| BackgroundTo date,the flap partial or total necrosis continues to be the most major complications following the pedicled island perforator flap transfer and is also a difficult challenge for the surgeon.How to improve the pedicled flap survival area is one of the difficult problems to be solved.Currently,the international academic community considered that the pedicled flap necrosis is not only associated with the anatomical characteristics of the flap itself but also related to some patient-dependent high-risk factors.The flap necrosis often occurs the choke zone between the adjacent angiosomes.If the linking patterns between the adjacent angiosomes within the proposed flap are the reduced-caliber choke anastomosis vessels,it is necessary to first perform a or multiple preliminary and strategic flap delay procedure to convert them into the true anastomotic vessels to increase the flap survival area.Flap surgical delay has been demonstrated to be a reliable and effective technique to improve the flap survival area.The histology basis of flap surgical delay effect——the dilation of the choke vessels and neovascularization——has been demonstrated.The dilation of choke vessels occurs dramatically between 48 and 72 hours following flap surgical delay and is a permanent and irreversible event;vascular endothelial growth factor(VEGF)can promote new vessels formation gradually,the immature new vessels gradually degenerate in the absent of VEGF.Those suggest that once flap delay period missed the optimal delay time,flap survival area cannot maximize.Thus,the conventional method delay time for assessing the maximum delay effect of the flap existed many shortcomings.It is of paramount for the surgeon to establish an objective,visualized and individualized criteria for evaluating the linking pattern between the adjacent angiosomes and predicting the maximum delay effect of the flap.Currently,most studies regarding risk factors of flap necrosis have focused on the risk factors of pedicled flaps of the lower extremity and free flaps.The study of the risk factors of pedicled flap necrosis is a controversial issue.Therefore,the risk factors of pedicled flap necrosis are still further studied and demonstrated.In addition,with regard to the tools of the perforator location and flap perfusion evaluation,hand-held acoustic Doppler ultrasonography can only assess the location of perforator;color duplex Doppler ultrasonography can determine the flow information,but cannot assess the linking patterns between the adjacent angiosomes and flap monitoring;Although computed tomographic angiography has high accuracy for the location of perforating,it cannot provide blood flow information,and has some disadvantages such as ionizing radiation,contrast agent allergy,intravenous contrast agent;magnetic resonance angiography has the disadvantages of long image acquisition time,intravenous injection contrast agent;although indocyanine green angiography can evaluate the perfusion of the skin flap,it has the shortcoming of intravenous contrast agent;dynamic infrared thermography has the advantages of noninvasive,evaluating skin flap perfusion,high precision of the location of perforating and inexpensive cost.ObjectiveBased on the above-mentioned research background,there are three purposes in this study.First,examining the usefulness and effectiveness of infrared(IR)thermography in visualizing the dilation of the choke vessels in a rat flap model.Second,to study the changes characteristics of infrared thermal imaging after flap surgical delay and to establish a sensitive and objective method for predicting the maximum delay effect via an IR thermography in a rat flap model.Finally,to identify the non-technical risk factors contributing to the pedicled island flap necrosis in the reconstruction of extremities.Material and MethodsFirst,a three-territory island flap was designed on one side of the rat dorsum.According to IR thermal imaging and the dorsum cutaneous vascular anatomy,the flap donor was divided into five regions from the cranial to caudal: the thoracodorsal(TD)angiosome,TD-PIC choke zone,posterior intercostal(PIC)angiosome,PIC-DCI choke zone and deep circumflex iliac(DCI)angiosomes.Surgical delay was performed by the ligation of the PIC perforator after raising the pedicled island flap.The study was divided into the normal group(n=8)and delay group(n=20).In the normal group(n=8),IR thermal images were correlated with the postmortem arteriograms with regard to the location of angiosomes,linking patterns.In the delayed group(n=20),the IR thermal imaging of the delay flap at different time intervals(1-day,2-day,3-day and 4-day delay period)was compared with that of the normal group in terms of the link pattern and temperature.Second,a rectangular three-angiosome flap was designed on the unilateral dorsum of the rat.A total of ninety-six rats were randomly grouped into 6 groups according to the various delay time: normal group and delay group(3-day,5-day,7-day,9-day and 11-day delay period).Evaluation of flap perfusion based on IR thermography,arterial density on the arteriograms,number of vessels >0.1mm in diameter,microvessel density and VEGF concentration were measured in the post-delayed flap.In