Equine Anaesthesia & analgesia COPY Flashcards
What drugs used in staning sedation?
How do we ‘top up’ duration of sedation?
- ‘Top up IV
Alpha 2 agonist infusion (detomidine, xylazine or romifidine)
AEs of Sedation? - Alpha 2 effects
- Sweating
- Ataxia
- Sinus bradycardia, 1st & 2nd degree AVB, respiratory depression
- Increased urination
- Ileus, oesophageal choke (Starve for a couple of hours after sedation)
- Gas distension, colic (repeated administration)
- Tachypnoea in febrile horses.
- Localised inflammatory response if drug accidently injected s/c or
peri-vascular - Horses can appear profoundly sedated but still startle and react with
well-directed kicks - Individual/breed differences in susceptibility – eg draft breeds very
sensitive to sedation
AEs of sedation with opioids?
- Ileus, Impaction colic
- Horse can startle
Describe sedation of foals under 2 weeks old ?
- Cardiac output directly related to heart rate: hypotension occurs quickly
- Avoid alpha-2 agonists due to cardiovascular effects
- Benzodiazepines and opioid combination readily causes recumbency
Multimodal analgesia - waht NSAIDS for equine?
Phenylbutazone, suxibutazone, fluxinin, melocixam, firocoxib, carprofen
What opioids in multimodal A?
Butorphanol, Morphine, Buprenorphine, Pethidine, Methadone
What locals can we. use?
Lidocaine, mepivicaine or bupivicaine
What adjunct analgesia ?
-> Infusions (of individual drugs or combinations)
-> Alpha 2
-> Paracetamol
-> Gabapentin
What does CEPEF stand for?
Confidential Inquiry into Perioperative Equine fatalities
What did SEPEF find was mortality within 7 d of procedure?
- All Patients: 1% (Prev 1.9%)
- ‘Noncolic’ patients: 0.6% (Prev 0.9%)
- ‘Colic’ patients: 3.4% (Prev 7.8%)
- Standing sedation 0.2%
- Causes: Fracture in recovery, post-operative colic, others
- Highest numbers of deaths during recovery
What factors increase the risk of Death ?
Total inhalant anaesthesia
Duration >2 hours
Increasing adult age
Out of hours anaesthesia
Midnight to 6am x 7.61
6pm to midnight x 2.15
Weekend x 1.52
Higher ASA physical status grade
Lack of premedication
What decreases risk of mortality?
Total intravenous anaesthesia (TIVA)
Duration <2 hours
Acepromazine premedication
What are some common Anaesthesia- associated complications?
- Fractures, joint dislocation
- Post-op colic, Post-anaesthetic ileus
- Cardiac arrest, cardiac arrhythmia
- Upper airway obstruction, Nasal Oedema, laryngeal paralysis
- Endotracheal tube complications
- Pulmonary oedema
- Post anaesthetic myopathy
- Neuropathy
- Spinal cord myelopathy or cerebral necrosis
- Hypoxaemia
- Hypotension
What complication from arterial and venous cannulation?
Venous thrombophlebitis
Inadvertant placement of venous cannula into caroti Artery
Exsanguination and air embolism
Accidental breaking, cutting of canula or loss of guidewire
What contributing factors to anaesthetic -associated complications?
- PAtient positioning
- Anaesthetic drugs
- Mechanical ventilation
- Pre-existing dx
- Human error
What common fractures during recovery?
Tibia, carpus, radius most common
Who gets more fractures?
Older TB mares over-represented - reduced bone density in PP mares?
What can they get as result of fractures during recovery?
- Reduced limb strength after repair
- Fatigue in severely ill horses
- Fracture of contralateral limb after fracture repair
- Also join luxations/ dislocations
What is the most common cause of peri-anaesthetic death?
Cardiac arrest
Risk factors to upper airwar obstruction?
- PRe existing left laryngeal hemiplegia
- Large body mass
- Prolonged anaesthesia
- Hypoxaemia
Signs of UAO?
- resp distress
- Blood stained foam pouring from nostrils and mouth
- Deterioration with hypoxemia, collapse and cardiac arrest may be rapid
Tx for UAO?
Establish an airway (ET tube or tracheotomy followed by symptomati tx (oxygen, furosemide, bronchodilation)
What has bilat laryngeal paralysis been associated with?
- Nerve damage due to neck extension
- LAryngeal nerve ischaemia
- Tissue oedema due to surgery
- LAryngeal oedema and spasm
- Functional airway collapse
Why can we get nasal oedema?
