 1. Specific Aims Objectives Specific Aim 1: To determine if Edi is a predictor of extubation readiness. Hypothesis: an increase of 20-50 in Edi from baseline prior to ERT will predict successful extubation. Specific Aim 2: If the patient fails the ERT - We hope to determine if NAVA will provide more information about why the patient failed the ERT. Hypothesis: a decrease in peak inspiratory pressure from baseline post ERT failure is predictive of high frequency diaphragm fatigue and subsequent successful ERT. 