Inhalants Anesthesia Flashcards
why use inhalant anesthesia
predictable effects (narcosis, muscle relaxation, not analgesic)
rapid adjustment of depth
minimal metabolism
economical
vapor
gaseous state of a substance that is a liquid at ambient temp and pressure
gas
exists in gaseous state a ambient temp and pressure
N2O
low blood gas PC
mild analgesic
acumulates in clased gas spaces
Xenon
expensive
mostly experimental at this time
Dalton’s Law of partial pressure
total pressure of a gas mixture is equal to the sum of the partial pressure of the individual gases
vapor pressure
pressure exerted by vapor molecules when liquid and vapor phases are in equilibrium
vapor pressure is dependent on…
temperature
increases with increasing temp; inversely related to boiling point
T/F desflurane is maintained in the gaseous form
True
blends with O2 to acheive vaporizer setting
saturated vapor pressure
maximum administration percentage
T/F vaporizers are needed to reduce the saturated vapor pressure to clinically useful doses
True
anesthetic vapors dissove in
liquids and solids
when is equalibrium reached
when the partial pressure of the anesthetic is the same in each phase
(partial pressure equal, but number of anesthetic molecules are not)
what is solubility expressed as
partition coefficient
what is the partition coefficient
concentration ratio of an anesthetic in the solvent and gas phase
describes the capacity of a given solvent to dissolve the anesthetic gas
what is the most clinically useful number
blood gas partition coefficient
what is the blood-gas partition coefficient
amount of an anesthetic in the blood vs. alveolar gas at equal partial pressures
the anesthetic in alveolar gas represents…
brain concentration
this is the location of effect
anesthetic dissolved in the blood is ppharmacologically…
Inactive
low blood gas PC
less anesthetic dissolved in blood at equal patial pressure
(more in alveoli)
short induction and recovery - more clinically useful
high blood gas PC
more anesthetic dissolved in blood at equal partial pressure
(less in alveoli)
long induction and recover
the partial pressure in the brain is equal to
partial pressure in the aveoli
how can PA be increased
increase the anesthetic delivery to alveoli
decrease removal from alveoli
how can PI be increased
increase vaporizer setting
increase fresh gas flow
decrease breathing cicuit
decrease removal from alveoli by
decrease blood solubilty of anethetic
decrease CO - patients with low CO will have a faster rse of PA
decrease alveolar-venous anesthetic gradient
T/F the higher the PI the more rapidly PA approaches PI
True
as uptake into blood decreases PI can be
decreased
anesthetic elimination requires
decrease in PA
how can you quickly decrease PA
turn off vaporizer
disconnect patient and flush O2
turn up O2 flow
increase ventilation (IPPV)
what is minimum alveolar concentration (MAC)
minimum alveolar concentration of and anesthetic that prevents movement in 50% of patients exposed to noxious stimulus
What is MAC used for
compare potency between agents
inverse relationship (high MAC = low potency)
T/F: Alveolar concentration is NOT the same as the vaporizer setting
True
what increases MAC
hyperthermia
hypernatremia
drugs causing CNS stimulation
what decreases MAC
hypothermia
hyponatremia
drugs causing CNS depression
MAP <50 mmHg
PaO2 <40 mmHg
PaCO2 >95 mmHg
pregnancy
age
what are MAC multiples
used to describe dose of gas in relation to pharmacologic and physiologic effect
1.2-1.4 times MAC ensures immobility in 95% of patients
T/F MAC is additive
True
(0.5 MACa) + (0.5 MACb) = 1 MACc
when is MAC important
changing gases in middle of a case
usig N2O
using partial intravenous anesthesia (PIVA)
cardiovascular effects of volatile anesthetics
CO, BP, SVR, contractility - decrease
HR - no change to increase
when is there an increase in intracranial pressure
>1 MAC
which doesnt suppress seizure activity
enflurane
renal effects of volatile anesthetics
decrease GFR and renal blood flow due to decreased CO
renal failure
what is compound A
produced from sevoflurance breakdown in CO2 absorbent
higher concentrations formed during: prolonged anesthesia, low fresh gas flow, desiccated absorbent
hepatic effects
reduce live blood flow and O2 delivery (decreased CO)
2 types of hepatotoxicity caused by halothane
increased liver enzymes
“halothane hepatitis” - immune mediated, often fatal
which inhalant anesthetic is more likely to cause malignant hyperthermia
halothane
Tx of malignant hyperthermia
discontinue volatile anesthetic, flush with O2, switch to new circuit if possible
provide 100% O2
administer dantrolene (muscle relaxant)
fluids, active cooling
max administration of N2O
75%
need at least 25% O2
CV effects of N2O
minimal CV and resp drepression
T/F N2O transfers to closed gas spaces
True
GI tract, sinuses, middle ear, pneumothorax, GDV, cuff of ET tube
avoid in disease states causing increased closed gas space
what is diffusion hypoxia
N2O administration is stopped, it diffuses quickly out of the blood into alveoli
displaces O2 from alveoli
if breathing room air → hypoxia
MAP with hypotension
<60 mmHg (small) and <70 mmHg (large)
what is the most appropriate and effective treatment for hypotension during inhalant anesthesia
turn down the vaporizer
if patient is light and hypotensive
add MAC-sparing drug then turn down vaporizer
opioids, benzo, lidocaine, ketamine
definitition of hypoventilation
PaCO2 >40 mmHg or EtCO2 >45 mmHg
what can happen is pop off is closed
pneumothorax
decreased CO
what signs are seen with stuck inspiratory-expiratory valves
rebreathing waveform on capnograph
what will you see with exhausted soda lime
rebreathing- waveform on capnograph
most common cause of laryngeal damage
from laryngoscope or stylet
tracheal tears are common in
cats
signs of tracheal tears
SQ emphysema
pneumomediastinum and pneumpretroperitoneum
T/F inhalant anestheritics have a very low therapeutic index
True
what indicates inadequate cerebral blood flow for consciousness
low blood pressure
MAP <50 mmHg
PA
partial pressure in the alveoli
PA =
gas delivery to alveoli - removal by the lungs
