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Anesthesia Guide for small animals in Veterinary medicine
Pharmacology (FAR 381)
University of Pretoria
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SMALL ANIMAL ANESTHESIA GUIDE
Dr. Bob Stein
1) GENERAL PROTOCOLS
a) Admission b) Pre-anesthetic Routine i) General ii) Physical Examination iii) Medications & Fluids iv) Screening Tests v) Specific Pre-anesthetic Protocols c) Anesthetic Induction i) General ii) Specific Induction Protocols d) Anesthetic Maintenance i) General ii) Specific Maintenance Protocols e) Recovery 2) INFORMATION BY CATEGORY OR DISEASE a) Addison’s Disease b) Blood Pressure Management c) Brachycephalic Breeds d) Bronchoscopy e) C-Sections f) Cardiac Disease g) Constant Rate Infusions h) CPR i) Diabetes mellitus j) Elective Surgeries k) Epidural Injections l) General Debilitation m) Intracranial Disease n) Liver Disease o) Local Anesthetics p) Monitoring q) Opioids r) Orthopedic Surgery
s) Pain Management t) Rabbit Anesthesia u) Renal Disease v) Sight Hounds w) Thoracotomy 3) INFORMATION BY SPECIFIC DRUG a) Alphabetically 4) DOSING CHARTS a) Alphabetically by generic name
ADMISSION
- It is recommended that a veterinarian or licensed veterinary technician supervise the patient admissions. a) A properly trained nonprofessional can be quite capable of handling this process but we recommend that a licensed professional be available to assist this individual should questions or concerns arise.
- The patient’s medical record should be reviewed for completeness.
- A pre-surgical review of the patient’s history should be performed prior to admission. An admission checklist or questionnaire can be a valuable tool to insure a thorough assessment of the patient. An example questionnaire is included at the end of this reference. a) Food should be withheld for 12 hours prior to admission in normal cats and dogs over age 4 months. i) For cats and dogs less than 4 months of age, hypoglycemia is a significant concern. (1) Withholding food for only 4 hours prior to anesthesia helps to minimize this concern. (2) Offering food within 2 or 3 hours of recovery is also recommended. b) Any medications or supplements given in the prior 7 days should be recorded and reviewed with a doctor. c) Any new health concerns should be recorded and reviewed with a doctor. d) Any previous anesthetic “problems” should be reviewed with owner, recorded and reviewed with a doctor. e) Pets with histories of excessive stress when kenneled, chewing at stitches or bandages, difficulty restricting activity, or difficulty maintaining pet in clean, dry area during recovery should be noted. f) Water should not be withheld prior to admission.
- Smaller growths should be marked for easy identification. a) The owner should show the admitting staff member where the growths are, and the staff member should mark them with the owner present. i) Hair can be clipped at the site or a marker used to identify the site.
- An accurate Estimate and Surgical Release Form should be reviewed with, and signed by, the owner. a) Please be vigilant for owners who may not understand the form or, in fact, may not be able to read the form. i) A resistance to sign the form may be one indication of this.
PRE-ANESTHETIC ROUTINE
1) GENERAL
a) A current weight must be obtained and recorded on the patient’s anesthetic record. b) An Emergency Drug Reference Sheet should be immediately accessible for all patients at all times. i) Some computer systems have an emergency drug component built into the software. If so, a customized reference should be produced for, and kept with, each patient. Alternatively, an emergency drug reference should be immediately available in the event it should be needed. The AAHA library has such a reference sheet if you do not have a current one. c) An Anesthetic Record should be prepared for each patient. A copy of an example sheet is included at the end of this reference.
