Species Specific Anaesthesia - Ruminants & Pigs PDF

SPECIES SPECIFIC ANAESTHESIA – RUMINANTS & PIGS MIMV 3rd year – 1st semester 15 October 2024 Ricardo Felisberto, DVM, Dipl. ECVAA, MRCVS  RUMINANT ANAESTHETIC DIFFICULTIES Restraint and handling risks Body weight may not be adequately estimated Ruminal tympany (bloat) Re...

SPECIES SPECIFIC ANAESTHESIA – RUMINANTS & PIGS MIMV 3rd year – 1st semester 15 October 2024 Ricardo Felisberto, DVM, Dipl. ECVAA, MRCVS  RUMINANT ANAESTHETIC DIFFICULTIES Restraint and handling risks Body weight may not be adequately estimated Ruminal tympany (bloat) Regurgitation of reticuloruminal contents Aspiration of regurgitated material or saliva leading to aspiration pneumonia Hypoventilation (hypercapnia and possibly hypoxaemia) Hypotension Neuropathy / myopathy (the latter is less common in the more bony dairy cattle) Fluid and electrolyte imbalances (loss of bicarbonate and phosphate in saliva) Limited number of licenced drugs  LEGISLATION & LICENSING Very few licensed products Xylazine & Detomidine; ketamine Need to use the Cascade to anaesthetise a food animal Complex legislation Drugs must be listed in the ‘Allowed Annex’ (EN 37/2010) If not, animal must be withdrawn from food chain  FOOD WITHHOLDING No consensus for ruminants Withholding food for 18 to 24h = reduces ruminal fermentation and bloat. Withholding food for > 24h = ketoacidosis in high production cattle + reduced body core temperature + increased fluidity in the rumen (↑ chances of reflux and aspiration) Recommended timing = 6 to 12h For young milk-fed animals = do not starve them (due to risk of hypoglycaemia and dehydration)  PREMEDICATION Ruminants tend to be docile Consider which drugs are licenced and allowed to administer to cattle in the country The goals are the same for all animals Facilitate handling Improve recovery, maintenance and recovery qualities Provide analgesia Sparing effect (balanced anaesthesia) Reduce stress response Xylazine and detomidine licensed Sedation not really necessary, but it has anaesthetic sparing effect and analgesia  XYLAZINE Cattle very sensitive Predictable sedation Use 1/10th dose used in horses Analgesic Antagonisable (Atipamezole) Muscle relaxation, especially if using ketamine  XYLAZINE Use 0.05 – 0.1 mg kg-1 IV (off license!) 0.1 – 0.2 mg kg-1 IM Use lower doses if want standing sedation Often recumbency induced Some animals may be intubated under xylazine alone! Uterine contraction – Contraindicated in last trimester  DETOMIDINE Cattle equally sensitive to detomidine as the horse May be less likely to induce recumbency Less effect on uterine tone Analgesic Antagonisable 10 – 40 µg kg-1 IM or IV (higher dose IM)  ACEPROMAZINE Unreliable No analgesia May increase likelihood of regurgitation Can severely prolong recovery  COMMON BOVINE ANAESTHETIC PROTOCOLS Adults: Xylazine 0.2 mg kg-1 IM → intubation → deepen with inhalation agent Xylazine 0.2 mg kg-1 IM followed by ketamine 2 mg kg-1 IV Calves: Xylazine 0.2 mg kg-1 + ketamine10 mg kg-1 mixed in same syringe IM (or 5 mg kg-1 ketamine IV following xylazine IM)  CHLORAL HYDRATE IN CATTLE Not licensed but still widely used by some practices (superceded by xylazine) ‘Basal narcotic’, narrow therapeutic window IV solution given by infusion to effect Metabolised in vivo to trichloroethanol (active agent) Delay between administration and peak effect → potential to overdose Therapeutic level very close to toxic level TAKE CARE!  