Prolonged anesthetic recovery

Failure to awaken, delayed awakening, and blunted responsiveness following anesthesia constitute a continuum which must be recognized, diagnosed accurately, and responded to appropriately. One must determine whether it is a normal recovery for this animal or a pathological delay. A delayed recovery results in continued depression of many organ systems. The possible etiologic factors, some obvious, others quite obscure, must be considered quickly to provide the patient with the best possible care. Diminished responsiveness is usually the result of a complex interaction between multiple factors. A systematic approach to treatment first begins by ensuring cardiac output, oxygenation, ventilation, and supportive care in all patients. Then consider the potential causes for prolonged recovery and either rule them out or treat them. First consider the potential causes for central nervous system depression. Several commonly encountered medical conditions enhance sensitivity to or decrease the elimination of anesthetic and sedative agents. The astute clinician will be aware of the medical condition and its impact on anesthetic drug effect and elimination to avoid prolonged recoveries.     

Llama anesthetic programs

Llamas are anesthetized conveniently with guaifenesin thiamylal mixes, or, for short periods of time, with xylazine/ketamine. Small individuals must be accurately weighed. Estimating weight without experience is dangerous in this species. The greatest levels of safety and control, especially for critical patients, is afforded by inhalation anesthesia techniques using small animal equipment. All neonates and juveniles can be masked readily but in adults intravenous induction is most satisfactory. Intubation is aided by a long blade laryngoscope. Blood pressure monitoring is best accomplished with an arterial line in the ear artery. However, doppler equipment on the tail or distal leg usually works well.     

Injectable anesthetics and anesthetic adjuncts

The purpose of this article is to review the use of selected anesthetics and anesthetic adjuncts in horses. Emphasis is placed on the pharmacologic bases of their use.     

Local anesthetic techniques for diagnosis of lameness

Successful diagnostic local anesthesia is dependent upon a thorough knowledge of appendicular anatomy, application of correct technique, and accurate interpretation. Use of cadaver specimens to review anatomy and practice needle placement is strongly recommended. A marker solution, such as new methylene blue, can be injected into cadaver limbs, which can be subsequently dissected to verify accuracy. Detailed interpretation of local anesthetic blocks in the lame horse reaches beyond the scope of this article. Interpretive difficulties, however, can be responsible for the failure of a block to provide useful information to the examiner, even though the block may have been performed in a technically correct manner.     

Feline anesthetic deaths in veterinary practice

Anesthetic complications appear relatively rare, though recent work suggests they are more common in cats than dogs. Current estimates indicate that approximately 0.11% (1 in 895 anesthetics) of healthy cats die of an anesthetic-related death, which is more than twice as frequent as has been recently reported in dogs (0.05% or 1 in 1849). Most of these deaths occurred in the postoperative period. A number of risk factors have been associated with death, including patient health status, age, weight, and procedure type and urgency. Endotracheal intubation and fluid therapy have been reported to be associated with increased odds of anesthetic death in cats and may reflect higher risk techniques in cats compared with dogs. Monitoring patient pulse and the use of a pulse oximeter were also recently reported to be associated with reduced risk of anesthetic death. These data can help veterinarians care for their patient under anesthesia and address greater attention to patient assessment and management before anesthesia, as well as more careful fluid administration and patient monitoring during and after anesthesia, which could reduce perioperative complications in cats.     

Comparative cardiovascular and pulmonary effects of sedatives and anesthetic agents and anesthetic drug selection for the trauma patient

