The effect of hypothermia and tissue perfusion on extended myocutaneous flap viability

Importance of Postoperative Use of External Warming Devices in Flap Reconstructive Surgery

Flap failure, partial or complete, can have great negative impact on the patient and the reconstructive outcome. The effect of thermal regulation on flap survival is well recognized. This article focuses on the importance of external warming devices as a standard on postoperative flap care to avoid any temperature-related vascular compromise. PubMed, Medline, and EMBASE search had been performed. More than 60 papers have been reviewed. Out of them, that 29 references have been included in this review. The authors emphasize on the importance of strict postoperative flap temperature control with active warming devices as a standard of practice to minimize any related microcirculatory changes.

Flap warming improves intraoperative indocyanine green angiography (ICGA) assessment of perfusion. An experimental study

BACKGROUND

Indocyanine green angiography (ICGA) is slowly replacing conventional methods of evaluating perfusion during flap surgery. Microcirculatory changes during flap elevation create a marked state of hypoperfusion intraoperatively leading to ICGA underestimation of tissue viability and consequent resection of viable tissue. We propose a novel method of flap warming to induce maximum vasodilation before performing ICGA to increase accuracy in assessing perfusion.

METHODS

Submental flaps harvested on a single perforator were created in 8 pigs. ICG angiography was performed in the intraoperative phase (ICGA-C), after inducing maximum vasodilatation by warming the flap at 42 °C (ICGA-W) and at 24H postoperative (ICGA-24). By setting a fluorescence threshold of 33% as indicative of necrosis, the flap surface deemed viable by ICGA was measured for ICGAC, ICGAW and ICGA24. The results were then compared to the actual flap survival observed clinically at 7 days.

RESULTS

The mean of ICG-C predicted flap survival (FS-C = 49.17%) is 12.97% lower than the mean of actual flap survival on postoperative day 7 (FS = 62.14%). The mean difference between ICG-W and ICG-24 predicted flap survival (FS-W and FS-24) and actual flap survival in the postoperative day 7 (FS) is lower, 3.13% and 2.15%, respectively. Average perfusion recovery over 24 h was 10.83% (FS-24-FS-C).

CONCLUSIONS

Conventional intraoperative ICGA underestimated perfusion in all cases. Warming the flap intraoperatively and achieving maximum vasodilation mitigates the effects of vasoconstriction and mimics the microcirculatory environment encountered at 24 h. Performing angiography after induced vasodilation improves ICGA assessment of flap perfusion.

The experimental study of shunt-decompression arterialized vein flap

Background

Arterialized vein flap is a kind of unphysiological flap. Unphysiological reconstruction of blood circulation leads to higher load than that supported by physiological flap and is the culprit of flap swelling, blood stasis, skin blistering, and necrosis after flap grafting. To resolve the multiple disadvantages of traditional flap grafting, by introducing the principles of fluid mechanics, shunt-decompression surgery is prepared to decline the circulation preload and improve the prognosis of arterialized vein flap grafting.

Methods

By introducing the principles of fluid mechanics, we established the model of shunt-decompression arterialized vein flap, which satisfied the common properties of general fluid that the interface pressure between object and fluid is reduced when the velocity of fluid is increased and vice versa-the effect of Bernoulli. Under this rule, we anastomose the arterialized vein to the branch of main artery of recipient region or make end-to-side anastomosis, which can maintain the blood flow of main artery, decrease the perfusion of flap, and preserve the decompressive effect of main artery to branches. From March, 2016 to September, 2016, we performed animal experiments on ten male bama mini pigs with average weight of 28 ± 2.35 kg. Superior epigastric artery of pig was used for feeding artery to arterialize the superficial epigastric veins. The total area of flap is 8 cm × 6 cm. End-to-side anastomosis and end-to-end anastomosis were established in experimental group and control group, respectively. Doppler speckle perfusion imaging apparatus was used to monitor the alterations of flap perfusion, blood flow of flap, tissue swelling and survival of flaps.

