Volatile Anesthetics Flashcards
1
Q
1. MAC is highest in neonates (0 to 30 days) versus other age groups with which of the following? A. isoflurane B. desflurane C. sevoflurane D. halothane E. none of the above
A
- C The MAC for inhalation agents varies with age. For most volatile anesthetics, the highest MAC values are for infants 1 to 6 months old. In infants younger than 1 month or older than 6 months, the MAC is lower for isoflurane, halothane, and desflurane. Sevoflurane is different. For sevoflurane the MAC for neonates 0 to 30 days old is 3.3%, for infants 1 to 6 months old is 3.2%, and for infants 6 to 12 months old is 2.5% (Hall Q321)
2
Q
- The rate of increase in the alveolar concentration of a volatile anesthetic relative to the inspired concentration (FA/FI) plotted against time is steep during the first moments of inhalation with all volatile anesthetics. The reason for this observation is that
A. volatile anesthetics decrease blood flow to the liver
B. there is minimal anesthetic uptake from the alveoli into pulmonary venous blood
C. volatile anesthetics increased cardiac output initially
D. the volume of the anesthetic breathing circuit is small
E. volatile anesthetics reduce alveolar ventilation
A
- B Alveolar partial pressure of a volatile anesthetic, which ultimately determines the depth of general anesthesia is determined by the relative rates of input to removal of the anesthetic gases to and from the alveoli. Removal of anesthetic gases from the alveoli is accomplished by uptake into the pulmonary venous blood, which is most dependent upon an alveolar partial pressure difference. During the initial moments of inhalation of an anesthetic gas, there is no volatile anesthetic in the alveoli to create this partial pressure gradient. Therefore, uptake for all volatile anesthetic gases will be minimal until the resultant rapid increase in alveolar partial pressure establishes a sufficient alveolar-to-venous partial pressure gradient to promote uptake of the anesthetic gas into the pulmonary venous blood. This will occur in spite of other factors, which are discussed in the explanation to question 13. (Hall Q322)
3
Q
- During spontaneous breathing, volatile anesthetics
A. increase tidal volume (VT) and decrease respiratory rate
B. increase VT and increase respiratory rate
C. decrease VT and decrease respiratory rate
D. decrease VT and increase respiratory rate
E. none of the above
A
- D At concentrations of 1 MAC or less, volatile anesthetics, as well as the inhaled anesthetic N2O, will produce dose-dependent increases in the respiratory rate in spontaneously breathing patients. This trend continues at concentrations greater than 1 MAC for all the inhaled anesthetic except isoflurane. With the exception of N2O, the evidence suggests this effect is caused by direct activation of the respiratory center in the central nervous system rather than stimulating pulmonary stretch receptors. Additionally, volatile anesthetics decrease VT and significantly alter the breathing pattern from the normal awake pattern of intermittent deep breaths separated by varying time intervals to one of rapid, shallow, regular, and rhythmic breathing (Hall Q323).
4
Q
4. Each of the following volatile anesthetics is an ether derivative EXCEPT A. halothane B. enflurane C. isoflurane D. desflurane E. sevoflurane
A
- A Halothane is derived from the hydrocarbon ethan by substitution with the halogens fluorine, bromine, and chlorine. The structure of this halogenated hydrocarbon makes halothane nonflammable and provides for low blood solubility, molecular stability, and anesthetic potency (Hall 324).
5
Q
- The reason desflurane is not used for inhalation induction in clinical practice is because of
A. its low blood/gas partition coefficient
B. its propensity to produce hypertension in high concentrations
C. its propensity to produce airway irritability
D. its propensity to produce tachyarrhythmias
E. its propensity to produce nodal rhythms
A
- Although desflurane has a low blood/gas partition coefficient (0.42) and should produce rapid induction of anesthesia, its marked pungency and airway irritation make inhalation inductions very difficult. Not only do patients dislike the scent, but the airway irritation often leads to coughing, increased salivation, breath holding, and sometimes laryngospasm (especially if the concentration is rapidly increased). In addition, with abrupt increases in concentration, patients often develop tachycardia and hypertension, thought to be due to increased sympathetic discharge (Hall Q325).
