ANAESTHETIC AGENTS Flashcards
Give examples of Inhaled anaesthetic agents
Halothane
Enflurane
Desflurane
Xenon
Sevoflurane
Isoflurane
Nitrous Oxide
Why can the Inhalational be dangerous in clinical practice
Low safety margin / low therapeutic index
Most of them are volatile liquids except
Nitrous oxide and xenon ( gases )
What is the MOA of Inhaled anaesthetic agents at the Macroscopic level
Decrease transmission of noxious / pain afferent information from the spinal cords to cerebral cortex
* Norxious stimuli - dangerous stimuli sensed by nociceptors
2) Inhibit spinal efferent activity reducing movement response to pain
3) depress cerebral blood flow and glucose metabolism
Moa at the synaptic level
1) Influence presynaptic release of neurotransmitters
2) Inhibit excitatory neurotransmitters (nicotinic, serotonergic and glutaminergic)
3) Augment / increase the inhibitory neurotransmitters (GABA , Glycine)
Uptake of the Inhalational anaesthetic agents depends on
1) Alveolar concentration of the anaesthetic agents
2) Uptake from alveoli by pulmonary circulation
Give the 3 main factors affecting alveolar concentration
1) Inspired concentration
2) Alveolar ventilation
3) Functional residual capacity
Give 4 main factors affecting uptake of the Inhalational anaesthetic agents by pulmonary circulation
1) Solubility
2) Pulmonary alveolar blood flow ( CO)
3) Alveolar - venous partial pressure gradient
4) Second gas effect
Explain the effect of the inspired concentration and three factors that affect this
The greater the concentration the faster the induction
1) Higher fresh has flow
2) Lower breathin system
3) Lower circuit absorption
How does alveolar ventilation affect the alveolar conc of the Inhalational anaesthetic agents
Increased alveolar ventilation increases take up by the pulmonary blood flow and replaces its alveolar concentration
Explain FRC
A larger FRC dilutes inspired conc of gases thus slower onset of anaesthesia
What is the main factor that determines both the rate of induction and recovery
Solubility
The lower the blood - gas partition coefficient …
The faster the induction and recovery
What is the effect of the plasma proteins
Increases blood solubility by inc
How does cardiac output affect the pulmonary uptake and induction of anaesthesia
A high carduac output increases the uptake but slows induction to anaesthesia
A low cardiac output has reduced uptake but faster induction due to increases alveolar pressures
Define the Minimum alveolar concentration
Minimum alveolar concentration at 1atm pressure that prevents movement in response to a standard surgical midline incision in 50% test population
Give the effects of the Inhalational anaesthetic agents at the Respiratoy system
1) Depress ventilation
2) Increase PaCO2
3) Decrease sensitivity of respiratory centres to CO2
4) Bronchodilation due to reduced airway resistance
Give the effect at CVS
1) Reduce mean arterial pressure and CO
2) Reduced system vascular resistance leading to hypotension
3) Sevoflurane prolongs QT interval
Give effects of Inhaled anaesthetic agents at
1)CNS
2) Liver
3) Kidney
CNS
I) Decrease cerebral metabolic rate amd oxygen consumption
II) Causes cerebral vasodilation this increasing ICP
III) Decreases the cerebral perfusion pressure
LIVER - Reduces hepatic blood flow
KIDNEY - Nephrotoxicity from the metabolism of halogenated agents to inorganic flouride
Define what is CPP
Cerebral perfusion pressure is the net pressure gradient of MAP - ICP that drives oxygen delivery to brain tissues
Halogenated anaesthetics can trigger what in skeletal muscle and what is the cause
Malignant hyperthermia in skeletal muscle caused by excessive release of Calcium from sarcoplasmic reticulum resulting in muscle contracture
Give symptoms of malignant hyperthermia
Muscle rigidity
High fever
Fast heart rate
Rhabdomyolysis
Hyperkalemia
Rapid breathing
Gibe a drugs used in the treatment of malignant hyperthermia
Dantrolene
What is the pathophysiology of malignant hyperthermia
Malignant hyperthermia usually occurs in patients with a mutated RYR1 (ryanodine receptor on the sarcoplasmic reticulum) .
