Elective high frequency oscillatory ventilation versus conventional ventilation for acute pulmonary dysfunction in preterm infants.

BACKGROUND: Respiratory failure due to lung immaturity is a major cause of mortality in preterm infants. Although intermittent positive pressure ventilation (IPPV) saves lives, lung distortion during its use is associated with lung injury and chronic lung disease (CLD). Conventional IPPV is provided at 30-80 breaths per minute while a newer form of ventilation called high frequency oscillatory ventilation (HFOV) provides 'breaths' at 10-15 cycles per second. This has been shown to result in less lung injury in experimental studies.

OBJECTIVES: The objective of this review is to determine whether the elective use of high frequency oscillatory ventilation (HFOV) as compared to conventional ventilation (CV) in preterm infants who are mechanically ventilated for the respiratory distress syndrome decreases the incidence of chronic lung disease (CLD) without adverse effects.

SEARCH STRATEGY: Searches were made of the Oxford Database of Perinatal Trials, MEDLINE, EMBASE, previous reviews including cross references, abstracts, conferences and symposia proceedings, expert informants, journal hand searching by the Cochrane Collaboration, mainly in the English language.

SELECTION CRITERIA: Randomized controlled trials comparing HFOV and CV in preterm or low birth weight infants with pulmonary dysfunction, mainly due to RDS, who are to be given IPPV. Randomization and commencement of treatment should have been as soon as possible after the start of IPPV and usually in the first 12 hours of life.

DATA COLLECTION AND ANALYSIS: The methodological quality of each trial was independently reviewed by the various authors. Each author extracted data separately; they were compared and differences were resolved. The standard method of the Cochrane Neonatal Review Group was used to synthesize the data using relative risk (RR) and risk difference (RD). From 1/RD the number needed to treat (NNT) for benefits, and number needed to harm (NNH) for adverse effects, were calculated. 95% confidence intervals were used.

MAIN RESULTS: Meta-analysis of the eight eligible studies comparing HFOV with CV revealed that there is no difference in mortality. There are trends toward decreases in CLD in survivors at 28-30 days, 'death or CLD at 28-30 days' and a significant reduction in CLD in survivors at 36-37 weeks postmenstrual age or discharge in the HFOV group (six trials, summary RR 0.73 (0.57, 0.93). There is a significant increase in severe (grades 3 & 4) intraventricular hemorrhage (IVH) and in any pulmonary air leak syndrome [summary RR 1.19 (1.03, 1.38)] in the HFOV group. Only 2 trials have included neurodevelopmental follow up and more survivors in the HFOV group are abnormal [summary RR 1.26 (1.01, 1.58)]. In the subgroup of six trials where a high volume strategy (HVS) was used for HFOV, this is associated with significantly lower rates of CLD in survivors at 28-30 days [three trials, summary RR 0.53 (0.36, 0.76)], of 'death or CLD at 28-30 days' [three trials, summary RR 0.56 (0.40, 0.77) and oxygen use at 36-37 weeks postmenstrual age or discharge [five trials, summary RR 0.72 (0.56, 0.93)]. There were no overall differences in the rates of IVH or PVL. One trial suggests that HFOV may reduce the cost of in-hospital care. In this group of trials HFOV is associated with a strong trend for an increased rate of gross pulmonary ALS (four trials, summary RR 1.54 (0.98, 2.42)] In the subgroup of two trials (HIFI 1989, Rettwitz-Volk 1998) not using a HVS there is no effect of HFOV on the rate of CLD; however, there is an increase in the rate of periventricular leukomalacia (PVL) [summary RR 1.64 (1.02, 2.64).

REVIEWER'S CONCLUSIONS: Benefits of HFOV in terms of CLD appear to be outweighed by concerns about increased rates of pulmonary air leak and severe IVH. Until these issues are resolved HFOV cannot be recommended as the routine method of giving mechanical ventilation to preterm infants with RDS. Future trials should target very preterm infants who are at most risk of CLD and infants should be randomized in gestational age strata. Important long term pulmonary and neurodevelopmental outcomes should be measured and reported. Economic effects should be assessed.