Results

The average flap perfusion (PU) at 1 week after surgery is 83.62 ± 3.14 in experimental group and 98.14 ± 6.54 in control group, respectively (P < 0.05), indicating the significant reduction of flap blood perfusion in experimental group as compared with control group. As to the survival of flaps, 7 flaps completely survived, 3 showed partial necrosis, and no one was found as complete necrosis in experimental group, while only 3 flaps survived, and 4 flaps and 3 flaps showed partial necrosis and complete necrosis in control group, respectively (P < 0.05).

Conclusion

Based on the physiological features of arterialized vein flap and its problems in clinical application, we improved the anastomosis strategy of flap grafting and obtained excellent experimental outcomes, which provides an insight for the clinical application of arterialized vein flaps.

Current insights into extracorporeal perfusion of free tissue flaps and extremities: a systematic review and data synthesis

BACKGROUND

Extracorporeal perfusion is a promising new technique for prolonged preservation of free flaps and extremities; however, uncertainties on perfusion settings and efficacy still exist. No overview of literature is currently available. This review systematically appraised available evidence comparing extracorporeal perfusion to static storage.

MATERIALS AND METHODS

An electronic systematic search was performed on June 12, 2016, in MEDLINE and EMBASE. Articles were included when evaluating the effect of extracorporeal perfusion of free flaps or extremities compared to that of a control group. Two independent researchers conducted the selection process, critical appraisal, and data extraction.

RESULTS

Of 3485 articles screened, 18 articles were included for further analyzation. One article studied discarded human tissue; others were studies conducted on rats, pigs, or dogs. Perfusion periods varied from 1 h to 10 d; eight articles also described replantation. Risk of bias was generally scored high; none of the articles was excluded based on these scores. Tissue vitality showed overall better results in the perfused groups, more pronounced when perfusing over 6 h. The development of edema was a broadly described side effect of perfusion.

CONCLUSIONS

Although tissue vitality outcomes seem to favor extracorporeal perfusion, this is difficult to objectify because of large heterogeneity and poor quality of the available evidence. Future research should focus on validating outcome measures, edema prevention, perfusion settings, and maximum perfusion time for safe replantation and be preferably performed on large animals to increase translation to clinical settings.

Use of vacuum-assisted closure to maintain viability of a skin flap in a dog

CASE DESCRIPTION

A 4-year-old sexually intact male Labrador Retriever-Poodle mix was admitted to the hospital for treatment of a wound in the left thoracic region. The wound had been debrided and primary closure had been performed by the referring veterinarian 4 days previously.

CLINICAL FINDINGS

The dog had a 20-cm-long wound covered by a large flap of skin that extended caudally from the scapula over the left side of the thorax. A 3-cm defect was evident at the cranioventral aspect of the wound, from which purulent material was being discharged. The skin flap was necrotic, and the skin surrounding the flap was bruised. Signs of pain were elicited when the wound and surrounding region were palpated. Other findings, including those of thoracic radiography, were unremarkable.

TREATMENT AND OUTCOME

The wound was debrided, and vacuum-assisted closure (VAC) was initiated for 3 days until a healthy bed of granulation tissue developed. A reconstructive procedure was performed with a rotation flap 3 days after VAC dressing removal. The VAC process was reinitiated 2 days following reconstruction because of an apparent failing of the skin flap viability. After 5 days of VAC, the flap had markedly improved in color and consistency and VAC was discontinued. Successful healing of the flap occurred without the need for debridement or additional intervention.

CLINICAL RELEVANCE

Use of VAC led to a good overall outcome for the dog, with complete healing achieved. Additional evaluation of this technique for salvaging failing skin flaps is warranted in dogs, particularly considering that no reliable method for flap salvage in veterinary species has been reported to date.

Effect of prolonged ischaemic time on muscular atrophy and regenerating nerve fibres in transplantation of the rat hind limb

Our aim was to test the influence of cold ischaemia on replanted limbs, focusing on muscular atrophy and neurological recovery. Inbred wild-type and green fluorescent protein (GFP) transgenic (Tg) Lewis rats aged 8–10 weeks were used. The amputated limbs were transplanted at several cold ischaemic times (0, 1, 8, 12, 24, 48, and 72 hours). An arterial ischaemic model and a denervation model were used as controls. To study nerve regeneration, a GFP limb was transplanted on to the syngenic wild Lewis rat. These animals were evaluated histologically, electrophysiologically, and immunohistochemically. The longer the ischaemic time, the more evident was atrophy of the muscles. Electrophysiological investigation showed that the latency at 3 weeks was longer in the transplantation models than in the normal controls, particularly in the longer ischaemia group. Larger numbers of migrating Schwann cells were seen in the group with no delay than in the group that had been preserved for 12 hours. Ischaemia after amputation of a limb causes muscle cells to necrose and atrophy, and these changes worsen in proportion to the ischaemic preservation time. A delay in nerve regeneration and incomplete paralysis caused by malregeneration also affect muscular atrophy.

