Michele T. Sasmor, William E Reus, Deborah J. Straker, and Lawrence B. Colen
VASCULAR RESISTANCE CONSIDERATIONS
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IN FREE-TISSUE TRANSFER ABSTRACT The closure of complex wounds is facilitated by microvascular free-tissue transfer. The greatest threat to the success of a free-tissue transfer is thrombosis of the microvascular anastomosis. Technical and pharmacologic advances have decreased the thrombogenic effect of abnormalities of a vessel's endothelial lining, and have decreased the coagulation ability of blood. Equally important to patency of the microvascular anastomosis is blood flow, which is inversely proportional to the total resistance provided by the microcirculatory beds downstream. Because different tissues possess different vascular resistances, some flaps may display more favorable hemodynamics than others. This study was designed to characterize vascular resistance, weight, volume, and surface area of the flaps available for transfer, and to identify favorable tissues for reconstruction from the standpoint of outflow resistances. Data were collected on patients undergoing free-tissue transfers and on experimental freetissue transfers harvested from canines and fresh cadavers. Results show that resistance is highest in fascial flaps, intermediate in composite bone and soft-tissue flaps, and lowest in muscle and musculocutaneous tissues. Resistance is lower in flaps harvested from the trunk, compared with those harvested from the extremities. The rate of microvascular complications increases as resistance within the flap increases. Muscle and musculocutaneous flaps harvested from the trunk have lower complication rates than fascial and fasciocutaneous flaps. Suggestions for choices of flaps are made, based on the inherent resistance in the various free flap tissues. Microsurgical free-tissue transfer is an established and reliable technique. Success rates in large series exceed 90 percent. Several factors influence the outcome of a free-tissue transfer.12 For example, increased experience lowers a microsurgeon's rate of flap failure. Also, the etiology of the defect seems to affect success, with failure occurring more frequently in traumatic wounds than in wounds resulting from congenital deformity or cancer ablation. Failure rates also vary with respect to the recipient site. The order of increasing failure rate by recipient site is upper extremity, breast, head and neck, and lower extremity. The most frequent cause of flap failure is anastomotic thrombosis. The donor tissue represents the vascular bed through which blood must flow after
passing the arterial anastomosis, prior to traversing the venous anastomosis. Different donor tissues (muscle, fascia, bone, and skin) might offer differing resistances to blood flow. High-resistance tissue might correlate with low blood flow and a higher rate of failure. This study examines the relationship between donor tissue, vascular resistance, and anastomotic complications in elective microsurgery.
MATERIALS AND METHODS STUDY POPULATION.
Between 1987 and 1989, 30
patients undergoing elective free-tissue transfer were enrolled in this study. There were 17 males and 13
Sections of General Surgery and Plastic and Reconstructive Surgery, Department of Surgery, Dartmouth-Hitchcock Medical Center, Hanover, New Hampshire, and Section of Plastic and Reconstructive Surgery, Eastern Virginia Medical School, Norfolk, Virginia Materials in this paper were presented at the Sixth Annual Meeting of the American Society for Reconstructive Microsurgery, Toronto, Canada, September, 1990 Reprint requests-. Dr. Sasmor, Section of Plastic and Reconstructive Surgery, Dept. of Surgery, Dartmouth-Hitchcock Medical Center, One Medical Center Drive, Lebanon, NH 03756 Accepted for publication lanuary 2,1992 Copyright © 1992 by Thieme Medical Publishers, Inc., 381 Park Avenue South, New York, NY 10016. All rights reserved.
