F. Anesthesia of pot bellied pigs
1. Dissociative anesthesia
a) Dissociative anesthesia is preferred for minor procedures and for induction.
b) Commonly used dissociative anesthetics include ketamine or tiletamine. The dissociatives are usually combined with a phenothiazine (acepromazine), or benzodiazepine tranquilizer (diazepam or zolazepam).
c) Ketamine and other dissociative drugs induce violent stimulus-related reactions during recovery. Car movement can be a trigger for these reactions. Such reactions may occur in pigs that appear to have otherwise recovered.
d) When administered with dissociative anesthetics, the benzodiazepine tranqulizers reduce violent post-anesthetic reactions. When injected into fat, the benzodiazepines are absorbed poorly. The water soluble dissociative anesthetics exit the fat more rapidly, and are not accompanied by the lipid soluble benzodiazepine. The result is an uninhibited dissociative agent.
CLINICAL TIP: TO ENSURE A COMPLETE RECOVERY PRIOR TO DISCHARGE, ANESTHETIZE PIGS EARLY IN MORNING AND DISCHARGE THEM IN THE LATE AFTERNOON. INCOMPLETELY RECOVERED PIGS BECOME FRENZIED IF STIMULATED.
CLINICAL TIP: REQUIRE THAT PIGS BE PRESENTED IN A CRATE OR CARRIER IN ORDER TO PREVENT ESCAPES AND LIMIT WILD REACTIONS IN THE BACK SEAT OF THE CLIENT'S AUTOMOBILE.
CLINICAL TIP: USE A 3.5 INCH SPINAL NEEDLE FOR INTRAMUSCULAR INJECTION OF DISSOCIATIVE ANESTHETICS INTO OBESE PIGS. THE LONG NEEDLE IS REQUIRED IN ORDER TO PENETRATE THE SUBCUTANEOUS FAT LAYER AND DEPOSIT THE DRUG INTRAMUSCULARLY. INTRAMUSCULAR INJECTION LESSENS THE FREQUENCY OF ADVERSE POST ANESTHETIC REACTIONS.
CLINICAL TIP: IF THE PIG IS STRUGGLING DURING RECOVERY FROM DISSOCIATIVE ANESTHESIA, IMMEDIATELY INJECT 0.1 MG/KG VALIUM INTRAMUSCULARLY, OR REANESTHETIZE IT WITH ISOFLURANE. KEEP THE PIG ANESTHETIZED WITH THE INHALANT FOR AN ADDITIONAL 20 TO 30 MINUTES. IF POSSIBLE GIVE INTRAVENOUS FLUIDS, DURING THE ANESTHESIA. ADMINISTER WARM BALANCED ELECTROLYTE SOLUTION INTRAVENOUSLY AT A DOSE OF 2 TO 4 % OF BODY WEIGHT. IF INTRAVENOUS FLUIDS CANNOT BE ADMINISTERED, OFFER COPIOUS QUANTITIES OF FRUIT JUICES AFTER THE PIG HAS RECOVERED. ADMINISTER A CASTILLE SOAP WATER ENEMA 48 TO 72 HOURS AFTER RECOVERY FROM THE ANESTHESIA.
e) Violent post anesthetic recoveries have occurred in 8 of over 1000 anesthetized VMTH patients. None of the patients died, but 3 have been anorectic and constipated for as long as 2 weeks post operatively. Enemas were administered to 1 pig. The pigs were given fruit juice, moist dog food, and semisolid baby starter. All affected pigs had increased plasma concentrations of creatine phosphokinase, indicating myopathy. Intravenous fluids were not administered. Reports of post anesthetic deaths from the field have been encountered.
f) A pig may remain anorectic for as long as 1 week after a violent recovery. Blood changes in these pigs include increases in the concentrations of serum urea nitrogen, aspartate aminotransferase, creatine phosphokinase, and after several days, creatinine. The pigs are often constipated. Attempt to give fluids, both orally and intravenously (if possible). Stimulate the pig to eat by offering canned soup, or baby starter formulas.
2. Combinations of dissociative anesthetics
a) Doses reported here are based upon published information. As with all anesthetic protocols, proper monitoring, and supportive care during anesthesia is required irrespective of the drugs administered.
b) Combination 1 (PREFERRED) Tiletamine, zolazepam
(1) The recommended intramuscular dose of telazol ranges between 1 and 4 mg/kg.
(2) The 1 mg/kg dose rate is preferred for most procedures.
(3) Overdoses (>4 mg/kg) in older pigs may result in prolonged anesthetic episodes. Prolonged sleep times are probably caused by high tissue concentrations of zolazepam.
