(670) Pulmonary Dead Space and Respiratory Support in the Pediatric Cardiac Intensive Care Unit

Introduction: Children being liberated from mechanical ventilation in the pediatric cardiac intensive care unit (PCICU) often receive noninvasive respiratory support. However, predicting the type and duration of postextubation support can be challenging. A potential tool to guide this decision is the dead space to tidal volume ratio (VD/VT). We hypothesized that elevated VD/VT would be associated with longer duration and higher level of respiratory support following extubation in the PCICU.

Methods: We conducted a retrospective cohort study of mechanically ventilated patients admitted to our PCICU between March 2019 and July 2021 with at least one VD/VT recorded before extubation. Using a predetermined cutoff of 0.30, subjects were divided into two groups: VD/VT < 0.30 and VD/VT ≥ 0.30. We recorded the type of postextubation respiratory support (room air, nasal cannula, high-flow nasal cannula, or continuous or bi-level positive airway pressure) at specified time intervals (24 hours, 48 hours, 72 hours, 7 days, and 14 days). We used Chi square analysis and the Mann-Whitney U test to compare categorical and ordinal variables between groups, respectively.

Results: A total of 226 patients were included in the study. Those with VD/VT ≥ 0.30 experienced a significantly longer median duration of postextubation respiratory support (4 [1.9–9.1] days vs 3 [1.2–5.3] days; P = .001) and had a higher likelihood of receiving high-flow nasal cannula at 24 hours following extubation (67% vs 45%, P = 0.02), a difference which persisted through 14 days following extubation. Respiratory support modality immediately postextubation and rate of extubation failure were not significantly different between groups (P = .53 and P = .53, respectively). Subjects with VD/VT ≥ 0.30 were more likely to be younger (0.1 [0.01–0.3] years versus 0.4 [0.1–1.5] years; P < .001) and have cyanotic congenital heart disease (59% vs 26%; P < .001).

Conclusions: VD/VT was associated with the length of respiratory support after extubation and increased use of non-invasive respiratory support over time, but not with the type of respiratory support at extubation. Patients with elevated VD/VT were also younger and more likely to have cyanotic congenital heart disease.