A study of perfusion of the distal free TRAM flap and not as a tool to assist in the trimming of questionable parts of a flap during surgery. The probable reason for this is that the flap is still in its acclimatization process during the course of the surgery. Nevertheless, the LDF proved to be a valuable method for monitoring the flap postoperatively for arterial occlusion due to the instant drop in LDF values, as was shown in two cases in this study. In an investigative setting the LDF was a valuable and non‐invasive tool to investigate ischemia‐related changes that occurred in zones I and IV. Compared to zone I the slow initial increase in microcirculatory blood flow in zone IV was followed by the steep increase on the second/third day (Figure 4.4). The low blood flow values in zone IV during the first measurements can be explained by Heitmann's26 fresh cadaver perfusion study where little or no staining of zone IV was found. Clinical perfusion studies by Holm et al.22 also confirmed the poor perfusion of zone IV during the operation. Both studies demonstrated poor arterial blood flow of zone IV through the deep inferior epigastric artery. An even larger obstacle may be the insufficient venous drainage of zone IV.27 These studies explain why survival of the zone IV portion of such flaps is so variable and unpredictable. The probable reason for this is that with the TRAM or DIEP flap with zone IV more than one adjacent angiosome of the selected deep inferior epigastric artery is included. Experimental and clinical studies have shown that when a flap is based on one artery, the anatomic territory of the adjacent artery can safely be included and that necrosis tends to occur if tissue is included beyond this territory.28,29 Blood flow in distal part of a flap, such as zone IV in the free TRAM flap, becomes dependent on connecting arterial and vein branches between the angiosomes. Our study shows poor perfusion of zone IV demonstrated by the low‐ischemic LDF values measured in zone IV during surgery (Figure 4.5). However all patients, with the exception of one with FC>10%, showed an increase in blood flow through zone IV with the steepest increase on the second to third day (Figure 4.3). This phenomenon cannot be explained by angiogenesis due to the short time elapse. It can only be explained by a dilatation or opening of existing (choke) vessels within the flap itself.30,31 This confirms the results of animal studies in which the progressive dilatation was shown, which was seen maximally at the level of the choke vessels. An accelerated rate of choke vessel dilatation was consistently seen between 48 and 72 h after surgery in these studies.30,32 Therefore the viability of zone IV depends on the number and dilatation time of the choke vessels. The dilatation of these choke vessels may be a target for possible interventions.31 Stimulating nitric oxide (a potent vasodilatator) availability has been shown to increase flap survival.33,34,35 Another possible mechanism may be to protect the tissue at risk until blood flow in the flap is sufficient to sustain viability.36 However, clinical studies have not been performed so far. The clinical relevance of these findings is that zone IV may be included in reconstructive surgery; however, patients' risk factors such as smoking should be noted. Smoking may impair the dilatation of the choke vessels, and proved to be a significant risk factor in 65
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