Final Term Exam Coverage Lesson 10-21-2021 PDF

CAGAYAN STATE UNIVERSITY COLLEGE OF VETERINARY MEDICINE CARIG CAMPUS PRINCIPLES OF VETERINARY SURGERY LECTURE MANUAL ROEL T. CALAGUI, DVM, MPH, PHD ASSOCIATE PROFESSOR...

CAGAYAN STATE UNIVERSITY COLLEGE OF VETERINARY MEDICINE CARIG CAMPUS PRINCIPLES OF VETERINARY SURGERY LECTURE MANUAL ROEL T. CALAGUI, DVM, MPH, PHD ASSOCIATE PROFESSOR Revised 2020 1|Principles of Veterinary Surgery, Cagayan State University R O E L T. C A L A G U I , DV M , M P H , P H D  LESSON 10 ANAESTHESIA AND ITS PRINICPLES Actions: Lowers sensitivity Diminishes motor responses to incoming stimulus Aspects: 1. Narcosis/unconsciousness 2. Sensory block 3. Motor block 4. Decrease of reflex activity Management of anaesthesia depends on: 1. Physical status of the animal 2. Breed and temperament of the animal 3. Type and duration of surgery 4. Skill of anaesthetist 5. Equipment and assistance available Pre-anaesthetic Examination/Management: 1. Give special attention to history of: 1. Nasal discharge 1. Coughing- may be due to inflammation of trachea and larynx 2. Choking 3. Dyspnea following exercise 4. Reluctance to exercise 5. Prolonged sitting 6. Abnormal intake/loss of food and water 7. Presence of thrills (patent ductus arteriosus) on chestwall 2. Inspect: Haircoat, body condition Dietary status whether obese/dehydrated/malnourished Hormonal abnormality 3. Auscultate lung sounds Absence of sounds – increased bronchial tone Moist rales – pleural friction, indicates lung disease. 4. Correct: Fluid balance before surgery to increase blood volume. Presence of dyspnea (indicates changes in the arterial ph and blood gas) by removing responsible fluid or gas causing it before administration of anaesthesia. Cyanosis of mucous membranes can be corrected by administering oxygen. 5. Inflammation of larynx and trachea increases risk of apneic response to irritating gas and cause laryngeal edema in intubation. Anaesthesia be delayed until swelling subsides or avoid giving gas anesthesia, instead give IV anesthetics. 6. Give pre-anesthetic medication to prevent copious secretions causing post operative atelectasis or pulmonary infection. 2|Principles of Veterinary Surgery, Cagayan State University R O E L T. C A L A G U I , DV M , M P H , P H D  7. Presence of hepatic/renal enlargement may indicate disease. Thus, proper selection of drugs and dose is considered. Laboratory Tests: PCV – for anaemia Urinalysis – specific gravity -BUN (indicates dogs beyond 5 years and those with renal disease) Radiography – for suspects of respiratory or cardiac diseases. General Considerations: All anaesthetics and narcotics except diethyl ether cause: Depression of alveolar ventilation during anesthesia. Hypercapnia (CO2 retention). Decrease arterial pH. Decrease cardiovascular stability and hypoventilation Decrease cardiac output by 25 – 40%. The body compensates these by stimulating the sympatho-adrenals to counteract the Cardio- vascular effect leading to: 1. Increase heart rate 2. Increase myocardial contraction 3. Increase peripheral resistance, predisposing further a drop in blood flow in certain vascular beds resulting to tissue anoxia. Management: 1. Increase oxygen supply 2. Check Hb normal level to prevent hypovolemia Pre-anaesthetic Medication General Purposes: 1. Allay apprehension and aid in restraint 2. Ease induction of animal and recovery 3. Pharmacologic adjunct to general anesthesia 4. Counteract side effects and reflex responses produced by anaesthetics. General Consideration: 1. Old and very young animals should receive minimum dose. 2. Vicious and excitable animals should receive massive dose Examples: 1. Anticholinergics- agents that block the passage of impulses through the parasympathetic nerves Functions: a. Inhibits salivation and mucus production in air tubes b. Prevents vomiting by blocking vagus nerve c. Lessens bradycardia 3|Principles of Veterinary Surgery, Cagayan State University R O E L T. C A L A G U I , DV M , M P H , P H D  Examples: 1. Atropine sulfate 2. Scopolamine hydrobromide 3. Glycopyrolate 4. Propantheline 5. Esopropamide 2. Narcotics- agents that depress the central nervous system with complete unconsciousness, amnesia and analgesia Functions: a. Good analgesic b. Decrease amount of general anesthesia c. Decrease coughing and emesis d. Prevents excitement during recovery e. Adjunct for barbiturates Examples: 1. Meperidine 2. Morphine sulphate 3. Tranquilizers- also known as calming drug; compounds that reduce anxiety and tension without affecting mental clarity Functions: a. Aid in restraint b. Anti-histaminic c. Anti-pyretic d. Anti-emesis e. Abolish reflexes f. Do not induce sleep g. No excitement upon recovery Examples: 1. Xylazine HCl 2. Acepromazine maleate 3. Droperidol 4. Azaperone 2 types: 1. Major tranquilizer- neuroleptics or antipsychotic agents such as acepromazine maleate 2. Minor tranquilizers or anxiety agents such as diazepam or valium 4. Antibiotics- agents that destroy bacteria Functions: a. For prophylaxis- given before onset of anesthesia 4|Principles of Veterinary Surgery, Cagayan State University R O E L T. C A L A G U I , DV M , M P H , P H D  Examples: a. Ampicillin, amoxicillin, gentamycin, cefazolin, etc. Dosage of commonly used Pre-anaesthetics: 1. Atropine sulfate- ( given 10-15 minutes prior to administration of Tranquilizer or sedative drug) Concentration: 0.5% solution or 1mg/ml Recommended dose: = 0.44 – 0.45 mg/kg IM, SC, IV for both dogs and cats Note: Not recommended to horse because it predisposes the animal to ileus Not recommended to ruminants because it will not lessen salivation but instead makes the saliva viscous -1% solution is instilled on the cornea for ophthalmic surgeries. 2. Meperidine “Demerol” Recommended dose: 6-10 mg/kg in dog 2-1 mg/kg in cat 3. Morphine SO4 Recommended dose: 1-2 mg/kg IM, SC in dog 0.1 mg/kg IM, SC in cat 4. Xylazine Hydrochloride “Rompun” Concentration: 2% solution or 20 mg/ml Recommended dose: 0.5 mg/lb IV or 1 mg/kg IM, SC, IV in dog and cat 0.11- 0.22 mg/kg IM in Ruminants ;lower dose for small ruminants; 1.1-2.2 mg/kg IM in horse 5. Acetylpromazine Maleate ( given 1-5 minutes prior to administration of general anesthetics; normally not given to docile patients) Concentration: 1% solution or 10 mg/ml Recommended dose: 0.25 – 0.5 mg/lb IV, IM, SC or 0.1-0.5 mg/kg IV, IM, SC in dog 0.1 – 0.2 mg/kg IM, SC in cat 0.04- 0.08 mg/kg IV, IM in Horse 6. Promazine Hydrochloride Recommended dose: 0.44- 1.1 mg/kg IV, IM in horse 7. Diazepam Recommended dose: 5.5 to 8.5 mg/kg IM in pig Drug categories of pre-anaesthetic medications: 1. Anticholinergics a. Atropine sulfate b. Glycopyrolate c. Scopolamine 5|Principles of Veterinary Surgery, Cagayan State University R O E L T. C A L A G U I , DV M , M P H , P H D 2. Tranquilizers, neuroleptics and sedatives a. Phenothiazines- (e.g. acepromazine, promazine) b. Butyrophenones- (e.g. droperidol, azaperone) c. Benzodiazepines- (e.g. diazepam, midazolam, zolazepam) d. α2 antagonist- (e.g. xylazine, detomidine, medetomidine) 3. Opioids a. Opioid agonists- (e.g. morphine, meperidine, oxymorphone, fentanyl) b. Opioid antagonist- (e.g. naloxone, nalorphine, butorphanol, buprenorphine) c. Opioid agonist-antagonist- (e.g. pentazocaine, butorphanol, buprenorphine) 4. Neuroleptanalgesics a. Fentanyl and droperidol (Innovar Vet) – for dogs, cats and pigs b. Acepromazine with morphine, meperidine or oxymorphine- dogs c. Xylazine and morphine- horses d. Xylazine and butorphanol- horses Spectrum of Activity of Pre-anesthetic Medications Drug Analgesia Muscle relaxation Sedation Phenothiazine Negative Not defined Negative Butyrophenones Negative Not defined Positive Benzodiazepines Negative Positive Negative Xylazine Positive Positive Positive Detomidine Positive Positive Positive Medetomidine Positive Positive Positive Opioids Positive ( except Negative Positive ( except naloxone) naloxone) Dosage of commonly used General anaesthetics 1. Ketamine Hydrochloride Concentration: 10% solution or 100mg/ml Recommended dose: 10-30 mg/kg IM, IV in dog and cat 2.2 -6.6 mg/kg IM in pig 11 mg/kg IM in Ruminants 2. Chloral hydrate Concentration: 7 % solution Recommended dose: 20-30 ml/45 kg IM in cattle 3. Thiobarbiturates( 1. Thiopental Na 2. Thiamylal Na) Concentration: 5-10 % Recommended dose: 6.6 -8.8 mg/kg IV in Horse Thiamylal Na - 0.01 mg/kg IV in cattle 6.6- 11 mg/kg IM, IV in swine 4. Tiletamine/ Zolazepam combination ( Zoletil). See package for recommended dose 6|Principles of Veterinary