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Pharmaco Yr 2 Term 2 > General Anesthesia > Flashcards

General Anesthesia Flashcards

1
Q

What is pain?

A

Pain is an unpleasant sensory or emotional experience associated with actual or potential tissue damage

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2
Q

What is General Anesthesia?

A

Medically induced coma with loss of protective reflexes resulting from the administration of one or more general anaesthetic agents

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3
Q

What are the 5 aims of General Anaesthesia?

A
  1. Unconsciousness
  2. Amnesia
  3. Analgesia
  4. Relaxation of skeletal muscles
  5. Loss of autonomic nervous system reflexes
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4
Q

What are the 3 ideal factors of a general anaesthetic?

A
  1. Rapid Onset - Induce smooth and rapid loss of consciousness
  2. Rapid Offset - Allow for prompt recovery of consciousness after discontinuation
  3. Wide Safety Margin and no adverse effects
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5
Q

What is Balance techniques?

A

Combining general anaesthetics to achieve all the desirable effects and favourable properties and minimise risks

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6
Q

Should GA be used for minor procedures?

A

No. Use LA or monitored anaesthesia instead

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7
Q

What is Monitored Anaesthesia?

A

Patient maintains a patent airway and responds to commands

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8
Q

What are the 4 stages of Anaesthesia?

A
  1. Analgesia - initially analgesia without amnesia, then both are achieved quickly
  2. Excitement - Amnestic but appear delirious, irregular respiration, may retch or vomit if stimulated
  3. Surgical Anaesthesia - Regular respiration recurs (stops) followed by Apnea. Loss of eye movements, eye reflexes
  4. Medullary Depression - Severe depression of brain stem and medullary function
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9
Q

What is the most reliable sign of surgical anesthesia?

A

Loss of motor and autonomic response to noxious stimuli

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10
Q

What other drugs are used in conjunction with anesthesia?

A

Opioid Analgesics
Muscle Relaxants
Cardiovascular Drugs
Ventilators

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11
Q

What are examples of inhaled gaseous analgesics?

A

Nitrous Oxide

Cyclopropane

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12
Q

What are examples of inhaled liquid analgesics?

A 
Ether
Halothane
Enflurane
Desflurane
Isoflurane
Sevoflurane
Methoxyflurane
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13
Q

What type of Anesthetic is commonly used now?

A

Inhaled Liquid Analgesics

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14
Q

What are the 5 factors that affect the rate at which a therapeutic brain concentration of inhaled analgesic is achieved?

A
  1. Solubility - low solubility in blood –> high arterial tension rapidly –> rapid equilibration with the brain –> fast onset of action eg. NO
  2. Anesthetic concentration in inspired air - increase = increase rate of transfer into blood/brain
  3. Rate and depth of pulmonary ventilation - increase –> increase anesthetics with moderate to high solubility (eg. haloethane) ; decrease (opioid analgesics) –> reduce onset
  4. Pulmonary blood flow - increase –> decrease in rate of rise of anesthetic (moderate to high solubility) tension in the blood and brain
  5. Arteriovenous Concentration Gradient - depends on uptake of anesthetic by tissues (lipophilic) = high, high conc gradient increases the time to achieve equilibrium with brain
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15
Q

What are the 6 factors that affect the rate of recovery from inhaled analgesia?

A
  1. Solubility in blood - insolube –> eliminated faster ; soluble –> accumulated in muscle, skin and fat
  2. Duration of exposure –> increase
  3. Pulmonary blood flow
  4. Rate of ventilation
  5. Hepatic metabolism (eg. haloethane)
  6. Bacteria in GI tract (eg. NO)
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16
Q

What is the mechanism of action of Inhaled Anaesthetics?

A

Modifies ion currents by direct interactions with multiple members of the ligand gated ion channel family

    • GABA - direct activation –> indirectly increase Cl flux
    • Glycine
    • Nicotonic

Acts at multiple levels of the CNS –> affects sensitivity of specific neurons and pathways esp for:

  1. Spino-thalamic tract (pain)
  2. Reticular activating system (consciousness)
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17
Q

What are the effects that inhaled anaesthetics has on our organ systems?

A
  1. Cardiovascular:
    a. Decreased mean arterial pressure –> reduction in cardiac output (haloethane, enflurane), decrease in systemic resistant (isoflurane, sevoflurane)
    b. Variable effect on heart rate
  2. Depression of myocardial function
  3. Respiratory:
    a. Decrease in minute ventilation (Apnea)
    b. Reduced response to hypercapnia (Respiratory Depressant)
    c. Increase apnoic threshold - important to support ventilation in recovery
    d. Depression of muco-ciliary function
    e. Bronchodilation (haloethane, sevolflurane)
  4. Brain: Increase cerebral blood flow by decreasing cerebral vascular resistance
  5. Renal: Impairs renal autoregulation by reducing renal blood flow
  6. Liver: Decreased hepatic blood flow
  7. Uterus: Halogenated anesthetics are potent uterine muscle relaxants
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18
Q

Why are inhaled anesthetics bad for patients with increased intracranial pressure? What inhaled drug should be used?

A

Because it also increases cerebral blood flow.

Nitrous Oxide - least likely to increase cerebral blood flow

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19
Q

Which inhaled drug can cause liver damage?

A

Haloethane - Hepatitis, sudden and severe liver necrosis (several days after anaesthesia)
Reactive metabolites may directly damage the liver or initiate immune mediated responses

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20
Q

Which inhaled drug can cause Renal Dysfunction?

