Tidal volume perception in a C1-C2 tetraplegic subject is blocked by airway anesthesia

We administered lidocaine aerosol intratracheal anesthesia to a ventilator-dependent, tracheostomized C1-C2 tetraplegic subject to determine its effect on her ability to detect small changes in tidal volume. A psychophysical test of volume detection was given before and immediately after a 20 percent lidocaine aerosol was delivered through the subject's cuffed tracheostomy tube. On each of three occasions, she reliably (p < .001) detected changes in tidal volume during a control period; on two of these occasions she could not detect the same volume after inhaling the anesthetic. On one occasion the anesthetic had no effect on volume perception, possibly because copious airway secretions interfered with lidocaine uptake. Subject-blinded control tests with saline aerosol inhalation did not affect detection. We concluded that this subject's tidal volume perception depended on mechanoreceptors in the lungs and thoracic airways and that local anesthetic interrupted these sensory signals when airway secretions were not excessive.