Test 1: 12 + 13: inhalant agents Flashcards
vapor pressure of isoflurane
240
vapor pressure of sevoflurane
160
vapor pressure of desflurane
664- very close to sea level pressure
means boiling point very close to room temp, need to be stored at high pressure to keep in liquid form
which inhaled anesthetics have the highest blood gas ratio and what does this mean
isoflurane has the highest
takes a longer time to cause change in the body when you change the amount of drug given
what does oil gas ratio mean
amount of drug disolved into the lipid/brain= more potent
iso: 91
servoflurane: 50
desflurane: 18
N2O: 1.4
how does generic variable bypass vaporizer work
used for iso and sevoflurane
made of bronze- keeps temp constant and therefore vaporization of drug constant
how does desflurane vaporizers work
desflurane boils at close to room temp 23.5°C
the vaporizer keeps drug at 39°C and at specific pressure= this allows for rate of vaporization to be constant
injects desflurane vapor into fresh gas stream
inhalant anesthetics cause what in the CNS
spinal cord and brain
inhibit sensory processing, nocicpetive signaling and motor response to pain
Brain
hypnosis and amnesia
loss of consciousness
analgesia
how do inhalant drugs work
↓ excitatory receptors: inhibit central ACh receptors and NMDA receptors in the brain
stops receptors from opening and sending AP
↑ function of inhibitory receptors: GABA A receptor, glycine, serotonin
MAC
minimum alveolar concentration
The anesthetic concentration preventing motor response to a supramaximal noxious stimulus in 50 % of subjects.
Correlates inversely with O/G part. coeff: the more lipophilic the drug the less drug you need to give to cause sedation
agent and species specific
— will decrease MAC valves
Increasing age (calmer when older)
Pregnancy (endogenous opioid release)
Hypothermia
Hypotension (MAP< 40 mmHg)
Hypoxemia (PaO2< 38 mmHg)
Hyponatremia
CNS depressant drugs/analgesics
— will increase MAC valve
- Hyperthermia
- Hypernatremia
- CNS stimulants
non-anesthetic cerebral effects of iso
non-anesthetic cerebral effects of sevoflurane
non-anesthetic cerebral effects of desflurane
adverse effects of inhaled anesthetics on respiratory system
central respiratory depression
↓ tidal volume (iso > sevo, des)
↓RR ( ↑ up to 1 MAC)
↑ PaCO2 Des>Iso = sevo
bronchodilation (iso= sevo>des)
adverse effect of iso on CV system
adverse effect of sevoflurane on CV system
adverse effect of desflurane on CV system
↓CO by ↓Ca into cell
Adverse effect of inhalants on kidney
↓ renal blood flow
↓ urine output
adverse effects of inhalants on liver
↓ blood flow to liver → ↓ drug metabolism by 50-70%
need to give lower doses of meds
adverse effects of inhalants on skeletal muscle
↓ muscle tone from ↓ Ca into the cell
Augmentation of neuromuscular
blockade by Non-Depolarizing
Neuromuscular Blockers
(NDNMB)
adverse effects of inhalants on fetus
↓ blood flow to fetus
why use sevoflurane over iso
faster induction and faster recovery
no pungent odor
can change depth of med faster
less ↓BP
less respiratory depressant
disadvantages of sevo vs iso
metabolized in the liver into inorganic fluoride ions
could be cause renal and liver damage in rats: not seen in man, dog or monkey
pros and cons of using desflurane
- Requires special vaporizer
- Irritating to airways
- Rapid induction & recovery (B/G 0.42; Low Tissue/Blood part. coeff.)
- Pharmacodynamic profile similar to isoflurane but less cardiac output depressant
- Basically no metabolism
why use nitrous oxide
analgesic properties
recumbency + inhalant anesthetics cause
increased PaCO2 → resp. acidosis and acidemia
hypoxemia
hypotension: tissue hypoperfusion, cardiac arrhythmias, muscle weakness
inhalant anesthetics cause vaso—-, inhibition of the — nervous system and — stress hormone release
vasodilation
ANS: negative-inotropic effect, ↓ of autonomic CV reflexes
increased
even though negative inotrope, CO stays similar cause vasodilation balances it out, when at normal levels
why use PIVA for anesthesia
use combo of injectable and inhalants with analgesics or NM blockers
- can reduce dose needed for each drug
- decrease adverse effects
- more rapid recovery
the use of balanced anesthesia will do what to PaCO2 and MAP
will decrease PaCO2= better respiratory function
will increase MAP= better perfusion
reduction in MAC is cause
- reduced stress response
- inhibition of intraoperative nocicpetion: improved analgesia and recovers faster
- improved overal perianesthetic outcome
how to monitor balanced anesthesia
- Palpebral reflexes less suppressed
- Hemodynamic parameters (esp. arterial blood pressures (ABP)) often closer to physiological values
- Plane of anesthesia appears often light despite no response to surgical stimulation
Indicators of light anesthesia in case of ketamine CRI
* Rapid nystagmus
* Sudden rises in HR, ABP, RR, skeletal muscle tone
factors that affect uptake, distribution and elimination of inhaled anesthetics
physical properties: gradient of anesthetic partial pressures
chemical properties: solubility in blood vs tissues
Physiological factors: RR and CO
distribution into muscle of IA will determine —.
how long stays in system, when pt will wake up
Desflurane faster then ISO and Sevo
change in the amount of IA med that machine is turned to →brain
Every change in concentration of IA in the CNS follows changes in the PP in the —
alveolar gas mixture and arterial blood
(brain follows changes in dose of inhaled anesthetic)
factors affecting inspired gas concentration
fresh gas flow rate (↑FGF = ↑rate of induction)
volume of breathing circuit (dead space)
absorption (tubing of machine can absorb some of the med
factors affecting alveolar concentration of IA
Delivery via circuit
machine setting
alveolar ventilation
(↑ ventilation= ↑ delivery)
pulmonary uptake: blood/gas solubility coefficient (B/G)
↑ solubility= ↓ rate of induction
blood and tissue act as sponge
pulmonary blood flow
(↑ the blood flow the slower the induction)
not relavant anymore
tissue uptake
tissue solubility, blood flow and partial pressure difference between arterial blood and tissue
how does pulmonary uptake affect alveolar concentration of IA
pulmonary uptake: blood/gas solubility coefficient (B/G)
↑ solubility= ↓ rate of induction
blood and tissue act as sponge
pulmonary blood flow
(↑ the blood flow the slower the induction)
not relavant anymore
tissue uptake
tissue solubility, blood flow and partial pressure difference between arterial blood and tissue
if the blood gas solubility coefficient is high what happens to rate of induction
lowers
blood and tissue act like a sponge
the higher the pulmonary blood flow the — the rate of induction of anesthesia
slower
with modern IA drugs almost irrelevant
the higher the tissue uptake the — the rate of induction
slower
(a) Tissue solubility of anesthetic agent
(b) Tissue blood flow
(c) Partial pressure difference between arterial blood and tissues
factors affecting arterial concentration of IA gas
VQ mixmatch
deadspace
intrapulmonary shunting
alveolar gas delivery is dependent on
- concentration and partial pressure
- ventilation rate
IA alveolar gas uptake is due to
blood gas solubility
pulmonary (alveolar) blood flow
tissue uptake
IA inspired gas is based on
FGF rate
absorption by breathing circuit
volume of breathing circuit
arterial concentration of IA is dependent on
V/Q mixmatch
how to cause rapid induction of IA
give higher dose 1-4 MAC depending on the med
which IA has the longest recovery time and why
sevoflurane (has higher amount that dissolves into muscle)
sevo ≃iso > des > nitro
