Muscle relaxants in canine anaesthesia 2: Clinical application

There are a variety of factors which are likely to influence the action of muscle relaxants in canine anaesthesia. These include age, body temperature and muscle diseases. Of the anaesthetic agents it is only the inhalational anaesthetic agents which significantly increase the duration of action of muscle relaxants. Antibiotic therapy particularly with the aminoglycoside antibiotics is likely to increase their duration of action. The indications for the use of muscle relaxants and the main contraindications such as the absence of anaesthetic equipment and the inability to ensure unconsciousness are discussed. The choice of anaesthetic technique together with a discussion on the premedication induction and maintenance of anaesthesia are important factors when using relaxants as is the technique of artificial ventilation. The various advantages and disadvantages of neuromuscular block monitoring are discussed as is the reversal of neuromuscular block.     

Interactions between vecuronium and suxamethonium in the dog

The non-depolarising muscle relaxant vecuronium (0.2 mg kg-1) was administered to four dogs. At 50 per cent return of neuromuscular activity, as measured by the train-of-four technique, the depolarising muscle relaxant suxamethonium (0.3 mg kg-1) was injected intravenously. At 50 per cent return of neuromuscular activity reversal of the block was achieved with atropine and neostigmine. The duration of action of suxamethonium was reduced by the prior administration of vecuronium. In the second series of experiments the order of administration of the suxamethonium and vecuronium was reversed. Suxamethonium (0.3 mg kg-1) was administered first and at 50 per cent recovery vecuronium (0.2 mg kg-1) was given. At 50 per cent recovery of the twitch response after vecuronium administration the block was reversed with atropine and neostigmine. The previous administration of suxamethonium prolonged the duration of the vecuronium induced neuromuscular block.     

Interactions between pipecuronium and suxamethonium in the dog

The depolarising muscle relaxant suxamethonium (0.3 mg kg-1) and the non-depolarising muscle relaxant pipecuronium (0.05 mg kg-1) were administered to four dogs. In the first series of experiments pipecuronium was administered intravenously, followed at 50 per cent of return of neuromuscular activity by suxamethonium. At 50 per cent return of activity atropine and neostigmine were administered to reverse the neuromuscular block. In the second series the sequence was reversed and pipecuronium was administered after suxamethonium. At 50 per cent recovery atropine and neostigmine were given. In the first series of experiments the time for the onset of suxamethonium block was significantly increased after prior administration of pipecuronium. However, in the second series of experiments the prior administration of suxamethonium had no significant effect on the duration of action of pipecuronium.     

Vecuronium infusion in the dog

The non-depolarising muscle relaxant vecuronium bromide was administered to 20 dogs undergoing a variety of surgical procedures under general anaesthesia. An initial dose of 0–1 mg/kg was administered and followed by an infusion of 0–1 mg/kg/hour. Reversal of the neuromuscular block was carried out with neostigmine and atropine.     

Depth of anaesthesia

One hundred and fifty years after the first general anaesthetic in 1846 our knowledge about the mechanisms of general anaesthetics is still very sparse. The concept ‘depth of anaesthesia’ was introduced by John Snow (1847). He described ‘5° of narcotism’. Because one single agent had to provide all the components of general anaesthesia, the main problem for the anaesthetist was to avoid morbidity and mortality associated with excessively deep anaesthesia. The introduction of curare in 1942 allowed muscle relaxation required for surgery during a lighter level of anaesthesia, but also changed the emphasis from the problem of too deep anaesthesia and death, to too light anaesthesia and litigation. The problem of awareness during general anaesthesia with muscle relaxants provided the main impetus for monitoring depth of anaesthesia. During daily clinical practice the anaesthesiologist relies on clinical signs to evaluate anaesthetic depth, although several studies have shown a poor correlation between the 2 (Cullen et al. 1972; Evans and Davies 1984; Russell 1993). Different methods have been used in attempts to measure anaesthetic depth (Evans and Davies 1984; Stanski 1994), but none have been developed to a state where they can be used routinely in the operating theatre. This review will cover some of the parameters used to evaluate anaesthetic depth.     

Interaction between atracurium and suxamethonium in the dog

The depolarising muscle relaxant suxamethonium (0.3 mg kg-1) and the non-depolarising relaxant atracurium (0.6 mg kg-1) were administered to four dogs. In the first series of experiments atracurium was administered, followed at 50 per cent return of neuromuscular activity by suxamethonium. At 50 per cent return of activity atropine and neostigmine were administered to reverse the block. In the second series of experiments the sequence was reversed and atracurium was administered after suxamethonium. At 50 per cent recovery atropine and neostigmine were given. In the first series of experiments it was demonstrated that the prior administration of atracurium reduced the duration of action of suxamethonium. However, in the second series it was shown that the prior administration of suxamethonium had no significant effect on the duration of action of atracurium.     

