SPEED OF INDUCTION & RECOVERY

SPEED OF INDUCTION & RECOVERY

Q. 1 Which of the following statements about inhalation anesthetic agents is wrong?

 A Sevoflurane is more potent than isoflurane

 B

Sevoflurane is less cardiodepressant than isoflurane

 C

Desflurane has lower blood-gas partition coefficient than sevoflurane

 D

Sevoflurane has a higher MAC than isoflurane

Q. 1

Which of the following statements about inhalation anesthetic agents is wrong?

 A

Sevoflurane is more potent than isoflurane

 B

Sevoflurane is less cardiodepressant than isoflurane

 C

Desflurane has lower blood-gas partition coefficient than sevoflurane

 D

Sevoflurane has a higher MAC than isoflurane

Ans. A

Explanation:

Sevoflurane is less potent than isoflurane as it lacks coronary vasodilating properties.

Ref:  Handbook of Clinical Anesthesia By Barash, Cullen, Stoelting , 5th Edition, Page 216; Handbook of Clinical Anesthesia By Paul G. Barash, Bruce F. Cullen, Robert K. Stoelting, M. Christine Stock, 6th Edition, Page 231


Q. 2

Partition coefficient of gas

 A

Measure of potency

 B

Directly proportional to potency

 C

Measures solubility

 D

All of the above

Ans. C

Explanation:

C i.e. Measures solubility


Q. 3

Least diffusion coefficient is for :

 A

Isoflurane

 B

Enflurane

 C

Halothane

 D

N20

Ans. D

Explanation:

D i.e N20


Q. 4

Diffusion hypoxia is seen during:

 A

Induction of anaesthesia

 B

Recovering anaesthesia

 C

Preoperatively

 D

Postoperatively

Ans. B

Explanation:

B i.e. Recovering anesthesia


Q. 5

At the end of anaesthesia after discontinuation of nitrous oxide and removal of endotracheal tube, 100% oxygen is administered to the patient to prevent:

 A

Diffusion Hypoxia

 B

Second gas effect

 C

Hyperoxia

 D

Bronchospasm

Ans. A

Explanation:

A i.e. Diffusion Hypoxia

  • (Ref : Willer 8/e p656, 3401)
  • On discontinuation of N2O administration, nitrous oxide gas can diffuse from blood to the alveoli, diluting O2 in the lung.
    • Produce an effect called “Diffusional hypoxia”.
  • To avoid hypoxia, 100% O2, rather than air should be administered when N2O discontinued.

Q. 6 Diffusion hypoxia seen during ‑

 A

Induction of anesthesia

 B

Reversal of anesthesia

 C

Post operative period

 D

None of the above

Ans. B

Explanation:

Ans. is ‘b’ i.e., Reversal of anaesthesia

Second gas effect and diffusion hvpoxia

  • In initial part of induction, diffusion gradient from alveoli to blood is high and larger quantity of anaesthetic is entering blood.
  • If the inhaled Concentration of anaesthetic is high (eg N20), Substantial loss of alveolar gas volume will occur and it creates negative intralveolar pressure that leads to removal of more gas from cylinder to alveoli Concentration effect.
  • If another inhalation agent is (eg Halothane) is being given at the same time, it also will be delivered to lung from the cylinder (due to negative intraalveolar pressure) Second gas effect.
  • During recovery reverse occurs – N20 having low blood solubility, rapidly diffuses into alveoli and dilutes the alveolar air –> partial pressure of oxygen in alveoli is reduced.
  • The resulting hypoxia is known as diffusion hypoxia.
  • Diffusion hypoxia can be prevented by continuing 100% 02 inhalation for a few minutes after discontinuing N20, instead of straight away switching over to air.

Q. 7 Speed of onset of action of local anaesthetics is indicated by –

 A Minimum alveolar concentration

 B

Blood : gas partition coefficient

 C

Oil : gas partition coefficient

 D

All of the above

Ans. B

Explanation:

Ans. is ‘b’ i.e., Blood : gas partition coefficient

Minimal alveolar concentration

  • It is the lowest concentration of the anaesthetic in pulmonary alveoli needed to produce immobility in response to a painful stimulus (surgical incision) in 50% individuals.
  • It is the measure of potency of inhalation GAs.

