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Pharm_GA_LA Flashcards

LA(1-17), GA(18-30) (46 cards)

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1
Q

What are the 2 major types (class) of Local Anaesthetics (LA)s?

A
  • Ester LAs
  • Amide LAs
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2
Q

MOA for Local Anaesthetics (LA)s

A

Stop axonal conduction by blocking sodium channels in the axonal membrane when applied locally in appropriate concentration
- Prevent Na ion entry
- Slow down or bring conduction to a halt

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3
Q

Many LA bind most strongly to which of the following states?
(1) Closed
(2) Activated
(3) Inactivated
(4) Deactivated

A

Many LA bind most strongly to the inactivated and activated states.

LA works better when there’s more pain.

The passage of train of action potentials causes the Na channel to cycle through open and inactivated states.

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4
Q

Mechanism behind the Onset of LA

Think Size & pH

A

Anaesthetics that penetrate the axon most rapidly have the fastest onset.

Small size -> High Lipid Soluility
Low Ionization (@Tissue pH) –> Faster Onset

pH dependency
LA molecules are weak bases (pKa 8-9),
mainly (but not completely) ionized at physiological pH

LA potency is strongly pH-dependent:
-Alkaline pH -> increased LA activity (proportion of ionized molecules is low)
-Acidic pH -> decreased LA activity (proportion of ionized molecules is high)

When skin is burnt, alkaline pH increases.
When skin is inflamed, LA does not work well

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5
Q

Different types/class of LA,
and how each of the class metabolize in the body system

A

Ester type - metabolize by blood esterases, higher chance of allergic reactions
(E.g. Procaine)

Amide type - metabolize by liver enzymes, low allergic reactions
(E.g. Lidocaine)

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6
Q

Pharmacokinetics of LAs
- Absorption

A

Absorption mainly by local action
- minimal amount will get into the bloodstream

Systemic Distribution by 2-compartment model
- Alpha phase: Steep exponential decline in LA, rapid distribution in blood & highly perfused organs (brains, liver, heart & kidney)
followed by
- Beta phase: Slower decline in LA, may assume a nearly linear rate of decline
Distribution to less perfused tissue (e.g. muscle, gut)

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7
Q

What is the S/E, A/E, or Caution in the use of LA?

A

Potential risk of Toxicity.

(LA blocks all types of voltage-gated sodium channels)

Unintended large doses of LA if accidentally injected by IV/ intra-arterial can give rise to systemic toxicity.

Over-dose of LA injected locally & subsequently leads to high & toxic blood level following absorption - hence the onset of toxic S/S may appear late as compared to the direct IV scenario (immediate)

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8
Q

How do we mitigate over the risk of toxicity in the use of LA?

A

LA can be combined with Epinephrine. (administer together, not before or after LA)

Epinephrine is a vasoconstrictor,
Hence reduced blood flow, rate of absorption into the system is slower.

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9
Q

List of LAs with high toxicity

A

Bupivacaine
Cocaine
O-tuluidine

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10
Q

List of LAs with high toxicity
- Bupivacaine

A

Bupivacaine is more cardiotoxic than most other LAs
(Double check if its suitable for cardiac patients)

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11
Q

List of LAs with high toxicity
- Cocaine

A

Cocaine blocks NA(Norepinephrine) reuptake,
Increased NA causes vasoconstriction & hypertension

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12
Q

List of LAs with high toxicity
- O-tuluidine

A

O-toluidine (metabolite of prilocaine)
- Causes methaemoglobin

Blood will start to turn blueish,
Ability to have oxygen exchange is compromised, treat by giving:
- IV methyleneblue/ ascorbic acid methaemoglobin to haemoglobin

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13
Q

Patient is allergic to PABA,
Which type of LA is suitable ?
(Amide / ester?)

A

Patient allergic to PABA, it will trigger an allergic reaction when given Ester type LAs.
Ester type LAs can be hydrolysed to PABA.
- Triggering an allergic reaction (mild to severe)
(skin rash, anaphylactic shock)

Amide type of LA is more suitable for patients allergic to PABA

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14
Q

Methods of Administration for LAs

A
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15
Q

Commonly used LAs for Ear, Nose, Throat procedures

A

Cocaine gives good penetration and vasoconstriction, thus most often used for ear, nose and throat procedures

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16
Q

Clinical applications for Epidural anaesthetics (Injected)

A

Epidural anaesthetics
Regional nerve block (analgesia)
Lidocaine, bupivacaine (may combine with opioid fentanyl to reduce LA dose)

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17
Q

Clinical applications for Dental anaesthesia (injected)

A

Dental anaesthesia
- Lidocaine (short time)
- Bupivacaine (long time)
(may combine with epinephrine -> vasoconstrictor -> control bleeding)

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18
Q

Different types/class of General Anaesthetics (GA)s

A
  • Inhalation Anaesthetics
  • Intravenous (IV) Anaesthetics
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19
Q

Classification of Inhalant GAs
(mode of administration)

Study These Flashcards
A

Volatile Liquids:
- Halothane
- Enflurane
- Desflurane
- Isoflurane
- Sevoflurane

Gases:
- Nitrous Oxide

20
Q

MAC

Study These Flashcards
A

Minimum alveolar concentration (MAC)

  • is an index of inhalation anaesthetic potency ie.
    low MAC = high anaesthetic potency
  • is defined as the minimum concentration of drug in the alveolar air that will produce immobility in 50% of patients exposed to a painful stimulus.
21
Q

Pharmacokinetics (PK) of GAs
- Absorption

Study These Flashcards
A
  1. concentration of anaesthetic in inspired air
  2. solubility of GA
  3. blood flow through lungs

Any incr. in the factors above will incr. GA uptake into blood.