Surgery, Cagayan State University R O E L T. C A L A G U I , DV M , M P H , P H D  -Contraindicated to Phenothiazine agents such as acepromazine maleate - give Atropine sulfate 10 minutes prior to its administration Concentration: 50mg/ml Drug Categories of Anesthetic Agents 1. Barbiturates Example: Long acting (8-12 hours) – e.g Phernobarbital Na, Barbital Na Intermediate (2-6 hours) – e.g Amobarbital Na Short acting (45 mins-1.5 hrs) – e.g Pentobarbital Na, Secobarbital Na Ultra short acting (5 -15 minutes) – e.g Thiopental Na, Thiamylal Na, Thialbarbitone Na, Methohexital 2. Non-barbiturates Example: a. Etomidine- rapid ultrashort acting b. Propofol- rapid ultrashort acting c. Chloral hydrate 3. Dissociative agents Example: a. Ketamine HCl b. Phencyclidine c. Tiletamine HCl 4. Inhalation Anesthetics Example: a. Volatile liquids- ether, desflurane, isoflurane, halothane, enflurane, methoxyflurane b. Anesthetic gas- nitrous oxide Local/Regional Anaesthesia Action: It blocks transmission of incoming impulses by raising the threshold level to stimulus. Contraindications: When the area is infected, fibrotic or deficient in circulation. Samples of Drugs: (If given in higher concentration they become good regional anaesthetics) 1. Lidocaine 2. Tetracaine 3. Novocaine 4. Procaine 5. Mepivacaine 6. Cetacaine 7. Piperocaine Administration : 1. Local or infiltration anesthesia- is the injection of the surgical site directly with analgesic/ anaesthetic agent. -contraindicated if inflammation occurs; best for skin tumour removal, tail or digit amputation 2. Regional – is the desensitization by blocking the major nerve(s) to a given region; also known as nerve blocking technique 7|Principles of Veterinary Surgery, Cagayan State University R O E L T. C A L A G U I , DV M , M P H , P H D  Commonly used local anesthetics for local and regional analgesia are: 1. 2% Lidocaine hydrochloride 2. 2 % Mepivacaine hydrochloride a. Infra-orbital nerve block - Injection into infra-orbital canal through the infra orbital foramen - 10 ml of solution desensitizes the anterior half of the face including the cheek teeth as far as the second molar. b. Mandibuloalveolar nerve block - Needle (15 cm long) injected into the vicinity of the angle of the jaws towards the mandibular foramen. - Blocks lower jaw, teeth and lower lip c. Cornual nerve - 2 to 3 cm infront of the horn, first toward the margin then underneath the horn. - Blocks the horn and the skin around the base d. Epidural Horse : Low epidural – between 1st and 2nd coccygeal vertebra or between 1st coccygeal and last sacral vertebra High epidural – lumbosacral foramen (3-4 finger's breadth behind the line connecting parts of the tuber coxae) Manner of Administration: Low epidural – needle is inserted to form an angle of 60° from the horizontal plane to avoid hitting the intervertebral disk. - Give 10-12 ml solution High epidural – injection is made through the trocar using the stylette to give stability. - Give 100 – 150 ml solution Cattle: Low epidural – same in horse -Needle forms 45° angle from the horizontal plane. - For medium size cow, give 10 ml solution High Epidural – same in horse however, it can lead to epidural abscess (irreversible paralysis Calves: -Use lumbo-sacral foramen. -Give 3-8 ml dose Dog: – site is in the lumbo-sacral foramen - Locate the iliac crest and insert the needle in the midline just behind the line joining the highest parts of the crests. - Give 2-10 ml dose slowly 8|Principles of Veterinary Surgery, Cagayan State University R O E L T. C A L A G U I , DV M , M P H , P H D  - No risk of sub-epidural hit because the dura ends at the 6-7th lumbar vertebra. Low epidural- between the 1st coccygeal and sacrum or between st nd the 1 and 2 coccygeal vertebra - do not exceed 1 ml. Intravenous Anaesthesia The stages of anesthesia are related to three ( 3) phenomena: 1. The progressive depression of the central nervous system from the cortex of the medulla. 2. The ability of the lower phylogenic centers of the brain compensate and take over basic functions following the depression of the lower area. 3. A special affinity of different drugs for different portions of the brain Classification of Barbiturate A. Based on the duration of action B. Based on the site of detoxification 1. Detoxified by the kidney- Barbital and Phenobarbital 2. Detoxified by the liver- Amobarbital, Aprobarbital, Hexethal, Hexobarbital, Pentobarbital Na, Probarbital, Propallylonal, and Secobarbital 3. Detoxified by both kidney and liver- Butethal, Cyclobarbital, Diallybarbituric acid, and Vinbarebital Characteristics of Barbiturates 1. Poorly tolerated by animals with renal, hepatic or cardiovascular disorders 2. Response of the CNS depends on: Route Concentration Speed of administration Potency and lipid solubility Degree of ionization and plasma binding 3. IV is the best route 4. Slow administration causes redistribution to non nervous tissues thus total dose requirement must be increased. 5. Rapid injection cause less chance for redistribution 6. When metabolic acidosis occurs due to shock from severe diarrhea, there is decreased plasma protein binding, which increases the non-ionized part of the drug. Therefore, -The drug becomes more available to the CNS -And deeper anaesthesia is produced. 7. Hepatic/renal deficiency – prolonged recovery leads to hypothermia Barbiturates decrease renal blood flow which leads to hypovolemia and prevents excretion of barbiturate by the kidney thus prolonging recovery period. 8. Recovery from a single dose is 15 minutes. 9|Principles of Veterinary Surgery, Cagayan State University R O E L T. C A L A G U I , DV M , M P H , P H D  9. 2-4 hours of intermittent administration leads to saturation of non nervous tissues and so recovery is dependent on the hepatic function to metabolize. 10. Dosages: 1. Pentobarbital sodium (6 or 6.5%) - 60 – 65 mg/ml (2 to 2.5% concentrations is preferred) Dose 30-40 mg/kg (lasts 2-3 hrs) Full recovery occurs after 6-8 hrs Give 1/3 to ½ doses, IV rapidly and the rest is used for maintenance dose. 2. Thiopental sodium Dose: 13 to 16 mg/kg, use endotracheal intubation to be transferred to inhalation anesthesia for maintenance. 3. Thiamylal sodium Dose: 18-30 mg/kg (1.5 times more potent than thiopental sodium) 4. Methohexital Dose: 5.8 mg/kg may produce muscle tremors during recovery. Inhalation Anaesthesia The main advantages of volatile agents over soluble anaesthetic agents: 1. Rapid change which can be effected in the depth of anaesthesia 2. The rapid recovery on their withdrawal 3. The ease with which the resuscitation can be effected following respiratory collapse Methods of administration: Some anaesthetic agents are liquid and must be vaporized before they can be inhaled; others are gaseous at room temperature and are stored in cylinders. A. Open Method A wire mask covered by 6- 8 layers of gauze is used in this method. As the liquid is dropped on the gauze it is vaporized by the inhalation of air. This method is difficult to control because of the rapid loss of anaesthetic. B. Semi-open Method In this method, a mask is surrounded with a towel, causing all the respired gases to pass through the vaporizing pad. This method permits better control of the level of anaesthesia but results in CO2 retention, and care must be exercised to avoid restricting the free exchange air. Features: Masks – must conform to the facial structures to minimize dead space created by the mask. Uses: Good for induction and maintenance of anaesthesia in small species. Anesthetic Agents: 1. Halothane 2. Methoxyflourane Any of the two above with combination of nitrous oxide 10 | P r i n c i p l e s o f V e t e r i n a r y S u r g e r y , C a g a y a n S t a t e U n i v e r s i t y R O E L T. C A L A G U I , DV M , M P H , P H D  75% NO2 + 25% 02 – serve as base for addition of halothane or methoxyflurane Ex. 0.25% halothane added and increased by 0.5% increments until 2 to 4% Maintenance concentration (halothane) = 1 to 2.5% Induction concentration (methoxyflurane) = 0.5 and 1.5% Maintenance concentration (methoxyflurane) = 0.25 and 0.75% Maintenance equipment: mask or endotracheal tube C. Semi-closed Method An external vaporizer and source of anaesthetic gas are used in this method. The gas is passed to a reservoir, in the form of a rubber bag, from which the patients breathes. Depending on the gas flow into the system, the patients may breathe only fresh gas or part of the exhaled gas maybe eliminated through a valve and part routed into the rebreathing bag. Rebreathing may or may not occur, and this is controlled by the gas flow rate and by the patient’s tidal and minute volume. D. Closed Method This method employs total re-breathing of the expired gases from which the CO2 is removed by an absorbent. The rate of oxygen inflow into the system is maintained at a constant low level, sufficient to replace the oxygen used by the patient. Two main types of closed circuit are used: 1. To and fro system- the to and fro apparatus consists of a water type soda lime absorber with rebreathing bag at one end, an expiratory valve at the other, a side arm for the addition oxygen and anaesthetic gases, and a mount for the connection to the patient. This circuit employs an external vaporizer and source of a gas. 2. Circle system Components: 1. Re-breathing bag -The bag is refilled during exhalation and by oxygen for anaesthetic gas; provides the animal’s respiratory minute volume. 