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. This evidence concerns the gene GSTM1 and obstructive sleep apnea syndrome.