Inhaled Agents Flashcards
What is the MOA of the inhaled anesthetics?
It is not completely understood, however, the Myer- Overton theory states that anesthesia occurs when a # of inhalation molecules dissolve in a lipid cell membrane which either inhibits gluatamate and aspartate or promotes GABA and glycine. Absorption of anesthetic molecules expands the hydrophobic region within the cell membrane beyond a critical amount which distorts channels necessary for action potential and synthetic transmission.
Which Inhaled Agents are contraindicated in MH?
All of the Volatile anesthetics are contraindicated in MH. Only N2O is considered safe.
What is the chemical structure and description of N2O?
It is the only inorganic anesthetic gas. It is a gas at room temperature. It is only inhaled agent that is not halogenated. There is a double bond between two N atoms with a single bond from each to the O atom.
What are the Pharmacokinetics of N2O?
- It is eliminated by exhalation
- Biotransformation occurs with less than 1% hepatic metabolism
- Fast on and fast off due to low BG coefficient
- can be used to create 2nd gas effect for other IAs (turn on N2O @ 70% will increase concentration & uptake of other gases so you can decrease the MAC of the other agents.
- 34x more soluble than N2
What are the side effects of N2O?
- CNS
- Increased CBF, ICP, and CMRO2.
- Decreased cerebral activity, blunts cerebral autoregulation
- Neuromusclar
- can cause skeletal muscle rigidity at Mac >1, potentiates the activity of NMB
- Respiratory
- Increased RR, Decreased TV, Increases PVR & RAP- not a good drug for pt. with known pulm. htn, cor pulmonale, or significant lung disease
- Unlike the other IA, it will cause BRONCHOCONSTRICTION
- no change in resting PaCO2,
- Decreased hypoxic drive
- DIFFUSION HYPOXIA
- CV
- SNS stimulation, increased CVP,
- no change in HR, BP, CO, SVR
- epi induced arrhythmias
- may reveal undiagnosed CAD
- GI
- NAUSEA/VOMITING
- can cause bowel distention
- Liver
- decreased hepatic blood flow
- Renal
- Decreased RBF, GFR, UOP
- Heme
- inhibits B12, suppresses myelin formation and DNA synthesis in larger doses, BONE MARROW SUPPESSION, can impair response to infection
- Other:
- unique: has some ANALGESIC properties
When in N2O contraindicated?
- Related to gas expansion
- Pneumothorax
- Lap surgery with CO2 insufflation
- Air embolism
- Tympanic membrane surgery
- Eye surgery
- Intestinal obstruction/surgery
- Intracranial air
- Pregnancy
- DNA suppression, esp. in 1st trimester
- Pulmonary HTN/ elevated R. atrial pressure
- Megaloblastic anemia
What is the dose of N2O?
- Vapor Pressure: 38,770
- b/g solubility: 0.47 (low- fast on)
- MAC dose: 105%
What is the drug class/ chemical description of Halothane?
Inhaled Volatile Anesthetic. It is a halogenated alkane derivative.
What is the MOA/ Pharmacodynamics of Halothane?
Same as all of the other IAs.
What are the side effects of Halothane?
- CNS
- Increased CBF, ICP
- Decreased CMRO2 (uncoupling), dec. cerebral activity, cerebral autoregulation blunted
- NM
- Halothane has the least amount of relaxant effect
- Most likely agent to cause MH
- Poteniates NMDRs
- Resp
- Potent brochodilator
- Increased RR, inc. resting PaCO2
- Decreased TV, severe depression of hypoxic drive
- Hypoxic pulmonary vasoconstriction inhibited
- CV
- Inc. CVP
- Myocardial depressant
- No change in SVR- the others volatiles decrease it
- Baroreceptor reflex is blunted. You’ll see no inc. in HR when BP drops.
- Decreased BP and CO
- coronary vasodilator
- Significant risk of arrhthmia (prolonged QT, decreased AV conduction, HIS, purkinje, common junctional rhythm, VF/VT)
- Increased sensitivity to EPI
- GI
- All IA can cause N/V
- Liver
- Halothane hepatitis (IgG mediated immune response from trifluroacetic acid)
- Renal
- Decreased RBF, GFR, and UOP
What are the contraindications to using Halothane?
- Liver failure
- caution in Cholecystitis
- CCB (increases myocardial depression)
- BBlockers (increases myocardial depression)
- TCAs (causes unstable BP)
- MAOIs (causes unstable BP)
- Aminophylline (inc. vent. arrhythmias)
- Hx. of MH (Halothane the most potent trigger)
- Aortic Stenosis
- avoid in kindey disease
- avoid in neuro cases
- avoid in pheochromocytoma
What is the dose of Halothane?
- Vapor Pressure : 243
- b/g coefficient 2.4 (intermediate onset)
- MAC: 0.74% (high potency)
What are the pharmacokinetics/ metabolism of Halothane?
- It is a nonflammable, sweet gas
- It has thymol as a preservative (can gum up the vaporizer)
- It is eliminated by exhalation and biotransformation
- It depends largely on hepatic metabolism (15-20%)
What is the mechanism of action/ pharmacodynamics of Enflurane?
- Enflurane has the same MOA as the other IAs
What is the drug class/ chemical structure of Enflurane?
Enflurane is a Volatile Anesthetic. It is an isomer of Isoflurane. It is a halogenated methyl ethyl ether.
What are the side effects of Enflurane?