2) PHYSICAL EXAMINATION
a) A pre-anesthetic physical examination should be performed and the information entered into the patient record i) This examination should be performed by a licensed technician or a staff veterinarian. Each practice should develop their own guidelines as to when the physical examination is to be performed by the doctor and when it can be performed by the technician. Generally speaking, this interval can be longer for younger pets exhibiting no health concerns and it should be shorter when dealing with geriatric and unhealthy patients. (1) Some States may require this PE be performed by a DVM and may stipulate the timing of this PE. Be familiar with your State requirements. We cannot detail State to State variation in this reference. b) A final categorization of the patient should be made based upon the following guidelines:
i) Excellent - animal with no organic disease or in whom the disease is localized and is
causing no systemic disturbance. (1) example - healthy 3 year old neuter.
ii) Good - animal with mild systemic disturbance which may or may not be associated with the
planned procedure. (1) example - mildly anemic patient, obese patient, geriatric patient.
iii)Fair - animal with moderate systemic disturbance which may or may not be associated with
the planned procedure and which usually interferes with normal activity but is not incapacitating. (1) example - mitral valve insufficiency, moderate anemia.
iv)Poor - animal with extreme systemic disturbances which are incapacitating and are a
constant threat to life and seriously interferes with the animal’s normal function. (1) examples - uncompensated mitral valve insufficiency, severe pneumothorax.
(a) A 5 ml/lb (10 ml/kg) bolus can be useful when Bp drops and needs to be addressed more quickly. This may be repeated once. ii) IV fluids should be administered through an infusion pump whenever available. (1) This is especially important for small patients and cardiac patients for whom fluid overload is a much more likely complication. (2) If an infusion pump is not available, a micro-dripset should be used when administering fluids to patients under 15 pounds or patients requiring more control over fluid rates. iii) Fluid bag and drip set protocol. (1) Date all fluid bags and drip sets when first put into service. (2) Switch IV extension sets between patients. (3) Always cover the drip set end with a new sterile needle. (4) Discard fluid bags and drip sets over 1 week old. (a) Immediately discard any fluid bags that contain cloudy fluid or those suspected to be contaminated. (b) Immediately discard any drip sets suspected to be contaminated. (5) A high visibility fluorescent orange label must be used to identify any medications added to a fluid bag.
4) PRE-ANESTHETIC TESTING
a) Pre-anesthetic testing is a consideration to allow detection of underlying disorders that may influence the management of the patient or influence the prognosis associated with any given disorder. The decision regarding when to perform preanesthetic tests and which tests to include is a decision that needs to be addressed individually by each practice. b) There is considerable debate as to the extent and timing of such testing. c) Blood samples should be drawn prior to premeds if it is not excessively stressful to the patient as premeds may influence the results of certain tests i) Example – Acepromazine can decrease patient PCV up to 30% d) If blood collection is not possible without premeds, or is too stressful, then administer premeds, wait 15 to 20 minutes, then collect samples (1) Make sure the laboratory results are labeled so as to indicate that they were collected post- premeds if acepromazine has been used.
SPECIFIC PRE-ANESTHETIC PROTOCOLS
1) Acepromazine (only)
a) General information i) A phenothiazine tranquilizer (1) Acepromazine has no direct analgesic properties ii) Acepromazine can be used alone, as a premedicant. However, it is more effective to use Acepromazine in combination with an opioid narcotic agent. (1) The addition of an opioid reduces the acepromazine dose, and therefore, also reduces the likelihood of hypotension or sustained, excessive sedation that can occur. b) Patient selection i) Recommended use (1) Use of acepromazine as a sole agent is not recommended
