Local and regional anesthesia in cattle.

Although general anesthesia commonly is used in cattle, there are some risks with its use. Local or regional anesthesia is safe and effective and is still the most desirable procedure in many situations. Many surgical procedures can be performed safely and humanely in cattle by using a combination of physical restraint, mild sedation, and local or regional anesthesia. Local anesthetic techniques are usually simple, inexpensive, and provide a reversible loss of sensation to a relatively well-defined area of the body.     

Local and regional veterinary history

Continuing a review, written in 1992, an overview is given of the five recent studies on local themes. The author emphasizes that telling a story of local traditions and usages, of striking personalities or personal experiences can illuminate the problems of a broader national or even international context. He points to the fact that the local archives contain many materials of veterinary historical relevance waiting for exploitation.     

Intravenous regional anesthesia (Bier block) in a dog.

Intravenous regional anesthesia was used in an adult dog as part of a balanced approach to general anesthesia for amputation of the 4th digit of its right hind limb. It allowed the concentration of isoflurane to be reduced to 0.5%.     

Pain management and regional anesthesia for the dental patient

Current standards of care in veterinary medicine dictate an adequate level of pain control for our patients. Effective pain control uses a proactive, multimode approach that starts with preoperative medications, includes the anesthetic protocol selected, and continues into the postoperative period. A basic understanding of the physiology of pain assists in selecting those agents and modalities best suited for individual patients. Analgesic drug selection and local anesthesia are both integral parts of pain control when performing surgery in the oral cavity. Local (regional) anesthesia plays an important part in the pain control of oral surgical patients. Regional anesthetic techniques are used for many common oral procedures, including extractions, periodontal flap surgery, treatment of traumatic injuries of the oral cavity, tumor removal, palatal surgery, periodontal therapy, and root canal therapy. This presentation will cover strategies for analgesia and the techniques and materials used in local/regional anesthesia in the oral cavity. Anatomic landmarks and guidelines for effective regional blocks will be covered.     

A review of ophthalmic local and regional anesthesia in dogs and cats

Objective

Orbital and globe surgeries are commonly performed in companion animals and are considered to cause moderate to severe pain. Regional anesthesia techniques can provide complete sensory blockade, analgesia for painful procedures and improve surgical conditions. The purpose of this review is to summarize local and regional anesthesia techniques for ophthalmic surgery in dogs and cats with emphasis on veterinary publications in the past 12 years.

Local anaesthetics for regional and intra-articular analgesia in the horse

During the course of a lameness examination, intra-articular or perineural administration of a local anaesthetic is often necessary to isolate the source of pain causing lameness. Local anaesthetics are useful for intraoperative and post-operative pain relief and may allow for elimination of, or a decrease in, general anaesthesia. Within recent years, new information has become available concerning the use of local anaesthetics for localisation of pain and for palliation of pain. New information indicates that

• Lidocaine is less efficacious than mepivacaine or ropivacaine in ameliorating lameness caused by pain.
• After administering a nerve block, loss of skin sensation may not correlate with loss of pain causing lameness.
• Local anaesthetic solution must be deposited within the sheath of the neurovascular bundle to be effective.
• The dose of a local anaesthetic, which is a factor of volume and concentration, affects potency and duration of a nerve block.
• Local anaesthetics are toxic to chondrocytes and synoviocytes. Lidocaine and bupivacaine appear to be more toxic than mepivacaine or ropivacaine. The clinical significance of the toxic effect of a single intra-articular injection of local anaesthetic is yet to be determined.
• Sodium bicarbonate can be added to a local anaesthetic solution to increase its potency and speed of onset.
• Epinephrine added to local anaesthetic solution prolongs and intensifies its analgesic effect.
• Mixing quick-acting, short-duration and slow-acting, long-duration local anaesthetics will not result in a quick-acting, long-duration drug combination.

     

Porcine regional brain and myocardial blood flows during halothane-O2 and halothane-nitrous oxide anesthesia: comparisons with equipotent isoflurane anesthesia

