This research is being done to compare two methods of giving fentanyl, a narcotic often given to patients following brain surgery and determine if one method has more side effects than the other. Both of these methods are available in the postoperative treatment of pain. This research also is being done to determine if patients receiving narcotic pain medicine will benefit from additional monitoring of carbon dioxide levels. Since narcotic pain medicines can slow down breathing, The investigators want to see if measuring exhaled carbon dioxide levels will help identify a slower breathing rate and improve safety.

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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

Adverse events were collected over the course of patient enrollment in the Neurosciences Critical Care Unit, within 24 hours of surgery.