The aim of the current study is to compare the effect of ventilator trigger sensitivity adjustment versus threshold inspiratory muscle training on arterial blood gases in mechanically ventilated patients.

Failed extubations are not uncommon in most ICUs, the failure rate ranging from 2 to 20%. Since failed extubation is associated with greater hospital morbidity and mortality and longer length of stay, it is imperative to identify screening techniques that minimize the number of failed extubations.

Many studies have been done on the effect of IMT by threshold IMT and adjustment of mechanical ventilator trigger separately, thereby, it is rational to compare between two methods of training to know which is more effective to help in weaning process through its effect on ABGs.

Inclusion Criteria:

1. Difficult to wean Guillain barre patients who have been on MV for at least 48 hours. Difficult to wean subjects have been defined as those who fail the first spontaneous breathing trial (SBT)and may require up to 3 SBTs or up to 7 d from the first attempt to achieve successful weaning (B´eduneau G. et al.,2017) and (Annia F. et al.,2019).
2. Age: >18 years.
3. Both sexes will be included.
4. Ventilator mode: Pressure support mode with FiO2≤ 0.5, positive end expiratory pressure (PEEP) will be<8-10cm/H2Oand respiratory rate < 25.
5. Conscious oriented patient with Glasgow coma score ≥13.
6. Alertness will be titrated to a Riker Sedation Agitation Score of 4.
7. PH>7.25, arterial oxygen saturation >90%.
8. Cardiovascular stability.
9. Maximal inspiratory pressure from 15 to 30 cm H2O and able to trigger spontaneous breaths on ventilator.

Exclusion Criteria:

1. Persistent hemodynamic instability as life threatening arrhythmias, acute heart failure.
2. Severe breathlessness, when spontaneously breathing.
3. Any progressive neuromuscular disease that would interfere with responding to inspiratory muscle training (non-stationary course).
4. Spinal cord injury.
5. Skeletal pathology (scoliosis, flail chest, spinal instrumentation) that would seriously impair the movement of the chest wall and ribs.
6. Patients on heavy sedation and respiratory muscle paralysis.
7. High peak airway pressure (barotraumas).
8. BMI ≥ 40.