Introduction to anaesthesia Flashcards
Define anaesthesia
loss of sensation resulting from pharmacological depression of nerve function
Define GA
state of unconsciousness produced by controlled reversible drug-induced intoxication of the CNS in which the patient neither PERCEIVES or RECALLS noxious stimuli. AKA ‘reversible death’.
Define local anaesthesia
temporary blockade of sensory nerves (usually with a simultaneous block of motor nerves too)
What are the components of GA? (the Triad of general anaesthesia)
Unconsciousness (‘narcosis’)
Analgesia (i.e. antinociception if anaesthetised)
Muscle relaxation
Define amnesia
no awareness of recall of anaesthesia or surgery
What else is essential to the anaesthetist other than the triad?
homeostasis - especially oxygen delivery to the tissues
What is meant by the trend to ‘lighten up’?
trend in modern anaesthesia. the use of several drugs with selective and complementary actions. The pharmacokinetic properties of these drugs should allow rapid onset, rapid recovery and rapid responses to changes in delivered doses.
Define balanced anaesthesia
use of smaller doses of a combination of drugs to achiev the various components of anaeshtesia, thus reducing the disadvantaages of using large doses of any one drug. It also offers a multi-dimensional approach to pain control - not only does it help to block autonomic responses to surgery and provide analgesia post-op, but may also pre-empt post-op pain hypersensitivity
Side effects -anaesthesia
Excessive physiological depression
Depressed homeostatic mechanisms (baroreflexes, pulmonary hypoxic esponse)
Specific drug effects (NSAIDs –> prostaglandin-mediated renal BF decreased)
What is the pulmonary hypoxic response?
where vessels to poorly ventilated bits of lung constrict and so are diverted to other areas.
Why do pre-op blood tests?
To detect subclinical disease which may influence anaesthetic management. One study this made a difference in 0.2% cases.
INDICATIONS: signalment, history, baseline values
What should be known about renal function and blood tests?
2/3 tissue loss before haematology/biochemistry signs
What are boxers more sensitive to?
Acepromazine
When should anaesthesia be induced in relation to feeding?
In non-emergency cases, wait at least 6 hours after last meal before inducing GA (small animals), 12 hours (horses) or not at all (small birds and rabbits)
What is often the first sign of cardiac disease and often the best test to predict how well an animal will cope with anaesthetic?
exercise tolerance
What may PU/PD indicate?
kidney, liver or endocrine disease, pyometra
What should you be wary of in trauma cases?
multiple injuries
ruptured diaphragm
ruptured bladder
traumatic myocarditis
When do patients die during anaesthesia?
2/3 die during the recovery period –> MONITOR!
What information should be obtained from the patient history? 10
Signalment Time of last meal Previous anaesthetics Cough Exercise tolerance PU/PD V/D Trama Seizures or fainting episodes Concurrent drug treatment
Define CEPSAF
What are the risks of death due to anaesthesia (dog, cat, rabbit, GP)?
Confidential Enquiry into Perioperative Small Animal Fatalities Healthy dog: 1 in 1849 die Healthy cat: 1 in 895 die Rabbit: 1 in 72 die Guinea pig: 1 in 26 die
Outline anaesthetic morbidity
Muscle and nerve damage Cerebral hypoxia--> poor recovery, memory loss and blindness Peripheral nn damage Spinal cord damage Post-anaesthetic cognitive dysfunction Renal dysfunction (due to hypotension)
Define CEPEF
Confidential Enquiry into Perioperative Equine Fatalities. Shows mortality rate in horses to be 1 in 100 or higher if colic.
Why is blindness relatively common after dentals and endoscopy?
entire blood supply in cats to brain is from maxillary artery so decreased BF to brain –> increased risk of temporary or permanent damage.
What factors influence anaesthesia risk?
physical status temperament staff facilities choice of anaesthetic technique.
What is a physical status score?
after patient evaluation, all findings can be used to allocate a physical status score to the animal. This is an adaptation of the American Society of Anaesthesiologists (ASA) scale for humans. Needs special attention during perioperative period. Only a measure of the physical status, not a measure of anaesthetic risk overall.
What are possible effects of waste anaesthetic gases?
No clear evidence. Possibly cancer, miscarriage, liver and kidney disease, immunological effects, psychological disturbances.
How safe is nitrous oxide?
More dangerous. Can inhibit DNA synthesis (i.e. is teratogenic in first trimester) and causes CNS damage)
How do pregnant staff need to be careful? 4
- Excellent scavenging measures
- Shouldn’t be allowed to fill vaporisers
- Keep away from recovery areas (where animals exhale significant amounts of volatile agent), especially if poorly ventilated.
- Special facemasks
What are COSHH regulations on waste anaesthetic gases?
Monitor environmental levels of waste anaesthetic gases every 6-12 months.
How can we minimise exposure? 7
- use scavenging systems (AGSS) properly
- service regularly (anaesthetic machines and vaporisers)
- avoid mask or chamber induction of anaesthesia
- inflate endotracheal tube cuff properly (prefereably before turning vaporisere on)
- fill vaporisers at end of day if possible (key-fillers or ‘Quick-fill system)
- cap bottles of anaesthetic before discarding
- leave patients attached to circuit as long as possible, with ETT cuff inflated.
- before disconnecting patient, flush circuit with oxygen and ‘dump’ the bag into the scavenging system
- ensure recovery areas are well-ventilated
- scavenge properly from circuits
- use low gas flow techniques if appropriate
What are the COSHH maximum exposure concentrations? (NO, isoflurane, sevoflurane, halothane)
Nitrous oxide: 100ppm
Isoflurane: 50ppm
Sevoflurane: 60ppm
Halothane: 10ppm
Outline an anaesthetic plan
Premedication Induction Maintenance Monitoring and care Recovery
Define anaemia
Low Hb/PCV –> decreased O2 delivery to tissues
What are the ‘transfusion triggers’ for Hb and PCV?
Hb concentration of 5-8g/dl
or PCV of 20%
Why is hypoproteinaemia something that is important to be aware of when inducing anaesthesia?
Changes in plasma albumin concentration alters the ratio of free drug: protein bound drug. The plasma proteins maintain circulating oncotic pressure. Risk of oedema if albumin is <20g/l.
What indicates kidney failure?
Blood urea >10mmol/L, creatinine >200mmol/L
Concurrent acideamia increases free drug concentrations, depresses myocardial contractility, shifts HbO2 dissociation curve to right.
IV fluids before anaesthesia to maintain BP
How is anaesthesia maintained?
Inhalation
TIVA
Monitoring (asleep? alive? likely to stay that way?)
Define TIVA
Total intravenous anaesthesia
Outline the ideal ‘depth of anaesthsia’
Deep enough to prevent movement and awareness. Light enough to prevent lasting damage (kidneys, CNS,muscle). Balanced anaesthesia.
