[Clinical experience of laryngeal mask airway combined with continuous intravenous propofol infusion during general anesthesia].

BACKGROUND: Propofol's greatest attributes are its pharmacokinetic properties which result in a rapid, clear emergency and lack of cumulative effects even after prolonged administration. It is a drug of popular choice for the maintenance of general anesthesia. The laryngeal mask airway (LMA), originally described by Dr. Brain is now a good alternative as the airway management technique. Because of its high success rate in securing a clinically acceptable airway in anesthetized patients, LMA has been proposed as a practical airway and conveyer for general anesthesia. This study was designed to observe and evaluate the feasibility of propofol infusion combined with N2O for maintenance of anesthesia, with a LMA as airway and conveyer during general anesthesia.

METHODS: Sixty patients, ASA class I-II, aged 15-59 years, were selected for this study. They were scheduled for upper-limb orthopedic surgeries in supine position. No patient was premedicated. Intraoperative monitoring included electrocardiography, pulse oximetry, end-tidal carbon dioxide and automatic non-invasive blood pressure. The agents for induction of anesthesia included atropine 0.01 mg/kg, atracurium 5 mg, fentanyl 2-3 micrograms/kg, 2% lidocaine 1.5-2 mg/kg, propofol 2 mg/kg, and succinylcholine 1-1.5 mg/kg, all of which were given intravenously in sequence. After that laryngeal mask airway (LMA) was inserted. The position of LMA was confirmed by even undulation of chest wall and breathing sound. Anesthesia was then maintained with nitrous oxide in 40% oxygen and continuous propofol infusion. The pumping rate was set to start at 6 mg/kg/h. Muscle relaxation was achieved by intravenous tracrium given intermittently. All patients were mechanically ventilated with a ventilator incorporated to the anesthesia machine. The ventilator was set to give a tidal volume of 8 ml/kg at a rate of 12-14/min. At the end of the operation, the propofol infusion and nitrous oxide were simultaneously discontinued. The effect of muscle relaxant was antagonized by atropine 1.0 mg and neostigmine 2.5 mg intravenously. The LMA was removed while the patient was awake and able to open mouth at request. They were followed 24 h postoperatively for inquiring intraoperative awareness and other complaints.

RESULTS: No patient was noted to experience awareness during the intraoperative period. Regarding LMA insertion, success in the first attempt was seen in 55 patients (90.2%). Success in the second attempt was seen in 5 patients (8.2%). Failure was encountered in one patient (1.6%). The average time of emergence was 92 +/- 3.4 min. The average rate of speed of propofol infusion was 6.29 +/- 0.97 mg/kg/h.

CONCLUSIONS: The combination of propofol infusion and N2O with laryngeal mask as airway and recovery was a good alternative in administration of general anesthesia.