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
What is the effect of most inhaled anesthetics on cardiac contractility? MAP?
Decreases both
Which two inhaled anesthetics reduce MAP mainly by myocardial depression with little effect on peripheral vascular resistance?
Halothane and enflurane
Which three inhalational anesthetics produce vasodilation and have little effect on cardiac output?
Isoflurane desflurane and sevoflurane
Which inhalational anesthetics would you give to someone with impaired myocardial function? Why?
Isoflurane desflurane and sevoflurane
Mainly act as vasodilators and don’t depress myocardial contractility
Which inhaled anesthetic lowers BP the least?
Nitrous oxide
Which inhaled anesthetic sensitizes myocardium to circulating catecholamines and can lead to ventricular arrthymias?
Halothane
Which two inhalational anesthetics should be avoided in patients with bronchospasm?
Isoflurane and desflurane
Which two inhaled anesthetics are the MOST respiratory depressant?
Isoflurane and enflurane
Which inhaled anesthetic is the LEAST respiratory depressant?
Nitrous oxide
Which inhaled anesthetic should be used in patients with increased ICP? Why?
Nitrous oxide
All inhaled anesthetics raise ICP, nitrous does it the least
Which inhaled anesthetics can cause tonic-clonic movements at high concentrations?
Enflurane (rarely and only at high conc)
Which inhaled anesthetic should you avoid in someone with a pneumothorax? Why?
Nitrous oxide - it enters air filled cavities faster than nitrogen can escape and can cause the cavity to swell and inc pressure
Patient after surgery develops severe life threatening hepatitis. What inhaled anesthetic was he most likely exposed to?
Halothane (H for Hepatotoxicity)
Which inhaled anesthetic can be nephrotoxic?
Methoxyflurane
Patient after emergency intubation with succinylcholine develops tachycardia, severe muscle rigidity, hypercalcemia and acidosis. What is this called? What inhaled anesthetic should absolutely be avoided? Treatment?
Malignant hyperthermia
Avoid halothane
Treat with dantrolene
A patient with an autosomal dominant defect in their RYR1 gene is susceptible to what condition? Why? What two drugs should be avoided?
Malignant hyperthermia - defective ryanodine receptor leads to uncontrolled release of calcium from the sarcoplasmic reticulum
Avoid succinylcholine and halothane
The ryanodine receptors on the sarcoplasmic reticulum is the equivalent of what receptor on the endoplasmic reticulum? What do they have in common?
IP3 receptor - both control calcium release
Why do you see hyperkalemia in malignant hyperthermia?
Energy stores in the muscle fiber are quickly depleted and the muscle fibers begin to die and release potassium (also myoglobin)
How do you test someone for susceptibility to malignant hyperthermia?
Halothane-caffeine test
Muscle biopsy fibers tested for strength of contraction when exposed to halothane and caffeine
A long-term dental nurse presents with megaloblastic anemia. What anesthetic agent was she most likely exposed to?
Nitrous oxide
What are the 4 drugs/class of drugs used for IV anesthesia?
Barbiturates
Propofol
Ketamine
Etomidate
What two ultrashort acting barbiturates are used for induction of anesthesia and short procedures?
Thiopental and methohexital
Which class of anesthetic reduces ICP?
IV anesthetics (inhaled increase it) - except ketamine which raises it
Which class of IV anesthetic can cause hyperalgesia?
Ultra-short acting barbiturates (thiopental and methohexital)
Which IV anesthetics should be avoided in patients with asthma? Why?
Ultra-short acting barbiturates (thiopental and methohexital)
Cause apnea, chest wall spasm, bronchospasm
Most popular IV anesthetic?
Propofol
Which IV anesthetic is also an antiemetic?
Propofol
What is the main method of elimination for IV anesthetics?
Liver metabolism
Which IV anesthetic is used in patients at risk for hypotension due to its minimal CVS and resp depression?
Etomidate
What is the only IV anesthetic that is both an analgesic and can stimulate the CVS?
Ketamine
A patient is experiencing perceptual illusions and vivid dreams. What IV anesthetic is he likely using? What is the MOA?
Ketamine (emergence phenomenon)
Blocks NMDA receptors (same MOA as PCP)
Which two IV anesthetics are combined for neurolept analgesia? Addition of what produces neurolept anesthesia?
Analgesia: droperidol + fentanyl
Add nitrous oxide for anesthesia
Neurolept = antipsychotic
What drug might be given as an adjuvant to anesthesia to prevent salivation and protect heart from bradycardia caused by inhalational agents? MOA?
Scopolamine - antimuscarinic
What antiemetic can be given as an adjuvant to anesthesia?
Ondansetron
What two opioids are common adjuvants to anaesthesia?
Fentanyl and morphine
What class of drug is given as an adjuvant to anesthesia to produce anterograde amnesia and for its anxiolytic effects?
Benzodiazepines (diazepam)
Anxiolytic = anti anxiety
Tx Ketamine dreams
Propofol
Diazepam