(a) 2 to 3 mg are frequently recommended maximum total dosages regardless of weight (2) Butorphanol 0 to 0 mg/kg (0 to 0 mg/lb) (a) 0 mg/lb is usually adequate for most patients (b) Higher dosages do not result in better analgesia and excitation can occur. iii) Cat (1) Acepromazine0 to 0 mg/kg (0 to 0 mg/lb) (2) Butorphanol 0 to 0 mg/kg (0 to 0 mg/lb) (a) 0 mg/lb is usually adequate for most patients iv) Route of administration (1) IV/IM/SC use (a) IV has a more rapid and profound effect (i) Use the lower end of the dose range for both agents when administering this combination IV (b) IM has a moderately rapid, moderately profound effect but is painful (c) SC is less painful though the effect is slower and less profound d) General Cost Category i) Moderate - acepromazine is inexpensive but butorphanol is of moderate expensive especially for larger dogs
3) Acepromazine & an Opioid (Hydromorphone, Oxymorphone, Morphine,
Fentanyl)
a) General information i) Combination of phenothiazine tranquilizer and a reversible opioid agonist ii) Compared to acepromazine & butorphanol, this combination provides somewhat greater sedation in dogs and a stronger analgesic influence of longer duration in both dogs and cats iii) Less sedative synergism exists between acepromazine and hydromorphone in dogs when compared to the sedative synergism that exists between acepromazine and morphine in dogs (see below) iv) Medetomidine may produce more consistent sedation and relaxation than acepromazine when combined with the mu opioids in cats b) Patient selection i) Recommended use (1) Generally for healthy animals in the Good to Excellent category (2) Larger, calmer, older patients may require much lower acepromazine doses (3) Smaller, stressed, younger patients may require higher acepromazine doses ii) Cautionary Information (1) All mu agonists can cause bradycardia and respiratory depression (2) Morphine and hydromorphone commonly cause vomition regardless of route (a) Oxymorphone is less likely to cause vomition regardless of route (3) Histamine release: morphine can cause a histamine release which may cause a transient hypotensive effect (a) This is more likely with IV use and is unlikely when morphine is given IM or SC (4) Mu agonists may cause a mild, transient hyperthermia in cats (5) Avoid acepromazine if: (a) History of seizures (i) Some anesthesiologists feel that seizures are of minimal concern at usual clinical acepromazine doses (b) Geriatric (i) It is generally recommended that acepromazine be avoided in geriatric patients. When used in older patients, substantially lower doses may be adequate (c) Debilitated (d) Liver dysfunction (e) Anemic (f) Hypotensive (g) Hypovolemic (h) Known patient sensitivity exists c) Dosage i) Dog
4) Buprenorphine (only)
a) General information i) Mixed agonist/antagonist opioid of moderately long duration depending on dose (1) Agonistic effect at mu opioid receptor (2) Extremely high receptor affinity gives buprenorphine an antagonistic effect when mixed with pure mu opioids like hydromorphone, oxymorphone, morphine, or fentanyl which may be a strategic advantage ii) Dose has significant influence on duration of effect but no influence on degree of analgesia iii) Undesirable effects are rare iv) Minimal sedation, limited reversibility, and moderate cost make this less attractive as a single agent premed v) There is a significantly delayed time of onset (1) 30 minutes when given IV (2) 45 to 60 minutes when given IM (3) SC use is not recommended b) Patient selection i) Recommended use (1) Aging or debilitated patients where an analgesic effect is desired but sedation is not (2) Routine surgeries and procedures that are not associated with severe pain ii) Cautionary information (1) Extremely high affinity makes this opioid difficult to reverse c) Dosage i) Dogs 0 to 0 mg/kg (0 – 0 mg/lb) ii) Cats 0 to 0 mg/kg (0 – 0 mg/lb) iii) The dose influences the duration of effect but not the degree of analgesia (1) 0 mg/kg 4 to 6 hour duration (2) 0 mg/kg 6 to 8 hour duration (3) 0 to 0 mg/kg 10 to 12 hour duration iv) Routes of administration (1) IV or IM (2) SC use is not recommended d) General Cost Category i) Moderate to high depending on dose
5) Butorphanol (only)
a) General Description i) Mixed agonist/antagonist opioid with short duration and very mild sedative effects (1) Agonistic effect at Kappa and sigma opioid receptors (2) Antagonistic effect at the mu receptor which may be a strategic advantage (3) Reversibility is a subject of debate b) Patient selection i) Recommended use (1) In patients where: (a) Acepromazine use is a concern (b) Some analgesia and mild sedation is desired (c) A mu agonist is not necessary or is of a concern ii) Cautionary information (1) The duration of analgesic effect is very short (a) 45 to 60 minutes in the dog (b) 60 to 90 minutes in the cat (2) Will antagonize mu agonists if given concurrently c) Dosage i) Dog 0 to 0 mg/kg (0 to 0 mg/lb) ii) Cat 0 to 0 mg/kg (0 to 0 mg/lb) iii) Increased dosages are NOT associated with an increase in analgesia (1) Doses exceeding 0 mg/kg (0 mg/lb) can cause undesirable excitatory effects iv) Routes of administration (1) IV, IM, or SC d) General Cost Category i) Moderate
