• Complete response (no PONV and no use of rescue medication) during the first 24 hours following anesthesia [ Time Frame: 1-24 hours post-operatively ] [ Designated as safety issue: No ]
  

• Nausea during the first 24 hours following anesthesia [ Time Frame: 1-24 hours post-operatively ] [ Designated as safety issue: No ]
  
• Vomiting during the first 24 hours following anesthesia [ Time Frame: 1-24 hours post-operatively ] [ Designated as safety issue: No ]
  
• Proportion of patients who use rescue medication during the first 24 hours following anesthesia [ Time Frame: 1-24 hours post-operatively ] [ Designated as safety issue: No ]
  
• Post Anesthesia Care Unit (PACU) length of stay (Phase I, Phase II) [ Time Frame: hours post-operatively ] [ Designated as safety issue: No ]
  
• Incidence of headache [ Time Frame: 1-24 hours post-operatively ] [ Designated as safety issue: No ]
  
• Degree of fatigue [ Time Frame: 1-24 hours post-operatively ] [ Designated as safety issue: No ]
  
• Overall satisfaction [ Time Frame: 1-24 hours post-operatively ] [ Designated as safety issue: No ]
  
• Alertness [ Time Frame: 1-24 hours post-operatively ] [ Designated as safety issue: No ]
  
• Admissions [ Time Frame: 1-24 hours post-operatively ] [ Designated as safety issue: No ]
  
• Amount of pain medication required [ Time Frame: 1-24 hours post-operatively ] [ Designated as safety issue: No ]
  

This is a prospective, randomized, double-blind, placebo-controlled study of caffeine, 500 mg, intravenously, in addition to standard anti-emetic prophylaxis, in the prevention of post-operative nausea and vomiting in patients undergoing ambulatory surgery under general anesthesia.

Consenting patients will be randomized to receive either a single dose of caffeine, 500 mg, or saline placebo, administered as a single IV dose approximately 15 minutes before emergence from anesthesia. All patients will receive our customary anti-emetic prophylaxis, determined by four major risk factors for PONV: female gender, nonsmoking status, history of PONV or motion sickness, and perioperative opioid use. Patients at low risk for PONV (no risk factors) will receive no prophylaxis; patients at moderate risk for PONV (1 or 2 risk factors) will receive dexamethasone 8 mg at induction plus dolasetron 12.5 mg approximately 15 min before the end of anesthesia; patients at high risk for PONV (3 or 4 risk factors) will receive the same treatment as those at moderate risk, plus additional prophylaxis at the discretion of the attending anesthesiologist (e.g., scopolamine patch, metoclopramide 10 mg IV, or other standard drugs).

Postoperatively, the presence of PONV will be recorded. If rescue medication is used, the amount and time of administration will be recorded. The length of stay in the PACU (Phase I and Phase II) will be recorded. Patients will be asked to report any headache, and to rate their nausea, pain, alertness, fatigue, and overall satisfaction in the PACU, and again by phone 24 hours postoperatively. Amount of pain medication utilized in the PACU will also be measured.