Effects of Anesthetic Technique on NK Cells

Inclusion Criteria: * 18 - 80 years old of either gender * Diagnosis of abdominal tumor scheduled for exploratory laparotomy with study surgeon * Must be able to have an epidural Exclusion Criteria: * ASA IV and above * Intolerance, allergy, or contraindication to use of either fentanyl or bupivacaine. * Significant coronary artery disease (abnormal stress test, myocardial infarction within the last 3 months) * Uncontrolled hypertension (BP \> 140/90) * Cardiac arrhythmias particularly prolonged QT syndrome * Drugs known to cause prolonged qT: class IA antiarrhythmics (quinidine, procainamide, dysopyramide), class III antiarrhythmics (sotalol, dofetalide, ibutalide, amiodarone), haloperidol, thioridazine, arsenic trioxide, HIV protease inhibitors, tricyclic antidepressants * Individuals with significant psychological disorders including: schizophrenia, mania, bipolar disorder or psychosis * Pregnant or lactating women * Morbid obesity (BMI \> 40 kg/m2) AND/OR weight \> 150 kg * Chronic renal failure ( creatinine \> 2.0 mg/dL) * Liver failure e.g., active cirrhosis * Alcohol or substance abuse within in the past 3 months * Uncorrected hypokalemia, hypomagnesemia, hypocalcemia (can be due to diuretics, mineralocorticoid use, laxatives) * Neuropathic pain * Chronic opioid consumption (\>30mg oxycodone or greater per day) * Cachexia from any cause * Systemic use of corticosteroids for greater than 2 weeks in the 6 months prior to surgery * HIV or other immunosuppressive condition * Preoperative INR \> 1.4 or platelet count \< 100 * Sepsis or overlying skin cellulitis at epidural catheter insertion site * Inability to tolerate/unwillingness to have an epidural catheter for intraoperative/postoperative pain control for any reason, including prior back surgery resulting in distorted anatomy that precludes neuraxial anesthesia. * Inability to tolerate an epidural solution of either fentanyl or bupivacaine or needs another form of specialized pain control.