A review of laboratory animal anesthesia with chloral hydrate and chloralose

Chloral hydrate (CH) and alpha-chloralose (CS) are often used to anesthetize laboratory animals although, to our knowledge, there have been no controlled studies of their anesthetic or analgesic effects. Induction of and recovery from anesthesia can be stressful, and anesthesia and analgesic quality have been questioned. Intraperitoneal (i.p.) administration of CH has resulted in adynamic ileus and peritonitis in rats, gastric ulcers in rats, and peritonitis in swine. Light anesthesia is induced in rats. In dogs, CH induces sedation to deep anesthesia when given intravenously. Gastric irritation in dogs can occur when CH is given orally. Chloral hydrate is considered a good sedative-hypnotic for farm animals. Intravenously administered CS anesthetizes dogs and cats for 5 to 10 hours, but the animals may require respiratory support. Chloralose appears to be a satisfactory anesthetic for dogs when stage III thiobarbiturate anesthesia is first induced. It is difficult to gauge the depth of anesthesia and analgesia with CS. In our clinical experience with swine and calves, CH given i.p. leads to adynamic ileus. We have found that CS given i.p. causes an inflammatory response in guinea pigs, rats, and calves. We observed that CS analgesia varies with the type of surgical procedure performed. Based on a literature review and our clinical experience, we suggest that CH or CS anesthesia should be preceded by administration of barbiturates, opioids, alpha-2 agonists, or phenothiazine tranquilizers. Chloral hydrate should only be used as a sedative or hypnotic for dogs; CS should not be used as a sole anesthetic agent. Neither drug should be used i.p. for survival surgery.