Anesthetic management of the head trauma patient

Objective: To describe the optimal anesthetic management of patients with brain injury, with emphasis on the support of oxygen delivery to the brain, and the effects of anesthetic agents on cerebral perfusion. Data sources: Clinical and experimental studies from both the human and veterinary neuroanesthesia literature. Summary: The management of patients following primary traumatic brain injury (TBI) significantly impacts outcome. Outcome can be improved by strategies that improve oxygen delivery to the brain and prevent cerebral ischemia. Anesthetic agents have widely variable effects on the blood supply to the brain and, therefore, choice of anesthetic agent can influence neurological outcome. Although in the past, anesthetic agents have been selected for their neuroprotective properties, it is increasingly being recognized that the support of cerebral perfusion during anesthesia contributes more significantly to a positive outcome for these patients. Support of cardiorespiratory function is, therefore, highly important when anesthetizing patients with TBI. Conclusion: Choice of anesthetic agent is determined by the extent of brain injury and intracranial pressure (ICP) elevation. Factors that should be considered when anesthetizing head trauma patients include the effects of anesthetic agents on the cardiac and respiratory systems, their effects on cerebral blood flow (CBF), ICP, and possible neuroprotective benefits offered by certain agents.     

Development of a retrobulbar injection technique for ocular surgery and analgesia in dogs

OBJECTIVE: To develop and compare 3 techniques for retrobulbar injection of local anesthetic agents for ocular surgery and analgesia in dogs. DESIGN: Prospective study. ANIMALS: 17 dogs (including 9 cadavers). PROCEDURES: Inferior-temporal palpebral (ITP), perimandibular, and combined superior-inferior peribulbar injection techniques were compared by assessing the distribution of latex after injection into the orbits of 5 canine cadavers; magnetic resonance imaging (MRI) evaluation of the distribution of contrast agent after injection in the retrobulbar space of 4 canine cadavers; and assessment of the efficacy and MRI evaluation of the anatomic distribution of injections of a lidocainecontrast agent mixture in 4 anesthetized, nonrecovery dogs. By use of the preferred technique (ITP), the ocular effects of lidocaine anesthesia were evaluated in 4 dogs; during a 2-week period after treatment, dogs underwent ophthalmic examination, Schirmer tear testing (STT), intraocular pressure (IOP) measurement, and Cochet-Bonnet esthesiometry. RESULTS: Of the 3 techniques, the ITP technique was the preferred method for retrobulbar administration of anesthetic agent in dogs because it was efficacious (pupil dilation and central rotation of the globe achieved in all eyes), easiest to perform, and provided thorough coverage of the intraconal retrobulbar space without complication. During the 2-week follow-up period, the ITP injection did not significantly affect STT, IOP, or Cochet-Bonnet esthesiometry values in dogs. CONCLUSIONS AND CLINICAL RELEVANCE: In dogs, retrobulbar administration of anesthetic agents via the ITP technique is a potential alternative to systemic administration of neuromuscular blocking agents for ophthalmic surgery and provides the additional benefit of local ocular analgesia.     

Local Anesthetics and Nuclear Medical Bone Images of the Equine Fore Limb

The effects of two local anesthetic agents on the diagnostic quality of nuclear medical bone images (NMBIs) of distal parts of the equine fore limb were investigated. Local effects on bone uptake of technetium 99m methylene diphosphonate (99mTc-MDP) 4 and 24 hours after perineural and intraarticular injection of mepivacaine hydrochloride and bupivacaine hydrochloride were evaluated in the carpal and metacarpophalangeal regions of 12 horses and ponies. Neither mepivacaine hydrochloride nor bupivacaine hydrochloride significantly altered the diagnostic quality of the NMBIs. The injection and subsequent action of local anesthetics do not appear to influence local bone uptake of 99mTc-MDP significantly.     

