Inhalational Agents

Question 1

What component of anaesthesia do inhalation pal agents supply

Answer 1

The hypnosis component

Question 2

Which inhalation all agents are in use today? What are their characteristics

Answer 2

Nitrous oxide, halothane, enflurane, isoflurane, sevoflurane and desflurane. Potent halogenated agents that are volatile liquids

Question 3

How do you administer the inhalational agents?

Answer 3

N2O delivery is controlled by the flow meter on the anaesthetic machine. Volatile agents are administered via individual, specially calibrated vaporizers

Question 4

Which agent is the only gas at room temperature and therefore not called a volatile agent?

Answer 4

Nitrous oxide

Question 5

What are the uses of inhalational agents?

Answer 5

1) maintaining anaesthesia
2) halothane and sevflurane for inhalational or gas induction (often done in children or someone with a compromised airway)
3) N2O may be used to provide intra operative and labor analgesia
4) N2O may be used to speed up inhalational induction and its use during the maintenance phase reduces the concentration of potent volatile agent required

Question 6

What are the features of an inhalational agent?

Answer 6

1. Cheap
2. Stable: easy storage, transport, use with soda lime, non flammable/ explosive
3. No metabolism: fewer toxic effects
4. Potent: allows one to use high inspired oxygen concentrations
5. No long term effects: no toxicity to personnel, patients or the environment
6. Non irritant odour: pleasant smell and easy inhalational induction
7. No respiratory depression
8. No cardiovascular depression
9. Hypnotic and analgesic
10. Readily reversible, neuroprotective and non- excitatory

Question 7

What does the composition of the gas mixture that the patient inspires depend on?
( factors affecting inspired concentration of anaesthetic agent)

Answer 7

1) volume of the breathing circuit
2) the fresh gas flow rate
3) any absorption of the inhalational agent by the breathing circuit

Question 8

What are the three major determinants of the alveolar concentration of anaesthetic agents?

Answer 8

1) inspired concentration: increasing the inspired concentration increases the alveolar concentration, the rate of its rise and speed of induction
2) uptake: the greater the uptake of the agent into the patients pulmonary circulation, the slower the rate of induction.
3) alveolar ventilation: induction is accelerated by hyperventilation

Question 9

What may cause the partial pressure of the agent to be different in systemic arterial blood and pulmonary capillaries?

Answer 9

Shunting of the pulmonary blood past non ventilated alveoli diluted the non shunted volume of blood. Shunts may be intra pulmonary or intra cardiac

Question 10

How are inhalational agents eliminated?

Answer 10

Through the alveolus

They are also metabolized by the cytochrome P450 of enzymes to a varying degree