Reperfusion Injury

The restoration of blood flow to ischemic tissues causes additional damage, which is termed reperfusion injury. All tissues are susceptible to reperfusion injury, but this susceptibility varies between tissues. Reperfusion has wide clinical relevance. It influences the outcome of patients after myocardial infarction, stroke, organ transplantation, and cardiovascular surgery. Advances in the treatment of reperfusion injury have created an opportunity for plastic surgeons to apply these treatments to flaps and reimplanted tissues. The main putative mechanisms identified in animal models involve leukocyte-endothelium interactions, reactive oxygen species, and the complement system. However, it has become evident that these fundamental biological systems are controlled by many interrelated pathways. Attempts to bypass this complexity have led to a search for the early "upstream" initiating events, rather than the "downstream" cascading events. This contrasts with current clinical efforts that are directed toward hypothermia, intraarterial flushing, and preconditioning. This article outlines the molecular and cellular events that occur during reperfusion injury and then reviews the efforts that have been made to exploit this knowledge for clinical advantage.

Efeito do alopurinol e terapia com oxigênio hiperbárico em modelo de reimplante de membro após isquemia quente em ratos

OBJETIVO: A isquemia prolongada leva a alterações na microcirculação tecidual e liberação de radicais livres do oxigênio conhecidas como fenômeno de não reperfusão. Foi testado um modelo experimental de reimplante de membro após isquemia quente e os efeitos do fármaco alopurinol e da terapia com oxigênio hiperbárico. MÉTODO: Foram realizadas amputações com preservação dos vasos e nervos dos membros posteriores direitos em 95 ratos. Os grupos modelos M1, M2, M3, M4 e M5 foram submetidos à isquemia quente de 0, 2, 4, 6 e 8 horas. As taxas de viabilidade dos membros isquêmicos após sete dias de avaliação foram 100%, 80%, 63,6%, 50% e 20%. Os grupos experimentais E1 e E2 foram tratados, respectivamente, com alopurinol e terapia com oxigênio hiperbárico após isquemia de 6 horas. As taxas de viabilidade foram 70% e 30%. Os resultados foram analisados estatisticamente pelo teste do Qui-quadrado. RESULTADOS: Os grupos M1, M2, M3, M4 e M5 foram estatisticamente diferentes entre si exceto os grupos M3 e M4. E1 resultou em uma viabilidade de membros maior que M4 e E2 resultou em uma viabilidade de membros menor que M4(resultados estatisticamente significantes). CONCLUSÕES: Os resultados sugerem que a administração do alopurinol após isquemia do membro por 6 horas aumenta a taxa de viabilidade dos membros isquêmicos, e a terapia com oxigênio hiperbárico diminuiu a viabilidade dos membros isquêmicos.

Evaluation of primary critical ischemia time for the deep circumflex iliac cutaneous flap in cats

OBJECTIVE

To evaluate the primary critical ischemia time for the deep circumflex iliac (DCI) cutaneous flap in cats.

STUDY DESIGN

In vivo model.

ANIMALS

Thirteen young adult female cats.

METHODS

An island skin flap was created on the right side of each cat based on the angiosome of the ventral branches of the DCI vessels. The cats were randomly assigned to a flap ischemia time ranging from 1 to 3 hours in 10-minute intervals. Microvascular clamps were used to occlude the artery and vein for the designated time. Flaps were sutured into position after the ischemic period. On day 3, fluorescein dye was administered and the flaps were evaluated under ultraviolet light to assess percent area of perfusion. On days 7 and 14, the percent area of survival was determined for each flap based on cutaneous morphometry.

