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MD4001 > General Anaesthetics > Flashcards

General Anaesthetics Flashcards

1
Q

What is general anaesthesia ?

A

Reversible, drug induced loss of consciousness, usually to allow a surgical procedure to be performed. May also involve elements of:

  • Analgesia
  • Muscle relaxation
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2
Q

Identify non-surgical procedure GA may be used in.

A

At extremes of age, and learning disability patients, for MRI/CT scans

Children, in treatments that require them to be still

Patients for electroconvulsive therapy

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3
Q

Identify the main administration routes for general anaesthetic agents.

A

Intravenous induction

Inhlational induction

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4
Q

Identify commonly used IV induction agents. Which of these is most frequently used ?

A
  • Propofol (most frequently use)
  • Thiopentone
  • Etomidate
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5
Q

What is the function of IV induction agents ?

A

Induce loss of consciousness in one arm brain circulation time

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6
Q

Identify commonly used inhlational anesthetic agents. Which of these is most frequently used ?

A
  • Nitrous oxide (gas)
  • Isoflurane (vapour)
  • Sevoflurane (vapour)
  • Desflurane (vapour)
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7
Q

What is the function of inhalational anesthetic agents ?

A
  • May be used to induce anaesthesia (children)

* More commonly used to maintain anaesthesia

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8
Q

How are inhalational anesthetic agents delivered to the patient ?

A

Via a breathing circuit

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9
Q

Which of the inhalational anesthetic agents can be used to induce anaesthesia ? Which cannot ?

A

Sevoflurane can be used to induce anesthesia. Isoflurane and Desflurane cause cough and laryngospasm and should not be used to induce general anaesthesia.

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10
Q

Identify the two most commonly used drugs to induce anesthesia.

A

1) Propofol

2) Sevoflurane

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11
Q

Which situations may inhalational anesthetics be used to induce anesthesia ?

A

If worried about compromised airway that may be obstructed, and worried that may not be able to maintain airway when patient is unconscious

This may constitute Total intravenous anesthesia (TIVA), “a technique of general anesthesia which uses a combination of agents given exclusively by the intravenous route without the use of inhalation agents”

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12
Q

Is it possible to maintain anesthesia with IV agents ?

A

Yes, propofol only.

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13
Q

Identify the three most commonly used drugs to maintain anesthesia.

A

Sevoflurane
Other volatile agent
Nitrous Oxide

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14
Q

What is Entonox ?

A
  • 50:50 nitrous oxide : oxygen
  • Good analgesic agent, used in labour (to manage childbirth) and in trauma
  • Self-administered, patient holds mouth piece (safety mechanism, if too drowsy let it go and patient wakes up)
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15
Q

Explain the pharmacodynamics of General Anesthetics.

A
  • The more lipid soluble: the more potent: the lower the MAC (minimum alveolar concentration, i.e. concentration required for 50% to fail to respond to surgical stimulus for any one drug)
  • The more blood soluble: the slower the onset

IDEAL DRUG insoluble in blood (speedy onset) and lipid soluble (potent)
BUT some drugs don’t fit lipid solubility theory (e.g. Isoflurane)

• Anesthetic agents also act on different receptors to inhibit or excite them (potentiate inhibitory receptors and dampen down excitatory receptors)

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16
Q

Identify the main receptors acted upon by anesthetic agents.

A

GABA A
NMDA Receptors
Sodium Channels
Background Potassium Channels

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17
Q

What current research is being done to develop future anesthetic agents ?

A
  • Research using knock-in mice
  • However, unlikely to be any new anaesthetics…economics! (small proportion of population will have an anesthetic, and only have one, V of drug used low, no incentive for more drugs to be developed)
18
Q

What are the specific functions of some of the subunits of the GABA receptor wrt anesthetics ?

A
  • Intravenous anaesthetics mediated by β3 subunit

* β2 subunit mediating IV hangover

19
Q

Identify the receptor(s) acted upon by the following drugs:

  • Etomidate
  • Propofol
  • Barbiturates
  • Volatile anesthetics
  • Nitrous Oxide
  • Xenon
  • Ketamine

As well as the general effect of each on consciousness and movement.

A

Refer to slide 21.

20
Q

What are the main uses of Ketamine ?

A

Useful in field anesthesia:

Very CV stable (no negative inotropic effects, does not drop BP) and does not depress respiration (keeps them breathing). Also very good analgesic. Often in the field, bad accidents and patient lost blood and heading towards shock, and not much equipment to maintain airway or breathing for them.

21
Q

Identify any side effects of Ketamine.

A
  • Emergence phenomena, patients hallucinate afterwards, have bad trips
  • In misuse, bladder problems (stone bladder, cannot expand or contract, patients often have to have cystectomies)
  • Dissociative “k-hole” (in misuse)
22
Q

Identify anesthetics which are also drugs of misuse.