CLINICAL TIP: PROLONGED RECOVERY TIMES DUE TO HIGH TISSUE BENZODIAZEPINE (VALIUM OR ZOLAZEPAM) CONCENTRATIONS CAN BE REVERSED BY INTRAVENOUS ADMINISTRATION OF FLUMAZENIL (ROMAZICON, ROCHE INC). ADMINISTER THE DRUG AT A DOSE OF 1 PART FLUMAZENIL TO 13 PARTS OF BENZODIAZEPINE.
c) Combination 2 Acepromazine, ketamine
(1) Acepromazine (0.22 mg/kg, intramuscularly), combined with ketamine, (20 mg/kg, intramuscularly).
(2) Give this combination intramuscularly.
(3) This combination produces the highest rate of post anesthetic motor reactions.
d) Combination 3 Telazol, xylazine
(1) Telazol (1 to 4.4 mg/kg, intramuscularly)
(2) Xylazine (2.2 mg/kg, intramuscularly)
(3) The drugs can be mixed in the same syringe.
e) Combination 4 Xylazine, ketamine
(1) Xylazine (2.0 mg/kg, intramuscularly)
(2) Ketamine (15.0 mg/kg to 20.0 mg/kg, intramuscularly)
(3) The high dose of ketamine may produce apnea and a means for ventilation or resuscitation must be available if this method is to be used safely.
****(4) Give this combination intramuscularly.
(5) Combine this combination with atropine preanesthetic (.05 mg/kg, subcutaneously).
(6) This combination provides less anesthesia, and rougher recoveries than selection number 5 below.
f) Combination 5 Xylazine, ketamine, butorphanol
(1) Xylazine (2.0 mg/kg, intramuscularly)
(2) Ketamine (5.0 mg/kg, intramuscularly)
(3) Butorphanol (0.22 mg/kg, intramuscularly)
(4) Extending surgical anesthesia
(a) Ketamine (1-2 mg/lb, intravenously)
(b) Xylazine (0.5-1 mg/lb, intravenously)
(5) Pigs lose their laryngeal reflex and can be intubated with this combination of drugs.
(6) This combination provides the most potent anesthesia and provides a smoother recovery than combinations 2, 3, and 4.
(7) The xylazine may be reversed with yohimbine (0.05 mg/kg, intravenously). Reversal results in transient decreases in blood bressure and tachycardia. You may not want to reverse a pig that has had significant hemorrhage, or is likely to have a substantially lowered blood pressure prior to reversal.
(8) ref: Nishimura, R, Sakaguchi, M, Mochizuki, M et al, Journal of Veterinary Medical Science, 1992 Aug, 54:615-20.
CLINICAL TIP: XYLAZINE CAN BE REVERSED USING YOHIMBINE (0.05 MG/KG INTRAVENOUSLY), OR TOLAZOLINE (1.1 TO 2.2 MG/KG, INTRAVENOUSLY). HIGHER DOSES OF YOHIMBINE INDUCE ROUGHER RECOVERIES. DOXAPRAM (0.50 TO 1.50 MG/KG, INTRAVENOUSLY), CAN BE ADDED FOR ENHANCED RECOVERY.
g) Combination 6 TKX- Telazol, xylazine, ketamine
(1) Reduces the amount of zolazepam, by reconstituting Telazol with xylazine and ketamine. The combination produces shorter recovery time than an equvalent dose of Telazol, with fewer adverse post anesthetic recoveries.
(2) The mixture is made by reconstituting Telazol with 2.5 ml of ketamine and 2.5 ml of xylazine (100 mg/ml), and 2.5 ml of Ketamine (100 mg/ml). The final concentration of ketamine and tiletamine each is 50 mg/ml. For tranquilization and light sedation, administer 0.03 to 0.06 mg/10 lbs of body weight intramuscularly. For deep sedation, administer between 0.09 to 0.12 ml/10 lbs of body weight. For maintenance of anesthesia, administer 1/4 to 1/2 of the original dose intravenously over 2 additional hours. Do not readminister the cocktail intramuscularly, because this will result in excessively long sleep times.
(3) The anesthesia produced by this mixture is sufficient for invasintravenouslye field surgeries. The pig should be intubated during longer surgical procedures, because the laryngeal reflex is lost.
(4) There is no significant advantage of combination 6 over combination 3 (telazol, 4.4 mg/kg and xylazine, 2.2 mg/kg).
ref: Ko, JC, Williams, BL, Smith, VL, McGrath, C et al, Comparison of telazol, telazol-ketamine, telazol-xylazine and telazol-ketamine-xylazine as chemical restraint and anesthetic induction combination in swine, Laboratory Animal Science, 43, 476-480, 1993.