Neuroanesthesia: A Review of the Effects of Anesthetic Agents on Cerebral Blood Flow and Intracranial Pressure in the Dog

Successful anesthetic management of dogs with reduced intracranial compliance requires a knowledge of the effects of various anesthetic agents on cerebral blood flow and intracranial pressure. The major physiologic factors that influence cerebral blood flow and intracranial pressure (ICP) include the cerebrovascular autoregulatory mechanism, intracranial compliance, blood pressure, and the partial pressure of carbon dioxide. Intravenous and inhalation anesthetic agents alter cerebral blood flow and intracranial pressure in the dog. These alterations can have profound effects in dogs with reduced intracranial compliance, necessitating proper anesthetic management. Suggested guidelines for neuroleptanesthetic and inhalation anesthesia regimens in dogs with reduced intracranial compliance include thorough presurgical evaluation, minimal patient stress during induction, use of an anesthetic protocol that minimizes ICP effects, and hyperventilation to maintain a Pco₂ within a range of 25 to 35 mm Hg.     

Clinical Anesthesia and Analgesia in Fish

Fish have become a popular experimental model and companion animal, and are also farmed and caught for food. Thus, surgical and invasive procedures in this animal group are common, and this review will focus on the anesthesia and analgesia of fish. A variety of anesthetic agents are commonly applied to fish via immersion. Correct dosing can result in effective anesthesia for acute procedures as well as loss of consciousness for surgical interventions. Dose and anesthetic agent vary between species of fish and are further confounded by a variety of physiological parameters (e.g., body weight, physiological stress) as well as environmental conditions (e.g., water temperature). Combination anesthesia, where 2 anesthetic agents are used, has been effective for fish but is not routinely used because of a lack of experimental validation. Analgesia is a relatively underexplored issue in regards to fish medicine. However, recent studies have investigated opioid agents, nonsteroidal antiinflammatory drugs, and local anesthetics to determine their efficacy in minimizing pain and discomfort. The opioid morphine and the local anesthetic lidocaine do have significant effectiveness in reducing pain-related responses in rainbow trout (Oncorhynchus mykiss). Studies aimed at developing reliable analgesic protocols should explore a wide range of analgesic drug classes in several fish species.     

Anesthesia techniques in sheep and goats

A variety of techniques can be used to anesthetize and restrain sheep and goats safely and humanely both in the clinic and in the field. The use of inhalational, injectable, and local anesthetic agents is discussed. Nontraditional agents (opioids and alpha-2 adrenergic agonists) for epidural analgesia also are reviewed because of their promising clinical application.     

Anesthesia and Analgesia in Rabbits and Rodents

Rabbits and rodents are popular pets and are often presented to veterinarians for evaluation and medical treatment. Anesthesia in exotic pets is required for many diagnostic and surgical procedures and is associated with a higher perioperative risk in rabbits and rodents when compared with dogs and cats. Inhalation anesthetic agents are commonly used as the sole source of anesthesia in small rodents, whereas injectable agents in combination with inhalation anesthesia are often used for rabbits and larger rodents. Analgesia is an important component of exotic pet medicine. Although it may be difficult to recognize signs of pain in companion exotic mammals, adequate pain management should always be provided. Opioid and nonsteroidal antiinflammatory drugs are the analgesic medications of choice, but others should be considered (e.g., local anesthetic agents). This article provides an update of the current literature regarding anesthesia and analgesia in rabbits and rodents.     

Anesthetic depth: the undefinable.

With many modern anesthetic drugs and combinations, the traditional signs of anesthetic depth as a continuum of increasing depression are often incorrect. The concept of "adequate anesthetic depth" is difficult to define because it depends on the end points chosen to define "adequate." Because both central nervous system excitant and depressant drugs can induce a stage of anesthesia, it is vital that those using these agents be keenly aware of the specific type of anesthetic agent or agents being used, and their effects.     

Anesthesia in ophthalmic surgery

Ophthalmic surgical patients can be routinely anesthetized without complications if the surgeon has a thorough understanding of the effects of anesthetic agents on ocular physiology. The regulation of intraocular pressure is important for successful ophthalmic surgery and can be greatly affected by the anesthetic procedure. Agents utilized to intentionally decrease intraocular pressure are often employed for intraocular procedures. These agents have profound systemic effects that must be anticipated. Adverse drug interactions between sympathomimetic mydriatics and halogenated inhalation anesthetics also must be considered.     

