Anesthetic consideration in dogs with traumatic myocarditis

The trauma patient is commonly encountered in veterinary practice. Traumatic myocarditis has often been overlooked due to its delayed onset and preoccupation with other traumatic problems. The traumatic heart is very sensitive and in itself can cause death. Often a trauma patient requires surgery and a proper anesthetic protocol must be used which does not increase the incidence of cardiac arrhythmias. A review of anesthetic management including preanesthetic medications, induction drugs and techniques and maintenance with inhalation anesthesia reveals the need for careful selection of medications. Isoflurane was shown to be beneficial in reducing the incidence of undesirable responses of these patients.     

AAHA anesthesia guidelines for dogs and cats

Safe and effective anesthesia of dogs and cats rely on preanesthetic patient assessment and preparation. Patients should be premedicated with drugs that provide sedation and analgesia prior to anesthetic induction with drugs that allow endotracheal intubation. Maintenance is typically with a volatile anesthetic such as isoflurane or sevoflurane delivered via an endotracheal tube. In addition, local anesthetic nerve blocks; epidural administration of opioids; and constant rate infusions of lidocaine, ketamine, and opioids are useful to enhance analgesia. Cardiovascular, respiratory, and central nervous system functions are continuously monitored so that anesthetic depth can be modified as needed. Emergency drugs and equipment, as well as an action plan for their use, should be available throughout the perianesthetic period. Additionally, intravenous access and crystalloid or colloids are administered to maintain circulating blood volume. Someone trained in the detection of recovery abnormalities should monitor patients throughout recovery. Postoperatively attention is given to body temperature, level of sedation, and appropriate analgesia.     

Cost comparison of anesthetic regimens in the dog and cat

Comparative costs of anesthetic regimens for the dog and cat were calculated. Various combinations of currently popular sedatives, tranquilizers, and anti-muscarinics (preanesthetic drugs), and anesthetic induction and maintenance drugs were studied. The preanesthetic drug affected overall anesthetic cost through its own cost, its effect on the amount of anesthetic drug necessary for intubation, and its effect on the amount of anesthetic necessary to maintain anesthesia. The combination of acetylpromazine-thiamylal-halothane was the least expensive regimen for both the dog and cat, whereas drug combinations that included isoflurane as the maintenance drug were the most expensive. In the cat, induction of anesthesia by use of N2O, O2, and halothane in a plexiglas chamber was more expensive than by the use of thiamylal.     

Anesthesia and pain control

Successful anesthetic management of the critically ill patient requires familiarity with the pharmacologic properties of a variety of anesthetic drugs. An understanding of the altered physiology present in the critically ill allows an anesthetic regimen to be selected that prevents an anesthetic-induced decompensation. Pain should never go untreated because of a fear of causing excessive physiologic depression. There are numerous options available to control pain. A technique suitable in one instance may be unsuitable in another; for example, an animal that has a significant degree of respiratory compromise may not tolerate the additional respiratory insult associated with narcotic use. A local anesthetic technique may be preferred in this situation. Often a local technique is all that is necessary to control postoperative pain. Furthermore, if pain is controlled for the first 4 to 6 h post-insult, often no further analgesic drugs need to be administered.     

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.     

VCARS – veterinary computerized anesthetic record system

VCARS, the Veterinary Computerized Anesthetic Record System, has been developed to capture pre-, peri- and post-anesthetic data using Tablet PCs, 802.11b wireless networks, and a web-based database. Patient demographics, anticipated procedures and anesthetist, service information and hematologic and chemistry values are imported from the Veterinary Medical Teaching Hospital patient information system. Using a wireless Tablet PC, pre-anesthetic examination findings are recorded and an anesthetic plan including anesthetic drugs and anesthetic and monitoring equipment is developed. During induction and maintenance of anesthesia, physiologic variables, drug, fluid, anesthetic gas and oxygen administration, laboratory values, patient location, and important events can be charted with the simplicity of a paper anesthetic record. This information can be manipulated for display in a variety of ways depending on the specific needs of the case. Tools for calculating optimal fluid rates and drug dosages are incorporated into the design. The anesthetic records from multiple cases can be viewed simultaneously using a centrally-located monitor. Detailed audit trails ensure data integrity. A high-end search engine will allow rapid and complete retrieval of patient and anesthetic information. Macromedia flash is used to allow temporary disconnection from the wireless network without losing the ability to view, add, or edit data. The initial stages of software development are nearing completion, a wireless network is in place and hardware is being purchased. A pilot study will be conducted using manual entry of physiologic data prior to integration of automatically captured patient physiological variables. It is anticipated that this system will drastically improve the accuracy of data collection and retrieval and will provide important information about anesthetic management allowing improvement in overall patient care.     

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.     

