How long does it take for a collapsed lung to cause respiratory failure?

Lung collapse: If you are otherwise young and healthy, respiratory failure will not occur. In general, it depends on the degree of collapse, duration, and whether you have other underlying lung disease in the non collapse lung.

Can be rapid: You are asking how long until respiratory failure if a lung is collapsed. It can be rapid. When doctors refer to a collapsed lung in a patient it may be from atelectasis. If that involves an entire lung then most patients will require positive pressure ventilation. Your doctors will see collapsed lung on x-ray. They will use bronchodilators and ask the respiratory therapist to help.

Tension rapid: If the collapsed lung (pneumothorax) creates enough pressure, it can compress the right side of the heart. This decreases the blood return to the heart. Without adequate blood return, your heart does not have enough blood to pump out to your body. This is called tension pneumothorax. If the pressure is not released, this is rapidly fatal.