addition,post-delayed flap viability was assessed with the flap survival area percentage.The sensitivity and specificity of the conventional method delay time for assessing the maximum delay effect of the flap were examined.Receiving operating characteristic(ROC)curve with the highest Youden-Index was used to identify the diagnostic standard for evaluating the flap maximum delay effect by means of an individualized and visualized infrared thermal imaging method.Also,the sensitivity and specificity were examined.Third,based on the inclusion criteria of the patients,a detailed review of hospital records was performed.Accordingly,228 patients were included in this study.Preoperative patientdependent characteristics,intraoperative records and postoperative wound infection were collected and analyzed as the risk factors of flap necrosis.Univariate analyses and multivariate Logistic regression analyses were used to identify the risk factors for the pedicled island flap necrosis.ResultsFirst,the postmortem arteriograms showed that the true anastomotic vessels were direct connection among the branches of adjacent artery perforators,whereas the choke anastomotic vessels were interrupted connection.The IR images have a temperature to color code scale with the white end of the scale representing warmer temperatures and the blue end representing colder temperatures.IR thermal imaging showed that a white hotspot existed on the surface of each angiosome;the true anastomotic vessels manifested a continuous white band linking the white hotspots on angiosomes,whereas the choke vessels presented a red zone in between the adjacent hotspots.After delay,the dilation of the choke vessels manifested itself as the replacement of the red zone between adjacent hotspots by the white band on IR thermography.Second,compared with the normal group,the surface temperature of the post-delayed overall flap increased significantly at the 3-day,5-day,and 7-day delay,but no significant difference in the 9-day and 11-day delay;since the 3-day delay,no significant difference in the relative temperature was detected among the angiosomes and choke zones;the surface temperature distributed evenly over the post-delayed flap.Since the 3-day delay,arterial density of choke zones,the number of vessels > 0.1 mm in diameter and VEGF concentration increased significantly compared with the normal group,but no significant difference was detected among the angiosomes and choke zones.Since the 5-day delay,the microvessel density increased significantly compared with the normal group,and no significant difference was found among the angiosomes and choke zones.Over delay time,there was no significant change in arterial density and the number of vessels > 0.1 mm in diameter;instead,both the microvessel density and VEGF concentration declined significantly.The maximum survival area percentage of the post-transferred flap occurred in the 5-day delay group(96.9%).There was a decreasing tendency of the survival area percentage to the delay time.The case with the maximum delay effect could be seen in all delay groups despite most common in the 5-day delay group.The sensitivity and specificity of the conventional methods delay time for evaluating the maximum delay effect were 38.5% and 90.9%,respectively.The sensitivity and specificity of individualized and visualized infrared thermal imaging method for evaluating the flap maximum delay effect were 84.6% and 77.3%,respectively.Third,the overall complications rate was 21.93%,including partial flap necrosis(10.09%)and total flap necrosis(5.70%).Postoperative wound infection rate was 14.91%.The results of multivariate logistic regression analyses suggested that flap area(OR=1.010,95% CI1.003-1.017,P=0.005)and postoperative wound infection(OR=17.707,95%CI6.300-49.762,P<0.001)were statistically significant risk factors for pedicled island flap necrosis in extremity reconstruction.Preoperative contamination of the wound bed(OR=18.481,95%CI 6.131-55.705,P<0.001)was a statistically significant risk factor for postoperative wound infection.ConclusionsFirst,IR thermography can accurately identify the linking patterns between the adjacent angiosomes and visualize the process of the dilation of choke vessels after a surgical delay.Second,visualized and individual infrared thermal imaging method can accurately predict the flap maximum delay effect,the diagnostic standards of which were described as follow:(1)after a surgical delay,the red area representing colder temperatures in between the adjacent angiosomes converted into the white area representing warmer temperature,and the post-delayed flap formed a larger white area;(2)the optimal cut-off point of relative temperature ratio was ?1.17,and the sensitivity and specificity were 84.6% and 77.3%,respectively.In addition,the maximum delay effect occurs as a result of the optimization of vasodilation and neovascularization after a surgical delay.Third,the flap area and postoperative wound infection were both independent risk factors for pedicled island flap necrosis in extremity reconstruction.Preoperative contamination of the wound bed was a major reason of postoperative wound infection. |
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