Sedation and field anaesthesia (TV4102, Lecture 27 Notes)

Provide the dosage for xylazine sedation protocols

Mild sedation: 0.02-0.04 mg/kg IV

Moderate sedation: 0.05-0.07 mg/kg IV

Deep sedation: 0.15-0.2 mg/kg IV

IM dose = IV dose × 2

List considerations of xyalzine sedation

- Very sensitive to xylazine (especially Brahmans)

- IV has faster onset (3min) and more intense level of chemical restraint and analgesia than IM (15min)

- Sensitivity is also affected by temperament and ambient temperature (especially in bulls)

- Effect lasts 30-60 minutes

- Depresses thermoregulatory mechanisms (consider hyperthermia or hypothermia)

List consequences of xyalzine sedation

- GI stasis can predispose to rumen tympany (bloat)

- Causes bradycardia, decreased cardiac output and lowered arterial blood pressure

- Abolishes swallowing reflex, regurgitation can result in pulmonary aspiration

- Causes marked salivation

- Increases uterine tone in pregnant animals (premature parturition in last month of pregnancy)

Discuss xylazine reversal

- Spontaneous recovery preferred

- Consider if prolonged recumbency, excessive cardiopulmonary depression or need for rapid recovery

- Tolazoline (difficult to source) or atipamazole (off-label use, no withholding periods established)

Discuss the ketamine stun

- Butorphanol (0.025 mg/kg ), some analgesia and degree of euphoria (off label-use)

- Xylazine (0.05 mg/kg ), low-dose sedative

- Ketamine (0.1 mg/kg ), provides dissociative component with amnesia, catalepsy and some analgesia

Catalepsy = diminished responsiveness usually characterised by atrance like state and constantly maintained immobility

Discuss caudal epidural with lignocaine and xylazine

- Longer duration of regional analgesia, as well as some degree of sedation

- Inclusion of xylazine extends the duration of caudal analgesia to 2-4 hours

- Xylazine (0.03 mg/kg LW) + 2% lignocaine (0.5 mL/50 kg LW)

Discuss high-volume caudal epidural with lignocaine and xylazine

- Combination of 2% lignocaine (1 mL/10kg LW) and xylazine(0.05 mg/kg LW)

- Abolishes sensation and function of the hindlimbs and abdominal region

- During recovery period animals are left undisturbed until recovery is complete

Discuss prevention of reguritation

- Withhold food for 24-36 hours

- Withhold water for 12 hours

- During recumbency, arrange head so that opening of the mouth is below level of the pharynx/larynx so saliva and regurgitated rumen contents can drain from the mouth (place wedge or cushion under the head-neck junction or mid-cervical region)

- When an endotracheal tube is used leave in place until animal is sitting up and withdrawing its tongue

Discuss approach to regurgitation

- Take all measures to sit the animal in sternal recumbency

- If the animal is severely bloated direct a tube into the oesophagus to relieve gas

*Passing a tube may stimulate more reflux and increase the risk of aspiration!

Discuss premedication

- Anticholinergic drugs not routinely used

Provide heavy sedation/anaesthesia

- Xylazine high dose IV

- Xylazine + Ketamine + ACP (one syringe)

- Xylazine IV sedation followed by Ketamine IV

- Triple drip, normal saline + ketamine + xylazine IV

- Xylazine + Ketamine IM (for very combative patients), followed by ketamine or 'triple drip' top-up IV

- High-volume caudal epidural

- Gaseous anaesthesia, using isoflurane or halothane

Describe xylazine high dose protocol

- Restrain cow in crush and head bail

- Apply halter and tie to secure post if possible

- Inject xylazine (0.2mg/kg IV) into the tail vein (or jugular vein)

- Release cow from crush fairly quickly, wait for cow to sit down, then roll her into lateral recumbency (right side if possible)

- May need to cast her, using ropes once in lateral recumbency, place a wedge or pillow under the head-neck junction

Describe xylazine/ACP/ketamine dose protocol

- Mix together in the same syringe

- Make sure whole dose goes IV

- During very hot weather, reduce dose by 20%

- Fractious, very stirred- up animals, increase dose by 10%

- Bos indicus bulls, decrease dose rates by 20-30%

- Top-up dose, ⅓ - ½ of original dose

Discuss endotrachel intubation

- Mouth gag placed first

- Digital palpation of the larynx

- Manually pull down on epiglottis and use finger to direct a guide tube (i.e. nasogastric tube) between the arytenoids into the larynx

- Direct endotracheal tube over the guide tube into the trachea

Discuss electro-immobilisation

- No anaesthesia or analgesia provided

- Procedures to examine eyes/mouth, checking ear tattoos, examining the penis and prepuce, and carrying out certain procedures such as replacing a prolapsed prepuce, cutting a persistent frenulum, removing warts or repairing preputial tears

Discuss monitoring

- Corneal reflex remains brisk

- Palpebral reflex may persist (depressed during inhalation anaesthesia)

- Eye rotates ventrally as aneasthesia deepens and only the sclera is seen, then rotates centrally during deep aneasthesia

Discuss lateral recumbency in bulls

- Choose the coolest time of the day

- Restrain in a crush, apply casting ropes (8-10 metres long) and halter, if possible

- Xylazine + ACP + Ketamine IV in one syringe (make sure to get full dose IV)

- Wait up to a minute, then coach bull out of the race/crush into a flat, open yard, don't wait too long

- If bull doesn't want to go down, pull on casting ropes

- Once down pull bull on to its side, pull the free end(s) of the casting rope out tight and tie off to a rail or post, hobble the back legs, have an assistant sit on the head/neck to keep bull down