2. Canister with alkaline earth - CO2 and H2O (resp. moisture) go into the carbonic acid + alkaline metal mixture in the canister; results to formation of sodium or calcium carbonate, water and heat; canister contains pH indicator which detects exhaustion or absorbing activity of the lime. 3. Y-piece valves for unidirectional gas flow - Features dome valves; creates resistance for one way direction of gas flow. 4. Breathing tubes – Diameter is 1.9 cm for large animal and 1.3 cm for small animals. 5. Inlet for fresh gas – Placed directly on the inhalation side or on the canister. 6. “Pop off” valve to allow escape of excess gas; located on the exhalation of the “y” piece; they pop at pressures greater than 1cm of water (air moisture) E. Draw over System 11 | P r i n c i p l e s o f V e t e r i n a r y S u r g e r y , C a g a y a n S t a t e U n i v e r s i t y R O E L T. C A L A G U I , DV M , M P H , P H D  - In this system, the patient’s inspiratory efforts draw air through ether container and cause vaporization. The concentration of ether, vapour depends on the area of the ether liquid exposed, the speed of movement of the gas through the chamber and the temperature of the ether during vaporization. Comparison of procedures for administering inhalant anaesthetics : 1. Open method - Does not require expensive apparatus. Anaesthesia is difficult to control 2. Semi-open method - Anaesthesia is better controlled. Possible lack of oxygen or CO2excess and risk of anoxia exists, especially if the end of the mask is obstructed. 3. Semi-closed method - Gas flow rate insures adequate exchange of gas to prevent oxygen lack or CO2 excess. Anaesthesia is well controlled, but because all exhaled gases are lost, the use of costly agents is expensive. This method is used mostly with N2O plus low levels of some other agent such as ether. 4. Closed Method - Requires expensive equipment, and soda lime is used up constantly. 5. Draw over Method - Requires little equipment, but uses large amount of ether. Tracheal Intubation The use of endotracheal tube offers a number of advantages during anaesthesia: 1. The airway is always patent and no foreign materials can be aspirated 2. Positive pressure respiration can be readily provided, and laryngospasm is prevented. 3. All the respired gases are available and can be controlled Agents used in Inhalation Anaesthesia 1. Diethyl ether - A colorless liquid which is irritating to skin and mucus membranes, and these tissues must be protected if a simple vaporizer such as gauze mask is used. 2. Divinyl ether - A clear liquid which forms a relatively non-irritant vapour. Much more potent than diethyl ether and will effect rapid induction of anaesthesia, but it is not advisable to continue administration of this drug for more than 30 minutes as it a can cause hepatic damage. 3. Halothane -This is a clear liquid with a sweet smell. Its vapour is non-irritating and non- flammable. It is stable and does not decompose during contact with soda lime. 4. Methoxyflourane - A clear liquid which has a boiling point higher than water, but it vaporizes easily. - Enters and leaves the body through the lungs as an inert gas. 12 | P r i n c i p l e s o f V e t e r i n a r y S u r g e r y , C a g a y a n S t a t e U n i v e r s i t y R O E L T. C A L A G U I , DV M , M P H , P H D  - Controlled accurately because it does not depend on the metabolic pathway of the kidney and liver for excretion - Minimal accumulative effect, with oxygen serving as medium for the anaesthetic gas. This therefore protects the animal from hypoxia. - Drug is carried to the brain via the arterial pressure which is related to the alveolar concentration (lung ability) - Anything which retards deep ventilation slows induction. Ex. Tachypnea, breathe holding, lung disease - Transfer from a thiobarbiturate for induction to an inhalant anesthesia is the standard procedure for maintaining anesthesia. Maintenance should be done before consciousness (15 min) 5. Cyclopropane - A colorless, sweet smelling, non-irritant gas. It forms an explosive mixture with air and oxygen, and does not decompose in the soda lime absorber. 6. Chloroform - A clear liquid with a sweet odor and a relatively non-irritating vapour. It is a hepatoxin, especially if administered following a period starvation or when the glycogen content of the liver is reduced. 7. Trichloroethylene - A blue stained liquid with a sweet smell. It does not volatilize readily at room temperature, and it is well known that it will decompose on exposure to light, air, or alkali to form phosphene gas. 8. Nitrous oxide - Not potent - Used as adjunct to halothane or methoxyflourane - Low solubility in blood and body tissues thus, inductions are rapid. - Barbiturates and analgesics +NO2 + muscle relaxants are a good combination Classical Stages of Anesthesia Note: The manifestation of the signs under each stage is recognizable only when using a slow acting general anesthetics such as Diethyl ether better known as Ether or could be dependent on the biological activity of the systems of the body of the subject. Stage 1 (Induction or Stage of Voluntary Excitement) Stage of prenarcosis, sedation and analgesia; reduced response to pain stimuli; active reflexes; slightly dilated pupils Stage 2 (Stage of Involuntary Excitement) Stage of an uninhibited response or excitement; nystagmus or oscillation of eye appears; not seen with induction by ultra short acting barbiturates Stage 3 (Stage of Surgical Anesthesia) Plane 1 – when response to stimuli is first lost; palpebral, corneal and anal reflexes are still present Plane 2- loss of palpebral reflex, some decrease in corneal reflex and some loss of tone of anal sphincter; nystagmus absent 13 | P r i n c i p l e s o f V e t e r i n a r y S u r g e r y , C a g a y a n S t a t e U n i v e r s i t y R O E L T. C A L A G U I , DV M , M P H , P H D  Plane 3- occurs as paralysis of intercostals muscle begins; corneal reflex gone; pupils begin to dilate Plane 4- deepest level of surgical anesthesia; reflects anesthetic overdose; drop in blood pressure and increase in pulse rate; ocular reflexes all absent; pupil dilated and does not respond to stimuli Stage 4 (Overdose) Stage of medullary respiratory paralysis; represents severe drug overdose; all reflexes gone; pupil widely dilated; respiration stops and vascular collapse occurs; death is imminent Monitoring During Anaesthesia 1. Effective anaesthesia obliterates the patient’s response to painful stimuli without depressing vital functions. 2. Do not put emphasis on any one sign but rather observe the animal as a whole 3. For minor surgery – light surgical anaesthesia For major surgery – deep surgical anaesthesia Signs to watch for: a. Eyeball turns medially and ventrally upon administration of Atropine sulfate. Pupil responding to strong light means a return to consciousness. b. Palpebral and pedal reflexes disappear at onset of light surgical anesthesia. They don’t return until the animal has fully recovered. c. Oral reflex – check resistance when jaws are opened. d. Masticatory muscles – strong in light anesthesia but absent in deep anesthesia. Indication or relaxed skeletal muscles. This sign is not effective in brachycephalic breeds. e. Ventilation – irregularity in rate and depth indicates that the animal is breathing with its diaphragm and is in light anesthesia. Regular and constant rate occurs in surgical anesthesia. Intercostals muscles when paralyzed and when chest wall moves inward indicate anesthetic over dosage. Hypercapnia (exaggerated respiratory movement and irregularity) with gasping and flaring of nostrils also indicate poor oxygenation. Monitor rate by observing thoracic movement or by auscultation. f. Heart rate – increase in light anesthesia due to sympathetic stimulation; decrease beyond surgical level in halothane and methoxyflurane. Monitor by peripheral pulse (very difficult when blood pressure is very low and when animal is draped) or by auscultation externally (difficult when animal is obese, BP, is low and animal is draped.) g. Mucous membrane- when cyanotic indicates inadequate oxygenation. h. Blood pressure palpate lingual artery. When there is low PB, palpation is difficult. i. Peripheral resistance- use capillary refill time (CRT). Post-anesthetic Management 1. Trachea and bronchi be aspirated from sticky secretions. 