RESULTS

All flaps had 100 percent area of survival throughout the study. On day 3, all flaps fluoresced uniformly compared with the surrounding skin. On days 7 and 14, all flaps were uniformly viable as confirmed by skin color, consistency, bleeding, and hair re-growth.

CONCLUSION

The DCI cutaneous flap in cats can withstand up to 3 hours of ischemia with predictable survival.

CLINICAL RELEVANCE

In a clinical setting, high success rates can be expected with microvascular transfer of the DCI cutaneous flap in cats when the ischemia time is <3 hours and precise surgical technique is used.

Effect of hypothermia on blood-flow responses in pedicled groin flaps in rats

Cooling is widely used for preserving tissues such as kidneys before transplantation and for preserving extremities before replantation. Hypothermia has also been shown to be effective in the temporary storage of free flaps. However, in the intact living body, cooling can be damaging to tissue and the body system. We used a custom-designed clamping method (after flap elevation, occlusion and release of the flap-feeding artery) and continuous laser Doppler flowmetry to investigate the effects of hypothermia on blood flow and postocclusive reactive hyperaemia in the flaps. The animal model used was the partially elevated epigastric flap of adult Sprague-Dawley rats. In the hypothermia group (n=12), the core temperature and the flap temperature were allowed to fall during anaesthesia. At core temperatures of 34.58 degrees C and 338 degrees C and after rewarming of the rat, the feeding artery was occluded for 30 s and 120 s to observe the changes in blood flow and postocclusive reactive hyperaemia in the flap. In the control group (n=12), the core temperature was maintained at more than 378 degrees C throughout the experiment. To compare the flap blood-flow responses to occlusion of the femoral artery in the hypothermia group and the control group, the postocclusive reactive hyperaemia periods (i.e. blood flow above baseline after clamp release) were analysed. Statistical analysis of the responses showed that the magnitude (P=0.024), duration (P<0.001) and amplitude (i.e. peak flow) (P=0.037) of postocclusive reactive hyperaemia were significantly decreased in the hypothermia group. Our results suggest that hypothermia significantly decreases blood flow and postocclusive reactive hyperaemia in the rat epigastric flap. This may increase the risk of ischaemic flap complications unless rewarming is performed.

Effect of hypothermia on the ischemic and reperfused rat skeletal muscle, monitored by in vivo (31)P-magnetic resonance spectroscopy

The aim of this study was to compare the ischemic and postischemic energetic changes of rat skeletal muscle in response to hypothermia or room temperature, monitored noninvasively and continuously by in vivo (31)P-magnetic resonance spectroscopy ((31)P-MRS). A model of pedicled rat rectus femoris muscle was developed and analyzed by in vivo (31)P-MRS at a magnetic field strength of 2.35 T. Measurements were performed at three time points: before ischemia, after 4 hours of ischemia, and after 1 hour of reperfusion. Three groups were studied: (1) sham-operated rats (n = 6); (2) rats subjected to room temperature (24-26 degrees C, n = 6); and (3) rats subjected to hypothermia (9-12 degrees C, n = 6). Blood perfusion was measured by laser Doppler flowmetry (LDF). In the hypothermic group, phosphocreatine (PCr) recovered to 75% and adenosine triphosphate (ATP) to 86%; in the room temperature group, the recovery was 53% and 51%, respectively (P < 0.05). Skeletal muscle subjected to hypothermia (9-12 degrees C) was found to recover to a higher postischemic energetic level compared with skeletal muscle subjected to room temperature. Hypothermia appears to be a simple and effective method with which to reduce the damage related to ischemia and reperfusion.

Microcirculatory changes following different temperature washouts in a free flap model

In spite of the extensive experimental work on vascular washout in free flap surgery, an optimal temperature for the washout solution has not been established. This study was designed to determine the effect of the washout solution temperature on the degree to which the microcirculation is cleared of blood. The cremaster muscle flap in the rat was used, in which the microcirculation can be directly viewed and the presence of blood and perfusion parameters within various vessels can be measured during and after washout. Washout was started with a single, high-pressure infusion and continued at 130 mmHg for 15 minutes. The temperature of the washout solution was either 2-3, 20-22, or 35 degrees C. In all three groups, washout cleared the microcirculation almost completely within the first minute. However, we observed that a cold or room temperature washout cleared the microcirculation more completely than a warm washout did. The temperature of the washout solution did not effect post washout capillary perfusion and/or arterial diameters.

