Title: Role of ultrasound in predicting weaning failure in children undergoing cardiac surgery: Prospective observational study
INTRODUCTION
Weaning failure, defined as reintubation within 24-48 hours of extubation, has an incidence of 10% in postoperative pediatric cardiac surgical patients. 1,2 The children undergoing cardiac surgery commonly develop pulmonary interstitial edema in the form of extravascular lung water (EVLW) collection as a result of inflammation mediated endothelial injury due to cardiopulmonary bypass (CPB) leading to prolonged mechanical ventilation (MV) . 3-5 The incidence in mortality has been upto 31% in critically ill children with non-cardiac acute respiratory failure presenting with excess EVLW of >10 ml/kg. 6 In addition to this, the inadvertent injury caused to the phrenic nerve during surgical manipulation, cold ice slush used in the pericardial cradle may cause diaphragmatic palsy (DP). 3-5 The incidence of DP after cardiac surgery is 0.3-12.8%. 7 It may present with postoperative respiratory distress, atelectasis, recurrent pneumonia or difficulty to wean from mechanical ventilation.1
Commonly used weaning indices are maximum inspiratory pressure, rapid shallow breathing index (RSBI), tracheal airway occlusion pressure at 0.1s, CROP index and leak test which can be performed to assess the extubation readiness . However, these indices are influenced by the combined functions of diaphragm, intercostal muscles, abdominal muscles and the compliance of the rib cage. Serial chest X-rays are routinely used to assess the post operative EVLW. 8,9 However, CXRs may be inaccurate when supine radiographs are used. The progressive elevation of hemi-diaphragm visualized on CXR suggest diaphragm palsy but the cumulative radiation dose given to the child will be very high.8-13 Fluoroscopy guided Sniff test, phrenic nerve conduction study and trans-diaphragmatic pressure movements are used for the assessment of the diaphragm but they are invasive procedures, have high radiation exposure, not easily available in all centers and involve transport of patient from ICU to the concern department for the investigation. 13
EVLW and diaphragm function can be easily measured and quantified at the post-operative bedside by ultrasonography by the Intensivists.14-17 This has a very small learning curve, can be followed in real time. However, the data on the feasibility and utility of B-lines and Diaphragm excursion and thickness measurements in post-operative pediatric patients is sparse. 18
In this study, we hypothesized that the severity of lung interstitial edema (EVLW) as shown by B-lines and diaphragm dysfunction measured by ultrasound, can be used as predictors of weaning failure from mechanical ventilation in pediatric patients undergoing cardiac surgery. The primary aim of our study was to observe the correlation between weaning failure, which we defined as re-intubation within 24-48 hours of extubation and ultrasonic assessment of EVLW and Diaphragm function in pediatric patients on MV after cardiac surgery and secondarily to observe correlation between weaning failure and other indices of weaning from mechanical ventilation , PaO2/Fio2 (PF ratio )ratio, rapid shallow breathing index,(RSBI) duration of mechanical ventilation and use of non-invasive ventilation and length of intensive care unit stay.
  1. METHODS
  2. Informed Consent
This prospective observational study was carried out after institute’s internal ethics committee clearance (INT/IEC/2016/2540) and CTRI registration (CTRI/2018/02/011677). Written informed consent were taken from parents or legal guardians of the patients.