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anesthesia for horses

Discussion in 'Anesthesiology' started by 2win, Nov 8, 2009.

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  1. 2win

    2win

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    Interesting read - http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1780238/


    A 12-hour preoperative fast was followed by placement of an IV catheter in the right jugular vein. Preoperatively, gentamicin sulfate (Gentamicin 100 mg/mL; The Butler Company, Dublin, Ohio, USA), 6.6 mg/kg body weight (BW), sodium penicillin (Crystapen 40 000 IU/mL; Bioniche pharma, Belleville, Ontario), 20 000 IU/kg BW, and phenylbutazone (Univet 200 mg/mL, Pharmaceuticals, Milton, Ontario), 4.4 mg/kg BW, were administered, IV. The horse was sedated with xylazine HCl (Xylamax 100 mg/mL; Bimeda MTC Animal Health, Cambridge, Ontario), 0.3 mg/kg BW, IV, and butorphanol tartrate (Torbugesic 10 mg/mL; Fort Dodge Animal Health, Iowa, USA), 0.07 mg/kg BW, IV. Profound sedation was evident after 5 min. General anesthesia was induced with ketamine HCl (Vetalar 115.4 mg/mL; Veterpharm Canada, London, Ontario), 2 mg/kg BW, IV, and diazepam (Diazepam 5 mg/mL; SABEX, Boucherville, Quebec), 0.3 mg/kg BW, IV. Blind oral intubation in left lateral recumbency was attempted with a 12-mm ID cuffed endotracheal tube. Several attempts to intubate were unsuccessful. Several smaller tubes were utilized in an attempt to secure the airway either orally or nasally. Both nasal openings were so small that insertion of the primary author’s 5th digit, in an attempt to intubate nasally, was impossible. The diameter of the nasal passage was estimated to be 6-mm. Two boluses of ketamine HCl (20 mg each) were administered, IV. Visual intubation, with the horse in sternal recumbency, using a large blade laryngoscope, polypropylene rigid stylet, and 8-mm ID endotracheal tube was attempted. Another 20 mg bolus of ketamine HCl was administered, IV, and the mouth held open. Abduction of the mandible by using both manual retraction and a small 5-cm polypropylene mouth gag was limited. On visual examination of the oral cavity, the tongue appeared to be fleshy and larger than normal, relative to the size of the oral cavity. In addition, the soft palate appeared to be excessively large in proportion to the oral cavity, partially obstructing visualization of epiglottis and the arytenoid cartilages. After repeated intubation attempts, the horse became cyanotic, so intubation was delayed and 100% oxygen was administered via a facemask.
    A video endoscope was passed, PO, with the horse in sternal recumbency, after preoxygenating for 10 min and administering an additional 20 mg of ketamine HCl, IV. The epiglottis was large, markedly thickened, and partially obscured by the soft palate. Both arytenoid cartilages were markedly thickened, but they abducted equally on inspiration and surrounded a very small glottis (Figure 2). A rigid styl[​IMG]et was advanced between the arytenoid cartilages as a guide and a 7.5-mm ID endotracheal tube (34 cm, length) was advanced over the stylet into the trachea. The endotracheal tube fit snugly and had to be carefully manipulated through the larynx. The area corresponding anatomically to the cricoid cartilage impeded the passage of the endotracheal tube. The rostral part of the larynx appeared to be funnel shaped, with the narrowest portion caudal to the vocal folds and within the cricoid ring. Caudal to the cricoid ring, the tracheal diameter was somewhat larger than that of the larynx. Once in place, the endotracheal tube cuff required 6 mL of air to form a secure seal with the trachea."

    And here an intubated bat:
    http://www.anaes.med.usyd.edu.au/images/ACVA/Egyptian-fruit-bat.jpg
    :laugh:
  2. nimbus

    nimbus Member Gold Donor

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    My daughter's hunter/jumper has had the xylazine/butorphanol cocktail a couple of times for minor procedures. Xylazine is alpha2 agonist like clonidine and precedex. Worked really well-- profound sedation, ventilation maintained, and appears to be gone after an hour or two. Thankfully he has not needed anything major in the time we've had him.
  3. jwk

    jwk AA-C ASA-PAC Contributor

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    Interesting read - horse intubations are usually not that difficult as I recall. The normal-sized tube for adult horses is in the 26-36mmID range, and the tube is passed manually into the trachea. The tricky part apparently is that space is tight, so you have to grasp the tube, advance it into the trachea, and then get your hand back out before it starts to go numb from pressure from all the surrounding tissue.

    Vet anesthesia, particularly large or exotic animals, is an absolutely fascinating subject. If you're able, spend a day at a vet school, or have a veterinary anesthesiologist give an inservice to your departement. I guarantee you they will have some pictures that will amaze you!
  4. nimbus

    nimbus Member Gold Donor

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    One of my co-residents helped out at the local zoo on a regular basis. He's even anesthetized a baby orangutan for ASD repair w/CPB. She had a rocky postop course but made a full recovery. He told me the snakes made him particularly nervous because their heartrate could drop to 1 or 2 BPM under anesthesia. It was a long wait for the next heartbeat to find out if the patient was still alive or dead.
  5. Gimlet

    Gimlet Cardiac Anesthesiologist

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    That's crazy, nimbus!