6
Q
6. A medical group planning a trip to South America has a large supply of old enflurane vaporizers (vapor pressure = 170 mm Hg). Which volatile could be delivered through an enflurane vaporizer such that the dialed setting equaled the vaporizer’s output? A. halothane B. sevolfurane C. isoflurane D. desflurane E. both halothane and isoflurane
A
- B A vaporizer’s specificity is based on the vapor pressure of the anesthetic agent for which it is made. Filling a vaporizer with an agent with a higher vapor pressure results in a higher concentration in the vaporizer’s output. Similarly, a volatile agent with a lower vapor pressure produces an output with a lower concentration than seen on the dial. Enflurane vapor pressure of 172 mm Hg (20C) most closely approximates the vapor pressure of sevoflurane which is 160 mm Hg. Remember D HI SE: Desflurane (669) > Halothane (244) = Isoflurane (240) > Sevoflurane (160) = Enflurane (172). (Hall Q326).
7
Q
- Select the true statement regarding blood pressure when 1.5 MAC N20-isoflurane is substrituted for 1.5 MAC isoflurane-oxygen.
A. blood pressure is less than awake value, but greater than that seen with isoflurane-O2
B. blood pressure is equal to awake value
C. blood pressure is greater than awake value
D. blood pressure is less than isoflurane-O2 pressure
E. blood pressure is unchanged
A
- A When N2O is substituted for an equal MAC value of isoflurane, the resulting blood pressure is greater than that seen with the same MAC value achieved with isoflurane as the sole anesthetic agent. When administered alone, N2O does not alter arterial blood pressure, stroke volume, systemic, vascular resistance, or baroreceptor reflexes. Administration of N2O increases heart rate slightly, which may result in a mild increase in cardiac output. In vitro, N2O has a dose-dependent direct depressant effect myocardial contractility, which is probably overcome in vivo by sympathetic activation (Hall Q327).
8
Q
- Which of the following groups of volatile anesthetics decrease systemic vascular resistance?
A. desflurane, sevoflurane, and isoflurane
B. halothane and isoflurane
C. desflurane and halothane
D. halothane and isoflurane
E. halothane only
A
- A All the present-day volatile anesthetics reduce blood pressure in a dose dependent fashion. Desflurane, sevoflurane and isoflurane do this primarily through reductions in systemic vascular resistance. Halothane and the obsolete agent, enflurane, produce hypotension via direct myocardial depression (Hall Q328).
9
Q
9. With which of the following inhalation agents is cardiac output moderately increased? A. halothane B. sevoflurane C. desflurane D. isoflurane E. nitrous oxide
A
- E Halothane tends to decrease the cardiac output, whereas sevoflurane, desflurane, and isoflurane tend to maintain cardiac output. Nitrous oxide tends to increase cardiac output primarily because of the mild increase in sympathetic tone (Hall Q329).
10
Q
- Select the FALSE statement about isoflurane (
A
- D At concentration of 1 MAC, isoflurane may attenuate antigen-induced bronchospasm, presumably by decreasing vagal tone. At similar concentrations, isoflurane will not reduce cardiac output in patients with normal left ventricular function. Additionally, isoflurane will decrease stroke volume, mean arterial pressure, and systemic vascular resistance in a dose-dependent manner. Cardiac output remains unchanged because decreases in systemic vascular resistance result in a reflex increase in heart rate that is sufficient to offset the decrease in stroke volume. However, dose-dependent decreases in both stroke volume and cardiac index can be seen when isoflurane is administered in concentrations greater than 1 MAC (Hall Q330).
11
Q
11. Abrupt and large increases in the delivered concentration of which of the following inhalational anesthetics may produce transient increases in systemic blood pressure and heart rate? A. desflurane B. isoflurane C. sevoflurane D. halothane E. nitrous oxide
A
- A Desflurane can (but does not always) produce an increase in blood pressure and heart rate when the concentrations are rapidly increased. This may be related to airway irritation and a sympathetic response. This has also occurred with isoflurane, but to a much less frequent and usually lower extent. The other agents listed do not cause this sympathetic response with a rapid increase in concentration. If desflurane is increased slowly or a prior dose of narcotic is given, this increase in blood pressure and heart rate may not occur (Hall Q331).