ANAESTHETIC MAINTENANCE Inhalational anaesthesia using any volatile Not nitrous oxide Triple drip techniques Chloral hydrate? Positioning: padded table; avoid too much pressure against superficial nerves (facial nerve)  PREMEDICATION - SMALL RUMINANTS Restraint is seldom a problem Therefore, premedication commonly omitted If used, likely to prolong recovery  XYLAZINE - SMALL RUMINANTS 0.2 mg kg -1 IM xylazine gives good sedation in sheep Goats more sensitive: 0.05 mg kg -1 IM usually adequate Slow IV injection probably better in both species: up to 0.15 mg kg -1 IV in sheep; 0.01 mg kg -1 IV usually sufficient in goats  XYLAZINE - SMALL RUMINANTS Profound hypoxaemia may occur in some animals Pulmonary oedema has been reported in some sheep given xylazine – due to pulmonary hypertension Sedation reversible with atipamezole  BENZODIAZEPINES - SMALL RUMINANTS Benzodiazepines provide good and predictable sedation in small ruminants Diazepam 0.5 -1 mg kg-1 IV or up to 2 mg kg-1 IM provides excellent sedation in sheep and goats  COMMON SMALL RUMINANT ANAESTHETIC PROTOCOLS 0.2 - 0.5 mg kg-1 diazepam IV followed by 2 - 5 mg kg-1 ketamine IV 0.2 mg kg-1 xylazine + 15 mg kg-1 ketamine mixed in the same syringe and given IM  ANALGESIA FOR RUMINANTS Tricky No opioids licensed Some NSAIDs licensed Use cascade and annexes Butorphanol is the only opioid in allowed annex (Regulation - 37/2010 - EN - EUR-Lex (europa.eu)) Utilise regional techniques where possible Pain recognition???? There are only 2 validated pain scales in large ruminants (both for acute pain): UNESP-Botucatu unidimensional composite pain scale - cattle (de Oliveira et al. 2014) Cow Pain Scale (Gleerup et al. 2015) Equally, there only 2 validated pain scales in small ruminants (sheep) (for acute postoperative pain): UNESP-Botucatu composite scale in sheep (Silva et al. 2020) Sheep grimace scale (Häger et al. 2017)  REGIONAL ANALGESIC TECHNIQUES Epidural analgesia and anaesthesia Intravenous Regional anaesthesia (extremities) Head blocks Cornual (disbudding) Petersen (whole of ipsilateral face) Retrobulbar (enucleation) Flank blocks Line Inverted L (flank surgery) Paravertebral (flank surgery)  RUMINANTS ANAESTHETIC CHALLENGES Endotracheal intubation Regurgitation Abdominal tympany Hypoventilation Salivation  INTUBATION OF RUMINANTS Small ruminants and young calves can be very difficult. Essential to have skilled assistance Use a laryngoscope with a long straight blade Use a ‘bougie’ or stylet to railroad the endotracheal tube over  INTUBATION OF RUMINANTS Adult cattle relatively easy Palpate larynx orally Guide endotracheal tube using fingers into larynx Small hands and arms an advantage! Can be intubated blind as in horses but 50% success rate Do not advance the ETT too deep into the trachea because the cuff may occlude the tracheal bronchus (ruminants and pigs)  REGURGITATION Intubation strongly advised – ensure adequate depth of anaesthesia Facilitates protection of airway Inflate cuff! If intubation not possible place a wedge under neck to lower the mouth, can also be done on recovery from anaesthesia  ABDOMINAL TYMPANY Will undoubtedly occur over time – eructation obtunded by anaesthesia GI motility depressed by α2agonists More problematic during lengthy procedures Some advocate placement of a rumen tube to release gas May have knock-on effect on respiratory system  HYPOVENTILATION & VQ MISMATCH May be a problem in conscious sedated animals too Hypercapnia and hypoxaemia may develop Hypoxaemia especially if breathing room air Due to respiratory muscles relaxation and respiratory centre depression If positive pressure is to be applied, do not exceed peak inspiratory pressure of 25 cmH2O because cattle’s lungs contain less fibrous connective tissue than the horses lungs, making them more prone to rupture and cause pneumothorax. Recumbency → splinting of the diaphragm against the lungs by the large abdominal viscera → atelectasis and hypoxaemia +/- hypoventilation Cattle and pigs have intense hypoxic pulmonary vasoconstriction; thus, inhibiting it with inhalational anaesthesia, may contribute significantly to V/Q mismatch.  