Venturi Mask (Air-Entrainment Mask)
4
1. Definition
A Venturi mask is a high-flow oxygen delivery system that provides a fixed and controlled fraction of inspired oxygen (FiO₂) by entraining a predetermined amount of room air using the Venturi principle.Usually color coded.
It ensures:
- Precise oxygen concentration
- High total gas flow
- Minimal influence of patient respiratory pattern
2. Principle of Venturi Mask
The functioning is based on two physical laws:
(A) Venturi Effect
When gas passes through a narrow constriction, velocity increases and lateral pressure decreases.
(B) Bernoulli Principle
The decrease in pressure around the jet draws surrounding air into the system through entrainment ports.
Result
High-velocity oxygen jet
↓
Negative pressure generated
↓
Room air entrained through side ports
↓
Mixing occurs
↓
Fixed oxygen concentration delivered
3. Air Entrainment Ratio
The ratio of entrained air to oxygen determines the FiO₂ delivered.
This produces a predictable oxygen concentration.
4. Color-Coded Venturi Valves(FiO₂ -24–60%)
|
Color |
Oxygen Flow |
Air:O₂ Ratio |
Approx FiO₂ |
|
Blue |
2 L/min |
24:1 |
24% |
|
White |
4 L/min |
10:1 |
28% |
|
Orange |
6 L/min |
5:1 |
31% |
|
Yellow |
8 L/min |
3:1 |
35% |
|
Red |
10 L/min |
1.7:1 |
40% |
|
Green |
12–15 L/min |
1:1 |
50–60% |
Total gas flow may reach 40–60 L/min, which exceeds patient inspiratory demand.
5. Why Venturi Mask Provides Fixed FiO₂
Unlike simple masks or nasal cannula:
- High total gas flow > patient inspiratory flow
Delivered FiO2 =Set FiO2
This is why it is called a fixed performance device.
6. Venturi Mask vs Other Oxygen Devices
|
Feature |
Nasal Cannula |
Simple Mask |
Venturi Mask |
|
Device type |
Low flow |
Low flow |
High flow |
|
FiO₂ |
Variable |
Variable |
Fixed |
|
Precision |
Low |
Moderate |
Very high |
|
Max FiO₂ |
~44% |
60% |
~60% |
7. Clinical Indications in ICU
1. COPD with Hypercapnia
Most important indication.
Reason:
Excess oxygen may worsen:
- CO₂ retention
- V/Q mismatch
- Haldane effect
Venturi mask allows controlled oxygen (24–28%).
2. Acute Exacerbation of COPD
Oxygen Targets (Guideline Recommended)
|
Patient |
Target SpO₂ |
|
COPD / hypercapnia risk |
88–92% |
|
Most ICU patients |
92–96% |
3. Type II Respiratory Failure
Used to avoid oxygen-induced hypercapnia.(Rise in PaCO₂ ≥5–10 mmHg after oxygen therapy)
Mechanism
|
Mechanism |
|
V/Q mismatch(High oxygen reverses Hypoxic Pulmonary Vasoconstricton) |
|
Haldane effect |
|
Hypoventilation (hypoxic drive) |
4. Post-extubation Oxygen Therapy
When controlled FiO₂ is required.
5. Moderate Hypoxemia
Used before escalating to:
- HFNC
- NIV
- Mechanical ventilation
8. Common Errors in ICU Use
Blocking Air Entrainment Ports
Example:
- Blanket covering ports
Result:
- FiO₂ becomes unpredictably high
Wrong Oxygen Flow
Each valve requires specific flow rate.
If lower flow used:
- Delivered FiO₂ changes.
Loose Mask Fit
Leads to:
- Air leak
- Lower FiO₂.
9. Troubleshooting
|
Problem |
Cause |
Solution |
|
Low SpO₂ |
Disease progression |
Increase FiO₂ valve |
|
High CO₂ |
Excess oxygen |
Reduce FiO₂ |
|
Poor oxygen delivery |
Blocked ports |
Clear ports |
|
Patient discomfort |
Mask tightness |
Adjust fit |