[Ventilation via a transnasally placed pharyngeal tube. Comparison with mask ventilation].

OBJECTIVE: The present prospective study was designed to investigate the respiratory function during ventilation via a tube inserted through the nose into the pharynx. Results were compared with respiratory parameters measured during conventional mask ventilation in the same patients.

METHODS: 20 ASA physical status I-II patients were studied after approval by the local Ethics Committee. Anaesthesia was induced with alfentanil 15 micrograms/kg and propofol 2.5-3.0 mg/kg and maintained with propofol, 12-15 mg/kg/h. Patients were ventilated via a facemask with oxygen and a tidal volume of approximately 8ml/kg (measurement A). After insertion of a tube (I.D. 7.0-7.5 mm) through the nostril into the pharynx ventilation was repeated in the same manner (measurement B). To secure airway seal a second person closed the patient's mouth and exerted cricoid pressure. Following neuromuscular blockade with suxamethonium (1.5 mg/kg) respiratory parameters were measured again (C). Measurements included pulse oximetry and side stream spirometry with continuous collection of the following data: airway pressure, inspired and expired tidal volume, dynamic compliance, expired volume in one second, inspiratory and expiratory oxygen and carbon dioxide concentration. Pressure-volume and flow-volume loops were displayed continuously.

RESULTS: Ventilation via facial mask or via pharyngeal tube with and without relaxation showed normal endtidal FECO2. The mean values were 4.5 +/- 0.7%, 4.8 +/- 0.4% and 4.6 +/- 0.7%, respectively. Mean oxygen saturation exceeded 98% in each period. Leakage during mask ventilation was 59.3 +/- 65.5 mL and decreased to 40.5 +/- 62.1 mL with the pharyngeal tube, whereas relaxation resulted in a significant increase to 92.3 75.0 mL. Compliance (Cdyn) and expired volume in one second (V 1.0) did not change significantly during the entire period of measurement.

CONCLUSION: The use of a pharyngeally placed tube proved adequate compared to conventional mask ventilation in 20 patients without underlying airway disease.