1. The success or failure of a flap depends upon how it is designed.
2. An axial flap has a certain territory. This territory has also been called an angiosome and can include skin, fascia and bone.
3. At the watershed area between two territories of adjacent flaps lie small vessels which will dilate if the area is delayed (see chapter 12). This delayed area can then be included after a certain interval in the original design of the axial flap. The area of the skin over the shoulder, for e.g., can be incorporated in the delto-pectoral flap if the skin over the shoulder is delayed in the axis of the intercostals perforators which run across the chest.
4. If planning is poor, and extra territorial tissue is included in the flap without a delay that part of the flap will die. As it happens, more often than not, this part, farthest from the base is the most critical in the reconstruction and the purpose of the flap may not be achieved. Not only that, there may be a deleterious effect on the surviving part of the flap because of the necrotic tissue in the dead part of the flap if it is not removed quickly.
5. In a random flap where a proportion of the one (base) to one (length) is maintained the flap succeeds in most parts of the body. However empirically this one-to-one rule can be transgressed in some parts of the body like the face where blood supply is abundant. A superiorly based naso-labial flap of outrageous dimensions, such as 1-4 or 5 will survive without a specific vessel because numerous vessels cris-cross the face in all directions.
6. When flaps die their death is somewhat dependent on their type. A ‘free’ axial pattern flap either survives completely or dies fully depending upon whether the microvascular anatomosis is patent or not. If such an anastomosis is blocked the flap can still be salvaged after the flow is re-established across the anastomosis which should be done in a short time (usually not more than a period of four hours).
Prabha Yadav and her group from TMH Mumbai add that the salvage of a ailing microvascular anastomosis should be treated as an emergency because the chances of flap salvage are inversely proportional to the time elapsed from the advent of thrombosis.
7. Any delay in establishing a patent anastomosis is dangerous. A dying flap takes recourse to anaerobic metabolism in order to survive. But the anaerobic state has certain consequences such as an increase in the number of polymorphonuclear cells which exhibit a marked tendency to adhere to each other. The anaerobic state also gives rise to harmful derivatives of oxygen called free oxygen radicals and superoxides. There is a built in mechanism in the anaerobic tissue to overcome to some extent these two events. If perfusion gets re-established suddenly after a few hours, this mechanism is overwhelmed by a flow of fresh blood, the leucocytes get pushed into the capillary network and the capillary web gets clogged leading to more production of oxygen free radicals and the flap will die in a very short time. The event horizon of how soon this reperfusion injury will occur is not clear. A reperfusion injury is commonest in replanted limbs and large muscle flaps are more vulnerable in this regard than cutaneous flaps.
8. A clogged capillary network is beyond any remedy and there is very little or no evidence that a pharmacological intervention will help. In fact there is no unanimity about any anti-clotting agent helping anymore than saline when the anastomosis is in progress. The use of a heparin solution being sprinkled over the site of anatomosis has an empirical basis and its use is more a tradition than an act based on science.
9. The best time to save a free flap is on the table by waiting to see if the anastomosis is patent by maneuvers such as gentle pressing on both the arterial and the venous side, the latter more carefully, delicately and frequently because the venous side fails more often in view of its non-pulsatile flow.
10. The best practice is to leave the site of the anastomosis open and to suture the rest of the flap and wait. Occasionally even a tight suture might impede the flow and can be modified to reduce any effect that it may have on the circulation. The best practice is to leave the skin over the anastomosis open.
Prabha Yadav and her group from TMH Mumbai add that the lie of the anastomosed vessels should be checked in different positions particularly in the head and neck. If the anastomosis is placed over a joint, a kink or tension in the anastomosis can be avoided by proper splintage leaving the flap area open for observation. Also drains left behind under the flaps should be carefully placed so as not to impinge on the anastomotic site.
11. Notwithstanding a variety of very sophisticated methods being available to judge the viability of a flap, the pin prick test, though its interpretation is subjective (the colour of the blood that oozes out), continues to be fairly reliable for a vast number of cases. A failure of the anastomosis on the arterial side usually results in a white flap (instead of pink or pink-brown). A venous outflow block increases the percentage of reduced unoxygenated haemoglobin and the flap turns blue. On pin pricks therefore, a sluggish flow of blue or dark blood is seen. It is usually easy to identify a well perfused flap which on being pricked will reveal bright red blood flowing out. For obvious psychological reasons a surgeon might, because of wishful thinking, not admit to himself or herself that a flap is dying. A quick inspection of the anastomotic site after an adverse pin prick test is the best time for re-exploration. At this stage a dilute solution of heparin is frequently used to help to extract the clots from the vessels so as to prevent re-clotting.
Prabha Yadav and her group from TMH Mumbai describe a failed arterial anastomosis resulting in a shriveled flap due to loss of turgor and failed venous anastomosis resulting in a blue, dusky, bloated flap.
12. A flap is extremely vulnerable when a blood clot forms underneath. A snugly fitting flap, of whatever type has no place whatsoever for such a clot, nor for that matter even for its benign counterpart of an organizing seroma. The presence of a clot as it hardens (and it does) over a period of time puts an unsurmountable burden on the pressure head within the capillary network. This situation needs to be guarded against particularly when systemic heparin is used. If the defect over which the flap is placed has been debrided just prior to the placement of the flap, a very thorough haemostasis is crucial. The very nature of indications for flaps is such that many a time a bone is the base of the defect. A blood clot therefore can only press over its softer exterior (the flap). Even in staged flaps where a part of the defect remains open near the bridge of the flap, this clot can come to occupy the under surface of the flap by blocking the exit route early. An early diagnosis of such a clot and its release and extraction by removing a few sutures can dramatically alter the fate of the flap for the better. Occasionally the whole flap may need to be taken off, haemostasis achieved and then put back.
