FLOW PATTERN OF RESPIRATORY GASES DURING SUPERIMPOSED HIGH-FREQUENCY JET VENTILATION (SHFJV) VIA THE JET LARYNGOSCOPE

High-frequency ventilation techniques have been applied for a number o f years for laryngeal surgery in order to ventilate patients without e ndotracheal tubes or catheters. A further development of high-frequenc y jet ventilation (HFJV) is the technique of superimposed HFJV (SHFJV) , which was achieved by combining low- and high-frequency jet streams. Although good clinical results were observed, which have been publish ed in the past, the clinical details of development of SHFJV have not been previously published. Methods. In order to understand and study t he mechanism of superimposition of a high-frequency jet stream, extens ive experiments on a lung simulator at defined measuring points, which represented the operating field in microlaryngeal surgery and the tra chea, were conducted prior to the clinical application of SHFJV. Resul ts. The measurements demonstrated that superposition of the two jet st reams led to greater velocity during inspiration, and therefore produc ed an increase in tidal volume and entrainment of inspiratory gas. Thi s demonstrates that it is possible to apply a HFJV technique in patien ts even with an open system. During expiration, the velocity of the lo w-frequency gas stream is decreased by the opposing flow of the high-f requency jet stream, leading to the buildup of positive end-expiratory pressure. The pulsations of the high-frequency jet stream induce cont inuous alveolar ventilation. The positioning of the jet nozzles in the jet laryngoscopy has the result that the velocities are already decre ased at the tip of the laryngoscope and decrease further with distance from the nozzles. This prevents possible damage to the laryngeal muco sa.