Comparison of cuff-pressure changes in LMA-Classic and the new Soft Seal laryngeal masks during nitrous oxide anaesthesia in spontaneous breathing patients.

BACKGROUND AND OBJECTIVE: There are concerns over the intra-cuff pressure of the laryngeal mask and laryngopharyngeal morbidity. In a randomized study, the authors compared cuff-pressure changes in the LMA-Classic and the new disposable Soft Seal laryngeal mask during nitrous oxide anaesthesia.

METHODS: Two-hundred adult patients were randomly assigned to a size 4 laryngeal mask in two equal-sized groups for airway management: (a) the re-usable LMA-Classic, or (b) the new disposable Soft Seal laryngeal mask. Anaesthesia was administered with fentanyl, propofol, nitrous oxide, O2 and sevoflurane. The cuff pressures, adjusted to 45 mmHg at insertion, were monitored continuously until the end of the operation without any further attempt to reduce cuff pressure. On removal of the laryngeal mask, any blood at all was considered positive. Patients were requested to report any sore throat at 2 and 24 h postoperatively.

RESULTS: During nitrous oxide anaesthesia, cuff pressures increased in the LMA-Classic group from 45 to 100.3 mmHg and from 45 to 46.8 mmHg in the Soft Seal laryngeal mask group (P < 0.001). The incidence of sore throat was significantly higher at 2 h postoperatively when using the LMA-Classic, although there was no difference at 24 h following the operation. Macroscopic blood was only seen on four occasions in the LMA-Classic group (not significant).

CONCLUSIONS: During nitrous oxide anaesthesia, cuff pressure increases in the LMA-Classic mask were significantly higher than those of the Soft Seal laryngeal mask. Trauma to patients, as assessed by the incidence of sore throat in the early postoperative period was significantly higher in the LMA-Classic group. Cuff pressures should be monitored during nitrous oxide anaesthesia when LMA-Classic is used but to do so is of less importance when using the disposable Soft Seal laryngeal mask.