Inhalation Anesthetics Flashcards
Inhalant Anesthetics
- Liquid agents vaporized in oxygen
- Administered via anesthetic breathing system by ET-tube, mask, or chamber
How are inhalant anesthetic agents measured
- Vapor pressure
- Blood-gas partition coefficient
- Minimum alveolar concentration (MAC)
Vapor Pressure
Measurement of the tendency of a liquid to evaporate
Vapor & Evaporation
Regarding Inhalant Agents
High vapor pressure = readily evaporate
* reach dangerously high concentrations
* administer using agent-specific precision vaporizer
Low vapor pressure
* may be administered with nonprecision vaporizer
Blood-gas Partition Coefficient
Measurement of the tendency of an agent to dissolve in blood
Blood-gas Partition Coefficient
Associations
- Speed of induction
- Recovery
- Change in depth of anesthesia
Low vs High Blood-gas Partition Coefficient
In regards to speed of induction, recovery, and change in depth of anesthesia
Low Partition Coefficient = Faster
High Partition Coefficient = Slower
MAC
- Minimum Alveolar Concentration
- Percent concentration of an agent
- Measurement of potency of agent
High vs Low MAC
High MAC = less potent
* more required to attain surgical anesthesia
Halogenated Anesthetics
Function and Causes
- Induce and maintain general anesthesia
- CNS depression
- Respiratory depression
- Hypothermia
- Hypotension
- Muscle relaxation
- No analgesic postoperatively
Halogenated Anesthetics
Examples
- Isoflurane
- Sevoflurane
Halogenated Anesthetics
& the Heart
Cause myocardial depression
* cardiac function maintained close to preanesthetic levels
Iso & Sevo
Vapor Pressure and Blood-gas Partition Coefficients
Both have:
* High vapor pressure - need precision vaporizer
* Low blood-gas partition coefficients - rapid induction, recovery, and change in anesthetic depth
Halogenated Anesthetics
Metabolism and Excretion
Both metabolized in Liver
Excreted primarily through lungs, but also by kidneys
Iso & Sevo
Metabolism
Metabolized by liver
Iso = better choice for those with kidney or liver disease
Sevoflurane and Fire/Heat
- Fire / heat production produced when used with dry CO2 absorbent
- More common when low oxygen flow rates used over long time
Sevoflurane and Fire/Heat
Preventions
- Turn machine off when not in use
- Replace absorbent granules regularly
- Avoid low oxygen flow rates for extended periods
- Monitor temperature of abosrbent canister
Desflurane
- Similar to Isoflurane
- Extremely high vapor pressure
- Low blood-gas partition coefficient
Desflurane
Vaporizer
Required expensive electronic vaporizer
* boiling point is near room temperature
Desflurane Effects
- More rapid inductions and recovery compared to sevoflurane
- Causes dose-related respiratory depression
Advantages of Anesthesia
- Elimination through lungs - liver and kidneys not as crucial
- Good control of aneshetic depth
- Newer agents less irritating to respiratory system
- Well tolerated
Disadvantages of Anesthesia
- Require constant monitoring
- Requires complex and expensive equipment
- Muscle relaxation
- No long term analgesia
Inhalation Anesthetic Agents
No longer commonly used
* diethyl ether
* methoxyflurane
* nitrous oxide
* halothane
Alveolar Concentration
- Inhalation anesthetic effects in brain related to anesthetic concentration in lungs
- Low concentration needed
- Concentration needed to prevent muscle movement in response to surgical stimuli
MAC Factors
Cause Decrease
Decrease means more sensitivity to anesthetic
* hypotension
* hypothermia
* aging
Lower the need for anesthetic levels
Partition Coefficient
Entry of anesthetic into body fluids and tissues
More soluable agent = slower induction/recovery
* slower it takes to get to brain tissues
Partition Coefficient & Anesthetic Gas
Volume of gas absorbed by a unit volume of liquid
* High concentration during induction
* Low concentration for maintanence
Diffusion Hypoxia
Occurs if a gas other than oxygen floods alveoli and displaced O2
* occurs with very insoluable gases
Vapor Pressue
Definition
Amount of pressure exerted by the gas form when gas and liquid are in equilibrium
Equilibrium
Regarding Vapor Pressure
Reached when the number of molecules going to gas and returning to liquid is equal
Votality & Vapor Pressure
High vapor pressure = high tendency to evaporate
* easily evaporate = High votality
Vapor Pressure Variations
Will vary with:
* physical property of the liquid
* temperature of the liquid
High Vapor Pressure Agents
Require precision vaporizer
* halothane
* isoflurane
* sevoflurane
Inhalation Anesthetic Drugs
Desired Properties
- Safe, no delayed toxicity
- Non-flammable/ Non-explosive
- Chemically stabe, no reaction to soda-lime
- Low MAC value
- Low blood solubility
- No irritation to mm
- No nausea
- Inexpensive
Nitrous Oxide
- Weak anesthetic drug - no anesthesia by itself
- Tank color is Blue
- Referred to as “laughing gas”
Nitrous Oxide
Anesthetic Effects
- Some depression of cerebral cortex
- Unchanged HR, cardiac output, BP
- Tachycardia will occur with hypoxia
Nitrous Oxide
Elimination & Metabolism
- Eliminated through lungs
- Very little is metabolized
- Completely gone within 2 minutes
Nitrous Oxide
Diffusion Hypoxia
- Occurs when N2O floods alveoli when turned off - rapid outflow of N2O
- Suppliment with O2 for 2-5 minutes after N2O turned off
Nitrous Oxide
Abuse
Potential for human abuse
* may cause death by hypoxia
Nitrous Oxide
Hollow body structures
Will rapidly diffuse into hollow structures and cause distention
Use caution with
* pneumothorax
* GI obstruction
* gastric torsion
* lung cyst
* diaphragmatic hernia
Ether
- Used as main inhalant anesthetic up until 1956
- Highly flammable
- Heavier than air; sink and form vapor cloud
- Good analgesia and margin of safety
Methoxyflurane
- Inhalant anesthetic agent
- Potent, highly soluble
- Slow induction and recovery
- Delayed kidney toxicity in humans
Halothane
- Inhalation anesthetic agent
- Lost popularity because it sensitizes the heart to epinephrine induced arrhythmias
Isoflurane
- Inhalation anesthetic agent
- Insoluble in tissues (blood and muscles)*
- Physically stable
More soluble in fat than blood
Isoflurane
Chemical Properties
- Colorless
- Ether-like odor
- Mild irritation to mm
- Heavier than air
- Non-flammable
Isoflurane
Patients & Protocol
Protocol for brachycephalics & high-risk
* pre-oxygenate for 3-5 minutes
* flow 3L/min
* calm patient during this time
Sevoflurane
Characteristics
- Non-pungent odor
- Less irritating to mm
- Suited for mask induction
Sevoflurane
Effects
High insoluble
* quick induction/recovery
* quick alteration to anesthetic depth
Low tendancy for cardiac arrhythmias
Sevoflurane
Concentrations
Higher concentrations cause rapid change in anesthetic depth
* may cause hypotension and respiratory depression
