Definitions
Extubation failure was defined as need for reintubation within 5 days of the first elective extubation.7,8 Respiratory status was assessed using ventilator set rate, fraction of inspired oxygen (FiO2) received, mean airway pressure and peak inspiratory pressure given by the ventilator along with the respiratory severity score (RSS: product of mean airway pressure and FiO2) and ventilation index (VI: product of the set rate, partial pressure of carbon dioxide in arterial or capillary blood (Pco2), and the difference between peak inspiratory and positive end-expiratory pressure divided by 1,000). Ventilation index was used as an objective measure of adequacy of ventilation in response to the respiratory support provided,16 and respiratory severity score (RSS) was used as an objective marker of oxygenation in relation to mean airway pressure received by the patient.17 We also analyzed blood gas parameters that included arterial or capillary blood gas pH and Pco2, and compared pre-extubation levels with levels 24 hours and 72 hours post reintubation.
Among those infants who failed extubation, time to reach pre-extubation respiratory status (such as RSS and VI) was defined as time to reach same level of these respiratory parameters or extubation to non-invasive ventilation, whichever occurred first.
Gestational age was estimated based on best obstetric approximation using early ultrasonography findings, date of last menstrual period, or modified Ballard score in that order.18 Small for gestational age (SGA) was defined as per the Olsen definition.19 The usual practice at our center through the study period was to use noninvasive ventilation whenever possible (NCPAP: nasal continuous positive airway pressure or NIPPV: nasal intermittent positive pressure ventilation), and to limit endotracheal intubation and MV to infants who were persistently apneic (≥3 episodes in a 24-hour period) and/or failed attempted noninvasive ventilation. Extubation was usually attempted at ventilator set rates of 16 to 20 breaths per minute, mean airway pressure of less than 8 cm H2O, and FiO2 below 0.4, with blood gas pH greater than 7.25 and Pco2 less than 60 mm Hg.