Regional distribution of brain and myocardial blood flow were examined in 9 instrumented isocapnic normothermic swine, using 15-microns diameter radionuclide-labeled microspheres injected into the left atrium. Minimal alveolar concentration (MAC) of halothane required to prevent gross purposeful movement in response to a noxious stimulus in 50% of the pigs was found to be 0.70%. Measurements were made on each animal during nonanesthetized state (control), 1.0 and 1.5 MAC halothane anesthesia, and the equivalent of 1.0 and 1.5 MAC halothane anesthesia, using 50% N2O. The order of anesthetized steps was randomized for each pig. Recovery periods of 60 minutes were interposed between the anesthetic treatments. During halothane + 50% N2O anesthesia, heart rate, cardiac output, mean aortic pressure, and rate-pressure product were higher than comparable levels of halothane-O2 anesthesia. Halothane caused dose-dependent vasodilatation in all regions of the brain. Cerebral, cerebellar, and brain-stem blood flows at 1.5 MAC halothane were 135%, 135%, and 115% of respective control values. Substitution of 50% N2O to maintain same MAC dose markedly exaggerated the increment in porcine cerebral and brainstem blood flows, especially at 1.0 MAC when perfusions in these regions were 204% and 128% of respective control values. At 1.5 MAC anesthesia produced by halothane + 50% N2O, the cerebral, cerebellar, and brain stem perfusions were 153%, 146%, and 129% of control values. Transmural myocardial blood flow decreased from control value with both levels of halothane anesthesia, but with equivalent MAC anesthesia produced by halothane + 50% N2O, myocardial perfusion remained near awake values.(ABSTRACT TRUNCATED AT 250 WORDS)     

Fish and amphibian anesthesia.

This article is designed to provide the veterinary practitioner with some basic information on how to anesthetize fish and amphibians. General guidelines regarding working with these aquatic animals are covered. Specific topics include methods of anesthetic delivery, anesthetic monitoring, and recovery. Various anesthetic regimes and dosages are presented both in the text and in table form.     

Intravenous regional anesthesia in isoflurane anesthetized cats: lidocaine plasma concentrations and cardiovascular effects

Objective To determine if intravenous regional anesthesia (IVRA) can be used in cats without resulting in excessive plasma lidocaine concentrations or adverse cardiovascular effects. Study design Prospective, blinded crossover study. Animals Seven healthy male young adult cats weighing 3.96 ± 0.63 kg. Methods At 2.3% end‐tidal isoflurane concentration, lidocaine (L) 3 mg kg^?1 (1%) or saline (S) was injected in a distal cephalic venous catheter after application of two tourniquets to that forelimb which remained in place for 20 minutes. Heart and respiratory rates, arterial blood pressures and ECG were recorded every 5 minutes during tourniquet application and for 20 minutes following tourniquet removal. Lidocaine plasma concentrations were measured 5 minutes after injection and 0.5, 1, 2, 4, 8, 20 and 40 minutes after tourniquet removal. End tidal isoflurane concentrations were reduced to 1.5–2.0% to elicit a response to toe pinch (RTP) in the contralateral leg. The study was repeated similarly in the contralateral leg and RTP was graded for 40 minutes. Response was also tested in the leg previously injected, the differences between the two scores determined and those differences compared between the L and S treatments. The data were analyzed using anova for repeated measures comparing values to baseline. Significance was set at p < 0.005 using the Bonferroni method for multiple comparisons. Results There were no significant differences in physiologic parameters at either isoflurane concentration. Differences in RTP were significantly larger in the lidocaine treatment. The highest mean lidocaine concentrations were measured 0.5 minutes after tourniquet removal after both injections and were 2.79 ± 1.05 and 3.10 ± 1.11 µg mL^?1. The highest individual plasma concentration was 6.46 µg mL^?1. Conclusion No adverse hemodynamic effects were evident after IVRA lidocaine in any cat. The lidocaine dose studied inhibited a RTP until 20 minutes after tourniquet removal. Lidocaine concentrations varied and were measurable prior to tourniquet removal. Clinical relevance IVRA may be a suitable technique for cats undergoing surgery of the distal limbs.     

Periparturient and neonatal anesthesia.

Small animal patients may need to be anesthetized in the periparturient period for emergency, nonobstetric reasons, elective ovariohysterectomy, or cesarean section. In each case, the physiologic changes in the dam must be accounted for in designing an anesthetic protocol, but the requirements of the fetuses will be different. Subsequent to birth, the neonatal animal may need to be anesthetized, and the unique physiology and pharmacology at this age is described.     

Epidural analgesia and anesthesia.

This review describes the beneficial effects of the use of epidural drugs for pre-emptive analgesia, intraoperative analgesia with an inhalant-sparing effect, and prolonged postoperative analgesia. Epidural morphine oxymorphone, or hydromorphone is recommended for use in small animals in combination with a local anesthetic of appropriate duration for procedures involving the hind end, although epidural morphine or hydromorphone may be more appropriate for procedures on the thorax and forelimbs. Side effects are few and can usually be easily managed, with the benefits outweighing any detrimental effects that might occur.     

Perineural and spinal anesthesia.

