Intravenous chloral hydrate anesthesia provides appropriate analgesia for surgical interventions in male Sprague-Dawley rats

The use of chloral hydrate as a sole maintenance anesthetic agent in rodent research has been controversial due to information in reference literature conflicting with that of primary research studies regarding its analgesic efficacy, and because of its associated tissue damage when administered intraperitoneally. Our aim was to assess the analgesic efficacy of chloral hydrate using an intravenous (i.v.) route of administration, in order to prevent the local tissue irritation or ileus that has been previously reported using intraperitoneal (i.p.) routes. We measured tail withdrawal latencies to a nociceptive thermal stimulus (infrared beam) in Sprague-Dawley rats –first when awake (unanesthetized), and then subsequently during i.v. chloral hydrate anesthesia. During anesthesia we also measured ongoing heart and respiration rates. Withdrawal latencies during chloral hydrate anesthesia were significantly higher, and
often maximal, indicating a robust analgesic effect. Importantly, both respiration and heart rate remained unchanged following exposure to the nociceptive stimulus, and were comparable to values observed under other anesthetics and during natural sleep.
Together with previous studies, these results demonstrate that i.v. chloral hydrate
provides excellent anesthetic depth and analgesic efficacy for surgical manipulations in rats.

These files require either OriginLab (https://www.originlab.com/) or Prism GraphPad (https://www.graphpad.com/) to open and view the data and our analyses.

The analgesia analysis file contains the raw tail withdrawal latencies for all 5 trials for each rat both anesthetized and unanesthetized, and the corresponding analyses. The physiology analysis file contains the comparison of the 30s pre-IR to 30s during IR for heart rate and breathing rate for 3 trials per rat, and the statistical comparisons we employed. Finally the normalized heart rate and respiration rate analysis contains the normalized instantaneous heart rate and respiration rate data for the duration of exposure to the IR stimulus per trial and the analysis of the slope.