Anaesthetic regimes for cataract removal in the dog

Dogs scheduled for elective removal of non-diabetic cataracts were assigned to one of four anaesthetic regimes. Thiopentone (Intraval Sodium; RMB Animal Health) or propofol (Rapinovet; Coopers Pitman-Moore) was used as the induction agent and with each agent half the animals were paralysed with vecuronium (Nor-curon; Organon Teknika) and ventilated mechanically, and half breathed spontaneously. Anaesthesia was maintained with halothane (Halothane-M&B; RMB Animal Health) and nitrous oxide (BOC) in oxygen. The use of muscle relaxants significantly improved the eye position and significantly reduced the lowest halothane vaporiser setting used during anaesthesia. Propofol produced a significantly shorter recovery time than thiopentone.     

The influence of anaesthesia on bronchography in dogs

The spread of the contrast medium, Dionosil Aqueous (Glaxo),* in the bronchi of three healthy dogs was investigated under a variety of anaesthetic techniques. The most reliable results were obtained when intermittent positive pressure ventilation (IPPV) was applied following anaesthetic techniques incorporating the use of neuromuscular blocking agents. Good results were also obtained using trichloroethylene anaesthesia. The reliability of results obtained using relaxant techniques was confirmed in clinical cases.     

Remote intramuscular injection of immobilising drugs into fish using a laser-aimed underwater dart gun

Sixty coldwater and warmwater fish ranging in weight from 2 to 35 kg were injected intramuscularly with the hypnotics alphaxalone-alphadolone and metomidate hydrochloride and the non-depolarising muscle relaxant gallamine triethiodide using a laser-aimed underwater dart gun. Alphaxalone-alphadolone produced sufficient sedation for easy netting within five to 20 minutes at doses between 0.3 and 0.5 ml/kg, with induction being somewhat faster in warmwater species. The pattern of induction was similar with metomidate but required doses of 40 to 60 mg/kg. The muscle relaxant gallamine triethiodide showed promise as a practical agent for the capture and handling of large fish by virtue of its smooth induction of paralysis at doses between 1 and 3 mg/kg and its reversible supplementation with orally administered metomidate hydrochloride.     

The use of sedatives,analgesic and anaesthetic drugs in the horse: An electronic survey of members of the American Association of Equine Practitioners (AAEP)

Reasons for performing study: To determine the sedative, analgesic and anaesthetic drugs and techniques that are used by equine veterinarians. Hypothesis or objectives: To provide equine veterinarians with information concerning veterinary use of anaesthetic techniques, a reflection of the collective experiences of the profession. Methods: A survey was conducted of those members of the American Association of Equine Practitioners (AAEP) with an electronic mail address on file with the organisation using proprietary, web‐based software. The survey was comprised of 30 questions divided into 8 sections: nonsteroidal anti‐inflammatory drugs; local anaesthesia; alternative techniques; standing chemical restraint; epidural anaesthesia; short‐term anaesthesia; long‐term anaesthesia; and a place for the respondent to make comments. Results: The response rate was 13.8% (952/6911) AAEP member veterinarians primarily use phenylbutazone and flunixin as anti‐inflammatory drugs, and lidocaine and mepivacaine for local anaesthesia. Combinations of drugs are preferred for standing chemical restraint. While many veterinarians frequently utilise short‐term anaesthesia, longer anaesthesia is less frequently performed. Conclusions: Most AAEP member veterinarians use sedatives in combination to provide standing chemical restraint. Extra‐label use of drugs is a core component of current equine sedation and anaesthetic practice. Potential relevance: Equine veterinarians can compare their choices of anaesthetic drugs with others practising equine medicine and surgery and may be stimulated to investigate alternative methods of providing comfort to horses.     

The Photomotor Reflex as an Indicator of Consciousness in the Immobilized Dog

Abstract— When a relaxant is used in conjunction with light general anaesthesia, it is not possible to distinguish between true unconsciousness, and consciousness masked by immobilization, by the usual reflexes involving voluntary muscle. Experiments are described which show that the photo-motor reflex (contraction of the pupil of the eye with increase in intensity of light stimulus), unlike the other reflexes commonly used for testing anaesthesia, gave a reliable indication of returning consciousness in a dog immobilized by a relaxant. The reflex was not affected by premedication with atropine, provided that the dose of atropine did not exceed 0.032 mg./kg. body-weight. The reflex is valid when anaesthesia is induced by barbiturate alone, or by a combination of barbiturate and ether.     

