Gas Inhalents (EB) Flashcards
Which current inhalation agents are volatile liquids?
iso Des Sevo
Which current inhalation agent is a gas?
nitrous oxide
What anesthetic properties are influenced by halogenation?
anesthetic potency, arrhythmic properties, flammability, chemical stability
Flammability of gases? NB?
gone for the potent agent. NB: N2O supports combustion
Why is recovery from gases so quick? Which one is the slowest?
barely any metabolism of the gases
Halothane is the slowest
Physical properties of an inhalant that determines the methods of administration? (4)
molecular weight - Boiling point - Liquid density (specific gravity) - *vapor pressure
Physical properties of an inhalant that influences drug kinetics (2)?
solubility of gases like
Blood gas solubility
Oil gas solubility
What is Dalton’s law?
each gas has it’s own partial pressure on a container’s walls
TP = sum of partial pressures
What is saturated vapor pressure?
molecules of a volatile liquid in a closed container at fixed temperature evaporate
What is vapor pressure?
pressure exerted by the gaseous phase in the container at equilibrium
The higher the standard vapor pressure, what does it mean for volatility?
The more volatile the agent, the higher the conc of molecules in gaseous phase.
Why is SVP important for anesthesia?
determines the concentration needed for anesthesia
Purpose of a vaporizer
dilute inhalational agents to a safe concentration
Modern vaporizers are (3)
Agent specific,
Concentration calibrated,
Temperature compensated
What special circumstances are needed because desflurance has a BP of 23.5 C?
vaporizer that is connected to electricity to warm it
Relation of the blood-gas partition coefficient and induction/recovery/change of anesthetic depth
inversly related
Relation of the oil-gas partition coefficient and anesthetic potency
direct correlation
Rate of concentration rise in blood influenced by (4)
Inhaled conc and FGF
Alveolar ventilation
Solubility in blood
Cardiac output
Sequence of partial pressure gradient
Vaporizer
Breathing system
Alveoli
Blood Brain
Primary objective of movement from anesthesia machine to the brain
Same partial pressures on either side of every tissue ‘interface’
How can you accelerated ‘washout’ from tissues
high FGF, Empty reservoir bag
Washout from different tissues occurs at _ rates
different
Factors affecting recovery (5)
- Alveolar ventilation
- Solubility
- CO
- Anesthesia duration
- Metabolism
What is minimum alveolar concentration (MAC)?
The minimal alveolar conc of an inhalant anesthetic at 1 atm that provides immobility in 50% of the subjects exposed to a supramaximal noxious stimulus.
Relationship between MAC and potency?
inversely related
List iso, sevo, des, halo, and N2O by lowest to highest MAC
Lowest - Halo – Iso - Sevo – Des - N2O – Highest
When is anesthetic gas measured?
Inhaled conc, Exhaled conc
What is the ET gas conc a reflection of?
agent’s tension in the brain
Factors that decrease MAC (8)
1-sedatives/analgesics/injectable anesthetics 2- N2O 3- increasing age 4- hypothermia 5- pregnancy 6- severe hypoxemia 7- severe hypercapnia 8- concurrent illness
What constitutes severe hypoxemia
PaO2 < 40 mm Hg
What constitutes severe hypercapnia
PaCO2 > 90 mmHg
Unique feature of N2O
only gaseously stored inhalant
Why is N2O even still used today?
provides analgesia
CV side effects of N2O
minimal
Onset and recovery of N2O
rapid
How is N2O usually given
combined with other inhalant anesthetic agent
MAC of N2O in animals
about 200%
Can you administer N2O with a vaporizer?
no
Why can you not administer less than 1/3 O2 in mixture with N2O?
proportioning device on modern flowmeters
What is the second gas effect? What gas has it?
N2O accelerates initial uptake of an anesthetic gas given concomitantly
What surgeries are contraindicated with N2O? Why?
THINGS WITH GAS FILLED SPACES
- Rumen
- Stomach (GDV)
- unfasted animals
- closed pneumothorax
- ocular surgery
Why does N2O have a risk of hypoxemia? How is this combated?
N2O rapidly diffuses into alveoli after administration is stopped.
Dilution of O2 in alveoli -> risk of hypoxemia.
Provide O2 for 10 minutes after turning off N2O
Advantages of N2O (3)
second gas effect
MAC
sparing
Analgesia
Disadvantages of N2O (5)
low potency Diffusion into gas-filled spaces Potential for hypoxia Drug abuse Environmental impact
Why are your dials sticky after using halothane?
0.01% thymol preservative in the halothane -> dissoves rubber
CV effects of halothane
Depressed myocardial contractility
Reduces CO, SV, MAP (dose dependent)
Arrhythmogenic
Why is halothane arrhythmogenic
sensitizes myocardial conduction to catecholamines
Potency of isoflurane? Why?
very potent
MAC 1.3%-1.6%
Resp effects of isoflurane?
resp depressant
CV effects of iso
decrease BP
Is iso put in a preservative?
no
Induction and recovery of iso
both rapid
Mac of sevo
2.3-2.6%
Is there a preservative in sevo?
no
How is compound A formed?
sevo degradation
When is compound A nephrotoxic?
in rats, At high concentration
What does compound A react with? What system therefore can it not be used in?
interaction with CO2 absorbent. Cant really be used in a rebreathing system
MAC of desflurane
7-10%
What is malignant hyperthermia?
potentially life-threatening myopathy
What triggers malignant hyperthermia?
all 4 current volatile inhalant agents ((and depolarizing neuromuscular blocking agents))
Animals most like to least likely to get malignant hyperthermia?
pigs»_space; horses and dogs > cats
CS of malignant hyperthermia
hyperthermia
Muscle fasciculation Tachycardia
How can you recognize early malignant hyperthermia?
monitoring temp and CO2 for early recognition
Tx of malignant hyperthermia
Discontinue trigger
Cooling
Dantrolene
US regulatory agencies for anesthetic gas toxicity (3)
NIOSH
OSHE
FDA
How does halothane kill you?
halothane hepatitis (hepatic necrosis and death)
