Randomised controlled trial of two methods of weaning from high frequency positive pressure ventilation. Prospective clinical comparison of two methods for mechanical ventilation of neonates: rapid rate and short inspiratory time versus slow rate and long inspiratory time. Decreased incidence of extra-alveolar air leakage or death prior to air leakage in high versus low rate positive pressure ventilation: results of a randomised seven-centre trial in preterm infants. Hyaline membrane disease. A controlled study of inspiratory to expiratory ratio in its management by ventilator.
Forty preterm infants suffering from respiratory distress syndrome were entered into a randomised controlled trial to assess the importance of the length of inspiratory time during weaning from high frequency positive pressure ventilation (HFPPV). Two weaning regimes were compared: in one (group A) inspiratory time was limited to 0.5 seconds throughout weaning, in the other (group B) ventilator rate was reduced by increasing both inspiratory and expiratory time (inspiration:expiration ratio constant) until inspiratory time reached 1.0 seconds. At ventilator rates of 20 and 40 breaths/minute an acute comparison was made in all 40 infants of the two inspiratory times; despite the lower mean airway pressure associated with the shorter inspiratory time blood gases were maintained. There was no difference in the incidence of pneumothoraces or need for reventilation between the two regimens but infants in group A had a shorter duration of weaning. We conclude limitation of inspiratory time to 0.5 seconds during weaning from HFPPV is advantageous to preterm infants with respiratory distress syndrome. A prospective comparison was made of the clinical courses of two groups of neonates ventilated according to different protocols: one group at rates of 20 to 40/minute with a one-second IT, and the other at a rate of 60/minute and 0.5 second IT. Other ventilator settings were adjusted within protocol limits to maintain desired blood gas values. Mean starting and highest PIP were lower in the rapid rate group. The results showed no difference in mortality, failure to remain within protocol limits, time requiring respiratory treatment or FiO2 more than 0.6, and incidence of PDA or chronic lung disease. There was a difference (P = 0.011) in number of infants developing pneumothoraces (14% in the rapid group vs 35% in the slow group). Rapid rate ventilation can be used to decrease the incidence of pneumothorax, reserving long IT and higher PIP for infants who cannot be oxygenated or ventilated without them. Two different ventilation techniques were compared in a seven-centre, randomised trial with 181 preterm infants up to and including 32 completed weeks gestational age, who needed mechanical ventilation because of lung disease of any type. Technique A used a constant rate (60 cycles/min), inspiratory time (IT) (0.33s) and inspiratory: expiratory ratio (I:E) (1:2). The tidal and minute volume was only changed by varying peak inspiratory pressure until weaning via continuous positive airway pressure. Technique B used a lower rate (30 cycles/min) with longer IT (1.0 s). The I:E ratio could be changed from 1:1 to 2:1 in case of hypoxaemia. Chest X-rays taken at fixed intervals were evaluated by a paediatric radiologist and a neonatologist unaware of the type of ventilation used in the patients. A reduction of at least 20% in extra-alveolar air leakage (EAL) or death prior to EAL was supposed in infants ventilated by method A. A sequential design was used to test this hypothesis. The null hypothesis was rejected (P = 0.05) when the 22nd untied pair was completed. The largest reduction in EAL (-55%) was observed in the subgroup 31-32 weeks of gestation and none in the most immature group (< 28 weeks). We conclude that in preterm infants requiring mechanical ventilation for any reason of lung insufficiency, ventilation at 60 cycles/min and short IT (0.33 s) significantly reduces EAL or prior death compared with 30 cycles/min and a longer IT of 1 s. We speculate that a further increase in rate and reduction of IT would also lower the risk of barotrauma in the most immature and susceptible infants. Sixty-nine neonates with severe hyaline membrane disease (HMD) were mechanically ventilated using either a 1:2 or a 2:1 inspiratory to expiratory (I/E) ratio. Survivors in the 2:1 group required a lower fraction of oxygen in the inspired air (FiO2) and lower end-expiratory pressure to achieve satisfactory oxygenation. During the first week of life, time of exposure to FiO2 greater than 0.60 while being mechanically ventilated was 29.7 +/- 7.5 hours for the 1:2 group and 6.6 +/- 2,7 hours for the 2:1 group, while time of exposure to end-expiratory pressure greater than 3 cm H2O was 49.4 +/- 7.9 hours for the 1:2 group and 13.4 +/- 7.4 hours for the 2:1 group. Mortality and the incidence of air leak, patent ductus arteriosus, intraventricular hemorrhage, necrotizing enterocolitis, bronchopulmonary dysplasia, and pulmonary hemorrhage were not different for the two groups. Using an increased I/E ratio during the acute phase of HMD improved oxygenation but did not alter morbidity or mortality.
Caution should be exercised in applying these results to modern neonatal intensive care, because the studies included in this review were conducted prior to the introduction of antenatal steroids, post natal surfactant and the use of synchronised modes of ventilatory support. Most of the participants had single pathology (HMD) and no studies examined the effects of IT on newborns ventilated for other reasons such as meconium aspiration and congenital heart disease (lungs with normal compliance). However, the increased rates of air leaks and deaths using long ITs are clinically important; thus, infants with poorly compliant lungs should be ventilated with a short IT.