195
females who ranged in age from 23 to 79 years (mean 47.5 years). Wound etiologies were: trauma (18 cases), cancer (9 cases), and neurotropic (3 cases). Additionally, 16 experimental flaps were raised in fresh cadavers and 17 flaps were raised in canines. MEASURING VASCULAR RESISTANCE. A flap with its pedicle was completely dissected and taken to the back table in the operating room. A solution of 50 cc of autologous blood, containing 100 U/ml of heparin and 30 mg/ml papaverine, was placed in an infusion pump (Fig. 1). Tubing A was attached to a pressure transducer and a digital pressure monitor, with the line zeroed to atmospheric pressure. Tubing B was connected to the largest intravenous catheter that could be easily accommodated by the donor artery. The flow rate was set at 1 cc/min and was allowed to flow until blood returned from the vein. Once venous return occurred, the transducer was allowed to equilibrate and a pressure reading was obtained from the monitor. The flow rate was then increased, the reading was allowed to equili-
MAY 1992
brate, and a pressure reading was taken. This procedure continued until physiologic pressures were achieved (not exceeding a mean pressure of 90 mmHg). The catheter was then removed and the artery freshened. The flap was transferred to the recipient site and the microvascular anastomosis was performed. The identical procedure was followed on the canine and cadaver flaps. However, normal saline with papaverine and heparin in the same concentrations was used instead of autologous blood to perfuse the cadaver flaps. CALCULATION OF RESISTANCE. Blood flow within the free-tissue transfer is a function of perfusion pressure and resistance within the tissue bed. Resistance was calculated using the hydraulic analogue of Ohm's law, R = P/F, where R = resistance (mmHg/ml/min), P = pressure (mmHg), and F = flow (ml/min). Resistance was calculated for each flap at each flow rate, and an average resistance was calculated. For statistical analysis, the chi-square test was used to compare resistances in different types of free flaps. APPLICATIONN TO SURGICAL OUTCOME.
Pressure transducer and monitor
TO evaluate
the significance of vascular resistance in a successful surgical outcome, we conducted a retrospective review of the results of 175 elective free-tissue transfers that were performed at the Dartmouth-Hitchcock Medical Center between 1983 and 1989. Flaps were defined as muscle/musculocutaneous, composite bone and soft tissue, and fascial/fasciocutaneous, and were further categorized based on donor site from the trunk, extremities, or scalp. Flap complications, including failures and reoperation for salvage, were noted.
RESULTS
Continuous infusion pump'
Free flap
196
Figure 1. Equipment for measuring vascular resistance in a free-tissue transfer. A constant infusion pump is connected to a pressure transducer and pressure monitor by "A," a saline-filled high-pressure tubing. Line "B" connects a 50 cc syringe with autologous blood containing heparin and papaverine from the infusion pump to an intravenous catheter secured in the donor artery of the freetissue transfer.
Average resistances were calculated for 13 types of free-tissue transfers and ranged from 12.5 mmHg/ ml/min to greater than 67 mmHg/ml/min. Table 1 lists each flap with its unique resistance value. Muscle and musculocutaneous flaps exhibited the lowest resistances, with composite bone and soft tissue constituting an intermediate level. Fascial/fasciocutaneous flaps yielded the highest vascular resistances. Flaps were grouped by site of harvest (Table 2). Donor tissue harvested from the trunk generated lower resistances than those harvested peripherally (Fig. 2). Statistical analysis of the clinical flaps showed a difference in resistances to the p < 0.04 levels, when muscle and musculocutaneous flaps harvested from the trunk were compared with the composite bone and softtissue flaps, along with the fascial and fasciocutaneous flaps harvested from the trunk and extremities. To evaluate the significance of the role that vascular resistance might play in successful surgical outcome, we referred to our larger group of 175 free tissue transfers. A variety of donor tissues were used to meet
Downloaded by: Universite de Sherbrooke. Copyrighted material.
JOURNAL OF RECONSTRUCTIVE MICROSURGERY/VOLUME 8, NUMBER 3
VASCULAR RESISTANCE CONSIDERATIONS/SASMOR, REUS, STRAKER, COLEN
Table 1. Average Resistances of Free Flaps TRAM Latissimus dorsi muscle Rectus muscle Serratus muscle Fibula and soft tissue Radial forearm Iliac crest and internal oblique muscle Dorsal thoracic fascia Gracilis muscle Scapular bone and soft tissue Iliac crest Lateral arm Temporal parietal fascia
Resistance in ntmtig/ml/min 12.5 13.5 14.2 18.4 22.2 25.4 27.5 28.9 30.2 32.5 35.0 37.8 67.0
Table 2. Distribution of Free Flaps by Category of Donor Site in 175 Elective Free Tissue Transfers Site Muscle/musculocutaneous Trunk Extremity Composite bone and soft tissue Fascial/fasciocutaneous Trunk Extremity Scalp
Number 66 30 27 23 16 13
the reconstructive requirements of diverse tissue defects (Fig. 3). Outcome was divided into three categories: flaps healing without complications; flaps with microvascular thrombosis requiring repeat operation for salvage; and flaps with microvascular thrombosis and flap failure (Table 3). An increase in microvascular complications was noted with the increase in vascular resistance. Complication rates were: 4.5 percent for muscle and musculocutaneous flaps harvested from the trunk, 11.1 percent for composite bone and soft tissue, 12.6
Figure 2. Average free flap resistances by category of donor tissue.
