 Investigators have explored physiological evidence of improving lung function to help determine the appropriate time to discontinue mechanical ventilation. One notable effort by Hubble et al was to obtain dead space to tidal volume ratio VdVt to determine extubation success after a 30 minute PSV trail prior to extubation9. They concluded that a VdVt ratio of less than or equal to 0.5 reliably predicted successful extubation 96. However, this only provides one part of the equation - lung function- but not necessarily the central nervous system interaction or the work of breathing associated. 