Anesthesia is a state of unconsciousness induced in an animal. The three components of anesthesia are analgesia (pain relief),
amnesia (loss of memory) and immobilization. The drugs used to achieve anesthesia usually have varying effects in each
of these areas. Some drugs may be used individually to achieve all three. Others have only analgesic or sedative properties and may be
used individually for these purposes or in combination with other drugs to achieve full anesthesia.
Curariform skeletal muscle relaxants or neuromuscular blockers (e.g. succinylcholine, decamethonium, curare, gallamine, pancuronium) are not anesthetics and have no analgesic effects. They may only be used in conjunction with general anesthetics. Normally, artificial respiration must be provided. Physiologic monitoring methods must also be used to assess anesthetic depth, as normal reflex methods will not be reliable.
It is important to realize that anesthesia is not a simple thing. It has profound effects on an animal's physiology because of the generalized central nervous system effects as well as specific effects on all other body systems. Thus, while anesthesia is necessary to prevent pain or distress in research animals, it must not be ventured into lightly. It is important to learn about the drugs you will be using and about the physiology of the animal you will be monitoring. Specific anesthetic drugs and their use are detailed below. All drug dosages are listed in UNM's formulary.
The Guide for the Care and Use of Laboratory Animals and the Institutional Animal Care and Use Committee Guidebook require that animals under anesthesia be carefully monitored to insure adequate depth of anesthesia, animal homeostasis, timely attention to problems, and support during anesthetic recovery. Monitoring includes, but is not limited to, checking anesthetic depth and physiological parameters (minimum: heart rate and respiratory rate) on a regular basis (minimum every 10 minutes).
Record keeping is an essential component of peri-operative care. For major surgical procedures on non-rodent mammals, an intra-operative anesthetic record must be kept and included with the surgeon’s report as part of the animal's records. In addition to the above requirements, the record should include all drugs administered to the animal, noting the dose, time, and route of administration. These records should be available to OACEC and any other personnel providing post-operative care. Although it is not required, OACEC strongly encourages the use of an intra-operative rodent anesthetic record during surgical procedures.
The required monitoring will vary according to the species and the complexity of the procedure, but should include:
The following are suggestions from the American College of Veterinary Anesthesiology for monitoring anesthetized animals:
Analgesia is the relief of pain. Pain is normally defined as an unpleasant sensory and emotional experience associated with potential or actual tissue damage. Pain is difficult to assess in animals because of the inability to communicate directly about what the animal is experiencing. Instead, indirect signs of pain are often used. Because of the difficulty of determining when an animal is in pain, animal welfare regulations require that analgesia be provided whenever a procedure is being performed or a condition is present that is likely to cause pain. In the absence of evidence to the contrary, it is assumed that something that is painful in a human will also be painful in an animal. It is best if analgesia can be provided to animals preemptively, or prior to the painful procedure, rather than waiting until after clinical signs of pain are observed. Analgesia is normally provided using one of several types of pharmaceutical preparations.
Inhalation anesthesia is superior to most injectable forms of anesthesia in safety and efficacy. It is easy to adjust the anesthetic depth. Because the anesthetics are eliminated from the blood by exhalation, with less reliance on drug metabolism to remove the drug from the body, there is less chance for drug-induced toxicity. Inhalation anesthetics are always administered to effect, because the dosage can vary greatly among individual animals and different animal species. The disadvantages to inhalant anesthesia are the complexity and cost of the equipment needed to administer the anesthesia, and potential hazards to personnel. All inhalant drugs are volatile liquids. They should not be stored in animal rooms because the vapors are either flammable or toxic to inhale over extended periods of time. In particular, ether must be stored in a proper hood or cabinet for flammable materials.
