Which action should be avoided when managing a casualty with gastrointestinal disturbance?

When managing a casualty with gastrointestinal disturbance, keeping them "nil by mouth" is the most appropriate action to avoid. This is due to the potential for complications that could arise if the individual is allowed to consume anything orally when experiencing such disturbances. For example, if the gastrointestinal tract is unable to process food or liquid due to nausea, vomiting, or other issues, ingesting anything can exacerbate these symptoms and lead to additional complications like choking or aspiration.

In many cases of gastrointestinal disturbances, healthcare protocols recommend withholding food and drink to prevent further irritation or complications, especially if medical intervention may be needed. By avoiding this action, the first aider ensures the casualty is kept in a safe condition until appropriate medical assistance can be provided.

The other options, such as encouraging the casualty to drink water, administering oxygen, and encouraging slow breathing, are generally acceptable practices depending on the severity and specifics of the case, and they may help manage symptoms or stabilize the individual's condition. Keeping nil by mouth is a precaution that should be considered to ensure safety in a potentially complicated situation like gastrointestinal disturbance.