Dead Space to Tidal Volume Ratio Is Associated With Higher Postextubation Support in Children

Abstract

Background: Extubation failure is associated with increased duration of mechanical ventilation, length of hospital stay, and mortality. An elevated dead-space-to-tidal-volume ratio (V_D/V_T) has been proposed as a predictor of successful extubation in children. We hypothesized that a higher V_D/V_T value would be associated with extubation failure and higher postextubation respiratory support.

Methods: This was a prospective, observational, cohort study. All subjects were < 18 y old and were extubated in the pediatric multidisciplinary ICU or the cardiac ICU at an academic medical center from June 2016 through March 2017. Using arterial blood gas analysis and mainstream volumetric capnography, daily V_D/V_T measurements were obtained on intubated subjects using an automated algorithm. Respiratory support upon extubation was based on the clinical team's judgment and defined as low (ie, room air or nasal cannula) or high (ie, high-flow nasal cannula, CPAP, or bi-level positive airway pressure). Subjects were monitored for 48 h after extubation for escalation in respiratory support and need for re-intubation.

Results: Of 189 subjects included in the analysis, 166 were successfully extubated and 23 (12%) required re-intubation. There was no significant difference in final V_D/V_T between those who extubated successfully and those who failed extubation, with a median V_D/V_T of 0.28 (interquartile range [IQR] 0.20-0.37) vs 0.29 (IQR 0.21-0.33), respectively (P = .87). Those who received a high level of support upon extubation had a higher V_D/V_T than those who received a low level of support, with a median of 0.32 (IQR 0.23-0.39) vs 0.25 (IQR 0.16-0.30), respectively (P < .001). This association remained significant when controlling for age, duration of intubation, and cyanotic congenital heart disease (odds ratio 1.63, 95% CI 1.18-2.24).

Conclusions: There was no significant relationship between V_D/V_T and extubation success, although V_D/V_T was associated with the level of respiratory support provided following extubation. Further studies should investigate whether the use of V_D/V_T can help reduce extubation failure rates with varying levels of postextubation respiratory support.

Keywords: critical care; dead space; extubation readiness; gas exchange; mechanical ventilation; pediatric; respiratory failure.