| Drug | MAC | Response | Toxicity | Comments |
| Ether | 3.2 | slow | liver | Pre-medication with an anticholinergic may be necessary to reduce excessive respiratory secretions. Induction and recovery can be rough. Flammable and can become explosive with prolonged storage. Ether must be used according to appropriate safety guidelines. |
| Chloroform | A hazardous agent (carcinogenic) and cannot be used at UNM. | |||
| Methoxyflurane | 0.2 | slow | nephrotoxicity - is potentiated by tetracyclines | It has good analgesic activity, but there is significant metabolism, ++ respiratory depression and + cardiac depression. This drug is not currently being manufactured. For a replacement, consider ether or diluted isoflurane. |
| Halothane | 0.9 | moderate | hepato- and nephrotoxicity if the animal is hypotensive | ++ cardiopulmonary depresssion, and a risk of malignant hyperthermia in some breeds/strains |
| Isoflurane | 1.5 | fast | none | ++ respiratory depression and + cardiovascular depression |
| Enflurane | 2.0 | fast | none | ++ cardiopulmonary depression and minimal respiratory depression |
| Nitrous Oxide | 180 | very fast | hepatotoxic | Cannot be used as a sole anesthetic agent. Do not exceed a 50% mix w/ oxygen and other inhalant agent to prevent hypoxia. Moderate analgesia is provided by nitrous. In general, use of nitrous oxide in animals is discouraged. |
| Carbon Dioxide (CO2 | 50-70 | very fast | cerebral anoxia | Can be used as an anesthetic for brief procedures and as a euthanasia agent. It has antinociceptive activity and causes unconsciousness prior to hypoxia. It is necessary to monitor carefully and work quickly, as animals die quickly (1-2 min) after losing consciousness, and likewise they wake up quickly when exposed to room air. Appropriate for quick procedures such as tail snipping, ear marking and orbital bleeding. Poses minimal hazard to personnel and can be used in laboratories or animal room. |
MAC: This is the % concentration of the drug needed to anesthetize 50% of animals. It does vary somewhat by species and by individual. 1.2X MAC is an approximate vaporizer setting for maintenance of anesthesia. Induction generally requires 2-3X MAC. MAC listed here is for rats (ether), mice (CO2), goat (enflurane) and dogs (all others).
Response: This refers to how rapidly concentrations in the blood change when the lung alveolar concentration is changed. Slow anesthetics have slow induction and recovery times.
Toxicity: Drugs that are metabolized by the body can cause toxicity, especially if a pre-existing organ dysfunction exists.
Some of the drugs listed here do not possess all three criteria for an anesthetic and must be used in combinations to achieve full anesthesia or may be administered individually for restraint, sedation or analgesia. Dosages for specific animals are linked from UNM's formulary. Often injectable drugs are used in combinations. These drugs tend to have synergistic effects. Mixing them can significantly reduce the dosage needed for any individual drug.
As with inhalation anesthesia, injectables are given to effect. Dosages listed are guidelines. Effects may vary among individuals. If a drug is scheduled by the Controlled Substances Act of 1970, licenses are required to purchase them, and written records must be kept of their use. University policy outlines these requirements. Anesthetic drugs that have exceeded their expiration date may not be used, even for terminal procedures
Injectable anesthetics are, in general, metabolized by the liver and excreted by the kidneys. Animals with liver or kidney disease should not be anesthetized with these agents. Inhalation anesthetics are safer for use in sick or debilitated animals, because there is minimal metabolism, the amount of anesthetic administered can be controlled and one can cease administration as the situation dictates. Injectable anesthetics offer the advantage of requiring less expensive equipment.
The generic and brand names of local anesthetics often have the suffix "caine". Common local anesthetics are procaine (Novacaine), bupivicaine and lidocaine (Xylocaine). Considerable experience and skill are necessary in the administration of local anesthetics to animals, and aseptic techniques must be employed. Some animals must be sedated before local anesthetics are injected.
Local anesthetics may be administered by several techniques. Anesthetic effects are seen within 15 minutes of administration and may last from 45 minutes to several hours, depending on the drug used.
An interesting use of local anesthetics is for amphibian and fish anesthesia. Tricaine and benzocaine can be added to water at a dose of from 25-100 mg/L, depending on the depth of anesthesia required. When the fish loses equilibrium (floats belly up) or an amphibian becomes inactive, it can be handled. For longer procedures, intermittent supplementation of anesthetic treated water to the gills or skin may be required. The animal is recovered in fresh water.
