YW - General Anaesthetics Flashcards
What is general anesthesia?
General anesthesia is a reversible, drug-induced loss of consciousness
What are 4 features of GAs?
- Anesthetics can be gases, hydrocarbons, alcohols, barbiturates, benzodiazepines, or even ketamine
- Different anesthetics offer varying degrees of analgesia (pain relief), amnesia (memory loss), and muscle relaxation
- Each class has a specific concentration range for effectiveness.
- General anesthetics are delivered systemically to reach the central nervous system (CNS)
What are the stages of general anesthesia? (5)
Stage 1: Analgesia (Pain Relief)
- Patient remains conscious and cooperative.
- Used for pain relief during childbirth or for accident victims (often nitrous oxide and oxygen mix).
Stage 2: Unconscious, No Reflex Depression
- Not ideal for surgery or childbirth (patient not cooperative enough for surgery, too deep for childbirth).
- Unpredictable breathing and gag reflex are challenges.
Stage 3: Surgical Anesthesia
- Desired depth for surgery.
- Gradual levels of unconsciousness and reflex depression.
- Lighter levels: Prevent movement for minor procedures.
- Deeper levels: Suppress reflexes for major abdominal surgery.
Stage 4: Respiratory Paralysis
- Deepest plane of anesthesia, breathing stops.
- Used cautiously to meet surgeon’s needs but carries risk.
Stage 5: Death
- Loss of vital reflexes, fatal outcome.
What factors determine the speed of induction and recovery? (4)
1) Blood/gas partition coefficient (blood solubility) - Lower solubility in blood leads to faster equilibration, meaning less drug needs to be transferred via lungs to achieve a given partial pressure.
2) Oil/gas partition coefficient (lipid solubility) - This affects how quickly the drug distributes to tissues.
3) Physiological factors:
- Alveolar ventilation rate: How well the lungs remove the anaesthetic from the blood.
- Cardiac output: How well the heart pumps the blood throughout the body.
4) Metabolism: Some anesthetics are broken down by the body, which can affect how long they last
What does a lower blood solubility mean?
Anesthetic enters bloodstream faster.
- Less drug dissolves, so it moves quicker to reach the effective level
- Less total drug is needed to achieve the desired effect
How do intravenous anesthetics act quickly?
They are lipophilic, meaning they dissolve easily in fats. This allows them to pass through the blood-brain barrier and reach the brain quickly.
- The effects of the medication wear off as it gets redistributed throughout the body to less perfused tissues (muscle and fat)
What is the Meyer-Overton rule?
The Meyer-Overton rule states that there is a strong correlation between a drug’s potency as an anesthetic and its lipid (fat) solubility
What are some potential protein targets of general anesthetics? (4)
1) Ligand gated ion channels.
- GABA receptor and glycine receptor (generally potentiated).
- Nicotinic acetylcholine receptors (inhibited).
- Glutamate receptor NMDA (inhibited).
2) Ion channels
- Voltage gated ion channels (Ca2+ activated K+ channels).
- K+ Leak Currents (Twin pore channel; ether a go-go).
3) G-protein coupled receptors (neuromodulators).
- Modelled against Rhodopsin and suggestions for other GPCRs
4) Transmitter release proteins.
- Evidence for direct binding to proteins that control release of neurotransmitters.
How do specific mutations affect anaesthetic action? (2)
1) Mutations at the GABA receptor a subunit (a291 and t415) and the GABA receptor b subunit (n265 and m286) potentiate effects at the GABA receptor.
- These are inhibitory receptors, so potentiation increases inhibition.
2) Mutations at the TASK3 channel (m159 and the 238-vlrflt-243 sequence) potentiate effects at the Twin pore K+ channels.
- When open, these channels inhibit, so potentiation increases inhibition.
What medications are used for general anesthesia in surgery? (5)
1) Induction (Loss of Consciousness):
- Propofol (fast-acting, fewer side effects)
2) Maintenance (Consciousness & Pain):
- Sevoflurane (inhalation anesthetic)
Opioids (IV analgesics for stronger pain relief)
3) Muscle Relaxation:
- Atracurium (neuromuscular blocking agent)
4) Parasympathetic Block:
- Atropine (reduces bradycardia and secretions)
5) Peri-operative Management:
Pre-operative:
- Benzodiazepines (reduces anxiety, may cause amnesia)
Post-operative:
- Droperidol or Metoclopramide (controls nausea and vomiting)
What are 3 benefits of GA medications?
- Fast induction and recovery
- Avoids deeper anesthesia stages (reduces risk of lost reflexes)
- Maintains homeostasis
