A nurse is caring for a client following application of a cast. Which of the following actions should the nurse take first?

Rationale:

A. SpO₂: Although 88% is low for the general population, it is often an acceptable baseline for clients with COPD. Their oxygen saturation targets are typically between 88–92% to avoid suppressing respiratory drive, so this value may not require immediate provider notification.

B. pH: A pH of 7.22 indicates respiratory acidosis, which is a serious and potentially life-threatening complication of COPD. This level of acidosis shows that the client’s ventilation is inadequate, and immediate intervention is needed. This is the most critical finding that requires provider notification.

C. Respiratory rate: A rate of 22 breaths/min is slightly elevated but not critical. It may be compensatory and expected in a COPD patient who is hypoxic or retaining CO₂. By itself, it doesn't warrant urgent notification unless it worsens.

D. Temperature: A temperature of 37.2°C (99°F) is within the normal range and does not indicate infection or acute illness. It is not a finding that necessitates notifying the provider at this point.

Rationale for Correct Choices

• Serotonin syndrome: This potentially life-threatening condition results from an excess of serotonin, typically due to drug interactions involving serotonergic agents. Combining citalopram, a selective serotonin reuptake inhibitor (SSRI), with St. John's Wort, a natural serotonergic herb, significantly increases the risk. Symptoms can include agitation, increased heart rate, tremor, hyperreflexia, and elevated temperature.
• Interaction between citalopram and St. John's Wort: St. John's Wort induces serotonin activity and may inhibit serotonin reuptake similarly to SSRIs. When taken together, the serotonergic effects of both substances can accumulate, placing the client at risk for serotonin toxicity. The client’s increased heart rate and lack of symptom improvement despite therapy raise concern for early serotonin imbalance.

Rationale for Incorrect Choices

• Anticholinergic toxicity: Citalopram does not have significant anticholinergic effects, and neither does St. John's Wort. Symptoms like dry mouth, blurred vision, urinary retention, or confusion are not present here, and this diagnosis is unrelated to the medication interaction described.
• Hyperkalemia: Neither citalopram nor St. John's Wort typically causes potassium elevation. The client has no renal impairment or medication (e.g., ACE inhibitors or potassium-sparing diuretics) that would support this risk.
• Severe neutropenia: Citalopram and St. John’s Wort are not associated with bone marrow suppression or neutropenia. There is no evidence of infection, fever, or blood dyscrasia.
• Metabolic syndrome: Although the client's mother has diabetes (a risk factor), the client has a normal BMI (22.1), is experiencing weight loss, not gain, and has no evidence of hypertension, hyperlipidemia, or insulin resistance, all of which are required criteria for metabolic syndrome.
• Adverse effect of citalopram: While citalopram has side effects (e.g., GI upset, sexual dysfunction), the client’s most significant risk stems from adding St. John’s Wort, not the SSRI alone.
• An adverse effect of famotidine: Famotidine (an H2 blocker) can cause occasional CNS effects in older adults but does not interact dangerously with citalopram nor lead to serotonin syndrome.
• Family history of diabetes mellitus: This does increase long-term risk for type 2 diabetes but does not explain the acute medication-related concern, which is serotonin syndrome from the citalopram–St. John’s Wort combination.
• Interaction between citalopram and famotidine: There is no significant pharmacologic interaction between these two medications that would increase serotonin or cause the client's symptoms.