These sedatives include acepromazine, chlorpromazine, droperidol (Innovar-Vet) and azaperone (Stresnil). These drugs have excellent sedative properties, as well as muscle relaxation, antiemetic and antiarrhythmogenic effects. They have no analgesic activity, but when administered with other anesthetics can potentiate their effect. Acepromazine is the most commonly used. It is recommended as a sole sedative in dogs and as an anesthetic premedication to improve both induction and recovery (it is long acting) in all species. Droperidol is usually only available in combination with the narcotic, fentanyl (Innovar-vet) and has been associated with aggressive behavior in dogs.
Disadvantages of these sedatives are that they are alpha adrenergic blockers and cause peripheral vasodilation which can lead to hypothermia. They may have prolonged activity in sight hounds. Acepromazine and chlorpromazine decrease seizure threshold, and are contraindicated in animals with CNS lesions. Because these sedatives lack analgesic activity it is important to realize that any painful stimulation of the animal may cause it to emerge rapidly from the sedated state.
The benzodiazapines include diazepam (Valium), midazolam (Versed) and zolazepam (Telazol). These drugs are anti-anxiety and anticonvulsant drugs with good muscle relaxation. They have minimal cardiovascular and respiratory effects. Sedation is minimal in most species, except for swine and nonhuman primates. The primary use of these drugs in anesthesia is in combination with other drugs. Ketamine-diazepam, midazolam-narcotic, and tiletamine-zolazepam (Telazol) combinations can be very useful for induction of general anesthesia and for short procedures. These drugs are regulated by the Controlled Substances Act and require special record keeping.
The thiazine derivatives include xylazine and medetomidine. These two drugs are very similar. They are alpha-2 adrenergic agonists. They cause CNS depression resulting in sedation, emesis and mild analgesia. They also cause hypotension, second degree atrio-ventricular block and bradycardia. Occasionally, aggressive behavior changes have been seen in dogs. They are very useful in combination with other drugs, like ketamine for anesthesia in rodents and swine. They are best avoided in dogs, cats and nonhuman primates, primarily because their significant side-effects can be avoided by using other drugs. They can be used alone for minor procedures in ruminants. It is important to note that the dose for these drugs in ruminants is 1/10 that used in other species. The effects of the thiazine derivatives can be reversed with yohimbine or atapimazole. Use of these drugs with the reversal agent shortens anesthetic recovery and greatly expands the safety and utility of these drugs. Xylazine is a potent analgesic in frogs appropriate for relief of post-surgical pain.
The opiates, sometimes referred to as narcotics, are a large class of drugs that exert their effects on the opiate receptors in the central nervous system. Depending on the receptors a drug is active against, and the type of action it has on the receptor, the effects of narcotics can be primarily analgesic, as with buprenorphine (Buprenex), pentazocine (Talwin) and nalbuphine (Nubain), or a mixture of analgesia and euphoria with sedation as with butorphanol (Torbugesic), fentanyl (Innovar-Vet), morphine, meperidine (Demerol) or oxymorphone. Opiates have little effect on the myocardium. However, there can be significant respiratory depression, as well as other side-effects such as nausea and vomiting, delayed gastric emptying, hypotension, and bradycardia. Some species may develop hyperexcitability if given certain opiates. These side-effects are seen more with the mixed effect opiates than the pure analgesics. Naloxone is a opiate antagonist that can be used to reverse the effects of other narcotics. Other opiates, like buprenorphine, nalbuphine and nalorphine, have mixed agonist-antagonist effects and may interfere with the effects of concurrently administered narcotics. All opiates are controlled substances and their use requires special record keeping. These drugs can be given alone as a post-procedural analgesic or in combination with other agents to provide balanced anesthesia, restraint with analgesia for minor procedures, or can be used to decrease the dose of an anesthetic that is needed to provide a surgical plane of anesthesia.
Don't forget to follow the University Controlled Substances Policy
The barbiturates are an acid ring molecule with various ring substitutes that imbue the drug with different properties. Barbiturates are also considered narcotics.
