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Background: The viability of microvascular free flaps depends upon various patient-based factors. The objective of this study was to identify patient factors that contribute to an increased risk of flap failure.
Methods: The American College of Surgeons National Surgical Quality Improvement Program database (ACS-NSQIP) was queried for all patients who underwent microvascular free tissue transfer from 2005 through 2012. Patients were identified by CPT code: 15756 (free muscle or myocutaneous flap with microvascular anastomosis), 15757 (free skin flap with microvascular anastomosis), 15758 (free fascial flap with microvascular anastomosis), and 19364 (breast reconstruction with free flap). Univariate analysis was performed to identify the association between free flap failure and the following factors: age, gender, race, body mass index (BMI), diabetes, smoking, alcohol, hypertension, intraoperative transfusion, functional health status, American Society of Anesthesiologists classification, operative time, and flap location. Factors yielding a significance of p <0.20 were included in multivariate logistic regression models in order to identify independent risk factor significance for flap failure. Furthermore, cases were stratified based upon recipient site (breast, head and neck, trunk, or extremity), and analysis was repeated in order to identify risk factors specific to each location.
Results: 1921 of 2103 patients who underwent microvascular free flap reconstruction met inclusion criteria. Univariate analysis of all free flaps yielded a significant association (p<0.05) between free flap failure and the following factors: gender, diabetes, alcohol, amount of intraoperative blood transfusion, ASA classification, and BMI. Multivariate logistic regression identified BMI as an independent variable associated with flap failure (Adjusted Odds Ratio = 1.078, p=0.006).
Conclusions: With specific regard to free tissue transfer used for breast reconstruction, BMI and smoking were identified as significant factors associated with flap failure. Multivariate logistic regression also identified BMI (AOR=1.08, p=0.035) and smoking (AOR=3.522, p=0.026) as significant independent risk factors associated with flap failure within this subset. Regarding head and neck flaps, univariate analysis identified a significant association with preoperative diagnosis of diabetes, volume of intraoperative blood transfusion, and operative time. Multivariate logistic regression identified operative time (AOR = 1.003, p=0.041) as a significant independent risk factor for flap failure in this subset. Regarding reconstruction of extremity defects, univariate analysis identified diabetes and hypertension as significant factors associated with flap failure. Multivariate logistic regression, however, did not identify any independent variables associated with flap failure. “Trunk flaps” accounted for the smallest subset of microvascular flaps. Risk factors were not identified this subset of patients. BMI was identified as an independent risk factor for flap failure among all microvascular free flaps and within the “breast flaps” subcategory. Smoking additionally was identified as an independent risk factor within “breast flaps.” Finally, increased operative time was a risk factor for flap failure among “head and neck flaps.”

Frequency of microvascular free flaps

Flap Classification	Number (%) of all flaps	Age (in years)	Failure rate
Breast flaps	1313 (68.4)	50.3	1.75
Head and neck flaps	472 (24.6)	61.6	2.75
Extremity flaps	127 (6.6)	48.7	2.4
Trunk flaps	9 (0.5)	54.9	0
All flaps	1921 (100)	53	2.0

Adjusted Odds Ratio of Flap Failure - Multivariate Analysis

Flap Classification	Risk Factor	Adjusted OR (95% C.I.)	Adjusted p-value
All flaps	Body mass index	1.078 (1.02-1.14)	0.006
Breast flaps	BMI and smoking	1.08 (1.01-1.16) 3.522 (1.16-10.70)	0.035 0.026
Head and neck flaps	Operative time	1.003 (1.00-1.01)	0.041