11 INHALATION ANAESTHETICS/ IV ANASTHETICS Flashcards
What is one understood mechanism of action of volatile anaesthetics
Possibly due its lipophilic properties. Causing non-specific expansion of lipid bilayer and consequent disruption of receptors/ ion channels
Describe the current thinking on mechanism of action of volatile anaesthetics
Though to enhance GABA activity (inhibitory NT). Multisite vs. unifying hypothesis.
Define ‘MAC’
A means of describing potency and dose. 1 MAC = minimum alveolar concentration to produce immobility on standard surgical stimuli (forearm incision) in 50% of patients. The more potent the drug the lower the MAC. Usually described as a percentage of alveolar gas.
What are some covariates that increase MAC
Young age, hyperthermia, heavy alcohol, hyperthyroid, drugs that are stimulants (amphetamines)
What are some covariates that decrease your MAC
Old age, hypothermia, hypothyroid, drugs such as opioids/ depressants, pregnancy, Low 02
Describe the pharmacodynamics of volatile anaesthetics
Hypnosis, immobility, amnesia, decrease cerebral metabolic rate for 02, increase cerebral blood flow and intracranial pressure, lower bp, vasodilation, resp depression, bronchodilation. Also reduce portal blood flow and renal blood flow.
Describe NO
Nitrous oxide. Rapid onset, low potency, analgesic, many adverse effects.
What are the modern agents
Methyl ethyl ethers
Describe isoflurane
Pungent, potent, medium onset, cardiac stability
Describe sevoflurane
Good for induction of children, non pungent, intermediate potency.
Describe desflurane
Pungent, intermediate potency, ideal for long surgeries.
Name three methyl ethyl ethers
Isoflurane, sevoflurane, desflurane.
Describe the concept of balanced anaesthesia and the components/ drugs that encompass it
Hypnosis/ amnesia (iv/ inhalation anaesthetics)
Autonomic areflexia (opioids)
Immobility (NMB)
Name five types of IV anaesthetics
Barbituates, phenols, imidazoles, phenycyclidine derivatives, benzodiazepines
Describe the mechanism of action of IV anaesthetics
Like inhalation anaesthetics mechanism not well understood. Thought to a) enhance GABA–> prolong Cl- current, hyper polarisation.
b) bind to PCP receptor and antagonise glutamate/ suppress excitation.
General pharmacokinetics of IV agents
highly lipid soluble and cross BBB. Acts on Vessel Rich Group organs. Then redistribute into fat and muscle. Metabolism slow.
Describe and give and example of brabituates
Thiopentone. Rapid onset, slow clearance, metabolised in liver, some decrease in peripheral resistance and BP, res depression and loss of airway reflexes. Used in emCS
Describe and give examples of phenols
Propofol. Rapid onset and offset. Fast clearance. Used in maintanence infusion. Causes resp depression and decreased BP.
Imidazoles
Etomidate. Good cardiovascular stability, rapid clearnace, causes adreno cortical inhibition. Causes myoclonus, epileptogenic.
Benzodiazapams
Midazolam. Anti epileptic. Slow onset and offset limits use.
Phencyclidine
Ketamine. Outlier- instead of GABA agonist, supresses excitation (glutamate at NMDA receptors). Has analgesic effect. Maintains airway reflexes, and res drive. Increases cerebral metabolic rate o2, CBF and ICP. complicated by dysphoria/ nightmares.