- with dorsal recumbency
- can lead to upper airway obstruction
Prevention of nasal oedema?
- Use lateral recumbency
- Orotracheal tube in situ or naso-pharyngeal tube placed for recovery to bride gap until nasal passages return to normal function
- Intra-nasal phenylephrine into ventral meatus at end of anaesthesia to reduce congestion and obstruction
What ET intubation complications can they get?
- Mild-moderate mucosal damage is common
- Haemhorrhage with potential for airway obstruction by
blood clots, aspiration - Laryngeal oedema, ecchymosis and haematomas, paresis
- Bilateral larnygneal paralysis (rare)
- Pharnygeal trauma
- Tracheal damage from cuff
- Secondary bacterial infection, pleuropneumonia
What can cause pulmonary oedema?
- UAO
- Micro-embolism
- Drug-associated capillary leakage
- Venous air embolism
- Mechanical causes (hydrostaticeffects)
what does PAM stand for?
Post Anaesthetic Myopathy and Neuropathy
What is PAM associated with?
- Dec muscle perfusion related to hypotension (MAP < 65mmHg)
- Prolonged duration of GA
- LAteral recumbency
- Larger body mass
Neuropathy?
slightly less common than myopathy but contributing factors similar to PAM
How do we PREVENT PAM ?
- Reduced pressure on all points
- Ensure major veins unobstructed
- Avoid tension (no overextended limbs)
- Facilitate muscle perfusion (positioning)
- Prevent hypotension (appropriate drug & dosage, close monitoring)
Who and how do horses get Spinal Cord Myelopathy
- Rare
- Young male and heavier breeds over represented
- Dorsal recumbency mostly
Aetiologies suggested for spinal myelopathy?
- Reduced perfusion and ischemia of the spinal cord in dorsal recumbency
- Reduced venous return due to compression of the vena cava by abdominal
contents - Vitamin E deficiency destabilizing spinal cord membranes
- Stretch ischaemia of the spinal cord
- Verminous arteritis
- Embolism
Hypoxiaemia is when PaO2 <?
PaO2 < 60mmHg
What causes of hypoxaemia?
- Low Fi02 (inspired oxygen fract)
- Hypoventilation
- Diffusion impairment
- Ventilation/perfusion (V/Q) mismatch
- CV shunting
Hypotension value?
MAP < 60 mmHg
When is hypotension more problematic?
with inhalational anaesthesia compared to TIVA (total IV a)
What physiology of hypotension?
Peripheral vasodilation -> dec peripheral resistance -> dec MAP -> dec tissue perf
T/F Hypotension is a contribution factor for myopathy/neuropathy
True
How would u treat hypotension?
- Dobutamine
- IVFT
What is the most commonly described per-anaesthetic complication in horses?
Post-operative colic (POC)
Incidence of POC?
1/3 - 1/10 cases
Describe POC
- Multifactorial
- Often no diagnosis - impaction implication tho
- Ortho seems to inc risk
- Morphine inc risk?
- sodium benylpenicillin or ceftiofur ?
What is a specific cause of POC?
Post-op ileus (POI)
What risk factors to POI?
- Duration of anaesthesia and surgery
- Type of surgery
- PCV at induction
- Inc TP
- Arabians
- Inc age
What considerations for field anaesthesia?
- Location (clean field)
- Tetanus prophylaxis
- Contigenecy planning (emergency drugs, ET tube? )
What is step 1a?
History, signalment, clinical exam -> consider anaesthetic risk
step 1b?
equipment checks & prep ->
- Check all anaesthetic and monitoring equipment is ready and working if
working in a hospital - Check for leaks
- Draw up medications (including emergency top-ups etc).
- Label syringes
What is step 2?
G I V E A C E P R O M A Z I N E ( A N D N S A I D )
* (Technically part of pre-med but done earlier than the rest)
What dose of ACP?
0.04-0.05mg/kg IM
i.e. 20mg for standard horse and 10mg for standard pony
What desirable effects of ACP?
- Mild sedation
- Improves recovery quality
- Anti-arrythmic
- Vasocilation
caution with entire males?
Describe step 3?
- IV Catheter
- Rinse mouth
- If hospital anaesthesia: remove or cover shoes
Step 4?
Premed -> neuroleptanalgesia
- ALpha 2 agonist + Opioid
give alpha 2 first THEN once effect seen give opioid
PREMED doses or duration of aciton
Step 5 ?
