The difficulties accompanying inhalational anesthetic administration in large domestic animals, prompted a search for better anesthetics. Liebig discovered chloral hydrate in 1832, and after experimenting in animals, Pierre-Cyprien Oré used it intravenously to produce anesthesia in humans in 1872. Humbert described its use in horses in 1875, at doses of 30–70 gm. It was given by mouth or via the rectum, and occasionally by intraperitoneal injection, usually as an adjunct to local or inhalation anesthesia. The later intravenous use of chloral hydrate in full anesthetic doses in the horse is credited to experiments conducted in Western Europe. Degive, a prominent Belgian professor, described this method of administration in horses, in 1908. Degive wrote (as quoted by Wright [13]):

“Chloral hydrate injected into the jugular vein of the horse … produces in 1 to 2 minutes complete general anaesthesia without causing preliminary excitement in the animal [as commonly seen with chloroform]. The method is most valuable when practiced with full aseptic precautions but it has been followed by several accidents which have put its value into doubt.”

Later, Wright wrote:

“It is a drug the value of which is continually being rediscovered. … Half a century later I … arrived at the same conclusion except to say that provided adequate technical care is exercised the doubt he [Degive] expresses becomes removed. In fact even today, with the great advances in our knowledge of anaesthesia and anaesthetics, it is my opinion that chloral hydrate by intravenous injections is the best method of inducing general anaesthesia in the horse …”

Organized veterinary medicine had but limited interest in anesthesia through much of the last quarter of the nineteenth century. In his review of the History of Veterinary Anesthesia [3], Smithcors notes:

“In the first volume of the ‘American Veterinary Review’ (1877), … there is but one reference to anesthetics, and none in volume 2….Early advocates of anesthesia, mainly Dadd and his colleagues, worked outside the pale of urbanized veterinary medicine. Perhaps one had to be a maverick to stray far from conventional practice.”

And in hisManual of Operative Veterinary Surgery Alexandre Liautard wrote [14]:

“In veterinary surgery, the indication for anesthesia has not, to the same extent as in human, the avoidance of pain in the patient for its object, … the administration of anesthetic compounds aims principally to facilitate the performance of the operation for its own sake….”

In the 1915 edition ofThe Principles of Veterinary Surgery, Louis Merillat echoed the above sentiments but noted a trend to a use of anesthesia to relieve pain [11]:

“Anaesthesia in veterinary surgery today is a means of restraint and not an expedient to relieve pain. So long as an operation can be performed by forcible restraint without imminent danger to the technique, the operator or the animal, the thought of anaesthesia does not enter in the proposition. But, on the other hand, when a certain technique requires perfect repose of the surgical field, or when there is danger of personal injury or injury to the animal, it issometimes (sic) administered, minority reports to the contrary notwithstanding.”

“(However, it is a matter of fact that practitioners who once begin the practice of administering inhalation anaesthetics for their operations soon find it indispensable to the success of their work. As they become more and more confident in their ability as anaesthetists they resort to this in all kinds of operations, minor and major, and the result is always the enlargement of their scope of usefulness as surgeons.)”

Humanitarian concerns for animals led to legislation in Great Britain (Cruelty to Animals Act, 1876), to restrict the use of animals in experiments to those persons who were licensed and had Home Office permission for particular procedures (later succeeded by the Animals [Scientific Procedures] Act of 1986). In 1913, the British Parliament discussed and later enacted an Anaesthetics Bill for Animals [15],’the Animals (Anaesthetics) Act of 1919 (reproduced in the appendix of Wright’s textbook [16]). It specified that general or local anesthetic must be used in specific surgical procedures in a horse, dog, cat or a bovine, and that the anesthetic must be “…of sufficient power to prevent the animal feeling pain”. Any person subjecting, or causing, or procuring, or being the owner of the animal subjected “… to an operation contrary to the regulations … shall be guilty of an offence under this Act” and liable upon conviction, for a fine and/or imprisonment. Its focus on general anesthesia inhibited the development of regional anesthesia until 1954. The 1919 Act was a precursor to legislation of the present day Act, i.e., The Protection of Animals (Anaesthetics) Act of 1954 and 1964 [7]. The 1964 version allowed veterinary surgeons to choose the type of anesthetic as long as it produced “adequate anaesthesia” [8].

In 1915, Hobday published the first English textbook devoted exclusively to veterinary anesthesia,Anaesthesia and Narcosis of Animals and Birds [15]. In his Preface he wrote that “The progress of anaesthetics in veterinary surgery has not been as rapid as it ought to have been, and it is in the hope that a small textbook specially devoted to the subject may be helpful in his direction.”