22
Q

Pharmacokinetics (PK) of GAs
- Distribution

Study These Flashcards
A

determined by regional blood flow -> which tissue(s) receive GA
Anaesthestic levels in these tissues equilibrate with those in blood quickly after of administration

23
Q

Pharmacokinetics (PK) of Volatile Liquids GAs
- Elimination

Study These Flashcards
A

Export in Expired breath
inhalation anaesthetics are eliminated almost entirely via the lungs
minimal hepatic metabolism

factors that determine uptake also determine elimination
eg. since blood flow to brain is the highest, anaethetic levels drop rapidly when administration is stopped

Metabolism
note: some metabolites can be toxic
eg. inorganic fluorides of isoflurane and enflurane are nephrotoxic; halothane is hepatotoxic

24
Q

Volatile Liquids GA
- Halothane

Study These Flashcards
A
  • First modern inhaled anaesthetic, standard for comparison
  • Volatile liquid, non-flammable and non-irritating
  • Potent (MAC 0.75%)
  • Medium rate of onset and recovery
  • Little or no analgesia until unconsciousness supervenes
  • Causes respiratory depression dose-dependently
  • Decreases B.P. due to depression of cardiac output Bradycardia & arrhythmia may also occur leading to hypotension and dysrhythmia
  • Relaxes skeletal muscle and potentiates skeletal muscle relaxants
  • May lead to halothane-associated hepatitis
25
Volatile Liquids GA - Isoflurane
Pungent smell Potent (MAC 1.4%) Medium rate of onset and recovery Similar to halothane with less hypotension and arrhythmia Decreases B.P. due mainly to decrease in systemic vascular resistance
26
Volatile Liquids GA - Sevoflurane
Potent (MAC 2%) More rapid rate of onset and recovery Metabolized in the liver to release inorganic fluoride, also nephrotoxic Unstable when exposed to carbon dioxide absorbents in anaesthetic machines, degrading to a compound that is potentially nephrotoxic
27
Gaseous GA - Nitrous Oxide
Odourless gas Non-flammable Rapid onset and recovery but lack potency (MAC 105%) **Nitrous oxide alone gives analgesia and amnesia but not complete unconsciousness or surgical anaesthesia** Patients undergoing GA receive nitrous oxide to **supplement the analgesic effects of primary anaesthetic** When used alone: as analgesic agent (eg. dentistry, during delivery*) Major concern: postoperative N&V * N2O use in obstetric is known as Entonox – a premixed N2O & O2, 50% each
28
Intravenous Anaesthetics
- an induction agent is a substance that induces unconsciousness - it does not necessarily keep you asleep for very long! **most agents depress respiration – you will need to take over ventilation of patients** may be used **alone or to supplement** the effects of inhalation agents
29
What are the advantages of using both inhaled and intravenous GAs
Inhaled + Intravenous anaesthetics (2 Advantages): 1.Permit dosage of the inhalation agent to be reduced, and 2.Produce effects that cannot be achieved with an inhalation alone
30
Intravenous GAs - 3 types
- Thiopentone - Propofol - Ketamine
31
Intravenous GAs - Thiopentone
* A barbiturate with extremely high lipid solubility * Enters the brain easily and rapidly - rapid onset of * action (unconsciousness occurs 10-20sec after IV) * Single Dose: Re-distributes to less vascularized tissues – ultra-short duration of action (Injected alone & w/o inhale agents, patients wake up ~10min) * Multiple doses/infusions: duration of action depends on clearance * Slow elimination, large Vd, active metabolite (pentobarbital), liver cirrhosis --> can result in prolongation of clinical action. * Extensively bound to plasma protein - small amount of free drug can be excreted by glomerular filtration + reabsorption in tubules. * Less than 1% excreted unchanged
32
Intravenous GAs - MOA
Cause CNS depression by potentiating the action of the neurotransmitter GABA on the GABA-A receptor-gated chloride ion channels
33
Intravenous GAs - Propofol
the **most common** IV anaesthetic used in Singapore – (ready made in injectable form, no need to re-constitute (unlike thiopentone) Induction rate is similar to thiopentone, and recovery is more rapid (patients move sooner and feel better) Used both for **induction & maintenance** Rapid onset (unconsciousness develops within ~60sec) Short duration of action (~3-5min following single injection) because rapid redistribution from brain to other tissues Extensively used in **"day surgery”** - needs continuous, low-dose infusion for extended effects Reduced post-operative vomiting (may be related to an anti-emetic action) Significant cardiovascular effect during induction (**decrease b.p. and negative inotropic) – hypotension** To be **used with caution in elderly patients,** patients with compromised cardiac function, hypovolemic patients
34
Benefits of using Propofol over Thiopentone