Anesthesia of the sighthound

The sighthounds are an ancient group of dog breeds that have been selectively bred for high-speed pursuit of prey by sight. Probably as a consequence of this selection process, these dogs have a number of idiosyncrasies that can potentially adversely affect their anesthetic management. These include (1) nervous demeanor which can lead to stress-induced clinical complications, such as hyperthermia; (2) lean body conformation with high surface-area-to-volume ratio, which predisposes these dogs to hypothermia during anesthesia; (3) hematological differences such as a higher packed cell volume and lower serum protein compared with other dog breeds which may complicate interpretation of preanesthetic blood work; (4) Impaired biotransformation of drugs by the liver resulting in prolonged recovery from certain intravenous anesthetics, especially thiopental; and increased risks of drug interactions. Safe anesthetic management of sighthounds should include sedative premedication and appropriate use of analgesic drugs to minimize perioperative stress. Thiopental, or any other thiobarbiturate, should not be used in these dogs. Propofol, ketamine/diazepam combination, and methohexital are recommended alternative intravenous anesthetics. Avoid coadministration of agents that inhibit drug biotransformation, such as chloramphenicol. Inhalation anesthesia using isoflurane is the preferred anesthetic maintenance technique. Core body temperature should be monitored closely and techniques to minimize hypothermia should be employed both during anesthesia and into the recovery period.     

Reptile anesthesia.

Successful reptile anesthesia requires patience, planning, and understanding of normal anatomy and physiology in health and disease. Reptiles make good anesthetic patients because of their physiologic resilience. New drugs that are not only safe and efficacious, but also result in relatively short recovery times, have greatly enhanced the design of anesthetic regimens. Further studies are required to quantitatively evaluate the physiologic effects of drugs used and validate available monitoring modalities for use in a wide variety of reptiles.     

Anesthetic management of thoracotomy

Successful anesthesia for thoracic surgery requires an understanding of the clinical disease and the physiologic changes accompanying the disease, as well as anesthetic agents available for use. The authors discuss selection of appropriate anesthetic drugs, perioperative management considerations, pharmacologic support, intraoperative monitoring and postoperative pain management.     

Evaluation of aqueous tear production in dogs following general anesthesia

Pre- and postanesthetic Schirmer tear test (STT) values were measured in 46 dogs. All subjects had normal preanesthetic STT values (18.3 +/- 2.8 mm per min in the left eye [OS] and 18.3 +/- 3.0 mm per min in the right eye [OD]). Significant differences were found between pre- and postanesthetic STT values. Significant decreases in tear production were evident for up to 24 hours following the anesthetic event. Subject age did not significantly influence the results. Duration of anesthesia significantly affected the rate of return to preanesthetic STT values, with anesthetic events greater than two hours in duration having a prolonged effect as compared to anesthetic events less than two hours in duration. Anticholinergic administration prior to or during anesthesia further lowered postanesthetic STT values.     

Anesthetic and analgesic techniques used for cats undergoing ovariohysterectomies in general practice in the United States

ObjectiveTo better document anesthetic and analgesic protocols used by veterinarians in general practice within the United States (US) when performing elective ovariohysterectomy in cats.Study designCross-sectional survey.PopulationVeterinary practitioners in the US who are members of the Veterinary Information Network Inc. (VIN).MethodsAn online anonymous survey was distributed to VIN members. The survey included questions pertaining to preanesthetic evaluation, premedication, induction, monitoring and maintenance protocols, and postoperative analgesia and sedation protocols when performing ovariohysterectomy in cats.ResultsA total of 1324 veterinarians completed the survey. Respondents (number; %) reported performing preanesthetic laboratory tests [packed cell volume (256; 19.3%), complete blood cell count (893; 67.4%) and biochemistry panels (1101; 83.2%)] and preanesthetic examinations (1186; 89.6%) on the morning of surgery. The most frequently administered drugs for premedication were dexmedetomidine (353; 26.7%) and buprenorphine (424; 32.0%). The most frequently administered induction agent was propofol (451; 61.3%), and isoflurane (668; 50.4%) was the most common agent for maintenance of anesthesia. The majority of respondents reported placing intravenous catheters (885; 66.8%), administering crystalloid fluids (689; 52.0%) and providing heat support (1142; 86.3%). Participants reported using perioperative and postoperative analgesia including opioids (791; 59.7%), non-steroidal anti-inflammatory drugs (NSAIDs; 697; 52.6%) and NSAIDs dispensed for home use (665; 50.2%). Cats were commonly released home on the day of surgery (1150; 86.9%), and most participants reported contacting owners for follow-up within 1–2 days (989; 74.7%).Conclusions and clinical relevanceAnesthetic protocols and management techniques for routine feline ovariohysterectomy differ widely among US veterinarians who are VIN members, and results from this study may be of use to evaluate anesthetic practices from this population of veterinarians.     