e per g Tissue .034
Resistance per cm2
—
.046 .136 .206
.037 .160 —
.220 .460 .210
.280 .150 .253
1.26 1.01 7.00
2.26 —
percent for fascial/fasciocutaneous flaps from the extremities, and 30.8 percent for superficial temporal fascial flaps (see Table 3). The rate of complication was statistically significant at p < 0.04, when comparing muscle/musculocutaneous flaps harvested from the trunk with fascial/fasciocutaneous flaps.
Downloaded by: Universite de Sherbrooke. Copyrighted material.
Type of Flap
DISCUSSION Early experimental work by vascular surgeons on femoropopliteal vein grafts indicated a correlation between intraoperative graft blood flow, distal arterial outflow, and ultimate graft patency. Although not 100 percent predictive, decreased graft flow at the time of surgery often leads to early thrombosis and graft failure. Administration of vasodilators or ipsilateral lumbar sympathectomy often leads to increased graft flow with improved patency. These findings implicate increased arterial outflow resistance as a factor in decreased arterial flow and ultimately in thrombosis of vein grafts.3-6 Ascer and colleagues 78 developed a technique, similar to the one used in our study, that intraopera-
Fascia Scalp
197
JOURNAL OF RECONSTRUCTIVE MICROSURGERY/VOLUME 8, NUMBER 3
MAY 1992
30 -,
25-
20-
15o
10-
5-
M
0E+0 12.5
22.2 25.4 27.5 28.9 30.2 32.5
13.5 14.2
35
67
37.8
Resistance in mrnHg/ml/min Figure 3. Average resistance in different types of free flaps, with the number of each type of flap used in our study population (n = 175).
Table 3. Total free flaps Muscle and myocutaneous Total Trunk Extremity Composite bone and soft tissue Fascial and fasciocutaneous Total Trunk Extremity Temporoparietal fascia
Free Tissue Transfers in 175 Elective Microvascular Procedures Number
Uncomplicated
Salvaged
Lost
175
158 (90.3%)
7 (4.0%)
10 (5.7%)
96 66 30 27
90 60 27 24
(93.8%) (95.5%) (90.0%) (89.0%)
52 23 16 13
44 21 14 9
(84.6%) (91.3%) (87.4%) (69.2%)
tively measures total outflow resistance in patients undergoing lower-extremity arterial reconstructions. Findings established high-resistance measurements as reliable predictors of graft failure. In cases where intraoperative resistance measurements were high, the addition of a second branch graft to a second outflow artery improved patency by increasing outflow and decreasing vascular resistance. Applying these principles to microvascular surgery, we propose that decreased vascular resistance within the free flap itself has several benefits. Increased flow rates allow increased velocity of blood elements. In particular, there is decreased platelet ad198 hesion at the anastomotic site. Preventing platelet
3 2 1 1
(3.1%) (3.0%) (3.3%) (3.7%)
3 1 2 2
(3.1%) (1.5%) (6.7%) (7.3%)
3 (5.8%)
5 2 1 2
(9.6%) (8.7%) (6.3%) (15.2%)
0 1 (6.3%) 2 (15.4%)
adhesion and subsequent platelet aggregation decreases the incidence of anastomotic thrombosis and maintains anastomotic patency. Postoperative care of a free-tissue transfer is directed toward maximizing cardiac output and reducing systemic vascular resistance. Treatment includes warmth, hydration, and analgesia which, in the periphery, enhance vascular flow. Despite these manipulations, our data indicate that flaps with inherently higher vascular resistance thrombose more frequently, requiring reoperation for salvage, or ultimately fail; those with lower resistance heal without complications. We suggest that tissue selection for free-tissue
Downloaded by: Universite de Sherbrooke. Copyrighted material.
ua> S
VASCULAR RESISTANCE CONSIDERATIONS/SASMOR, REUS, STRAKER, COLEN
Downloaded by: Universite de Sherbrooke. Copyrighted material.
V
B
Figure 4. Similar anterior tibial wounds treated with two types of free-tissue transfer. A rectus muscle free-tissue transfer with split-thickness skin graft was used in 4A; a lateral arm fasciocutaneous flap was used in 4B. Both healed with good coverage.
