4 - General Anaesthetics Flashcards
General Anaesthetics Parameters (5) That Are Reversible
Analgesia
Amnesia
Loss of consciousness
Inhibition of sensory and autonomic reflexes
Skeletal muscles relaxation
Stages of Anesthesia (Guedel’s Signs): 1 - Stage of Analgesia (3)
Analgesia
Amnesia
End of this stage there is LOC and goes to next stage
Stages of Anesthesia (Guedel’s Signs): 2 - Stage of Excitement (6)
LOC and begins to respire on own
Disinhibition
Delirious excitement
Irregular respiration
Amnesia
Reflexes enhanced, unpleasant stage that is reduced
Stages of Anesthesia (Guedel’s Signs): 3 - Stage of Surgical Anesthesia (5)
Deep unconsciousness
Respiration is regular
Muscle relaxation
Planes 1,2,3, and 4 depending on patient size, eyeball reflexes, and diaphragmatic/chest muscles paralysis
Most surgeries are performed in plane 3
Stages of Anesthesia (Guedel’s Signs): 4 - Stage of Medullary Paralysis/Toxic (2)
Severe respiratory and cardiovascular depression
Toxic
Types of General Anaesthesia (2)
Intravenous - used to induce anaesthesia
Inhalation - used to maintain anaesthesia
Intravenous Anaesthetics: Barbiturates (2 Drugs + statement)
Thiopental
Methohexital
Used to INDUCE anaesthesia
Intravenous Anaesthetics: Benzodiazepines (2)
Midazolam
Diazepam
Intravenous Anaesthetics: Opoid Analgesics (4)
Morphone
Fentanyl
Sufentanil
Alfentanil
Intravenous Anaesthetics: Others (3)
Propofol
Ketamine
Etomidate
Inhaled Anaesthetics: Gas (1 and Taken up by?)
Nitrous Oxide (Less soluble in blood (low coefficient), so faster induction of anesthesia)
Take up by alveoli by gas exchange
Inhaled Anaesthetics: Volatile Liquids (5 and Taken up by?)
Halothane (More soluble in blood (high coefficient), so slower induction of anesthesia)
Enflurane
Isoflurane
Desflurane
Sevoflurane
Take up by alveoli by gas exchange
Balanced Anaesthesia Defined
Combination of intravenous and inhaled drugs
Inhaled Anaesthetics: Pharmacokinetics (Steps)
Anaestheic machine –> Breathing circuit via FGF –> Lungs –> Arterial and Venous blood –> Brain and back
Factors Affecting Uptake and Distribution (2)
The concentration of an inhaled anesthetic in a mixture of gases is proportional to its partial pressure –> Higher the partial pressure of the gas in alveoli –> faster uptake of gas into the blood and into brain, faster inducing
Increase partial pressure by increasing the dose (concentration) of anaesthetic
The speed of induction of anesthesia depends on blood gas solubility
Blood Gas Solubility: Gas Partition Coefficient Defined (Long)
Relative Affinity of an anesthetic/gas towards the blood compared with that of INSPIRED GAS
So, if the anaesthetic agent has more affinity towards the blood, it means it’s more soluble in blood (higher coefficient); if towards inspired air, less soluble in blood (lower coefficient)
An agent with a high coefficient that’s more soluble in blood, the MORE of the agent MUST BE DISSOLVED to RAISE the PARTIAL PRESSURE (so it takes time) –> INDUCTION of ANESTHESIA WILL BE SLOWER
On the other hand…
An agent with low coefficient that’s less soluble in blood diffuses from inspired air to the alveoli to blood, the rise in partial pressure will be much quicker (since it’s not soluble in blood) and rate of inducing anaesthesia will be faster
Blood Gas Solubility: Coefficient
Less than 1 ==> Less soluble in blood, arterial tension rises quickly, fast onset of action of anesthesia (e.g. NO)
Greater than 1 ==> Highly soluble in blood, arterial tension rises slowly (takes time), slow onset of action of anesthesia
Minimum Alveolar Concentration (MAC) Defined (4)
Measure of potency
Concentration of anesthetic at which 50% of subjects do not show a motor response to a surgical incision (so basically, dose of anesthesia required to perform surgery) –> Usually MAC of 1
If MAC value is low: potency is high (so only a small dose required for anasthesia)
1.3 MAC –> nearly 100% will NOT respond to stimuli