Validity of Empirical Estimates of the Ratio of Dead Space to Tidal Volume in ARDS
Bibliographic record
Abstract
BACKGROUND: The ratio of dead space to tidal volume (V D /V T ) is a clinically relevant parameter in ARDS; it has been shown to predict mortality, and it determines the extent to which extracorporeal CO 2 removal reduces tidal volume (V T ) and driving pressure (ΔP). V D /V T can be estimated with volumetric capnography, but empirical formulas using demographic and physiological information have been proposed to estimate V D /V T without the need of additional equipment. It is unknown whether estimated and measured V D /V T produce similar estimates of the predicted effect of extracorporeal CO 2 removal on ΔP. METHODS: We performed a secondary analysis of data from a previous clinical trial including subjects with ARDS in whom V D /V T and CO 2 production ( V ˙ CO 2 ) were measured with volumetric capnography. The estimated ratio of dead space to tidal volume (V D,est /V T ) was calculated using standard empiric formulas. Agreement between measured and estimated values was evaluated with Bland-Altman analysis. Agreement between the predicted change in ΔP with extracorporeal CO 2 removal as computed using the measured ratio of alveolar dead space to tidal volume (V Dalv /V T ) or estimated V Dalv /V T (V Dalv,est /V T ) was also evaluated. RESULTS: V D,est /V T was higher than measured V D /V T , and agreement between them was low (bias 0.05, limits of agreement –0.21 to 0.31). Differences between measured and estimated V ˙ CO 2 accounted for 57% of the error in V D,est /V T . The predicted reduction in ΔP with extracorporeal CO 2 removal computed using V Dalv,est /V T was in reasonable agreement with the expected reduction using V Dalv /V T (bias –0.7 cm H 2 O, limits of agreement –1.87 to 0.47 cm H 2 O). In multivariable regression, measured V D /V T was associated with mortality (odds ratio 1.9, 95% CI 1.2–3.1, P = .01), but V D,est /V T was not (odds ratio 1.2, 95% CI 0.8–1.8, P = .3). CONCLUSIONS: V D /V T and V D,est /V T showed low levels of agreement and cannot be used interchangeably in clinical practice. Nevertheless, the predicted decrease in ΔP due to extracorporeal CO 2 removal was similar when computed from either estimated or measured V Dalv /V T .
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.129 | 0.539 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.002 |
| Bibliometrics | 0.002 | 0.001 |
| Science and technology studies | 0.000 | 0.004 |
| Scholarly communication | 0.003 | 0.003 |
| Open science | 0.003 | 0.003 |
| Research integrity | 0.002 | 0.002 |
| Insufficient payload (model declined to judge) | 0.003 | 0.001 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".