The inhaled anaesthetic agents usually trigger this receptor causing an excessive release of Calcium from sarcoplasmic reticulum and interference of calcium returning to storage.
This creates high intracellular calcium leads to high muscle contractility
Give four main uses of IV induction drugs
1) Induce anaesthesia prior to maintenance anaesthesia
2) Sole drugs for short procedure
3) Maintain anaesthesia by IV infusion
4) Provide sedation
Give for physical properties of an ideal IV induction agent
Water soluble
Stable to light
Non irritant
Cheap
Give 4 pharmacokinetic properties of an ideal IV induction agent
1) Rapid onset (one arm - brain circulation)
2) Rapid redistribution
3) Rapid metabolism and clearance
4) No active metabolites
Give four pharmacodynamic properties of IV induction agents
Wide therapeutic index
Minima CVS and Respiratory effects
No adverse effects
No hang over
Safe
Give three Barbiturates
Sodium Thiopental
Thiamylal
Methohexital
Give the
1) Duration it takes for unconsciousness in Thiopental
2) Duration of anaesthesia
10-30 seconds
5-8 minutes
Thiopental doses are increased and reduced in
Increased in children
Reduced in elderly
Dose reduction of Ythiopental is seen in premedication with which drugs
Benzodiazepines
Opiates
a2 agonists
Give relative potency to Thiopental of
1) Thiamylal
2) Methohexital
Thiamylal is equipotent and Methohexital is 3x more potent
Give the organs system effects of the Barbiturates in
1) CNS
2) CVS
3) Respiratory
CNS
1) Reduce cerebral metabolic rate
2) Reduce cerebral blood flow and ICP
3) Reduce intraocular pressure
4) Anticonvulsants
B) CVS
1) Hypotension due to decreased cardiac contractility and venodilation
2) Tachycardia- compensatory to low BP
C) RESPIRATORY
Respiratory depressant that causes wheezing in asthmatics
Propofol is active metabolite of
Fospopofol
What enzyme metabolizes fospropofol to propofol
Endothelial alkaline phosphatase
Give four PK of Propofol
1) Highly protein bound
2) Has a large volume of distribution
3) Metabolized in liver by sulfation and glucunoridation
4) Excreted renally
Propofol acts on which receptor
GABA-A receptor agonist
Propofol is seen to decrease various things in the CNS , these are
1) Cerebral metabolic rate
2) Cerebral blood flow
3) Intraocular pressure
4) ICP
5) Reduced brains information integration capacity as seen on EEG
Give the CVS effects of Propofol
Hypotension due to vasodilation and decreased myocardial contractility
Give the respiratory effects of Propofol and how do es this effect differ from barbiturates
They cause respiratory depression but less bronchospasm and thus can be used in asthmatics
What is the effect of propofol on
1) Nausea and Vomiting
2) Pregnancy
Antiematic
Safe in pregnancy
What is PRIS with propofol and what are the symptoms
Propofol infusion syndrome is caused by infusion of high doses of propofol . Symptoms include
- Bradycardia followed by cardiac failure
- Rhabdomyolysis
- Metabolic acidosis
- Hyperkalemia
- Hyperlipidemia
- Liver enlargement
- Kidney failure
Give three indications for use of Ketamine
Hypertensives
Asthmatics
Paediatrics
In contrast to barbiturates and propofol , Ketamine has which effects in the CNS
Increased cerebral metabolic rate
Increased cerebral blood flow
Increased ICP
Increased intraocular pressure
Ketamine can cause a nervous condition knowns as
Catalepsy - rigid body , slowing of body functions , salivation , lacrimation , pupillary dilation , increased muscle tone
What are the CVS effects of Ketamine
Hypertension
Tachycardia
Increased cardiac output
Ketamine is C/I in?
Myocardial infarction as it increases oxygen myocardial consumption
