Veterinary Anesthesia Lab 2 PDF

Program: Veterinary Medicine Program Course: Anesthesiology & Diagnostic Imaging Code: STG421 Date: 14/ 10 /2024 Dr. Mahmoud Fathy Ahmed Dr. Mohammed Kamal Dr. Mahmoud Abdallah Lecturer of Surgery, Anesthesiology Teaching Assistant Teaching Assistant and Radiology Tranq...

Program: Veterinary Medicine Program Course: Anesthesiology & Diagnostic Imaging Code: STG421 Date: 14/ 10 /2024 Dr. Mahmoud Fathy Ahmed Dr. Mohammed Kamal Dr. Mahmoud Abdallah Lecturer of Surgery, Anesthesiology Teaching Assistant Teaching Assistant and Radiology Tranquilizers and sedatives  Definitions ❑ Tranquilization (ataraxia) (neurolepsis): State of tranquility and calmness in which the animal is relaxed, reluctant to move, awake, unconcerned with its surroundings, and potentially indifferent to minor pain; sufficient stimulation will arouse the animal. ❑ Sedation: A mild degree of CNS depression in which patient is awake but calm (accompanied by drowsiness) sufficient stimulation will arouse the animal  Indications 1- Used as preanesthetic medication in order to: Overcome the fear of the animal. Promote skeletal muscle relaxation. Decrease the amount of the anesthetic drugs so decrease their toxicity. Decrease irritability of CNS during administration of anesthesia. So they produce smooth anesthetic induction and recovery  Indications 2- Beneficial pharmacological actions: Anti pyretic. Anti histaminic. Hypotensive. Anti spasmodic. Anti convulsant. Antiemetic  Indications 3- Used during transportation of the animal. 4- Used for examination of the animal. 5- Used before radiological examination. 6- Used for relaxation of penis for examination and treatment. 7- Used for minor operation as opening an abscess and standing procedures. 8- Used before administration local and regional analgesia  General symptoms 1- Animal becomes unaware of its surroundings. 2- Relaxation and hanging the head. 3- Dropping of eyelids and ear. 4- Sluggish reflexes (ear, corneal, pedal, anal and skin). 5- Hypothermia. Before After Sedation with Xylazine Before After Eyelid dropping  General symptoms 6- Struggling gait and knuckling at carpi. 7- Relaxation of penis in cattle and horse. 8- Salivation, muzzle dryness and partial or complete paralysis of the tongue in cattle. In small animal: 1- Lie in dark place and protrude third eyelids. 2- Decrease in the temperature Types of tranquilizers and Sedatives I- Phenothiazine derivatives II- Butyrophenones III- Benzodiazepines IV-Alpha2 adrenoceptor agonists  Phenothiazine derivatives & Butyrophenones Phenothiazines: acepromazine, promazine, chlorpromazine Butyrophenones: droperidol, azaperone. Phenothiazines and butyrophenones differ in chemical structure but they share many similar pharmacological properties.  Phenothiazine derivatives & Butyrophenones These agents are classified as major tranquilizers (neuroleptics). Major clinical indications: 1- Provide anxiolysis. 2- Reduce the concurrently administered anesthetic dose 3- Provide additional sedation synergistic with other prescribed sedatives or analgesics.  Phenothiazine derivatives & Butyrophenones Cardiovascular effects: 1- Vasodilation and hypotension. Therefore, its use is contraindicated in shock, hypotensive, or anemic patients. 2- bradycardia (reported in Boxer dogs) resulting in death 3- Phenothiazines possess antiarrhythmic effects (reducing the incidence of ventricular arrhythmias).  Phenothiazine derivatives & Butyrophenones CNS effects: 1- Do not produce analgesia, but improve the analgesic effects of other drugs 2- Produce mental calming, decrease motor activity, and increase threshold for responding to external stimuli. 3- Antiemetic effects (Useful as antiemetics. Acepromazine and droperidol administered 15 minutes before opioids lower the incidence of vomiting). 4- Thermoregulation is depressed  Phenothiazine derivatives & Butyrophenones CNS effects: 4- Lowering seizure threshold, so avoid using it in a patient that is likely to induce seizure (e.g. myelogram). However, they may inhibit chemically induced seizures (e.g., ketamine)  Phenothiazine derivatives & Butyrophenones Respiratory effects: 1- Reduce respiratory rate; may decrease tidal volume when administered in large doses 2- When combined with opioids and hypnotics, the phenothiazines have additive effect and respiratory depression may occur.  Phenothiazine derivatives & Butyrophenones Liver: Primary organ of metabolism is the liver; should be avoided in animals with moderate to severe liver disease. Also in geriatric and pediatric animals No specific reversal give IV fluids shock dose, and α- adrenergic agonist (phenylephrine).  