Key investigations

The key investigations for tapentadol poisoning are:

• electrocardiogram (ECG)
• blood gas analysis—partial pressure of arterial carbon dioxide (PaCO₂) is the most reliable measure of hypoventilation and may quantify both the degree of ventilatory impairment and its subsequent response to treatment. The test is required if the patient is not maintaining adequate oxygenation on room air
• chest X-ray if there is hypoxia in the absence of respiratory depression—this should alert the clinician to the possibility of other respiratory pathology (eg aspiration pneumonitis, pulmonary oedema).