Left Ventricular Diastolic Dysfunction as a Predictor of Weaning Failure From Mechanical Ventilation
Condition: Left Ventricular Diastolic Dysfunction; Weaning Failure; Mechanical Ventilation Complication; Diaphragmatic Disorder
MeSH terms: Ventricular Dysfunction, Left
Study type: Observational

Summary: 
      Both premature and delayed extubation prolong the duration of mechanical ventilation and the
      intensive care unit (ICU) length of stay and increase morbidity and mortality. Therefore,
      accurate prediction of postextubation distress and the early diagnosis of the causes
      responsible for failure of a trial of pressure support ventilation are of paramount
      importance to improve the outcome of mechanically ventilated patients in the ICU.

      This observational study is designed to test the ability of cardiac and diaphragm function
      assessed by bedside ultrasound to predict extubation failure within 48 h and re-intubation
      within 1 week after extubation.
    

Detailed description: 
      Weaning from mechanical ventilation is the process of gradual ventilatory support reduction
      to the patient subjected to mechanical ventilation for more than 24 hours. Determining the
      correct time to extubate mechanically ventilated patients is a crucial issue in the critical
      care practice.

      Spontaneous breathing trial (SBT) is recommended to predict weaning outcome. However, 13% to
      26% of patients who are extubated following a successful SBT need to be reintubated within 48
      hours.

      Traditional indicators, such as respiratory rate (RR), minute ventilation, tidal volume (VT),
      and the rapid shallow breathing index (RSBI), can reflect patients' integral conditions, but
      none has shown great prognostic accuracy for weaning failure.

      Although there are several causes of weaning failure, cardiac function deterioration during
      the weaning process combined with acute pulmonary edema is considered the leading cause of
      weaning failure. The transition from positive to negative thoracic pressure increases venous
      return and left ventricular afterload, decreases left ventricular compliance and may induce
      cardiac ischemia. All of these factors tend to increase ventricular filling pressures and may
      consequently lead to weaning-induced pulmonary edema. The efficacy of echocardiography for
      predicting weaning failure has been reported, however there is debate over the predictive
      value of echocardiography in this setting continues due to differences in weaning technique
      and outcome evaluation.

      The diaphragm is the principal respiratory muscle. With an excursion of 1 to 2 cm, it
      provides nearly 75% of the resting pulmonary ventilation, while during the forced breathing,
      its amplitude is up to 7 to 11 cm. However, the diaphragm is vulnerable to damage from
      hypotension, hypoxia, and sepsis, which are very common in critically ill patients. While in
      surgical patients, diaphragm dysfunction is often caused by acute insults such as trauma or
      surgical procedures. In addition, mechanical ventilation itself can decrease the force of the
      diaphragm and induce diaphragmatic dysfunction, named as ventilator-induced diaphragmatic
      dysfunction. Many studies have shown that Diaphragm dysfunction is responsible for a number
      of pulmonary complications, including atelectasis and pneumonia, which are risk factors for
      extubation failure. and might lead to weaning failure and long-term mechanical ventilation.

      Some studies have reported that diaphragmatic excursion (DE) or and diaphragmatic thickening
      fraction (DTF) could predict extubation failure.

      Although transthoracic echocardiography and diaphragm ultrasound have been confirmed in
      independently assessing extubation outcomes, few studies have shown their different roles in
      the weaning process until now.
    

Intervention name(s): transthoracic echocardiography
Intervention type(s): Diagnostic Test
Intervention description(s): Trans-mitral flow velocities (peak early diastolic E and peak late diastolic A) will be recorded with pulsed-wave Doppler, placing the sample volume at the mitral valve tips from the apical 4-chamber view; deceleration time of the E wave (DTE) will be measured. Peak early diastolic velocity will be obtained with tissue Doppler imaging (TDI), in the apical 4-chamber view, positioning the pulsed-wave Doppler sample volume at or 1 cm within the septal insertion sites of the mitral leaflets, so as to cover the longitudinal excursion of the mitral annulus in both systole and diastole. Then, the E/A ratio and the trans-mitral inflow E wave to mitral annular e' (E/e) will be calculated.Diaphragmatic thickness will be assessed in the zone of apposition of the diaphragm to the rib cage between the 8th and 10th intercostal spaces using a 3-12 MHz linear array probe , we will record changes in diaphragm vertical excursion using M-mode ultrasound.
Other intervention name(s): diaphragm ultrasonographic
Observational model: Cohort
Time perspective: Prospective
Sampling method: Probability Sample
Study population: 
        All patients aged more than 40 years who are intubated and mechanically ventilated for more
        than 48 hours, with improvement of underlying cause of acute respiratory failure and
        considered ready to undergo a spontaneous breathing trial (SBT) by the attending physician
        on the basis of readiness-to-wean criteria used in our surgical ICUn Criteria
      
Keywords: Mechanical Ventilation Complication; Left Ventricular Diastolic Dysfunction; Pulmonary Edema; echocardiography