Application of the self-inflating bulb to a hollow intubating introducer.

BACKGROUND: The aspiration test, performed by a self-inflating bulb (SIB), is a simple and reliable method to detect an accidental esophageal intubation. The aim of the study, in case of employment of a hollow intubating introducer (HII), was to verify the possibility to directly perform the test with the introducer and its efficacy in allowing the detection of its position. EXPERIMENTAL DESIGN: prospective, randomized study. ENVIRONMENT: operating theater in a university hospital. PATIENTS: adult patients, without evidence of gastro-esophageal or tracheobronchial pathologies, scheduled for elective surgery. INTERVENTIONS: patients were randomized in two groups T (HII was placed in trachea) and E (HII was positioned in the esophagus). Under general anesthesia, a HII was placed in either the trachea or the esophagus. A blinded anesthesiologist connected the SIB to the HII and performed the test twice. MEASUREMENTS: the anesthesiologist inferred the position of the device, based on the re-inflation observed. RESULTS: One hundred subjects were studied. In group E patients, a prompt and complete re-inflation of the bulb was never observed and the anesthesiologist correctly inferred the position of the HII. Occasionally (3.5% of cases), in group T patients, a prevented or incomplete re-inflation of the bulb occurred, leading to an incorrect judgment of the HII position. CONCLUSIONS: The aspiration test with the SIB allows the proper detection of the introducer in esophagus. When used in combination with a HII, both time and local trauma associated with an erroneous, introducer-guided esophageal intubation in case of difficult laryngoscopy may be reduced.

Work of breathing-tidal volume relationship: analysis on an in vitro model and clinical implications.

OBJECTIVE: Work of breathing (WoB) is currently employed to assess the afterload on the respiratory muscles and to estimate the energy expenditure for breathing. Since WoB depends on the ventilated tidal volume (TV), WoB*L(-1), the indicized form of WoB has been employed as a measure of WoB which is independent of TV. Actually, the independence of WoB*L(-1) from the ventilated TV has never been demonstrated. The aim of this study was to verify the predicted TV-independence of WoB*L(-1) on an in vitro model. METHODS: Our experimental model was constituted as follows: two endotracheal tubes, with internal diameter measuring respectively 6.5 and 8.5 mm, were alternatively connected with two rubber balloons whose compliance was respectively 0.02 and 0.06 L/hPa; the system was mechanically ventilated at ten different tidal volumes, ranging from 0.3-1 l. Flow rate was kept constant (35 l/m) during the whole experiment. RESULTS: Both elastic components of the model showed a static volume-pressure relationship which was linear in the experimental range of TV. In all combinations of resistance and compliance WoB increased quadratically whereas WoB*L(-1) increased linearly with the growing TV (p < 0.001). CONCLUSIONS: These results demonstrate the TV-dependence of WoB*L(-1) and suggest that WoB*L(-1), if TV changes, cannot be considered as an index of respiratory muscle afterload and should not be used as a guide for weaning patients from the mechanical ventilation. Finally, we introduced a new parameter (WoB1L) which seems to be a more TV-independent measure of respiratory work.