Methods

The study was approved by the Clinical Research Ethics Committee of the Chinese University of Hong Kong.

Inborn preterm infants admitted consecutively into our neonatal intensive care unit for the treatment of RDS were considered eligible for the study if they satisfied the following criteria: gestation < 32 weeks; birthweight < 1.5 kg; requirement for mechanical ventilation; and parental consent to the study. All the infants were given two doses (5 ml/kg per dose) of intratracheal synthetic surfactant (Exosurf, Burroughs Wellcome Corporation, UK) 12 hours apart. The first dose was given within 1 hour of birth. The infant was enrolled if a blood gas obtained between 6 to 10 hours after the second dose of surfactant (19 to 23 hours after birth) showed an arterial PO₂:alveolar PO₂ ratio of < 0.25. Alveolar PO₂(PAO₂) was calculated from the alveolar gas equation PaO₂ = PIO₂ −PaCO₂/R + PaCO₂ × FI O₂ ×(1−)/R where PIO₂ is the partial pressure of oxygen in the inspired gas and equals the difference between the atmospheric pressure (760 mm Hg or 101.3 kPa) and the saturated water vapour pressure (47 mm Hg or 6.3 kPa), PaCO₂ is the arterial carbon dioxide tension and R is the respiratory quotient and equals 0.8. Infants who were dying and those with significant congenital malformation were excluded. The infants enrolled were randomised by computer generated random numbers into treatment (group 1) and control groups (group 2); allocation to the groups was carried out by opening opaque, sealed envelopes. The calculation of the required number of infants in each group was based on a previous report on the early use of systemic dexamethasone which showed that successful extubation at 2 weeks of age was accomplished in 57% of the treated group and in 28% in the placebo group.3 A sample size of 26 in each group would result in a power of 0.8 for detecting a difference of this size with an α error of < 0.05.

All the infants were given intravenous penicillin and netilmicin shortly after birth, after a blood count and blood culture specimens were obtained. The antibiotics were discontinued after three days if the infants showed no sign of sepsis and the blood culture remained negative. All infants were continuously monitored for their heart rate, respiratory rate, and transcutaneous oxygen saturation (SaO₂). Blood pressure was monitored continuously through an indwelling arterial catheter when available, or hourly using the oscillometric method (Dinamap XL Vital Signs Monitor, Johnson and Johnson Medical Inc, USA). Capillary blood glucose concentration was tested four times daily using the strip method (Haemo-Glukotest, Boehringer Mannheim, GmbH, Germany). True blood glucose was measured when the Haemo-Glukotest showed the presence of hyperglycaemia (blood glucose > 7 mmol/l).

Each infant in group 1 (n=27) was given two puffs of fluticasone by metered dose inhaler (MDI) (Flixotide; Glaxo, UK; 250 μg per puff), and in group 2 (n=26) two puffs of placebo provided by the same manufacturer, 12 hourly for two weeks. The first dose was given within 24 hours of birth. The label on the MDI canisters had been removed so as to conceal the identity of the contents.

Aerosol delivery was carried out by an investigator not involved in the clinical management of the patients or data collection. Immediately before aerosol delivery, an MV15s Aerochamber was inserted between the Y-connector of the ventilator circuit and endotracheal tube. After suctioning of the endotracheal tube, two puffs of the aerosol (fluticasone or placebo, as appropriate) were actuated into the spacer one minute apart immediately before the inspiratory phase of a ventilator generated breath. The MDI canister was vigorously shaken for at least 10 seconds before each actuation. The spacer was removed one minute after the second puff.

Extubation was considered when the FIO₂ and ventilator rate were decreased to < 0.4 and ⩽ 10 breaths a minute, respectively. The decision to extubate was made by the attending neonatologists who were blinded to the study protocol and the nature of the aerosol given to the infants. After the endotracheal tube was removed oxygen was administered via a head box at a concentration 10% higher than that of the ventilator gas. Subsequently, FIO₂ was adjusted so that the infant’s SaO₂ was maintained between 90% to 93%. All infants were given a loading dose (6 mg/kg) of intravenous aminophylline immediately before extubation, followed by a maintenance dose of 2.5 mg/kg every 12 hours. Infants extubated before day 14 continued to receive the aerosol delivered through a neonatal Aerochamber (Trudell, Canada), which had been modified by removing its one way non-rebreathing valve. This modification has been shown to increase the amount of aerosol delivery.14 The face mask of the Aerochamber was replaced with a Laerdal Resuscitation mask (Laerdal, Stavanger, Norway) which has a smaller dead space and tighter fit to the face. The face mask was placed tightly over the infant’s face, covering the nose and the mouth during aerosol delivery. After delivery of the second dose, the infant was allowed to breathe into the Aerochamber for 1 minute before the system was removed.

