Aim-To examine the delivered volume during "high volume strategy" high frequency oscillation, used as rescue treatment in preterm infants; and to identify factors, other than frequency and oscillatory amplitude, influencing the magnitude of volume delivery. Method-Twenty infants (median gestational age 29 weeks) were studied on 45 occasions. Two oscillator types were used (SensorMedics and SLE). Delivered volume was measured under clinical conditions with the arterial blood gases within a predetermined range. A specially calibrated pneumotachograph system was used. Results-Overall, the median delivered volume was 2.4 ml/kg (range 1.0 to 3.6 ml/kg); on 32 occasions the delivered volume was greater than 2.0 ml/kg and on seven greater than 3.0 ml/kg. The delivered volume related significantly to disease severity; there was an inverse correlation between delivered volume and both the oxygenation index (OI) (r=−0.51) and AaDO 2 (r=−0.54). Conclusion-Delivered volume during HFO may, in certain infants, exceed the anatomical dead space, permitting some direct alveolar ventilation. (Arch Dis Child Fetal Neonatal Ed 1998;78:F148-F150) Keywords: high frequency oscillation; prematurity; delivered volume Gas exchange is maintained during high frequency oscillation (HFO), yet it has been claimed that the delivered volume is small. Although in an animal model delivered volumes of about 2-3 ml/kg have been recorded, 3 in another study 4 the volumes were as low as 10% of the anatomical dead space. This would mean that during HFO mechanisms of gas exchange, other than those occurring during normal tidal breathing, must take place.5 It is, however, diYcult to measure volume delivery accurately at fast frequencies. We have already shown that recording devices with apparently adequate frequencies of response do not behave linearly as the rate is raised above 5 Hz. 6 Fortunately, we have been able to construct a reproducible calibration curve, such that it was possible to use a simple pneumotachograph system to measure reliably the delivered volume during HFO. Results from a pilot study 6 suggested that the delivered volume during HFO could, in certain infants, be as high as 3 ml/kg. The aim of this study was to determine the magnitude of delivered volume during HFO in preterm infants and whether this was influenced by factors other than frequency and oscillatory amplitude.
MethodsTwenty infants were studied, their median gestational age was 29 weeks (range 24-37), birthweight 1090 g (range 570-2694), and postnatal age when first studied was 2 days (range 1-16). All the infants had respiratory distress syndrome and had received a median of two doses of exogenous surfactant (range 1-3). Six infants were studied on more than one occasion (median 5, range 2-11). None of the infants was paralysed at the time of study. Estimates were made of the volumes of gas delivered to the lungs during HFO. Infants were receiving HFO as rescue treatment-that is, the clinician in charge felt the blood gases to be poorly responsive to conven...