Phenothiazine derivatives & Butyrophenones 1-Acepromazine: It has a powerful spasmolytic effect on smooth muscle including that of the gut. It causes paralysis of the retractor penis muscle (paraphimosis) and protrusion of the penis from prepuce in bulls and stallions. It has antiemetic, antihistaminic and hypothermic actions. Stallion with paraphimosis  Sheep& Horse Cattle Dog goat IV 0.03 0.02 - 0.05 0.05 (mg/kg) IM 0.05- 0.05 0.1 0.1 (mg/kg) 0.1 Increase risk of Side regurgitation due to effect relaxation of the cardiac sphincter  Benzodiazepines They provide minor tranquilization at clinically used dose. They are centrally acting muscle relaxants and possess antiseizure effects Diazepam (Valium®), midazolam (Versed®), and zolazepam (in Telazol®) are most commonly used in veterinary practice.  Benzodiazepines 1- Inducing a mild calming effect, but clinically it is rarely given as the sole sedative. 2- They are favored in animals that are in increased risk of cardiopulmonary failure because they possess very minimal effect. 3- Stimulate appetite and produce pica  Benzodiazepines For synergistic effect it is most commonly combined with opioid analgesics (in dogs) or dissociative (in cats), which provides greater degree of sedation as well as analgesia.  Benzodiazepines In some dogs paradoxical excitement or aggression can be observed when given alone, believed to be through disinhibition of suppressed behavior. The excitement is seen most notably in hyperactive and young animals, but less frequently in depressed and geriatric animals.  Benzodiazepines 1-Diazepam, : Dose: 0.2 – 0.4 mg/kg dog and cat 0.02-0.1 mg/kg horse IV should be injected slowly to prevent pain and venous thrombosis  Benzodiazepines 2-Midazolam: It is 2-5 times more potent than diazepam, but the unit cost is still more expensive. The typical clinical dose is 0.2 – 0.4 mg/kg in dogs and cats. 0.01-0.04 mg/kg in horse  Benzodiazepines 3-Zolazepam: This is only used in combination with tiletamine in Telazol This mixture is essentially identical to Ketamine-diazepam (Ket-Val) mixture in many pharmacophysiologic aspects. Their use is popular for exotic species.  Benzodiazepines They have specific antagonists such as flumazenil 0.01- 0.10 mg/KG IV (expensive)  Alpha2 adrenoceptor agonists ❑ Examples: 1. Xylazine 2. Medetomidine 3. Detomidine 4. Dexmedetomidine 5. Romifidine  Alpha2 adrenoceptor agonists Produce mild analgesia. Good muscle relaxation is usually present (centrally acting muscle relaxant). These drugs provide moderate to heavy sedation. Animals still respond to stimuli (aggressive dogs should still be muzzled when handled, horses may still kick in response to sudden touch).  Alpha2 adrenoceptor agonists ❑ Alpha-2 antagonists: Atipamezole, yohimbine and tolazoline are available to reverse the alpha-2 agonistic side effects such as excessive CNS or CVS complications. Atipamizole (20- 100 mcg/kg), Yohimbine (0.05-0.3 mg/kg) Tolazoline (0.5-1.5 mg/kg).  Alpha2 adrenoceptor agonists Cardiovascular effects 1- Initial transient hypertension followed by prolonged hypotension (biphasic changes), 2- Bradycardia and second degree atrioventricular block, and decreased cardiac output. Respiratory effects Decreased respiratory rate, with a variable effect on tidal volume, but at clinically useful dose it is of minor concern.  Alpha2 adrenoceptor agonists Other clinical effects: 1- Increasing blood glucose level. 2- Decreasing intestinal motility. 3- Increasing urine production 4-Increasing uterine contractions which may lead to premature delivery or abortion (noted only in cattle). 5- Inducing vomiting. 6- Ataxia  Alpha2 adrenoceptor agonists Clinical use: 1- Decrease anxiety, provide chemical restraint with relatively dependable sedation (addition of opioids recommended for more predictable outcome), 2- Potentiate effects of other drugs and provide analgesia and muscle relaxation.  Alpha2 adrenoceptor agonists Duration of action : It is dose dependent, and typically lasts 10 to 30 minutes of sedation and restraint for xylazine and 1 to 3 hours for medetomidine. The drugs are metabolized by the liver, and undergo urinary and biliary excretion.  Alpha2 adrenoceptor agonists 1-Xylazine: It’s a potent narcotic, sedative and analgesic which cause C.N.S. depression, as well as, muscle relaxation based on inhibition of intra neural transmission of impulses in the C.N.S. Its effect develops within 10-15 min after I/M injection & 3-5 min after I/V injection  Alpha2 adrenoceptor agonists 1-Xylazine: Xylazine causes laryngeal relaxation and cough suppression. Vomiting is frequently seen in the cat and the dog due to central alpha 2 activation. The thermoregulatory center is depressed and hypothermia is observed. Hyperglycemia and glucosuria are due to depressed insulin release in the pancreas. Inhibition of ADH release results in diuresis.  