A

Ketamine

Nitrous Oxide

23
Q

What is the route of administration when Ketamine is misused ?

A

Sniffed/snorted

24
Q

Which class of controlled drugs does Ketamine belong to ?

A

Class B

25
Q

Which parts of the CNS do anesthetic agents act on ?

A

Anesthetic agents acts on Thalamus, but also cortex, brainstem, and on spinal cord for muscle relaxation

26
Q

Explain the pharmacokinetics behind waking up.

A

Patients wake up because of redistribution of the drug.

-Giving drug into bloodstream (either, by IV injection or inhaled into lungs)
-Brain has big blood supply so large amount of drug gets into brain and concentration in brain rises
-When brain concentration is high, patient becomes unconscious
-When cease administration, concentration in brain falls, drug comes out of brain, re-enters bloodstream, and goes to the intermediate compartment (muscles, skin, other organs), or into vessel poor compartment which is essentially fat (fat acts a large reservoir in body, drugs are lipid soluble). When this occurs, and brain concentration drops, patient wakes up
STILL DRUG IN THE BODY, JUST REDISTRIBUTED

27
Q

Briefly state how most anesthetic agents are metabolised, and excreted.

A

Mosy of drugs metabolised by liver, excreted by kidneys.

28
Q

Identify side effects of most anesthetics.

A

1) Hangover effect (because anticipate low levels of drug hanging around so patient reaction time slowed)
2) CV effects (virtually all anaesthetic agents will to a greater or lesser effect have a negative inotropic effect on the heart and will reduce systemic vascular resistance, i.e. drop BP)
3) Respiratory Depression (may lead to obstruction of the airway, partly due to lost muscle tone)

29
Q

Identify any anesthetic agents without a negative inotropic effect on the heart.

A

Ketamine (positive effect on sympathetic system, maintains BP)

30
Q

What is the mechanism of respiratory depression of anesthetic agents ?

A

IV agents: fall in respiratory rate

Inhalational agents: Fall in tidal V

Hence minute V falls (for both), pCO2 rises

31
Q

What is the clinical implication of the respiratory depression effect of anesthetic agents ?

A

Must be prepared to maintain patient airway

32
Q

Identify the properties of an ideal anesthetic agent.

A 
• Act rapidly
• Pleasant (no pain if IV, good smell if inhalational)
• Cheap to manufacture 
• Stable (soda lime)
• Analgesic effect
• Amnesic effect
• Minimal “hangover” (quick discharge)
• NOT Irritant on veins or airways
• NOT Emetic
• Minimal effects on other systems
- Breathing
- Cardiovascular
• NOT produce toxic metabolites
• NOT cause histamine release / anaphylaxis
33
Q

What is the function of soda lime with anesthetic agents ?

A

Use soda lime to absorb CO2 in anesthetic breezing circuits (so want anesthetic agents to interact with that)

34
Q

Why do we want to avoid emesis in the context of anesthetic agents ?

A

Partially unconscious patient and emesis, may have inhalation aspiration (which may result in pneumonia)

35
Q

Identify the main pros and cons of Thiopentone as an anesthetic agent, and state the clinical situation where it may be used.

A

THIOPENTONE

  • Pros: Quicker for getting patients off to sleep
  • Use if patient in on full stomach and is an aspiration risk
36
Q

Identify the main pros and cons of Etomidate as an anesthetic agent, and state the clinical situation where it may be used.

A

ETOMIDATE

  • Pros: CV Stable
  • Cons: Painful injection + patients gets twitchy and wriggly as unconsciousness occurs
  • Patient with septic shock or CV unstable in general
37
Q

Identify the main pros and cons of Propofol as an anesthetic agent, and state the clinical situation where it may be used.

A

PROPOFOL

  • Pros: Dampens down laryngeal reflex (patients don’t go into laryngospasm when intubated or given masks)
  • Cons: Drops BP and causes respiratory depression
  • Painful injection
38
Q

To what extent is Ketamine ever given for analgesia ?

A

Ketamine is a very good analgesic agent, sometimes given in subanaesthetic doses for analgesia.

39
Q

What is the inhalational induction drug of choice ? for obese patients ?

A

Sevoflurane (least irritant on the airway)

Desflurane used in obese patients

40
Q

Identify other non-anesthetic agents which may be used in conjunction with anesthetics. What is their function ?

A

Midazolam (to give less inductive anesthetic e.g. popofol, also because latter may cause drop in BP)

Anti-emetic

Morphine (analgesic)

41
Q

Identify the main factors which affect selection of anesthetic drugs and techniques.

A
  1. health and requests of the patient (e.g. if on full stomach use Thiopentone)
  2. the properties of the drugs (children, gas or needle ?)
  3. the requirements of surgery (does surgery need more muscle relaxant? does it require patient to be fully still?)

MD4001 (74 decks)

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