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     

Investigations of toxicity episodes involving chemotherapeutic agents in Victorian poultry and pigeons

This series of case reports details observations on toxicity episodes in poultry due to a variety of chemotherapeutic agents. These problems arose owing to overdosage, variation in species susceptibility, potentiation of the toxic effects of one substance by the presence of another substance, and particular disease or other on-farm factors. Ignorance and accident were responsible for some of these situations. The episodes involved monensin, salinomycin, nicarbazin, sulphaquinoxaline, dinitolmide, dimetridazole, nitrofurans, streptomycin, and 3-nitro-4-hydroxyphenylarsonic acid.     

Pharmacokinetics of inhaled anesthetics in green iguanas (Iguana iguana)

OBJECTIVE: To test the hypothesis that differences in anesthetic uptake and elimination in iguanas would counter the pharmacokinetic effects of blood:gas solubility and thus serve to minimize kinetic differences among inhaled agents. ANIMALS: 6 green iguanas (Iguana iguana). PROCEDURES: Iguanas were anesthetized with isoflurane, sevoflurane, or desflurane in a Latin-square design. Intervals from initial administration of an anesthetic agent to specific induction events and from cessation of administration of an anesthetic agent to specific recovery events were recorded. End-expired gas concentrations were measured during anesthetic washout. RESULTS: Significant differences were not detected for any induction or recovery events for any inhalation agent in iguanas. Washout curves best fit a 2-compartment model, but slopes for both compartments did not differ significantly among the 3 anesthetics. CONCLUSIONS AND CLINICAL RELEVANCE: Differences in blood:gas solubility for isoflurane, sevoflurane, and desflurane did not significantly influence differences in pharmacokinetics for the inhalation agents in iguanas.     

Sedation and anesthesia of pet rabbits

Pet rabbits frequently become stressed when handled and may require sedation or chemical immobilization for procedures such as blood collection, IV catheter placement, radiography, deep ear cleaning, and dentistry. Common surgical procedures requiring general anesthesia include spay, castration, gastrotomy, cystotomy, and orthopedic procedures. Rabbits may be difficult to safely sedate or anesthetize. Individual rabbits may have varying sensitivity to the depressant effects of anesthetics. The apparent sensitivity of the rabbit's respiratory center to anesthetic drugs and the narrow range between anesthetic and toxic doses in this species add to the unpredictable character of rabbit anesthesia. Furthermore, mortality following anesthesia and surgery in sick rabbits is common. Strategically, safe anesthesia of rabbits must include the planning of procedures so that anesthetic time is minimized. Clinicians must be on guard for individual variation in response to drugs. Minimizing the use of cardiovascular depressant agents, use of agents with a high therapeutic index, and careful titration of doses to effect, along with thorough cardiorespiratory monitoring, will permit attainment of appropriate anesthetic depth with the widest margin of safety. This article presents several injectable and inhalant anesthetic protocols that may assist in effective management of many types of rabbit patient.     

Local and regional anesthesia.

Local anesthetics have the unique ability to produce complete blockade of sensory nerve fibers and prevent or pre-empt the development of secondary (central) sensitization to pain. For this reason, local and regional anesthetic techniques are often used with opioids, alpha 2-receptor agonists, dissociatives, and anti-inflammatory drugs as part of a multimodal strategy to manage pain. Lidocaine and bupivacaine are the local anesthetics used most commonly in dogs and cats. Lidocaine has a fast onset (10-15 min) and an intermediate duration of action (60-120 min), and is used for short diagnostic and surgical procedures. Bupivacaine has a slow onset (20-30 min) and a long duration of action (240-360 min), and is used to control pain both preoperatively and postoperatively. Local anesthetics are relatively safe if they are administered correctly. Administration of an excessive dose and accidental intravenous administration are probably the most common causes of systemic toxicity in small animals. Doses of local anesthetics, especially those for cats and small dogs, should always be calculated carefully. In many animals, the most simple and elegant way to control pain perioperatively is to perform a local or regional anesthetic block. Veterinarians should not hesitate to incorporate local and regional anesthetic techniques into their pain management strategies for dogs and cats.     

