Inhaled Anesthetics 2 Flashcards
Name places N20 will have fast equilibrium
pulmonary blebs
air bubbles in blood
gas bubble in the eye
name places N20 will have slow equilibrium
bowel
pneumoperitoneum
How can N20 affect the middle ear?
can increase pressure in middle ear and damage tympanic membrane graft.
if N20 is discontinued quickly how can it impact the ear?
quickly decrease middle ear pressure leading to serous otitis
What is an SF6 Bubble? How is it used?
sulfur hexafluoride bubble
used in retinal detachment surgery to hold retina in place while it heals
Risk of N20 use with SF6 bubble?
N20 can increase pressure in the bubble leading to retinal compression and permanent blindness.
N20 guidelines for SF6 bubbles. How soon to DC before and how soon safe to use after?
Must stop it 15min before placement
need to avoid for 7-10 days afterwards
N20 guidelines for other bubbles besides SF6
Air: avoid N20 for 5 days
perfluoropropane: avoid for 30 days
silicone oil: no CI to N20
How does N20 affect Vit B12 and what does this cause?
N20 irreversibly inhibits Vit B12 > inhibited methioine sythase > impaired folate metabolism and impaired myelin production
this can cause:
decreased DNA synthesis
neuropathy
megaloblastic anemia (bone marrow suppression)
immunocompromise
what conditions increase the associated risks of N20 use?
pernicious anemia
alcoholism
vegan diet
recreational N20 use
MAC awake?
0.4-0.5 during induction
0.15 during recovery
MAC level to prevent movement in 95% of patients?
MAC 1.3
MAC level required to prevent awareness and recall?
assumed to be MAC 0.4-0.5
What factors increase MAC?
chronic Etoh use
^ CNS neurotransmitters
acute amphetamine intoxication
acute cocaine intoxication
MAOIs
Ephedrine
Levodopa
Hypernatremia
1-6mo of age
Hyperthermia
Red hair by 19% (science is questionable)
drugs that can decrease MAC?
acute etoh intoxication
lithium
lidocaine
hydroxyzine
IV anesthetics
What can decrease MAC other than drugs?
hyponatremia
prematurity
Age > 40
hypothermia
MAP < / = 50
hypoxia
anemia < 4.3 ml O2 / dL blood
CPB
metabolic acidosis
hypo-osmolarity
pregnancy
24-72 hrs post partum
PaCO2 > 95
do thyroid levels affect MAC?
no not directly
but sever hypothyroidism > decreased CO > slower onset of anesthetics > easy to accidentally overdose patient
do you get more HoTN from VA + N20 or VA alone?
from VA alone. N20 doesn’t drop BP as much
which inhaled agents can increase HR?
Des, Iso, and N20.
how does N20 affect SNS?
it activates SNS and ^ HR
how does inhaled anesthetics affect cardiac contractility?
slight decrease, except for N20. N20 has no affect on contractility alone.
N20 with opioids though will cause myocardial depression
which volatile agent decrease SVR the least?
Sevo
which volatiles cause the most coronary dilation? can volatiles lead to cardiac ischemia?
Iso > Des > Sevo
historical concern for coronary steal syndrome but VAs actually precondition myocardium and protect against ischemia.
What is the Myer-overton rule?
lipid solubility is directly proportional to the potency of inhaled anesthetics
what is the unitary hypothesis?
all volatile anesthetics have simillar mech of action but work on different sites
what is the old-school assumed mech of action of VAs
assumed to be on the lipid bilayer of neurons
Newer understanding about VAs mech of action?
- stimulate inhibitory receptors
- inhibit stimulatory receptors
inhibitory pathways VAs work on
GABA-A R
glycine R
potassium channels
stimulatory pathways VAs work on?
NMDA receptor
nicotinic R
sodium channels
dendritic spine function and motility
on what receptor do VAs work in the brain? what kind of receptor is it?
GABA-A
ligand gated chloride channel
where do VAs work in the spinal cord? What do they cause?
provide immobility in the ventral horn of spinal cord by inhibiting:
glycin R
NMDA R
Na channel
In what part of the brain do VA produce amnesia?
amygdala & hippocampus
In what part of the brain do VA produce autonomic effects?
pons and medulla
where do VA produce analgesia?
spinothalamic tract
where do VAs produce immobility?
ventral horn of spinal cord
N20 and Xenon mech of action
NMDA antagonism
Potassium 2P channel stimulation
do not stimulate GABA-A Receptor
where are central chemo receptors found? What do they control?
medulla and control PaCO2
for every 1mmHg ^ in PaCO2 ventilation ^ by 3ml/min
how do VA cause resp depression?
depress central chemo receptors
depress resp muscles including: uppper airway m. diaphragm, intercostal m.
