Anaesthesia Flashcards
What is balanced anaesthesia
Practice of using smaller doses of many different kinds of medication rather than higher doses with fewer drugs
How long should animals be fasted before anaesthetic
> Dogs and cats - 6-8 hours
Ruminants - 24/48 hour
Horse - 8 hours ( even though cant vomit, full abdomen can decrease functional residual capacity
Rabbits and rodents cant vomit so doesnt matter
Ferret - 4 hours
What are you looking for in a pre anaesthetic blood test
> Older animals testing renal and liver function
Detect any underlying diseases
Get baseline figures so can detect post op changes
PCV > 20% need transfusion
Testing for adequate albumin because its the primary serum binding protein. Therefore decreased albumin results increased free drug and a delayed recovery
What are the mortality risks of anaesthetic
Dog - 1:1850 Cat - 1:900 rabbit 1:72 Horse - 1:100 ( worse in colic cases) Chinchilla and guinea pig - 1:33
Describe the ASA class classification
> ASA I - Normal healthy animal
ASA II - Mild systemic disturbance, no clinical signs (e.g mild diabetes or obese)
ASA III - Moderate systemic disturbances with mild clinical signs ( e.g anaemia, pyrexia or symptomatic heart disease)
ASA IV - Severe systemic disturbance that is a constant threat to life (e.g severe heart failure or sepsis)
ASA V - Not expected to survive 24 hours without intervention ( GDV or severe trauma)
Whats the role of a pressure regulator on an anaesthetic machine
Reduce cyclinder pressure to a safer level ( Atomospeheric pressure)
What is a circuit factor and how do you calculate minute volume
Circuit factor - Fresh gas flow needed to prevent rebreathing. Expressed as a multiple of the animals minute volume
MV = Tidal volume x Respiratory rate
*Tidal volume is estimated at 10-15ml/kg
Why is an initial high flow rate required for a rebreathing system
Needed to flush air out of system so it doesnt dilute anaesthetic agent. Once a stable plane of anaesthesia is established can reduce flow rate to 50ml/kg
What are the common premedications
- Phenothiazine - Acepromazine
- Alpha 2 agonsit - Medetomidine/xylazine
- Benzodiazipines - midazolam and diazepam
Commonly combined with opoids (morphine/methadone) as it enhances then sedative effected of the drugs and provides analgesia
Describe pros and cons and contraindications of Acepromazine
Wait for 20minutes for effect Pros: > Inexpensive > Anti arrythmic > Antagonise CRTZ - no vomiting > Long acting tranquilzer ( 4-8 hours)
Cons:
> No analgesia
> Less reliable sedative in aggressive animals
> Vasodilation and hypotension
Contraindications:
> Decreases seizure threshold so avoid in these patiens
> HCM and left ventricular hypertension
What are the pros and cons and contraindications of medetomidine
Commonly used for short procedures in healthy animals. Also used for aggressive animals Pros: > Provides good analgesia > Reliable in a variety of species > short acting ( 1-1.5 hours) > Antagonizable
Cons: > Arrythmogenic > Increases BP and urine production > Cardio/respiratory depression > more expensive > Inhibits Beta cells in pancreas = hyperglycaemia
Contraindications:
> Diabetes patients
> Patients with cardio-respiratory disease
> ASA III or above
What are the pros and cons of benzodiazapines (midazolam/diazapam)
Ideal for neonates, geriatrics, those at risk of seizures, cardiac impairment and when muscle relaxation is needed ie in fracture repairs.
Pros:
> Minimally effects CV & respiratory function
> Myorelaxation - excellent muscle relaxant
> Tranquilizer in neonates and geriatric patients
> Anti convulsivant (anti seizure)
Cons:
> Not a reliable sedative agent
> Possible paradoxic reaction - excitement ( give with opoids)
> Antagonists are expensive
> Myorelaxation may result in decreased respiratory function
What receptors do opoids bind to and what are the side effects
Opoids bind to u receptors (providing analgesia) and k receptors (cause dysphoria). Side effects; > sedation > respiratory depression > vomitting > dysphoria > myosis (constriction) in dogs and mydriasis (vasodilation) in cats > bradycardia > urinary retention
What are the common opoids used in practice
> Morphine - Potent u receptor agonist. cheap and not licenced
> Methadone - u agonist. Onset time is 10 minutes, lasting 2-4 hours. Blocks CRTZ preventing vomiting, licenced in dogs
> Butorphanol - k & u agonist = Mild sedative and poor analgesic. used in combination with other sedatives
> Buprenorphine - Licenced in small animals
> Fentanyl - Potent u agonist. Short acting and often infused during surgery
What is the most common inducing agent and what are its possible side effectis
Propofol
> Rapid onset and rapid metabolism
> Can cause tremors due to imbalance between parasympathetic and sympathetic nervous system
> Metabolism slower in cats - deficiency in several conjugation pathways
> When used with a alpha 2 agonist causes bradycardia, resulting in longer onset
What is alfaxalone
Induction & maintenance agent that can be given IM or IV. Rapid onset of action with short duration. Poorly soluble so marketed with cyclodextrin. Less cardio pulmonary depression that propofol. Excitement on recovery if not adequately sedated.
What is ketamine
A dissociative anaesthetic - Also analgesic action at sub anaesthetic doses. Given IM (stings)or IV.
If given alone causes rigidity and excitation. always combined with another sedative.
> Used in horses after profound alpha 2 agonist sedation in combination with benzodiazepine ( counter act muscle rigidity).
> Intubation difficult as cranial reflexes preserved therefore gag reflex present.
> Stimulates sympathetic system causing increase in BP and Hr ( good for geriatrics)
What is the ‘triple combination’
Ketamine + medetomidine + opoids > Used for aggressive cats and dogs > IM and onset in 3-5 mins > Suitable for short duration procedure > 3-5mg/kg
Why is thiopental no longer licenced
Was an induction agent. No longer licenced because if given extravacularly causes necrosis.
What is etomidate
Induction agent which is minimally depresses the Cv and respiratory system. Good for sick and compromised patients. Depresses cortisol production for 6 hours.
between sevoflurane and isoflurane which has the higher partition coefficient and what does this mean clinically
Sevolflurane has a lower partition coefficient. This means that patient is induced quicker and recovers quicker.
What is MAC and what effects it
Minimum alveolar concentration is the concentration of vapour in lungs required to prevent movement (due to surgical pain) in 50% of population.
*Isoflurane has a lower MAC than sevo
Influenced by: > dose of sedative/premed > severe anaemia > Severe hypotention > Pregnancy > Hypo/hyperthermia > Age = a decrease in age causes an increase in MAC
What is the Bispectral index
Monitors the patients electroencephalograms (electrical activity in brain). Provides a single number ranging from 0-99, 0= dead and 100= fully awake. Between 40-60 is a good level of anaesthesia
How can blood pressure be monitored and what are normal values
Non invasive - doppler flow detection
> Probe tapped to metatarsal or tail where pulse can be felt
> Cuff placed proximal to dopple probe and attached to manometer
> Cuff inflated untill pulse no longer audible, cuff gently released and reading taken
> can have automatically inflated cuff (oscillometric)
Invasive - Arterial catheterisation
> Catheter placed in peripheral artery & attached to manometer or electronically transduced.
- Dog - Systolic=140 diastolic=75 mean=100
Cat - Systolic=180 Diastolic=100 mean=135
Horse - Systolic=110 Diastolic=70 mean=90
