Anaesthesia (Small and equine) Flashcards
ASA statuses?
ASA 1: normal healthy animal
ASA 2: mild systemic disease
ASA 3: moderate systemic disease
ASA 4: severe systemic disease, constant life threat
ASA 5: moribund, not expected to survive following 24h
Aims of anaesthesia?
Unconsciousness
Analgesia
Muscle relaxation
Which anaesthetic drugs do/do not achieve analgesia, unconsciousness and muscle relaxation? (ACP, benzo, a2, opioids, barb, ket, propofol, inhalation, N2O, local)
Analgesics: - A2 agonists - Opioids - Ketamine - N20 - local Sedatives: - ACP - A2 agonists - Opioids Loss of consciousness: - Barbiturates - Ketamine - Propofol - Inhalationals Muscle relaxation: - ACP - Benzodiazepines - A2 agonists - Barbiturates - Propofol - Inhalationals
What is balanced anaesthesia?
Using safe doses of 2+ agents or methods to:
- Reduce dose of each
- Reduce side effects
- Optimise analgesia
Advantages and disadvantages of injectable induction of anaesthesia?
Advs:
- Not much equipment needed
- Generally rapid and smooth
- No enviro pollution
Disadvs:
- Once delivered, retrieval impossible
- Must have accurate weight (good estimate in LA)
- CV and resp depression
- Accidental self administration
Ideal induction agent?
Easy to put into solution and stable with a long shelf life Cheap Not painful on injection Rapid onset Smooth induction and recovery Rapid redistribution, metabolism and clearance No active metabolites Safe No side effects Analgesia Muscle relaxation
Propofol - Side effects? Benefits over alfaxolone?
Vasodilation with no compensatory increase in HR (-> hypotension -> reduced blood flow to vital organs)
Post-induction apnoea (so should pre-oxygenate for 5 mins)
Cats:
- Repeated doses are cumulative (takes couple of days to remove from body)
- Potential for Heinz body anaemia (due to oxidative damage to RBCs)
Alfaxalone - Side effects? Benefits over propofol?
Vasodilation with compensatory increase in heart rate (so CO maintained better than propofol)
Post-induction apnoea (but less than propofol)
Not cumulative in cats (can use multiple times in short period)
Can give IM and IV
More twitching than propofol (avoid in seizure patients as can’t tell if seizing or twitching)
Ketamine - Features? Side effects?
Excellent analgesia
Induction agent
Increase in sympathetic tone - vasoconstriction
Direct negative inotrope
(So CO maintained due to opposite effects of vasoconstriction and negative inotropy)
Often get post-induction apnoea
Can give IM and IV
Causes muscle rigidity - ideally use with a drug that gives muscle relaxation
Propofol/alfaxolone and ketamine often used for co-induction - uses analgesia of ketamine and reduce doses to reduce side effects
Dogs and cats will often salivate excessively
Often will keep cranial nerve reflexes so hard to tell how asleep
Good in horses as small volume needed, takes about 2 mins to work, often go down nicely
Etomidine - What is it? When used?
Induction agent Only one with virtually no CV effects Good for animals with CV compromise Stops adrenal glands working Not really used in practice
Thiopental - What is it? When used?
Induction agent Stopped using in UK Used in equine Only drug able to use at sensible volume when horse is too light on table CV effects - arrhythmias etc
Advantages and disadvantages of inhalation agents for induction of anaesthesia?
Advs: - Doesn't require IV access Disadvs: - Prolonged induction time - Likely to cause distress - Airway irritation - Enviro pollution - Requires tight fitting mask or chamber - Increased risk of death compared to injectable
Don’t use unless have to
Sevoflurane if have to - smells nicer, quicker induction, reduced chance of dying
Why monitor anaesthesia?
Maintain physiology Maintain adequate anaesthetic depth Prevent pain Safety Legal implications
What reflexes/other visual things can be monitored during anaesthesia? How do they change with depth?
Palpebral reflex: brisk/spontaneous -> sluggish -> absent (check both as becomes refractory)
Anal: brisk -> sluggish -> absent tone
(Corneal)
Eye position: central -> ventral -> central
Pupil: dilated -> constricted -> dilated
Lacrimation: decreases as deepens
Changes in autonomic tone: sweating
Muscle tone: tension in tendon of sternocephalicus, jaw tone
Movement = either very light or about to die
CV monitoring under anaesthesia?
HR/pulse:
- Dogs: 50-120
- Cats: 60-140
- Horses: 24-40
Central vs peripheral artery palpation gives indication of perfusion
Mucous membrane colour indicates oxygenation and perfusion
CRT depends on blood volume and capillary tone:
- <1 second = poor perfusion or hypovolaemia
- >2 seconds = maldistributive shock
Respiratory monitoring under anaesthesia?
Normal rate: - Dog and cats: 10-30 - Horses: 8-10 Bradypnoea: - Too deep - Hypocapnia - Isoflurane, propofol, fentanyl - Alkalosis Tachypnoea: - Too light - Hypoxia, hypercapnia - Methadone - Poor analgesia - Acidosis Watch reservoir bag movement - % inhaled Mucous membrane colour - cyanosis = severe hyperaemia
Normal blood pressure under anaesthesia?
Systolic: 80-130mmHg
Diastolic: 40-60mmHg
Mean: >60mmHg
Types of blood pressure monitoring under anaesthesia? Advs and disadvantages?
