This prospective study will be carried out on mechanically ventilated patients in the medical, surgical and respiratory intensive care units of JSS University hospital, a tertiary care center after obtaining approval from Institutional ethics committee and informed consent from the relatives of all enrolled patients.

 Patients on mechanical ventilator support for a period of ≥ 48hr will be assessed clinically by acute physiology and chronic health evaluation II (APACHE II) score.

  The decision to wean patients from ventilator support will be taken by the Intensivist and primary ICU team and put on a Spontaneous Breathing Trial (SBT) when patients meet the following criteria-

1)     Resolution of the underlying pathology that led to the need for intubation and ventilatory support

2)     Calm, Cooperative and easily arousable

3)     PaO2>60mmhg and PaCO2<50mmhg as assessed Arterial Blood Gas (ABG) analysis.

            4)FiO2<0.5

            5)Positive end expiratory pressure (PEEP)≤5

            6)PaO2/FiO2>200

            7)Respiratory Rate<35/min

            8)Hemodynamically stable without the need of vasopressor support.       

   Once the Intensivist and the primary ICU team decide that the patient has been successfully weaned from ventilator support, the patient will be put on a spontaneous breathing trail (SBT) under low level pressure support (pressure support ≤ 8 and PEEP ≤ 5  on PSV mode) or a T piece circuit for a period of 2 hours and the primary investigator called.

  Right hemidiaphragmatic parameters namely diaphragmatic excursion, diaphragmatic contraction velocity and diaphragmatic thickness fraction will be measured by the primary investigator 30 minutes into the 2 hour SBT using the GE LOGIQ P6 PRO ultrasound system.The Intensivist and the primary ICU team are blinded to these measurements.

   Tidal volume, respiratory rate, minute ventilation will be also measured and RSBI calculated at this time by the primary investigator.

  Patients who pass the SBT without any clinical deterioration will be extubated under the supervision of the Intensivist and the primary ICU team.

   Criteria for failure of SBT is defined as follows-

1)Alteration of mental status defined as a decrease in GCS <10

2)Respiratory rate > 35/min

3)Systolic Blood Pressure >180mmHg or < 90mmHg

4)Heart Rate >130bpm or increase in 20% from baseline heart rate

 All patients who successfully pass a SBT and extubated will be followed up for a period of 48 hours to assess for extubation failure and the need for reintubation.

  Extubation failure will be defined as patients who require reintubation or Noninvasive ventilatory support within 48hrs of extubation. The decision to reintubate or initiate Non Invasive Ventilatory support will be made by the Intensivist and primary ICU team based on their clinical and parametrical judgement.

 Based on the above observations, Patients are divided into two groups-

GROUP 1 – Patients who are successfully weaned of ventilator support, pass a SBT and extubated and do not require any non-invasive ventilatory support or reintubation within 48 hours of extubation.

GROUP 2 – Patients who do not pass a SBT or pass a SBT but require Non invasive ventilatory support or reintubation within 48 hours of extubation.