Oxygen, temperature and humidity of inspired gases and their influences on airway and lung tissue in near-term lambs
ABSTRACT PurposeThe relative contributions of factors influencing lung injury immediately after birth are poorly understood. We hypothesized
that oxygen content and humidity of inspired air would influence markers of pulmonary inflammation in ventilated lambs.
MethodsLambs delivered at 140days gestation (term=150days) were assigned to one of five groups (n=5–6/group): unventilated controls, or ventilation with 21 or 100% O2 that was either heated and humidified or cold and dry. Lambs were ventilated gently for 3h: blood gases were recorded regularly.
Bronchoalveolar lavage and samples of tracheal mucosa and lung were collected post mortem.
ResultsArterial pH was lower [mean difference (95% CI): −0.07 (−0.13, −0.03)], while there was an increase in PaCO2 [mean difference (95% CI): 10.2 (2.4, 17.9)] and fold change in lung pro-inflammatory IL-1β cytokine mRNA [mean difference
(95% CI): 28.3 (0.3, 56.2)] or IL-8 [mean difference (95% CI): 27.8 (7.9, 47.7)] cytokine mRNA expression with 100% O2 relative to 21% O2. Cold dry inspired gas did not influence gas exchange or dynamic mechanics at 3h compared to heated humidified gas. Compared
to 100% inspired O2, cold dry inspired gas had less marked effect on fold change in lung pro-inflammatory IL-1β cytokine mRNA [mean difference
(95% CI): 27.2 (−0/8, 55.1)] or IL-8 [mean difference (95% CI): 14.5 (5.5, 34.4)] cytokine mRNA expression, although cilial
dysfunction/damage was evident on electron microscopy, especially when exposure to cold dry gas was combined with hyperoxia.
ConclusionsIn near-term neonatal lambs ventilated for 3h, hyperoxia was associated a more powerful stimulus for pulmonary dysfunction
and upregulation of inflammatory cytokines than cold dry gas.
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ABSTRACT: To review the available literature on the relationship between the humidity and temperature of inspired gas and airway mucosal function. International computerized databases and published indices, experts in the field, conference proceedings, bibliographies. Two hundred articles/texts on respiratory tract physiology and humidification were reviewed. Seventeen articles were selected from 40 articles for inclusion in the published data verification of the model. Selection was by independent reviewers. Extraction was by consensus, and was based on finding sufficient data. A relationship exists between inspired gas humidity and temperature, exposure time to a given humidity level, and mucosal function. This relationship can be modeled and represented as an inspired humidity magnitude vs. exposure time map. The model is predictive of mucosal function and can be partially verified by the available literature. It predicts that if inspired humidity deviates from an optimal level, a progressive mucosal dysfunction begins. The greater the humidity deviation, the faster the mucosal dysfunction progresses. A model for the relationship between airway mucosal dysfunction and the combination of the humidity of inspired gas and the duration over which the airway mucosa is exposed to that humidity is proposed. This model suggests that there is an optimal temperature and humidity above which, and below which, there is impaired mucosal function. This optimal level of temperature and humidity is core temperature and 100% relative humidity. However, existing data are only sufficient to test this model for gas conditions below core temperature and 100% relative humidity. These data concur with the model in that region. No studies have yet looked at this relationship beyond 24 hrs. Longer exposure times to any given level of inspired humidity and inspired gas temperatures and humidities above core temperature and 100% relative humidity need to be studied to fully verify the proposed model.Critical Care Medicine 12/1996; 24(11):1920-9. · 6.12 Impact Factor
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