Anesthesia for the acute abdomen patient

Patients with acute abdomen often have marked physiologic and pathologic changes, making anesthesia both challenging and potentially hazardous for the patient. A thorough understanding of the pathophysiologic mechanisms of cardiovascular function under anesthesia and selection of appropriate anesthetic protocols are critical to a successful anesthetic outcome. The goal is to produce anesthesia while minimizing depression of the cardiovascular system. Monitoring and management of acid-base and cardiovascular function serve to ensure appropriate oxygen delivery to the tissues during anesthesia. Postoperative management can significantly influence patient outcome following anesthesic recovery, and must therefore be considered in the anesthetic plan. Finally, pain management in all patients is an important aspect of case management, and should not be overlooked. This article serves to educate the clinician in the above-described areas in regard to the acute abdomen patient.     

Parenteral Anticholinergics in Dogs With Normal and Elevated Intraocular Pressure

Dogs given parenteral anticholinergic drugs have been thought to be at risk for development or exacerbation of elevated intraocular pressure (IOP). In a randomized, blinded, placebo-controlled study, we evaluated the effect of intramuscular glycopyrrolate (0.01 mg/kg) on pupil diameter and IOP in unanesthetized normal dogs. Treatment with glycopyrrolate did not change pupil diameter or IOP from baseline, nor were there differences between glycopyrrolate and saline-treated (control) dogs. In addition, the authors retrospectively reviewed the medical records of 2,828 dogs undergoing general anesthesia between April 1987 and September 1990 to determine if there was an association between parenteral anticholinergic medication and postanesthetic elevation in IOP. The authors also determined the frequency of bradycardia requiring anticholinergic therapy during anesthesia in dogs with glaucoma. Of the 2,828 cases reviewed, the records of 46 dogs coded for glaucoma were examined in detail. The 46 dogs underwent 62 episodes of anesthesia, with 23 episodes including exposure to an anticholinergic drug. An increase in IOP from preanesthetic to postanesthetic measurement occurred in three dogs. One of these dogs received anticholinergic medication for bradycardia during anesthesia. The postanesthetic elevation in IOP in this dog was probably not drug related. Preanesthetic anticholinergic administration did not affect the incidence of anticholinergic administration for bradycardia during the anesthetic episode. Anticholinergic therapy during anesthesia was more frequent when the preanesthetic medication included an opiate drug. These studies do not indicate an association between parenteral anticholinergic administration and elevations in IOP.     

Cesarean section. Anesthetic management and surgical technique

Cesarean section can be an elective procedure but more often it is an emergency procedure that is made necessary because of dystocia. A successful outcome for both the maternal and fetal patients is primarily dependent on a thorough understanding of the physiologic alterations during normal and abnormal pregnancy and parturition. A complete history and physical examination are necessary for assessment of the dam and planning of fluid therapy and anesthetic technique. Timely coordination of presurgical preparation, anesthesia, and the surgical procedure is crucial. Because little documentation exists to prove that any one anesthetic protocol is best, this article will stress the basic principles of obstetrical anesthesia and patient management.     

Geriatric pharmacology.

When faced with the geriatric dog or cat, the practitioner should consider the following: 1. Avoid using any drugs at all unless there are definite therapeutic indications. If the patient has some degree of renal insufficiency, try to select drugs that are hepatically metabolized and excreted in bile rather than eliminated by the kidneys (eg, doxycycline, tolfenamic acid). If hepatic insufficiency is present, select drugs that do not undergo metabolism before renal excretion (eg, penicillins, cephalosporins). 2. If therapeutic drug monitoring is available, tailor the drug dosage regimen to that specific patient (eg, phenobarbital, digoxin, amino-glycosides). 3. If therapeutic drug monitoring is unavailable, determine if there are clinically proven adjusted dosage regimens for specific drugs. The package insert on human pharmaceutics often gives guidelines for adjusting dosages in geriatric patients. 4. If the drug has not been sufficiently studied to have dosage adjustment recommendations, determine if there is sufficient information about its kinetics to estimate the proper drug dose in a geriatric patient. Some general guidelines for commonly used drugs in geriatric veterinary patients are provided in Table 1. In general, if the Vd changes in your patient, change the dose. If the elimination half-life changes, change the dosing interval. 5. Carefully monitor treated patients for signs of efficacy and toxicity.     

Anesthesia for geriatric patients.

Choosing the best anesthetic agents for each geriatric animal does not in itself ensure a successful outcome. Aggressive, careful, vigilant monitoring during the anesthetic and recovery periods is required to detect and correct alterations in homeostasis that may develop during the perianesthetic period. With appropriate preoperative screening, informed choice and judicious dosing of anesthetics, and careful monitoring and supportive care, the risk of anesthesia in geriatric animals can be greatly reduced.     

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.     

General anesthesia for horses with specific problems

We have discussed anesthetic techniques, special considerations, and expected complications involved in anesthetizing horses for abdominal, orthopedic, and head and neck surgery, and myelography and have described expected physiologic dysfunction that may require changes in anesthetic technique or supportive measures. The objective is high-quality patient care and reduction in anesthesia-related morbidity and death.