Capnography during jet ventilation for laryngoscopy

Jet ventilation is often used during laryngoscopy to permit improved visualization of the larynx and to eliminate a potentially flammable endotracheal tube when laser surgery of the airway is performed. Observation of chest wall movement and blood gas analysis are the usual standards for assessing the adequacy of ventilation during jet ventilation. It is reasonable to hypothesize that measurement of end-tidal CO₂ concentrations during jet ventilation can be used to assess the adequacy of ventilation during jet ventilation. To test this hypothesis, end-tidal CO₂ concentrations were determined during mechanical ventilation through an endotracheal tube and during jet ventilation. At the time that each end- tidal measurement was obtained, a sample of arterial blood was also obtained for later blood gas analysis. For both mechanical ventilation and jet ventilation, well defined relationships between end-tidal CO₂ and arterial CO₂ tensions were obtained. However, the relationships are distinct: the difference in arterial to end-tidal CO₂ tension during supraglottic jet ventilation at a conventional respiratory rate was found to be 13.4 ± 6.8 mm Hg (mean ± SD) compared with 5.7 ± 5.2 mm Hg obtained during conventional ventilation through an endotracheal tube.