A Venturi adapter usually identifies an intended oxygen concentration and a required oxygen-source flow. These are different quantities. Read the markings and instructions on the actual device; colour alone is not a reliable way to identify a prescribed setting.
What the percentage means
FiO₂ is the fraction of oxygen in the gas breathed in. A percentage printed on a Venturi adapter describes the mixture it is designed to provide under specified conditions. The adapter draws room air into an oxygen stream through its air-entrainment openings.
The percentage is not a litres-per-minute instruction and is not the patient's oxygen-saturation target. A saturation reading comes from monitoring the person; the adapter marking describes the delivery equipment. Confusing these numbers can lead to an incorrect setup.
What the flow marking means
The source-flow marking tells the operator how the device is intended to be supplied. Because room air is added, the total gas reaching the mask can differ from the oxygen flow shown at the source. The exact relationship depends on the adapter and its permitted operating conditions.
Do not turn the flow control as a way to invent a new oxygen percentage. The required adapter, setting and any changes must follow the clinical plan and manufacturer instructions. The BTS oxygen guideline discusses controlled oxygen delivery within monitored care, not a universal home adjustment chart.
Check the complete setup
Confirm the adapter identity, mask and tubing with the person providing the equipment. Keep the packaging or model details for reordering. Do not mix loose adapters from different kits or use an unreadable component on the assumption that its colour is familiar.
The oxygen source must be compatible with the adapter's requirements, including its concentration and flow. A connector that fits, or a flow number within a concentrator's maximum, does not by itself establish that the printed mixture will be delivered. Ask the clinical team and supplier to verify the combination.
Keep air-entrainment openings unobstructed as instructed. Bedding, clothing, tape or improvised fittings can interfere with the intended operation. Ask for a demonstration of the correct arrangement and which checks a caregiver should make.
Know when the plan needs review
If a Venturi mask is prescribed for home use, obtain written instructions for the exact adapter, source setting, monitoring and response to problems. Ask what to do if the device is damaged, the markings are missing or the patient cannot tolerate it. Do not choose a replacement setting from an internet colour chart.
Worsening symptoms need clinical assessment even when the equipment appears correctly assembled. For how controlled-oxygen interfaces differ from reservoir masks, read .