Non invasive BP:
- Oscillometric or Doppler
- Intermittent readings or SBP or MAP
- No risk of infection
- Need correctly fitting cuffs (easy to get inaccurate values)
Invasive BP
- Continuous readings of SBP, DBP and MAP
- Invasive/risk of infection
- Allows arterial blood sampling (blood gases)
- More expensive equipment
What is pulse oximetry? What does it tell you? Normal values? Limitations?
Measures % saturation of oxygen of Haemoglobin (SpO2) Normal: 97-99% Measures pulse Indirect indication of perfusion (plesthysmograph) Limitations: - Hypotension/vasoconstriction - Affected by bright light - Non pigmented mucosa - Movement sensitive - Probe may blanch capillary bed - 'Beeps' may be over-interpreted
What is capnography? What are normal values? What does it tell you? Parts of curve?
Measures end tidal CO2 (EtCO2) Normal: 35-45mmHg >60mmHg = hypoventilation <35mmHg = hyperventilation Other uses: - correct placement of ETT - Confirms pulmonary circulation (CCPR) - Indicates problems e.g. with breathing system Curve: - Respiratory baseline (should be 0) - Expiratory upstroke - Alveolar plateau - EtCO2 - Inspiratory downstroke
What is sedation?
Mental calming
Sleepiness and disinterest in environment
Decreases responsiveness to a stimuli
Animals can still be aroused
Why use a premedication?
Relieves anxiety Smooths induction, maintenance and recovery phases Anaesthetic sparing effects Pre-emptive analgesia Reduces muscle tone
Reasons to use sedation?
Premedication
Chemical restraint
May provide analgesia
Reduce muscle tone
Ideal premedication?
Reduce fear and anxiety Easy to administer Quick onset Reasonable duration of action Antagonisable Predictable and reliable Safe Effective in many species Minimal resp, CV and other side effects Analgesia Muscle relaxation Amnesia
Ideal sedative?
High therapeutic index Reliable and predictable Rapid onset of action Well absorbed by all routes Non irritant to tissues Non painful on injection No side effects Practical volume to administer Analgesia and some muscle relaxation Antagonisable
Acepromazine - Type of drug? Effects? Side effects? Onset? Duration?
Phenothiazine
Mental calming die to dopamine antagonism
Commonly used as a premedication, often with opioids
Unpredictable sedative
No analgesia
Many other sites of action leads to side effects
Potentiates CNS depressant effects of other sedative and anaesthetic agents
Vasodilation, hypotension, bradycardia (-> CV collapse -> syncope, especially in brachycephalic dogs) - care in CV compromised patients
Will cause pharyngeal muscle relaxation (problem in brachycephalic dogs)
Anti-emetic
Anti-histaminic
Avoid in very excited animals
Can cause excitation at high doses/overdoses
Beware in paediatric patients
Avoid in breeding stallions
Hypothermia
Not reversible
Onset: 30-40 mins
Duration: 4-6 hours
Azaperone - Type of drug? How does it work? When used? Side effects?
Butyrophenones
Used in pigs
Antidopaminergic and anti-adrenergic effects in reticular activating system of CNS
Avoid large doses in boars - penile prolapse
Care in brachycephalic pigs
Hypothermia
A2 agonists - Examples? How it works? Advs? Side effects? Care?
Examples:
- Xylazine
- Detomidine
- Medetomidine
- Dexmedetomidine
- Romifidine
How it works:
- Suppression of activity in reticular activating system
- A2 agonism in the locus coeruleus in brainstem
Advs:
- Analgesia (of shorter duration than the sedation)
- Muscle relaxation
- Reversible: atipamezole
- All can be given IV, IM or SC
- Some can be given transmucosally/oromucosally
- Predictable, dose dependent sedation
- Sedation may be profound
- Anaesthetic sparing effect
Side effects:
- Hormonal effects - diuresis, hyperglycaemia
- GI effects
- Sweating
- Initial hypertension and peripheral vasoconstriction -> reflex bradycardia -> relaxation of peripheral vascular tone -> eventual state of peripheral vasculature and BP stays fairly close to normal
- Significantly reduces CO
- Sinus arrhythmia, SA block and AV blocks possible
- High doses can lead to hyperaemia
- Can be absorbed across mucous membranes
- Suppression of thermoregulation
Care in CV compromised patients!
Care in sick/debilitated patients!
Care if diabetes mellitus!
Care if laryngeal dysfunction!
Benzodiazepines - What do they do? How do they work? Effects? Side effects? Examples?
Unreliable sedation in healthy animals
Useful in ‘at risk’ patients
GABA-specific benzodiazepine binding sites - brain and spinal cord
Central muscle relaxation
No analgesia
Anticonvulsant
Side effects:
- Minimal CVS depression
- Midazolam will cause greater CV depression than diazepam at higher doses
- Minimal respiratory depression
- Enhances the depression caused by other drugs
- Binds to some plastics (giving sets etc)
- Postural muscle weakness
- Care if hepatic disease
Can be reversed by flumazenil or surmazenil
Examples:
- Midazolam
- Diazepam
(None licensed)
Opioids - What do they do? Effects? Side effects? Examples?
Potent, efficacious analgesics Bind to opioid receptors Also effects on resp, GIT and CV systems Can cause sedation alone in severely compromised animals where low level sedation is required But often sedation is poor Used with other sedatives to improve the quality of sedation Can be antagonised Examples: - Pethidine - Methadone - Morphine - Fentanyl - Buprenorphine - Butorphanol