2. Lungs be inflated with oxygen 2 or 3 (x) to reverse atelectasis due to anesthesia. Endotracheal intubation should be left and oxygen provided until swallowing and coughing 14 | P r i n c i p l e s o f V e t e r i n a r y S u r g e r y , C a g a y a n S t a t e U n i v e r s i t y R O E L T. C A L A G U I , DV M , M P H , P H D return. 3. Respiration is stimulated by flexing limbs, slapping animal lightly and rolling the animal. 4. Atropine sulfate is given again to the dog whose breed salivates profusely to prevent aspirating saliva. 5. Food and water are with held for 2 hours if larynx is desensitized with local anesthetics 6. Keep BT at 20 – 240C 7. Cages should not be too small and with no protuberances. 8. Analgesic is given when animal is fully recovered. Ex. Paracetamol, Flunixine meglumine Anesthetic Emergencies 1. Respiratory Arrest Reasons: a. drug depression b. anoxia due to cardiac c. hyperventilation d. obstruction of air massages Management: a. Stop anesthetic administration b. Check patency of airways c. Give 100% oxygen by re-breathing bag d. Blow into the patients nostrils e. Analeptics are given only when ventilation is under control. Ex. Nalorphine / levallorphan, given IV slowly to effect Doxapram HCL – 1 to 2 mg / kg f. Supportive treatment: Physiologic dieresis Alkalinization of Urine 2. Cardiac Arrest Reasons: a. drug depression b. hypercarnia c. hypoxia d. severe electrolyte imbalance e. cardiac arrhythmia f. primary cardiac pathology g. obstruction of venous return Symptoms: a. No pulsation in major arteries / bleeding from wounds. b. Heart sounds absent c. Mucous membrane cyanotic with a prolonged capillary refill time Management: a. Institute treatment to avoid brain damage that could occur 2 – 44 mins. After cardiac arrest. b. Stop anesthetic administration c. Give increased levels of oxygen d. Cranial end of the animal must be lowered at 30 degrees angle 15 | P r i n c i p l e s o f V e t e r i n a r y S u r g e r y , C a g a y a n S t a t e U n i v e r s i t y R O E L T. C A L A G U I , DV M , M P H , P H D  e. Do chest massage 1. Position dog on its right side and place sand bag under the thoracic wall. 2. Apply downward rapid compressions on the venral half of the thorax for 1 – 2 mins at a rate of 60 – 80 compressions per minute. 3. In small animals, the fingers of both hands are place under the vertebral column while both thumbs are on the midsternum References and Readings Bojrab, M.J. (1998) Current Techniques in Small Animal Surgery. 4th Edition, RR Donneley Sons & Company. Hickman, J., Houlton J., and Edwards Barrie. 1995. Atlas of Veterinary Surgery. 3rd edn. University Press, Cambridge. Slaughter, D.2003.Textbook of Small Animal Surgery. 3rd edn. Blackwell Publishing Inc. Tranquilli, W. J, Thurmon , J.C., and Grimm K.A..2007. Veterinary Anesthesia and Analgesia. 4th edn. Blackwell Publishing Inc. 16 | P r i n c i p l e s o f V e t e r i n a r y S u r g e r y , C a g a y a n S t a t e U n i v e r s i t y R O E L T. C A L A G U I , DV M , M P H , P H D LESSON 11 PHARMACOLOGY AND APPLICATION OF PARENTERAL ANESTHETIC AGENTS A overabundance of injectable agents are available in veterinary practice to fulfill the need for premedication, induction, maintenance, and postoperative analgesia; to alleviate anxiety and motor activity (chemical restraint); and to provide profound muscle relaxation (neuromuscular blocking agents) when indicated. While some agents, such as the dissociative drugs, serve multiple roles (premedication, induction, and maintenance), parenteral drugs are summarized according to primary effects. Because no drug available today possesses all the “ideal” qualities, anesthetic selection is a compromise based on the patient, the procedure, and the available agents, equipment, and expertise. Inhalation agents come closest to possessing the majority of qualities described for an “ideal” anesthetic agent. Premedication agents are used to aid in animal restraint (calming effect), reduce anxiety, provide analgesia, provide muscle relaxation, decrease the requirements for potentially more dangerous drugs used for induction and maintenance, promote smooth transition from consciousness to unconsciousness and vice versa during the induction and recovery periods, respectively, and minimize autonomic reflex activity. Induction agents are used to provide a smooth transition from consciousness to unconsciousness, which facilitates intubation and transition to the maintenance protocol. Some agents used for induction also are useful, as repeat boluses or constant rate infusion, for maintenance of anesthesia. Other drugs serve a variety of roles including sparing the more cardiorespiratory depressing drugs used for induction and maintenance and muscle relaxation. The following alphabetical list (by chemical name) summarizes drugs that might be used in veterinary anesthesia (MOA is mechanism of action; DOA is duration of action, these numbers are only guidelines as DOA is influenced significantly by concurrently administered drugs and individual patient status). Route of administration for every agent is listed in parentheses after DOA and includes intravenous (IV), intramuscular (IM), subcutaneous (SC), and per os (PO). In general, the onset of effect occurs within 5 minutes for drugs administered intravenously. When drugs are administered intramuscularly, onset of effect is in 15 minutes; subcutaneous administration requires a slightly longer time to take effect (20–30 minutes). Categories and Major Effects of Injectable Anesthetic Agents Used inVeterinary Medicine (text has specific agent information Use/Category Effects/Comments Premedications Anticholinergics Decrease secretions, prevent bradycardia Atropine Glycopyrrolate Tranquilizers Alleviate anxiety and decrease motor activity; provide no analgesia, synergize activity of other agents; promote 17 | P r i n c i p l e s o f V e t e r i n a r y S u r g e r y , C a g a y a n S t a t e U n i v e r s i t y R O E L T. C A L A G U I , DV M , M P H , P H D  muscle relaxation Major tranquilizers: Acepromazine Use is relatively common in all species (phenothiazine Azaperone Use is predominantly in swine and some exotic species (butyrophenone) Minor tranquilizers: Diazepam Minimal sedation unless combined with opioid or alpha2(benzodiazepine) agonist Midazolam More rapid onset of effect and not painful when given IM)SC (compared to diazepam, which is recommended for IVuse only) Benzodiazepine Specific reversal agent for benzodiazepines Antagonist Alpha2 agonists Provide analgesia, sedation, and muscle relaxation; cardiovascular effects are profound (conduction disturbances, hypotension) but usually well-tolerated in healthy patients; significant sparing effect when used prior to inhalant anesthesia Xylazine Shortest duration of effect Detomidine Longest duration of effect Romifidine Not currently approved for use in United States Alpha2 antagonists Specific reversal agents for alpha2 agonists; may promote hypotension through vasodilatory effects especially when administered rapidly IV Tolazoline Nonspecific antagonist Opioids Provide analgesia and sedation (degree of effects vary with agent); used for preemptive and postoperative analgesia. Opioid (μ) agonists: Major side effect is respiratory depression; greatest potential for abuse Butorphanol Commonly used in veterinary medicine; moderate analgesia; may be used to reverse μ agonists 18 | P r i n c i p l e s o f V e t e r i n a r y S u r g e r y , C a g a y a n S t a t e U n i v e r s i t y R O E L T. C A L A G U I , DV M , M P H , P H D  Nalbuphine Not scheduled but minimally effective as an analgesic agent;may be used to reverse μ agonists Nalorphine Used for antagonist effect, rarely used clinically Diprenorphine Used