199
JOURNAL OF RECONSTRUCTIVE MICROSURGERY/VOLUME 8, NUMBER 3
transfers should include consideration of the vascular resistance of the donor tissue. Selecting a hemodynamically favorable flap is a preoperative decision that can reduce resistance locally, allowing increased vascular flow in the region of the anastomosis. Many types of flaps can be used. However, the flap with the least resistance may prove to have fewer complications and lower failure rates than flaps of higher resistance (Fig. 4).
REFERENCES
Oliva A, Lineaweaver W, Yim K, etal: Long-term results following failed tissue transplantations: Fifteen-year experience with 49 failed transplants. Presented at the 6th Annual Meeting of the American Society for Reconstructive Microsurgery, Toronto, Canada, September 1990 Mannick ), lackson B: Hemodynamics of arterial surgery in atherosclerotic limbs: Direct measurement of blood flow before and after vein grafts. Surgery 59:713, 1966 Mundth E, Darling R, Moran J, et al: Quantitative correlation of distal arterial outflow and patency of femoropopliteal reversed saphenous vein grafts with intraoperative flow and pressure measurements. Surgery 65:197, 1969 Terry J, Allan J, Taylor G: The relationship between blood flow and failure of femoropopliteal reconstructive arterial surgery. Brit I Surg 59:549, 1972 Dean R, Yao I, Stanton P, Bergan J: Prognostic indicators in femoropopliteal reconstructions. Arch Surg 110:1287, 1975 AscerE.Veith F, Morin L, etal: Components of outflow resistance and their correlation with graft patency in lower extremity arterial reconstruction. I Vase Surg 1:817, 1984 Ascer E, Veith F, Morin L, et al: Quantitative assessment of outflow resistance in lower extremity arterial reconstructions. I Surg Res 37:8, 1984 Downloaded by: Universite de Sherbrooke. Copyrighted material.
1. Kasabian A, Siebert J, Shaw W, Colen S: Trends in free flap failure: A review of 43 free flap failures in 800 consecutive free flaps. Presented at the 6th Annual Meeting of the American Society for Reconstructive Microsurgery, Toronto, Canada, September 1990
MAY 1992
200
VASCULAR RESISTANCE CONSIDERATIONS
Downloaded by: Universite de Sherbrooke. Copyrighted material.
IN FREE-TISSUE TRANSFER ABSTRACT The closure of complex wounds is facilitated by microvascular free-tissue transfer. The greatest threat to the success of a free-tissue transfer is thrombosis of the microvascular anastomosis. Technical and pharmacologic advances have decreased the thrombogenic effect of abnormalities of a vessel's endothelial lining, and have decreased the coagulation ability of blood. Equally important to patency of the microvascular anastomosis is blood flow, which is inversely proportional to the total resistance provided by the microcirculatory beds downstream. Because different tissues possess different vascular resistances, some flaps may display more favorable hemodynamics than others. This study was designed to characterize vascular resistance, weight, volume, and surface area of the flaps available for transfer, and to identify favorable tissues for reconstruction from the standpoint of outflow resistances. Data were collected on patients undergoing free-tissue transfers and on experimental freetissue transfers harvested from canines and fresh cadavers. Results show that resistance is highest in fascial flaps, intermediate in composite bone and soft-tissue flaps, and lowest in muscle and musculocutaneous tissues. Resistance is lower in flaps harvested from the trunk, compared with those harvested from the extremities. The rate of microvascular complications increases as resistance within the flap increases. Muscle and musculocutaneous flaps harvested from the trunk have lower complication rates than fascial and fasciocutaneous flaps. Suggestions for choices of flaps are made, based on the inherent resistance in the various free flap tissues. Microsurgical free-tissue transfer is an established and reliable technique. Success rates in large series exceed 90 percent. Several factors influence the outcome of a free-tissue transfer.12 For example, increased experience lowers a microsurgeon's rate of flap failure. Also, the etiology of the defect seems to affect success, with failure occurring more frequently in traumatic wounds than in wounds resulting from congenital deformity or cancer ablation. Failure rates also vary with respect to the recipient site. The order of increasing failure rate by recipient site is upper extremity, breast, head and neck, and lower extremity. The most frequent cause of flap failure is anastomotic thrombosis. The donor tissue represents the vascular bed through which blood must flow after
passing the arterial anastomosis, prior to traversing the venous anastomosis. Different donor tissues (muscle, fascia, bone, and skin) might offer differing resistances to blood flow. High-resistance tissue might correlate with low blood flow and a higher rate of failure. This study examines the relationship between donor tissue, vascular resistance, and anastomotic complications in elective microsurgery.
