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.
- METHODS
- 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.