Airway Responses During Desflurane Anesthesia Via a Laryngeal Mask Airway: Effects of Fentanyl Pretreatment

After obtaining approval from the institutional review board and informed consent, 100 patients, 18-64 years of age, scheduled for elective superficial and peripheral surgery of less than 2 h duration would be enrolled in this prospective, randomized, double-blind, placebo-controlled study. Patients will be randomly assigned to one of two anesthetic techniques according to a computer-generated random numbers table. Patients will receive either fentanyl or saline prior to induction of anesthesia, while the rest of the anesthetic and analgesic technique will be standardized for all patients.

Exclusion criteria will include obesity (body mass index >30), pregnancy, history of gastroesophageal reflux, hiatal hernia, significant cardiovascular, pulmonary (e.g., reactive airway disease), hepatic, renal, neurologic, metabolic, and endocrine disease as well as history of alcohol and drug abuse as well as those requiring tracheal intubation.

After premedication with midazolam 2 mg, patients will be transferred to the operating room. On arrival in the operating room standard monitors and the BIS (BiSpectral Index)monitor will be applied. Patients will then be preoxygenated for 2-3 minutes with 100% oxygen, which will be followed by administration of either fentanyl 1 µg/kg (made up to 10 ml saline) or 10 ml saline (prepared by a person not involved in the study). Induction of anesthesia will be performed 2-3 minutes after administration of the study drug with propofol 2.0 - 2.5 mg/kg after lidocaine 2% 20-30 mg. After loss of eyelash reflex an appropriate size LMA will be placed. If the patients become apneic, manual ventilation will be performed with oxygen/nitrous oxide and desflurane, 3% dialed concentration initially and then titrated to maintain the BIS value of 50-60.

Anesthesia will be maintained with desflurane titrated to achieve a BIS value of 50-60, along with 50% nitrous oxide and oxygen. Once spontaneous breathing resumes, fentanyl 25-50 µg will be administered to achieve a respiratory rate of 10-15 breaths/minute. Additional propofol/fentanyl will be administered, if deemed necessary by the attending anesthesiologist. All patients will receive dexamethasone 4 mg, IV after induction of anesthesia and ondansetron 4 mg 20-30 minutes prior to the end of surgery. Desflurane will be discontinued after closure of the surgical wound.

A blinded observer will record patient demographics (age, weight, height) and history of smoking from preoperative evaluation. Data collected during the intraoperative period will include need for manual ventilation and duration of manual ventilation, duration of anesthesia, total doses of propofol and fentanyl, and time from discontinuation of desflurane until patient first follows verbal command as well as heart rate (HR), mean arterial blood pressure (MAP), end-tidal carbon dioxide, oxygen saturation, and end-tidal gas concentration will be recorded every 15 minutes.