The 'fixed performance' venturi: effect of downstream pressure on outflow and FIO2

Area of Science:

• Medical Devices
• Respiratory Therapy
• Biomedical Engineering

Background:

• Fixed performance venturi devices are intended to deliver a specific oxygen concentration at an outflow exceeding adult peak resting inspiratory flow rates (approx. 30 L/min).
• Previous literature noted venturi device sensitivity to downstream resistance but lacked detailed investigation.

Purpose of the Study:

• To examine the impact of increased downstream pressure on the outflow and delivered oxygen concentration of standard venturi devices.
• To determine if venturi devices maintain predetermined oxygen concentrations under varying downstream resistance.

Main Methods:

• Five standard venturi devices (24-60% O(2)) were tested.
• Outflow and oxygen concentration were measured under increasing downstream pressure conditions.

Main Results:

• Venturi device outflow was highly sensitive to small increases in downstream pressure.
• A minimal increase in pressure (2-3 mmH(2)O) halved the outflow of 24-40% O(2) venturi devices and increased oxygen concentration.
• The 60% O(2) venturi device delivered a maximum of 30 L/min at zero downstream pressure, with flow decreasing further under pressure.
• For all tested devices, increased downstream pressure led to decreased outflow and altered oxygen concentration, often falling below typical adult peak tidal flow.

Conclusions:

• Standard venturi devices are not consistently fixed performance under conditions of increased downstream resistance.
• Clinical use of venturi devices requires careful consideration of downstream resistance to ensure adequate oxygen delivery.
• Further research is needed to develop venturi systems with stable performance across varying physiological conditions.