P11: General Anaesthetics Flashcards
(50 cards)
What are the 3 main effects of GA
Sedative
Hypnotic
Analgesic
What are sedatives, hypnotics and analgesics
- Sedative - compound that reduces irritability or excitation
- Hypnotic - compound that induces sleep
- Analgesic - compound that reduces pain sensation without loss of consciousness
Name typical GAs in use
Desfluorane sevofluorane Fentanyl Propofol Thiopentone Isofluorane
What are the 4 stages of Anaesthesia
- Analgesia Stage
- Excitement Stage
- Surgical Anaesthesia Stage
- Medullary Depression Stage
What happens in the 3rd plane of the Analgesia Stage
Complete analgesia and amnesia, disorientation, vertigo/ataxia, increased respisation, BP and HR
What happens in the excitement stage of anaesthesia
Loss of consciousness to automatic breathing
What can happen to respiration in the surgical anaesthesia stage
Automatic respiration to respiratory paralysis
What happens in the first plane of surgical anaesthesia
Cessation of eye movements, loss of swallowing reflex
What happens in the second plane of surgical anaesthesia
Laryngeal reflex lost, tear secretion increases, regular deep breathing, response to skin stimulation lost
What happens in the third plane of surgical anaesthesia
Progressive intercostal paralysis, diaphragmatic respiration persists, pupils dilated and light reflex lost
What happens in the fourth plane of surgical anaesthesia
Complete intercostal and diaphragmatic paralysis (apnea)
What happens in the medullary depression stage
Stoppage of respiration to death - medullary paralysis = respiratory depression, vasomotor collapse and death
What can be used to prevent many of the changes found in the stages of anaesthesia
Neuromuscular blockers
What is the lipid theory of GA mechanisms
- Relationship between lipid solubility and anaesthetic potency
- Anaesthesia occur if solubilisation of the GA in the lipid bilayer causes a redistribution in membrane lateral pressure
- Ion channels in particular are highly sensitive to membrane lateral pressure
- Increased pressure prevents channels opening limiting neural excitation
What is the protein theory of GA mechanisms
- Specific targeting of CNS receptors
- GABA, Glycine, 5-HT and ionotropic glutamate receptors and voltage gated ion channels
What are the 2 major classes of GA and give examples of each
Intravenous - propofol, thiopnetone
Inhalation -
- Gaseous - Nitrous Oxide
- Voltaile liquids - desfluorane, sevofluorane, isofluorane, halothane
Define the Minimum Alveolar Concentration (MAC)
Steady state partial pressure (%) of an inhalational agent required for immobility of 50% of subjects exposed to a noxious stimulus (surgical incision)
What is the Minimum Alveolar Concentration (MAC) used for
- Provides a means to compare the potency of the various inhalational agents
- Serves as a guide to determining dose
50% of the MAC dose (MAC awake) gives what response from patients
50% of patients can be woken
100% of the MAC (MAC) dose gives what response from patients
50% of patients wont move at surgical incision
130% of the MAC dose (ED95) gives what response from patients
95% of patients will not move at surgical incision
150-200% of the MAC dose (MAC-BAR) gives what response from patients
50% of patients have blocked autonomic responses
Describe the characteristics of sevoluorane and its MAC value
Rapid-acting Volatile liquid anaesthetic Non-irritant Rapid recovery MAC - 2.1% NB - has largely replaced halothane
Describe the side effects of sevofluorane
- Can trigger malignant hyperthermia
- Can increase intracranial pressure
- Little effect on heart rhythm compared with other volatile anaesthetics