for antagonist effect; short duration of action may allow ”renarcotization“ after reversal Opioid antagonists: Used “to effect” to reverse opioid agonists and agonist/ antagonists Naloxone Short duration of action may allow “renarcotization” after reversal Dissociative agents Dose-dependent effect provides quieting and immobilization at low doses and general anesthesia at higher dosages, somatic analgesia; poor viscera analgesia Ketamine Tiletamine (Telazol™) Commercial product combined with zolazepam in 1:1 (mg) ratio Chloral hydrate Sedative/hypnotic: used for large animal sedation; no longer used as large animal general anesthetic due to narrow safety margin and prolonged recoveries; effective IV, PO, rectally Induction/maintenance agents Barbituates Short and ultrashort-acting; high pH makes them irritating to tissues Pentobarbital Short-acting oxybarbiturate; recovery >6–24 hr; rarely used for clinical anesthesia due to availability of agents with shorter duration of effect Methohexital Ultrashort-acting oxybarbiturate (rapidly metabolized); not commonly used Thiopental Ultrashort-acting thiobarbiturate (rapidly redistributed): risk of rough, prolonged recovery if used as repeated bolus or in presence of hepatic disease; common use in veterinary practice Dissociative agents Dosages of dissociatives will contribute to rough prolonged recoveries (especially tiletamine) 19 | P r i n c i p l e s o f V e t e r i n a r y S u r g e r y , C a g a y a n S t a t e U n i v e r s i t y R O E L T. C A L A G U I , DV M , M P H , P H D  Propofol Produces rapid loss of consciousness; recovery is fast due to rapid metabolism, making it useful for induction and maintenance Etomidate Produces rapid loss of consciousness; recovery is fast due to rapid metabolism, making it useful for induction and maintenance Adjunct agents Glyceryl guaiacolate Central-acting muscle relaxant used in large animals to reduce (guaifenesin) requirements of induction and maintenance agents; 5 and 10% (horses only) solutions— 10% solution causes hemolysis in species other than horses Neuromuscular Act at neuromuscular junction to block neurotransmission, blocking agents resulting in muscle paralysis; ventilatory support is required;useful adjunct for ocular, orthopedic, and abdominal procedures and for patients that resist mechanical ventilation; sparing effect on concurrently used drugs; no inherent analgesic effects Nondepolarizing Competitive (reversible) interference with acetylcholine at competitive postsynaptic muscle membrane; many agents currently agents: available with variable duration of action, cardiovascular effects, ability to induce histamine release, duration and onset of effect and cost (text descriptions are given only for those with current or historical, and relatively common, use in veterinary medicine) Turbocurarine Use is largely reserved for research Gallamine Use is largely reserved for research and some exotic species Pancuronium Relatively long duration of effect Vecuronium Intermediate duration of effect Atracurium Short duration of effect cis-Atracurium Short duration of effect Mivacurium Short duration of effect Rocuronium Intermediate duration of effect Doxacurium Relatively long duration of effect 20 | P r i n c i p l e s o f V e t e r i n a r y S u r g e r y , C a g a y a n S t a t e U n i v e r s i t y R O E L T. C A L A G U I , DV M , M P H , P H D  Depolarizing Nonreversible depolarization of postsynaptic muscle membrane Succinylcholine Ultrashort acting, rapid onset; side effects preclude routine use Acetylcholinesterase Reverse competitive NMBs by allowing acetylcholine to inhibitors: mulate at synaptic cleft and restore normal muscle function; side effects are associated with stimulation of muscarinic receptors and prevented by prior administration of an anticholinergic agent Properties of an “Ideal” Anesthetic Agent 1. Does not require metabolism for termination of action and elimination (reversible or respiratory elimination). 2. Permits rapid and easily controlled induction, changes in anesthetic depth and recovery. 3. Is not irritating to any tissue. 4. Does not depress cardiopulmonary function. 5. Produces adequate muscle relaxation and analgesia for surgical procedures. 6. Is compatible with other drugs. 7. Is nontoxic to the patient and humans. 8. Is inexpensive, stable, and noninflammable. 9. Requires no special equipment for administration. References and Readings Bojrab, M.J. (1998) Current Techniques in Small Animal Surgery. 4th Edition, RR Donneley Sons & Company. Hickman, J., Houlton J., and Edwards Barrie. 1995. Atlas of Veterinary Surgery. 3rd edn. University Press, Cambridge. Slaughter, D.2003.Textbook of Small Animal Surgery. 3rd edn. Blackwell Publishing Inc. Tranquilli, W. J, Thurmon , J.C., and Grimm K.A..2007. Veterinary Anesthesia and Analgesia. 4th edn. Blackwell Publishing Inc. 21 | P r i n c i p l e s o f V e t e r i n a r y S u r g e r y , C a g a y a n S t a t e U n i v e r s i t y R O E L T. C A L A G U I , DV M , M P H , P H D LESSON 12 PRE-OPERATIVE, OPERATIVE AND POST- OPERATIVE PREPARATIONS IN SURGERY Pre-operative Preparation 1. Animal is bathed prior to surgery. Matted hair is removed 2. Pre-anesthetics such as Atropine sulfate, antibiotics, hematinics and tranquilizers are given. Incision site is shaved. 3. Animal is anesthetized. Site is washed with germicidal soap and water, generously lathering with frequent rinsing. 4. Table is covered with foam or towels. Heat lamps or heating pads place against the patient cause burns thus, this should be used cautiously. 5. Animal is positioned to make site accessible. -Elevate the hindquarters for lower abdominal surgery -Lower hindquarters for cranial abdominal surgery -Lumbar region is padded for kidney operation to elevate these at surgical site. -Give IV fluid administration prior to surgery for any IV medication. 6. Respiration and body temperature are monitored. Surgeon checks any color changes in exposed tissues. 7. Final skin preparation inside the operating room is done. Sponge with scrubbing solution and 70% alcohol and paint with 2% tincture of iodine. 8. Surgeon prepares himself by doing hand scrubs. Hands and arms are washed with soap and water and scrubbed with brush on each surface followed by rinsing. The pattern is repeated thrice or within 10 minutes. Finally, hands and arms are wet with 70% alcohol. Mask and cap should be worn prior to scrubbing. Surgeon wears gown after and then gloves are worn over. During Operation: 1. Prepare the instruments on time table such as sutures, sponges, surgical instruments and fluids. 2. Final check is done on the patient – state of anesthesia, position, IV Catheters. 3. Inspect the proposed incision line before draping. 4. Draping: Place 2 sterile towels parallel to the incision line. Fold the towel edges on either side of the wound edge. Place 2 towels at the cranial and caudal ends of the incision line and fasten with towel clamps. Finally, place the drape with the center window over the towels and fasten with two clamps. 5. Incisions: Scalpel used for skin incision is discarded for further use. Another scalpel is used for deepening the incision. 6. Hemostasis: 22 | P r i n c i p l e s o f V e t e r i n a r y S u r g e r y , C a g a y a n S t a t e U n i v e r s i t y R O E L T. C A L A G U I , DV M , M P H , P H D  Inject systemic hemostatics, ligate or apply local pressure. Do not rub tissue with sponge. 7. Dissection: Blunt dissection is done only if the line of cleavage is not clear or one is avoiding blood vessels. Use double sharp scissors; for grasping tissues. Use toothed forceps and not hemostats. 8. During Operation: -Monitor pulse rate, color, respiration of patient, body temperature and other vital signs. -Avoid leaning/resting your hands to the patient -Avoid using heavy drapes -Surgical area must be tidy -Used sponge and instruments must be placed on separate containers. Post Operation: 1. Decrease anesthetics and remove drapes. 2. Hypothermia case - wrap the animal with drape and place heating pad nearby or use bottle containers with hot water wrapped with cloth and then apply into the body surface. Hyperthermia case – baths the legs and head with cool running water. 3. When reflexes return, withdraw the endotracheal tube. 4. Pads when the animal thrashes during recovery. 5. Recovery room should be quiet and dark, preferably walls and floorings are padded with soft materials to avoid injury during recovery 6. If pain is present, give analgesic 7. Wet mouth with fresh water for quieting affect. References and Readings Bojrab, M.J. (1998) Current Techniques in Small Animal Surgery. 