General Anesthetics Flashcards
What is the difference between general and balanced anesthesia?
General anesthesia involves analgesia, amnesia, loss of consciousness, suppression of reflexes, and skeletal muscle relaxation. No single drug can achieve this so balanced anesthesia is the use of several drugs in combination to achieve all the desired effects
What 5 findings must be seen in general anesthesia? Which drugs achieve this?
Analgesia Amnesia Loss of consciousness Suppression of reflexes Skeletal muscle relaxation
No single drug can do all of this.
Which has a faster onset, inhalational or IV agents?
IV - inhalational are not rapid
Which of the 5 effects of general anesthesia do the halogenated hydrocarbons lack?
Analgesia
What are the two groups of inhaled anesthetics? Name them
Gases: nitrous oxide
Volatile liquids: MHIDES - “rane
Methoxyflurane, halothane, isoflurane, desflurane, enflurane, sevoflurane
Which group of general anesthetics is used to sedate patients who must be mechanically ventilated for long periods?
IV anesthetics
Which type of anesthetic is used in the maintanence of anesthesia after giving one IV?
Inhaled
If an inhaled anesthetic is very soluble in blood, is it more likely to have a fast or slow rate of onset?
More soluble = slower onset
Less soluble = quicker onset
If an inhaled anesthetic is highly liposoluble, is it likely to be more or less potent?
More liposolubility = more potent
What effect do inhaled anesthetics have on the lungs?
Bronchodilation
Inhaled anesthetics work by positive modulation of what two receptors?
GABAa and glycine - the two inhibitory ones
Describe MAC for general anesthetics.
Concentration that results in immobility in 50% of patients when exposed to noxious stimuli like a surgical incision.
It is the standard comparison for potency of general anesthetics
If the MAC of an anesthetic is low, what is that drugs potency like?
MAC is low for potent anesthetics
High for less potent agents
Increasing the MAC from 1.1 to 1.3 can change the percent of people immobilized from 50% to 95%. Explain how this is possible
Small changes in MAC make a large difference due to the steep dose response curve of inhalational anesthetics
If you give 0.7 MAC of one drug and 0.3 MAC of another, how many total MAC effect do you see?
1.0 MAC - they are additive
Which inhaled anesthic has the highest MAC? Lowest? What does this say about their potency?
Nitrous oxide has highest MAC - lowest potency
Methoxyflurane has lowest MAC - highest potency
If a drug has a MAC of 104, what can you conclude about the uses of this drug in anesthesia? Which drug is it likely to be?
You’d need 104% of the drug to achieve anesthesia so it is not possible with this drug alone. It is likely nitrous oxide which is commonly combined in anesthesia
What does the oil:gas partition coefficient tell you about a drug? If it goes up, how is potency affected? MAC?
It is a measure of liposolubility and because potency goes up with increasing liposolubility:
The higher the lambda(oil:gas) is, the more liposoluble, the more potent (also MAC decreases with increasing potency)
What 5 parameters determine how quickly an anesthetic reaches the brain?
Solubility Concentration in inspired air Pulmonary ventilation rate Pulmonary blood flow Concentration gradient of drug between arterial and venous blood
What does the blood:gas partition coefficient tell you about an anesthetic? If it is low, what does that tell you about the speed of onset of action?
It tells you how soluble a drug is in the blood versus the air. If the drug is not very soluble in blood, it will have a faster rate of onset (nitrous oxide is much faster than methoxyflurane in the inhalational anesthetics)
How are the oil:gas and the blood:gas partition coefficients related to each other? To MAC?
Oil:gas = potency and blood:gas = solubility/rate of onset
High potency correlates with slower onset
They are directly related to each other and both indirectly related to MAC. As MAC decreases, both coefficients increase.
Lower MAC = higher potency but slower onset (methoxyflurane)
How does an increase in cardiac output affect the rate of rise of the anesthetic in arterial tension? Why?
Inc CO slows the rate of rise because a higher amount of blood is being exposed to the same amount of drug. It gets diluted
If a drug distributes quickly into the tissues, how does this affect the rate of onset? Why?
Uptake by tissues slows the onset because less is making it to the brain
How does the time of elimination change for an inhalational anesthetic that is not very soluble vs one that is very soluble?
If it has LOW solubility, elimination mirrors the rate of induction regardless of the duration of administration.
If it has HIGH solubility, recovery depends on the duration of the administration of the drug. This is because it will have accumulated in fat and will be released slowly forms a depot