Dose-response relationship of atracurium besylate in the halothaneana-esthetised pig

The dose response relationship for the intermediateacting non-depolarising muscle relaxant, atracurium besylate in the pig was determined using evoked electromyography. An incremental dose technique was used in seven Large White/Landrace crossbred pigs anaesthetised with nitrous oxide and halothane. ED50 and ED95 were 510 ± 87 μg kg⁻¹ and 1150 ± 270 μg kg⁻¹, respectively. Although these values may represent an overestimate, they provide a reasonable guideline for the use of atracurium by veterinary anaesthetists.     

Restraint and anaesthesia of primates

The methods available for the restraint and anaesthesia of captive primates are discussed, emphasising the differences between the techniques for primates and those for other mammals; the importance of humane methods of physical restraint is emphasised. The agents available for chemical restraint and surgical anaesthesia are considered in terms of their ease of administration, the dose rate required, speed of induction and recovery, analgesic properties, muscle relaxation and side effects. New agents are available which are potentially useful in primates.     

Neuromuscular blocking agents in equine anesthesia

In summary, neuromuscular blocking agents can be used safely and to advantage in equine anesthesia. Muscle-relaxant use in equine anesthesia has been helped by the development of new relaxants such as atracurium, which has a reliable and reproducible duration of action. There are certain cases that benefit particularly by the use of relaxants but their use is not limited to these cases. These cases involve horses that experience persistent movement and hypotension during anesthesia, are undergoing ophthalmic or abdominal surgery or fracture repair, or are severely ill. Horses receiving muscle relaxants during anesthesia require mechanical ventilation, and neuromuscular blockade should be monitored with a peripheral-nerve stimulator.     

A NEW METHOD OF CLOSED CIRCUIT ANAESTHESIA UTILISING HALOTHANE AND METHOXYFLURANE

Experiences with a new technique of closed circuit anaesthesia used for 1003 surgical cases involving cats and dogs are described. The technique utilises the combined vapors of methoxyflurane and halothane from dual, low-resistance vaporisers situated in series, and supported by low flow rates of 100% oxygen in the inspiratory limb of the anaesthetic machine. This anaesthetic circuit can be adapted for many surgical procedures involving both controlled and spontaneous ventilation techniques and for young and old animals. The technique is considered safe, economical and easily managed and pollution of the operating theatre is eliminated by the use of the completely closed circuit.     

Anaesthesia in two species of large Australian skink

The use of ketamine hydrochloride and sodium pentobarbitone in the anaesthesia of two species of Australian skink was examined. The effects of ketamine at ambient temperatures of 15 degrees C and 30 degrees C were studied. Ketamine produced consistent responses up to and including anaesthesia at dose rates of 170 to 230 mg/kg at 30 degrees C. The effect of temperature on the anaesthetic dose, respiratory and cardiac rates, muscle relaxation, analgesia and the onset and duration of anaesthesia was examined. Respiration in both species was depressed but heart rate was increased in Bobtail skinks (Tiliqua rugosa) and depressed in King's skinks (Egernia kingii). Muscle relaxation was good when anaesthetic doses were given. Generally, the onset and duration of anaesthesia were extended at 15 degrees C while the dose rates required for this effect were reduced. Although there was individual variation in the response to ketamine, it was found to be a useful and practical agent for the anaesthesia of large skinks. Pentobarbitone was found to be unsuitable as an anaesthetic agent because it produced inconsistent results and several fatalities.     

Hypobaric intrathecal anaesthesia for partial hemipelvectomy in a dog.

OBJECTIVE : To report the intrathecal use of a hypobaric anaesthetic solution for partial hemipelvectomy in a nine-year-old, neutered female, Golden Retriever dog, weighing 34 kg. METHODS : Under inhalational anaesthesia, with the dog lying in lateral recumbency and the surgical side uppermost, 1.9 ml of a hypobaric solution containing 3.42 mg of bupivacaine and 0.66 mg of morphine were administered in the subarachnoid space at L5-6 level 30 minutes before surgery. Following the intrathecal injection the dog was maintained for five minutes in a 10 degrees head-down position, then for three minutes in a 10 degrees head-up position. RESULTS : Apart from a transient increase in heart and respiratory rates during resection of the sartorius muscle, which was treated with a plasma Target Controlled Infusion (TCI) of fentanyl, spinal anaesthesia provided cardiovascular stability and excellent relaxation of the surgical site. Neither motor blockade nor proprioceptive deficit were apparent in the contra-lateral hind limb at recovery, 200 minutes after injection. Postoperatively, rescue analgesia was not required in the 48 hours following surgery. CLINICAL SIGNIFICANCE : In dogs, the use of intrathecal hypobaric bupivacaine and morphine as a part of a balanced anaesthetic protocol should be considered during unilateral major orthopaedic surgeries of the pelvis and hind limb, as it allowed a reduction in the dose administered compared to isobaric solutions, providing selective spinal anaesthesia, excellent long-lasting analgesia, and rapid recovery of ambulation.     

