Inhalational Anesthetics Flashcards
These factors will slow induction
Factors that will increase uptake, reduce the rate of rise of the FA/FI ratio, and will have a slowed induction include:
1) Increased CO
2) Increased solubility
3) Increased concentration gradient
These factors can help speed up induction
1) Increased alveolar ventilation
2) Increased FGF
3) Increase the FD to supraphysiologic levels (overpressuring) (similar to giving a bolus of an IV drug)
4)
What is the concentration effect?
The administration of a high concentration of a gas increases its own concentration in the lung and speeds the rate of rise of the FA/FI
What is the second gas effect?
Administering a high concentration of a gas increases its own concentration, the rate of rise of its own FA/FI, and the concentration and rate of rise of the FA/FI of a second (companion) gas
What was the first halogenated hydrocarbon anesthetic
Fluroxene
Combining fluorine decreased flammability, but was withdrawn from the market b/c it caused organ toxicity
These factors will decrease the MAC
Increasing age Hypothermia Hyponatremia Hypotension < 40mmhg Pregnancy Hypoxemia (< 38 mmHg) Anemia (4.3 ml/dl) Opioids Ketamine Benzodiazepines Clonidine A2 agonists Local Anesthetics ETOH (acute)
The effect of halogens
Lower weight halogens (like fluorine) have lower potency than heavier ones like Cl-
Chlorine: leads to more stable compounds, but also causes myocardial depression
Florine: Reduced flammability, but has the potential for renal damage (fluoride ions will inhibit sodium reabsorption in the ascending loop)
These factors do NOT affect MAC
Type of stimulus Sex Species Duration of anesthesia Acid/Base disturbances PaO2 (as long as it's between 40-500 torr)
These factors will decrease MAC
Increasing age Hypothermia Hyponatremia Hypotension (MAP < 40) Hypoxemia (<4.3mL/dL)
Other factors that you would typically expect: Opioids Benzos A2 agonists Ketamine LAs Acute ETOH intoxication
These factors will decrease the necessary MAC
Youth under 1 y/o
Hyperthermia
CNS stimulants (cocaine)
If no muscle relaxant is on board, 95% of patients will need this % increase in MAC to avoid movement
10-30% increase in MAC
What is MAC awake, and what are the doses?
MAC awake is the MAC concentration that still permits voluntary response
1/3 MAC for Sevo, Iso, and Des
1/2 MAC for Halothane
60% MAC for N2O
Halothane produces these two types of hepatotoxicity in susceptible patients
1) A mild, self-limited post-op hepatotoxicity will develop in 20% of patients
- Causes N/V, lethargy, fever, and minor increases in transaminase levels
- May occur not due to the drug itself, but because of the decrease in hepatic blood flow it causes, and resulting decrease in hepatic oxygenation
2) Halothane hepatitis
- Occurs in 1:10,000 to 1:30,000 cases
- Causes extensive hepatic necrosis and death is possible
- This is most likely an immune-mediated hepatotoxicity, because IgG antibodies are present in 70% of those diagnosed
Classic presentation of volatile agent associated hepatitis
Fever, N/V, anorexia, chills, myalgia, rash, fever, arthralgia, and eosinophilia. This is followed by jaundice 3-6 days later.
Risk factors for VA associated hepatitis
PRIOR EXPOSURE Age > 40 Mexicans Genetic susceptibility Multiple brief procedures within a brief period of time Enzyme induction