4th Edition, RR Donneley Sons & Company. Hickman, J., Houlton J., and Edwards Barrie. 1995. Atlas of Veterinary Surgery. 3rd edn. University Press, Cambridge. Slaughter, D.2003.Textbook of Small Animal Surgery. 3rd edn. Blackwell Publishing Inc. Tranquilli, W. J, Thurmon , J.C., and Grimm K.A..2007. Veterinary Anesthesia and Analgesia. 4th edn. Blackwell Publishing Inc. 23 | P r i n c i p l e s o f V e t e r i n a r y S u r g e r y , C a g a y a n S t a t e U n i v e r s i t y R O E L T. C A L A G U I , DV M , M P H , P H D  LESSON 13 ASEPTIC SURGERY Objective: Prevent contamination of wound done by the surgeon so that wound heals without infection. Sources of contamination: 1. Patient 2. Operating room 3. Instruments 4. Team Surgical Packs: Sterilization is achieved by: Physical – dry heat even for sharp instruments, it will not dull the edges of the instruments - 3200F for 1-2 hours - Most autoclave may damage instruments, scorch fabrics, Chemical – good for instruments but not effective if diluted Gas – flammable ex. Ethylene oxide -Prior to sterilization, instruments be cleaned with cool water and detergent, fabrics should do laundered Pack Preparation 1. Arrange according to order of projected use, materials to be used first must be on top. 2. Avoid densely packing of materials. 3. Always pack 2x as many instruments 4. Additional packs are wrapped separately. 5. Properly wrapped packs remain sterile for 6 months. 6. For longer storage, freshly sterilized packs are stored in plastic bags and then sealed. Failure in sterilization: 1. Too tight packs 2. Insufficient temperature 3. Short exposure time to heat Conduct of Team 1. Never turn backs on a sterile surface. 2. Unsterile areas must not be touched. 3. Arms and hands remain above the waist and below the shoulder. 4. Only the gown area between waist and shoulder is considered sterile. 5. Avoid excessive movement and minimize conservation. 6. Lift instruments when receiving them, don’t drag them. 24 | P r i n c i p l e s o f V e t e r i n a r y S u r g e r y , C a g a y a n S t a t e U n i v e r s i t y R O E L T. C A L A G U I , DV M , M P H , P H D Possible breaches in Surgery resulting to sepsis Sources of contamination: 1. Patient 2. Operating room 3. Instruments 4. Team Failure in sterilization: Too tight packs Insufficient temperature Short exposure time to heat Conduct of Team to avoid contamination 1. Never turn backs on a sterile surface. 2. Unsterile areas must not be touched. 3. Arms and hands remain above the waist and below the shoulder. 4. Only the gown area between waist and shoulder is considered sterile. 5. Avoid excessive movement and minimize conservation. 6. Lift instruments when receiving them, don’t drag them. References and Readings Bojrab, M.J. (1998) Current Techniques in Small Animal Surgery. 4th Edition, RR Donneley Sons & Company. Hickman, J., Houlton J., and Edwards Barrie. 1995. Atlas of Veterinary Surgery. 3rd edn. University Press, Cambridge. Slaughter, D.2003.Textbook of Small Animal Surgery. 3rd edn. Blackwell Publishing Inc. Tranquilli, W. J, Thurmon , J.C., and Grimm K.A..2007. Veterinary Anesthesia and Analgesia. 4th edn. Blackwell Publishing Inc. 25 | P r i n c i p l e s o f V e t e r i n a r y S u r g e r y , C a g a y a n S t a t e U n i v e r s i t y R O E L T. C A L A G U I , DV M , M P H , P H D  LESSON 14 SUPPORTIVE CARE DURING ANESTHESIA Supportive care during general anesthesia contributes significantly to a successful outcome. Factors to consider: 1. increased patient risk and prolonged, 2. complex, and invasive procedures, 3.increase the critical need for supportive measures that will assure patient homeostasis during the anesthetic period. Supportive care begins preoperatively with a thorough patient evaluation including physical examination and appropriate diagnostic evaluation and correction of any abnormalities identified, especially fluid and electrolyte deficits and pH abnormalities. Intraoperative support includes appropriate fluid administration, assurance of acid-base balance, ventilatory support, administration of adjunct drugs as indicated, provision of external heat and positioning considerations. The most critical factor guiding supportive care during the anesthetic period is adequate monitoring. Monitoring is the link between recognition of developing problems and rapid correction before the problem becomes life threatening. Fluid Therapy Fluid therapy usually is unnecessary for short procedures in healthy patients, although it is always advisable to have intravenous access established for any anesthetized patient, in case of unexpected blood loss, the need for cardiorespiratory supportive drugs, or additional injectable anesthetic agents. For high-risk patients undergoing invasive, prolonged procedures, fluid administration provides replacement for intraoperative evaporative losses and third space losses associated with surgical trauma or the existing primary disease process, and it helps maintain cardiovascular stability and organ perfusion, which are altered by anesthetic agents. Most commonly and for most species, a balanced crystalloid fluid similar in composition to extracellular fluid (e.g., LRS or Normosol-R) is administered at a rate of 10 ml/kg/hr. After the initial two hours of anesthesia, if blood loss is minimal and arterial pressure stable, decreasing the fluid rate to 4–8 ml/kg/hr is recommended to avoid excessive dilution of packed cell volume\ (PCV) and total protein, especially during prolonged procedures. These fluid rate guidelines must be adjusted, based on the individual patient, blood or other body fluid loss (e.g., third space loss), and blood pressure monitoring, to assure adequate tissue perfusion. The following guidelines are for fluid therapy in the perioperative period: 1. Abnormalities identified on preoperative evaluation, including dehydration and acid-base and electrolyte imbalances, should be corrected prior to induction of anesthesia, whenever possible. 2. Fluids that do not contain an alkalinizing agent (i.e., 0.9% saline, 5% dextrose, Ringer’s) tend to promote metabolic acidosis (by dilution) if used for prolonged periods. 26 | P r i n c i p l e s o f V e t e r i n a r y S u r g e r y , C a g a y a n S t a t e U n i v e r s i t y R O E L T. C A L A G U I , DV M , M P H , P H D 3. Blood loss may be replaced with crystalloid fluids at three times the estimated blood volume as long as PCV remains above 20%. This guideline is based on the fact that crystalloid fluids distribute to the entire extracellular fluid volume (ECF), which is approximately three times the blood volume. 4. Fluids to which glucose has been added (for 2.5%, add 25 mg/ml; for 5%, add 50 mg/ml) should be administered to neonates, small patients (9 yr >40 kg dogs >7.5 yr cats >12 yr Physiologic changes: Decreased metabolic rate Decreased maximal cardiac output Decreased alveolar gas exchange Decreased organ reserve including liver and kidneys Increased fat Decreased anesthesia requirements Complete physical exam, blood workup, other diagnostic tests as indicated by physical exam findings. Management: Select reversible premedication with minimal cardiac and respiratory effects: opioid + benzodiazepine. Preoxygenate Induction: mask, propofol, thiopental, diazepam-ketamine. Isoflurane or sevoflurane for maintenance. Consider local/regional techniques to spare requirements. Monitor ECG and ABP. Administer fluids at conservative rate. Support ventilation during anesthesia. Provide adequate analgesia and oxygen postoperatively. Neonates Preparation: Considerations Increased metabolic demands Cardiac output is rate dependent Response to hypotension is less well-developed PCV and TP slightly less than adults More susceptible to hypothermia increased surface area to body mass ratio less body fat poorly developed thermoregulatory center Increased susceptibility to dehydration greater body water content less ability to concentrate urine Hepatic function not fully developed limited ability to metabolize drugs limited glycogen stores Management: Select reversible premedication with minimal cardiac effects: consider anticholinergic premedication when drugs known to decrease HR are used (e.g., opioids). Premedication: opioid + benzodiazepine. Induction: mask induction, propofol, diazepam-ketamine. 