- does not req. constitution (ready made IV) - less post-op side effects - rapid onset, rapid recovery - short duration of action
35
Concerns of using Propofol
Significant cardiovascular effect during induction (**decrease b.p. and negative inotropic) – hypotension** To be **used with caution in elderly patients,** patients with compromised cardiac function, hypovolemic patients
36
Intravenous GAs - Ketamine
* racemic (potency: S- > R+); I/M, oral, rectal routes * Produces a state known as **dissociative anaesthesia** ie. patient feels dissociated from environment * **Can cause sedation, immobility, analgesia, and amnesia** * Rapid induction; Responsiveness to pain is lost * **Metabolized in liver **to less active metabolite, excreted in urine & bile *** Large Vd, rapid clearance -> suitable for continuous infusion without the lengthening in duration of action** * Unpleasant psychologic reactions (hallucination, disturbing dreams, delirium) may occur during recovery from ketamine **Risks of psychologic adverse reactions may be reduced with premedication of diazepam or midazolam** * It is the** only IV anaesthetic that possess analgesic property ** -> hence very popular in 3rd world country as the only anaesthetic, due to the lack of other anaesthetic agents.
37
Adjuncts Anaesthetic ? what are these for?
- Sedation - Amnesia - Analgesia - Lower GA doses used - Reduce GA side effects
38
List of adjuncts anaesthetics / post-op care
**1) Benzodiazepines** Anxiolytics, amnesia, sedation prior to induction of anaesthesia **2) α2 Adrenergic Agonists** Sedation prior to and/or during procedures in non-intubated patients **3) Analgesics** Typically administered with GA to reduce anaesthetic requirement **4) Neuromuscular Blocking Agents** Induction of anaesthesia to relax muscles (jaw, neck, airway) to facilitate laryngoscopy and endotracheal intubation
39
List of adjuncts anaesthetics / post-op care - BZD
**1) Benzodiazepines** Anxiolytics, amnesia, sedation prior to induction of anaesthesia Used for anxiolysis, amnesia and sedation prior to induction of anaesthesia (perioperative period) or Used for sedation during procedures not requiring GA Rapid onset when used for induction (unconsciousness develops in 80sec; peak ~2min); sedates ~30min when used by itself. **Metabolized in liver** (elderly tend to be more sensitive, slower recovery) Midazolam (BZD group of drugs) usually has a high therapeutic index -> it has relatively lesser cardiovascular & respiratory depressing effect compare to other IV anaesthetics. **Side effects are compounded **by concurrent usage of other agents (e.g. in Michael Jackson’s case - where multiples drugs had been administered) **Adverse effects can be minimized** by injecting midazolam slowly (over 2 or more minutes) and by waiting another 2 or more minutes for full effects to develop before dosing again
40
List of adjuncts anaesthetics / post-op care - α2 Adrenergic Agonists
**Dexmedetomidine (I/V)** - Highly selective α2 adrenergic receptor agonist - Short term sedation (<24hrs) - Sedation and analgesic effects (doesn’t produce reliable GA even at maximal doses) - Little respiratory depression Tolerable decrease in blood pressure and heart rate Undesirable side effects: nausea, dry mouth, hypotension, bradycardia
41
List of adjuncts anaesthetics / post-op care - Analgesics (NSAIDs)
- Minor surgical procedures -> COX-2 inhibitors and paracetamol - Opioids (Fentanyl, morphine) – perioperative period - Agonist activity at µ-opioid receptors - Relative potency to morphine [duration of action]: - Choice – based primarily on duration of action - Metabolized in liver (except remifentanil is hydrolyzed by tissue & plasma esterases) - Excretion: urine, bile
42
List of adjuncts anaesthetics / post-op care - Neuromuscular blockers
- Depolarizing: **Succinylcholine** - Non-depolarizing (eg. **vecuronium**) - Administered during induction of anaesthesia to relax muscles of jaw, neck, airway --> facilitate laryngoscopy and endotracheal intubation - Aids many surgical procedures and provide additional insurance of immobility Note: barbiturates will precipitate when mixed with muscle relaxants --> should be allowed to clear from the IV line prior to injection of muscle relaxant
43
Nitrous oxide differs from other Gas in __ ?
Nitrous oxide differs from other Gas in : (1) very high MAC, cannot be used alone to produce GA & (2) high analgesic potency, frequently combined with other Gas to supplement their analgesic effects
44
Principle adverse effects of GA
Principal adverse effects of GA: - depression of respiratory - cardiac performance
45
Differences between GA and LA
GA produce unconsciousness and insensitivity to painful stimuli
46
(____) Mac = (___ ) Potency
(Low) MAC = (High) potency Mechanism of action by inhalation anaesthetics

Critical Care_Oncology (7 decks)

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