The Cerebrovascular Response to Hypocapnia in Children Receiving Propofol
Bibliographic record
Abstract
In Brief Hypocapnia is used to treat acute increases in intracranial pressure during neurosurgery. Cerebrovascular reactivity to carbon dioxide (CCO2R) is preserved above 35 mm Hg ETco2 in children during propofol anesthesia; however, a plateau effect has been suggested below 35 mm Hg. To further delineate this phenomenon, we measured CCO2R by transcranial Doppler (TCD) sonography over small increments in ETco2 in 27 healthy children. Anesthesia comprised a standardized propofol infusion and a caudal epidural block. A TCD probe was placed to measure middle cerebral artery blood flow velocity (Vmca). ETco2 was adjusted between 24 and 40 mm Hg at 1–2 mm Hg increments using an exogenous source of CO2. There was an exponential relationship between ETco2 and Vmca above an ETco2 value of 30 mm Hg (r = 0.82). However, Vmca did not change with ETco2 less than 30 mm Hg (r = 0.06). There were no significant changes in heart rate or arterial blood pressure. We conclude that when contemplating methods to decrease brain volume and intracranial pressure, hyperventilation to ETco2 values less than 30 mm Hg may not be necessary in children receiving propofol, as no further reduction in cerebral blood flow velocity will be achieved. IMPLICATIONS: Cerebrovascular reactivity to CO2 is preserved above 30 mm Hg ETco2 in children during propofol anesthesia but lost below 30 mm Hg. Reducing ETco2 values to less than 30 mm Hg in children receiving propofol anesthesia may not result in any further reduction in cerebral blood flow velocity.
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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 | 0.000 | 0.002 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.000 | 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".