39 | P r i n c i p l e s o f V e t e r i n a r y S u r g e r y , C a g a y a n S t a t e U n i v e r s i t y R O E L T. C A L A G U I , DV M , M P H , P H D  Maintenance: isoflurane or sevoflurane, nonrebreathing system. Administer glucose-containing fluids (2.5–5%). Provide external heat sources. Postoperative period: maintain oxygen delivery as long as possible and provide warm environment. References and Readings Bojrab, M.J. (1998) Current Techniques in Small Animal Surgery. 4th Edition, RR Donneley Sons & Company. Hickman, J., Houlton J., and Edwards Barrie. 1995. Atlas of Veterinary Surgery. 3rd edn. University Press, Cambridge. Slaughter, D.2003.Textbook of Small Animal Surgery. 3rd edn. Blackwell Publishing Inc. Tranquilli, W. J, Thurmon , J.C., and Grimm K.A..2007. Veterinary Anesthesia and Analgesia. 4th edn. Blackwell Publishing Inc. 40 | P r i n c i p l e s o f V e t e r i n a r y S u r g e r y , C a g a y a n S t a t e U n i v e r s i t y R O E L T. C A L A G U I , DV M , M P H , P H D  Lesson 17 ANESTHETIC MANAGEMENT OF DOGS A variety of protocols are available to provide chemical restraint/premedication, induction of anesthesia, and total parenteral anesthesia in dogs (Table 10–1). A neuroleptanalgesic (tranquilizer plus opioid) combination will minimize anxiety and struggling for catheterization, minimize requirements for induction and maintenance agents, and provide preemptive analgesia. Popular and economical combinations are acepromazine with morphine (moderate to severe pain), hydromorphone (moderate to severe pain), or butorphanol (mild to moderate pain). Diazepam can be substituted for acepromazine when the latter is contraindicated. Midazolam provides a convenient (but expensive) alternative. 41 | P r i n c i p l e s o f V e t e r i n a r y S u r g e r y , C a g a y a n S t a t e U n i v e r s i t y R O E L T. C A L A G U I , DV M , M P H , P H D 42 | P r i n c i p l e s o f V e t e r i n a r y S u r g e r y , C a g a y a n S t a t e U n i v e r s i t y R O E L T. C A L A G U I , DV M , M P H , P H D  Thiopental and diazepam-ketamine are economical and effective induction agents, but repeated bolus administration can contribute to a rough, prolonged recovery and both thiopental and ketamine have specific contraindications. Thiopental causes prolonged recovery in sighthounds due to an inherent inability to metabolize the drug efficiently; alternatives include diazepam-ketamine and propofol. Propofol has become a popular drug in veterinary medicine due to its rapid effect, short duration, and lack of cumulative effect, which allows it to be used as repeated boluses or constant rate infusion without significantly increasing recovery time. Even though more expensive than thiopental, propofol’s rapid recovery and lack of arrhythmogenic effect make it an excellent alternative agent. Applying local and regional anesthetic techniques appropriate to the procedure (most conveniently following anesthetic induction) provides preemptive and postoperative analgesia and further decreases anesthetic maintenance requirements. Dogs are prone to regurgitation and aspiration. Anesthetized patients should be intubated to assure a patent and protected airway, especially if fasting status is unknown or time will not permit an adequate fast (emergencies). Dogs are relatively easy to intubate by direct visualization of the larynx, which is aided by adequate anesthetic depth and use of a laryngoscope. Intubation provides a route for oxygen delivery with or without inhalant administration and an effective means for providing ventilatory support. Appropriate tube sizes for dogs cover a wide range from 3.0 to 14.0 mm internal diameter. An intravenous catheter should be placed in a peripheral vein for procedures anticipated to take longer than 30 min and when administration of additional anesthetic agent is likely. The most common sites are the cephalic and lateral saphenous veins. A secure access provides a route for intraoperative fluid and supportive drug administration and for emergency drug administration, should cardiopulmonary arrest occur. Recovery should occur in a warm quiet area with external heat provided in most cases. Extubation is performed with the cuff deflated when swallowing is noted. When there is evidence of regurgitation or when blood has collected in the pharyngeal region, the oral cavity should be swabbed and the tube removed with the cuff still inflated once swallowing is observed to remove any debris that has settled around the tube within the trachea. Patients with underlying airway compromise (brachycephalic breeds, history of a collapsing trachea) should remain intubated as long as possible and closely observed until recovery is complete. Animals should be observed until vital signs have returned to normal. References and Readings Bojrab, M.J. (1998) Current Techniques in Small Animal Surgery. 4th Edition, RR Donneley Sons & Company. Hickman, J., Houlton J., and Edwards Barrie. 1995. Atlas of Veterinary Surgery. 3rd edn. University Press, Cambridge. Slaughter, D.2003.Textbook of Small Animal Surgery. 3rd edn. Blackwell Publishing Inc. Tranquilli, W. J, Thurmon , J.C., and Grimm K.A..2007. Veterinary Anesthesia and Analgesia. 4th edn. Blackwell Publishing Inc. 43 | P r i n c i p l e s o f V e t e r i n a r y S u r g e r y , C a g a y a n S t a t e U n i v e r s i t y R O E L T. C A L A G U I , DV M , M P H , P H D  Lesson 18 ANESTHETIC MANAGEMENT OF CATS Total parenteral anesthetic protocols seem to be more popular and widely used in cats than dogs for a variety of reasons, including greater resistance to handling and restraint, more difficult venous access, more difficult intubation, and greater effectiveness with less occurrence of side effects associated with dissociative agents. Several protocols are available for short- term injectable anesthesia (Table 11–1). However, for complicated, prolonged procedures and high-risk cats, inhalation maintenance following premedication and induction is more controllable and safer (see Table 11–1). Pure opioid agonists have been reported to cause excitement in cats, but risk of this side effect is minimized with concurrent use of a tranquilizer or when an agonist-antagonist (butorphanol) is used. 44 | P r i n c i p l e s o f V e t e r i n a r y S u r g e r y , C a g a y a n S t a t e U n i v e r s i t y R O E L T. C A L A G U I , DV M , M P H , P H D  The feline respiratory center is more susceptible to the depression associated with thiopental and propofol and transient apnea is common. Some cats will produce excessive respiratory secretions when the dissociative agents are used, which may be counteracted by anticholinergic agent administration. As a rule, cats tend to resent and resist restraint more than dogs. Various devices, such as cat bags and feline muzzles, often are necessary to ensure the safety of personnel and the animal. Always close the doors to avoid escape when working with cats. Most cats can be restrained adequately with scruffing and stretching (holding the skin behind the neck with one hand and the rear limbs with the other and applying gentle tension) for injection of premedication. For resistant animals, adding ketamine or telazol in low dosage to the premedication protocol improves the quality of the catheterization/induction sequence. Many of the local and regional techniques, such as epidural and local nerve blocks, are effective and feasible in cats to provide preemptive and postoperative analgesia. When indicated (high-risk animal, repeat injections, prolonged procedures), an IV catheter should be inserted. Cats seem to resist the necessary restraint as much as the actual catheter placement so premedication usually is required. Sites include the cephalic, medial saphenous, and femoral veins. Laying the animal in lateral recumbency for placement in the medial saphenous vein seems to be less stressful for some anxious, aggressive patients. Feline intubation is more challenging than in dogs. While visualization usually is good, the feline larynx is reactive and prone to laryngospasm, which makes intubation more difficult and increases the risk of trauma.S Cats are more challenging to monitor. Esophageal stethoscopes are helpful for ausculting both respiration and heart sounds. Respiratory monitors and capnometers usually are effective but add to dead space. Pulse quality is more difficult to assess; the best site for pulse palpation is the femoral artery, which may not always be accessible. Recovery usually is rapid in cats following inhalation anesthesia, unless severe hypothermia has developed. Providing a warm environment and thermal support facilitate recovery. Close attention to body temperature is important, as cats seem prone to hyperthermia as body activity increases during recovery, seemingly independent of the protocol used. As a general rule, once the body temperature reaches 99°F, thermal support should be removed. Cats with elevated temperature (>104°F) benefit from the application of alcohol to the pads and a fan to dissipate heat; animals act seemingly normal during this period of increased temperature; thermoregulation returns to normal usually within 24 hr. References and Readings Bojrab, M.J. (1998) Current Techniques in Small Animal Surgery. 