[Preoxygenation with the NasOral((R)) system or the standard face mask?]

Adequate preoxygenation of patients before onset of apnea for orotracheal intubation is of major importance in general anaesthesia. Various preoxygenation techniques are available but a face mask providing an oxygen supply via the circle absorber system of a mechanical respirator is most frequently used. Recently, a new device for preoxygenation - the NasOral((R)) system - has become available. The aim of the present study was to compare the efficacy of intrapulmonary oxygen storage with either the NasOral((R)) device or the standard face mask.

After informed and written consent and ethics committee approval was obtained, 40 elective patients (ASA I and II) undergoing surgical procedures of the neck and mouth area, were enrolled in this randomized, prospective study. In group A ( n=20), preoxygenation was performed using the NasOral((R)) system. Patients inhaled 100% oxygen through the nose and exhaled orally through unidirectional valves. In group B ( n=20), a conventional face mask with an O(2) flow of 15 l/min and an open airway pressure release valve was used for preoxygenation. In both groups preoxygenation lasted for 2.5 min. Induction of general anaesthesia was performed in a standardized manner. After intubation patients were not ventilated until the O(2) saturation in pulse oximetry (psaO(2)) dropped to 95%. This time of apnea was recorded in both groups and we determined the hemoglobin concentration (cHb) after beginning of ventilation.

There were no significant differences with regard to demographic data and cHb. Time of apnea leading to a O(2) saturation of 95% was 6.0+/-2.1 min in group A and 6.3+/-2.1 min in group B (mean+/-SD, p>0.05).

Both the NasOral((R)) system and the face mask are effective for intrapulmonary oxygen storage. In both systems the O(2) flow has to be adequately high and the masks have to be held tightly in order to avoid any contamination of the inhaled oxygen with nitrogen. Due to its unidirectional flow, the NasOral((R)) system additionally requires the patient to be cooperative. As the NasOral((R)) system is more expensive and has no clinical advantages without apneic oxygenation, we prefer the standard face mask for patient preoxygenation.