Test 1- Equine Anesthesia

Question 1

General Concerns of Anesthesia

Answer 1

• Anesthetized horses – due to size subject to significant hypoventilation and possible hypoxemia- atelectasis;ventilation/ pulmonary mismatch
• Heavy horses, heavily muscled -improper positioning and padding can lead to muscle myositis or nerve paralysis
• Proper and vigilant monitoring of vital signs necessary to prevent/recognize hypotension and other abnormalities in order to institute corrective measures in a timely manner

Question 2

Evaluation

Answer 2

• Good history –
• Exercise capacity – poor performance may be associated with cardiac or pulmonary disease
• Quarter Horse- genetic testing HYPP
• Past episodes of exertional

rhabdomyolysis – increased risk of post –operative myositis

• History of drug reactions? – ie. antibiotics

Question 3

HYPP

Answer 3

Hyperkalemic Periodic Paralysis

Inheritable disease of a genetic defect in Na channels of muscle in QH ( ~4% of all QH)

• Point mutation in Na channel gene – results in ‘leaky’ channel leading to inability to regulate K levels in blood
• Muscle excitability, muscle tremors; weakness –respiratory failure; hyperkalemia- fatal
• Maintenance or recovery phase
• Pre-operative acetazolamide-( diuretic – helps excretion K) - be prepared for hyperkalemia treatment ( Ca+; Na HCO3; glucose/insulin)

Question 4

Preparation

Answer 4

14 ga long IV catheter should be placed in the jugular for standing surgical procedures as well as for general anesthesia – including field anesthesia ideally

• Proper clip and surgical prep necessary
• Lidocaine bleb; small stab incision with blade or 14 ga needle

Question 5

What do you need to avoid when placing a jugular catheter?

Answer 5

AVOID THE CAROTID ARTERY

An injection of xylazine into the carotid artery – will produce violent reaction, possible seizure

Question 6

Preparation

Answer 6

• No grain 24 hr –hay withheld 6 hrs, but water always- However some still fast for 8- 12 hrs
• Shoes should be removed ( general anesthesia ) and soles are picked and washed; horse brushed to remove surface dirt; straw, etc
• Most people wrap all legs for protection
• If intubation is planned rinse mouth ( dose syringe) with water until no evidence of hay runs out
• Antibiotics – generally are given immediately before or during premedication

Question 7

Sedatives

Answer 7

Alpha 2 agonists – most effective sedation/ restraint in the equid

• Duration of action detomidine > ;

romifidine> xylazine ( all approved for equine)

• Dexmedetomidine is sometimes used as CRI intraoperatively ( not approved for equine)

Question 8

Xylazine Vs Detomidine

Answer 8

Question 9

Ace

Answer 9

Mild sedation; indifference to suroundings –but unpredictable calming -given prior to α2 agonist sedation – not a replacement

• Will potentiate effects of other sedatives
• 0.02-0.05 mg /kg IM ( 0.01-0.03mg/kg IV) – can use with

Xylazine 20 - 30 min after Acp

• Avoid in ill/cardiovascular compromised horses; young foals
• Caution in breeding stallions – possible persistent penile paralysis ( < 1 in 10,000)
• Excited stressed horses - - more prone to hypotension (circulated epinephrine β2 vasodilation )

Question 10

Opiods

Answer 10

• Opioids, although are used for analgesia, do not result in the quality of sedation as seen in dogs and should never be used alone in the equid
• •

•

Increased motor activity; sweating; excitement side effects if dosage rate is too high (rates are lower than in small animals)

Pure agonists – controversial – susceptable to colic? ( but can be used) – but may produce ileus; constipation- usually from high or repeated dosages

but α2s also have similar effects

Question 11

A Word about Ketamine

Answer 11

• Dissociative anesthetic –produces cateleptic state - trance, loss of sensation and consciousness with muscle regidity
• All animals but especially equids – must be well sedated before ketamine – otherwise, excitation, seizure –like activity may occur
• Eyes remain open; palpebral often present; which makes depth evaluation a little difficult to evalute
• Often we include diazepam ( midazolam) with the ketamine induction even after the xylazine- improved muscle relaxation
• Xyl + butorphanol – then diazepam and ketamine
• Ketamine/diazepam inductions are the preferred induction for equids by most – small volume( 10-15 ml) given rapidly; consistent, reliable fall ‘dog sit ‘

Question 12

Adequately sedated horse

Answer 12

• Dropped head
• Extruded penis
• Horse – obligate nose breather – avoid nasal edema must keep/hold head up

Question 13

Injectable anesthesia- #1 castration

Answer 13

• Xylazine1.1waitforsedation+ ketamine 2.2 mg/kg IVmg/kg ketamine)
• 10-20 minutes anesthesia
• Add butorphanol -0.02-0.05 mg/kg IV –after the xylazine ( ~ 1/10 of dog dose) increases duration ~30-35 min ; better quality sedation
• Morphine 0.1 mg/kg – not as good sedation, IMO
• ‘Top up doses’ – ketamine/ xylazine 1/3 -1/2 original doses – 10-15 min

Question 14

Guaifenesin (GG)

Answer 14

GG 5 % centrally acting muscle relaxant – no/very little sedation/no analgesia

• Will cause serious tissue necrosis if not in vein!!!!!
• To improve quality of induction; muscle relaxation; reduces dosage rate of the anesthetic
• No/minimal cardiovascular or respiratory depression unless very high dosages ( > 100 mg/kg )

Question 15

Triple Drip ‘

Answer 15

Add to 500 ml GG 5 %: 500 mg ketamine and 250 mg xylazine

Start immediately after induction – at 1-1.5 ml/kg/ hr ( or to effect by maintaining adequate depth

Respiration and hemodynamic values usually remain normal limits unless excessive GG dose

Question 16

Intubation in a horse

Answer 16

• Check pulses and color-!

• Head extended – blind intubation

• PVC pipe –mouth speculum
• Advance and rotate tube , aiming‘up’- if resistance pull back and try again
• Usually falls right in; inflate cuff

Question 18

Where do you place the arterial catheter in a horse?

Answer 18

Transverse facial, facial, dorsal metatarsal

Question 19

Expected- normal values for anesthesia

Answer 19

HR – ⊀ 25 ⊁60 bpm – prefer 35-45 bpm Ventilator -6-8 bpm with a tidal volume ~10

ml/kg to maintain ETCO2 30-35 mmHg • PaCO2 will be ~ 5-10 mmHg higher

Keep MAP at least 70 mmHg
Expect SPO2 –> 97 ( should be 100%) Arterial blood gas to confirm PaO2 , PCO2

Question 20

Hypercarbia/hypoxemia

Answer 20

Horses will hypoventilate the longer they are down and hypercarbia worsens with time- unless on a ventilator

• If no oxygen is provided- hypoxemia will develop –
• Reason why injectable/field procedures should not exceed ~1 hr ( if no oxygen and ventilatory measures are available)
• General anesthesia – if procedures > 1 hr- horses should ventilated to maintain PaCO2
• However, anesthetized large animals may ( often) develop significant ventilation/perfusion mismatch- which may result in hypoxemia – even on 100% oxygen
• Reason we evaluate blood gases

Question 21

What is the recovery rate in horses like?

Answer 21

recovery complication rate is the highest among species