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Performance of the New Single-Use AMBU Laryngeal Mask in Different Head Positions
Harald V. Genzwuerker, M.D., Jochen Hinkelbein, M.D., Renée Krivosic-Horber, M.D., Carin A. Hagberg, M.D., Frank Samsoe Jensen, M.D.
Inst. of Anaesthesiology and Intensive Care Medicine, University Hospital Mannheim, Mannheim, Germany.
Objective: The new single-use AMBU laryngeal mask (AMBU, Denmark) is supposed to allow easy insertion and adapt to different head positions due to a special form of the airway tube. With a soft cuff, a high airway seal is possible according to the product information. Ease of insertion, insertion access, airway seal and ventilation in different head positions are tested in a sub-group of patients included in one center as part of a multicenter trial (Combined international multi-center phase I and II study verifying the safety and performance of the Ambu A/S Laryngeal mask for patients undergoing routine anaesthesia - Denmark, France, Germany, USA) to evaluate the device.

Methods: After approval of the local institutional review board and obtaining written informed consent, 30 ASA I and II patients without history of cervical spine problems undergoing elective surgical procedures were included in the trial. Standard monitoring (ECG, blood pressure, pulse oximetry) was attached. Anesthesia was induced with Fentanyl 3.5 μg per kg and Propofol 2.5 mg per kg after preoxygenation with a facemask for three minutes. No muscle relaxants were used. The AMBU laryngeal mask was inserted according to manufacturer´s instructions. Time was measured from removal of the facemask until first tidal volume of at least 6 ml per kg. When ventilation was sufficient, the correct position of the device was verified with a fibrescope. Airway leak pressure was tested with a cuff pressure of 60 cm H2O by closing the valve of the circle system until air leakage was noticed over the mouth or stomach. The patient´s head was initially placed on a standard pillow, height 7 cm. The presence or absence of an oropharyngeal leak and a square wave end tidal CO2 trace as well as equal chest movements and a tidal volume of at least 6 ml per kg were documented. If all criteria were fulfilled, in the sub-group studied the patient´s head was rotated to the left side at an angle of approx. 30 degrees and the same parameters were recorded after 5 tidal volumes. The same procedure was performed with the head rotated to the right side, with chin lift in a neutral position and with the head on the operating table without a standard pillow. The head was returned to a neutral position on a standard pillow and ventilation was performed with the laryngeal mask airway for the whole duration of the surgical procedure.

Results: Demographic data of patients are listed in table 1. Insertion was possible in the first attempt in all patients. A size 4 AMBU laryngeal mask was used in 11 patients, size 5 in 19 patients. Insertion time was 19.7 ± 15.4 seconds. Airway leak pressure was 27.3 ± 4.3 cm H2O. No leak was detected in any of the positions tested in any patient. Sufficient ventilation in all five positions with square wave end tidal CO2 traces and equal chest movements was observed in all patients. Ventilation with a tidal volume of 7.8 ± 1.3 ml per kg was performed for 109 ± 39 minutes without any adverse events.

Conclusion: In a clinical trial, the single-use AMBU laryngeal mask allows airway maintenance in different head positions. Insertion success rate is high with an airway leak pressure well above 20 cm H2O.

Anesthesiology 2004; 101: A1590
Demographic data
Patient sex18 male, 12 female
Age47.6 ± 15.1 years
Height1.71 ± 0.07 m
Weight74.9 ± 12.8 kg
Body mass index25.4 ± 3.3 kg per m²