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.