Abstract
BACKGROUND: Humidification of inspired gases during mechanical ventilation is essential to maintain structure and function of the respiratory mucosa. Humidity has been most often provided by heated humidifiers. More recently passive humidifiers, (PH) or artificial noses, have been used in selected cases. We evaluated the moisture output of 21 passive humidifiers. DESCRIPTION OF DEVICE: Twenty-one PHs were studied including 11 hygroscopic con-denser humidifiers (HCH), 7 hygroscopic condenser humidifier filters (HCHF), and 3 heat and moisture exchanger filters (HMEF). EVALUATION METHODS: All devices were tested for moisture output (mg H2O/L), and resistance (cm H2O. L. s-1) according to International Standard Organization (ISO) 9360. Moisture output was measured by determining weight loss from a water bath during a 2-hour period of ventilation at 3 combinations of frequency (f) and tidal volume (VT) (20 breaths/min at 500 mL, 10 breaths/min at 1,000 mL, and 20 breaths/min at 1,000 mL). Dead space was measured by measuring pressure change in the PH during delivery of volume from a calibrated syringe. Resistance was calculated by measuring pressure drop across the PH at a flow of 1 L/s. EVALUATION RESULTS: Moisture output ranged from 19.6 to 33.2 mg H2O/L. As a group, HCHF performed better than HCHs and HMEFS. Dead space ranged from 19 to 94 mL. Resistance ranged from 0.7 to 3.5 cm H2O L s-1. CONCLUSIONS: The ISO 9360 system allows ranking of devices in terms of moisture output, dead space, and resistance. These values can all be integrated by the clinician to intelligently choose an appropriate PH. We caution that these results apply specifically to the conditions tested and that results obtained clinically will vary with patient variables, such as temper-ature and minute ventilation. [Respir Care 1996;41(8):736-743]
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