The dissociative anesthetics include ketamine (Vetalar, Ketaset) and tiletamine (Telazol). These drugs are easy to use and have a wide margin of safety for most laboratory species. They are cyclohexamine compounds, chemically related to piperazine and phencyclidine (PCP). The dissociative anesthetics uncouple sensory, motor, integrative, memory and emotional activities in the brain, providing there is a functional cerebral cortex. The state induced by high doses of ketamine is best described as catalepsy and is not accompanied by central nervous system depression. There is depression of respiratory function, but cardiovascular function is maintained. Muscle relaxation is very poor.
Ketamine and Telazol are supplied in a solution of 100 mg/ml. Telazol is a 50-50 mixture of tiletamine and zolezepam, a benzodiazepine. These drugs can be injected intramuscularly, intraperitoneall or intravenously. IP and IM injections of the dissociative anesthetics can be painful, as the drug is very acidic. Induction time for IM administration is three to five minutes; peak effect lasts about 20 min in most laboratory species. IP induction times are longer than with IM administration and recovery may be prolonged. Because the volumes needed are very small, in small animals there is no real advantage to IP injection and IM injection should be used whenever possible. Induction time following IV administration is rapid with only about 10 min of anesthesia provided. Approximately 1/2 of the dose should be given when dosing IV. The drug can be supplemented as needed.
The swallowing reflex is often preserved in animals receiving dissociative anesthetics. This may help prevent aspiration pneumonia if the animal regurgitates. However, this is not 100% and fasting and intubation are still recommended when using these anesthetics. The animal's eyes will usually remain open and the corneas should be protected with a layer of ophthalmic petrolatum or other suitable ointment. These drugs have poor analgesic activity, especially for visceral pain, and should be used in conjunction with an analgesic for abdominal, intracranial, orthopedic, ophthalmic or thoracic surgery.
Don't forget to follow the University Controlled Substances Policy
Propofol - is a sedative/hypnotic that can be used for induction or maintenance of general anesthesia. Analgesic effect is poor and addition of an analgesic to the anesthetic regimen is necessary for surgery. The drug comes as an emulsion that must be mixed and used within several days. The advantages of propofol are that it has rapid induction and recovery times. It can be easily titrated and given to effect for prolonged periods without resulting in prolonged recovery. The disadvantages are that it must be given intravenously, it is expensive, it may result in apnea and it can cause bradycardia and hypotension.
Alpha Chloralose - or chloral hydrate is a mild hypnotic drug that does not produce complete anesthesia because of its poor analgesic properties. Chloral hydrate is shorter acting (1-2 h) than alpha chloralose (8-10 h). The primary advantage of these drugs is the minimal cardiopulmonary depression seen at the normal doses (high doses can cause severe respiratory depression). The disadvantage is that they can only be used alone for non-painful procedures. In addition, the drugs are very irritating to the GI tract, causing adynamic ileus if given IP and ulcers if given orally. Therefore IV use is the only route recommended. These drugs should not be used if any other alternative is available.
Tribromoethanol - is a short-acting anesthetic used in rodents for surgeries. The drug has rapid induction and recovery (15 min of surgical anesthesia and up to 90 min for complete recovery). The effect on animals is reported to be quite variable. Tribromoethanol was commonly used in the past but its use is now discouraged. Abdominal adhesions caused by IP administration have been reported to cause high post-procedural mortality, however, other studies have not demonstrated this. Tribromoethanol is not available commercially and must be prepared. Sterile preparation procedures are essential. The drug must be stored in the dark at 4°C to prevent degradation.
Urethane - is a long-acting (8-10h) anesthetic with minimal cardiopulmonary depression. The drug is used for long procedures in rodents. However, it is carcinogenic and is only allowed to be used with special justification and only for terminal (acute) procedures.
Analgesics are pain relievers most often given after a surgery. Narcotic analgesics have already been described above. Nonsteroidal anti-inflammatory drugs (NSAIDs) may also be used for their analgesic effect. The NSAIDs consist of drugs like aspirin, ketoprofen, acetaminophen, flunixin and ketorolac. There are a large number of these drugs available, however, relatively few are used in animals. NSAIDs are, in general, less potent analgesics than are the narcotics. However, in specific instances they can have similar activity.