Wright laid the foundations ofmodern veterinary anesthesia. He qualified and spent the early part of his career as a veterinary surgeon in the Department of Surgery at the Beaumont Hospital of the Royal Veterinary College, London. He moved to the veterinary school at the University of Liverpool in 1941, where he established the Field Station. Like Hobday, Wright’s interest in anesthesia lay in his desire as a surgeon to avoid pain, to provide a safe anesthetic, and to ensure a proper environment for the performance of surgery. He published his first edition ofVeterinary Anaesthesia in 1941. In 1961, Wright and LW Hall (of Cambridge University) co-authored the 5th edition. In 1966, the 6th edition appeared asWright’s Veterinary Anaesthesia and Analgesia, with Hall as the single author. No textbook of veterinary anesthesia has been published for a longer time, and it recently reached its 10th edition (now authored by Hall, KW Clarke and C Trim).

Two major advances occurred in the decade before World War II [4]: the introduction of barbiturates and epidural anesthesia to clinical practice. In America, Kreutzer [17] reported the first use of pentobarbital (administered intraperitoneally; IP) in veterinary anesthesia. Two years later in Britain, Wright published his own experiences with IP pentobarbital in 100 dog and cat patients. Humans were given barbiturates intravenously, and this route was soon applied to animals [18]. Some veterinarians thought that this method, particularly for anesthetic induction was “…infinitely superior to the accepted methods of inhalation anesthesia; in fact by its introduction canine surgery became revolutionized [19].” Shortly thereafter, thiopental and later thiamylal were found to be more satisfactory for many common needs of veterinary medicine, like short periods of deep sedation and anesthesia for minor surgery [20]. Following intravenous barbiturate anesthetic induction, the needle was maintained in situ in the vein, and the attached syringe taped to the (usually) patient’s foreleg for ease of added drug dosing as needed.

Such a technique was common in a small animal-focused clinical practice, when I entered the profession in 1967. Until I purchased my first inhalation anesthetic machine (with in-circuit glass vaporizer) from a regional General Services Administration (federal agency disposing of obsolete/unwanted medical equipment) auction in 1968, most anesthetics I administered in general veterinary practice were barbiturates. The notable exception was the use of diethyl ether for short-term anesthetic management of cats undergoing routine castration or abscess incision and drainage. Why ether? Part of the problem was poorly socialized, especially rural and semi-rural cats. In addition, the re-used needles of that time had varying degrees of sharpness. Accordingly, it was easier for the veterinarian and cat to place the fasted cat into a top-hinged wooden box with glass panel. The lid was quickly closed after a few milliliters of diethyl ether were poured onto the box floor. If additional anesthetic time was needed, more ether was administered using an open-drop technique.

Short and ultrashort acting barbiturates which appeared in the 1930s remained two of the most widely used anesthetic drugs (as a sole agent) in both small and large animal practice until late in the twentieth century. Their use as a sole agent however, required large doses to eliminate movement in response to pain. Accordingly, recovery times were undesirably prolonged.

To deal with the prolonged recovery time, during the 1970s, the increasing use of halothane and the newly introduced enflurane supplanted pentobarbital. In the 1980s, the introduction of ketamine and isoflurane as primary agents, either alone or in various species-related anesthetic drug cocktails, and then propofol (especially in small animals), gradually replaced the ultra-short acting barbiturates. In the past decade, a few investigators have used desflurane to accelerate recovery from anesthesia in large and fractious animals. Sevoflurane has seen an expanded, but still small clinical application for companion animals and horses. Cost has limited a broader application of both anesthetics. Isoflurane remains, by far, the primary inhaled anesthetic in veterinary medicine.

The development of local and regional anesthetic techniques for human patients fostered similar developments in veterinary medicine. For example, since the late part of the nineteenth century, local anesthesia has been used to assist diagnosis of the cause of lameness in horses. In the US, in 1924, Bemis and colleagues published a summary of regional nerve blocks in contemporary use with horses [21]. Regional anesthesia achieved only limited popularity in veterinary medicine because both local and regional anesthesia require a cooperative patient. Smithcors notes, “It remained for veterinarians Retzgen of Berlin [and also Pape and Pitzch] in 1925, and Franz Benesch of Austria in 1926, to demonstrate in horses and cattle respectively, that epidural anesthesia with the needle introduced distal to the spinal cord proper, was a safe technique. [3]” In 1940, Farquharson described paravertebral blocks of thoracic and lumbar nerves for abdominal operations (eg, rumenotomy and exploratory laporatomy) in standing cattle [22]. In 1953, Larson introduced the internal pudendal (pudic) nerve block for anesthesia of the penis and relaxation of the retractor penis muscle in bulls [23].

Veterinary anesthesiology did not exist as a discipline before 1950. Surgeons and general practitioners gave anesthesia as part of their care. The first veterinarians devoting their practice exclusively to anesthesia and its clinical development were Barbara Weaver and Leslie Hall (Fig. 23.2). Weaver qualified from the Royal Veterinary College (RVC) in 1949, and was appointed House Surgeon, then Lecturer at the RVC Beaumont Animals Hospital, London. Hall qualified in 1950, also from the RVC. After three months in general practice he was awarded a Veterinary Education Trust research training scholarship to work under E. Amoroso in the Physiology Department of the RVC. He was awarded a PhD degree from London University in 1957 for an investigation of the control of arterial blood pressure under general anesthesia.