Oxygen jet ventilation for microlaryngoscopic procedures.

Sir,—Intermittent jets of oxygen may be used to ventilate patients undergoing microlaryngoscopy with a Venturi injector or by flushing oxygen directly through a small-bore endotracheal tube as we have used in 10 adult patients (table I). The patients were premedicated with pethidine 75 mg and atropine 0.6 mg and anaesthesia was induced with propanidid 250-500 mg followed by suxamethonium 100 mg, and was maintained with an i.v. infusion of suxamethonium 0.1% at a rate of 0.1 ml/kg, min". After topical laryngeal analgesia, the trachea was intubated with a Lanz low-pressure cuff tube (i.d. 5 mm). The cuff was inflated with 20-30 ml of air in order to occlude the trachea around the tube. The proximal end of the tube was fitted to a Y adaptor, one arm of which was connected by highpressure tubing to the pipeline oxygen supply delivered at 414 kPa, while the second arm was always unoccluded. The flow of oxygen was interrupted by a manually operated valve. The patients were ventilated with intermittent jets of oxygen of 1-s duration via the sidearm of the connection at a rate of 10 per minute and expiration occurred via the unoccluded second arm. In all patients, arterial Pco2 and Po2 were measured before induction of anaesthesia, and near the end of the procedure which lasted from 15 to 30 min (table I). Airway pressure during jet ventilation, as measured by a Statham transducer, ranged between 35 and 50 cm H2O at the proximal end of the tube and between 10 and 20 cm H2O above the carina at a level just below the tube. The Venturi principle has been used to ventilate patients during bronchoscopy (Sanders, 1967) and also during microlaryngoscopy by attaching the oxygen injector to the laryngoscope itself (Albert, Shibuya and Albert, 1972; Lee, 1972), or by flushing oxygen directly into the trachea via translaryngeal (Carden and Crutchfield, 1973; Spoerel and Greenway, 1973), or transtracheal (Spoerel, Narayanan and Singh, 1971) cannulae which operate as injectors. In all these techniques, the patient is ventilated with oxygen and entrained air. A simpler method which provides a higher oxygen concentration and minimal air entrainment is to flush oxygen directly via the sidearm of the bronchoscope (Carden, Trapp and Oulton, 1970; Baraka, 1974) or via a small endotracheal tube (El-Naggar, 1975). A similar principle may be applied for ventilation of patients undergoing microlaryngeal surgery. El-Naggar and others (1974) have shown that oxygen jet ventilation via a small-bore cuff tracheal tube during microlaryngoscopy produces higher Pao, and lower Paco, values than those obtained during ventilation via injectors or narrow catheters. In their technique, the cuff is deflated intermittently to allow expiration around the tube. In our technique, patients are intubated by a low-pressure cuffed endotracheal tube (i.d. 5 mm). This small-bore tube occupies only 1/5 to 1/4 of the adult's laryngeal inlet and thus provides satisfactory access to the larynx. The low-pressure cuff was kept inflated continuously, in contrast with the technique of El-Naggar and colleagues (1974), in order to maintain occlusion of the trachea around the small-bore tracheal tube during both inflation and expiration. This ensures effective ventilation, prevents aspiration and avoids fogging of the microscope lens by blood particles. As judged by the arterial Po2, Pco2 and airway pressures, the technique described provides adequate ventilation, and ensures high oxygenation with minimal air entrainment. ANIS BARAKA MUSA MUALLEM Lebanon