What should be the first action of a psychiatrist if a patient on lithium presents with confusion and unsteadiness?

In situations where a patient on lithium presents with confusion and unsteadiness, the first step a psychiatrist should take is to obtain a lithium level. Lithium is a mood stabilizer used in the treatment of bipolar disorder and is known for having a narrow therapeutic range. This means that the differences between effective and toxic levels are small, and patients can easily experience toxicity, especially if there have been changes in their health status, fluid status, or diet.

By checking the lithium level, the psychiatrist can quickly ascertain whether the patient's confusion and unsteadiness are due to lithium toxicity. Symptoms of toxicity can include confusion, tremors, unsteadiness, and in severe cases, it can lead to serious complications. Knowing the lithium level will provide crucial information that can guide further management and treatment decisions.

While other actions such as assessing diet, considering gastrointestinal issues like parasites, or referring the patient to an internist might be relevant later in the evaluation, checking the lithium level is the most direct and urgent step given the immediate risk of lithium toxicity. This assessment will enable timely intervention that can be life-saving, making it the priority in this clinical scenario.