Humidity during high-frequency oscillatory ventilation compared to
intermittent positive pressure ventilation in extremely preterm
neonates: an in-vitro and in-vivo observational study.
Abstract
Background: Inappropriate humidification of inspired gas during
mechanical ventilation can impair lung development in extremely low
birthweight (ELBW) infants. Humidification depends on multiple factors,
such as the heater-humidifier device used, type of ventilation, and
environmental factors. Few studies have examined inspired gas
humidification in these infants, especially during high-frequency
oscillatory ventilation (HFOV). Our objective was to compare humidity
during HFOV and intermittent positive pressure ventilation (IPPV), in
vitro and in vivo. Methods: In-vitro and in-vivo studies used
the same ventilator during both HFOV and IPPV. The bench study used a
neonatal test lung and 2 heater-humidifiers with their specific
circuits; the in-vivo study prospectively included preterm infants born
before 28 weeks of gestation. Results: On bench testing, mean
absolute (AH) and relative (RH) humidity values were significantly lower
during HFOV than IPPV (RH = 79.4% ± 8.1% vs 89.0% ± 6.2%,
P<0.001). Regardless of the ventilatory mode, mean relative
humidity significantly differed between the 2 heater-humidifiers (89.6%
± 6.7% vs 78.7% ± 6.8%, P=0.003). The in-vivo study included 10
neonates (mean ± SD gestational age: 25.7 ± 0.9 weeks and birth weight:
624.4 ± 96.1 g). Mean relative humidity during HFOV was significantly
lower than during IPPV (74.6% ± 5.7% vs 83.0 ± 6.7%, P=0.004).
Conclusion: Relative humidity was significantly lower during
HFOV than IPPV, both in vitro and in vivo. The type of heater-humidifier
also influenced humidification. More systematic measurements of humidity
of inspired gas, especially during HFOV, should be considered to
optimize humidification and consequently lung protection in ELBW
infants.