An oxygen flow meter is a medical device used to regulate and accurately measure the volume of oxygen gas delivered from a supply source to a patient. This instrument ensures the prescribed amount of oxygen reaches the user in clinical or home care settings. The flow meter provides visual confirmation of the flow rate, which is important for the safety and effectiveness of oxygen therapy.
Understanding the Flow Meter’s Components
The most common type of oxygen flow meter, often called a Thorpe tube, consists of distinct parts that control and display the gas flow. At the center is a transparent, tapered tube, which is wider at the top than the bottom. Inside this tube is a small indicator, typically a spherical float or ball, which is lifted by the force of the flowing oxygen.
Adjacent to the tube is a numbered gauge, known as the scale, calibrated to display the flow rate in Liters Per Minute (LPM). The flow rate is controlled by an attached needle valve, operated by a control knob or dial at the bottom of the meter. This knob manually adjusts the size of the opening, regulating the amount of oxygen permitted to enter the tapered tube. The meter also features an inlet connection to the oxygen source and an outlet connection for the patient’s tubing.
Interpreting the Flow Rate
To correctly read the oxygen flow meter, the observer must first ensure they are aligned at eye level with the float. Because the float is spherical, the measurement is taken from the exact center of the ball, not the top or the bottom edge. Aligning the center of the ball with the corresponding line on the adjacent scale indicates the current flow rate in Liters Per Minute.
The scale features major numbered hash marks and smaller lines in between, which represent increments of the flow rate. For example, on a meter scaled up to 15 LPM, the markings between 1 and 2 may represent 0.5 LPM increments. The flow meter must be maintained in an upright, vertical position to ensure gravity acts consistently on the float for an accurate reading.
If the float remains stationary at the bottom of the tube, it indicates that the flow is either completely turned off or no oxygen is reaching the meter. This absence of movement signals that the system is not actively delivering oxygen to the patient. While most meters use this float system, some units, like certain digital models, display the flow rate as a number. The float-type remains widely used due to its mechanical reliability and clear visual feedback.
Safe Adjustment and Troubleshooting
When adjusting the flow meter, only set the rate to the specific Liters Per Minute prescribed by a healthcare provider. Adjusting the flow beyond the prescribed setting can be harmful and may not provide the necessary therapeutic effect. To increase the flow, the control knob is typically turned gently in a counter-clockwise direction.
Conversely, turning the control knob clockwise will decrease the flow rate by closing the needle valve. When adjusting, turn the knob slowly and wait for the float to stabilize before confirming the setting against the scale’s center line. Once the correct rate is confirmed, the knob should not be moved again until a different rate is medically required.
If the meter is set to a flow rate but the float does not move, or the flow seems low, several simple issues should be checked. First, ensure the tubing is securely connected to the outlet and is not kinked or twisted, which can block the gas flow. If using a humidifier bottle, check that it is bubbling, which confirms that oxygen is passing through the system. A non-responsive meter may also indicate that the main oxygen source is empty or the supply valve is closed, requiring a switch to a backup supply.