Inhalational Agents: Effects on MSK, Neuro, Hepatic, Renal, and Metabolism Flashcards
____ cause a dose dependent relaxation skeletal muscle
inhaled volatile agents
nitrous oxide has no effect
the higher the MAC multiple, the greater the ___
fade on tetanus
volatile agents can be used instead of ___ or to __
NMB
enhance the effect of NMB
the enhanced effect of NMB may be from __ or __ effects or from effects on ___- inhibit nicotinic receptors ____
pre- or post-junctional
spinal motor neurons
incompletely at MAC
practical application of inhaled anesthetics enhancing effect of NMB
- decrease dose of nondep NMB 25%
- decrease frequency of redosing
- myasthenia gravis patients- give no NMB
- patient with hepatic or renal impairment
__ has a longer duration depending on the volatile agent interaction:
desflurane-
sevoflurane-
isoflurane-
propofol-
rocuronium
desflurane- 90 min
sevoflurane- 59 min
isoflurane- 35 min
propofol- 35 min
prolonged recovery from NMB when __ is maintained
volatile concentration
must maintain __ on TOF
one twitch
__ is also a factor in prolonging recovery from NMB with volatile agents
increased age
as the % concentration of volatile was decreased when vecuronium infusion was maintained, __ increased
the twitch height
different results with different agents may be explained by
methodology of study
different results with different agents- with cisatracurium and rocuronium, ___ caused prolonged block, but ___ didn’t
sevoflurane
isoflurane
different results with different agents- with vecuronium, __ and __ both prolonged block
sevo and iso
all volatile agents are additive effect with
succinylcholine
iso causes more rapid shift from ___ to ___ block with succ infusion
phase I to phase II
volatiles cause a __ dependent enhancement of nondep NMB (recovery of ToF 1 twitch)
time
volatile agents can cause impairment of __ of nondepolarizing NMB
reversal
carefully administer ___, use ___, and consider using ___ in lieu of NMB if possible
NMB
twitch monitor
relaxant effect of volatile
volatile anesthetics cause ___ relaxation of the uterine smooth muscle
dose-dependent relaxation
__ MAC causes __ relaxation of uterine smooth muscle
0.5
modest
__ MAC causes significant relaxation of uterine smooth muscle
> 1
positive implication of uterine smooth muscle
desirable relaxation for removal of retained placenta
negative implication of uterine smooth muscle
contribute to increased blood loss with uterine atony
__ does not alter uterine contractility in doses used to provide analgesia during vaginal delivery
nitrous oxide
nitrous oxide can be useful to __ and __ during vaginal delivery
decrease volatile
avoid benzodiazepines, opioids
volatiles decrease in __ blood flow
maternal uterine
to avoid decreases in maternal uterine blood flow maintain MAC
< 1.5
can have amnesia with no neonatal distress at __ MAC with __ N2O
0.5
50%
consider avoiding ___ in presence of fetal distress
N2O
volatile cross __ rapidly
placenta
exhaled rapidly by neonate
all volatile agents can trigger
MH (even without succinylcholine)
__ is the most potent trigger of MH
halothane
__ is a much weaker trigger of MH and is considered ___
nitrous oxide
on the “safe list” of MHAUS
MH causes a pathologic change in
muscle; hypermetabolic state
with MH, exposure to triggering agents cause the __ receptor to release ___ from the __ to enter the muscle cell
ryanodine
calcium
sarcoplasmic reticulum
with MH, muscle contraction occurs due to
interaction of actin and myosin
in MH, __ and __ metabolism increase producing massive amounts of __, __, and ___
aerobic and anaerobic muscle
heat, carbon dioxide, and lactate
in MH, ___ allows leakage
muscle membrane permeability
time to onset of MH with desflurane trigger only
260 min
time to onset of MH with isoflurane trigger only
140 minutes
time to onset of MH with halothane trigger only
35 minutes
cerebral metabolic oxygen requirements (CMRO2) decrease at approximately
0.4 MAC as the patient moves toward unconsciousness
reduction in CMRO2 is
dose dependent
once ___ is produced, further increases in the agent concentration do not further decrease CMRO2
an isoelectric EEG
CRMO2 =
electrical activity 60% + cellular homeostasis 40%
CMRO2 decreases normal response with no volatile anesthesia
brain matches (couples) its blood flow with its metabolic requirements
when metabolic demands decrease, blood vessels ___ and CBF ___
constrict (CVR increases)
decreases
two opposing factors with volatile anesthetics and CMRO2
- vasoconstriction from reduction of CMRO2
- vasodilation from anesthetic agent directly
CRMOs decrease has no uncoupling if
less than or equal to 1 MAC of iso or des
uncoupling can occur at
higher doses
N2O causes increased __ and __ however there is still uncoupling due to __
CMRO2 and CBF
the greater increase in CMRO2 than CBF
uncoupling is
decreased CRMO2 at the same time that CBF is increased- paradoxical (they supply the brain with more blood flow than it needs)- CBV increases
if uncoupling does not occurs, it is said that