The advantages of the NSAIDs are that they do not cause sedation nor are they addictive as are the narcotic analgesics. There are no special recordkeeping requirements. In addition, they are more effective against pain caused by inflammation, such as is seen with tissue repair, orthopedic surgery, infection and injury.
The NSAIDs have several side-effects related to their pronounced anti-prostaglandin (anti-cyclooxygenase and in some cases lipooxygenase) activity. This is peripheral with most drugs, but is primarily central with acetaminophen. These effects can alter immune function, platelet function and can cause gastrointestinal ulceration. In addition, the NSAIDs all have the potential to cause nephro- and hepatotoxicity. This is variable among species. Cats, in particular, are sensitive to the NSAIDs. Acetaminophen is contraindicated is cats due to risk of methemoglobinemia.
Acetaminophen - mild analgesic, antipyretic, no effect on platelet function/bleeding time
Aspirin - mild analgesic, antipyretic, antiinflammatory, affects platelet function/bleeding time
Carprofen is a nonsteroidal antiinflammatory drug with antiinflammatory and analgesic effects and lower risk for toxicity in animals than other NSAIDS.
Flunixin meglumine (Banamine) - potent analgesic, antiinflammatory, antipyretic. Has potential for GI ulceration, hepato- and nephrotoxicity.
Ketoprofen - moderate potency analgesic, antiinflammatory, antipyretic. Has potential for GI ulceration, hepato- and nephrotoxicity, affects platelet function/bleeding time.
Ketorolac (Toradol) - potent analgesic, antiinflammatory, antipyretic. Has potential for hepato- and nephrotoxicity, less potential for GI ulceration than other NSAIDs, affects platelet function/bleeding time.
In general, by mixing anesthetic and analgesic drugs, the dose required for each individual drug is reduced, sometimes quite dramatically. Start at the low end of the dose range listed; you can always give more if needed! Drugs not listed below can be mixed using the same concepts, mix a sedative or hypnotic with an analgesic. Do not mix drugs in the syringe until you have determined that they are compatible when mixed. If in doubt administer separately.
Ketamine/Diazepam: Mix drugs 1:1 by volume and administer 0.1 ml/kg IV for restraint, anesthetic induction or for non-painful procedures. This gives excellent muscle relaxation, has minimal respiratory or cardiovascular depression and the animals wake up smoothly and quickly (within 10-15 min). Visually, these drugs do not appear to mix completely.
Ketamine/Acepromazine: Mix 10 mg acepromazine (1 ml) with 1 g (10 ml) ketamine and give 0.1-0.3 ml/kg mixture IM or IV (up to 0.6 ml/kg in rodents and rabbits). Good for restraint, but not for painful procedures.
Acepromazine/Butorphanol: Mix drugs 1:1 by volume (using 10 mg/ml butorphanol) and administer at 0.01-0.02 ml/kg IV or IM. Creates a hypnotic state that is good for restraint and minor procedures that cause some pain.
Ketamine/Acepromazine/Butorphanol: Mix 10 mg acepromazine (1 ml), 10 mg butorphanol (1 ml) with 1 g (10 ml) ketamine and give 0.1-0.3 ml/kg of mixture IM or IV (up to 0.6-0.8 ml/kg in rodents and rabbits). Good for restraint and moderately painful procedures. More cardiac and respiratory depression will be seen with this mixture than with ketamine alone.
Ketamine/Xylazine: Mix 1:1 by volume (using 20 mg/ml xylazine) and give 0.1-0.3 ml/kg IM, IP or IV of mixture (up to 0.5-1.5 ml/kg in rodents and rabbits). Good for restraint and painful procedures. More cardiac and respiratory depression will be seen with this mixture than with ketamine alone. Reversal with yohimbine 0.1-0.15 mg/kg or atipimazole recommended to shorten recovery times. Addition of 0.01 ml butorphanol per ml of solution will enhance analgesia.
Ketamine/Midazolam/Butorphanol: A mixture of 40 mg/kg ketamine, 2 mg/kg of midazolam and 0.1 mg/kg butorphanol provides good muscle relaxation and surgical anesthesia in rodents. (Mix 0.4 ml each ketamine and midazolam with 0.01 ml of 10 mg/ml butorphanol and administer 0.8 ml/kg).
