Publications of the Experiences with Prototypes

 

 

Early during his residency training in internal medicine, Frass was integrated in the in-hospital cardiopulmonary resuscitation (CRP) team and had to care for critically ill patients at the intensive care unit of his department. However, he had no formal training in airway management (AM) techniques and less experiences in face-mask ventilation and conventional laryngoscopy and tracheal intubation. The esophageal obturator airway (EOA) was the only commercially available backup device in situations of difficult/impossible face-mask ventilation and/or tracheal intubation at this time. Despite working functionally well in experienced hands, the major disadvantage of the EOA was, that when placed into the trachea, the airway of the patient was completedly blocked; furthermore, difficulties with obtaining an air-tight face-mask seal (by less experienced operators) and injuries to the esophagus (probably due to the extensive length of the EOA) have been reported (2).

 

The problems with obtaining an airtight seal around the face were solved by replacement of the integrated face mask of the EOA by a large balloon occluding the oropharynx when inflated (2); by filling out the oropharyngeal cavity, the inflated balloon sealed both the mouth and the nose. The inflated oropharyngeal balloon also guaranteed strong anchoring of the device during ventilation and transportation even without fixation. In order to provide the possibility of ventilation after either esophageal or tracheal placement, a second tube with a distal open end was added parallel to esophageal tube for use when placed into the trachea. In an experimental study (3), the double-lumen esophageal-tracheal combitube (ETC, placed into the esophagus) showed encouraging results regarding ventilation and oxygenation compared to tracheal intubation.

 

In 1987, Frass and co-workers (5) published their first experiences with ETC prototypes in clinical practice. This study included 38 patients requiring AM and ventilation during CRP; immediate airway control and positive-pressure ventilation was successful in all of these patients. Blood gas analyses (obtained in 12 patients) during esophageal ETC placement and mechanical ventilation were comparable to those of subsequent mechanical ventilation (with unchanged ventilatory variables) via a standard tracheal tube (TT). In the following year, they published a further study testing the promptness and effectiveness of the ETC and the TT for rescue ventilation (4). Prompt establishment of a patent airway and effective ventilation and oxygenation (documented by blood gas analyses) were obtained with both devices.

 

Frass and co-workers (6) also tested the effectiveness of ventilation and oxygenation with the ETC (placed into the esophagus) in a crossover study comparing both the ETC and TT in more than 30 patients under general anesthesia presented for elective surgery. The mean arterial oxygen tension was even higher during mechanical ventilation with the ETC, probably due to the formation of an individual positive end-expiratory pressure during expiration through the hypopharyngeal perforations of the esophageal ETC lumen. This phenomenon was confirmed by a further crossover study in 12 surgical patients under general anesthesia (7). In this study, again the mean arterial oxygen tension was higher during mechanical ventilation with the ETC (placed into the esophagus). The following differences in intratracheal pressure and flow could be found for the ETC when compared with the TT: smaller rising pressure during inspiration, prolonged expiratory flow time, and formation of a small positive end-expiratory pressure - factors responsible for the improved arterial oxygen tension with the ETC. Ventilation (carbon dioxide removal) through the ETC compared with the TT was the same.    

 

 

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