A preliminary assessment of the intubating laryngeal mask airway.

Abstract

Key words: Laryngeal mask airway, Intubating laryngeal mask airway, Endotracheal intubation The laryngeal mask airway (LMA) has been widely used for airway management in general anesthesia or cardiopulmonary resuscitation [1]. Insertion of the LMA is less invasive and easier than conventional orotracheal intubation. The clinical applications of the LMA have been various. When the LMA is used for airway maintenance, not only can tracheoscopic and laryngoscopic examinations be safely performed, but orotracheal intubation is also possible in cases with dif- ficult intubation [2]. However, the conventional LMA permits an endotracheal tube (ETT) with a maximum of 6.0ram ID, and a fiberscope is often necessary to pass through the mask aperture bars. The intubating laryngeal mask (ILMA) is a prototype of the LMA which is designed to introduce the ETT into the trachea. The ILMA has a shorter metal main stem, and the inner diameter of the main stem is larger than that of the conventional LMA, which allows a 7.5 or 8.0mm ID ETT. In the present study, we tested the performance of endotracheal intubation using a size 4 ILMA in 40 adult patients who underwent general anesthesia. The study was approved by the hospital ethical com- mittee, and informed patient consent was obtained. We studied 40 patients ASA I, II, or III, aged 20 to 80 years, who were undergoing elective gynecological or general surgical procedures. These cases include 2 patients whom we expected to be difficult to intubate with the laryngoscope (Cormack grade IV on laryngoscopy). Pa- tients with a history of gastroesophageal reflux were Address correspondence to: K. Nakazawa Received for publication on January 6, 1997; accepted on May 27, 1997 excluded. Before induction of anesthesia, a pulse oximeter and ECG monitor were attached. Anesthesia was induced with propofol, 2 to 2.5mg-kg -1, and vecuronium, 0.2 mg.kg -1. Additional propofol was given as necessary. The method of insertion of the ILMA was almost identical with that of the conventional LMA. The tip of the mask was placed on the hard palate with the aperture anterior and then advanced in a smooth movement [3]. After the ILMA was inserted, it was connected to the anesthetic machine by a semiclosed anaesthetic breathing system, and the patient was ventilated with 50% nitrous oxide and 2% isoflurane or 2.5% sevoflurane in oxygen. Two minutes later, a 7.5 mm ID ETT was passed through the ILMA. When endotracheal intubation had failed, a fiberoptic scope was passed into the aperture of the mask, and the viewfinding was scored according to the system of Brimacombe [4]. Subsequent intubation was tried again by changing the position of the mask by moving the attached handle up and down. If intuba- tion could not be achieved after three attempts, the ILMA was removed and the intubation was performed by laryngoscopy. Patients were divided into four groups: group 1, suc- cessful endotracheal intubation at the first attempt: group 2, successful endotracheal intubation at the sec- ond attempt: group 3, successful endotracheal intu- bation at the third attempt: and group 4, intubation not successful after three attempts. The patient's head and neck were not manipulated during insertion of the ILMA or endotracheal intubation. The ease of ILMA insertion, condition of ventilation through the ILMA, and intubation of the ETT were assessed by one of the authors. Demographic data were analyzed by one-factor ANOVA, and if the differences were significant, mul- tiple comparison was carried out by Tukey's test. The male/female ratio was compared by the chi-square test. P < 0.05 was taken as significant.