Critically ill patients who (1) are not able to maintain their airway, (2) cannot breathe on their own, or (3) both, are ones who often require tracheal intubation and support from a breathing machine (mechanical ventilator). When the patient is ready to be liberated from the mechanical ventilator because the initial insult for intubation has been resolved, the patient is screened using the readiness to wean test in preparation for extubation. As the patient passes this screening, a spontaneous breathing test (SBT) is initiated. Currently, there are many debates surrounding which SBT technique is most favorable. At Toronto General Hospital, the clinical team uses a zero-end expiratory pressure (ZEEP) trial. Once the patient successfully passes their SBT they are then extubated.
The patient will undergo a spontaneous breathing trial of continuous positive airway pressure (CPAP) of 5 cmH2O and ZEEP, in which time the investigators will be using a new technology called electrical impedance tomography (EIT), to study and compare the end expiratory lung volume (EELV); investigators will use an esophageal catheter to measure and monitor pressures in the lung, and also assess the patient's work of breathing. This will be repeated once the patient has been extubated safely.
Adult patients intubated and ventilated
Contraindication for esophageal catheter insertion: upper gastrointestinal surgery within prior 6 weeks, actively bleeding esophageal varices
Bronchopleural fistula
Contraindication for electrical impedance tomography: chest burns, skin lesions in the thorax, chest wall bandaging limiting electrode placement, unstable spinal lesions or fractures
Pregnancy
Eligible patients admitted to the medical surgical intensive care unit (MSICU) at Toronto General Hospital (TGH) requiring invasive mechanical ventilation, after obtaining consent. Inclusion will be stratified in a 1:1 ratio between lung transplant and non-transplant patients.
Case-only
Prospective
Not listed
Change in end-expiratory lung volume (EELV) between the varying conditions (CPAP 5, ZEEP, and post-extubation).
End-expiratory lung volume is assessed using Electrical Impedance Tomography (EIT) and expressed in milliliters (mL) across all three conditions: 1. CPAP 5 cm H₂O 2. ZEEP (Zero End-Expiratory Pressure) 3. Post-extubation
Discriminative ability of occlusion maneuvers to detect expiratory muscle effort
The ability of occlusion maneuvers to detect presence of expiratory muscle effort, measured with the gold standard (gastric pressure), will be assessed with receiver operating characteristic curves.
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