Objective: To integrate and compare the effects of tranquilizer/sedatives and anesthetic drugs on various parameters of cardiovascular function in normal dogs and in dogs stressed by hypovolemia, anemia, and endotoxemia, and to discuss the relative merits and appropriate precautions of anesthetic drugs with respect to specific patient physiologic complications. Data sources: Personal data and experiences in conjunction with veterinary and human clinical and research studies. Human and veterinary data synthesis: Drugs that produce calming, sedation, muscle relaxation, analgesia, and loss of consciousness have the potential to produce marked cardiorespiratory effects particularly in hemorrhaged, hypovolemic‐traumatized animals. Acute but key cardiovascular components that are affected by sedative and anesthetic drugs include heart rate and rhythm, venous return (preload), systemic vascular resistance (afterload), and myocardial contractile (inotropic) and relaxation (lusitropic) properties. In addition, all sedative and anesthetic drugs alter or depress normal baroreceptor reflex activity, thereby inhibiting or eliminating the animal's normal physiologic response to decreases in arterial blood pressure and predisposing to tissue hypoperfusion, decreased oxygen delivery, and oxygenation. Oxygen delivery needs to be adequate to meet the metabolic (oxygen) requirements of the patient. Decreases in oxygen delivery to tissues increases oxygen extraction, thereby maintaining tissue oxygenation (supply‐independent oxygen consumption phase) until compensatory processes reach their limit and any further decrease in oxygen delivery causes a decrease in oxygen consumption (supply‐dependent oxygen consumption phase). The critical oxygen delivery that defines the transition between these 2 phases is generally higher in the anesthetized state than in the awake state. The effect of anesthetics on critical oxygen delivery at comparable anesthetic dosages is pentobarbital=ketamine>alfentanil>etomidate=propofol>inhalational anesthetics. Anesthetics generally decrease oxygen consumption from the awake, baseline state; exceptions are ketamine and ether. Ketamine, however, increases oxygen delivery and oxygen extraction. Conclusions: The transition from the awake to the anesthetized state is a huge imposition on the physiology of animals and, therefore, should be accomplished with great care and proper vigilance. Rapid, ‘crash’ induction of anesthesia should be avoided in hypotension‐prone animals and slow, prolonged induction should be avoided in animals with respiratory disorders. It is not recommended to implement an unfamiliar protocol in critical patients, even if it might be pharmacologically preferable. Familiarity with an anesthetic drug is a very important reason for its selection.     

The effect of the anesthetic Tilest in swine

The clinical signs and effects on the cardio-respiratory system of Tilest were checked out in weaners. The intramuscular injection of 10 mg/kg BW Tilest caused a rapid immobilisation on an average duration of 33.7 +/- 15 minutes. The muscle relaxation was generally good. Analgesia could not obtained. Heart- and respiratory-rates increased during lateral recumbency. Blood pressure decreased initially. The influence on the arterial blood pH-value and the blood gases are insignificant. In connection with trials to get up the lactate value and the body temperature increased. The CK- and ASAT-activities increased 2 to 6 hours after injection with a wide individual variation. During recovery the pigs were excited and salivated.     

Disposition of anesthetic and anesthetic-related agents in ruminants

Many factors may influence the actions and fates of anesthetic and anesthetic-related agents in ruminant animals. These considerations need to be taken into account when these drugs are employed clinically. Some of the major principles governing the disposition of CNS-active drugs are reviewed, with special emphasis on the uniqueness of ruminant animals. General pharmacokinetic considerations are also covered as a preamble to a commentary on the kinetic characteristics of anesthetic and anesthetic-related agents that are commonly used in domesticated ruminants.     

Balanced anesthetic techniques in dogs and cats

The term "balanced anesthesia" refers to the use of a mixture of drugs, such that the advantages of small amounts of drugs are used without having to contend with the disadvantages of large doses of any one drug. In veterinary practice, inhalant drugs are usually administered alone to maintain anesthesia, and balanced anesthetic techniques are rare. Unfortunately, cardiopulmonary function is reduced in dose-dependent fashion by inhalant drugs and deepening the level of anesthesia in order to modify autonomic responses to noxious stimuli may increase morbidity and mortality. This article justifies the use of balanced anesthetic techniques in veterinary practice and describes the advantages gained by the use of nitrous oxide, continuous opioid infusion, epidural/spinal opioid administration, and transdermal opioid administration. These techniques, described in detail in the article, are easy to learn, relatively inexpensive, may decrease patient morbidity and mortality, and will provide the veterinarian with smoother operating conditions.