Pharm Quiz #6 Flashcards
What is the current definition of Anesthesia?
Immobility in the face of noxious stimuli and amnesia for intraoperative events
The ___ the MAC of an anesthetic, the ___ the oil-gas partition.
lower, higher
The ___ the oil-gas partition coefficient, the ___ potent the vapor.
higher, more
How does the blood gas partition coefficient affect potency?
It doesn’t
What is the relationship between MAC and the oil-gas partition?
it is inverse
What is the relationship between lipid solubility and anesthetic potency?
The greater the lipid solubility, the greater its potency.
What is the “take-home” message about OGPC?
The higher the OGPC, the greater the lipid solubility is and the greater the potency is because OGPC x MAC in atmospheres = 1.8 atms
What is the modern theory of anesthesia?
Potency determined by position and orientation of anesthetic in the bilayer.
What are two ways pain is meditated by immobility?
- enhancing K+ ion channels
2. Glycine and GASBa receptors mediated reduction of spinal neuron action potentials
Where are Isoflurane sites of action in the brain(3)?
- brainstem
- cerebral cortex
- hippocampus
2 primary receptors of Isoflurane involved in the CNS.
- GABAa
2. Nicotinic acetylcholine receptors
What are the 3 goals of Isoflurane administration?
- reversible effect on the CNS producing immobility in the face of noxious stimuli AND amnesia
- immobility mediated via spinal cord anesthesia
- amnesia mediated by the brain
What are the physical properties of Isoflurane? racemic mixture? odor? BGPC? OGPC? vapor pressure? metabolism rate?
racemic mixture of 50:50(R and S optical isomers) ethereal and pungent odor BGPC of 1.46 OGPC of 91 vapor pressure of 238 metabolism rate of 0.2%
Does Isoflurane produce compound A?
No
What is the MAC value for Isoflurane?
1.2%
What factors reduce Isoflurane MAC?
age, opioids, benzos, clonidine, nitrous oxide, barbs, pregnancy, epidural anesthesia, local anesthesia, shock, trauma, major illnesses, hypothermia, hypothyroidism
Isoflurane prefers blood ___ times more than the gas phase, its blood gas partition coefficient would be ___?
1.4( or 1.4:1)
Isoflurane’s BGPC is ___ than des/sevo, suggesting induction and emergence ___ than des/sevo.
greater, slower
Isoflurane’s use on ___ cases will ___ recovery more than use on ___ cases.
longer, slow, shorter
How does Isoflurane compare to other volatile agents in speed emergence?
Isoflurane has greater solubility than sevo and des so more it enters the arterial side of circulation from the lungs, prolonging emergence. Likewise, obese patients may experience a slower emergence with Iso.
Does Isoflurane have any mutagenic affects?
No, although it may weakly decrease the body’s ability to fight infection.
How does the addition of nitrous oxide for an equal MAC fraction with Isoflurane affect ventilatory status?
It lessens the ventilatory depressant effects
What is the state describing Isoflurane’s affect on the lungs?
breathing like a lizard on a hot rock
The dose related to ventilatory depressant effects of Iso that leads to apnea is?
around 2 MAC
Isoflurane causes airway irritation beginning at about what MAC?
1, so not at sub-MAC doses. By the time the patient is ready to extubate your much lower than this.
In the VA from greatest to less airway irritation: Des—>Iso—>Sevo
Should Isoflurane be used for inhaled induction?
NO! it has a pungent odor
For a deep extubation, what MAC Iso is needed?
at least 0.85
How does Isoflurane affect ANS response to incubation as compared to Sevoflurane?
Iso blocks ANS response to intubation greater than Sevo
What affect does Iso have on hypoxic pulmonary vasoconstriction(HPV)?
Iso alters HPV minimally @ routine anesthetic concentrations with minimal clinical significant. HPV is a mechanism that diverts blood flow from hypoxic areas to optimize gas exchange.
How does Iso affect blood pressure and by what mechanism?
Iso drops your blood pressure by decreasing the SVR
Iso has ___ vagolytic effects than Desflurane.
less, vacolytic = increased HR with abrupt increases in concentration
How does adding N2O to Iso affect circulatory changes?
lower BP, reduced SVR, Lower CI—> from the ISO
BUT greater HR, higher PAPs and higher CVPs—>from the nitrous
How does Iso administration affect temps?
the prolonged vasodilatation secondary to its acceptance of a broad range of temps before peripheral vasoconstriction occurs leads to lower temps and greater incidences of post-op shivering
How does spontaneous ventilation under Isoflurane increase venous return?
lower intrathoracic pressures and greater sympathetic activity due to associated increases in PaCO2.
What is the MAC BAR of Iso when combined with 60% nitrous? What is it with an additional combination of 3 mcg/kg fentanyl?
1.3 MAC —> with 3mcg/kg fentanyl lowers the MAC BAR to 0.4 MAC
Isoflurane and increase autonomic activity under anesthesia so you should give opioids!
At what level MAC can Iso attenuate baroreflexes?
@ greater than 1 MAC
At what level MAC does Iso cause circulatory collapse?
3 MAC
At what level MAC does Iso cause apnea?
2 MAC—>so apnea would be seen before circulatory collapse
What effect does Isoflurane have on the myocardium?
It depresses it
What effects does Iso have on “coronary steal”?
Any reduction in regional coronary blood flow under anesthesia is due to hypotension not “coronary steal”.
How does Iso affect hepatic and renal perfusion?
It dose not adversely affect either one
How does Iso affect cerebral vascular resistance and ICP?
It decreases cerebral vascular resistance which may lead to increases in ICP
How are increase ICP treated?
hyperventilate to about 30 mmHg pCO2
What affect does Iso have on malignant hyperthermia?
- Iso can trigger MH
- administration of succinylcholine may potentiate the MG triggering capacity of Iso
What analgesic properties does Isoflurane have?
it has limited analgesic properties and @ 0.2 MAC Iso does not influence pain perception
At what level MAC does Iso depress somatosensory evoked potentials and abolish them?
> 1.3 MAC
How does Isoflurane affect cerebral metabolic rate?
it decreases it, while also decreasing CVR and increasing ICP
How can Isoflurane administration affect the elderly?
may induce apoptosis(programmed cell death), aggression of amyloid beta protein and may contribute to postop cognitive dysfunction
What % metabolism does Isoflurane undergo and why?
0.2% metabolism due to the fluorination of isoflurane(5 fluorine atoms)
What can Isoflurane metabolism lead to via the cytochrome p450 pathway?
post anesthesia hepatitis
How can Isoflurane affect the liver?
Iso may cause post-anesthesia hepatitis and hepatic necrosis!
This is caused by metabolism to trifluoroacetic acid which can form covalent attachments to hepatic proteins.
How does Isoflurane affect the kidneys?
It DOES NOT produce compound A, avoiding the nephrotoxicity of theoretical concerns associated with Sevoflurane
Are there any contraindications to low flow and closed circuit techniques?
No….and at identical flow rates, isoflurane is 1/2 the cost of des and sevo
Iso also resist metabolism and degradation by CO2 absorbents
