Clinical evaluation of high-frequency positive-pressure ventilation (HFPPV) in laryngoscoy under general anaesthesia.

A technique for automatic ventilation during laryngoscopy under general anaesthesia was evaluated in a lung model and in 5 patients (3--57 y) submitted for routine laryngoscopy. this technique has been given the name laryngoscopic HFPPV and utilizes an insufflation frequency (f) of 60 per min and a relative insufflation time (t%) of 22%. Ventilation is given via a nasotracheal insufflation catheter. Laryngoscopic HFPPV permits laryngeal surgery with a virtually unobstructed surgical field under complete muscular relaxation. The alveolar ventilation of the patient may be controlled by adjustment of the pressure of the anaesthetic gas mixture and there is no air entrainment through the larynx during insufflation. This makes possible use of O2/N2O mixtures and the oxygenation of the patient may be controlled by adjustment of the oxygen concentration of the anaesthetic gas mixture. As there is a continuous upward has flow through the larynx, blood or pieces of loose tissue are not sucked down into the trachea. A simple ventilation nomogram for clinical use is proposed. Adequately used, this nomogram guarantees safe ventilation during laryngoscopic HFPPV. An Fio2 of 0.3--0.4 gives adequate arterial oxygenation.