Study questions how vets interpret cranial epidural coverage
Bottom line
A new conceptual analysis in Frontiers in Veterinary Science argues that veterinarians should be more careful about how they interpret “cranial abdominal coverage” after caudal epidural local anesthetic administration in dogs and cats. Author Shotaro Nagahama says favorable perioperative outcomes don’t necessarily prove that local anesthetic reliably reached or fully blocked the cranial abdominal segments in question. The paper separates four different ideas that are often conflated in practice and in the literature: anatomical spread of injectate, functional block of targeted stimuli, physiologic tolerance during surgery, and overall clinical performance. It also highlights a mismatch between some feline ovarian surgery outcomes reported with 0.3 mL/kg regimens and CT mapping data showing that even cumulative iohexol volumes of 0.75 to 1.0 mL/kg did not consistently reach bilateral T10-T11 foramina. (frontiersin.org)
Why it matters: For veterinary professionals, the paper is less a rejection of caudal epidurals than a reminder not to overinterpret success in the OR. Prior guidance already shows that cranial spread depends on factors including volume, concentration, injection rate, epidural space anatomy, posture, and body condition, and that larger volumes can increase the risk of sympathetic blockade, hypotension, bradycardia, and respiratory compromise. In that context, Nagahama’s analysis pushes clinicians to distinguish “the patient did well” from “the cranial abdomen was completely blocked,” especially when planning analgesia for procedures involving ovarian pedicles or other cranial abdominal structures. (frontiersin.org)
What to watch: The next step is prospective work that links imaging or anatomical mapping with functional sensory testing and perioperative physiologic outcomes, rather than relying on clinical impression alone. (frontiersin.org)
Key facts
- Article type
- Conceptual analysis
- Journal
- Frontiers in Veterinary Science
- Author
- Shotaro Nagahama
- Species
- Dogs and cats
- Main point
- Good perioperative outcomes do not prove complete cranial abdominal blockade after caudal epidural local anesthetic administration
- Key distinction
- Separates anatomical spread, functional block, physiologic tolerance, and overall clinical performance
- Feline data
- 0.3 mL/kg ovarian surgery regimens had mixed results
- CT mapping finding
- Cumulative iohexol volumes of 0.75 to 1.0 mL/kg did not consistently reach bilateral T10-T11 foramina
A new paper in Frontiers in Veterinary Science is asking the profession to slow down and be more precise when discussing cranial abdominal coverage after caudal epidural local anesthetic administration in dogs and cats. In a conceptual analysis published in 2026, Shotaro Nagahama argues that good surgical conditions or acceptable perioperative outcomes should not automatically be taken as evidence that a caudal epidural produced complete, reliable blockade of cranial abdominal targets. (frontiersin.org)
That matters because caudal epidurals are a familiar part of small-animal anesthesia, and they’re often used to reduce nociceptive input, lower inhalant and analgesic requirements, and blunt the surgical stress response. Existing reviews describe the technique as valuable for procedures caudal to the diaphragm, but they also emphasize that the extent of sensory, motor, and autonomic blockade depends on several variables, including injectate volume, concentration, injection velocity, posture, epidural fat, and the size of the epidural space. (frontiersin.org)
Nagahama’s paper focuses on a problem that’s easy to miss in day-to-day practice: clinicians and researchers may use the same phrase, “coverage,” to describe very different things. The analysis distinguishes anatomical distribution of the injectate from functional attenuation of a predefined stimulus, physiologic tolerance during surgery, and broader perioperative clinical performance. That distinction is central to the article’s argument. A patient may remain stable, or require less rescue analgesia, without that meaning the epidural created a complete bilateral block at the exact thoracolumbar segments supplying the surgical target. (frontiersin.org)
The feline data discussed in the paper illustrate the issue. According to the abstract, 0.3 mL/kg epidural regimens used in ovarian surgery have produced mixed clinical results, while target-oriented CT mapping did not show uniform bilateral reach to the T10-T11 foramina even when cumulative iohexol volumes reached 0.75 to 1.0 mL/kg. The author notes that differences in injectate, dosing sequence, and study endpoints make head-to-head dose-response comparisons difficult, but concludes that consistent, complete bilateral cranial abdominal coverage is a less plausible explanation for favorable outcomes at 0.3 mL/kg. (frontiersin.org)
That skepticism fits with the broader literature. A 2017 Frontiers review reported that 0.2 mL/kg local anesthetic volumes generally desensitize caudal abdominal structures, while volumes above about 0.2 to 0.25 mL/kg may spread more cranially, sometimes as far as thoracic or cervical levels, but at the cost of greater risk for hypotension, bradycardia, and respiratory compromise from sympathetic or phrenic involvement. More recent canine work on coccygeal epidurals also found that increasing volume from 0.1 to 0.3 mL/kg did not produce dramatic differences in cranial spread, underscoring that dose alone may not predict clinically meaningful segmental blockade. (frontiersin.org)
Direct expert reaction to this specific paper appears limited so far, which isn’t unusual for a newly accepted conceptual analysis. Still, the article is consistent with current anesthesia guidance that stresses structured planning, monitoring, and multimodal analgesia rather than assuming a single technique will fully cover every painful input. It also aligns with practical educational resources that note cats carry added technical considerations for epidurals because the spinal cord extends more caudally, increasing the chance of inadvertent subarachnoid puncture at the lumbosacral space. (pubmed.ncbi.nlm.nih.gov)
Why it matters: For veterinary teams, the takeaway isn’t that caudal epidurals are ineffective. It’s that success should be defined more carefully. If a surgeon reports a smooth ovariohysterectomy or a patient’s inhalant requirement drops, that may reflect partial neuraxial blockade, multimodal systemic analgesia, timing effects, or physiologic tolerance, rather than dependable blockade of all cranial abdominal afferents. That distinction affects case selection, informed consent with pet parents, rescue analgesia planning, and how practices teach younger clinicians to interpret epidural performance. It may also support broader use of complementary regional techniques, or thoracic approaches in selected referral settings, when a truly cranial target is the goal. (frontiersin.org)
What to watch: The key next step is prospective research that combines imaging-confirmed spread with sensory testing, physiologic monitoring, and clinical outcomes in live dogs and cats, so the field can better define when caudal epidurals are enough on their own, and when they should be treated as one component of a multimodal plan. (frontiersin.org)