Alpha2 adrenoceptor agonists 1-Xylazine: Xylazine has marked ecbolic effects and should not be used in the last third of pregnancy. (nor at conception: for example in ovum transplants)  Alpha2 adrenoceptor agonists 1-Xylazine: ❑ Doses: In cattle: cattle are more sensitive to xylazine. 0.05-0.1 mg/kg IM is sufficient to produce deep sedation as they lie down with in 10-20 min and lasts for 30min while recovery complete in 2-3 hours.  Alpha2 adrenoceptor agonists 1-Xylazine: ❑ Doses: In equines: a dose of 0.5 -1.1 mg / kg I/M or IV has analgesic properties particularly in colic. Sedation is maximal after about 5 minutes and lasts 30–60 minutes In sheep: 0.1-0.2 mg/kg IM produce sedation for many hours. In goat: 0.02 mg/kg In dog and cat: 1-3 mg/ kg I/M.  Alpha2 adrenoceptor agonists 1-Xylazine: ❑ Side effects: 1- It abolishes the swallowing reflex so that regurgitation can result in pulmonary aspiration. 2- GIT motility is decreased & bloat may develop while diarrhea may be observed 12-24 hours after sedation. 3- Hyperglycemia persists for 10 hours after xylazine administration.  Alpha2 adrenoceptor agonists 1-Xylazine: ❑ Side effects: 4- Increase urine production within 30 minutes after administration and continues for 2 hours. 5- Use of xylazine in animals with urethral obstruction may result in rupture of urinary bladder or urethra.  Alpha2 adrenoceptor agonists 1-Xylazine: ❑ Contraindications: 1-Animal suffering from liver & respiratory dysfunction. 2-Last month of gestation due to: increase premature birth, retained placenta, and increase blood sugar. 3-In early stage of pregnancy: because the wall of the pregnant uterus contracts more or less strongly. This gives rise to certain difficulties in the diagnosis of early gestation.  Alpha2 adrenoceptor agonists 2-Medetomidine: It is the most potent and specific of this group It has displaced the use of xylazine in the dog and the cat. It causes marked ataxia in the horse even at low doses. Dose is approximately 2 µg/kg  Alpha2 adrenoceptor agonists 3-Detomidine: It is a potent alpha 2 agonist, primarily used in the horse. In horses maximum sedation effect is achieved at 0.01– 0.02 mg/kg IV (equipotent of 1 mg/kg of xylazine) or 0.04 mg/kg IM. It has less ecbolic effect than xylazine, so is preferred over xylazine in late pregnancy Dose requirement is similar for horses and cattle. OPIOIDS  Opioids Morphine, fentanyl, oxymorphone, meperidine, butorphanol, pentazocine, buprenorphine, nalbuphine The drugs bind to opioid receptors in the CNS which usually have inhibitory effects on neurons. Primary clinical effects are analgesia and sedation. In horses: Opioids are used in conjunction with tranquilizer or sedative because they can produce excitement when administrated alone.  Opioids Respiratory depression (apnea). It is important to monitor any animal that have received an opioid. They make minimal depression for cardiac contractility (can be used with cardiac diseased animals). Thermoregulation is impaired by Opioids delaying return of a normal temperature following anesthesia. Animals that have received opioids may be hypersensitive to external stimuli, particularly noise  Opioids Ventilatory support may be required to counteract the respiratory depression. Naloxone, and diprenorphine are pure antagonists to opioids.  Opioids ❑ Clinical Use: 1. Provide analgesia. 2. Decrease anxiety. 3. Provide sedation/chemical restraint (variable, depends on species, agent and dose). 4. Decrease doses of other agents for synergism.  Opioids ❑ Clinical Effect: The cardiopulmonary effects include bradyarrhythmias - usually easy to correct with anticholinergics, minimal effect on blood pressure and cardiac output. The respiratory depression accompanies with opioid agonist administration and is dose dependent.  Opioids ❑ Clinical Effect: Vomiting. Defecation (initial effect), urinary retention/constipation with continued use. Excitatory effects at high doses in some species (cat, horse). Best used with neuroleptics to avoid the excitement.  Opioids ❑ Clinical Effect: Duration of action depends on the type of agents used as well as dose and route of administration, widely ranging from 30 minutes (fentanyl) to several hours (buprenorphine). These drugs are metabolized by the liver (extensive first pass metabolism, hence not very effective orally administered) and excreted in bile and urine.  Opioids ❑ Some examples of commonly used combinations are: morphine + diazepam morphine + medetomidine butorphanol + medetomidine or diazepam morphine or hydromorphone + acepromazine hydromorphone + diazepam or medetomidine oxymorphone + acepromazine oxymorphone + diazepam oxymorphone + medetomidine fentanyl + droperidol