CLINICAL TIP: THE INCIDENCE OF POST ANESTHETIC HYPERACTINTRAVENOUSLYITY IS LOWEST WITH ZOLAZEPAM AND TILETAMINE. THIS DRUG COMBINATION IS PREFERRED FOR INDUCTION OF INHALATIONAL ANESTHESIA, AND FOR PERFORMING MINOR PROCEDURES. THERE IS LITTLE CHANCE OF APNEA WHEN USED AT A MAXINTRAMUSCULARLYUM DOSAGE OF 2.0 MG/KG. INJECT THE DRUG INTRAMUSCULARLY.
h) Combination 7 Propofol- medetomidine
(1) Meditomidine (30-60 microgram/kg, intramuscularly)
(2) Propofol (4-6 mg/kg, intravenously)
(3) Inject the propofol over 60 seconds because propofol causes apnea.
(4) The combination can be injected by constant infusion of 4 to 8 mg/kg/hour.
i) Combination 8 Medetomidine-midazolam
(1) Medetomidine intramuscularly 40 ęg/kg
(2) Midazolam (0.2 mg/kg intramuscularly)
(3) The drugs may be mixed in the same syringe prior to injection
(4) Reversal of the medetomidine may be achieved by administration of atipamezole (80 to 160 ęg/kg, intramuscularly).
(5) Reversal of the midazolam may be achieved by administration of flumazenil (100 ęg/kg, intramuscularly).
(6) Administration of atipamezole alone may provide sufficient reversal effect for the combination.
(7) This combination of anesthetic agents has not been used in clinical patients at the VMTH.
Nishimura, R, Kim, H, Matsunaga, S, Hayashi, K, et al, Antagonistic effects of atipamezole and flumazenil on medetomidine-midazolam induced sedation in laboratory pigs, Journal of Veterinary Medical Science, 55, 789-793, 1993.
i) Combination 8 "Triple drip" Glyceryl guiacolate, ketamine, xylazine
(1) Glyceryl guiacolate (5% W:V in 5% glucose solution)
(2) Ketamine (2 mg/ml)
(3) Xylazine (1.0 mg/ml)
(4) Induction dose = 1/3 to 1/2 ml/lb, intravenously
(5) Maintenance dose 1 ml/lb/hour, intravenously
(1) 2 to 4 mg/kg, intravenously
(2) Repeat as required
(3) Be prepared to intubate and ventilate the pig, because this is a strong respiratory depressant.
(1) This drug is given intravenously at doses ranging between 6 and 10 mg/kg. The drug is most useful for procedures lasting 10 to 15 minutes, or for induction of gas anesthesia.
(2) Thiopental is not commonly administered to miniature pigs because of the difficulty of venipuncture in a non anesthetized pig.
3. Inhalational Anesthesia of Pot Bellied Pigs
a) Inhalation anesthesia on an intubated patient is the safest and most effective of all methods.
b) The malignant hyperthermia gene does not appear to have widespread distribution among the North American strains of pot bellied pigs.
c) One case of postanesthetic hyperthermia has been described. The pig was successfully treated by application of evaporative cooling. The reversiblity differentiated this condition from that of classical malignant hyperthermia of commercial pigs.
d) Induce the patient with 1 mg/kg of tiletamine zolazepam combination. As soon as the pig becomes unresponsive, apply a mask and deliver isoflurane at 3 to 4%. The flow rate should be approximately 10 ml/kg of body weight. Intubate the pig when it reaches the appropriate plane of anesthesia. Clinical signs that indicate the pig is ready for intubation include loss of jaw tone, ventral rotation of the eye, and prolapsing of the third eyelid. The palpebral reflex should disappear, but anal tone and corneal reflex should be retained. Use a mask fashioned from a gallon bleach bottle for anesthetizing pigs weighing more than 150 kg. Clean the bottle and cut off the bottom. Apply a liberal amount of white adhesive tape around the cut edge, and fix the delivery tubing of the anesthetic machine into the small hole at the screw cap end. Seal the junction with white adhesive tape.
e) Some pigs can be mask induced without chemical sedation. For this, hold the pig by the leash, with the feet on the ground, and the hindquarters in a corner. Push the mask firmly onto the nose, and deliver the anesthetic until the pig becomes recumbent. For prolonged procedures, an endotracheal tube should be inserted. To administer additional anesthetic without intubation, affix the bottle to the nose using 3 inch adhesive tape. Be careful that the pig does not become overstressed. If it struggles and screams excessively, stop, and administer injectable anesthesia.