Induction -> (ensure well sedated)
Ketamine (2.2mg/kg IV) and a central muscle relaxant (benzo) i.e. Diazepam or Midazolam (0.5mg.kg)
KEtamine and midazolam licensed in UK
What alternatives for induction?
- Combinations of ket plus another drug e.g.g propofol or thiopental or GGE
- GGE IV to effect
What happens after induction?
- Et tube
- inital checks and prep
- Urinary cath
What point of putting urinary cath?
- Urinary catheters placed during most equine anaesthetics in the theatre setting
- Enables monitoring of urine production
- Avoid excessive urination in the recovery box resulting in a wet, slippery floor
- (Alpha-2 agonists result in increased urine production)
describe Step 6
Maintenane with TIVA:
- Field environment or short surgery
- KEt induction gives 10 mins of surgical anesthesia
What to do if need more than 10 mins?
- Short procedures: maintain with intermittent bolus doses
- Longer: infusion rate
How do we do top up bolus of KET?
- Ket every 8 mins (2 min onset time)
- 1/3 induction dose
alternative: thiopental (when patient moves)
In addition to KET bolus we can also give …?
- If used xylazine for premed give 1/2 premed dose with every ketamine top up
- If used detomidine for premed: give 1/2 premed dose with every other ketamine top up
How would u formulate a variable rate infusion (“triple dip)
ADVANTAGESmore stable plane of A
DISAD: relative cost ; 90 mins max
How do we get maintenance with inhalants?
Iso or Sevo in longer surgeries
Trend now towards PIVA (Partial IV anaesthesia) instead of Inhalant ALONE
What can PIVA involve?
Can involve CRIs of ALpha2 , lidocaine, ket, opioids
Is spontaneous ventilation used much?
- Spontaneous ventilation possible but in theatre environments, controlled
ventilation is commonly used for adult horses
Why do we use controlled ventilation more?
- Recumbency and most aneasthetic drugs induce hypoventilation
- Hypoventilation is when ventilation unable to match the metabolic
rate of the body and is characterized by a rising partial pressure of
arterial CO2
(PaCO2
).
- Hypoventilation is when ventilation unable to match the metabolic
- Values of PaCO2 of > 4.7-6KPa (35-45mmHG) = hypercapnia
What monitoring in field?
PHYISOLOGYICAL Parameters:
- Pulse (facial artery ; rate 30-45 in adult anaesthetised)
- MM
- RR
- Shivering & inc muscle tension= inadequate plne of anaesthesia (movement)
Eye position & reflexes (unreliabel with ket
Anal reflex
Monitoring in theatre?
- Physiological parameters & reflexes including temp
- Eye position
- Pulse oximeter
- BP (invasive via arterial cath of facial artery or non invasive)
- ECG
- Capnography
Detail eye position for theatre monitoring ?
- Surgical anaesthesia: central with sluggish palpebral
Too light: eye rotates, palpebral brisk - Too deep: eye central, no palpebral reflex
Detail ECG?
- Min 3 points of contact
- Base-apex orientation
DETAIL Capnography
- Monitoring for hypercapnia
- Evidence that circulatory system is capable of CO2
transport (a
fall in cardiac output results in a reduced EtCO2 when
ventilation is constant). - Also useful for confirming ET intubation, identifies gas
leakages and reveals abnormal ventilation patterns
Detail Arterial Blood gas analysis
- Rapid, direct, intermittent measurements of PaCO2
and PaO2
,
calculated values for SaO2
, acid-base balance, electrolytes,
lactate, urea and creatinine - Evaluating ABG and pH recommended in cases where
hypoxaemia and/or hypercapnia is suspected or likely to occur - Not usually necessary in healthy, routine cases.
Describe Theatre environemnt Recovery?
- Additional sedation if pre-med worn off
- (alpha 2 + opioid)
- Oxygen supplementation in recovery box
- Observe from a distance (peep holes, CCTV)
- If entering the box, ensure clear escape route
Safety - ET tube often removed once light/swallowing, and
nasopharyngeal tube placed - Unassisted or assisted rope recovery both common
Detail Field Environment Recovery?
- Anaesthetist usually stays with horse until ready
to stand - Headcollar and lead rope
- Kneeling on neck
- Keep in lateral as long as possible
- Additional sedation if pre-med worn off
- Less likely to be needed in field
FOr ANY recovery what to remember?
Minimise noise/ light stimulation (towel over upper eye, pack ears?