Blood : gas partition cofficient

  • It is the measure of solubility of agent in blood.
  • It determines the speed of onset and recovery.
  • Higher the blood : gas partition cofficient, lesser the speed of induction and recovary —> more blood soluble agents have slower induction and recovery.

Oil : gas partition cofficient

  • It is the measure of lipid solubility of the agent, and therefore solubility in the fat – rich tissues of the CNS.
  • This equates with the potency of individual agents.
  • There is a direct relationship between the minimum alveolar concentration (MAC) value of inhaled anaesthetic agents and lipid solubility in terms of the oil/gas partition cofficient.

Q. 8 Speed of onset of action of local anaesthetics is indicated by –

 A Minimum alveolar concentration

 B

Blood : gas partition coefficient

 C

Oil : gas partition coefficient

 D

All of the above

Ans. B

Explanation:

Ans. is ‘b’ i.e., Blood : gas partition coefficient

Minimal alveolar concentration

  • It is the lowest concentration of the anaesthetic in pulmonary alveoli needed to produce immobility in response to a painful stimulus (surgical incision) in 50% individuals.
  • It is the measure of potency of inhalation GAs.

Blood : gas partition cofficient

  • It is the measure of solubility of agent in blood.
  • It determines the speed of onset and recovery.
  • Higher the blood : gas partition cofficient, lesser the speed of induction and recovary —> more blood soluble agents have slower induction and recovery.

Oil : gas partition cofficient

  • It is the measure of lipid solubility of the agent, and therefore solubility in the fat – rich tissues of the CNS.
  • This equates with the potency of individual agents.
  • There is a direct relationship between the minimum alveolar concentration (MAC) value of inhaled anaesthetic agents and lipid solubility in terms of the oil/gas partition cofficient.

Q. 9

Second gas effect is ‑

 A Displacement of N20 by Oxygen

 B Displacement of oxygen by N20

 C

Facilitation of inhalation of Halothane by N20

 D

Removal of oxygen by N20 from alveoli during recovery from general anaesthesia

Ans. C

Explanation:

Ans. is ‘c’ i.e., Facilitation of inhalation of halothane by N20


Q. 10

Blood : Gas partition coefficient is a measure of ‑

 A

Potency of anaesthetic agent

 B

Lipid solubility of agent

 C

Blood solubility of agent

 D

None

Ans. C

Explanation:

Ans. is ‘c’ i.e., Blood solubility of agent

Blood : Gas partition coefficient (B:G coefficient)

  • It is the measure ofsoluhility ()Dire agent in the blood. Agent with low blood solubility (low B : G coefficient) will have high concentration in alveolar air as it will diffuse less through the alveolar capillary membrane because of low blood solubility. Since alveolar concentration determines the induction and recovery, induction & recovery will be fast with agent with less B : G partition coefficient; and induction & recovery will be slower with agents with high B : G partition coefficient.
  • Desflurane has minimum B : G partition coefficient (least blood solubility) —> Has Fastest onset and recovery.
  • Methoxyflurane has maximum B : G partition coefficient (Maximum blood solubility) —> Has slowest onset & recovery.
  • Speed of onset & recovery in decreasing order (Increasing order of B : G partition coefficient and blood solubility):-

Desflurane (0.42) > Cyclopropane (0.44) > N20 (0.47) > Sevoflurane (0.69)>Isoflurane (1.38) > Enflurane (1.8) > Halothane (2.4) > Chloroform (8) > Trilene (9) > Ether (12) > Methoxyflurane (15).


Q. 11

Blood : Gas partition coefficient is a measure of ‑

 A

Potency of anaesthetic agent

 B

Speed of induction and recovery

 C

Lipid solubility of agent

 D

None

Ans. B

Explanation:Ans. is ‘b’ i.e., Speed of induction and recovery

  • Minimum alveolar concentration (MAC) —> Measure of potency.
  • Blood : Gas partition coefficient Blood solubility of anaesthetic agent and determines the speed of induction & recovery.
  • Oil : Gas partition coefficient -4 Lipid solubility of anaesthetic agent and is related to potency of anaesthetic agent.


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