Cold storage of rat skeletal muscle free flaps and pre-ischemic perfusion with modified UW solution

We used the rat medial gastrocnemius free flap, based on a pedicle of the femoral artery and vein, in order to test the tolerance of skeletal muscle to cold ischemia-reperfusion (IR) injury, and to determine whether tolerance can be enhanced by pre-ischemic perfusion with tissue/organ preservation solutions. Muscle flaps (n = 6 per group) were subjected to variable periods of cold storage (0, 1, 2, 3, or 4 days) and 24-h normothermic reperfusion. Muscle viability, as determined by nitroblue tetrazolium (NBT) histochemical staining of viable mitochondria and supported by histological examination, was 100%, 26%, 11%, 4%, and 1%, respectively. Using 24-h cold storage/24-h reperfusion as the experimental conditions, groups of muscle flaps (n = 5 per group) were perfused immediately before cold storage with either modified, colloid-free University of Wisconsin (UW) solution, a solution described by Kohout et al. (Br J Plast Surg 1995;48:132-144) or normal saline. Perfusion with modified UW solution or Kohout's solution increased survival to 33% (P < 0.05) and 28% (not statistically significant), respectively, compared with the 19% viability of separate groups of nonperfused or saline-perfused controls. These findings indicate that cold-stored skeletal muscle is highly susceptible to cold IR injury and that the viability can be increased by prior perfusion with a tissue preservation solution such as modified UW solution.

Subzero nonfreezing preservation in a murine limb replantation model

This study was designed to examine the most effective temperature for hypothermic storage, without freezing, to prolong ischemic tolerance in an amputated murine hindlimb model. We measured freezing points in the calf muscle and the subcutaneous tissue of the foot in the amputated limbs of Fisher 344 strain male inbred rats. The highest freezing point was -1.5 degrees C, which was recorded in the calf muscle. To prevent freezing in any of the tissues in the amputated limb, the temperature for the lowest nonfreezing preservation was defined as -1 degrees C. The amputated limbs were preserved at subzero nonfreezing temperature (-1 degrees C) and at 4 degrees C for 4, 8, 12, 24, 48, and 72 h, and were then transplanted to other inbred rats by microsurgical techniques. We evaluated the vascular patency of the anastomoses by direct observation and performed histological examinations on the seventh day after replantation. Subzero nonfreezing preservation of a limb at -1 degrees C for 72 h was significantly superior to hypothermic preservation at 4 degrees C for 72 h in terms of anastomotic patency rates (P < 0.05). The histology of skeletal muscles preserved at -1 degrees C for 8 h showed greater similarity to the normal situation than the histology of those preserved at 4 degrees C for 8 h. Bone viability with osteoblastic activity was maintained in grafted limbs preserved at -1 degrees C for 72 h, but in the limbs preserved at 4 degrees C for 72 h the bone was not viable, showing no osteoblastic activity. Clinically, the period of ischemia in major limb replantation at normal ambient temperatures is limited to about 6 h. In this study, the maximum ischemia time for replantation of a limb containing muscle tissue was prolong to 8 h at -1 degrees C, but the maximum ischemia time at 4 degrees C could not be prolonged to 8 h. Our results suggest that, in the major replantation of a limb containing muscular tissue, hypothermic preservation at -1 degrees C would be more useful than preservation at 4 degrees C.

