Ultrasound Imaging of the Lumbar Spine in the Transverse Plane: The Correlation Between Estimated and Actual Depth to the Epidural Space in Obese Parturients
Bibliographic record
Abstract
BACKGROUND: Prepuncture lumbar ultrasound scanning is a reliable tool to facilitate labor epidural needle placement in nonobese parturients. In this study, we assessed prepuncture lumbar ultrasound scanning as a tool for estimating the depth to the epidural space and determining the optimal insertion point in obese parturients. METHODS: We studied 46 obese parturients, with prepregnancy body mass index (BMI) >30 kg/m(2), requesting labor epidural analgesia. Ultrasound imaging was done by one of the investigators to identify the midline, the intervertebral space, and the distance from the skin to the epidural space (ultrasound depth, UD) at the level of L3-4. Subsequently, an anesthesiologist blinded to the UD located the epidural space through the predetermined insertion point and marked the actual distance from the skin to the epidural space (needle depth, ND) on the needle with a sterile marker. The agreement between the UD and the ND was calculated using the Pearson correlation coefficient and a paired t-test. Bland-Altman analysis was used to determine the 95% limits of agreement between the UD and the ND. RESULTS: The prepregnancy BMI ranged from 30 to 79 kg/m(2), and the BMI at delivery was 33-86 kg/m(2). The Pearson correlation coefficient between the UD and the ND was 0.85 (95% confidence interval: 0.75-0.91), and the concordance correlation coefficient was 0.79 (95% confidence interval: 0.71-0.88). The mean (+/-SD) ND and UD were 6.6 +/- 1.0 cm and 6.3 +/- 0.8 cm, respectively (difference = 0.3 cm, P = 0.002). The 95% limits of agreement were 1.3 cm to -0.7 cm. Epidural needle placement using the predetermined insertion point was done without reinsertion at a different puncture site in 76.1% of parturients and without redirection in 67.4%. CONCLUSIONS: We found a strong correlation between the ultrasound-estimated distance to the epidural space and the actual measured needle distance in obese parturients. We suggest that prepuncture lumbar ultrasound may be a useful guide to facilitate the placement of epidural needles in obese parturients.
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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 | 0.001 | 0.010 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 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 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 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".