Description

Inclusion criteria:

• Adults of either sex (≥18 years)
• Non-c0mmunicative, endotracheally intubated in the past 24 hours.
• Expected to require ≥24 hours of mechanical ventilation.

Exclusion criteria:

• Continuous neuromuscular blockade.
• Ventilated on Airway Pressure Release Ventilation mode.

Ventilator measured airway pressure and flow signals will be streamed at 31.25 Hz into 131.1-s time windows (epochs) for up to 5 days. A recursive algorithm will compute individual breath's inspiratory effort (Pmus) and calculate the inspiratory effort time-pressure product (PmusPTP cmH₂O·s·min-¹).

Trained staff will assess the Mechanical Ventilation-Respiratory Distress Observation Scale (MV-RDOS), an intermittent and subjective assessment of dyspnea, at least twice daily. These will be time-matched to the airway signal epochs to determine their degree of correlation by Pearsons R2.

Using receiver operating characteristic (ROC) area under the curve (AUC) analysis, the investigators will determine a dyspnea threshold for PmusPTP equivalent to the dyspnea cut-off for MV-RDOS > 2.6, and report sensitivity/specificity.

To address possible label misclassification, the investigators will train six supervised classifiers on concordant data pairs and apply a unanimity ensemble to label discordant pairs as "dyspneic", not dyspneic" and undetermined". Ensemble determined labels conflicting with those classified by MV-RDOS will be excluded from a secondary analysis.

Primary outcome will be Pearson's R2 (PmusPTP vs MV-RDOS). Secondary outcome will be 28-day ventilator-free days.