HEAT AND MOISTURE EXCHANGERS FOR HUMIDIFY ING THE INSPIRED AIR OF INTUBATED PATIENTS IN INTENSIVE-CARE MEDICINE - AN INVESTIGATION OF HUMIDIFICATION PROPERTIES OF HEAT AND MOISTURE EXCHANGERS UNDER CLINICAL CONDITIONS

Heat and moisture exchangers (HME) are used as artificial noses for in tubated patients to prevent tracheo-bronchial or pulmonary damage resu lting from dry and cold inspired gases. HME are mounted directly on th e trachel tube, where they collect a large fraction of the heat and mo isture of the expired air, adding this to the subsequent inspired brea th. The effective performance depends on the water-retention capacity of the HME: the amount of water added to the inspired gas cannot excee d the stored water uptake of the previous breath. This study evaluates the efficiency of four different HME under laboratory and clinical co nditions using a new moisture-measuring device. Methods. In a first st ep, the absolute efficiency of four different HME (DAR Hygrobac, Gibec k HumidVent 2P, Pall BE 22-15 T, and Pall BE 100) was evaluated using a lung model simulating physiological heat and humidity conditions of the upper airways. The model was ventilated with tidal volumes of 500, 1,000, and 1,500 ml and different flow rates. The water content of th e ventilated air was determined between tracheal tube and HME using a new high-resolution humidity meter and compared with the absolute wate r loss of the exhaled air at the gas outlet of a Siemens Servo C venti lator measured with a dew-point hygrometer. Secondly, the moisturizing efficiency was evaluated under clinical conditions in an intensive ca re unit with 25 intubated patients. Maintaining the ventilatory condit ions for each patient, the HME were randomly changed. The humidity dat a were determined as described above and compared with the laboratory findings. Results and discussion. The water content at the respirator outlet is inversely equivalent to the humidity of the inspired gases a nd represents the water loss from the respiratory tract if the patient is ventilated with dry gases. Moisture retention and heating capacity decreased with higher volumes and higher flow rates. These data are s imple to obtain without affecting the patient and can easily be interp reted. It was demonstrated that, compared to physiological conditions, the DAR Hygrobac and Gibeck HumidVent 2P - HME coated with hygroscopi c salts - were able to maintain sufficient inspiratory humity and heat . The Pall-HME, solely a condensation humidifier, did not meet the phy siological requirements.