inhaled anesthetics 2 Flashcards
N2O is how much more soluble than nitrogen
34x
nitrogen B:G partition coefficient
0.014
nitrous oxide B:G partition coefficient
0.46
how nitrous oxide affects compliant space versus non complaint space (think volume and pressure)
where anatomically does N2O increase pressure (in non compliant air spaces) (2)
middle ear
brain during intracranial procedures
N2O can increase volume and pressure in the following anesthesia equipment (3)
ETT cuff
LMA cuff
balloon tipped pulmonary artery catheter
SE of N2O induced B12 inhibition
inhibits methionine synthase (required for folate metabolism and myelin production)
fire risk and N2O
not flammable but does support combustion so there is a risk when electrocautery is used during laparoscopy surgeries where pneumoperitoneum is induced
MAC value for
iso
sevo
des
N2O
essential triad of anesthetic action includes
- amnesia
- areflexia
- LOC
MAC awake during induction versus recovery MAC awake
during induction ~.4-.5
recovery MAC awake .15
MAC bar
requirement to block autonomic response during painful stimulus and is ~1.5
awareness and recall are assumed to be prevented at
.4-.5 MAC
volatile anesthetic potency is increased by (4)
(think lytes, drugs, patient factors)
hyponatremia
lithium
clonidine
old age
things that increase MAC
drugs
electrolytes
age
body temp
other
things that decrease MAC
drugs
electrolytes
age
body temp
other
things that have no effect on MAC
electrolytes
other
hypo or hyperkalemia
hypo or hypermagnesemia
hyper or hypothyroidism
gender
PaCO2 15-95mmHg
HTN
disorders of which electrolyte affect MAC?
sodium
meyer overton rule
lipid solubility is directly proportional to potency
unitary hypothesis r/t volatile anesthetics
all anesthetics share a similar MOA but each may work at a different site
primary receptor for volatiles in the brain v spinal cord and where they produce immobility
brain: GABA-A (most likely increase duration that chloride channel remains open)
sc: NMDA
immobility: ventral horn of sc
as a general rule, volatiles have the following effects on stimulatory and inhibitory receptors
most important sites of volatile anesthetics on spinal cord
glycine receptor stimulation
NMDA receptor stimulation
Na channel inhibition
gaseous anesthetics (N2O and xenon) act on which 2 receptors
NMDA
K 2P channel stimulation
sites of anesthetic action: targets for amnesia and function
amygdala: emotion, response to pain formation of stress response
hippocampus: memory formation
sites of anesthetic action: target for autonomic regulation and function
pons and medulla: control center for autonomic reflexes
sites of anesthetic action: targets for unconsciousness and function
cerebral cortex: higher order cerebral functions
thalamus: relay station of sensory and motor input to the cortex
RAS: influences consciousness and arousal
sites of anesthetic action: target for immobility and function
ventral horn: upper and lower motor neurons synapse here
sites of anesthetic action: targets for analgesia and function
spinothalamic tract: nociceptive signals along ascending pain pathway are ihibited
how desflurane affects HR, BP, CO, SVR
how isoflurane affects HR, BP, CO, SVR
how sevoflurane affects HR, BP, CO, SVR
how N2O affects HR, BP, CO, SVR
how xenon affects HR, BP, CO, SVR
how halogenated agents decrease MAC (in a dose dependent fashion)
decreased intracellular calcium in VSMC–>systemic vasodilation –> decreased SVR and venous return
decreased intracellular ca in myocyte–>myocardial depression–> decreased inotropy
how halogenated agents affect cardiac conduction in a dose dependent fashion
decrease in SA node automaticity
decreased conduction velocity through AV node, His purkinje system, ventricular conduction pathways
increased duration of myocardial repolarization by impairing outward K current. increases AP duration which prolongs QT interval
altered baroreceptor function
why do des and iso increase HR
resp irritation activates SNS
potency of coronary artery vasodilation (greatest to least)
iso>des>sevo
every 1mmHg in PaCO2 above baseline increases MV by
3mL/min
volatile anesthetics cause a dose dependent depression of which chemoreceptors
central chemoreceptors
can you assist patients breathing to off set PaCO2
not really because apneic threshold is 3-5mmHg below what the patient is maintaining for PaCO2 during spontaneous ventilation
which agent impairs hypoxic ventilatory response the least
desflurane
(the idea is that the agents that undergo the greatest amount of bio transformation in the body affect HPV the most so halothane>sevo>iso>des)
afferent path for carotid bodies versus aortic bodies
carotid bodies (glossopharyngeal nerve CN9)
aortic bodies (vagus n)
impaired response to hypoxia occurs at ___ MAC
.1
does .1 MAC impair response to PaCO2
no
neurophysiological effects of inhaled anesthetics
volatile agents cannot reduce CMRO2 any further after it gets to
isoelectric state (1.5-2 MAC)
volatile agents and CMRO2/CBF relationship
after .5MAC, uncoupled. CMRO2 decreases while CBF increases
N2O in relation to CBF/CMRO2
increases CBF in relation to CMRO2
sevo/iso/des and CSF production/reabsorption
MEPs monitor the integrity of the
corticospinal tract
SSEP’s monitor the integrity of the
dorsal column (medial lemniscus)
be concerned about nerve ischemia when amplitude decreases by _______ OR latency decreases by ______
amplitude >50%
latency >10%
which anesthetic agent is a methyl isopropyl ether
sevo
which anesthetic agents are methyl ethyl etheres
des and iso
