Nitrous oxide induction agent

 

Nitrous oxide induction agent

Nitrous oxide induction agent

Nitrous oxide induction agent is a weak anaesthetic agent and not suitable as a sole anaesthetic agent.

Nitrous oxide induction agent is used to hasten inhalational induction of anaesthesia due to its “concentration and second gas effects”. There is a smooth and pleasant induction.

The recovery from anaesthesia is rapid; however, a “diffusion hypoxia” may occur due to large volume of N2O in the lung. This can be prevented by administering oxygen during recovery.

 

At 100% inspired concentration, uptake of anesthetic creates a void that draws sufficient gas down the trachea to replace the gas taken up. Because the replacement gas concentration is 100%, uptake cannot modify the alveolar concentration. This explains why the rise in nitrous oxide shown in Figure 21-2 is more rapid than the rise in desflurane despite their nearly equal blood-gas partition coefficients: the nitrous oxide was given at an inspired concentration of 70%, whereas that of desflurane was 2%.

The concentration effect results from two factors, a concentrating effect and augmentation of inspired ventilation. The first rectangle represents a lung containing 80% (volumes per 100 volumes) nitrous oxide. If half this gas is taken up, the remaining 40 volumes exist in a total of 60 volumes, for a concentration of 67%. That is, uptake of half the nitrous oxide does not halve the concentration because the remaining gases are “concentrated” in a smaller volume. If the void created by the uptake of 40 volumes is filled by drawing an equal volume of gas into the lungs (an augmentation of inspired ventilation), the final concentration equals 72%

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