Ruminant Anesthesia

Last updated on November 12, 2001

Special considerations with ruminants

Local and spinal anesthesia

Sedation and premedication

General anesthesia

Anesthetic Maintenance

Anesthetic Monitoring

Analgesia

Problems with ruminant anesthesia

1. Ventilation: rumen dilates and causes hypoventilation. Can be minimized by 24-48 hour fast and/or sulfa boluses to cut down flora somewhat. During surgery a stomach tube can be placed or a trocar. Hypoventilation in sheep=PaCO2>55 mm Hg, for cattle >70 mm Hg. Hypoxia in sheep at PaO2<70 mm Hg, cattle <60 mm Hg.{4206}

2. Regurgitation{4206}

Active: explosive discharge, caused by trying to intubate when too light

Passive: dribbles constantly, caused by too deep anesthesia which relaxes the sphincter

3. Salivation{4206}

Atropine works for only 5 minutes, and thickens secretions too much. Use glycopyrrolate if needed for bradycardia or vagal stimulation.

4. Postanesthetic myopathy/neuropathy: prevent with padding and positioning{4206}

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Local and spinal anesthesia

1. Lidocaine (with epi for regional, without epi for spinal) has rapid onset and short duration (60-90 minutes)

2. Bupivacaine has slower onset but longer duration (4-6 hours)

3. Regional blocks work well but are technically harder to do. Toxicity signs are twitching and seizures progressing to depression, hypoventilation, tachycardia, and cardiovascular collapse. Use for castration and dehorning.

4. Spinal anesthesia is easy at the L6-7 or lumbosacral interspace. Do not use in adult cattle as they don't like the paralysis of hind legs. Epidural is harder to achieve and requires 1/3 higher dose.{4206}

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Sedation and Premedication

1. Goats more likely to become distressed and vocalize than sheep or cattle. Diazepam 5-10mg IV helps, as does local infiltration of lidocaine.{4206}

2. Phenothiazines: ace works well for mild sedation and prolongs recovery from other anesthetics. Good in pregnant ruminants because uterine blood flow is maintained. Minimal cardiac depression although blood pressure decreases.{4206}

3. Alpha-adrenergic agonists: profound sedation but good analgesia. Undesirable side effects limit usefulness (bradycardia, second degree AV block, hypotension, decreased cardiac output, hyperglycemia, bloat, diuresis, disturbed thermoregulation). Reverse with idazoxan, tolazoline, atipamezole. Reversal useful if these drugs are used to provide restraint for brief procedures.{4206}

4. Benzodiazepines

Diazepam works well in sheep; midazolam works better and faster to produce recumbency. Flumazenil reverses midazolam and they jump up like a shot.{4206}

5. Pentobarbital works well as a sedative in low doses (2mg/kg IV){4206}

6. Chloral hydrate: reliable sedative often used orally in cattle that are wild{4206}

7. Opioids: poor analgesia if any, shorter duration than in dogs. Not really recommended for small ruminants.{4206}

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General Anesthesia

1. Barbiturates

Pentobarbital still a good drug in ruminants, and may be good enough analgesia for surgical procedures.{4206}

Thiopental is good for short knock-down for imaging. Ruminants eliminate it quickly because of large amount of muscle. Longer duration in goats due to less muscle mass. May produce more regurgitation and salivation.{4206}

2. Propofol depresses cardiac output less than thiopental in sheep, and causes transient apnea and hypotension if given too fast. Need analgesic along with it for surgical procedures.{4206}

3. Ketamine combos

Ketamine/xylazine: slowest recovery to standing of all single-dose techniques which limits its usefulness. Supplement with oxygen to combat hypoxemia. Lower dose (2.2mg/kg ketamine and 0.1mg/kg xylazine) still induces anesthesia but has shorter duration and fewer side effects.{4206}

Ketamine/diazepam IV (2.75mg/kg and 0.2mg/kg) is preferred induction of sheep at CSU. There is little cardiopulmonary dysfunction, small volumes of drugs are used, recover in 15-20 minutes. Higher doses (approximately double) used by others result in slight decrease in cardiac output and transient hypotension and hypoxemia.{4206}

Ketamine/midazolam worked well in one-month-old lambs, maintained on halothane. Buprenorphine and flunixin were used for analgesia.{3540}

4. Telazol (12-24mg/kg IV) has few advantages over ketamine cocktails. Sheep take over 2 hours to recover, calves were down for 60 minutes on a single dose. Depresses cardiac output, blood pressure, ventilation and PaO₂, and increases systemic vascular resistance. Does work well in capture guns for cattle.{4206}

5. Guaifenesin works well for induction when combined with either ketamine, propofol or thiopental.{4206}

6. Induction with halothane or isoflurane can be achieved with a face mask or nasotracheal tube.{4206}

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Anesthetic Maintenance

1. Inhalants work best, particularly isoflurane which maintains cardiac output. Neonatal ruminants' cardiac output is heart-rate dependent (like NHPs). However, there may be more hypoventilation than with halothane because respiratory rate is slower with isoflurane.{4206}

2. Triple drip (guaifenesin, xylazine and ketamine) works well for short procedures.{4206}

Anesthetic Monitoring

1. Signs: chewing in response to stimulation, regurgitation, eye position and corneal reflex, in that order, sort of. Eye is dorsolateral in lightly-anesthetized sheep, returning to forward and dilated when adequately anesthetized.{4206}

2. Systolic blood pressure is the most accurate indirect measurement. Roughly, MAP should remain >60 mm Hg to prevent hypotension. Dobutamine is most potent and effective for hypotension, but ephedrine is less arrhythmogenic and easier to administer.{4206}

3. Ventilation: end-tidal CO₂ checked against periodic arterial gases.

4. Pulse oximetry: keep SaO₂ > 90%.

5. Blood loss of 25% of blood volume (which is 7-8% of body weight) can be tolerated. If transfused, do cross-match for safety.{4206}

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Analgesia

1. Signs of pain: altered feeding pattern, decreased intake, lagging behind herd, abnormal gait or posture, reluctance to flee when human in flight zone. Goats may vocalize but sheep and cattle don't.{4206}

2. Pre-emptive analgesia works because of either altered sensitivity of peripheral nociceptors or altered excitability of CNS neurons.{4206}

3. Opioids don't work well, possibly because sheep have different distribution and density of receptors in the CNS.{4206}

4. Alpha adrenergic agonists work well in sheep. Clonidine lasts 1-2 hours.

5. NSAIDS: flunixin and dipyrone are effective in sheep. Phenylbutazone seems to work in cattle and sheep. Carprofen is a novel NSAID with a long half-life in sheep (48-72 hours) that apparently works as well as flunixin or dipyrone.{4206}

6. Local or regional anesthetics

7. Spinal analgesia: not opioids in sheep, but morphine may work in goats. Xylazine works well in sheep but not in cattle because there is some hindlimb ataxia which they don't like.{4206}

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