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.