Telazol/Xylazine: Reconstitute powdered Telazol with 5 ml of 20 mg/ml xylazine instead of saline. Administer at 0.05-0.1 ml/kg IV or IM in large animals and up to 0.4 ml/kg IM in rodents. Do not use Telazol in rabbits or mice. More cardiac and respiratory depression will be seen with this mixture than with Telazol alone. Reversal with yohimbine 0.1-0.15 mg/kg (IM or IV) or atapimazole at 0.25 (IM) or 0.2 (IV) mg/kg is recommended to shorten recovery times.
Anesthetic induction using injectable anesthetics is fairly simple. It involves admininisistration of the drug and monitoring the depth of anesthesia. Supportive care may be needed. Maintenance of injectable anesthesia can be through repeated bolus doses of the drug or through a constant infusion. Infusion rates are calculated based on the clearance time of the drug. Bolus dosing is simpler. Typically, 1/2 of the original dose is given for repeat doses.
Injectable anesthetics can be administered by various routes depending upon the specific compound. The most frequently used routes of administration in laboratory animals are intraperitoneal, intramuscular and intravenous. Less frequently used routes, among others, are intrathoracic, oral and rectal. Techniques are described below. Contact OACC at 272-0418 for training materials on handling animals and administering injections.
Induction of inhalation anesthesia can be difficult. Anesthetic gases are irritating to eyes and nasal passages. Animals may resist as they begin to lose consciousness or they may stop breathing temporarily. For this reason induction using a mask or nose cone held over the animal's nose can only be performed on smaller or non-fractious animals. In smaller animals gas can be delivered into an induction chamber large enough to contain the entire animal. Induction via a nose cone or chamber requires delivery of the anesthetic gas at 2-3x MAC. Frequently an injectable anesthetic is used to induce anesthesia and the inhalation agent is used for maintenance.
Maintenance of inhalation anesthesia is normally accomplished by delivering approximately 1.2 MAC to an animal via a mask or nose cone, or directly into the lungs via an endotracheal tube. Intubation is recommended whenever possible, particularly when a procedure will be prolonged. Endotracheal access is essential to provide ventilation support.
The most complicated aspect of using inhalant anesthesia is the delivery system. A delivery system must provide the anesthetic gas to the animal at a known and constant rate. It must also ensure that animals receive adequate oxygen. There are several types of delivery systems typically used in laboratory animals. A more complete discussion of anesthetic delivery systems is available here.
The drop system is the most basic type of anesthetic delivery system. It involves application of the anesthetic gas to an absorbent material that is then placed in the bottom of an anesthetic chamber or nose cone device. The gas mixes with the air in the chamber until it reaches a concentration equal to the vapor pressure of the gas. For this reason drop systems have been traditionally used with low vapor pressure anesthetics such as methoxyflurane or with slow acting drugs like ether. Some success has been achieved by mixing high vapor pressure drugs such as halothane or isoflurane at a concentration of 15% by volume with mineral oil and using this mixture in the drop system.
Problems with a drop system and how to deal with them:
Left: a non-re-breathing nose cone that can be used with a large animal anesthetic machine; Middle: a typical drop system closed anesthetic chamber; Right: a gas scavenging system that can be used with a drop system.
The best method of delivering an inhalant anesthetic is with an anesthetic machine. These machines precisely mix the gas with air or oxygen and can be easily adjusted. Machines can vary in construction and design. Anesthetic machines typically require more training to learn to operate.
A variety of things must be done to prepare for anesthesia. Once animals are under anesthesia they must be monitored closely while they are anesthetized to ensure that they do not become too deep and die, and to ensure that they do not become too light and experience pain from the surgical procedure. Normal physiologic functions such as body temperature, respiration and cardiovascular function must also be monitored and supported while the animal is anesthetized. For all major surgical procedures on non-rodent mammals, an intra-operative anesthesia record must be kept and included with the surgeon's reports as part of the animal's record. The anesthetist must be prepared to handle emergencies if they occur.