CLINICAL TIP: A SILICONE CAT MASK CAN BE USED FOR MAINTAINING PIGS WITHOUT AN ENDOTRACHEAL TUBE. THE MASK FORMS A SEAL WITH THE SNOUT, AND REDUCES DEAD SPACE IN THE ANESTHESIA CIRCUIT. THE MASKS ARE AVAILABLE FROM ANESCO INC, 115 ETTER LANE, GEORGETOWN, KY, 40324 . THIS MASK CANNOT BE USED FOR LONG-TERM DELIVERY OF ANESTHETIC OR FOR HIGH RISK ANESTHESIAS.
f) Although expensive, isoflurane is preferred because it has most rapid effect and the shortest recovery period of all inhalational anesthetics. The concentration of anesthetic vapor during induction should not exceed 3%. After induction and anesthesia, adjust the gas concentration upward or downward as needed. g) The approximate MAC (minimum anesthetic concentration) of halothane is 1.5%, but can range between 0.5 and 3.0%.
h) The approximate MAC of isoflurane is 1.5 %
i) Orotracheal intubation
(1) Cuffed orotracheal tubes should be inserted when the medical condition is complicated or long (>20 minutes of duration). Medical conditions that require endotracheal intubation include debilitation, hypovolemia, hypotension, and hypercarbia.
(2) Because of the pig's long, narrow mouth, serpentine airway, profuse salivation, and limited jaw movement, and indistinct arytenoid processes, visualization of the aditus laryngeus is difficult. The tortuous curvature of the airway limits the freedom to manipulate the epiglottis with the tip of the laryngoscope blade.
CLINICAL TIP: PRIOR TO ENDOTRACHEAL INTUBATION, ASPIRATE SALIVA FROM THE AIRWAY USING SUCTION. TO REDUCE THE SALIVARY FLOW, PREMEDICATE THE PIG WITH ATROPINE. ADMINISTER 0.05 MG/KG OF ATROPINE OR 0.01 MG/KG OF GLYCOPYRROLATE SUBCUTANEOUSLY.
(3) Method for intubation
(a) Insert strips of unrolled gauze behind the incisors of the upper and lower jaws. Pull on the strips in order to open the mouth. Extend the head and neck while pulling the tongue from the mouth. Insert a laryngoscope blade in order to illuminate the pharynx. If necessary, aspirate saliva from the pharynx in order visualize the epiglottis. With the tongue extended, depress the epiglottis using the tip of the laryngoscope blade. Spray 0.5 ml of lidocaine over the aditus laryngeus, through a 16 gauge Angiocath catheter. Insert an 8 french Sovereign urethral catheter into the aditus laryngeus, and push an endotracheal tube over the catheter. Spin the endotracheal tube as it is passed over the catheter and into the aditus laryngeus,. Begin the procedure with the tip of the tube curved ventrally. Place the end of the tube on the arytenoid folds which reflexively close when touched. Push the tube past the closed vocal folds while rotating and exerting downward pressure. When the tube is inserted, the pig will cough reflexively, and will expel a large amount of air from the tube. Inflate the balloon, and connect the anesthetic machine. Tubes measuring 5 to 7 mm are commonly used for orotracheal intubation of adult pigs. Tubes as small as 2 to 4 mm in diameter are required for pigs weighing less than 2.5 to 5 kg.
Recommended endotracheal tube sizes for pigs of different body weights
Range of sizes
Range of body weights (kg) Range of french no. Range of diameter (mm) 0.5 to 1.5 8 to 12 2.5 to 4.0 4 to 6 14 to 16 4.5 to 5.2 8 to 18 18 to 22 6.0 to 7.0 20 to 26 20 to 24 6.5 to 8.0 30 to 40 26 to 30 8.5 to 10.0
Data are from Kumar, A, and McCullough, N, General anesthesia for newborn pigs, Lab Anim Sci, 29, 251, 1979.
CLINICAL TIP: DO NOT PERFORATE THE AIRWAY WITH THE SOVEREIGN CATHETER. INTRATHORACIC AIRWAY LEAKS RESULT IN EITHER PNEUMO- MEDIASTINUM OR TENSION PNEUMOTHORAX. PIGS WITH PNEUMOTHORAX GASP AND BECOME CYANOTIC WHILE UNDER ANESTHETIC. THE LUNG SOUNDS ON THE AFFECTED SIDE OF THE CHEST ARE ABSENT. THE AFFECTED PIGS REMAIN UNESTHETIZED DESPITE HIGH CONCENTRATIONS OF ANESTHETIC VAPOR.
(4) A ventral diverticulum anteroventral to the arytenoid fold, and a narrow, sigmoid airway are major obstacles for orotracheal intubation. Swine also have a deep pharyngeal diverticulum dorsal to the larynx. This structure may be lacerated during the intubation.