12
Q
12. Discontinuation of 1 MAC of which volatile anesthetic followed by immediate introduction of 1 MAC of which second volatile anesthetic would temporarily result in the greatest combined anesthetic potency? A. halothane followed by desflurane B. sevoflurane followed by desflurane C. halothane followed by isoflurane D. isoflurane followed by desflurane E. isoflurane followed by halothane
A
- A Of all the options listed, desflurane has the lowest solubility constant, which results in a very rapid rise in FA/FI. The rate of rise is very similar to that seen with nitrous oxide and results in the most rapid attainment of 1 MAC concentration once the new volatile anesthetic has been initiated. Halothane has the highest blood/gas solubility coefficient of all the options, reflecting the largest quantity of gas stored in the blood. This reservoir will result in the slowest decline in the alveolar concentration of this volatile upon discontinuation. The combination of these different solubilities ultimately will result in the highest combined MAC when 1 MAC of halothane is discontinued and 1 MAC of desflurane is introduced (Hall Q332).
13
Q
- Cardiogenic shock has the greatest impact on the rate of increase in FA/FI for which of the following volatile anesthetics?
A. isoflurane
B. desflurane
C. sevoflurane
D. N2O
E. the impact will be about the same for all agents
A
- A The alveolar partial pressure of an anesthetic is determined by the rate of input relative to removal of the anesthetic from the alveoli as explained in question 12. During induction, the anesthetic gas is removed from the alveoli by uptake into the pulmonary venous blood. The rate of uptake is influenced by cardiac output, the blood/gas solubility coefficient, and the alveolar-to-venous partial pressure difference of the anesthetic. At a lower cardiac output, a slower rate of uptake of volatile anesthetic from the alveoli into the pulmonary venous blood results in a faster rate of increase in the alveolar concentration. This will result in an increased alveolar inspired gas concentration (FA/FI). Uptake of poorly soluble anesthetic gases from the alveoli is minimal and the rate of rise of FA/FI is rapid and virtually independent of cardiac output. Uptake of the more soluble anesthetics such as isoflurane, from the alveoli into the pulmonary venous blood can be considerable and will be reflected by a slower rate of rise of the FA/FI ratio. Cardiogenic shock will have the smallest impact on the most insoluble agents, such as desflurane, sevoflurane, and N2O, whereas the impact on the rate of rise of FA/FI of the relatively soluble anesthetic gases, such as isoflurane, will be more profound. Decrease CO -> decrease uptake -> faster induction. (Hall Q333).
14
Q
14. The vessel-rch group receives what percent of the cardiac output? A. 45% B. 60% C. 75% D. 90% E. 95%
A
- C. The vessel-rich group that receives approximately 75% of the cardiac output is composed of the brain, heart, spleen, liver, splenic bed, kidneys, and endocrine glands. It constitutes, however, only 10% of the total body weight. Because of this large blood flow relative to tissue mass, these organs take up a large volume of volatile anesthetic and equilibrate with the partial pressure of the volatile anesthetic in the blood and alveoli during the earliest moments of induction (Hall Q334).
15
Q
15. Which of the following volatile anesthetics undergoes the greatest degree of metabolism? A. enflurane B. isoflurane C. halothane D. desflurane E. sevoflurane
A
- Of the choices listed, halothane undergoes oxidative metabolism to the greatest extent (approximately 20%), followed by sevoflurane (approximately 3%), isoflurane (approximately 0.2%), enflurane (approximately 3%), and desflurane (approximately 0.02%). Enflurane and sevoflurane may produce fluoride ions, which can be of concern during longer cases because of their potential for nephrotoxicity. Fluoride ion-induced nephrotoxicity is characterized by the inability of the kidneys to concentrate urine, presumably by direction inhibition of adenylate cyclase activity, which is necessary for the normal function of antidiuretic hormone (ADH) at the distal convoluted tubules. This results in ADH-resistant diabetes insipidus, that is, nephrogenic diabetes insipidus characterized by polyuria, dehydration, hypernatremia, and increased serum osmolarity. (Hall 335).
