The covariates included age, BMI, hemoglobin (Hb), length of stay (LOS), duration of surgery, sex, ethnicity, American Society of Anesthesiologist (ASA) Status, smoking, obstructive sleep apnea (OSA), diabetes mellitus (DM), DM on insulin, ischemic heart disease (IHD), congestive cardiac failure (CCF), cerebrovascular accident (CVA), creatinine > 2 mg/dl, day of week of operation. The gene discussed is GSTM1; the disease is clubfoot.