In both groups infants with significant respiratory problems after 14 days of age were given open label systemic dexamethasone, as decided by the attending neonatologist. In our unit treatment with systemic steroids is considered in infants older than 3 weeks of age who remain ventilated with FIO₂ > 30% or breathing spontaneously in an oxyhood with FIO₂ > 40%. The two groups were compared for the following outcomes: successful extubation by days 7 and 14 of age; death; oxygen dependency at 28 days of postnatal age and 36 weeks after conception; complications, including hyperglycaemia, hypertension, sepsis confirmed by blood culture, pulmonary air leak (interstitial emphysema, pneumothorax, or pneumomediastinum), periventricular haemorrhage and leucomalacia, retinopathy of prematurity, patent ductus arteriosus, and necrotising enterocolitis; and bacterial colonisation of the airway. Extubation was considered to be successful if the infant was able to breathe spontaneously without the endotracheal tube or assisted ventilation for at least 48 hours without a significant increase in respiratory effort and deterioration in blood gas values. Hyperglycaemia was defined as a blood glucose reading > 7 mmol/l.15 The number of infants with high blood glucose concentration >10 mmol/l was also compared between the two groups. Hypertension was defined as two consecutive readings of systolic or diastolic blood pressure greater than 80 mm Hg and 45 mm Hg, respectively.16 Cranial ultrasound scanning was performed at 6, 14, and 28 days of age, and whenever periventricular haemorrhage was suspected clinically. Symptomatic patent ductus arteriosus was treated with intravenous indomethacin after confirmation by echocardiogram. Clinically significant patent ductus arteriosus refractory to indomethacin treatment was closed by surgical ligation. Ophthalmological screening for retinopathy of prematurity was started at 4 weeks of age. Necrotising enterocolitis was diagnosed by the presence of pneumatosis intestinalis or intestinal perforation on abdominal radiograph, or for those requiring surgical intervention, on laparotomy. Tracheal aspirate was obtained for bacterial and fungal culture immediately before the first dose of aerosol, and at 3, 5, 7 and 14 days of age.

Static respiratory system compliance (Crs) and resistance (Rrs) were measured immediately before the start of aerosol treatment, and repeated on days 3, 7, and 14 in infants who remained intubated and ventilated. Both Crs and Rrs were measured using a SensorMedics Pulmonary Cart (SensorMedics Inc., Yorba Linda, CA, USA) using the passive flow–volume technique.17 The measurement was carried out using a pneumotachograph (Hans Rudolph Inc., USA) with a small dead space (1.8 ml) connected to the endotracheal tube. A breath was accepted for analysis only when the occlusion pressure reached a stable plateau. In each measurement Crs and Rrs were obtained from the mean values of at least 10 acceptable breaths with a coefficient of variation of less than 10%.

The particle size distribution of the fluticasone aerosol was estimated by collecting the contents of 10 actuations of the metered dose inhaler into an Anderson Cascade Impactor operating at 28.3 l/min. The amount of fluticasone collected at each stage of the Impactor was assayed spectroscopically (Hitachi Spectrophotometer, Trudell, Canada). The experiment was repeated by actuating the inhaler into an MV15s Aerochamber connected to the Y-connector of a continuous flow ventilator circuit similar to that used in the infants. The aerosol was collected into the impactor after passing through an endotracheal tube connected to the exit of the Aerochamber. The test was carried out using endotracheal tubes of two different sizes: 2.5 mm and 3.0 mm internal diameter. Each experiment was repeated six times and the mass median aerodynamic diameter (MMAD) and geometric standard deviation (GSD) calculated.

The dose of fluticasone available at the end of each size of endotracheal tube was measured by collecting single doses in unit-dose collection tubes and assaying the drug as above.

Comparison between the two groups was made using the non-paired Student’s t test for continuous variables, and the χ² test for rates and proportions. Serial measurements within the same group were compared by repeated measures analysis of variance (ANOVA), followed by the Bonferronit test when the ANOVA test showed a significant difference. Between group comparison of serial changes in lung mechanics with time was made by multivariate analysis using unbalanced repeated measures models with first order autoregressive covariance matrices (BMDP/Dynamic Program 5V, release 7, BMDP Statistical Software Inc., Los Angeles, CA, USA). Wald statistics were used to check the significance of the differences between the two groups over time.