Any cause of respiratory failure may cause respiratory muscle fatigue. A high respiratory rate, poor tidal volumes, use of accessory muscles, an inability to complete sentences and somnolence are all signs of exhaustion. Paradoxical or see-saw breathing is a sign of impending respiratory arrest.
It is often difficult to predict from a single assessment how well, or for how long, a patient will tolerate this state of affairs. An ongoing deterioration and failure to respond to therapy are features more likely to prompt intervention. Eventually, a reduction in respiratory rate may precede respiratory arrest.
It often becomes apparent on the initial assessment, that the patient is too exhausted and there is no time to wait for a response to treatment. In this situation, prompt action (intubation and ventilation) can be life saving.