Volume delivery during high frequency oscillation

Abstract

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...

High-frequency oscillatory ventilation: What large-animal studies have taught us!

“…A tidal volume of 4.4 ± 1.2 mL/kg was delivered at an I:E of 1:1, delta pressure of 60 cm H 2 O, and rate of 4 Hz. These findings were similar to those observed in other smaller animal models (30)(31)(32). It is interesting to speculate that at the capability of current adult oscillators with delta pressures of 90 cm H 2 O and rates of 3 Hz, tidal volumes of ≥6 mL/kg would be delivered during HFO in this 30-kg lavage injury sheep model.…”

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New Generation Neonatal High Frequency Ventilators: Effect of Oscillatory Frequency and Working Principles on Performance

“…There is no consensus about the ideal V T for HFOV, but studies in animals 17,18 and pre-term neonates 19 have shown that a V T of 2-3 mL/kg allows optimal gas exchange during HFOV. Although the use of these new generation neonatal ventilators is intended for the neonatal population unlike the 3100A (a ventilator that can be used with patients larger than neonates), some of them might not have sufficient power to deliver required V T for adequate gas exchange, especially when used in full-term infants at high oscillatory frequencies.…”

Comparison of two inspiratory: expiratory ratios during high frequency oscillation

“…To compensate for this, the average value of the inspiratory and expiratory volumes was determined, which was then converted to the actual volume delivered using the calibration curve. We had previously validated using the mean of the inspiratory and expiratory volume trace when inspiration only took 30% of the cycle time [9]. The delivered volume did not dier signi®cantly between dierent levels of humidity (0±80%) or inspired oxygen concentrations (21± 100%).…”