During oxygen rounds, if an oxygen flow meter reads 0 L/min despite the knob being open, which issue is most likely the cause?

The situation described indicates that the oxygen flow meter reads 0 L/min even though the control knob is open. This suggests that there is a disruption in the flow of oxygen reaching the patient. The most likely cause in this scenario is a clogged down-tube.

A clogged down-tube would prevent oxygen from flowing through to the patient, which would directly result in a reading of 0 L/min on the flow meter. This occurs because the flow meter is measuring the rate of gas flowing through the system, and if the pathway is blocked, no gas can pass through to generate a measurable flow.

Other issues like a large hole in the cannula or a loose humidifier bottle would likely lead to oxygen escaping the delivery system rather than causing a reading of zero on the flow meter. Additionally, a low water level in the humidifier generally does not interfere with flow readings unless it affects pressure in the system, but it would not directly cause a reading of zero in this context. Therefore, a clogged down-tube fits the scenario as the most plausible explanation for the flow meter reading 0 L/min.