Association Between Dead Space to Tidal Volume Ratio and Duration of Respiratory Support After Extubation in Critically Ill Children

Background: The dead-space-to-tidal-volume ratio (V_D/V_T) has been used to successfully predict extubation failure in children who are critically ill. However, a singular reliable measure to predict the level and duration of respiratory support after liberation from invasive mechanical ventilation has remained elusive. The objective of this study was to evaluate the association between V_D/V_T and the duration of postextubation respiratory support.

Methods: This was a retrospective cohort study of subjects who were mechanically ventilated and admitted to a single-center pediatric ICU between March 2019 and July 2021, and who had been extubated with a recorded V_D/V_T. A cutoff of 0.30 was chosen a priori, with subjects divided into 2 groups, V_D/V_T < 0.30 and V_D/V_T ≥ 0.30, and postextubation respiratory support was recorded at specified time intervals (24 h, 48 h, 72 h, 7 d, and 14 d).

Results: We studied 54 subjects. Those with V_D/V_T ≥ 0.30 had a significantly longer median (interquartile range) duration of respiratory support after extubation (6 [3-14] d vs 2 [0-4] d; P = .001) and longer median (interquartile range) ICU stay (14 [12-19] d vs 8 [5-22] d; P = .046) versus the subjects with V_D/V_T < 0.30. The distribution of respiratory support did not differ significantly between V_D/V_T at the time of extubation (P = .13) or at 14 d after extubation (P = .21) but was significantly different during the intervening time points after extubation (24 h [P = .01], 48 h [P < .001], 72 h [P < .001], and 7 d [P = .02]).

Conclusions: V_D/V_T was associated with the duration and level of respiratory support needed after extubation. Prospective studies are needed to establish if V_D/V_T can successfully predict the level of respiratory support after extubation.