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A 26 week infant is about to be delivered by emergency caesarean section to a mother with placental abruption and fetal distress. No antenatal steroids have been administered to the mother. You are called to attend the delivery. You are setting up the equipment when the respiratory therapist suggests that we should use high frequency oscillatory ventilation (HFOV) as primary mode of ventilation. He also cites few articles suggesting benefit of high volume strategy HFOV over conventional ventilation (CV). You wonder if there is enough evidence to support the intervention.
Structured clinical question
In very low birth infants with respiratory distress syndrome [patient], is elective high frequency oscillatory ventilation using high volume strategy [intervention] better than conventional mechanical ventilation [comparison] in decreasing chronic lung disease or mortality at 36 weeks corrected gestational age [outcome]?
Search strategy and outcome
Secondary sources—Cochrane Library (Issue 4, 2002): (one relevant systematic review). Medline (1996–2002).
Cochrane: “high frequency ventilation” AND “infant, newborn” OR “infant, preterm”. Medline: “high frequency ventilation” and “infant, newborn” OR “infant, preterm” AND “chronic lung disease OR bronchopulmonary dysplasia” AND “randomised clinical trial”.
Overall, 13 RCTs of HFOV versus CV were found in the search, of which eight met the eligibility criteria of the Cochrane review and are included in the review. Two RCTs have been published since the Cochrane update. The remaining four trials have not been published in sufficient detail for analysis.
See table 2.
Chronic lung disease (CLD) remains a serious and common problem among very low birth weight infants despite the use of antenatal steroids and postnatal surfactant therapy to decrease the incidence and severity of respiratory distress syndrome (RDS). This condition affects nearly third of all very low birth weight infants with RDS (Henderson-Smart et al). The aetiology of CLD is multifactorial and lung inflammation due to mechanical ventilation, oxygen toxicity, or infection contributes to its development. A well performed systematic review (Henderson-Smart et al) did not find any substantial advantage of HFOV over CV in management of preterm infants with RDS. The authors concluded that the borderline benefits of HFOV in terms of CLD appear to be outweighed by concerns about increased rates of IVH and airleaks, despite the fact that these side effects are not statistically significant.
CLINICAL BOTTOM LINE
The aetiology of chronic lung disease is multifactorial and choice of ventilation does not affect its incidence.
High frequency oscillatory ventilation (HFOV) is probably not superior to conventional ventilation as primary mode of ventilation in preterm infants with respiratory distress syndrome for prevention of chronic lung disease or mortality at 36 weeks. However, use of HFOV is safe and not associated with increased risk of intraventricular haemorrhage or airleaks.
Important long term neurodevelopmental outcomes should be addressed for infants treated with HFOV, as should the economic effects of introducing a new mode of ventilation.
The two largest contemporary trials (Johnson et al and Courtney et al) published recently showed contrasting results. The results of the study by Johnson et al were similar to the majority of previous trials which did not show a difference between the two modes of ventilation for the combined outcome of CLD or death. In contrast, Courtney et al found a small difference favouring HFOV. These two trials were very different in their ventilatory strategy. The trial by Johnson et al provided target guidelines for blood gases and specified only the inspiratory time and ventilatory rate. The rest of the ventilatory management was at the discretion of the attending clinician and reflects common NICU practice around the world. On the other hand, the ventilatory strategy in the study by Courtney et al was strictly protocol based.
So, what do we find? Even in the most well controlled situations and experienced hands, HFOV does not confer a clinically significant advantage in terms of CLD and mortality at 36 weeks.
We extracted data from the Cochrane systematic review (Henderson-Smart et al) for the trials comparing HFOV using high volume strategy versus CV and combined that with the data from the trials by Johnson et al and Courtney et al. The resulting meta-analysis (seven trials and 2069 infants) showed a borderline statistically significant reduction in the incidence of CLD or death in the HFOV group (summary RR 0.90, 95% CI 0.83 to 0.98; NNT 20, 95% CI 11 to 100). There was no evidence of difference in the incidence of grade 3 or 4 IVH (summary RR 0.97, 95% CI 0.78 to 1.19) or pulmonary airleaks (summary RR 1.04, 95% CI 0.87 to 1.25).
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