Ultrasonography for Prediction of Extubation Success: a Holistic Approach

Weaning patients in the intensive care unit (ICU) from the mechanical ventilator is a critical period and accounts for 40% of the duration of mechanical ventilation itself. Weaning failure includes failing the initial spontaneous breathing trial (SBT) and patients with extubation failure. Extubation failure is defined as reintubation or need for rescue non-invasive ventilation within 48 hours following extubation. Patients failing extubation experience increased time spent on the mechanical ventilator and even increased mortality rates. Given these risks, predicting readiness for extubation is of key importance in the ICU.

Studies have shown, that US is a viable tool for routine use due to its bedside availability and non-invasiveness, while still maintaining excellent predictive values for its respective applications. For this reason, over the past years, critical care ultrasonography (US) has become an important part of routine bedside assessment Lately, the diaphragm has been studied extensively, due to its strong role in sustaining spontaneous breathing. Especially predicting extubation outcomes

has become a great field of interest and different studies have been conducted on this topic. Currently, indices such as diaphragm thickening (Tdi), diaphragm thickness (Tdi%) and diaphragm motion are the most frequently used parameters. Of these, thickening fraction seems to be the most promising to predict successful extubation.

However, all of the studies conducted, solely looked at diaphragm function and compared them to current standards such as the rapid shallow breathing index, while disregarding other factors strongly correlated to extubation failure, e.g. respiratory and cardiac function, as proposed by Mayo et al. Taking heart and lung function into account as well seems to be an interesting approach, because additional measurements could possibly improve predictive value while putting no further burden on the patient. Furthermore, both heart and lungs can be assessed quickly and easily by ultrasound. Cardiac parameters that are potentially useful are left ventricular function, mitral diastolic inflow and cardiac output. Regarding the lungs, pleural effusion is associated with rate of success for extubation. Effusion is detected easily and recent studies have shown, that in an ICU setting a simple 8 region protocol is sufficient to detect extra vascular lung water.

The investigators hypothesise that a holistic US approach, including measurements of heart, lungs and diaphragm, will be superior to the core diagnostic parameters of the diaphragm in predicting extubation success in mechanically ventilated critical care patients.