Aim 3: The primary outcome of this aim is aPiMax < 30 cmH2O.The analysis will focus on determining whether the degree of patient effort of breathing is independently associated with the development of respiratory muscle weakness. For the acute phase, the investigators will generate a time-weighted average PRP during the acute phase and graph it against aPiMax at the first SBT. They will subsequently dichotomize aPiMax at the first SBT and compare mean time weighted average PRP in the acute phase between aPiMax groups (> 30 vs. ≤ 30 cmH2O). For the weaning phase, the investigators will graph the changes in aPiMax throughout the weaning phase (from first failed SBT until successful SBT) against time-weighted average PRP, with the anticipation that low PRP will be associated with either further reductions in aPiMax, or no improvement, while PRP in the physiologic range of 150-400 will be associated with improvement in aPiMax. The investigators will subsequently dichotomize aPiMax (at 30 cm H2O) at the time of successful passage of an SBT and compare time-weighted average PRP in the weaning phase between aPiMax groups. Subsequently, the investigators will build a multivariable logistic regression model on the outcome of aPiMax ≤ 30 cmH2O to determine if time-weighted PRP in the acute phase, weaning phase or both have an independent association with preserving aPiMax, after controlling for confounding variables.