Local and regional anesthetic techniques are useful tools for the equine practitioner. These techniques allow surgery to be performed without the risk and cost of general anesthesia. There are, however, risks associated with the local and regional techniques. Neurotoxicity, although rare, may occur when 200 mL or more of a local anesthetic are infiltrated in a short period of time to a 450-kg horse. More likely, horses may become ataxic after nerve blockade in the limbs. This ataxia may lead to self trauma because the horse may not know where the limbs are actually being placed. Although local and regional anesthesia may not always be easy to achieve, persistence and practice will result in consistent nerve blockade.     

Quantitative anesthesia.

Quantitative anesthesia is delivering anesthetic and oxygen in known quantities, the dosage based on calculations for their uptake. The uptake is not linearly related to body weight but is linearly related to body weight raised to a power. The dosage of inhaled anesthetics is calculated by the method of Lowe. The oxygen consumption and cardiac output are estimated by formulas that relate physiologic functions to the body weight in kilograms, raised to a power.     

Propofol anesthesia.

Although questions may still remain regarding the use of this unique sedative-hypnotic drug with anesthetic properties in high-risk patients, our studies have provided cardiopulmonary and neurological evidence of the efficacy and safety of propofol when used as an anesthetic under normal and selected impaired conditions in the dog. 1. Propofol can be safely and effectively used for the induction and maintenance of anesthesia in normal healthy dogs. Propofol is also a reliable and safe anesthetic agent when used during induced cardiovascular and pulmonary-impaired conditions without surgery. The propofol requirements to induce the safe and prompt induction of anesthesia prior to inhalant anesthesia with and without surgery have been determined. 2. The favorable recovery profile associated with propofol offers advantages over traditional anesthetics in clinical situations in which rapid recovery is important. Also, propofol compatibility with a large variety of preanesthetics may increase its use as a safe and reliable i.v. anesthetic for the induction and maintenance of general anesthesia and sedation in small animal veterinary practice. Although propofol has proven to be a valuable adjuvant during short ambulatory procedures, its use for the maintenance of general anesthesia has been questioned for surgery lasting more than 1 hour because of increased cost and marginal differences in recovery times compared with those of standard inhalant or balanced anesthetic techniques. When propofol is used for the maintenance of anesthesia in combination with a sedative/analgesic, the quality of anesthesia is improved as well as the ease with which the practitioner can titrate propofol; therefore, practitioners are able to use i.v. anesthetic techniques more effectively in their clinical practices. 3. Propofol can induce significant depression of respiratory function, characterized by a reduction in the rate of respiration. Potent alpha 2 sedative/analgesics (e.g., xylazine, medetomidine) or opioids (e.g., oxymorphone, butorphanol) increase the probability of respiratory depression during anesthesia. Appropriate consideration of dose reduction and speed of administration of propofol reduces the degree of depression. Cardiovascular changes induced by propofol administration consist of a slight decrease in arterial blood pressures (systolic, mean, diastolic) without a compensatory increase in heart rate. Selective premedicants markedly modify this characteristic response. 4. When coupled with subjective responses to painful stimuli, EEG responses during propofol anesthesia provide clear evidence that satisfactory anesthesia has been achieved in experimental dogs. When propofol is used as the only anesthetic agent, a higher dose is required to induce an equipotent level of CNS depression compared with the situation when dogs are premedicated. 5. The propofol induction dose requirement should be appropriately decreased by 20% to 80% when propofol is administered in combination with sedative or analgesic agents as part of a balanced technique as well as in elderly and debilitated patients. As a general recommendation, the dose of propofol should always be carefully titrated against the needs and responses of the individual patient, as there is considerable variability in anesthetic requirements among patients. Because propofol does not have marked analgesic effects and its metabolism is rapid, the use of local anesthetics, nonsteroidal anti-inflammatory agents, and opioids to provide postoperative analgesia improves the quality of recovery after propofol anesthesia. 6. The cardiovascular depressant effects of propofol are well tolerated in healthy animals, but these effects may be more problematic in high-risk patients with intrinsic cardiac disease as well as in those with systemic disease. In hypovolemic patients and those with limited cardiac reserve, even small induction doses of propofol (0.75-1.5 mg/kg i.v.) can produce profound hypotens     

Avian anesthesia.

Providing a safe anesthetic environment is the key to successful avian anesthesia. Knowledge and understanding the anatomic and physiologic differences between birds and mammals help to prevent most emergency situations and guide responses in critical situations. Thorough preanesthetic history and examination, correction of underlying conditions, and use of simple anesthetic protocols all optimize the outcome of the procedure. Finally, critical monitoring helps to anticipate most crises and reduces incidences of mortality and morbidity in avian anesthesia.