PRACTICAL PROBLEMS WITH VETERINARY ANAESTHESIA MACHINES

Many types of anaesthetic machines are available to practicing veterinary surgeons, ranging from the obsolescent to the most modern. To practice anaesthesia safely, veterinary surgeons should understand the functions of the machines, vaporizers, and breathing systems with which they work. In addition, veterinary surgeons should employ procedures for evaluation of their anaesthetic equipment to assure, as much as possible, safety for their patients and the personnel who use the apparatus.     

Evaluation of the anaesthetic effects of combinations of ketamine, medetomidine, romifidine and butorphanol in European badgers (Meles meles)

OBJECTIVE: To evaluate the effects of three anaesthetic combinations in adult European badgers (Meles meles). STUDY DESIGN: Prospective, randomized, blinded, experimental trial. ANIMALS: Sixteen captive adult badgers. METHODS: The badgers were each anaesthetized by intramuscular injection using the three techniques assigned in random order: romifidine 0.18 mg kg(-1), ketamine 10 mg kg(-1) and butorphanol 0.1 mg kg(-1) (RKB); medetomidine 0.1 mg kg(-1), ketamine 9 mg kg(-1) and butorphanol 0.1 mg kg(-1) (MKB); and medetomidine 0.1 mg kg(-1) and ketamine 10 mg kg(-1) (MK). Initial drug doses were calculated based on a body mass of 10 kg. Additional anaesthetic requirements, time to drug effect, duration of action and recovery from anaesthesia were recorded. Heart rate and rhythm, respiratory rate and rhythm, rectal and subcutaneous microchip temperature and oxygen saturation were recorded every 5 minutes. Depth of anaesthesia was assessed using: muscle tone; palpebral and pedal reflexes; and tongue relaxation at these time points. Blood samples and a tracheal aspirate were obtained under anaesthesia. Atipamezole was administered if the badger had not recovered within 60 minutes Parametric data were analysed using anova for repeated measures, and nonparametric data using Friedman's, and Cochran's Q tests: p < 0.05 was considered significant. RESULTS: All combinations produced good or excellent muscle relaxation throughout the anaesthetic period. RKB had the shortest duration of anaesthesia (16.8 minutes compared with MKB 25.9 minutes and MK 25.5 minutes) and antagonism was not required. RKB depressed respiratory rate less than MK and MKB. There was no significant difference between techniques for heart rate and rhythm. CONCLUSIONS AND CLINICAL RELEVANCE: All combinations provided anaesthetic conditions suitable for sampling and identification procedures in adult badgers. The RKB protocol provided a significantly shorter period of anaesthesia when compared with the combinations containing medetomidine.     

The incidence of spontaneous movements (myoclonus) in dogs undergoing total intravenous anaesthesia with propofol

ObjectiveTo evaluate the incidence of myoclonus (involuntary movements during anaesthesia, unrelated to inadequate hypnosis or analgesia, and of sufficient severity to require treatment) in dogs anaesthetized with a TIVA of propofol with or without the use of fentanyl.Study designRetrospective clinical study.AnimalsDogs, undergoing general anaesthesia for clinical procedures between January 2012 and January 2013 and subject to TIVA with propofol.MethodsA retrospective analysis reviewed the medical and anaesthetic records. Animals with existing or potential neurological or neuromuscular pathology in the anamnesis or upon clinical examination and cases with incomplete clinical records were excluded. Myoclonus was considered as involuntary muscle contractions which did not cease following a bolus administration of propofol or fentanyl and, due to their intensity and duration, made continuation of the procedure impracticable without other drug administration. Tremors, paddling or muscle spasms, explicable as insufficient hypnosis or analgesia, and transient excitatory phenomena only present during the awakening phase, were not considered as myoclonus.ResultsOut of a total of 492 dogs undergoing anaesthesia, six mixed breed dogs (1.2%), one male and five females, American Society of Anaesthesiologists (ASA) physical status I, median (range) weight 20.5 (7–37) kg and age 1.5 (1–5) years had myoclonus according to the aforementioned definition. In all subjects, myoclonus appeared within 20 minutes after induction of anaesthesia, and mainly involved the limb muscles. All subjects appeared to be in an adequate plane of anaesthesia before and during myoclonus.Conclusions and clinical relevanceThis study shows that 1.2% of dogs, undergoing TIVA with propofol with or without fentanyl administration, developed myoclonus, which required to be, and were treated successfully pharmacologically. The cause of this phenomenon is yet to be determined.