The Association Between Ventilatory Ratio and Mortality in Children and Young Adults.

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 × [Formula: see text])/(age-adjusted predicted minute ventilation × 37.5). AVDSf was calculated as [Formula: see text]. 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 nonsurvivors 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 < .001). In logistic regression and competing risk regression analyses, VR was not associated with mortality or rate of extubation at any given time (competing risk death; all 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: subdistribution 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.

Ventilator Liberation in the Pediatric ICU.

Despite the accepted importance of minimizing time on mechanical ventilation, only limited guidance on weaning and extubation is available from the pediatric literature. A significant proportion of patients being evaluated for weaning are actually ready for extubation, suggesting that weaning is often not considered early enough in the course of ventilation. Indications for extubation are often not clear, although a trial of spontaneous breathing on CPAP without pressure support seems an appropriate prerequisite in many cases. Several indexes have been developed to predict weaning and extubation success, but the available literature suggests they offer little or no improvement over clinical judgment. New techniques for assessing readiness for weaning and predicting extubation success are being developed but are far from general acceptance in pediatric practice. While there have been some excellent physiologic, observational, and even randomized controlled trials on aspects of pediatric ventilator liberation, robust research data are lacking. Given the lack of data in many areas, a determined approach that combines systematic review with consensus opinion of international experts could generate high-quality recommendations and terminology definitions to guide clinical practice and highlight important areas for future research in weaning, extubation readiness, and liberation from mechanical ventilation following pediatric respiratory failure.

Accuracy of Transcutaneous Carbon Dioxide Levels in Comparison to Arterial Carbon Dioxide Levels in Critically Ill Children.

BACKGROUND: Widespread use of transcutaneous PCO2 (PtcCO2 ) monitoring is currently limited by concerns many practitioners have regarding accuracy. We compared the accuracy of PtcCO2 with that of PaCO2 measurements in critically ill children, and we investigated whether clinical conditions associated with low cardiac output or increased subcutaneous tissue affect this accuracy. METHODS: We performed a single-center prospective study of critically ill children placed on transcutaneous monitoring. RESULTS: There were 184 children enrolled with paired PaCO2 and PtcCO2 values. Subjects had a median age of 31.8 mo (interquartile range 3.5-123.3 mo). Most children were mechanically ventilated (n = 161, 87.5%), and many had cardiac disease (n = 76, 41.3%). The median PaCO2 was 44 mm Hg (interquartile range 39-51 mm Hg). The mean bias between PaCO2 and PtcCO2 was 0.6 mm Hg with 95% limits of agreement from -13.6 to 14.7 mm Hg. The PtcCO2 and PaCO2 were within ±5 mm Hg in 126 (68.5%) measurements. In multivariable modeling, cyanotic heart disease (odds ratio 3.5, 95% CI 1.2-10, P = .02) and monitor number 2 (odds ratio 3.8 95% CI 1.3-10.5, P = .01) remained associated with PtcCO2 ≥ 5 mm Hg higher than PaCO2 . Serum lactate, fluid balance, renal failure, obesity, vasoactive-inotrope score, and acyanotic heart disease were not associated with high or low PtcCO2 values. In 130 children with a second paired PtcCO2 and PaCO2 measurement, predicting the second measured PaCO2 by subtracting the initial observed difference between the PtcCO2 and PaCO2 from the subsequent measured PtcCO2 decreased the mean bias between observed and predicted PaCO2 to 0.2 mm Hg and the 95% limits of agreement to -9.4 to 9.7 mm Hg. CONCLUSIONS: PtcCO2 provides an acceptable estimate of PaCO2 in many critically ill children, including those with clinical conditions that may be associated with low cardiac output or increased subcutaneous tissue, although it does not perform as well in children with cyanotic heart disease. PtcCO2 may be a useful adjunct monitoring method, but it cannot reliably replace PaCO2 measurement.