How do VA affect normal breathing?
decrease tidal volumes
body tries to compensate by increasing RR but this is not enough to offset rise in PaCO2
how doe VA shit CO2 response curve?
down and to the right
where is the apneic threshold?
typically 3-5mmHg below PCO2 that is maintaned during spontaneous ventilation
how do VA affect airway diameter?
halogenated agents are bronchodilators but this is minimal unless there is increased airway resistance.
Exception: Des can induce bronchospasm in asthmatics
where are peripheral chemo receptors? what do they monitor?
carotid body
measure PaO2
what is the PaO2 trigger level for pheripheral chemo receptors ot stimulate ^minute ventilation?
PaO2 < 60 causes stimulation to increase minute ventilation
what are carotid bodies most sensitive too? what are aortic bodies most sensitive to?
carotid bodies: changes in PaO2, PaCO2, H+
aortic bodies: changes in BP
pathway for afferent info from carotid bodies to resp center?
via glossopharyngeal n.
pathway for afferent infrom for aortic bodies to resp center?
vagus nerve
how doe VAs affect peripheral chemo receptors? for how long?
impair them for several hours after anesthesia
what MAC level impairs response to actue hypoxia but not PaCO2
0.1 MAC
what cells in carotid body provide sensory arm to hypoxic drive?
glomus cells
what is the mech of action for VA inhibiting the hypoxic drive? when is this clinically relevant?
theory is reactive oxygen species from VA metabolism impair glomus type I cells.
agents with the most biotransformation inhibit the hypoxic drive the most (sevo>iso>des)
clincial relevance: important for pts that rely on hypoxic drive to breath. I.E. emphysema or sleep apnea. Des is best for these patients.
does N20 affect carotid bodies response to hypoxia? how?
yes, but in different way than VAs
how do pain and surgical stimulation affect the bodies response to CO2 and the hypoxic ventilatory drive?
reverse depression of response to CO2
do not reverse depression of hypoxic ventilatory drive
How do VA affect CMRO2 and CBF?
decrease CMRO2 and ^ CBF causing uncoupling.
this obviously increases CBV and ICP
at what MAC level can you get isoelectric state?
1.5-2.0 MAC
how does N20 affect CMRO2 and CBF?
increases both CMRO2 and CBF
describe the paradoxical effect VAs have on CMRO2 and CBF. Waht is the one downside?
typically decreased CMRO2 causes vasoconstriction to decrease CBF, but VA cause CMRO2 and vasodilation… so what really happens? vasodilation or constriction?
Bottom line: at MAC > 0.5 VA increase CBF even though they decrease CMRO2
VA increase ICP from the increased CBF
what VA can cause seizures at 2.0 MAC?
sevo
Waht conributes to CMRO2? what are VA actually decreasing when they decrease CMRO2?
CMRO2
1. electrical activity 60%
2. cellular homeostasis 40%
VA only decrease CMRO2 by decreasing electrical activity. Once isoelectric VAs can not decrease CMRO2 any further.
name each type of evoked potential
SSEP
MEP
VEP
BAEP
what part of spinal cord does SSEP monitor? what perfuses this region?
monitor integrity of dorsal column (medial lemniscus) whish is perfused by post. spinal arteries
what part of spinal cord do MEPs monitor? what perfuses this region of spinal cord?
corticospinal tract perfused by ant. spinal artery
how often are BAEP and VEP used?
very rarely
what changes on evoked potential warrant concern about ischemia?
if amplitude decreaes by about 50% or latency increases by about 10%
best anesthetic method to conserve evoked potentials?
TIVA without N20
which evoked potentials are most sensitive to anesthetic agents?
visual evoked potentials
which evoked potentials are most resistant to effects of anesthetics?
BAEP. you can use any drugs with BAEP monitoring.
how does ketamine affect evoked potentials?
enhances the signals
what are some things besides meds that can affect evoked potentials?
hypoxia
hypercarbia
hypothermia
what to do if evoked potentials decrease during surgery
- have surgeon investigate surgical cause
anesthetic mgmt:
increase persusion
^ BP
volume expansion
transfusion (if anemic)
what is the wake up test?
old school technique now abandonded for SSEP and MEP monitoring
I think used in scoliosis surgery??
they would wake people up in the middle of surgery
if they can omve hands but not fet surgeon needs to decrease distraction (stretching) on spinal column
risk of wake up test
extubation
losing lines
air embolism
awareness
pain
damage to surgical instrumentation
