC SURGERY RESULTS
The 50 arteries averaged approximately 0.9 mm in diameter and immediate patency was achieved in IOOper cent of these vessels with long-term patency in 98 per cent. The cause of the single occlusion was not evident. The initial 50 veins averaged approximately I .I mm in diameter and immediate patency was obtained in 98 per cent with a long-term patency in 80 per cent (3-41 days). The percentage of veins occluded at various times is shown in the Table. Though the numbers involved were too small to be statistically significant, it appears that an apparent improvement in results occurs after the 2nd post-operative week. TABLE Relationship
of the time of examination
to the percentage of veins occluded
Days after operation
Veins examined
Veins c ccluded
Percentage occluded
3-7
I.5
3
20.0
5 I
29’4 16.6
I
8.5
8-14 15-26 35-41
17 6 I2
To avoid falsely high patency rates the second group of 25 veins of similar diameter was evaluated during the 2nd post-operative week. Immediate patency was IOO per cent and 92 per cent were found patent during the 2nd week. One occluded vein examined on the 12th day was exposed in a large, open, infected wound. The other had no distinguishing characteristics. In the first 50 veins the relationship of the surgeon’s judgment of the technical adequacy of the anastomosis, the amount of spasm and the amount of blood coming in contact with the external wall of the vessel was recorded. The numbers involved are too small to be statistically significant but it is our impression that the technical adequacy of the anastomosis is the most important factor in assuring the ultimate patency of the vein with spasm and bleeding being relatively less so. As only 3 vessels were occluded in 50 arteries and the final 25 veins, evaluation of these factors in these 75 vessels yielded no further useful information. In the initial 50 operative sites in 27 rabbits, 7 wounds showed clinical signs of wound infection: an open wound or excessive collection of turbid fluid or pus. Only one however contained an occluded vein. DISCUSSION In microarterial anastomosis, the surgeon should endeavour to achieve an ultimately leak-free anastomosis with as few sutures as possible to avoid medial necrosis and arterial occlusion. The cuffing technique allows the surgeon to achieve this with fewer sutures than would otherwise be necessary (McLean and Buncke, 1972). Sutures which pass through the full thickness of the vessel wall probably cause less medial disruption than sutures which pick up only part of the wall. Most human arteries of this size have a consistency similar to rabbits’ arteries and require approximately the same number of sutures. In micro-venous anastomoses accurate approximation should take precedence over fear of suture crowding. The latter is frequently associated with vein wall necrosis, but in contrast to arteries does not usually lead to occlusion. On the other hand, poor apposition of the vein edges has been shown to be one of the most frequent accompaniments of venous occlusion (Baxter et al.). Human veins of this size generally have a more sub-
MICROVASCULARTECHNIQUE, PATENCY RATES AND RELATED FACTORS
131
stantial consistency of their walls and require fewer sutures than the rabbit’s femoral vein. The apparent improvement in vein patency after the 2nd post-operative week is probably due to a dissolution or dislodgement of a small occluding plug at the anastomotic site and is to be differentiated from recanalisation which takes place more slowly. Flow may also be established around the anastomosis by collateral vessels and patency rates after 2 weeks in vessels of this size may be falsely high. This confirms the findings of other series that patency rates after the 2nd post-operative week have been consistently higher than those before (DeWeese and Niguidiia, 1960; Chase and Schwartz, 1963; Collins and Douglas, 1964; Ts’ui et al., 1966; Hattori et al., 1970; O’Brien et al., 1970; Baxter et al., 1972; Tamai et al., 1972; Kolar et al., 1973; Ketchum et ul., 1974). With very small vessels of about 0.5 mm diameter Acland (1972) found that many occluding thrombi plugs had dissolved before 2 weeks. We found that occlusion occurred mostly within the first 72 hours as did Ketchum er al. (1974). Our experience with replantation has shown that few are lost from vascular failure after the first week (O’Brien et al., 1973) and in microvascular free flap transfers no losses have occurred after 3 days (O’Brien et al., 1974). Therefore the patency rate of vessels approximately I mm in diameter can be accurately determined immediately after the 1st week. While no anticoagulants were used in this series, experience with experimental digital replantations after 24 hours cold storage (Hayhurst et al., 1974) and clinical repiantations (O’Brien et al., 1974) have demonstrated the advisability of anticoagulants where vascular damage has occurred from trauma or long periods of ischaemia. SUMMARY Microvascular repairs of 50 rabbits’ femoral arteries averaging 0.9 mm in diameter gave an immediate patency rate of IOO per cent and a follow-up patency rate of 98 per cent after 3-41 days. The patency rate of 50 veins averaging 1.1 mm in diameter was 98 per cent immediately after surgery and 80 per cent after 3-41 days. No anticoagulants or antispasmodics were used. An additional 25 vein repairs with sufficient additional sutures to ensure more accurate apposition of the vein edges resulted in IOO per cent immediate patency and 92 per cent patency when examined during the 2nd week, the period which reveals the truest patency rate. Technical adequacy of the microvascular repair is the most important factor in ensuring final patency. This work was carried out in part under grants from the National Health and Medical Research Council of Australia, the Ramaciotti Foundation and the Nu$ield Foundation. Grateful appreciation is expressed to LIr Thelma Baxter for the histopathology and to Miss Madeleine McEniry, Miss Sue Askew and Mr Tom Elezovic for their excellent technical assistance.
