Respiratory care clinics of North America
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Humidification devices and techniques can expose the airway mucosa to a wide range of gas temperatures and humidities, some of which are excessive and may cause injury. Humidified gas is a carrier of both water and energy. The volume of water in the gas stream depends on whether the water is in a molecular form (vapor), particulate form (aerosol), or bulk form (liquid). ⋯ Humidifiers, however, do not measure the gas temperature at the patient airway but only at the circuit wye. To compensate for any cooling of the gas as it passes from the wye to the patient the gas temperature at the wye must be set higher than core temperature. To safely avoid the risk that this higher temperature may accidentally reach the patient and cause an injury, the average gas temperature at the wye should restricted to less than 43 degrees
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In summary, current data indicate that body temperature cannot be controlled efficiently by changing inspired gas temperature. Inspired gas temperature should therefore be maintained at 32 degrees C to 34 degrees C for intubated patients and other efforts should be made to optimize body temperature.
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Respir Care Clin N Am · Jun 1998
ReviewHumidification practices in the Adult Intensive Care Unit, Prince of Wales Hospital.
In the Adult Intensive Care Unit of The Prince of Wales Hospital, Sydney, Australia, inspiratory gas is humidified to saturation at 37 degrees C. This stops the buildup of dried sputum within the endotracheal tubes and thus prevents blocked tubes and the increased resistance caused by partial obstruction. Inspiratory and expiratory hose heater wires are used to produce a completely dry circuit, allowing the elimination of water traps and circuit support arms without the resistance of a heat and moisture exchanger.
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Nosocomial pneumonia remains an important problem in patients undergoing mechanical ventilation, being associated with high mortality and morbidity and considerable expenditure. In the past respiratory equipment has been implicated in the development of nosocomial pneumonia and strict recommendations for cleaning and maintenance have been practiced. It is now known that the circuit and other equipment rapidly become contaminated with microorganisms originating from the patient's upper airway flora. ⋯ Current evidence suggests that circuit contamination usually is a result rather than a cause of airway colonization and does not have an important role in the pathogenesis of nosocomial pneumonia. Provided that reasonable infection control measures are taken, circuit contamination does not pose a risk to the ventilated patient. Although bacterial filters placed in the circuit effectively prevent circuit contamination they do not significantly reduce the incidence of nosocomial pneumonia in patients receiving mechanical ventilation.
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Humidification during anesthesia is important to prevent adverse changes in the upper airways and possible pulmonary compromise. These changes may take place in less than 1 hour using dry nonhumidified anesthetic gases. Consequently, some method of humidification should be employed for all but the shortest of surgical procedures requiring general anesthesia. ⋯ It may be preferable to have a gas with a lower temperature and higher relative humidity because a warmer gas that is less saturated may result in increased desiccation from the upper airways. Humidification for neonatal and pediatric patients requires special consideration of resistance, work of breathing, and dead space. Further work is necessary with regard to the use of HMEs in this population of patients undergoing general anesthesia.