7) Medetomidine
a) General Description i) Alpha-2 agonist ii) Medetomidine can be used alone, however it is often combined with an opioid for a synergistic effect. (1) Addition of an opioid allows a reduction of the Medetomidine dose and reduces the likelihood of the more dramatic negative cardiovascular effects that alpha-2 agonists can cause iii) Substantially reduces induction agent need iv) Potent sedative and analgesic v) Effects can be completely reversed using atipamazole (1) The more complete the sedation reversal, the more complete the reversal of the analgesic effect (2) Partially reversing the agent may allow you to retain some of the analgesic benefit of the drug b) Patient selection i) Recommended use (1) Normal, young, healthy patients in the excellent category ii) Cautionary information (1) Use of medetomidine in older or more debilitated patients requires significant reductions in dosage and more vigilant attention the patient’s cardiovascular status (2) Stressed patients may not respond as well (a) Isolate in quiet, dark room if possible to facilitate effect (b) Additional medetomidine may be given after 20 minutes if further sedation is required iii) Can cause bradycardia (1) Anticholinergic use is controversial c) Dosage i) Dogs 0 to 0 mg/kg (0 to 0 mg/lb) (a) Doses above 0 mg/kg (0 mg/lb) should be used with careful attention to patient selection ii) Cats 0 to 0 mg/kg (0 to 0 mg/lb) (a) Doses above 0 mg/kg (0 mg/lb) should be used with careful attention to patient selection iii) Routes of administration (1) IV/IM use (a) IV has a much more rapid and profound effect (i) Use lower doses - approximately 50% of the dose you would consider giving IM (b) The epaxial muscles are the preferred site of injection for more predictable drug absorption
(i) Needles of appropriate length to penetrate through subcutaneous fat and into muscle must be selected. Larger dogs will commonly require a 1½” needle d) General Cost Category i) High – especially if reversal agent, atipamazole, is used
(b) The epaxial muscles are the preferred site of injection for more predictable drug absorption (i) Needles of appropriate length to penetrate through subcutaneous fat and into muscle must be selected. Larger dogs will commonly require a 1½” needle d) General Cost Category i) High – especially if reversal agent, atipamazole, is used
9) Medetomidine & an Opioid (Hydromorphone, Oxymorphone, Morphine, or
Fentanyl)
a) General Description i) An alpha-2 agonist and a mu opioid agonist (1) The synergistc effect of these two agents allows for a substantial reduction in the medetomidine dosage thereby reducing the likelihood of the more dramatic negative cardiovascular effects that alpha-2 agonists can cause ii) Substantially reduces induction agent need iii) Potent sedative and analgesic effects iv) Effects can be completely reversed using atipamazole and naloxone (1) The more complete the sedation reversal, the more complete the reversal of the analgesic effects (2) Partially reversing the agents may allow you to retain some of the analgesic benefit of the drugs b) Patient selection i) Recommended use: (1) Normal, young, healthy patients in the excellent category ii) Cautionary information (1) Use of medetomidine in older or more debilitated patients requires significant reductions in dosage and more vigilant attention the patient’s cardiovascular status (2) Stressed patients may not respond as well (a) Isolate in quiet, dark room if possible to facilitate effect (b) Additional medetomidine may be given after 20 minutes if further sedation is required iii) Can cause bradycardia (1) Bradycardia may be more profound than with medetomidine alone (2) While the use of anticholinergic is still controversial, the addition of the opioid often justifies the use of anticholinergics. c) Dosage i) Dogs (1) Medetomidine 0 to 0 mg/kg (0 to 0 mg/lb) (a) Doses above 0 mg/kg (0 mg/lb) should be used with careful attention to patient selection (2) One of the following opioids: (a) Hydromorphone 0 to 0 mg/kg (0 to 0 mg/lb) (b) Oxymorphone 0 to 0 mg/kg (0 to 0 mg/lb) (c) Morphine 0 to 1 mg/kg (0 to 0 mg/lb) (d) Fentanyl 0 to 0 mg/kg (0 to 0 mg/lb) ii) Cats (a) Same as the dogs
Anesthesia Guide for small animals in Veterinary medicine
Course: Pharmacology (FAR 381)
University: University of Pretoria
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