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Physiology Of Anaesthesia > Physiology of Anaesthesia > Flashcards

Physiology of Anaesthesia Flashcards

1
Q

What is Anaesthesia?

A

The elimination of sensation by the controlled, reversible suppression of nervous function with drugs.

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2
Q

What are the 3 aims of anaesthesia?

A
  • Humanitarian
  • Technical
  • Legal
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3
Q

What are the 2 Legislation?

A

Protection of Animals (Anaesthetics) Act, 1964.

Misuse of Drugs Act, 1971

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4
Q

Do we have control of respiration?

A
  • The respiratory system is responsible for the uptake of volatile anaesthetic agents.
  • Most agents depress ventilation, therefore it is important when monitoring a patient, to have a knowledge of the respiratory system.
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5
Q

How is Respiration controlled?

A

Largely an unconscious event, it is controlled by the PONS an MEDULLA of the hindbrain.

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6
Q

What is Neural control?

A

During inspiration/expiration specialised receptor cells within the walls of the bronchioles of the lungs detect the degree to which the walls of the lungs are stretched/deflated.

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7
Q

What is Hering Breuer Reflex?

A

When the lungs have reached their max distension/deflation, impulses are sent from the receptor cells via the vagus nerve to the respiratory centre in the brain.

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8
Q

Respiration can be stimulated by one of two ways. What are they?

A
  • Reduction in O2 content of arterial blood

- An increase in the C02 content of arterial blood.

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9
Q

What are the two types of chemo-receptors?

A

Central & Peripheral

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10
Q

Where is the Central Chemo receptors?

A

Situated along the surface of the medulla oblongata and are sensitive to increases in C02.

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11
Q

Where is the Peripheral Chemo-receptors?

A

Situated in the aorta & carotid body close to the carotid arteries. These receptors are sensitive to a fall in the O2 content of blood.

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12
Q

What involves the Cardiovascular System?

A
  • Heart
  • Blood vessels
  • Blood
  • Elements of the autonomic nervous system
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13
Q

How does the heart work?

Recap question.

A

The heart is in two halves, the right side carrying deoxygenated blood to the lungs. The left delivering oxygenated blood to the peripheral tissues.

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14
Q

What is Perfusion?

A
  • The movement of sufficient volumes of blood containing oxygen and glucose, through the tissue beds.
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15
Q

What do anaesthetics do to the cardiovascular system?

A

Depresses the function, perfusion, and can cause oxygen and glucose deprivation to vital tissues.

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16
Q

Why is the control of heart rate important?

A

Regulation is important since the heart rate and stroke volume (and thereby cardiac output) has to be varied to meet the body’s needs.

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17
Q

What is Tachycardia?

A

Excessive heart rate

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18
Q

Why would patient be showing signs of tachycardia?

A
  1. Sympathetic nervous system (fight or flight)
  2. Pain
  3. Medical: hyperthyroidism, CHF.
    Severe tachycardia can cause a reduction in cardiac output which can lean to cardiac arrest.
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19
Q

What is Bradycardia?

A

Excessive slowing of the heart rate.

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20
Q

Why would patient be showing signs of bradycardia?

A

Excessive slowing the HR, can cause hypotension and reduce cardiac output.

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21
Q

What is Arrhythmia?

A

A deviation from the normal rhythm of the heart.

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22
Q

What is Sinus Arrhythmia?

A

A normal alteration in the rhythm of the heart, the heart quickens on inspiration and slows during expiration - dogs, horses.

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23
Q

What does VPC stand for?

A

Ventricular Premature contractions.

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24
Q

Is VPC normal under anaesthesia?

A

Yes, only halothane anaesthesia.

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25
Q

Blood pressure is determined by what?

A
  • Cardiac output

- Systemic vascular resistance

26
Q

What is cardiac output?

A

The volume of blood ejected by the heart per minute.

27
Q

How is cardiac output determined?

A

By stroke volume (volume of blood ejected per beat) and heart rate.

28
Q

The diameter of the pre-capillary sphincters is controlled by?

A 
- Oxygen and Carbon 
Dioxide Levels
- Neural Control 
- Hormones
- Drugs (e.g. ACP).
29
Q

How is blood pressure controlled?

A

Blood pressure is monitored by pressure receptors called baroreceptors, which are primarily located in the carotid sinuses, aortic arch and in the walls of the heart itself.

30
Q

What happens if deviations occur? (blood pressure)

A

Hypotension or hypertension, these receptors send impulses to the cardiovascular centres in the brain (medulla).

Which in turn transmits messages to the peripheral blood vessel and the heart via the autonomic nervous system.

31
Q

Which two types of drugs used to effect the central nervous function?

A
  1. DEPRESSANTS

2. STIMULANTS

32
Q

What are classed as depressants?

A
  • GA
  • Sedatives
  • Hypnotics
  • Narcotics
  • Tranquillisers
  • Neuroleptics
  • Neuroleptanalgesics
33
Q

What is a Sedative?

A

Cause dose dependant central nervous depression, producing drowsiness, lethargy and reduced activity.

