Inhalation Anesthetics Flashcards
Inhalation Anesthetics Pros
Control of the airway Control ventilation Control drug uptake & elimination
Inhalation anesthetics Cons
Specialized *expensive* equipment Equipment failure
Inhalation anesthetics Dosage
Concentration (volume%) of inspired gas Partial Pressure
Partial Pressure conversion 4% Halothane
4% Halothane = 0.04 F1 hal = 4 kPa
Partial Pressure conversions kPa, atm, bar, mmHg, psi, cm water
101 kPa 1 atm 1 bar 760 mmHg 15 psi 1000 cm water
Inhalation anesthetics Uptake
Taken up by lungs
Inhalation anesthetics Elimination
Excreted mostly unchanged by lungs Alveolar concentration ~ brain concentration
Inhalation anesthetics Saturated vapor pressure
Ability of anesthetic to evaporate Match druge with proper vaporizer, varies greatly
Inhalation anesthetics Rubber & plastic solubility
Concern with older agents -Soluble into tubes
Inhalation anesthetics Blood/Brain coefficient
Concern with older agents
Inhalation anesthetics Blood/Gas coefficient
Solubility Influences rate of uptake/distribution Speed of induction, recovery, change of anesthetic level
Inhalation anesthetics Physical factors Solubility
Completely insoluble = not into brain Relatively insoluble = fast induction & recovery Soluble anesthetics = longer induction & recovery
Inhalation anesthetics Soluble anesthetics
Longer induction, recovery Large Vd = more drug to be absorbed More potent drugs
Inhalation anesthetics Physiologic factors
Ventilation Cardiac output
Inhalation anesthetics Ventilation
No breathing = no drug uptake -Induction drug –> apnea –> IPPV –> Large drug quantities -Lung disease (thickening of blood/gas barrier)
Inhalation anesthetics Cardiac output
No heartbeat = no systemic drug uptake Shock –> decreased CO Excitement –> increased CO
Inhalation anesthetics Distribution
All are fat-soluble Penetrate most tissues Fat reservoirs Cross placenta
Inhalation anesthetics MAC
Minimal alveolar concentration -Anesthetic at steady state which will prevent purposeful movement in response to supramaximal noxious stimulus in 50% of individuals (similar to ED 50) -Varies across species
Inhalation anesthetics MAC for maintenance
~1.3 for maintenance -Animal’s state of excitement/pain -Premedication
Table of MAC for species
Graph Below
Inhalation anesthetics Pharmacologic effects overview
General anesthesia Some muscle relaxation (not with NO) No analgesia Respiratory depression Cardiovascular depression
Inhalation anesthetics Pharm effects on CNS
Depression (anesthesia) Amnesia (Supraspinal site) Immobility / no response to noxious stimuli (spinal site) Predisposed to seizure activity (enflurane & sevoflurane) Vasodilation
What two drugs have a predisposiiton to seizure activity?
Enflurane & sevoflurane)
Inhalation anesthetics Describe vasodilation effects
Increased cerebral blood flow –> intracranial pressure
Inhalation anesthetics Pharm effects on Respiratory
Dose-dependent depression (incr PaCO2) Bronchodilation Airway irritation
Inhalation anesthetics Which drugs have bronchodilation effects
D-I-S-H -flurane Desflurane Isoflurane Sevoflurane Halothane
Inhalation anesthetics Which drugs show airway irritation
Desflurane in humans -Breath-holding -Coughing -Laryngospasm
Inhalation anesthetics Pharm effects at cardiovascular system
Dose-related decreased myocardial contractility Alteration of organ blood flow Sensitization of heart to catecholamines
Inhalation anesthetics Describe effect of decreased myocardial contractility
Stroke volume Cardiac output Hypotension (peripheral vasodilation) Halothane>isofluorane=desflurane=sevoflurane
Inhalation anesthetics Pharm effects at liver
Hepatocellular injury -Reduced blood flow -Direct toxicity - halothane?
Inhalation anesthetics Pharm effects at kidneys
Reduced blood flow & GFR -Transient increase in serum urea nitrogen, creatinine, inorganic phosphate -Direct toxicity - methoxyflurane
Inhalation anesthetics Which drug has direct toxicity to the kidneys
Methoxyflurane
Inhalation anesthetics Pharm effects at skeletal muscle
Relaxation Malignant hyperthermia (halothane in pigs) Enhance effects of competitive Neuromuscular Blockers
What medication can cause malignant hyperthermia in pigs?
Halothane
What can halothane cause in pigs?