Mild hypothermia protects against ischaemia-reperfusion injury in rabbit skeletal muscle

In three groups of rabbits, the rectus femoris muscle was subjected to 4 hours of total ischaemia. In Group 1 (normothermia, n = 5) the core temperature was maintained within the range 36-38 degrees C for the duration of ischaemia. In Group 2 (total hypothermia, n = 5) the core temperature was allowed to fall to 31.5-33.5 degrees C. In Group 3 (muscle only hypothermia, n = 5) core temperature was maintained as in Group 1 but the muscle temperature was allowed to fall to 29.5-31.5 degrees C. After 24 hours of reperfusion the muscles were harvested and measurements made of muscle viability, oedema and myeloperoxidase content. The mean (s.e.m.) muscle viability of Group 1, 19.5 (3.8)%, was significantly less than that of both Group 2, 86.0 (2.0)%, and Group 3, 87 (4.1)%, (P < 0.001). Muscle oedema and myeloperoxidase levels were elevated in all experimental groups, but differences were not significant. These findings indicate that ischaemia-reperfusion injury in skeletal muscle in this model is highly temperature-sensitive, small reductions in muscle temperature during ischaemia providing significant protection against ischaemia-reperfusion injury.

Effect of ischemia and three different perfusion solutions on the rabbit epiphyseal growth plate

An isolated vascularized knee joint model was used (1) to determine the minimum ischemia time that produced growth retarding damage to the epiphyseal plate and (2) to evaluate whether intra-arterial perfusion could reduce the ischemia damage. Experiment 1 consisted of 31 rabbits in 5 groups: 0, 2,4,6, and 8 hr of warm ischemia produced by clamping the pedicle. Experiment 2 consisted of 18 rabbits in which 10 ml of one of (1) Euro-Collins, (2) University of Wisconsin solution, or (3) heparinized blood were perfused through the joint without ischemia. Experiment 3 consisted of 21 rabbits in which one of the three solutions was perfused for a short period during 6 hr of ischemia. Growth of the tibia was followed radiographically every month over 3 months, and the growth plates were evaluated histologically after sacrifice. Results showed that at least 6 hr of ischemia was needed before longitudinal growth was reduced; less ischemia time caused overgrowth. Histologic damage was found in all animals to some degree. Perfusion alone without ischemia had no detrimental effect on growth or histology. The growth reduction at 6 hr of ischemia was minimized by perfusion with every solution. Heparinized blood was the most effective and Euro-collins was the least effective.

The effect of hypothermia on changes in isometric contractile function in skeletal muscle after tourniquet ischemia

The effect of hypothermia on changes in contractile function of skeletal muscle observed after an episode of tourniquet ischemia has been investigated. Male Wistar rats were subjected to 2 hours of unilateral hypothermic (n = 33) or normothermic (n = 39) pneumatic tourniquet ischemia of a hind limb. Isometric contractile function was measured bilaterally from the gastrocnemius muscles after 1, 7, 14, 28, or 42 days of recovery. Compared to muscle subjected to normothermic ischemia, muscle that underwent hypothermic ischemia demonstrated more twitch tension at 1 day postischemia, higher maximum tetanic tension at all time periods, including 6 weeks after ischemia, and greater muscle weight at 6 weeks. Rat gastrocnemius muscle function is much better 1 day to 6 weeks after 2 hours of hypothermic ischemia than after 2 hours of normothermic ischemia. The results thus document the benefit of hypothermia during tourniquet ischemia in preventing or minimizing the changes in isometric contractile function observed after normothermic ischemia.

Anatomy and circulation of the canine skin

The skin of the dog has several anatomic differences from human skin. Skin thickness, hair growth, and circulation vary regionally in the dog and between breeds to some degree. Direct cutaneous arteries supply the canine skin. The deep or subdermal layer is closely associated with the panniculus muscle (where present) and should be elevated with the overlying skin during routine flap elevation or undermining procedures. Flaps in the dog elevated without inclusion of a direct cutaneous artery and vein have been termed subdermal plexus flaps to avoid confusing them with random flaps in the human based on musculocutaneous vessels. Axial pattern flaps developed for veterinary clinical use are discussed, several of which have potential for free flap transfer in cutaneous reconstructive surgery.

Major limb replantation in children

This retrospective study evaluated patients under 18 years of age who underwent major limb replantation between 1976 and 1989 at Louisville Hand Surgery. The age of the 15 patients followed for between 1 and 8.5 years (mean 4.2 years) ranged from 2 to 17 years (mean 9.8). Of amputations, 40% were guillotine, 40% were limited crush-avulsions, 7% were extended crushing, and eight were of an upper extremity and seven of a lower extremity. Average warm/total ischemia times were 4.8/14.8 hr in failures and 1.1/7.5 hours in successful replantation. Overall limb survival was 87%. Among the patients, 93% felt that their replanted limb functioned and looked better than a prosthesis; 87% of patients had a sensory recovery of more than S2+ in the lower extremity or S3 in the upper extremity; and 38% of upper extremity replantation patients had two-point discrimination of less than 15 mm.

