—Thank you for referring to me the letter from Dr. Salem regarding our report, “Preoxygenation: Comparison of Maximal Breathing and Tidal Volume Techniques.”1The arterial oxygen tension (P02) at the end of the traditional technique of preoxygenation or after using the eight-deep-breaths technique was not significantly different in group A or in group B. However, both techniques of preoxygenation resulted in Pa02values that were significantly higher than those achieved after using the four-deep-breaths technique.
Using the four-deep-breaths technique, P02at the end of preoxygenation was significantly increased by increasing the oxygen flow from 5 L/min (256 ± 73 mmHg) to 20 L/min (317 ± 67 mmHg). The report does not recommend the use of 20 L/min O2for preoxygenation. Although the report shows that such a high flow improves preoxygenation by the four-deep-breaths technique, it does not suggest that this technique can achieve the P02levels achieved by the traditional ventilation technique or by the eight-deep-breath technique.
Ventilation volume per minute (tidal volume × respiratory rate/min) is the main factor that determines arterial carbon dioxide tension. The minute ventilation volume resulting from eight-deep-breaths (of approximately 1000 ml) per minute is approximately equal to the volume that is achieved using traditional tidal volume breathing of 500 ml at a rate of 14 to 16 breaths per minute. Thus, we cannot explain the adequate preoxygenation achieved by the eight-deep-breaths technique by a lower arterial carbon dioxide tension value.
Our report considers the time of preoxygenation using the different techniques as the time of preoxygenation before rapid-sequence induction of anesthesia. Whatever technique of preoxygenation is used, the face-mask oxygenation must be maintained until complete apnea is achieved to avoid the breathing of air that counteracts the rationale of preoxygenation. A major reason for inadequate preoxygenation is the premature removal of the face mask or a leak under the mask that allow the inspiratory entrainment of room air. 2
In conclusion, our report shows that preoxygenation using the eight-deep-breaths technique for 60 s is superior to the four-deep-breaths technique for 30 s. The report does not claim that the eight-deep-breaths technique is the method of choice for preoxygenation, and only recommends that the technique can be used as an alternative to the traditional technique of preoxygenation in patients undergoing rapid-sequence induction of anesthesia and in other circumstances in which tracheal intubation or ventilation may be difficult to achieve.