Materials and methods
This retrospective study investigated a cohort of head and neck patients who underwent oncologic resection and free tissue transfer between January 2017 and July 2019 at a quaternary referral unit in Sydney, Australia. Following institutional ethics approval (HREC/X20-0337/LH20.074), patients were identified using the prospectively maintained Sydney Head and Neck Institute (SHNCI) database and included if they had undergone primary or secondary free flap reconstruction. Patients were excluded if operative time was not recorded. Operative time data was collected for each patient and was defined as the time interval between entering and leaving the operating room. Operative time was analyzed as a continuous variable (number of hours) and dichotomized based on the mean.
Potential confounders assessed included patient gender, age, American Society of Anesthesiologists (ASA) classification, Charlson comorbidity index (CCI), tumor site, elective tracheostomy, defect type (mucosal or cutaneous), reconstruction type defined as fasciocutaneous (soft tissue) or composite (osseo-cutaneous, myo-osseous, myo-cutaneous), osseous resection (mandibulectomy, maxillectomy, craniectomy or temporal bone resection), prior radiotherapy or head and neck surgery.
Outcomes of interest were complication rate, return to theatre (operating room), and length of stay, defined as the number of inpatient days including the day of surgery. Complications were divided into medical and surgical. Medical complications included myocardial infarction, pneumonia, pulmonary embolism, urinary tract infection, stroke, deep vein thrombosis, sepsis, and renal insufficiency. Surgical complications included both recipient site and donor site complications, flap loss (partial or total), wound infection, wound dehiscence, orocutaneous fistula, and hematoma as well as any event necessitating return to theatre.
Statistical analysis was performed using Stata version 12.0 SE (StataCorp LP, College Station, TX, USA). Complication rates and return to theatre were analyzed using univariable and multivariable logistic regression and presented as odds ratios (OR) and confidence intervals (CI). Length of stay was analyzed as count data using a negative binomial regression. Operative time was included in all multivariable models as the intervention of interest. Covariates were selected based on statistical significance on univariable analysis, however patient age and comorbidity scale were included a priori . The choice of comorbidity scale (ASA or CCI) was determined by statistical significance. Continuous variables were transformed where required. A p-value < 0.05 was considered statistically significant.