    In the Aug 2009 ASA Newsletter there was an article by an anesthesiologist in Michigan who was asked to help anesthetize three Western Lowland gorillas (endangered species) for TEE. He was told he was only needed for "assistance," because a veterinary anesthesiologist would be there, but on the day of surgery the vet anesthesiologist turned out to be a 1st year resident in her 2nd week of training!

    Page 26: http://www.asahq.org/Newsletters/Aug09NL_Mobile.pdf
  6. 2win

    2win

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    Indeed, the subject is amazing...
    How do you use xylazine +ketamine? Thx
  7. eventualeventer

    eventualeventer Bird Nerd C/O 2015

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    I have also seen horses intubated without tactile cues, just sticking the tube down there. The cats and dogs I've seen anesthetized were also intubated by tilting the head and sticking the ETT in with a flashlight for visualization.

    I agree, it is fascinating to watch large animal anesthesia (large meaning a real sized horse, not a weanling who is smaller than typical for a miniature breed!). They have to start out and end up upright, as opposed to lying in a hospital bed, so induction and recovery are that much more complicated than even a dog or cat. A rough recovery can kill a horse - if they thrash or try to stand while they are still too ataxic, they can cause irreparable fractures.

    2win, I'm not a vet or MD, but I've seen a number of horses anesthetized, so I'll try to explain what I've seen and then someone with more experience can fill in the blanks. I'm assuming you were asking about xylazine/ketamine in horses/large animals, right?

    Xylazine is given (1 mg/kg IV, 2-4x the dose used for standing sedation) until the horse is profoundly sedated. It may take 3-5 minutes for the sedation to reach full effect. They usually have their head hanging almost on the ground and are mildly ataxic (they sway back and forth a bit but are still able to keep their balance). They will wake up partway if stimulated but quickly go back to dozing. Once they reach this point of sedation, ketamine (2-2.5 mg/kg) is given. Ideally, the horse starts to "go under" quite rapidly and you gently push their head up as they sit down on their haunches and then buckle in front and become laterally recumbent.

    One of the most interesting cases of anesthetic weirdness I've seen was in a yearling filly who had cut her leg on a fence. The vet attempted to repair the laceration under standing sedation but the filly was *cough* uncooperative (i.e., he could not even get it cleaned and blocked). Several doses of detomidine/butorphanol sedation were given but the filly remained awake enough to kick out. The decision was made to try to anesthetize her fully for treatment of the leg; I *think* additional detomidine was given, and she was led to a stall. When the ketamine was given, she did not sit back and lie down as expected, but started leaning forward on to the person holding her head (i.e., me). She continued leaning forward and made no attempt to go down, so another dose of ketamine was given. She lurched towards the corner of the stall and kept leaning forward; she was in such an awkward position that the vet was worried she would break her neck falling forward against the wall. The attempt at anesthesia was abandoned and we managed to get halter and tail ropes on her and over the stall walls so that we could support her until she recovered. She was anesthetized the next day with no complications. I wonder if this inability to anesthetize her with ketamine was due to inadequate premedication (she had been sedated but she repeatedly overcame the sedation when stimulated) or some sort of response to the repeated stimulation that interfered with the effects of the drugs. Any thoughts?
  8. Bertelman

    Bertelman Maverick!

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    You bet. I'm thankful I reconsidered my career choice to become a vet.
  9. amyl

    amyl ASA Member

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    jumper? me too. my horse vet uses a bier block technique w a bisphosponate to prevent the progression of degenerative OA. Barbaro (the derby winner a few years back who broke his leg) was supposedly managed w epidurals for pain. horses are particularly interesting, esp in that the typical narcotics, fentanyl, etc are not options. horses have a one way GI tract. ileus can be fatal and often requires surgery with significant morbidity (ie: likely end of performance career) and mortality. vets are picking up lots of anes-based tricks...
  10. eventualeventer

    eventualeventer Bird Nerd C/O 2015

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    Yup, I've seen a couple horses who had intermittently dosed epidurals for pain (only alpha-2 agonists and opiates, no LA). Mila makes a "bubble" that you can put 100cc's of solution into that you attach to the epidural catheter and tape to the horse's back for an epidural CRI, but I haven't seen it used.

    Butorphanol CRI's are used sometimes and the horses seem to do well, but morphine can make them very agitated. I have seen fentanyl patches used in horses with laminitis, but they didn't do jack. They may not have been dosed high enough, though. Generally, the pain control algorithm seems to go NSAIDs --> lidocaine CRI (also used after every abdominal surgery as a prokinetic) --> butorphanol CRI --> detomidine CRI. Low-dose ketamine CRI's have been described in the literature, but I have not met any vets who have used them in horses. DMSO is used a lot as a supposed anti-inflammatory and anti-oxidant, including in some horses with chronic conditions like laminitis.

    Fortunately, horses do not pester you for drugs, although one horse who had an epidural catheter in for multiple days would turn around and back up towards the resident when he entered the stall for her morning dose.

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