flow-metabolism coupling mechanism is preserved
affects change in CBF
- dose of volatile
- other drugs administered (propofol, opioids, barbiturates, nitrous)
- rate of change of concentration of volatile
- ventilation (hyper)
dose dependent __ in CBF
increase
normocarbia with > 0.6 MAC causes
- cerebral vasodilation
- decreased cerebral vascular resistance
- increased CBF (potential increased ICP)
- decreased CMRO2 (uncoupling should result in decreased CBF)
cerebral vasodilation agents
iso = des > sevo
increase CBF occurs within
minutes of administration of inhaled agents
increase CBF is independent of
MAP
increase of CBF is sustained for
as long as 4 hours during anesthetic
lower metabolism of isoflurane =
less CO2 production, less vasodilation
des, sevo, and iso maintain the cerebral vascular reactivity to
carbon dioxide at less than 1 MAC
iso 1 MAC preserves
autoregulation of CBF
__ eliminates autoregulation
halothane
at 1.5 MAC, sevo preserves ___ better than iso- as dose increase above 1 MAC, __ is affected
autoregulation
autoregulation
uncoupling at higher dose (>1 MAC) =
CBF is maintained (unchanged or higher) and CMRO2 is decreased (iso>halothane)
isoflurane may blunt __ processes results from cerebral ischemia due to transient ___ during carotid endarterectomy
necrotic
regional ischemia
(cerebral oxygen supply-demand balance is improved)
cerebral vasodilation and increased CBF raise risks of
increased ICP
hyperventilation to decrease PaCO2 to ___ counters the increased ICP
30 mmHg
to counter increased ICP, start hyperventilation at ___ with iso, sevo, des
start of agent
to counter increased ICP, start hyperventilation at ___ with halothane
before agent is started
isoflurane does not change production of CSF but
decreases resistance to reabsorption (increases reabsorption)
the result of iso not producing CSF is
only minimal increases in ICP even if CBF increases
des may ___ CSF production
increase or not change
sevo __ CSF production
deceases
N2O ___ in CSF production
causes no increase in
cerebral vasculature normal response to hypocarbia
vasoconstriction (goal PaCO2 30-35 mmHg- effective 4-6 hours)
cerebral vasculature normal response to hypercarbia
vasodilation
HTN patients cerebral vasculature effects
1 MAC iso with 67% nitrous was more effective than 1 MAC sevo with 67% nitrous in controlling vascular resistance with PaCO2 manipulation
diabetic patients effects on cerebral vasculature
impaired control of vascular resistance with PaCO2 manipulation with both 1 MAC of iso and sevo with 67% nitrous
__ changes to EEG
dose-dependent
less than 0.4 MAC will have __ and __ on EEG
increased frequency and voltage
at 0.4 MAC, EEG change are
activity shifts to anterior portions of the brain (transition from excitement to unconsciousness)
EEG changes at 1 MAC
increased voltage and decreased frequency (bigger, slower waves)
EEG changes at 1.5 MAC
deeper level of anesthesia- burst suppression occurs
EEG changes at 2 MAC
possibly flat
__ does not produce burst suppression at clinical levels
halothane
des, iso, and sevo can ___ seizure activity related to drugs like lidocaine
suppress
__ has been associated with seizure activity
sevo
increased incidence of seizures with
- higher concentration of sevo (2 MAC)
- hypocarbia
- repeated auditory stimulation
- pre-existing seizure disorder
evoked potentials monitor
the transmission of the impulse from the periphery to/through the cord
evoked potentials are typically utilized with
spinal fusion for scoliosis- monitoring to protect the spinal cord
___ depress SSEP
all potent inhaled anesthetics
volatiles cause ___ reduction in evoke potential
dose-dependent
__ evoked potential is the most sensitive and __ is the most resistant
visual
brainstem
__ or __ are indication of ischemia OR can be related to the volatile agent with evoked potential monitoring
an increase in latency (time of stimulus in periphery and onset of EP recorded by scalp electrode)
decrease in amplitude
evoked potentials are monitored at __ MAC
0.5-0.7
for research on evoke potential, __ can be utilized at 1.3 MAC
sevo
for research on evoke potential, __ can be utilized at 0.5-1 MAC
isoflurane
for research on evoke potential, __ can be utilized at 0.5-0.7 MAC
halothane
nitrous oxide effects on evoked potentials
may profoundly decrease amplitude so AVOID
volatile anesthetics do not cause __ amnesia
retrograde
__ MAC of iso prevent awareness and __ MAC of nitrous oxide required to prevent awareness
0.4
> 0.5-0.6
learning may be altered at
low concentration (0.2 MAC)
__ may increase the concentration required to prevent awareness
surgical stimulation
volatile cause impairment of cerebral regulation of
temperature control
inhaled agents reset the threshold for
regulation of temperature control to a lower level
nitrous oxide has __ of an effect on temperature regulation
less
(substitution of N2O impairs the threshold less)
volatiles cause the center for temp regulation to permit