REFERENCES ACLAND, R. (1972). Prevention of thrombosis in microvascular surgery by the use of magnesium sulphate. British Journal of Plastic Surgery, 25, 292. ACLAND, R. (1973). Personal communication. BAXTER, T. J., O’BRIEN, B. McC., HENDERSON,P. N. and BENNETT, R. C. (1972). The histopathology of small vessels following microvascular repair. British journal of Surgery, 59, 617. CHASE,M. D. and SCHWARTZ,S. L. (1963). Suture anastomosis of small arteries. Surger_y, Gynecology and Obstetrics, 117, 44. COLLINS, R. E. and DOUGLAS, F. M. (1964). Small vein anastomosis with and without operative microscope. Archives of Surgery, 88, 740.
132
BRITISH
JOURNAL
OF PLASTIC
SURGERY
DEWEESE, J. H. and NIGUIDIIA, F. (1960). The replacement of short segments of vein with functional autogenous venous grafts. Surgery, Gynecology and Obstetrics, IIO, 303. HATTORI, H., KILLEN, D. A. and GREEN, J. W. (1970). Suture materials and technique on patency of anastomosed arteries of less than 1.5 mm in diameter. American Journal qf Surgery, 36, 352. HAYHURST, J. W., O’BRIEN, B. McC., ISHIDA, H. and BAXTER, THELMA J. (1974). Experimental digital replantations after prolonged cooling. The Hand (in press). HENDERSON, P. N., O’BRIEN, B. McC. and PAREL, J. M. (1970). An adjustable double microvascular clamp. Medical Journal of Australia, I, 715. KETCHUM. L. D.. WENNEN, W. W., MASTERS, F. W. and ROBINSON, A. W. (1974). Esverimen&l use -of Pluronic F68. in micro;ascular surgery. Plastic and iie’construYtive Surgery, 53 288. KOLAR, L., WIEBERDINK, J. and RENEMAN, R. S. (1973). Anticoagulation in microvascular surgery. European Surgical Research, 5, 52. MCLEAN, D. H. and BUNCKE, H. J. (1973). Use of the Saran Wrap cuff in microsurgical arterial repairs. Plastic and Reconstructive Surgery, 51, 624. O’BRIEN, B. McC,., HENDERSON, I’. N., BENNETT, R. C. and CROCK, G. W. (1970). Microvascular surgical technique. Medical Journal of Australia, I, 722. O’BRIEN, B. McC. (1973). A modified triploscope. British Journal of Plastic Surgeq, 26, 301. O’BRIEN, B. McC., MACLEOD, A. M., MILLER, G. D. H., NEWING, R. K., HAYHURST, J. W. and MORRISON, W. A. (1973). Clinical replantation of digits. Plastic and Reconstructive Surgery, 52, 490. O’BRIEN, B. McC. and HAYHURST, J. W. (1973). A new metallized microsuture and micraneedle holder. Plastic and Reconstructive Sureerv. ~2. 677. O’BRIEN, B. McC., MORRISON, W. A., ISHIDA, H., MACLEOD, A. M. and GILBERT, A. (1974). Free flap transfers with microvascular anastomoses. British Journal of Plastic Surgery, 27, 220. TAMAI, S., SAROUCHI, N,, HORI, Y., TATSUMI, Y. and OKUDA, H. (1972). Microvascular surgery in orthopaedlcs and traumatology. Journal of Bone andJoint Surgery, 54B, 637. TS’UI, C. Y., FENG, Y. H., K’ANG, C. Y., :I, C. M., UYU, Y. C., CH’EN, C. C., SHIH, Y. F., WANG, W. H., CHIANG, L. I?., CH’IU, H. I’., MA, S. C., LIN, P. L. and CH’EN, C. (1966‘). Microvascular anastomosis and transplantation. Chinese Medical 3ourna1, 85, 610.