Magnetic resonance imaging for detection of arterial and venous occlusion in canine muscle flaps and bowel segments

Magnetic resonance imaging (MRI) was performed on 16 muscle flaps and eight jejunal segments in dogs to assess its usefulness in detecting vascular occlusion. Arterial or venous occlusion was carried out in 11 muscles and six bowel segments, with the remaining sham flaps serving as controls. Imaging was performed over 2 hours using a spin echo pulse sequence with T2 weighting. Arterial occlusions in muscles resulted in T2 values 15-30% higher than controls, while venous occlusion produced T2 values 55-75% higher than controls. Differences became significant (p less than 0.05) at 10 minutes after venous occlusion and at 35 minutes after arterial occlusion. Differences between occluded and control bowel segments, although demonstrating a similar trend, failed to reach statistical significance in this preliminary study. The authors conclude that magnetic resonance imaging may be a valuable method for early detection of venous and arterial occlusion in muscle flaps. Further study may also demonstrate this technique to be useful in the diagnosis of ischemic bowel.

A comparison of the cutaneous trunci myocutaneous flap and latissimus dorsi myocutaneous flap in the dog

Latissimus dorsi and cutaneous trunci myocutaneous flaps of equal dimension and location were randomly elevated on opposite sides of the thorax in 10 dogs (group 1) and resutured to their respective bed. The procedure was repeated in four additional dogs (group 2); however, the short perforating branches of the thoracodorsal artery and vein were divided at the base of each cutaneous trunci myocutaneous flap, whereas the cutaneous pedicle and underlying cutaneous trunci muscle were divided in the latissimus dorsi myocutaneous flaps to determine subsequent skin survivability and the major source of circulation of each myocutaneous flap. There was little difference in the percentage of skin survival between the latissimus dorsi and cutaneous trunci myocutaneous flaps in group 1 dogs. Circulation to the "skin island" of group 2 latissimus dorsi myocutaneous flaps originated from intramuscular anastomotic connections between the major branch of the thoracodorsal artery entering the latissimus dorsi muscle and the proximal lateral intercostal arteries perforating the muscle. Ligation of the short perforating branches of the thoracodorsal artery resulted in partial skin necrosis in all group 2 cutaneous trunci myocutaneous flaps. Results from this study indicate that it is unnecessary to elevate the latissimus dorsi muscle for major skin flap elevation and survival. The thicker latissimus dorsi myocutaneous flap is more difficult to develop surgically and appears to have no clinical major advantage over the more mobile cutaneous trunci myocutaneous flap or the adjacent thoracodorsal axial pattern flap for closure of large skin defects within the radius of flap rotation.

The effect of perfusion on post-operative viability in the replanted rabbit ear: measured by laser Doppler flowmetry and skin temperature

The effect of perfusion by heparinized Ringer solution on post-operative microcirculation in rabbit ear replants was studied. One ear in each of five rabbits was replanted after perfusion with heparinized Ringer solution and these were compared with five replantations of rabbit ears without perfusion. The ears were studied post-operatively for 2 1/2 days by skin temperature monitoring and Laser Doppler Flowmetry (LDF). During the first day after replantation the perfused ears had better capillary flow, whereafter no significant differences were noted. LDF was more sensitive to changes in capillary blood flow, and this seems to make the reproducibility of LDF poor. It is, however, a suitable method for continued observation of post-operative viability.

The effect of temperature on blood flow in island and free skin flaps: an experimental study

Skin blood flow is especially susceptible to temperature change, as the skin has an important role in body thermoregulation. The effect of temperature on blood flow in an experimental skin flap model in the dog has been measured using an electromagnetic flowmeter. the flap blood flow varied directly with temperature. In the range 22 degrees C-38 degrees C, this relationship was linear, the increase in the flap blood flow being 3.41% per degree Celsius. However, outside this temperature range the change was much greater.