Inhalant anesthetics Flashcards
Which type of inhalant anesthetics quickly reach equilibrium?
- Relatively insoluble anesthetics
- More soluble anesthetics
- Relatively insoluble anesthetics (fast induction and recovery)
- If completely insoluble will not get into brain
- More soluble anesthetics take longer to reach equilibrium (longer induction and recovery); large Vd, more drug to be absorbed to fill this volume
What are physiologic factors that affect inhalant anesthetics?
-
Ventilation
- No breathing = no drug uptake
- Induction drug > apnea > IPPV > large quantities of drug
- Lung disease (eg. fibrosis)
-
Cardiac output
- No heartbeat = no systemic drug uptake
- Shock > decreased cardiac output
- Excitement > increased cardiac output (patient goes down quicker and harder)
T or F. Because inhalant anesthetics have to reach the CNS, they are all fat solube and penetrate most tissues.
True; fat reservoirs, also cross placenta
_____________________ of an anesthetic at steady state which will prevent purposeful movement in response to noxious stimulus in 50% of individuals (similar to ED50).
Minimum alveolar concentration (MAC)
- Different for different drugs and species
- Often ~1.3 MAC for maintenance (used as a unit)
- Influenced by: state of excitement, premedication (will need to lower), and pain (will need higher)
Do inhalant anesthetics cause analgesia?
No
- Nitrous oxide is the exception, causes some analgesia
Do inhalant anesthetics cause sedation?
General anesthesia
- CNS depression (anesthesia) and amnesia
Do inhalant anesthetics cause muscle relaxation?
Some
- Malignant hyperthermia (highest risk with halothane)
- Enhance the effects of competitive NMB
- Nitrous oxide is the exception, does not cause muscle relaxation; also causes some analgesia; gas, not a vapor
Do inhalant anesthetics have cardiorespiratory effects?
Yes, dose-dependent respiratory depression (increased PaCO2) and dose-dependent cardiovascular depression
- Cardiovascular: decreased myocardial contractility; reduced blood flow to liver and kidneys (reduced GFR); sensitization of heart to catecholamines (halothan); peripheral vasodilation (hypotension)
- Halothane > isoflurane = desflurane = sevoflurane
Inhalation anesthetics do what to the body temperature?
Hypothermia (from vasodilation and impaired shivering)
Which inhalant anesthetic is the most arrhythmogenic, the most potent cerebral vasodilator, and has more significant cardiorespiratory side effects (depression)?
- Desflurane
- Sevoflurane
- Isoflurane
- Halothane
- Nitrous Oxide
- Halothane (not really used anymore)
- 60-80% eliminated in exhaled air
- 12% metabolized by liver to trifluoroacetic acid, chlorine, and bromine radicals > excreted in urine
- Trifluoroacetic acid may be the cause for hepatic damage seen sometimes in humans
- Thymol (preservative) builds up in vaporizer (clean up step)
Which inhalant anesthetic is the most commonly used in the USA?
- Desflurane
- Sevoflurane
- Isoflurane
- Halothane
- Nitrous Oxide
- Isoflurane
Which inhalant anesthetics do not undergo metabolism (~0.2%) (spares the liver) and also maintains the cerebral circulation autoregulation?
- Desflurane
- Sevoflurane
- Isoflurane
- Halothane
- Nitrous Oxide
- Isoflurane
- Blood/gas coefficient 1.4 (works faster, halothane is 2.4)
- Anticonvulsant effects
- Similar respiratory depression and effects on renal blood flow, but less effect on hepatic blood flow (compared to halothane)
- More enhancement of NMB
Which inhalant anesthetic has fast induction, minimal metabolism (~3%), low cerebral vasodilation?
- Desflurane
- Sevoflurane
- Isoflurane
- Halothane
- Nitrous Oxide
- Sevoflurane
- Low blood/gas coefficient (0.65)
- Less cerebral vasodilation, similar cardiovascular and respiratory effects, and similar enhancement of NMB (compared to isoflurane)
- Reacts with soda lime (CO2) absorbent
Which inhalant anesthetic has the fastest induction time, but needs a special vaporizor because of its high vapor pressure ($$$)?
- Desflurane
- Sevoflurane
- Isoflurane
- Halothane
- Nitrous Oxide
- Desflurane
- Lowest blood/gas coefficient (0.45), change in depth and recovery
- Does not undergo metabolism (0.02%)
- Compared to isoflurane: similar cardiovascular effects, more respiratory depressant, similar muscle relaxation and effect on liver blood flow, renal blood flow less affected, and similar enhancement of NMB
T or F. Nitrous oxide is a better analgesic than it is an anesthetic.
True
- Good analgesic, but not a potent anesthetic
- MAC= 200-250%
- Anesthetic adjuvant (give with another inhalant)
- 66% induction and maintenance
Which delivery methods would you use for animals that are too fractious to gain IV access, animals with ‘no veins’, very tiny animals, neonatal animals, or for C-section?
- Boxing down
- Masking down
- Intranasal cannula
