What investigations are recommended to confirm the diagnosis of hypercapnic respiratory failure in a primary care setting?

Recommended investigations to confirm hypercapnic respiratory failure in primary care:

• Measure arterial or arterialised capillary blood gas when the person is awake to assess for ventilatory failure, specifically to detect elevated partial pressure of carbon dioxide (PaCO2) above 7.0 kPa, which indicates hypercapnia.
• Use pulse oximetry to assess oxygen saturation if there are clinical features of severe respiratory compromise, but be cautious as pulse oximeters can sometimes overestimate or underestimate oxygen saturation, especially in people with dark skin.

Note: Do not delay treatment for acute ventilatory failure to carry out further investigations. Respiratory polygraphy and transcutaneous CO2 monitoring are not typically performed in primary care but may be used in specialist settings.

These investigations help confirm hypercapnic respiratory failure and guide urgent management or referral.

Citations: NICE NG115,NICE NG202