MATERIALS AND METHODS STUDY POPULATION.
Between 1987 and 1989, 30
patients undergoing elective free-tissue transfer were enrolled in this study. There were 17 males and 13
Sections of General Surgery and Plastic and Reconstructive Surgery, Department of Surgery, Dartmouth-Hitchcock Medical Center, Hanover, New Hampshire, and Section of Plastic and Reconstructive Surgery, Eastern Virginia Medical School, Norfolk, Virginia Materials in this paper were presented at the Sixth Annual Meeting of the American Society for Reconstructive Microsurgery, Toronto, Canada, September, 1990 Reprint requests-. Dr. Sasmor, Section of Plastic and Reconstructive Surgery, Dept. of Surgery, Dartmouth-Hitchcock Medical Center, One Medical Center Drive, Lebanon, NH 03756 Accepted for publication lanuary 2,1992 Copyright © 1992 by Thieme Medical Publishers, Inc., 381 Park Avenue South, New York, NY 10016. All rights reserved.
195
females who ranged in age from 23 to 79 years (mean 47.5 years). Wound etiologies were: trauma (18 cases), cancer (9 cases), and neurotropic (3 cases). Additionally, 16 experimental flaps were raised in fresh cadavers and 17 flaps were raised in canines. MEASURING VASCULAR RESISTANCE. A flap with its pedicle was completely dissected and taken to the back table in the operating room. A solution of 50 cc of autologous blood, containing 100 U/ml of heparin and 30 mg/ml papaverine, was placed in an infusion pump (Fig. 1). Tubing A was attached to a pressure transducer and a digital pressure monitor, with the line zeroed to atmospheric pressure. Tubing B was connected to the largest intravenous catheter that could be easily accommodated by the donor artery. The flow rate was set at 1 cc/min and was allowed to flow until blood returned from the vein. Once venous return occurred, the transducer was allowed to equilibrate and a pressure reading was obtained from the monitor. The flow rate was then increased, the reading was allowed to equili-
MAY 1992
brate, and a pressure reading was taken. This procedure continued until physiologic pressures were achieved (not exceeding a mean pressure of 90 mmHg). The catheter was then removed and the artery freshened. The flap was transferred to the recipient site and the microvascular anastomosis was performed. The identical procedure was followed on the canine and cadaver flaps. However, normal saline with papaverine and heparin in the same concentrations was used instead of autologous blood to perfuse the cadaver flaps. CALCULATION OF RESISTANCE. Blood flow within the free-tissue transfer is a function of perfusion pressure and resistance within the tissue bed. Resistance was calculated using the hydraulic analogue of Ohm's law, R = P/F, where R = resistance (mmHg/ml/min), P = pressure (mmHg), and F = flow (ml/min). Resistance was calculated for each flap at each flow rate, and an average resistance was calculated. For statistical analysis, the chi-square test was used to compare resistances in different types of free flaps. APPLICATIONN TO SURGICAL OUTCOME.
Pressure transducer and monitor
TO evaluate
the significance of vascular resistance in a successful surgical outcome, we conducted a retrospective review of the results of 175 elective free-tissue transfers that were performed at the Dartmouth-Hitchcock Medical Center between 1983 and 1989. Flaps were defined as muscle/musculocutaneous, composite bone and soft tissue, and fascial/fasciocutaneous, and were further categorized based on donor site from the trunk, extremities, or scalp. Flap complications, including failures and reoperation for salvage, were noted.
RESULTS
Continuous infusion pump'
Free flap
196
Figure 1. Equipment for measuring vascular resistance in a free-tissue transfer. A constant infusion pump is connected to a pressure transducer and pressure monitor by "A," a saline-filled high-pressure tubing. Line "B" connects a 50 cc syringe with autologous blood containing heparin and papaverine from the infusion pump to an intravenous catheter secured in the donor artery of the freetissue transfer.
