Ultrasound for Assessment of Extubation Readiness

Study Design and setting:This is a prospective descriptive pilot study that will be conducted on infants born at < 28 weeks gestation who meet eligibility criteria and are admitted to the Neonatal intensive care at Mount Sinai Hospital. Enrolment of eligible infants will start after obtaining approval from Mount Sinai Research Ethics Board and parent's consent.

Time of assessment: Parents of infants on invasive mechanical ventilation who are eligible for the study will be approached for consent. Once the decision made by attending physician to extubate the infant, Chest ultrasound (Lung ultrasound + diaphragmatic function assessment) will be done. Chest ultrasound will be done before next feeding to avoid any interference of a full stomach on diaphragmatic assessment.

Study procedure: Decisions about extubation will be as per the clinical judgment of the physician in-charge of the infant and will not in any way based on Chest ultrasound measurements. A lung ultrasound combined with diaphragmatic function assessment will be done by one of the investigators prior to extubation. The result of Chest ultrasound will be masked for the clinical team to avoid any influence of the Chest ultrasound result on the extubation decision. On the other hand, if the attending physician requests Chest ultrasound for the purpose of the ongoing clinical management or to help with making extubation decision then the result of the study will be disclosed to the physician and this infant will be excluded from the study.

A random sample of 20% of eligible infants will have lung ultrasound scoring and diaphragmatic function assessment done twice by 2 operators (with various levels of Chest ultrasound expertise). None of the operator will be aware of the result of Chest ultrasound done by the other operator for the same patient. Lung ultrasound severity score, diaphragmatic thickness fraction and diaphragmatic excursion will be calculated. Inter-rater agreement will be assessed using raw percentage of agreement (Pa), Cohen's and Kappa (κ), and G wet agreement coefficient (AC1). Intra-class correlation will be determined for variables with continuous measurements (mixed factorial design). High-resolution linear and curvi-linear ultrasound probes of 20-5 and 10-3 MegaHertZ will be used to assess lung ultrasound score and to measure diaphragmatic thickness and diaphragmatic excursion [amplitude] respectively using both B-mode and M-mode.

Lung ultrasound assessment technique: Chest ultrasound will be performed in a standardized manner. A longitudinal scan of the anterior and lateral chest walls will be performed. Three chest areas for each side (upper anterior, lower anterior, and lateral) will be assessed. Each area will have a score of 0 to 4 points with the total score ranges from 0 to 24 which inversely correlating with lung aeration.

Diaphragmatic assessment technique: Diaphragm assessment will be performed in the supine position. For measuring diaphragmatic excursion, the curvilinear probe will be placed on the lower intercostal spaces between the mid-clavicular and anterior axillary lines on the right side. Using the B mode, the proper exploration line of the diaphragm will be detected by directing the beam perpendicular to the posterior third of each hemi-diaphragm. By M mode, the cyclic caudal diaphragmatic displacement with respiration will be measured as the perpendicular distance between the most caudal point of the liver or spleen at the end of expiration and the end of inspiration. The average of three respiratory cycles will be taken.

The assessment of the diaphragmatic efficiency as a pressure generator will be evaluated using the diaphragmatic thickness fraction. Diaphragmatic thickness will be measured at the apposition zone which can be obtained by placing the linear transducer above the 10th rib in the mid-axillary or anterior axillary lines in the right intercostal spaces. By B-mode, three distinct layers will be seen, the diaphragm as a hypo-echoic area bordered by two clear echogenic lines of the pleural membrane (upper line) and the peritoneal membrane (lower line). Using M-mode tracing, inspiratory diaphragmatic thickness will be measured as the maximum perpendicular distance between pleural and peritoneal layers and by the same way expiratory diaphragmatic thickness will be recorded. diaphragmatic thickness Fraction will be calculated using the following formula: diaphragmatic thickness Fraction equal to [(inspiratory thickness _ expiratory thickness)/expiratory thickness] x100. The average of the calculated diaphragmatic thickness Fraction from three respiratory cycles will be estimated. All Chest Ultrasound assessments will be undertaken using a standard aseptic technique.