Malignant hyperthermia
Inhalation anesthetics Effect on body temperature
Hypothermia -Increased heat loss, vasodilation, decreased heat production, impaired shivering
Inhalation anesthetics Vapor drugs
From liquids DISH -Desflurane -Isoflurane -Sevoflurane -Halothane
Inhalation anesthetics Gases
NO warrior princess Nitrous Oxide Xenon
Halothane Elimination
-Falling out of fashion -Most potent cerebral vasodilater -60-80% eliminated in exhale -Liver biotransformation by cytochrome p450
Halothane Liver biotransformation
by Cytochrome p450 -Trifloroacetic acid, chloride, bromide
Halothank Respiratory & CV effects
Respiratory & cardiovascular depression
Which drug is the most potent cerebral vasodilator?
Halothane
Which drug is the most arrhythmogenic?
Halothane
Halothane Cardiac affect
The most arrhythmogenic -Sensitizes heart to epinephrine -Premature ventricular extrasystoles (VPCs)
Halothane Hepatitis effects
Decreased hepatic blood flow Human vs. domestic animals Metabolite- immune-mediated reaction
Halothane Thymol
Preservative Builds up in vaporizers
Isoflurane Effects at CV and respiratory (Compared to halothane)
Less cardiac depression than halothane Same respiratory as halothane
Isoflurane Renal effect
Renal blood flow decreased like halothane
Isoflurane Liver & muscle effect
Liver & muscle blood flow less affected than with halothane
Isoflurane Effects of NMB
More potent enhancer of NMB effects than halothane
Isoflurane General info
Most used in USA Isomer of enfluane Almost no metabolism Anticonvulsant Cerebral circulation autoregulation maintained
Isoflurane Choice drug for what conditions?
Choice for critically ill patients & neurosurgery
What is the choice drug for critically ill patients and neurosurgery?
Isoflurane
Isoflurane Cerebral effects
Less cerebral vasodilation than halothane
Desflurane Vapor pressure
High vapor pressure = special vaporizer
Desflurane Blood/Gas coefficient
The lowest. 0.45 Fast induction Change in depth & recovery
Desflurane Metabolism
Does not undergo metabolism (0.02%)
Desflurane Similarity to Isoflurane
Similar in cardiovascular effects & cerebral vascular effects
Desflurane Respiratory effect compared to isoflurane
More respiratory depressant than isoflurane
Desflurane Liver blood flow effect
Decreased Liver blood flow like isoflurane
Desflurane Renal blood flow
Not substantially altered
Desflurane Muscle relaxation
Similar to isoflurane
Desflurane NMB effects
Similar to isoflurane *Potent enhancer of NMB effects*
Sevoflurane Blood/gas coefficient
Low= 0.65 Fast induction, change in depth & recovery
Sevoflurane Cerebral vasodilation
Less than isoflurane & desflurane
Sevoflurane CV & respiratory effects
Similar to isoflurane
Sevoflurane What absorbent does it react with
Soda lime (CO2) absorbent -Compound D (nephrotoxic LD50=400ppm in rates) -Flow rates of 2L/min in humans
Sevoflurane What makes it nephrotoxic
Fluoride ion
Sevoflurane Renal or hepatic injury in domestic animals?
No
Sevoflurane NMB enhancement
Similar to isoflurane to enhance effects of competitive NMB
Nitrous Oxide
AKA N2O, Laughing gas -Comes in cylinders -Low blood/gas coefficient (0.47) -Non-potent anesthetic -Builds up in circle systems
Nitrous Oxide As an anesthetic
Not potent MAC= 200-250% Anesthetic adjuvant (give with inhalation anesthetic) 66% induction & maintenance
Nitrous Oxide Second gas effect
Large % of volume of gas moves higher–>lower tension until @ equilibrium NO- more fresh, faster induction
Nitrous Oxide Fink Effect
Diffusion hypoxia -Opposite to 2nd gas effect -Displacing alveolar gas (including Oxygen) -Give 100% O2 on recovery
Nitrous Oxide As an analgesic
Good analgesic
Nitrous Oxide CV & respiratory effects
Low CV & Resp depression
Nitrous Oxide CNS effects
Increases cerebral blood flow Increases cerebral metabolic rate Increases intracranial pressure
Nitrous Oxide Liver & Kidney effects
Minimal effect on function
Nitrous Oxide Muscle relaxer
Poor relaxation Weak trigger of MH
Nitrous Oxide Diffusion problems
Diffuses into air-filled spaces (pneumothorax, colic)
Nitrous Oxide Risk to pregnant women
Abortion
Inhalation Anesthetics No longer used
Methoxyflurane Enflurane
Methoxyflurane
No longer used inhalation anesthetic Good analgesic & muscle relaxant Slow induction & recovery Nephrotoxic (fluoride ions)
Enflurane
No longer used inhalation anesthetic Seizure activity
Inhalation Anesthetics Other delivery methods
Boxing down Masking down Intranasal cannula **For fractious animals, tiny animals, neonates, C-section**