Changes in equine carpal joint synovial fluid in response to the injection of two local anesthetic agents

The effects of repeated arthrocentesis and injection of local anesthetic agents, lidocaine HCl or mepivacaine HCl on the equine middle carpal joint were investigated. Synovial fluid samples were evaluated before, and 12, 24 and 48 hours following, treatment. The greatest changes from pretreatment values occurred in synovial fluid cellularity. Repeated arthrocentesis caused a moderate increase in cell counts, while injection of local anesthetics caused a greater increase. Alterations in mucin clot quality, hyaluronic acid content, fluid viscosity, total protein and immunoglobulin G were generally of no significance. The most sensitive sampling time to detect changes caused by a given treatment was 24 hours following treatment while the 12 hour sampling period appeared to be the best at detecting differences between treatments. Repeated arthrocentesis has a definite effect on synovial fluid composition but the effects appear to decrease with repeated centesis. Lidocaine HCl and mepivacaine HCl are irritating to the synovial environment. Clear differences between responses to the drugs could not be identified.     

Newer neuromuscular blockers. Is the practitioner ready for muscle relaxants?

Current research on the development of new neuromuscular blocking agents is directed towards producing agents that have a rapid onset of action and predictable duration of action and recovery times, with minimal hemodynamic effects. For the veterinary practitioner, these newer agents should be considered when muscle relaxation is required for certain surgical procedures. Care must be taken to monitor paralyzed patients appropriately to ensure adequate ventilation and anesthetic depth. Vigilant monitoring should exist during the recovery period for the development of muscle weakness from residual blockade and the ability to reverse the effects of neuromuscular blockade. The use of neuromuscular blocking agents in veterinary patients should continue to increase as newer drugs and better monitoring techniques are developed.     

Traditional and non-traditional uses of anesthetic drugs--an update.

Many new or modified injectable anesthetic techniques are available for use in horses. This increased availability allows the clinician to select the technique most appropriate for the patient and clinical circumstance. The use of sedative and anesthetic drugs in managing a variety of anesthesia-related and unrelated aspects of patient care is also increasing. As we begin to use these techniques in the clinical management of our patients, it is important to remember that, while there are more options, no single anesthetic agent or combination of agents is devoid of undesirable effects. Knowledge of the pertinent advantages and disadvantages of the drugs when used individually and in combination and appropriate patient monitoring are essential to ensure a positive outcome.     

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.     

Tropical fish medicine. Anesthesia in fish

1. Before using anesthesia in fish, check water quality parameters for tropical fish aquariums in the locality. 2. Monitor any changes in water quality that result from anesthetic administration, especially pH and alkalinity. Have adequate buffering agents available to counter these changes. 3. Use one or two preferred agents, and become familiar with the effects they produce. 4. Where possible, withhold food from fish for 24 hours prior to administration of the anesthetic agent. 5. Try to anesthetize a few fish in a group first as a test batch. Wait 12 to 24 hours for signs of delayed mortality before proceeding to anesthetize the rest of the fish. 6. Always provide adequate aeration in holding vessels. 7. Where practical, use water that the fish has come from in the anesthetic tank. 8. Always have a container of the same water for the fish to recover in.     

Clinical Anesthesia in Reptiles

The clinical use of anesthetic agents in reptiles presents a number of unique challenges because of the diversity of the class Reptilia with respect to natural history, size, anatomy, and physiology. Reptiles are commonly maintained as companion animals, widely displayed in zoological institutions, and many species serve as subjects in laboratory facilities. Therefore, to become a skillful clinician, developing an understanding of anesthetic efficacy across reptile species is important. The objective of this review is to provide a current perspective on the practical application of anesthetic agents in commonly maintained pet reptile species.