Average resistances were calculated for 13 types of free-tissue transfers and ranged from 12.5 mmHg/ ml/min to greater than 67 mmHg/ml/min. Table 1 lists each flap with its unique resistance value. Muscle and musculocutaneous flaps exhibited the lowest resistances, with composite bone and soft tissue constituting an intermediate level. Fascial/fasciocutaneous flaps yielded the highest vascular resistances. Flaps were grouped by site of harvest (Table 2). Donor tissue harvested from the trunk generated lower resistances than those harvested peripherally (Fig. 2). Statistical analysis of the clinical flaps showed a difference in resistances to the p < 0.04 levels, when muscle and musculocutaneous flaps harvested from the trunk were compared with the composite bone and softtissue flaps, along with the fascial and fasciocutaneous flaps harvested from the trunk and extremities. To evaluate the significance of the role that vascular resistance might play in successful surgical outcome, we referred to our larger group of 175 free tissue transfers. A variety of donor tissues were used to meet
Downloaded by: Universite de Sherbrooke. Copyrighted material.
JOURNAL OF RECONSTRUCTIVE MICROSURGERY/VOLUME 8, NUMBER 3
VASCULAR RESISTANCE CONSIDERATIONS/SASMOR, REUS, STRAKER, COLEN
Table 1. Average Resistances of Free Flaps TRAM Latissimus dorsi muscle Rectus muscle Serratus muscle Fibula and soft tissue Radial forearm Iliac crest and internal oblique muscle Dorsal thoracic fascia Gracilis muscle Scapular bone and soft tissue Iliac crest Lateral arm Temporal parietal fascia
Resistance in ntmtig/ml/min 12.5 13.5 14.2 18.4 22.2 25.4 27.5 28.9 30.2 32.5 35.0 37.8 67.0
Table 2. Distribution of Free Flaps by Category of Donor Site in 175 Elective Free Tissue Transfers Site Muscle/musculocutaneous Trunk Extremity Composite bone and soft tissue Fascial/fasciocutaneous Trunk Extremity Scalp
Number 66 30 27 23 16 13
the reconstructive requirements of diverse tissue defects (Fig. 3). Outcome was divided into three categories: flaps healing without complications; flaps with microvascular thrombosis requiring repeat operation for salvage; and flaps with microvascular thrombosis and flap failure (Table 3). An increase in microvascular complications was noted with the increase in vascular resistance. Complication rates were: 4.5 percent for muscle and musculocutaneous flaps harvested from the trunk, 11.1 percent for composite bone and soft tissue, 12.6
Figure 2. Average free flap resistances by category of donor tissue.
e per g Tissue .034
Resistance per cm2
—
.046 .136 .206
.037 .160 —
.220 .460 .210
.280 .150 .253
1.26 1.01 7.00
2.26 —
percent for fascial/fasciocutaneous flaps from the extremities, and 30.8 percent for superficial temporal fascial flaps (see Table 3). The rate of complication was statistically significant at p < 0.04, when comparing muscle/musculocutaneous flaps harvested from the trunk with fascial/fasciocutaneous flaps.
Downloaded by: Universite de Sherbrooke. Copyrighted material.
Type of Flap
DISCUSSION Early experimental work by vascular surgeons on femoropopliteal vein grafts indicated a correlation between intraoperative graft blood flow, distal arterial outflow, and ultimate graft patency. Although not 100 percent predictive, decreased graft flow at the time of surgery often leads to early thrombosis and graft failure. Administration of vasodilators or ipsilateral lumbar sympathectomy often leads to increased graft flow with improved patency. These findings implicate increased arterial outflow resistance as a factor in decreased arterial flow and ultimately in thrombosis of vein grafts.3-6 Ascer and colleagues 78 developed a technique, similar to the one used in our study, that intraopera-
Fascia Scalp
197
JOURNAL OF RECONSTRUCTIVE MICROSURGERY/VOLUME 8, NUMBER 3
MAY 1992
30 -,
25-
20-
15o
10-
5-
M
0E+0 12.5
22.2 25.4 27.5 28.9 30.2 32.5
13.5 14.2
35
67
37.8
Resistance in mrnHg/ml/min Figure 3. Average resistance in different types of free flaps, with the number of each type of flap used in our study population (n = 175).
