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The conditioning of medical gases with hot water humidifiers

During invasive mechanical ventilation due to the dryness of medical gases is necessary to provide an adequate level of conditioning. The hot water humidifiers (HWH) heat the water, thus allowing the water vapor to heat and humidify the medical gases. In the common HWH there is a contact between the medical gases and the sterile water, thus increasing the risk of patient's colonization and infection. Recently to avoid the condensation in the inspiratory limb of the ventilator circuit, new heated ventilator circuits have been developed. In this in vitro study we evaluated the efficiency (absolute/relative humidity) of three HWH: (1) a common HWH without a heated ventilator circuit (MR 730, Fisher & Paykel, New Zeland), (2) the same HWH with a heated ventilator circuit (Mallinckrodt Dar, Italy) and (3) a new HWH (DAR HC 2000, Mallinkckrodt Dar, Italy) with a heated ventilator circuit in which the water vapor reaches the medical gases through a gorotex membrane, avoiding any direct contact between the water and gases. At a temperature of 35°C and 37°C the HWH and heated tube were evaluated.

The absolute humidity (AH) and relative humidity (RH) were measured by a psychometric method. The minute ventilation, tidal volume respiratory rate and oxygen fraction were: 5.8 ± 0.1 l/min, 740 ± 258 ml, 7.5 ± 2.6 bpm and 100%, respectively. Ventilator settings were maintained constant for all the study period. The measurements were taken after 60 min of continuous use.

At 35°C the output of the MR 730 with a heated tube was insufficient to provide adequate levels of conditioning, while at 37°C all the three devices were satisfactory.

Table 1 Results as mean ± SD

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Chiumello, D., Cressoni, M., De Grandis, C. et al. The conditioning of medical gases with hot water humidifiers. Crit Care 8 (Suppl 1), P1 (2004).

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  • Water Vapor
  • Mechanical Ventilation
  • Respiratory Rate
  • Direct Contact
  • Tidal Volume