The end-tidal alveolar dead space fraction for risk stratification during the first week of invasive mechanical ventilation: an observational cohort study

Abstract

Background The end-tidal alveolar dead space fraction (AVDSf = [PaCO2−PETCO2]/PaCO2) is a metric used to estimate alveolar dead space. Higher AVDSf on the first day of mechanical ventilation is associated with mortality and fewer ventilator-free days. It is not clear if AVDSf is associated with length of ventilation in survivors, how AVDSf performs for risk stratification beyond the first day of ventilation, or whether AVDSf adds predictive value to oxygenation (oxygenation index [OI]) or severity of illness (Pediatric Risk of Mortality [PRISM III]) markers. Methods Retrospective single-center observational cohort study of children and young adults receiving invasive mechanical ventilation. In those with arterial or capillary blood gases, AVDSf was calculated at the time of every blood gas for the first week of mechanical ventilation. Results There were 2335 children and young adults (median age 5.8 years [IQR 1.2, 13.2]) enrolled with 8004 analyzed AVDSf values. Higher AVDSf was associated with mortality and longer length of ventilation in survivors throughout the first week of ventilation after controlling for OI and PRISM III. Higher OI was not associated with increased mortality until ≥ 48 h of ventilation after controlling for AVDSf and PRISM III. When using standardized variables, AVDSf effect estimates were generally higher than OI for mortality, whereas OI effect estimates were generally higher than AVDSf for the length of ventilation in survivors. An AVDSf > 0.3 was associated with a higher mortality than an AVDSf < 0.2 within each pediatric acute respiratory distress syndrome severity category. The maximum AVDSf within 12 h of intensive care unit admission demonstrated good risk stratification for mortality (AUC 0.768 [95% CI 0.732, 0.803]). AVDSf did not improve mortality risk stratification when added to PRISM III but did improve mortality risk stratification when added to the gas exchange components of PRISM III (minimum 12-h PaO2 and maximum 12-h PCO2) (p < 0.00001). Conclusions AVDSf is associated with mortality and length of ventilation in survivors throughout the first week of invasive mechanical ventilation. Some analyses suggest AVDSf may better stratify mortality risk than OI, whereas OI may better stratify risk for prolonged ventilation in survivors than AVDSf.

Capnometry after an inspiratory breath hold, PLATCO2, as a surrogate for PaCO2 ${P}_{{\mathrm{aCO}}_{2}}$ in mild to moderate pediatric acute respiratory distress syndrome: A feasibility study

“…10,11 Physiological dead space (V D /V T ) is associated with outcomes in ARDS. [12][13][14] In a clinical study, Bhalla et al 15,16 found a good correlation between AVDSf and V D /V T in PARDS but had a large bias. Despite this, several studies demonstrated that AVDSf is an excellent indicator of alveolar dead space and has a strong association with mortality in PARDS after controlling for other markers of severity, such as hypoxemia.…”

“…Physiological dead space ( V D / V T ) is associated with outcomes in ARDS 12–14 . In a clinical study, Bhalla et al 15,16 found a good correlation between AVDSf and V D / V T in PARDS but had a large bias.…”

PCV‐VG combined individualized PEEP determination in one‐lung ventilated patients with PEEP step change direction: A randomized controlled trial

“…V T , PEEP, airway peak pressure (P peak ), airway mean pressure (P mean ), and Cdyn of the patients were also recorded. In addition, the arterial blood gas analyzer I‐STAT 300 (Abbott, USA) was used to record blood gas indicators and ventilation efficiency parameters, such as the arterial partial pressure of carbon dioxide (PaCO 2 ), oxygenation index (OI), respiratory index (RI), alveolar‐arterial oxygen partial pressure difference (A‐aO2), and dead space fraction (V D /V T ) during T 1 ‐T 3 11–13 . Parameters were calculated using the following equation: V D /V T = (PaCO 2 ‐P ET CO 2 )/PaCO 2 .…”