Variation in Arterial CO 2 is a Stronger Determinant of Brain Tissue Oxygenation Than its Synchronous Value in Critically Ill Patients With Acute Brain Injury
Bibliographic record
Abstract
OBJECTIVES: In critically ill patients with acute brain injury (ABI), maintaining intracranial pressure (ICP) and brain tissue oxygenation (PbtO2) within targets could prevent secondary neurologic injury. Tight control of CO2 (Paco2), a potent regulator of cerebrovascular tone, is generally advocated, but its vasomotor effect may be short-lived. Our aim was to compare the effect of the synchronous Paco2 vs. its variation from a previous baseline on PbtO2 and ICP. DESIGN: We performed a post hoc analysis of a prospective cohort study collecting arterial blood gas (ABG) values alongside synchronous neuromonitoring variables. Linear mixed-effects models were fitted to evaluate the association between Paco2 and/or Paco2 variation from its average of the last 8-24 hr vs. PbtO2 and ICP, while controlling for cerebral perfusion pressure and Pao2. SETTING: Mixed medical-surgical ICU of Sacré-Coeur Hospital, an academic trauma center in Montreal, Canada. PATIENTS: All consecutive adult patients admitted for ABI with ICP and PbtO2 monitoring between May 2017 and November 2021. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: We included 78 patients with 3047 ABG-neuromonitoring couplets. The model using the variation of Paco2 from its average of the last 24 hr displayed the best performance for the prediction of PbtO2 (coefficient 0.37; 95% CI 0.21-0.53). The strongest predictor of ICP was the variation of Paco2 from its average of the last 8 hr (coefficient 0.17; 95% CI 0.10-0.23). CONCLUSIONS: Variation in Paco2 from baseline is a more significant determinant of PbtO2 and ICP than the absolute Paco2 value at a given time. There may be a baseline vasomotor reset when patients are exposed to a given level of CO2 for 8 to 24 hr. Therefore, sustained intentional manipulation of Paco2 is unlikely to have lasting effects and slower correction rates of high or low Paco2 could help prevent brain tissue hypoxia or intracranial hypertension, respectively.
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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 | 0.005 | 0.016 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.002 | 0.000 |
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".