The association between ventilatory ratio and mortality in children and young adults

Abstract

BACKGROUND: The ventilatory ratio (VR) is a dead-space marker associated with mortality in mechanically ventilated adults with ARDS. The end-tidal alveolar dead space fraction (AVDSf) has been associated with mortality in children. However, AVDSf requires capnography measurements, whereas VR does not. We sought to examine the prognostic value of VR, in comparison to AVDSf, in children and young adults with acute hypoxemic respiratory failure. METHODS: We conducted a retrospective study of prospectively collected data from 180 mechanically ventilated children and young adults with acute hypoxemic respiratory failure. VR was calculated as (minute ventilation × PaCO2 )/(age-adjusted predicted minute ventilation × 37.5). AVDSf was calculated as (PaCO2-PETCO2 )/PaCO2 . RESULTS: VR and AVDSf had a moderate correlation (rho 0.31, P < .001). VR was similar between survivors at 1.22 (interquartile range [IQR] 1.0–1.52) and non-survivors at 1.30 (IQR 0.96–1.95) (P = .2). AVDSf was lower in survivors at 0.12 (IQR 0.03–0.23) than nonsurvivors at 0.24 (IQR 0.13–0.33) (P .3). An AVDSf in the highest 2 quartiles, in comparison to the lowest quartile (AVDSf < 0.06), was associated with higher mortality after adjustment for oxygenation index and severity of illness (AVDSf ≥ 0.15–0.26: odds ratio 3.58, 95% CI 1.02–12.64, P = .047, and AVDSf ≥ 0.26: odds ratio 3.91 95% CI–1.03–14.83, P = .045). At any given time after intubation, a child with an AVDSf ≥ 0.26 was less likely to be extubated than a child with an AVDSf <0.06, after adjustment for oxygenation index and severity of illness (AVDSf ≥ 0.26: sub-distribution hazard ratio 0.55, 95% CI 0.33–0.94, P = .03). CONCLUSIONS: VR should not be used for prognostic purposes in children and young adults. AVDSf added prognostic information to the severity of oxygenation defect and overall severity of illness in children and young adults, consistent with previous research.