Mechanical ventilation is a life-saving treatment for critically ill patients who are unable to breathe on their own. At the time of recovery, separation from the ventilator is performed without difficulty for the majority of patients. However, approximately 15% of patients experience extubation failure, i.e. they are re-intubated after extubation within a period of 48 hours to 7 days. Patients who fail extubation are exposed to a longer duration of mechanical ventilation, higher rates of ventilator-acquired pneumonia, higher morbidity, and higher ICU mortality. Therefore, it is of relevant importance for clinicians to identify patients who are at risk of extubation failure as soon as ventilation has been discontinued. However, current clinical assessment has poor predictive performance: some physiological variables can be helpful but can only be obtained invasively using esophageal and gastric catheters.

Using ultrasound measurements to assess the activity of the respiratory muscles could be of particular interest for this purpose. By showing an early recruitment of the accessory muscles as well as diaphragm dysfunction or hyperactivity, ultrasounds could help clinicians pay greater attention to such patients and therefore try to apply specific therapeutics. There are several advantages to ultrasounds: they are non-invasive, available in most intensive care units, and previous studies have reported reasonable reliability of the measurements.

In the present study, we aim to assess the contractility of the respiratory muscles (diaphragm, intercostal, and sternocleidomastoid) using ultrasounds to identify patients who may be at risk of extubation failure and/or ICU readmission.

This study is a single centre, prospective, physiologic study in extubated patients (n = 110) to assess the contractility of the diaphragm, intercostal, and sternocleidomastoid muscles. The purpose is to determine whether employing ultrasounds early after extubation is a useful diagnostic tool to identify patients who may be at risk of extubation failure and/or intensive care unit (ICU) re-admission. The study will be performed in the Medical-Surgical ICU of St. Michael's Hospital.

Once the clinical team has decided to extubate the patient, the research team will approach the patient for consent (if capable) or the patient's substitute decision maker. Demographic information will be extracted from the medical chart and entered into the study case report form (CRF). Ultrasounds of the diaphragm, intercostal, and sternocleidomastoid muscles will be performed within 2 hours of extubation and repeated within 24 hours of extubation (if feasible). The following physiological and biological variables will be collected before and after the spontaneous breathing trial (SBT): mode of ventilation and settings, Arterial Blood Gas (ABG) results, heart rate, arterial blood pressure, peripheral capillary oxygen saturation (SpO2), respiratory rate, Glasgow Coma Score (GCS), temperature, fluid balance in the last 24 hours, Sequential Organ Failure Assessment (SOFA) score, and rapid shallow breathing index (RSBI). At the time of the ultrasound measurements, the following physiological variables will be collected: heart rate, arterial blood pressure, SpO2, respiratory rate, Glasgow Coma Score (GCS), cough, Intensive Care Delirium Screening Checklist (ICDSC), ambient air, oxygenation, use of non-invasive ventilation (NIV), level of dyspnea, level of comfort, nasal flaring, Medical Research Council (MRC) score, and the Respiratory Intensive Care Observation Scale (RICOS). Outcome data will be recorded including: extubation failure, use of NIV and/or high-flow nasal oxygen cannula post extubation, re-intubation, ICU discharge/re-admission status, and tracheostomy. A 7-day follow-up after ICU discharge will signify completion of the study.

Inclusion Criteria:

• Invasive mechanical ventilation ≥ 48 hours
• Successful spontaneous breathing trial completed and extubation decided by the attending physician

Exclusion Criteria:

• Withholding or withdrawal of life support
• Patients under extracorporeal membrane oxygenation circuit
• Impossibility to perform ultrasound of the diaphragm of the two accessory muscles: neck surgery, C-spine collar, Halo vest, morbid obesity. Patients will be enrolled as long as access to at least two locations is feasible (intercostal, diaphragm, or sternocleidomastoid).
• Known (hemi) diaphragm paralysis

Extubated ICU patients.