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.