Safety Study of Analgesia After Craniotomy Surgery With End Tidal (ET) Carbon Dioxide (CO2) Monitoring

Inclusion Criteria: * Adult male and female, English speaking patients undergoing supratentorial craniotomy for tumor under general anesthesia at the Johns Hopkins Hospital will be eligible for this study. Exclusion Criteria: * pregnant women * patients with post operative neurological changes * patients who remain intubated post-operatively * patients who require the use of concomitant administration of sedatives * patients who are unable to initiate a PCA bolus * patients who are unable to communicate verbally * patients who are allergic to fentanyl * patients who have a history of narcotic abuse * patients who have a history of chronic pain requiring opioids * patients who have been in any investigational drug trial within 1 month of the treatment day * patients who have chronic respiratory insufficiency