THE EFFECT OF INSTRUMENTAL DEAD SPACE ON MEASUREMENT OF BREATHING PATTERN AND PULMONARY MECHANICS IN THE NEWBORN

The effect of the instrumental dead space on breathing pattern and the values of pulmonary mechanics was evaluated because of concern about the relatively large dead space of 26 mL in a commercially available s ystem. Sixty-three healthy newborn infants were studied with a system as commercially supplied, and with the dead space eliminated using a 2 L/min biased flow. This led to a significant reduction in mean (+/-SD ) values of respiratory rate from 56.8 (+/-11.7) to 48.2 (+/-11.7) bre ath/min (P < 0.0001), tidal volume from 5.2 (+/-1.3) to 4.9 (+/-0.9) m L/kg (P < 0.05), minute volume from 284 (+/-68) to 220 (+/-63) mL/min/ kg (P < 0.0001), and work of breathing from 13.7 (+/-6.6) to 11.8 (+/- 7.6) g . cm/kg (P < 0.02). There was a significant increase in dynamic lung compliance from 5.2 (+/-1.5) to 5.6 (+/-1.2) mL/cm H2O (p < 0.01 ) but no difference for total pulmonary resistance 39.6 (+/-22.8) and 38.8 (+/-22.2) cm H2O/L/sec. This shows that the instrumental dead spa ce prevents measurement of the basal breathing patterns and alters the values of pulmonary mechanics. It is, therefore, important to use equ ipment with low dead space or make efforts to remove it by using a bia sed flow system such as we describe when measuring breathing patterns and pulmonary mechanics in the newborn. (C) 1993 Wiley-Liss, Inc.