4th Edition, RR Donneley Sons & Company. Hickman, J., Houlton J., and Edwards Barrie. 1995. Atlas of Veterinary Surgery. 3rd edn. University Press, Cambridge. Slaughter, D.2003.Textbook of Small Animal Surgery. 3rd edn. Blackwell Publishing Inc. Tranquilli, W. J, Thurmon , J.C., and Grimm K.A..2007. Veterinary Anesthesia and Analgesia. 4th edn. Blackwell Publishing Inc. 45 | P r i n c i p l e s o f V e t e r i n a r y S u r g e r y , C a g a y a n S t a t e U n i v e r s i t y R O E L T. C A L A G U I , DV M , M P H , P H D  Lesson 19- ANESTHETIC MANAGEMENT OF BIRDS Birds frequently require general anesthesia for a veterinarian to perform procedures normally accomplished with physical restraint in most other species as well as complicated and invasive procedures. General anesthesia is challenging in birds due to less familiarity with avian anatomy, greater resistance to restraint, lower margin of safety for injectable agents, less experience with catheterization and intubation techniques, more difficulty in monitoring, and currently, limited information on effective analgesic agents. Capture and restraint should be performed in a quiet and safe environment and done quickly to minimize the stress of chasing. Passeriformes may be restrained with the bird cradled in the palm of the hand and the head gently restrained between the index and middle fingers. For the larger Psittaciformes, a two-hand technique is required (Figure 12–1). Head restraint is vital to avoid bites to the handler and accomplished by creating a ring around the bird’s neck with one hand and applying gentle pressure against the base of the skull and lower mandible. The other hand is placed around the legs to gently support the body. A towel can be used to protect the hand near the head. It is essential to not restrict thoracic movement or compromise the airway. Restraint techniques for adult ratites cannot be described in the confines of this reference book; for information, readers are referred to the recommended reading list. Anesthetic induction and maintenance with isoflurane is the protocol of choice for pet birds and raptors. Sevoflurane also appears to be effective and currently is gaining popularity. Dosages for some injectable protocols are available and listed in Table 12–1; however, these agents usually fail to produce stable and safe levels of anesthesia and should not be used unless gas anesthesia is unavailable. Larger birds, such as ratites, will require an injectable premedication and induction protocol (see Table 12–1) because mask induction is prolonged and dangerous except in debilitated patients. Intubation is relatively easy to perform in avian species as the glottis is readily apparent at the base of the tongue when the beak is opened. Psittaciformes have a fleshy tongue, which must be pulled forward carefully to expose the glottis. 46 | P r i n c i p l e s o f V e t e r i n a r y S u r g e r y , C a g a y a n S t a t e U n i v e r s i t y R O E L T. C A L A G U I , DV M , M P H , P H D  For cases with airway obstruction or to perform procedures in the oral cavity, inhalant anesthesia can be delivered into the air sacs. Percutaneous catheters (14–18 ga; 2–3 cm) may be placed in the caudal thoracic or abdominal air sacs using sterile technique. A small skin incision is required to expose the air sac membrane. The catheter is inserted and the skin secured around the catheter; the catheter is connected to an endotracheal tube adaptor for delivery of the anesthetic agent. The approximate site of entry is at the last intercostal space. 47 | P r i n c i p l e s o f V e t e r i n a r y S u r g e r y , C a g a y a n S t a t e U n i v e r s i t y R O E L T. C A L A G U I , DV M , M P H , P H D  Subcutaneous fluid administration sites include the propatagium (wing web), intrascapular, and inguinal regions. Dextrose-containing fluids (LRS or Normosol with 2.5–5.0% dextrose, half strength LRS, or saline with 2.5% dextrose) are recommended. Sensitivity to anesthesia is variable among avian species and individual birds can develop complications rapidly; therefore, monitoring heart and respiratory rates is essential. 48 | P r i n c i p l e s o f V e t e r i n a r y S u r g e r y , C a g a y a n S t a t e U n i v e r s i t y R O E L T. C A L A G U I , DV M , M P H , P H D During surgical anesthesia, birds should be relaxed and unresponsive to painful stimulation; corneal and pedal reflexes are slow and the palpebral reflex is lost. Respiration should be slow, regular, and deep, with rates usually ranging from 12–30 breaths/min. Temperature should be monitored, especially during long procedures, to avoid development of hypothermia. External heat sources should be provided; maintaining a body temperature of 101–103°F is recommended. Recovery usually occurs within 5–15 min after inhalant delivery is discontinued and should occur in a warm, quiet, and dimly lit environment. Birds should be wrapped loosely in a towel and gently restrained until extubated and able to stand. For prolonged recovery, birds may be left in a padded enclosure with close observation, once extubated. References and Readings Bojrab, M.J. (1998) Current Techniques in Small Animal Surgery. 4th Edition, RR Donneley Sons & Company. Hickman, J., Houlton J., and Edwards Barrie. 1995. Atlas of Veterinary Surgery. 3rd edn. University Press, Cambridge. Slaughter, D.2003.Textbook of Small Animal Surgery. 3rd edn. Blackwell Publishing Inc. Tranquilli, W. J, Thurmon , J.C., and Grimm K.A..2007. Veterinary Anesthesia and Analgesia. 4th edn. Blackwell Publishing Inc. 49 | P r i n c i p l e s o f V e t e r i n a r y S u r g e r y , C a g a y a n S t a t e U n i v e r s i t y R O E L T. C A L A G U I , DV M , M P H , P H D  LESSON 20 ANESTHETIC MANAGEMENT OF REPTILES A variety of reptilian species may be presented with the need for chemical restraint and general anesthesia, and this represents a unique challenge, including limited sites for parenteral agent injection and IV access, a major tendency to become apneic during anesthesia (which often prevents use of mask induction), difficulty in cardiac auscultation, and limited usefulness of available monitoring tools. Restraint techniques are relatively simple for most reptiles but may become more challenging in infrequently encountered aggressive patients. Lizards are restrained by enclosing in the hand if small or securing on a flat surface then applying gentle pressure to the neck and caudal the remainder of the body supported with the other hand or on a flat surface. Turtles require minimal restraint but present a unique problem in that the head usually is inaccessible for physical examination. To view the head, applying a gentle pinch to a front limb usually will cause it to emerge from the shell. Two preanesthetic considerations are important for reptiles. Allow at least 24 hr of hospitalization prior to anesthesia for acclimation. The optimal temperature for most species is 86–88°F. Second, an accurate weight is important to calculate dosages for premedication, which is necessary for induction in most reptile patients. Fasting in reptiles generally is not recommended; the exception is snakes, for which a large meal ingested just prior to anesthesia could impede cardiovascular function; therefore, a 24-hr (minimum) fast is recommended. Various sites for blood collection have been reported—lizards (toenail, ventral tail vein); snakes (ventral tail vein, heart, palatine vein); turtles (toenail, brachial plexus)—and may be required for the workup of complicated cases. Induction and intubation for maintenance with inhalant anesthesia (preferably isoflurane) is facilitated by IM administration of ketamine. Sites for IM injection include the front legs (lizards, chelonians) and the paravertebral muscles (lizards, snakes). A nonrebreathing system for inhalant delivery is recommended for reptiles weighing