16. General anaesthesia, inhalational anaesthetics Flashcards
(15 cards)
What is general anaesthesia?
General anaesthesia is the complete loss of sensory, voluntary and reflexive motor activity, while keeping the respiratory and vasomotor centre functioning. Analgesia is NOT the same. We have general and local anaesthesia
- Local anaesthesia = Without loss of consciousness
- General anaesthesia = Total loss of consciousness
Definitions of analgesia and anaesthesia
Analgesia = Lack of pain sensation
Anaesthesia = Lack of sensation, total loss of motoric activity and pain relief
General anaesthesia, mechanism of action
1. Presynaptic action
Calcium channels are blocked and the neurotransmitter release is decreased.
Normally, for a neuron to send a message, it release neurotransmitters which depends on the calcium entering the cell through the calcium channels.
2. Postsynaptic action
After neurotransmitters are released, they travel to the next nerve cell and bind to the receptors there.
The drugs of general anaesthesia make the binding harder, we call this depression of excitatory neurotransmission.
At the same time, general anaesthesia can enhance the effect of GABA, which is an inhibitory neurotransmitter, by binding to a specific site on the GABAA receptor called allosteric activation, making it easier for GABA to inhibit the nerve cell (neuron)
Name the different stages of general anaesthesia
1. Stage 1
Analgesia begins, the induction phase. The patient experiences disordered consciousness
2. Stage 2
Excitement phase.
The patient might experience signs of delirium and agitated behaviour. It occurs as the patient transitions from consciousness to unconsciousness
3. Stage 3
Surgical anaesthesia. Characterised by unconsciousness, amnesia, immobility and unresponsiveness to surgical stimulation.
4. Stage 4
Overdose., leading to respiratory paralysis
What is inhalational anaesthetics?
are used for the induction and maintenance of general anesthesia as well as sedation, by inhalation
Active substances of inhalational anaesthetics
- Desflurane
- Sevoflurane
- Isoflurane
- Dinitrogen monoxide
- Halothane (!! BANNED !!)
Inhalational anaesthetics, desflurane
Less potent
Very safe
Minimal metabolism
High price
Inhalational anaesthetics, Sevoflurane
Safe to use, but less potent
Short onset and quick awakening ⭢ less frequent excitation.
NOT recommended in status epilepticus
Inhalational anaesthetics, Isoflurane
Less potent, irritating
Low hepatic metabolism
Shorter onset and awakening
It is a good anticonvulsant
Inhalational anaesthetics, dinitrogen monoxide
It is a gas that can help with analgesia and sedation with a concentration above 50%.
Dinitrogen monoxide MAC (Minimum Alveolar Concentration) is greater than 100% and is used with other anaesthetic agents, giving extra oxygen when used.
It is not metabolised; the body does not break it down
Inhalational anaesthetics, halothane
Most potent drug
It is non-irritating and has a pleasant smell.
!! BANNED !! due to hepatotoxicity
Mechanism of action in case of inhalational anaesthetics
The anaesthetic is mixed with oxygen and inhaled by the animal, and travels to the lungs and then into the bloodstream. The bloodstream carries the anaesthetics to the brain. Because the anaesthetics are fat-soluble, they can easily cross the BBB and enter the brain tissue.
Inhalational anaesthetics affect multiple receptor and ion channels
1. Enhancing inhibitory signals:
Enhancing the GABA receptors
2. Block excitatory signals:
3. Specific receptor interactions: They work on GABA receptors, NMDA receptors.
Inhalational anaesthesia, indication
General anaesthesia
Inhalational anaesthesia, pharmacological effect
- Unconisuness
- Muscle relaxation
- Bronchodilation
- Anticonvulsive effect
Inhalational anaesthesia, side effects
- Respiratory irritations
- Dose-dependent cardiovascular depression
- Pre- and post-narcotic excitation, mostly seen with sevoflurane
