Assessing Diaphragm Muscle Inactivity in Mechanically Ventilated ICU Patients

Background: Mechanical ventilation is a life saving intervention in patients with acute respiratory failure, for instance, due to infection or trauma. The main goals of mechanical ventilation are to improve oxygenation and decrease the load imposed on the respiratory muscles. Unfortunately, mechanical ventilation comes with adverse events including disuse atrophy and weakness of the respiratory muscles. The diaphragm is the main muscle for inspiration and therefore this clinical entity is commonly referred to as ventilator-induced diaphragm dysfunction (VIDD). Several studies have shown that inspiratory muscle weakness is associated with adverse outcomes, including prolonged duration of mechanical ventilation. Inactivity or disuse is a recognized risk factor for the development of VIDD: disuse may result from excessive unloading of the diaphragm by the ventilator. Therefore, clinicians aim to limit the risk of VIDD by using ventilator modes that allow patients to perform at least part of the total work of breathing when deemed clinically appropriate. However, even when these so-called assisted modes for ventilation are used, excessive unloading of the diaphragm may occur; without using technology that allows monitoring of diaphragm function, the clinician is often uncertain as to whether this muscle is indeed actively working. Continuous recording of the electrical activity of the diaphragm (EAdi) is used to monitor diaphragm muscle activity in ICU patients. Furthermore, sonographic measurements of diaphragm thickness allows for an easy quantification of diaphragmatic activity (thickening fraction) as well as providing a potentially useful mechanism for studying diaphragm injury and function during mechanical ventilation.

Aim: To assess the duration of diaphragm muscle inactivity in patients admitted to the ICU using EAdi monitoring and to assess the correlation between diaphragm thicknening fraction, as measured by ultrasound, and electrical activity, as measured by EAdi.

Hypothesis: Diaphragm muscle inactivity frequently occurs in the early phase of ICU admission Design: Observational pilot study in ventilated adult ICU patients admitted to the ICU at St Michael's Hospital. The investigators aim to enroll 75 patients.

Primary outcome: Time from catheter positioning to first EAdi (> 5 uV last at least 5 minutes)

Inclusion Criteria:

• Patient admitted to the ICU
• Intubation in the ICU or < 12 hours before admission
• Expected duration of mechanical ventilation > 48 h
• Edi monitoring tube / catheter in situ by the clinical team

Non-inclusion Criteria:

• Anticipated removal of EAdi tube within 48 hours of ICU admission (e.g., for MRI, for endoscopic intervention)
• High risk for intracranial hypertension or proven intracranial hypertension due to severe neurotrauma or substantial intracranial hemorrhage because these patients will likely need Magnetic Resonance Imaging. This can be discussed on a case-by-case basis based on the severity and initial findings
• Lack of Servo-i NAVA capable ventilator, lack of EAdi catheter

Exclusion Criteria:

• Phrenic nerve lesions (past medical history)
• Contraindications to the insertion of a naso- or oro-gastric (feeding) tube
• Patients already intubated for > 12 hours