Introduction to anaesthesia

Question 1

Define anaesthesia

Answer 1

loss of sensation resulting from pharmacological depression of nerve function

Question 2

Define GA

Answer 2

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’.

Question 3

Define local anaesthesia

Answer 3

temporary blockade of sensory nerves (usually with a simultaneous block of motor nerves too)

Question 4

What are the components of GA? (the Triad of general anaesthesia)

Answer 4

Unconsciousness (‘narcosis’)
Analgesia (i.e. antinociception if anaesthetised)
Muscle relaxation

Question 5

Define amnesia

Answer 5

no awareness of recall of anaesthesia or surgery

Question 6

What else is essential to the anaesthetist other than the triad?

Answer 6

homeostasis - especially oxygen delivery to the tissues

Question 7

What is meant by the trend to ‘lighten up’?

Answer 7

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.

Question 8

Define balanced anaesthesia

Answer 8

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

Question 9

Side effects -anaesthesia

Answer 9

Excessive physiological depression
Depressed homeostatic mechanisms (baroreflexes, pulmonary hypoxic esponse)
Specific drug effects (NSAIDs –> prostaglandin-mediated renal BF decreased)

Question 10

What is the pulmonary hypoxic response?

Answer 10

where vessels to poorly ventilated bits of lung constrict and so are diverted to other areas.

Question 11

Why do pre-op blood tests?

Answer 11

To detect subclinical disease which may influence anaesthetic management. One study this made a difference in 0.2% cases.

INDICATIONS: signalment, history, baseline values

Question 12

What should be known about renal function and blood tests?

Answer 12

2/3 tissue loss before haematology/biochemistry signs

Question 13

What are boxers more sensitive to?

Answer 13

Acepromazine

Question 14

When should anaesthesia be induced in relation to feeding?

Answer 14

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)

Question 15

What is often the first sign of cardiac disease and often the best test to predict how well an animal will cope with anaesthetic?

Answer 15

exercise tolerance

Question 16

What may PU/PD indicate?

Answer 16

kidney, liver or endocrine disease, pyometra

Question 17

What should you be wary of in trauma cases?

Answer 17

multiple injuries
ruptured diaphragm
ruptured bladder
traumatic myocarditis

Question 18

When do patients die during anaesthesia?

Answer 18

2/3 die during the recovery period –> MONITOR!

Question 19

What information should be obtained from the patient history? 10

Answer 19

Signalment
Time of last meal
Previous anaesthetics
Cough
Exercise tolerance
PU/PD
V/D
Trama
Seizures or fainting episodes
Concurrent drug treatment

Question 20

Define CEPSAF

What are the risks of death due to anaesthesia (dog, cat, rabbit, GP)?

Answer 20

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

Question 21

Outline anaesthetic morbidity

Answer 21

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)

Question 22

Define CEPEF

Answer 22

Confidential Enquiry into Perioperative Equine Fatalities. Shows mortality rate in horses to be 1 in 100 or higher if colic.

Question 23

Why is blindness relatively common after dentals and endoscopy?

Answer 23

entire blood supply in cats to brain is from maxillary artery so decreased BF to brain –> increased risk of temporary or permanent damage.

Question 24

What factors influence anaesthesia risk?

Answer 24

physical status
temperament
staff
facilities
choice of anaesthetic technique.

Question 25

What is a physical status score?

Answer 25

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.

Question 26

What are possible effects of waste anaesthetic gases?

Answer 26

No clear evidence. Possibly cancer, miscarriage, liver and kidney disease, immunological effects, psychological disturbances.

Question 27

How safe is nitrous oxide?

Answer 27

More dangerous. Can inhibit DNA synthesis (i.e. is teratogenic in first trimester) and causes CNS damage)

Question 28

How do pregnant staff need to be careful? 4

Answer 28

• 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

Question 29

What are COSHH regulations on waste anaesthetic gases?

Answer 29

Monitor environmental levels of waste anaesthetic gases every 6-12 months.

Question 30

How can we minimise exposure? 7

Answer 30

• 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

Question 31

What are the COSHH maximum exposure concentrations? (NO, isoflurane, sevoflurane, halothane)

Answer 31

Nitrous oxide: 100ppm
Isoflurane: 50ppm
Sevoflurane: 60ppm
Halothane: 10ppm

Question 32

Outline an anaesthetic plan

Answer 32

Premedication
Induction
Maintenance
Monitoring and care
Recovery

Question 33

Define anaemia

Answer 33

Low Hb/PCV –> decreased O2 delivery to tissues

Question 34

What are the ‘transfusion triggers’ for Hb and PCV?

Answer 34

Hb concentration of 5-8g/dl

or PCV of 20%

Question 35

Why is hypoproteinaemia something that is important to be aware of when inducing anaesthesia?

Answer 35

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.

Question 36

What indicates kidney failure?

Answer 36

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

Question 37

How is anaesthesia maintained?

Answer 37

Inhalation
TIVA
Monitoring (asleep? alive? likely to stay that way?)

Question 38

Define TIVA

Answer 38

Total intravenous anaesthesia

Question 39

Outline the ideal ‘depth of anaesthsia’

Answer 39

Deep enough to prevent movement and awareness. Light enough to prevent lasting damage (kidneys, CNS,muscle). Balanced anaesthesia.