The proposed study is a pilot prospective, single-blinded, randomized controlled trial evaluating the effects of two routine, standard-of-care, anesthetic techniques on natural killer cell population size and cytotoxicity in patients undergoing exploratory abdominal laparotomies.

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.