Inspiratory Muscle Training in Difficult to Wean Patients: a Randomised Controlled Trial

1. Introduction.

Weaning covers the entire process of liberating the patient from mechanical ventilation (MV) support and the endotracheal tube or tracheostomy. For the majority of mechanically-ventilated patients spontaneous breathing (weaning) can be successfully accomplished quickly and easily, however, this is not the case for 15-30% of ventilated patients. The most common factors leading to weaning failure are i) respiratory muscle fatigue ii) hypercapnia iii) dyspnoea and iv) anxiety. Along these lines, a proposed a mechanism that may contribute to weaning failure namely the ''stealing effect'' theory. More specifically, the ''stealing effect'' theory hypothesizes that during the weaning process the energy demand of the respiratory muscles can increase to such an extent that respiratory muscles may deprive oxygen and blood of other tissues such as the brain. In fact, at least for the brain, the decrease in blood and oxygen delivery could theoretically predispose this organ to dysfunction. Restriction in oxygen delivery to the brain could have an adverse impact on the function of the respiratory muscles per se by impairing the output of the respiratory centre and of neuromuscular competence of the ventilatory pump, rendering the ventilatory pump incapable of inflating the lungs thus exaggerating respiratory muscle fatigue and leading to weaning failure. Inspiratory muscle training (ΙΜΤ) is a non-pharmacological and cost-effective treatment which has been shown to improve the functional capacity of the inspiratory muscles in patients with respiratory muscle weakness whilst has been recently proposed as a possible additional component of weaning strategies. Implementation of an IMT program may decrease the energy demands of inspiratory muscles by improving inspiratory muscles breathing efficiency on the one hand and by optimizing the respiratory muscle oxygen utilization on the other hand. Enhancement in muscle strength and contractile function, as well as oxidative capacity in response to IMT that have been documented in patients with chronic lung diseases in response to IMT, may increase the oxygen utilization by the inspiratory muscles thus decreasing the demand of blood flow and oxygen in favour of the cerebral cortex.

The aims of the project are:

In an observational study design:

1. To investigate whether the inspiratory muscles steal blood and oxygen from the cerebral cortex (''stealing effect'').
2. To investigate the effect of the ''stealing effect'' theory on weaning outcomes.