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Higher Dead Space Is Associated With Increased Mortality in Critically Ill Children

Anoopindar K Bhalla¹, Sanjay Belani, Dennis Leung

¹1Department of Anesthesiology and Critical Care Medicine, Children's Hospital Los Angeles, Los Angeles, CA. 2Department of Pediatrics, Keck School of Medicine, University of Southern California, Los Angeles, CA.

Critical Care Medicine

|July 23, 2015

Insights

Increased dead space in mechanically ventilated children is linked to higher mortality. This finding, using end-tidal alveolar dead space fraction, may aid in pediatric critical care risk stratification.

Area of Science:

Pediatric Critical Care Medicine
Respiratory Physiology
Clinical Outcomes Research

Background:

Elevated dead space is a known mortality predictor in adult respiratory failure.
Evidence linking dead space to mortality in pediatric populations is less established.

Purpose of the Study:

To investigate the association between dead space and mortality in mechanically ventilated children.
To evaluate the utility of end-tidal alveolar dead space fraction as a prognostic marker.

Main Methods:

Single-center retrospective review of 712 mechanically ventilated children with arterial catheters.
Calculation of end-tidal alveolar dead space fraction ((PaCO2-PETCO2)/PaCO2) from arterial blood gases.
Multivariate analysis controlling for oxygenation, inotropic support, and illness severity.

Main Results:

Initial and Day 1 mean end-tidal alveolar dead space fraction were significantly associated with mortality (ORs 1.59-1.95).
Associations remained significant after individual adjustments for oxygenation (PaO2/FIO2, OI), inotrope score, and PRISM III.
Dead space was not independently associated with mortality when controlling for the combined severity of illness variables.

Conclusions:

Increased dead space correlates with higher mortality in critically ill children.
End-tidal alveolar dead space fraction may serve as a valuable bedside tool for risk stratification.
Further research may refine its role alongside other severity indices.

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Abstract

Objective:

Elevated dead space has been consistently associated with increased mortality in adults with respiratory failure. In children, the evidence for this association is more limited. We sought to investigate the association between dead space and mortality in mechanically ventilated children.

Design:

Single-center retrospective review.

Setting:

Tertiary care pediatric critical care unit.

Patients:

Seven hundred twelve mechanically ventilated children with an arterial catheter.

Interventions:

None.

Measurements And Main Results:

The end-tidal alveolar dead space fraction ((PaCO2-PETCO2)/PaCO2), a dead space marker, was calculated with each arterial blood gas. The initial end-tidal alveolar dead space fraction (first arterial blood gas after intubation) (per 0.1 unit increase: odds ratio, 1.59; 95% CI, 1.40-1.81) and day 1 mean end-tidal alveolar dead space fraction (odds ratio, 1.95; 95% CI, 1.66-2.30) were associated with mortality. The relationship between both initial and day 1 mean end-tidal alveolar dead space fraction and mortality held in multivariate modeling after controlling for any of the following individually: PaO2/FIO2, oxygenation index, 24-hour maximal inotrope score, and Pediatric Risk of Mortality III (all p<0.01), although end-tidal alveolar dead space fraction was no longer significant after controlling for the combination of oxygenation index, 24-hour maximal inotrope score, and Pediatric Risk of Mortality III. In 217 children with acute hypoxemic respiratory failure, initial end-tidal alveolar dead space fraction (per 0.1 unit increase odds ratio, 1.38; 95% CI, 1.14-1.67) and day 1 mean end-tidal alveolar dead space fraction (per 0.1 unit increase odds ratio, 1.60; 95% CI, 1.27-2.0) were associated with mortality. Day 1 mean end-tidal alveolar dead space fraction remained associated with mortality after controlling individually for any of the following in multivariate models: PaO2/FIO2, oxygenation index, and 24-hour maximal inotrope score (p≤0.02), although end-tidal alveolar dead space fraction was no longer significant after controlling for the combination of oxygenation index, 24-hour maximal inotrope score, and Pediatric Risk of Mortality III.

Conclusions:

Increased dead space is associated with higher mortality in critically ill children, although it is no longer independently associated with mortality after controlling for severity of oxygenation defect, inotrope use, and severity of illness. However, because end-tidal alveolar dead space fraction is easy to calculate at the bedside, it may be useful for risk stratification and severity-of-illness scores.

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