Anaesthesia Flashcards
What is analgesia?
Decrease or absence of pain.
What is pain?
Conscious perception of a noxious stimuli
What is local anaesthesia?
A loss of sensation restricted to a small body area (e.g. finger)
Achieved by blocking specific terminal nerves using LA.
What is regional anaesthesia?
Loss of sensation in a more extended body are (e.g. limb)
Achieved by blocking major nerves or multiple terminal nerves using LA or analgesic drugs.
What is general anaesthesia?
Pharmacologically induced state of absence of consciousness.
The patient will not respond to any stimuli (including pain).
Achieved by administering intravenous or inhalant anaesthetics.
Should always be combined with analgesia & muscle relaxation.
What is sedation?
Pharmacologically induced state of reduced level of consciousness.
May be associated with a lack of memory.
When combined with analgesia, can further reduce level of pain perception.
What are the 4 stages of anaesthesia?
- disordered consciousness, voluntary movement.
- excitement.
- surgical anaesthesia.
- overdose
What happens in stage 1 anaesthesia?
Patient is conscious but not acting normal.
Agent acts on cerebral cortex, rendering its function more acute but unbalanced (except for pain perception).
Profoundly modified by pre-medication.
What happens in stage 2 anaesthesia?
Unconsciousness.
Patient may exhibit signs of excitement.
Patient can move through stage 2 quicker if drugs are administered faster.
May be unnoticeable with heavy pre-medication.
What happens in stage 3 anaesthesia?
Tranquil phase of narcosis (resembling natural sleep). Goal of anaesthesia: to maintain this level of narcosis for as long as required. 4 planes (light, medium & deep)
What happens in stage 4 anaesthesia?
Signs of severe shock. Weak pulse. Not breathing. Dilated pupils. Reflexes absent. Loss of sphincter tones.
To which stage of GA does the following clinical signs in a dog correspond:
Eyes ventro-medial, decreased RR, palpebral reflex absent, corneal reflex present, relaxed jaw tone?
Stage 3, plane 2 (ideal GA for surgery).
What does pre-anaesthetic patient evaluation include?
- History.
- Physical exam.
- Pain assessment.
- Clinical diagnostics (at least CBC/biochem: PCV, TS, BUN, BG)
- Other considerations (e.g. breed, recent trauma, concurrent drugs).
- Classification of physical status (ASA status).
What 3 systems are most heavily affected by GA?
CNS, cardiovascular & respiratory (must assess in physical exam).
How does pain affect GA?
Pain increases dosage of anaesthetic needed, thus causing more side effects.
Pain also causes patient stress and reduces healing.
Consider NSAIDs and/or opioids for prophylactic pain treatment.
Why consider prophylactic treatment of pain?
Reduces GA dose needed.
Minimise wind-up and hyperalgesia.
Synergistic with pre-medication (improves sedation).
What are the 6 different ASA physical statuses?
- normal healthy patient.
- patient with mild systemic disease (e.g. obesity)
- patient with severe systemic disease.
- patient with severe systemic disease that is a constant threat to life (e.g. GDV)
- moribund patient who is not expected to survive without operation (e.g. late GDV)
- declared brain-dead patient whose organs are being removed for donor purposes.
Why is fasting recommended in most patients?
GA relaxes lower oesophageal sphincter and decreases GI motility:
Risk of regurgitation & aspiration.
Risk of bloat (presses on diaphragm and restricts respiration).
Risk of ileus (painful and poor recovery).
What are is difference in pre-anaesthetic patient preparation between monogastrics, ruminants and small mammals/birds/neonates?
Monogastrics (dogs, cats, horses): withhold food 12 hrs, no withholding of water.
Ruminants: withhold food 12-36 hrs, water for 12 hrs.
Small mammals, bids and neonates: short to no fast (risk of hypoglycaemia), no withholding of water.
What is the protocol for pre-anaesthetic preparation in diabetic patients?
Schedule procedure for 1st of the morning.
Evening meal and insulin the night before.
Small meal in the middle of the night with 1/2 dose insulin.
No morning meal.
Check glucose pre-op:
If normal (<500g/dL) no AM insulin).
If >500g/dL): 1/2 dose insulin.
If low - provide supplemental glucose.
What are the aims of premedication?
To calm the patient.
To provide peri-operative analgesia.
To reduce the total amount of anaesthetic (and its side effects).
To reduce nausea & vomiting.
To smoothen recovery.
To reduce autonomic side effects (HR, BP less reactive during surgery - CNS less reactive to noxious stimuli).
What factors dictate the type of agents used for pre-medication?
Animal temperament:
e.g. alpha-2 agonists like medetomidine for more aggressive patients Vs. benzodiazepines or phenothiazines (acepromazine) for more docile patients.
Duration of procedure:
e.g. ACP lasts 6-8 hrs and is long acting (good for longer procedure).
Ability to antagonise the agent:
e.g. important for very sick/old patient that cannot metabolise agents well on their own.
Health status of patient:
e.g. choosing agents with less effects on the cardiovascular system (NOT alpha 2s, possibly small dose ACP) for patients with cardiovascular disease.
Availability of the drug.
Personal preference.
Why combine traquilizer/sedative agents with opioids for premedication?
Synergistic effects (decrease the dose of both sedation & analgesia required, meaning less side effects).
Produces reliable & safe sedation.
Reduced the dose of induction and maintenance anaesthetic agent.
Provides pre-emptive analgesia.
What agents can we use for sedation?
Phenothiazines (e.g. ACP)
Alpha 2 agonists (e.g. xylazine LA, medetomidine SA, dex-medetomidine SA, romifidine LA , detomidine LA).
Benzodiazepines (e.g. diazepam, midazolam).