A

Methoxyflurane

Releases fluoride during metabolism

21
Q

What toxic side effect can inhaled GA drugs have?

A

Malignant Hyperthermia
Autosomal dominant skeletal muscle disorder
GA triggers hypertension, tachycardia, severe muscle rigidity, hyperthermia and acidosis
Increase in muscle cell calcium

Treatment: Dantrolene to reduce calcium and supportive measures

22
Q

What is haloethane usually used for?

A

Adults: maintain anesthesia - medium onset and recovery
Children: Induction

23
Q

What is Nitrous Oxide usually used for?

A 
Adjunct, Labour pain
Lacks potency
20%: significant analgesia
30-80%: sedation
80% (max): cannot give complete unconsciousness or surgical anaesthesia
24
Q

What are IV anesthetics used for?

A

Induction: Onset of action is faster as it goes directly into bloodstream
Short outpatient procedures: Recovery is sufficiently rapid
Combined with inhaled or LA: Lack analgesic properties

25
Q

What is the mechanism of action of Barbiturates (IV GA)?

A
  1. Binds to GABA receptors and facilitates actions of GABA by increasing duration of GABA gated chlorine channel opening
  2. Acts on AMPA receptors to depress glutamate mediated excitation
  3. Non-synaptic membrane effects
26
Q

Which IV GA drug is desirable for patients with raised intracranial pressure? Why?

A

Thiopental

Decreases cerebral metabolism, O2 consumption and blood flow.

27
Q

What is an inducing GA drug?

A

Barbiturate - Thiopental

28
Q

What is the mechanism of action of Benzodiazepines (IV GA)?

A

Potentiates GABAergic inhibition by increasing the efficiency of GABA without directly activating GABA receptors, through an increase of the frequency of GABA gated chloride channel openings.

29
Q

What are examples of Benzodiazepines?

A

Diazepam
Lorazepam
Midazolam

30
Q

What is the Benzodiazepines used for?

A

Pre-anesthetic Medication and Adjuvants during procedures

Properties: Sedative, Anxiolytic and Amnestic

31
Q

What is are 2 negative effects of Benzodiazepines?

A

High dosages are required for deep sedation –> prolongs anesthetic recovery
Treatment: Flumazenil (benzodiazepine antagonist - short duration of action of 90 mins hence may need multiple doses)

May cause anterograde amnesia

32
Q

What is the mechanism of action of Propofol (IV GA)?

A
  1. Potentiation of GABA receptor activity –> slows the channel closing time
  2. Sodium channel blocker
  3. Endocannabinoid system activity - endogenous lipid based retrograde neurotransmittor
33
Q

What is the most popular IV GA?

A

Propofol! Rate of onset as rapid as barbiturates, but rate of recovery is even faster

34
Q

What is Propofol used for?

A 
Induction
Maintenance
Sedation
Monitored Anesthesia
Procedural Sedation
35
Q

Which GA drug induces Dissociative Anesthesia?

A

Ketamine

36
Q

What is the mechanism of action of Ketamine (IV GA)?

A

NMDA receptor antagonist

37
Q

What is Dissociative Anesthesia?

A

Catatonia (cannot move), amnesia, analgesic WITHOUT lost of consciousness

38
Q

What is special about Ketamine?

A

Only IV anesthetic with both analgesic and anesthetic properties.

39
Q

Who should Ketamine be used on?

A

Poor risk elderly patients
Those in cardiogenic or septic shock
Stimulates the CVS through stimulation of Sympathetic CNS and inhibiting uptake of noradrenaline

40
Q

Who should Ketamine not be used on

A

Neurosurgical Patients

Increases Intracranial Pressure

41
Q

What are the negative side effects of Ketamine?

A

Post-operative disorientation, illusions and dreams

42
Q

What is Balanced Anaesthesia?

A
  1. IV for induction
  2. Inhaled for maintenance
  3. Muscle relaxants to facilitate tracheal intubation and to optimise surgical procedures
  4. LA to provide pre- or peri-operative analgesia
  5. Cardiovascular Drugs to control transient autonomic responses to noxious surgical stimuli
43
Q

What are some alternatives to GA?

A

Monitored Anesthesia Care

Conscious Sedation

44
Q

What is Monitored Anesthesia Care?

A

LA + IV GA
The patient is sedated, analgesic and amnestic BUT allowed to continue breathing by themselves.

  1. Midazolam (pre-mediation)
  2. Titrated, variable rate propofol infusion (moderate to deep sedation)
  3. Opioid Analgesics/Ketamine (analgesia and amnesia)
45
Q

What is Conscious Sedation?

A

Sedated but conscious (NO DEEP SEDATION)

  1. Midazolam, Diazepam (reversible by Flumanezil)
  2. Propofol (sedation)
  3. Opioid Analgesics (reversible using Nalaxone)
46
Q

What is Opioid Analgesics reversible with?

A

Nalaxone

47
Q

Does GA reduce risk of Tranurethral resection of the prostate (TURP) syndrome?

A

Yes!

Positive pressure ventilation increases venous pressure and reduces absorption of irrigation fluid.

48
Q

What are IV GAs?

A

Barbiturates - Thiopental
Benzodiazepines - Diazepam, Lorazepam, Midazolam
Propofol
Ketamine

Pharmaco Yr 2 Term 2 (11 decks)

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