Two hundred and fifty patients were assessed preoperatively using the Mallampati classification and by measuring their thyromental distances. The ease or difficulty of direct laryngoscopy was assessed at the time of induction of anaesthesia. Retrognathia was seen in 15.6% of patients and the incidence of difficult laryngoscopy without external laryngeal pressure was 8.2%. It was found that both assessments predicted less than two in three difficult laryngoscopies and had highfalse positive rates. It was found that external laryngeal pressure often improved the view of the glottis in difficult laryngoscopies.

Summary Successful management of difficult tracheal intubation by retrograde intubation has been reported for almost 50 years and can be used whether or not it is anticipated. There are numerous reports of variations to the basic technique to enhance reproducibility of this guided blind procedure. A review and analysis of the equipment and techniques provides a better understanding of this effective technique.

This study assessed the safety of sevoflurane anaesthesia using two Komesaroff vaporizers inside the circle with both spontaneous and controlled ventilation. Sevoflurane concentrations were continuously monitored using a mass spectrometer and the anaesthetic depth was easily controlled. Involuntary movements occurred in eight patients and breathholding occurred in five patients after inhalational induction. With continuous monitoring of sevoflurane concentrations, induction and maintenance of anaesthesia using a vaporizer inside the circle is safe during both controlled and spontaneous ventilation. However the high incidence of involuntary movements may limit the feasibility of induction in spontaneously breathing patients.

The sevoflurane output from the Oxford Miniature Vaporizer (OMV) was measured in a series of bench tests in a drawover system. Using a range of settings on two OMVs in series, output ranged from 0.5 to 5.9% with a 600 ml tidal volume at a rate of 12 breaths/min produced by a Penlon Multivent. The OMVs' output was steady over 40 minutes. In tests with tidal volumes ranging from 300 ml to 1200 ml, the OMVs' output was lower at higher minute volumes. When continuous flow of carrier gas at 7.2 l/min was used, the output was lower than at the equivalent intermittent flow rate. Using two OMVs with a drawover system appears to be a feasible technique for the induction and maintenance of sevoflurane anaesthesia. Clinical tests of sevoflurane drawover anaesthesia are now required so that the advantages of sevoflurane can gain wider application in field and military anaesthesia.

The procedure of retrograde tracheal intubation has been facilitated by the use of a multilumen catheter guide. When used as an anterograde guide, it would easily follow the retrograde guide and would direct placement of the tracheal tube atraumatically. A new technique is described that allows stabilization of the anterograde catheter and its insertion deep inside the trachea to prevent dislodgement of the tracheal tube from the laryngeal inlet. This catheter guide may also be used as a conduit for high-frequency jet ventilation with monitoring of the airway pressure, thus providing wider margins of safety in patients with difficult upper airways.