16
Q
16. With a properly functioning circle system, each of the following is a potential disadvantage to low flow anesthesia EXCEPT A. hypercarbia B. hypoxia C. increased compound A exposure D. increased carbon monoxide exposure E. higher serum fluoride levels
A
- A Hypoxia is always a concern with low flow or closed circuit anesthesia especially is N2) is used. Carbon monoxide can be formed when volatiles (desflurane, enflurane, isoflurane worst offenders) are exposed to desiccated CO2 absorbents containing KOH and NaOH (Baralyme and soda lime). Similarly, halothane and sevoflurane are unstable in hydrated CO2 absorbents and form compound A (with sevoflurane and a similar compound with halothane). Fluoride ions are formed in the metabolism of the obsolete volatile, enflurane as well as with isoflurane, sevoflurane and halothane (with reductive metabolism). These unwanted byproducts are ordinarily found in low concentrations with high flow anesthetic techniques because of the large volumes of fresh gas wash them away. With low flow or closed circuit anesthetic techniques, such molecules can accumulate. Since low flow or closed circuit anesthetics require, by definition, a circle system that always includes a CO2 absorber, hypercarbia is no more a concern than with high flow anesthetics. Regardless of the technique chosen, hypercarbia can exist if the absorbents are exhausted or if the one-way valves fail. (Hall 336)
17
Q
- How would a right mainstem intubation affect the rate of increase in arterial partial pressure of volatile anesthetics?
A. it would be reduced to the same degree for all volatile anesthetics
B. it would be accelerated to the same degree for all volatile anesthetics
C. There would be no change if PaO2 is 60 mm Hg or greater
D. it would be reduced the most for poorly soluble agents
E. it would be reduced the most for highly soluble agents
A
- D The situation described in this question is that of a transpulmonary shunt. In patients with transpulmonary shunting, blood emerging from unventilated alveoli contains no anesthetic gas. This anesthetic-deficient blood mixes with blood from adequately ventilated, anesthetic-containing alveoli producing an arterial anesthetic partial pressure considerably less than expected. Because uptake of anesthetic gas from the alveoli into pulmonary venous blood is less than normal, transpulmonary shunting accelerates the rate of rise in the FA/FI ratio but reduces the rate of increase in the arterial partial pressure of all volatile anesthetics. The degree to which these changes occur depends on the solubility of the given volatile anesthetic. For poorly soluble anesthetics, such as N2), transpulmonary shunting only slightly accelerates the rate of rise in FA/FI ratio, but significantly reduces the rate of increase in arterial anesthetic partial pressure. The opposite occurs with highly soluble volatile anesthetics, such as halothane and isoflurane.
18
Q
- Halothane, unlike desflurane and isoflurane, does not cause tachycardia. The most reasonable explanation for this observation is that halothane
A. lacks intrinsic sympathomimetic properties
B. lacks vagolytic properties
C. causes direct cardiac depression
D. has intrinsic parasympathomimetic properties
E. inhibits baroreceptor reflexes
A
- E In unanesthetized subjects, a reduction in arterial blood pressure will elicit an increase in heart rate via the carotid and aortic baroreceptor reflexes. In contrast to isoflurane, desflurane and sevoflurane, halothane profoundly inhibits these baroreceptor reflex responses. Therefore, despite reductions in arterial blood pressures by halothane, heart rate usually remains unchanged. (Hall 338)
19
Q
- Isoflurane, when administered to healthy patients in concentrations less than 1.0 MAC, will decrease all the following EXCEPT
A. cardiac output
B. myocardial contractility
C. stroke volume
D. systemic vascular resistance
E. ventilatory response to changes in PaCO2
A
- A Cardiac output remains unchanged because decreases in systemic vascular resistance result in a reflex increase in heart rate that is sufficient to offset the decrease in stroke volume. However, dose dependent decreases in both stroke volume and cardiac index can be seen when isoflurane is administered in concentrations greater than 1 MAC. (Hall 339)
20
Q
- Increased VA will accelerate the rate of rise of the FA/FI ratio the most for
A. desflurane
B. sevoflurane
C. isoflurane
D. halothane
E. it will accelerate FA/FI for all of these equally
A
- The rate of input of volatile anesthetics from the anesthesia machine to the alveoli is influenced by three factors: VA; the inspired anesthetic partial pressure; and the characteristics of the anesthetic breathing system. Increased VA will accelerate the rate of increase in FA/FI for all volatile anesthetics. However, the magnitude of this effect is dependent on the solubility of the volatile anesthetic. The rate of increase in FA/FI depends very little on VA for poorly soluble anesthetics because the uptake of these is minimal. In contrast, the rate of increase in FA/FI for highly soluble volatile anesthetics depends significantly on VA. Halothane is the most soluble volatile anesthetic listed in this question (blood/gas solubility coefficient 2.54). Therefore, an increase in VA will accelerate the rate of increase in FA/FI the most for halothane. Blood/gas solubility coefficients for the other volatile anesthetics are as follows: enflurane 1.90, isoflurane 1.46, sevoflurane 0.69, desflurane 0.42, and N2O 0.46. (Hall 340)
21
Q
21. Select the correct order from greatest to least for anesthetic requirement. A. adults > infants > neonates B. adults > neonates > infants C. neonates > infants > adults D. neonates > adults > infants E. infants > neonates > adults
A
- E Anesthetic requirement increases from birth until approximately age 3 to 6 months. Then, with the exception of a slight increase at puberty, anesthetic requirement progressively declines with aging. For example, the MAC for halothane in neonates is approximately 0.87%, in infants it is approximately 1.2%, and in young adults approximately 0.75%. A notable exception to this pattern is seen with sevoflurane. Here MAC is the highest with neonates. If the question only pertained to sevoflurane, the correct response would have been C. Hall 341.
