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The Pall bacterial filter was tested as a potential heat and moisture exchanger on a model patient, placed on a circle absorber system, and clinically. The laboratory study was conducted during mechanical ventilation at a V of 6 L/min with fresh gas inflows of 1,3 and 6 L/min. The model patient introduced carbon dioxide into the circuitry at a rate of 200 ml/min. The resistance of the filter was tested before and after each experiment. With all fresh gas inflows, absolute humidity increased from around 19 mg H2O/L at the start of experimentation to about 27 mg H2O/L within 30 mm. Maximum humidities reached were 28 /- 0.7 mg H2O/L, 27.6 /- 0.5 mg H2O/L, and 27.7 /- 0.5 mg H2O/L within 3 hr, with fresh gas inflows of 1, 3, and 6 L/min, respectively. Variations in inspired humidity were also assessed at minute volumes of 4 and 5 L/min with fresh gas inflows of 6 and 3 L/min. Increases in percent dead space were negligible when the filter was inserted between the model patients (assumed to weigh between 70-40 kg) and the circuit. There was no statistically significant increase in pressure with gas flows of 50 L/min when the instrument was dry (0.02 /- 0.001 cm H2O/L-min-1) or when it was wet (0.02 /- 0.002 cm HzO/L-min-1). The clinical study was conducted on ten adult anesthetized patients breathing through the bacterial filter and ten controls. The loss of body temperature was 0.2[degrees]C when the filter was used and 1.5[degrees]C when the filter was not used. Arterial blood gas tensions were within normal limits when the bacterial filter was used as a humidifier.

(C) 1984 International Anesthesia Research Society