How a Venturi Mask Works
A Venturi mask delivers precise, controlled oxygen concentrations by using the Venturi principle: high-velocity oxygen flow through a narrow jet entrains a fixed amount of room air through ports in the mask adaptor, creating a predictable oxygen-air mixture regardless of the patient's breathing pattern. 1
The Venturi Principle Mechanism
The core mechanism relies on physics rather than patient variables:
- Oxygen flows at high velocity through a narrow orifice in the color-coded adaptor, creating negative pressure that pulls (entrains) room air through side ports in the cage surrounding the jet 1
- The ratio of entrained air to oxygen is fixed by the size of the jet orifice and the entrainment ports, which determines the final oxygen concentration delivered 1
- The total gas flow produced (oxygen plus entrained air) is substantially higher than the oxygen flow rate alone—for example, a 24% mask at 2 L/min oxygen generates 51 L/min total gas flow 1
Why the Concentration Stays Constant
The key advantage over other oxygen delivery systems:
- Increasing the oxygen flow rate does NOT increase the oxygen concentration—it only increases the total gas flow available to meet the patient's inspiratory demand 2
- The oxygen percentage remains stable even when patients have variable breathing patterns, high respiratory rates, or increased inspiratory flow 1
- This differs fundamentally from nasal cannulae or simple face masks, where the final inspired oxygen concentration varies with the patient's minute ventilation and breathing pattern 1
Color-Coded System and Flow Rates
Each color corresponds to a specific oxygen concentration with minimum required flow rates:
- Blue = 24% (typically 2 L/min oxygen, produces 51 L/min total flow) 1
- White = 28% (typically 4 L/min oxygen, produces 44 L/min total flow) 1
- Additional concentrations available: 31%, 35%, 40%, and 60% 2, 1
Critical Clinical Consideration for High Respiratory Rates
For patients breathing faster than 30 breaths/min, the oxygen flow rate must be increased above the minimum specified on the packaging to ensure the total gas flow can meet the patient's peak inspiratory demand 2. This prevents dilution by room air but does not change the oxygen concentration delivered 2.
Common Pitfall to Avoid
The most frequent error is misunderstanding that turning up the oxygen flow on a Venturi mask does not give the patient "more oxygen" in terms of concentration—it only ensures adequate total flow 2. To increase oxygen concentration, you must switch to a different color adaptor, not just increase the flow rate.
Clinical Accuracy
Research demonstrates that fixed Venturi systems deliver oxygen concentrations within 1-2% of their nominal values in most patients 3, 4, though performance can be affected by dead space reinspiration from the mask (typically 0.2-0.6% CO2) 3 and by tachypnea requiring flow rate adjustment 3.