Most anesthetics cause direct depression of the respiratory center in the brain and reduce ventilation. This is complicated by other factors that may interfere with respiration. When an animal is in lateral recumbency the lung that is down is being compressed by the rest of the body. Likewise, animals in dorsal recumbency may experience compression of the diaphragm by abdominal viscera. The airway may be compromised by regurgitated food or pharyngeal and tracheal secretions that normally would be removed by reflex swallowing or coughing. These reflexes are lost during anesthesia. There are several ways to monitor and support the ventilation of an anesthetized animal.
Many anesthetics have direct effects on the heart or vasculature, decreasing cardiac output and blood pressure. This is further complicated by increased fluid requirements during anesthesia and surgery that may result in hypovolemia. Fluid requirements are increased because: breathing dry, cold oxygen (if inhalant anesthesia is used) increases respiratory fluid loss; the animal has not received its normal fluid intake since it was fasted; fluid may be lost through hemorrhage or exposure of moist viscera to room air; many anesthetics are metabolized in the kidney (creating a slight diuresis minimizes renal toxicity).
To minimize the effects of surgery and anesthesia on hydration:
If the animal has pale mucous membranes, the capillary refill time is greater than 2 seconds, or if the other cardiovascular parameters are out of normal range (determine normal for the species you are using!) you may have a cardiovascular emergency. Increasing the rate of intravenous fluid administration will improve cardiac output temporarily. However the depth of anesthesia will need to be reduced and if there is a primary cardiac problem it will require specific treatment. Consult with an RAR veterinarian for more information on anesthetic emergencies.
Animals frequently become hypothermic during anesthesia because of inhalation of cold gases, exposure of body cavities to the room air, and loss of normal thermoregulatory mechanisms and behaviors. Hypothermia depresses all physiologic functions, including respiration and cardiac function, slows the metabolism of anesthetics and results in prolonged recoveries. All of these can contribute to anesthetic death. Hyperthermia is less common, but may occur because of excessive application of heat, hot surgery lights or malignant hyperthermia in genetically pre-disposed animals. To thermoregulate your patient:
Water blanket and heater
The depth of anesthesia must be monitored carefully. Animals that are too light will experience pain and may move during the procedure. Animals that are too deep run the risk of experiencing cardiopulmonary arrest. If an animal is too light the anesthesia should be supplemented, if too deep, animals on gas anesthesia can be turned down. Animals given injectable anesthetics can not be lightened directly. Instead respiratory and cardiovascular support must be administered until the anesthetic is metabolized and the animal begins to lighten on its own.
To monitor the depth of anesthesia, perform the following:
| Anesthetic Emergency Drugs | Dose (mg/kg) | Indications |
| Doxopram (Dopram) | 1-5 IV (10x in farm animals) | Respiratory stimulant, for complete respiratory arrest only, use with CPR |
| Furosemide (Lasix) | 2- IV, IM | For pulmonary edema. Administer as needed |
| Naloxone (Narcan) | 0.04 IV | For reversal of narcotic sedation or respiratory depression |
| Yohimbine | 0.1-0.15 IV | Reversal of xylazine or detomidine sedation |
| Atropine | 0.02-0.04 IV | For bradycardia |
| Epinephrine (1:1000) | 0.1 ml/kg IV, IT, IC, IM | For cardiac arrest only. Administer IV, intratracheal or intracardiac and perform cardiac massage |
| Lidocaine | 2, IV (0.5 mg/kg in cats) | For diagnosed ventricular tachycardia only. Administer to effect and monitor |
Monotoring and support must continue until the animal is completely recovered from anesthesia. Complete recovery means the animal is able to hold itself in a normal upright position, has returned to normal body temperature and all physiological indices are within normal limits. Anesthetic recovery can be rapid for gas agents and short anesthetic episodes. Recovery time can be prolonged if animals were under for a long time or if injectable agents were used.
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The information contained in this site is intended as a reference for University of New Mexico investigators, and animal husbandry and veterinary staff. Drug information and dosages are derived from a variety of sources and do not necessarily guarantee safety or efficacy. Information obtained through this site should not be relied upon as professional veterinary advice. Any medications administered or procedures performed on animals should only be performed by or under order of a qualified, licensed veterinarian.
