A simple new technique to measure the effective dead space of the face mask with a water volumeter in infants.

Measuring the effective dead space (EDS) of a face mask has been difficult in infants and the appropriate volume being deducted from lung volume measurements has varied between laboratories. This study measured EDS in 16 infants (age range, 5-36 months) who have cystic fibrosis, undergoing lung volume measurement by N2 washout. A thin plastic bladder, whose neck resided in the mask port, was shaped to fill a size 1 clear face mask. A water volumeter was made by inserting the body of a 20 mL plastic syringe into the neck of the bladder forming a tight seal with a snug fit against the inner surface of the mask port. The mask was placed on a horizontal surface and water was added until a level appeared in the syringe body (V1). At end-inspiration, the mask was briefly placed on the mouth and nose of the sleeping infant, causing the water level to rise in the syringe body (V2). The actual total dead space (V) of the mask when connected to the mouth port of the slide valve was 23 mL. EDS = V- (V2 - V1). Mean (95% confidence interval (95%CI)) EDS was 12.4 (95% CI 11.2, 13.6) mL. The smallest EDS was 8 mL since the connected ports (dead space, 8 mL) were unlikely to be penetrated by the infant's nose or lips. EDS decreased with increasing body weight and height, but seemed to be influenced by individual facial features too. In conclusion, a reliable noninvasive volumetric technique for the routine measurement of the effective dead space in infants has been developed.