13. A blood clot is also known to release harmful oxygen radicals and therefore constitutes a double edged weapon. A clot that remains unrecognized is an excellent medium for organisms to grow, particularly because many indications for flap cover involve infected cavities which, a thorough debridement notwithstanding, are never really free of offending bacteria. An infected blood clot is like an abscess under the flap – not the best of the situations for a composite tissue which is recovering from a gross physiological insult only a few days earlier.
14. An axial or a random flap when cut on three sides becomes devoid of the bulk of its nerve supply. The local neurotransmitters therefore cause vasoconstriction as a protective response and this has maximum effect on the distal portion of the flap. Over the next couple of days in a properly designed and executed flap this gets reversed only if the base of the flap and the bridge (in a distant flap) remain in a state of ease. The base must be free of pressure, of dressings or a plaster or a splint (if used) and the bridge must neither be stretched nor rumpled on itself. The recipient site of the flap should ideally be higher than the base to aid venous drainage and the flap should not have any collection underneath. Any deviation from these conditions may adversely affect the return to normalcy from the early phase of vasoconstriction, particularly in the distal part of the flap.
15. A proper execution of the surgery itself is a matter of craft based on sound knowledge of anatomy and a familiarity with a particular procedure or flap. That as it may be, some flaps are more easily executed than others. A fascio-cutaneous flap in the upper or middle calf is a matter of an easy peel once the deep fascia is identified, cut and then fixed to the skin with stitches or staples to prevent separation. As opposed to this, in a groin flap where the vessel (superficial, circumflex, iliac) has left the femoral sheath earlier, and then travels in the fat between the two layers of the superficial fascia, the dissection needs to be undertaken carefully.
16. The same holds true of scalp flaps where the thin, innermost vascular layer of the pericranial tissue needs to be carefully preserved by identifying it because the defects in the scalp when flaps move are rarely ever amenable for primary closure, sometimes even after tissue expansion and will need to be skin grafted which will not be possible if bare bone gets exposed.
17. The nature of death of flaps is somewhat different for each type of flap. As mentioned earlier, a free flap belongs to the all or none category. It survives fully or can die quickly and in its entirety and has therefore no chance for revascularization from its bed in that short period. A random or an axial pattern flap moved locally or over a distance, particularly if it is thin and if the recipient bed on which it is put has even a modicum of potential for revascularization is at an advantage because within a matter of days cross vascularisation can begin. An axial flap unless it is very long or is based on skeletonised vessels also has a random supply at its base and therefore has a fighting chance to survive at least partly. A random flap with safe dimensions is the hardiest of them all but its dimensional restrictions mean its uses are restricted.
18. In an anecdote narrated to this author while this chapter was being written, about the preceding point, Prabha Yadav, the head of Oncological Reconstruction at Tata Memorial Hospital mentioned a case of an osteocutaneous (fibula) free flap transferred to the face, having survived for two weeks, then suffered a block at the anastomotic site in the neck due to a fulminating infection leading to sequestration of the fibula but the skin survived because by that time it had been neovascularised from the peripheral, facial skin.
19. Of the other factors that may adversely affect the outcome of flap surgery, long standing poor general health, atherosclerosis, diminished cardio respiratory function and an immunologically compromised patient constitute the standard candidates and they are not greatly different from the causes that adversely affect the take of a skin graft.
20. What stands out however is the habit of smoking, particularly if the habit has continued for several years, and though weaning prior to surgery is advisable, proper controlled scientific trials show that chronic smokers have a high rate of complications compared to non-smokers.
21. Seemingly adequate, but in fact histologically inadequate excision of malignant tumors also adversely affects healing of flaps and this is particularly so in cancers around the oral cavity where poor oral hygiene is an added factor and cannot really be improved prior to removal of the tumor.
22. A dead flap is best excised quickly. However, there is a rider to this rule in case of ‘non-free flaps’. This concerns what is perceived as a superficial loss after a few days. Such doubtful areas can be tangentially excised till the bed bleeds and then can be secondarily grafted. What is achieved can be quite remarkable because if the deeper tissues are already neovascularised and the graft takes, the original purpose of the flap is almost fully realized. Some months later the area can look quite unremarkable from the rest of the flap.
23. When a flap dies and is excised (even tangentially), it is best that the tissue is sent for a bacterial culture. Though not mentioned earlier, in spite of thorough debridement of recipient areas, if a bacterial culture has not been obtained at that time, and suitable antibiotics are not started, flaps can die due to infection because they are not entirely resistant by way of their own local, immune system.
24. This is particularly true in cases of trauma where a waiting period of two or three days is advisable after debridement and stabilization of fractures. There might be tissue in such a wound which is moribund but looks good to all outward appearances and dies in the period following debridement. A flap placed on such a tissue and sutured over it suffers doubly as it can be attacked by the infection already present and also has little chance of cross-vascularisation from this area.