a lower range of temperatures to exist before cutaneous vasoconstriction occurs
volatiles permit a lower temperature before
the body attempts to regulate heat loss and heat production
temperature regulation is __ dependent
dose
__ can also lead to temperature loss
vasodilation
heat is transferred from __ to __ which causes
core to periphery
a decrease in core temp of 0.5-1 degree C in the first half-hour of anesthesia
__ have greater inhibition of temperature regulation than others
the elderly
neuroapoptosis causes neurotoxicity in animals- ___, ___, and ___ contributing to remodeling of neuronal circuitry and development remodeling
altered neurogenesis
neurite growth
synapse formation
neurotoxicity in animals led to
- cognitive deficits, delayed learning
- impaired memory formation and retention
- altered motor and behavioral development
FDA issues a safety announcement advising that
repeated or lengthy exposures to anesthetic and sedative drugs prior to age 3 years have the potential to harm the development of children’s brains
in iso, des, and sevo had maintained ___ blood flow and __ or increased __
total hepatic
hepatic artery blood flow
portal vein blood flow
halothane effect on hepatic blood flow
hepatic artery vasoconstrictor so decreased
metabolism % or desflurane
0-0.02
metabolism % of isoflurane
0-0.2
metabolism % of sevoflurane
5-8
metabolism % of halothane
15-40%
N2O metabolism
not at all in the liver; 0.004% in the gut from normal flora
determinants of metabolism
- chemical structure
- hepatic enzyme activity
- blood concentration
chemical structure is __ or __
ether bond or carbon-halogen bond
hepatic enzyme activity effecting metabolism
- cytochrome P450 induced or depressed
- obese- increased fluoride concentrations
blood concentration effects on metabolism
< 0.1 MAC undergoes extensive metabolism in the liver (less soluble- quicker out via lungs)
__ are metabolized
all inhaled anesthetics just to varying degrees
the concern of metabolism is
the fluoride
the metabolites of concern with metabolism are
trifluoroacetic acid (TFA) and inorganic fluoride
metabolic pathways are __ for des, iso, sevo
oxidative
metabolism of halothane
principally oxidation by cytochrome P-450 enzymes when oxygen is present, but reductive metabolism when hepatocyte PO2 decreases
trifluoroacetic acid (TFA) produced by
the biodegradation of has, iso, and des
trifluoroacetic acid causes
acetylation of proteins on the surface of hepatocytes to form antigens to which antibodies form
with TFA, there is a connection between
its hepatic production and hepatotoxicity via an immune pathway
inorganic fluoride is produced by
biodegradation of sevo in the liver and only minimally in the kidney; thus little negative effect on the kidneys
same level of inorganic fluoride produced as with methoxyflurane which causes ____ but no evidence of ____ with sevo
renal failure
renal injury
(even in patients with pre-existing renal damage)
infrarenal production of inorganic fluoride (methoxyflurane) is a bigger problem for __ than ____
nephrotoxicity
inorganic fluoride produced from hepatic metabolism (sevo)
inorganic fluoride historically, has no renal effects when
peak plasma fluoride concentrations < 40 mcm/L
inorganic fluoride historically, has subconical toxicity when
50-80 mcm/L
inorganic fluoride historically, has clinical toxicity when
> 80 mcm/L
level of __ is the indicator that renal toxicity may occur however __
50
no renal damage even with levels exceeding this level
__ and __ are less soluble and exhaled more and less metabolized
enf and sevo
high output renal failure (unresponsive to vasopressin) is the inability to
concentrate urine, polyuria, hypernatremia, hyperosmolatiry, increased plasma creatinine
studies have shown no renal necrosis after
sevo
have been cases of transient impairment of __ and __ in patient exposed to sevo and with peak plasma inorganic fluoride levels > 50 mcm/L
renal concentrating ability
increased excretion of beta-N-acetylglucosaminidase (NAG)
NAG is
an indicator of acute proximal renal tubular injury
renal effects show no
elevation in BUN or creatinine
with preexisting renal disease show
no increased risk for damage
renal effects
- renal blood flow is reduced (may effect urine output intraoperatively)
- decreased glomerular filtration rate
- decreased urinary output
renal effects are due to
the decrease in CO and systemic BP
__ attenuates renal effects
preop hydration
___ causes release of ADH
surgical stress, not inhaled anesthestics
___ might also cause ADH release to contribute to decreased urine output
fluid status changes
___ may cause inability to concentrate urine causing high output and decreased response to vasopressin
Compound A
__ have been seen with compound A
proteinuria, glucosuria, enzymuria
no renal necrosis
to decrease the risk of compound A
- minimum flow of 2 L/min if case longer than 2 hours (1 L/min is less than 2 hours)
- lower concentrations of sevo
- avoid KOH and NaOH in CO2 absorbent
- avoid increased temp in CO2 absorbent