Question:
Rapid induction of anaesthesia occurs with which of the following inhalational anaesthetics?
Rapid induction of anaesthesia occurs with which of the following inhalational anaesthetics?
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Speed of induction tracks a low blood:gas coefficient, but the drug must also be non irritating to the airway; desflurane is fastest on paper but too pungent for mask induction.
Updated On: Jul 8, 2026
- Isoflurane
- Halothane
- Desflurane
- Sevoflurane
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Verified By Collegedunia
The Correct Option is D
Solution and Explanation
Step 1: Know what controls the speed of induction.
How fast a patient goes to sleep with an inhaled agent depends mainly on the blood:gas partition coefficient. A low coefficient means the drug does not dissolve much in blood, so the alveolar and brain levels rise fast and induction is quick.
Step 2: Compare the coefficients of the four drugs.
Halothane has a coefficient of about 2.4, the highest of the group, so it works slowly. Isoflurane is about 1.4, faster than halothane but still slow. Sevoflurane is about 0.65 to 0.69. Desflurane is the lowest, about 0.42, which on paper makes it the fastest of all.
Step 3: Check why desflurane is not used for induction.
Desflurane is pungent and irritates the airway. Breathing it in through a mask causes coughing, breath holding, and even laryngospasm, so it cannot be used to put a patient to sleep. It is only added after the airway is already secured, usually for keeping the patient asleep during surgery.
Step 4: Match sevoflurane to real mask induction.
Sevoflurane has a low blood:gas coefficient and a pleasant, non irritating smell. This combination lets it be breathed in smoothly through a mask without coughing, so the brain level climbs fast and the patient goes to sleep quickly. This is why it is the standard drug for inhalational induction, especially in children.
Step 5: Rule out isoflurane and halothane.
Both of these have higher blood:gas coefficients than sevoflurane, so they dissolve more in blood before the brain level rises. Induction with either is noticeably slower and less smooth.
Final Answer:
Among the options that can actually be used for smooth inhalational induction, sevoflurane is the fastest.
\[ \boxed{\text{Sevoflurane}} \]
How fast a patient goes to sleep with an inhaled agent depends mainly on the blood:gas partition coefficient. A low coefficient means the drug does not dissolve much in blood, so the alveolar and brain levels rise fast and induction is quick.
Step 2: Compare the coefficients of the four drugs.
Halothane has a coefficient of about 2.4, the highest of the group, so it works slowly. Isoflurane is about 1.4, faster than halothane but still slow. Sevoflurane is about 0.65 to 0.69. Desflurane is the lowest, about 0.42, which on paper makes it the fastest of all.
Step 3: Check why desflurane is not used for induction.
Desflurane is pungent and irritates the airway. Breathing it in through a mask causes coughing, breath holding, and even laryngospasm, so it cannot be used to put a patient to sleep. It is only added after the airway is already secured, usually for keeping the patient asleep during surgery.
Step 4: Match sevoflurane to real mask induction.
Sevoflurane has a low blood:gas coefficient and a pleasant, non irritating smell. This combination lets it be breathed in smoothly through a mask without coughing, so the brain level climbs fast and the patient goes to sleep quickly. This is why it is the standard drug for inhalational induction, especially in children.
Step 5: Rule out isoflurane and halothane.
Both of these have higher blood:gas coefficients than sevoflurane, so they dissolve more in blood before the brain level rises. Induction with either is noticeably slower and less smooth.
Final Answer:
Among the options that can actually be used for smooth inhalational induction, sevoflurane is the fastest.
\[ \boxed{\text{Sevoflurane}} \]
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