In 30 patients with normal pulmonary function receiving respirator therapy, the inspired air was heated and moisturised with either Hygrotherm (a thermostatically-controlled water bath evaporator) (group H) or Engstrom-Edit (a hygroscopic moisture and heat exchanger) (group E). Prior to randomizing and after 24, 48 and 72 hours, the following measurements were undertaken: (1) the temperature and humidity of the inspired air, (2) resistance of the airways and static compliance, (3) arterial blood-gas analyses, measurement of FiO2 and calculation of alveolo-arterial oxygen difference. On the day of randomizing, after 72 hours and after six days, x-rays were taken of the lungs and the tracheal secretion was cultured. Significantly higher temperatures in the inspired air were demonstrated in group H, 32.4 +/- 2.9 degrees celcius, compared with group E 26.2 +/- 1.6 degrees celcius. The humidity in group H was, similarly, significantly higher 34.0 +/- 2.5 mg H2O/l than in group E, 22.5 +/- 3.1 H2O/l (p < 0.01). During the first 48 hours, no difference was observed between the therapeutic groups as regards alveolo-arterial oxygen difference, airway resistance or static compliance. After 72 hours, the static compliance was significantly lower in group E. The numbers of pulmonary complications were not statistically significantly different. The Engstrom-Edith hygroscopic moisture and heat exchanger may be employed for moistening the inspired air during respirator treatment of patients with normal pulmonary function for up to 48 hours.

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