34
Q

What is Hypnotic?

A

A drug that induces sleep, the depth of the sleep is dose dependant.

35
Q

What is a Narcotic?

A

A substance that depresses the CNS causing diminished or complete unconsciousness.

36
Q

What is a Tranquilliser?

A

‘Ataractics’, they have a quietening effect that reduces anxiety.

37
Q

What is a Neuroleptic?

A

These products a state of mental detachment, they relieve emotional distress without affecting the level of consciousness e.g acepromazine.

38
Q

What is Neuroleptanalgesia?

A

Is a state produced by combining neuroleptics with opioid analgesics, they are dose dependant and at high levels will cause loss of consciousness. e.g. ACP/Morphine.

39
Q

What product is a Stimulant?

A

Doxapram

40
Q

In summary how does anaesthesia affect the body?

A

Anaesthesia significantly affects the respiratory, Cardiovascular, Hepatic and Renal functions.

41
Q

What is Local anaesthesia?

A

Temporary loss of sensation in one part of the body, produced by a topical or injected agent without altering the level of consciousness.

42
Q

Why might local analgesia be a good thing?

A
  • Prevents/reduce central sensitisation and wind up.
  • Reduced requirement/side effects of volatile anaesthetics.
  • Pre-emptive analgesia
  • Multi-modal analgesia
43
Q

What is the mechanism of action with local anaesthesia?

A
  • Bind to voltage-gated sodium channels in peripheral neurons.
  • Block sodium influx
  • Stop action potential from spreading.
44
Q

How does Lidocaine Work?

A
  • quick onset of action (10-20mins)
  • short duration (up to 2hours)
  • rapid intra-operative analgesia.
45
Q

How does Bupivacaine work?

A

duration of action up to 6 hours
Speed of onset 30-40 mins
- more appropriate for post op analgesia.

46
Q

How does Ropivicaine work?

A

Closely related to bupivacaine but lower toxic potential.

47
Q

How does Proparacaine work?

A
  • Slow onset of action (30 mins)
  • Duration of action 30-60 mins.
  • Little mucosal irritation, often used in the eye.
48
Q

How does Amethocaine (Tetracaine) work?

A
  • Often used in eye.

- Duration of action - 4 hours.

49
Q

How does Prilocaine work?

A
  • Mixed with lidocaine in EMLA cream
  • Topical Analgesia
  • One of its metabolites can cause methamoglobinaemia
50
Q

When can local anaesthesia be used on Large animals?

A
  • As a diagnostic nerve blocks for lameness in equine medicine.
  • Analgesic components of balanced anaesthesia.
  • Post -op anaesthesia
51
Q

Why might local anaesthesia be less widely used in small animal surgery?

A
  • GA relatively safe
  • Small animals unlikely to lie still long enough for surgery without chemical restraint.
  • Local anaesthetic techniques usually easier to perform under sedation or GA.
52
Q

What is a Splash Block?

A

= Local anaesthetic applied directly to surgical site or wound before closure.
May be effective, drugs not being applied directly to nerves.

53
Q

What is Infiltration anaesthesia?

A
  • Placement of anaesthetic drug in or near the area to be anaesthetised.
    Used to desensitise dermal and SQ tissues.
    Minor diagnostic and surgical procedures.
54
Q

How is wound soak catheters applied?

A
  • Placed at the end of surgery, sutures loosely in place.
  • Post -op (24-36 hours), local anaesthetic agents can be infected into the catheter to provide topical analgesia.
  • Usually allows systemic analgesics to be reduced: contributes to multi-modal protocol.
55
Q

How is Intra articular applied?

A

Injection of local anaesthetic to provide analgesia following joint surgery or arthroscopy.
- Usually infused at the end of surgery before closure so that they are not flushed out of the joint.

56
Q

What two techniques are used for an intra-pleural anaesthesia?

A

Thoracocentesis

Chest tube placement

57
Q

What is regional anaesthesia?

A
  • Nerve supply to a specific region or area is blocked.

- The nerves must be readily palpable and follow a fixed course next to an easily identifiable anatomical structure.

58
Q

What is regional anaesthesia (part 2)?

A
  • A nerve stimulator can be used to locate the peripheral nerve. This can increase accuracy and therefore effectiveness.
59
Q

What is Intravenous regional anaesthesia?

A
  • IVRA/Bier Block

- A local anaesthetic agent is injected intravenously, distal to a tourniquet on a limb.

60
Q

What equipment, is required for an Epidural?

A

Spinal needle, syringes and needles, sterile gloves, sterile saline, preservative free bupivacaine +/- preservative free morphine.

61
Q

Where do we locate the injection for Epidural?

A

Spinal is rare, L5 -L6 into the CSF. Epidural L7 - S1 between dura matter and periosteum to block nerves as leaves spinal cord

62
Q

What are the complications with local anaesthetics?

A

-Local Toxicity
- Systemic Toxicity
- CNS Toxicity
- Cardiovascular toxicity
-

Physiology Of Anaesthesia (1 decks)

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