Efficacy of preoxygenation with tidal volume breathing - Comparison of breathing systems

Background: Preoxygenation before tracheal intubation is intended to increa se oxygen reserves and delay the onset of hypoxemia during apnea. Various s ystems are used for preoxygenation, Designed specifically for preoxygenatio n, the NasOral system uses a small nasal mask for inspiration and a mouthpi ece for exhalation, One-way valves in the nasal mask and the mouthpiece ens ure unidirectional flow. This investigation compares the efficacy of preoxy genation using the standard circle system with the NasOral system and five different resuscitation bags. Methods: Twenty consenting, healthy volunteers were studied in the supine p osition for 5-min periods of tidal volume breathing using the circle absorb er system, the NasOral system, and five resuscitation bags in a randomized order. Data were collected during room air breathing and at 30-s intervals during 5 min of oxygen administration. Inspired oxygen, end-tidal oxygen, a nd end-tidal nitrogen were measured by mass spectrometry. Results: At 2.5 min of oxygenation, end-tidal oxygen plateaued at 88.1 +/- 4.8 and 89.3 +/- 6.4% (mean +/- SD) for the circle absorber and NasOral sys tems, respectively. This was associated with inverse decreases in end-tidal nitrogen. At no time did these end-tidal oxygen or nitrogen values differ from each other. Three of the resuscitation bags (one disk type and two duc k-bill type with one-way exhalation valves) delivered inspired oxygen more than 90%, and the end-tidal oxygen plateaued between 77 and 89% at 2 min of tidal volume breathing. The other two resuscitation bags (both duck-bill b ags without exhalation valves) delivered inspired oxygen less than 40%, and the end-tidal oxygen values ranged between 21.8 +/- 5.0 and 31.9 +/- 8.7%. Conclusions: The circle absorber and NasOral systems were equally effective in achieving maximal preoxygenation during tidal volume breathing. Resusci tation bags differed markedly in effectiveness during preoxygenation; those with duck-bill valves without one-way exhalation valves were the least eff ective. Thus, the use of these bags should be avoided for preoxygenation.