SALIVATION Adult cattle can produce 50L saliva per 24 hours; Sheep 16 L Some have advocated anticholinergics (drying agents) Make saliva more viscid and difficult to clear Anticholinergics are ONLY indicated for treatment of bradycardia Position head correctly to facilitate drainage Electrolyte derangement may develop with excessive bicarbonate loss  RUMINANT MAINTENANCE Any volatile suitable but only isoflurane in annexes (EU 37/2010) Respiration generally fast and shallow as anaesthesia proceeds Hypercapnia is common Blood pressure usually well maintained IV fluids required to replace copious salivary losses  RUMINANT RECOVERY Due to high incidence of regurgitation under anaesthesia, ET tube should be removed LATE with cuff partially inflated. Support in sternal recumbency as soon as possible Recoveries are normally quiet and calm  PIGS Porcine preparation / premedication: Withhold food for 8 - 12 hrs water for 6 hrs Good pre-op examination may be impossible Sedation always necessary in adult pigs prior to anaesthesia  AZAPERONE Butyrophenone Cheap and effective Causes mild vasodilation (hypothermia) and respiratory stimulation 1 - 8 mg kg -1 IM (boars 1 mg kg -1 IM max.) Sedation obvious within 20 mins ESSENTIAL TO LEAVE QUIETLY  PIGS - OTHER SEDATIVES α2 agonists offset effects of ketamine, but do not produce reliable sedation in pigs ACP causes less profound sedation than azaperone, but will reduce squealing Ketamine - very useful!  PIGS AND ANTICHOLINERGICS Pigs have small airways relative to their size Atropine is often recommended for pigs prior to induction of anaesthesia (~0.04 mg kg-1) as an antisialogogue  COMMON PIG ANAESTHETIC PROTOCOLS 2 mg kg -1 azaperone + 2 - 5 mg kg-1 ketamine mixed IM followed by 0.2 mg kg -1 midazolam + ~2 mg kg -1 ketamine mixed IV Midazolam 0.2 mg kg -1 with ketamine 5 mg kg-1 deep IM Detomidine 100 µg kg -1 + butorphanol 0.2 mg kg -1 + ketamine 5 mg kg -1 mixed and given IM Maintenance of anaesthesia: only Isoflurane on the allowed annex; but the choice between inhalant anaesthesia vs total intravenous anaesthesia depends of facilities, equipment and familiarity with techniques.  PIGS ANAESTHETIC CHALLENGES Licensed drugs (similar to ruminants) Restraint (challenging, noisy, fast) IM injection (thick layer of subcutaneous fat, long needle to reach muscle; use remote injection technique; inject behind ears) IV access (relatively easy in the auricular vein; jugular catheterisation is very difficult) Intubation (narrow oral cavity, difficult to open mouth; thick fleshy tongue; pharyngeal diverticulum; small rima glottidis; tilted larynx; convoluted proximal trachea; narrow trachea; laryngeal spasm) Respiratory depression (respiratory depression; muscle relaxation) Body temperature (hypothermia is common as azaperone is vasodilator; hairless; large skin surface area, thus high heat dissipation; provide active warming for long anaesthesia) Malignant hyperthermia  MALIGNANT HYPERTHERMIA It’s an uncommon pharmacogenetic biochemical myopathy which manifests itself during general anaesthesia with some anaesthetic and ancillary agents Larger incidence in certain breeds overrepresented: Poland China Pietrain Landrace Large White But can occur in any breed (and any species!)  Abnormal receptor (ryanodine 1) which, once triggered remains opened for longer and leads to excessive intracellular calcium concentration and enhanced muscle contraction (fasciculations) Enhanced excitation-contraction coupling  MALIGNANT HYPERTHERMIA Triggers for malignant hyperthermia: Halothane (but other inhalant agents may also be involved) Succinylcholine Clinical signs: Generalised muscle rigidity (starts at the toes) Blotchy (spotted) skin Severe and sustained temperature rise Hyperkalaemia Hypercapnia Metabolic acidosis  MALIGNANT HYPERTHERMIA Treatment: Remove all inhalant anaesthetics, replace breathing system, soda lime canister, replace inhalant anaesthesia for total intravenous anaesthesia, promote mechanical ventilation to decrease arterial carbon dioxide Promote active cooling Dantrolene (post-synaptic muscle relaxant that reduces excitation- contraction coupling; inhibits calcium release from the sarcoplasmic reticulum by inhibiting ryanodine-sensitive calcium channels (2-10 mg/kg IV) Check for electrolytes (hyperkalaemia may develop and require treatment) Administer sodium bicarbonate if severe acidaemia, low bicarbonate and low base excess