22
Q
22. Which of the following inhalational agents is MOST likely to produce a decrease in systemic blood pressure by causing a junctional rhythm? A. desflurane B. halothane C. isoflurane D. sevoflurane E. nitrous oxide
A
- Although a junctional rhythm can develop after any of the drugs listed, it is most common with halothane. (Hall 342)
23
Q
23. A 31-year-old moderately obese female is receiving a general anesthetic for cervical spine fusion. After induction and intubation, the patient is mechanically ventilated with isoflurane at a vaporizer setting of 2.4%. The nitrous oxide flow is set at 500 mL/min and the oxygen flowmeter is set at 250 mL/min. The mass spectrometer displays an inspired isoflurane concentration of 1.7% and an expired isoflurane concentration of 0.6%. Approximately how many MAC of anesthesia would be represented by the alveolar concentration of anesthetic gases? A. 0.5 MAC B. 0.85 MAC C. 1.1 MAC D. 1.8 MAC E. 2.1 MAC
A
- C Two principles of MAC must be considered in this situation. First, MAC is additive, so the fraction of MAC of each individual gas must be added to arrive at total MAC. The second is that alveolar concentrations of soluble agents are reflected more accurately by end-expiratory concentrations rather than either inspiratory concentrations or gradients between inspiratory and expiratory concentrations. Because nitrous oxide is very insoluble it is reasonable to assume equilibrium will be established early. The inspiratory concentration of nitrous oxide approximately 0.6 MAC, should approximate the alveolar concentration. However, the expiratory concentrations of the more soluble volatile anesthetics should be used to estimate the alveolar concentration. The end-expiratory isoflurane concentration of 0.6 reflects approximately 0.5 MAC, which in addition to 0.6 MAC of nitrous oxide would be closest to answer C, 1.1 MAC. (Hall 343).
24
Q
- The graph in the figure depicts: X axis - Time (min). Y axis - FA/FI. 3 curves labeled 1% N2O, 40% N2O, 75% N2O.
A. the second gas effect
B. the concentration effect
C. the concentrating effect
D. the effect of solubility on the rate of rise of FA/FI
E. diffusion hypoxia
A
- B The figure shown in this question depicts the concentration effect. Note that the inspired anesthetic concentration not only influences the maximum alveolar concentration that can be attained but also the rate at which the maximum alveolar concentration can be attained. The greater the inhaled anesthetic concentration, the faster the increase in FA/FI. A high PI is necessary during initial administration of an inhaled anesthetic. This initial high PI (i.e., input) offsets the impact of uptake into the blood and accelerates induction of anesthesia as reflected in the PA. This effect of the PI is known as the concentration effect. Clinically, the range of concentrations necessary to produce a concentration effect is probably possible only with nitrous oxide. The second gas effect is a distinct phenomenon that occurs independently of the concentration effect. The ability of the large-volume uptake of one gas (first gas) to accelerate the rate of increase of the PA of a concurrently administered companion gas (second gas) is known as the second gas effect. For example, the initial large volume uptake of nitrous oxide accelerates the uptake of companion gases such as volatile anesthetics and oxygen.