- CNS
- Increased CBF, ICP, IOP
- Decreased cerebral activity, dec. CMRO2, cerebral autoregulation is blunted
- Increases CSF production and dec. CSF outflow= high ICP
- Seizures- do not use in pt. with seizure d/o
- DO NOT HYPERVENTILATE TO DECREASE ICP- hypcarbia makes a more favorable condition for seizures.
- NM
- potentiates NMDR
- Resp
- Increased RR, inc. resting PaCO2
- Decreased TV
- Marked resp. depression at 1 MAC
- Abolishes hypoxic drive
- Decreases mucociliary function
- Bronchodilator
- CV
- Decreased SVR, BP, CO
- Increased HR (baroreceptor)
- depressed myocardial contractility
- Pronlongs QT
- Increased risk of arrhythmia with epi use
- GI
- N/V
- Liver
- decreased HBF
- Renal
- decreased RBF, GFR, UOP
- Fluoride levels could lead to high ouput renal failure
What the contraindications to using Enflurane?
- Renal dysfunction
- Seizures
- MH
What is the dose of Enflurane?
- Vapor Pressure: 175
- b/g coefficient: 1.8 (intermediate solubility)
- MAC- 1.7% (high potency)
What are the pharmacokinetics/ how is enflurane metabolized?
- Enflurane is a mild, sweet gas
- It is eliminated by biotransformation and exhalation
- It is 2-5% metabolized by the liver
- It has the potential for nephrotoxicity d/t fluorine content
What are the pharmacodynamics/ mechanism of action of N2O?
The same as the other IAs
What are the pharmacokinetics/ how is N2O metabolized?
- It is eliminated by exhalation and biotransformation
- < 1% metabolized by the liver
What is the drug class/ chemical structure of Isoflurane?
- It is an inhaled volatile anesthetic
- It is a halogenated methyl ethyl ether
- It is an isomer of enflurane
What is the MOA/ pharamacodynamics of Isoflurane?
The same as the other IAs
What are the side effects of Isoflurane?
- CNS
- Increased CBF, ICP
- Decreased CMRO2
- Increased CSF reabsorption
- NM
- potentiates NM blockade
- Resp
- bronchodilator
- CV
- Decreased SVR but BP and CO maintained
- Increased HR, mild Beta stimulation, but CV stable
- Coronary artery dilation BUT may cause CORONARY STEAL
- GI
- N/V
- Liver
- no change in hepatic blood flow (good drug for liver and kidney disease)
- Renal
- decreased RBF, GFR, UOP
What are the contraindications to using Isofluane?
- Pediatrics- has a pungent odor, may cause coughing and laryngospasm
- MH
What are the pharmacokinetics/ metabolism of Isoflurane?
- Isoflurane is eliminated by exhalation and biotransformation
- Isoflurane has <0.2% hepatic metabolism
What is the dose of Isoflurane?
- Vapor pressure: 239
- b/g coefficient: 1.4 (intermediate solubility)
- MAC: 1.2% (potent)
What is the MOA/ pharmacodynamics of Desflurane?
Same as the other IAs
What is the drug class/ chemical structure of Desflurane?
- Desflurane is a volatile inhaled anesthetic
- It is a flurinated methyl ethyl ether
- It has a similar structure to Isoflurane
What are the Pharmacokinetics/ metabolism of Desflurane?
- Eliminated by exhalation and biotransformation
- Hepatic metabolism <1%
- May create CO with low flows
- Uses a TEC 6 vaporizer
- Fast on and fast off
What are the side effects of Desflurane?
- CNS
- Increased CBF, ICP
- Decreased CMRO2
- NM
- potentiates NMB
- Resp
- bronchodilation
- irritating to the airway- pungent odor can cause coughing, bucking and laryngospasm
- Carbon monoxide risk of used with low flows (check your CO2 absorber, keep it fresh)
- CV
- Decreased BP, SVR
- Increased HR (no change in CO)
- DOES NOT DILATE THE CORONARY ARTERIES
- GI
- Nausea and vomiting
- Liver
- decreased HBF
- Renal
- decreased RBF, GFR, and UOP
What are the contraindications to using Desflurane?
- MH
- Pediatrics induction
What is the doe of Desflurane?
- Vapor Pressure: 664
- b/g coefficient: 0.42
- Mac 6%
What is the drug class/ chemical structure of Sevoflurane?
- Fluorinated methyl isopropyl ether
What is the mechanism of action of Sevoflurane?
same as the other IAs
What are the side effects of Sevoflurane?
- CNS
- Increased CBF, ICP
- Decreased CMRO2
- NM
- Resp
- Bronchodilation
- CV
- Decreased SVR, BP, CO
- Increased HR
- no change in CVP
- GI
- Nausea/Vomiting
- Liver
- Hepatic blood flow maintained
- Renal
- Can cause accumulation of Compund A and nephrotoxicity with low flows (keep flows 2L)
- Decreased RBF, GFR, UOP
What are the contraindications to using Sevoflurane?
- MH
- Severe renal disease
What is the dose of Sevoflurane?
- Vapor pressure: 157
- b/g coefficient: 0.69
- MAC: 3%
What is the metabolism/ pharmacokinetics of Sevoflurane?
- Ideal for pediatrics- sweet & non-pungent
- minimal airway irritation
- expensive
- eliminated via exhalation and biotransformation
- Hepatic metabolism 2-3%