Table 3. Total free flaps Muscle and myocutaneous Total Trunk Extremity Composite bone and soft tissue Fascial and fasciocutaneous Total Trunk Extremity Temporoparietal fascia
Free Tissue Transfers in 175 Elective Microvascular Procedures Number
Uncomplicated
Salvaged
Lost
175
158 (90.3%)
7 (4.0%)
10 (5.7%)
96 66 30 27
90 60 27 24
(93.8%) (95.5%) (90.0%) (89.0%)
52 23 16 13
44 21 14 9
(84.6%) (91.3%) (87.4%) (69.2%)
tively measures total outflow resistance in patients undergoing lower-extremity arterial reconstructions. Findings established high-resistance measurements as reliable predictors of graft failure. In cases where intraoperative resistance measurements were high, the addition of a second branch graft to a second outflow artery improved patency by increasing outflow and decreasing vascular resistance. Applying these principles to microvascular surgery, we propose that decreased vascular resistance within the free flap itself has several benefits. Increased flow rates allow increased velocity of blood elements. In particular, there is decreased platelet ad198 hesion at the anastomotic site. Preventing platelet
3 2 1 1
(3.1%) (3.0%) (3.3%) (3.7%)
3 1 2 2
(3.1%) (1.5%) (6.7%) (7.3%)
3 (5.8%)
5 2 1 2
(9.6%) (8.7%) (6.3%) (15.2%)
0 1 (6.3%) 2 (15.4%)
adhesion and subsequent platelet aggregation decreases the incidence of anastomotic thrombosis and maintains anastomotic patency. Postoperative care of a free-tissue transfer is directed toward maximizing cardiac output and reducing systemic vascular resistance. Treatment includes warmth, hydration, and analgesia which, in the periphery, enhance vascular flow. Despite these manipulations, our data indicate that flaps with inherently higher vascular resistance thrombose more frequently, requiring reoperation for salvage, or ultimately fail; those with lower resistance heal without complications. We suggest that tissue selection for free-tissue
Downloaded by: Universite de Sherbrooke. Copyrighted material.
ua> S
VASCULAR RESISTANCE CONSIDERATIONS/SASMOR, REUS, STRAKER, COLEN
Downloaded by: Universite de Sherbrooke. Copyrighted material.
V
B
Figure 4. Similar anterior tibial wounds treated with two types of free-tissue transfer. A rectus muscle free-tissue transfer with split-thickness skin graft was used in 4A; a lateral arm fasciocutaneous flap was used in 4B. Both healed with good coverage.
199
JOURNAL OF RECONSTRUCTIVE MICROSURGERY/VOLUME 8, NUMBER 3
transfers should include consideration of the vascular resistance of the donor tissue. Selecting a hemodynamically favorable flap is a preoperative decision that can reduce resistance locally, allowing increased vascular flow in the region of the anastomosis. Many types of flaps can be used. However, the flap with the least resistance may prove to have fewer complications and lower failure rates than flaps of higher resistance (Fig. 4).
REFERENCES
Oliva A, Lineaweaver W, Yim K, etal: Long-term results following failed tissue transplantations: Fifteen-year experience with 49 failed transplants. Presented at the 6th Annual Meeting of the American Society for Reconstructive Microsurgery, Toronto, Canada, September 1990 Mannick ), lackson B: Hemodynamics of arterial surgery in atherosclerotic limbs: Direct measurement of blood flow before and after vein grafts. Surgery 59:713, 1966 Mundth E, Darling R, Moran J, et al: Quantitative correlation of distal arterial outflow and patency of femoropopliteal reversed saphenous vein grafts with intraoperative flow and pressure measurements. Surgery 65:197, 1969 Terry J, Allan J, Taylor G: The relationship between blood flow and failure of femoropopliteal reconstructive arterial surgery. Brit I Surg 59:549, 1972 Dean R, Yao I, Stanton P, Bergan J: Prognostic indicators in femoropopliteal reconstructions. Arch Surg 110:1287, 1975 AscerE.Veith F, Morin L, etal: Components of outflow resistance and their correlation with graft patency in lower extremity arterial reconstruction. I Vase Surg 1:817, 1984 Ascer E, Veith F, Morin L, et al: Quantitative assessment of outflow resistance in lower extremity arterial reconstructions. I Surg Res 37:8, 1984 Downloaded by: Universite de Sherbrooke. Copyrighted material.
1. Kasabian A, Siebert J, Shaw W, Colen S: Trends in free flap failure: A review of 43 free flap failures in 800 consecutive free flaps. Presented at the 6th Annual Meeting of the American Society for Reconstructive Microsurgery, Toronto, Canada, September 1990
MAY 1992
200
