Free-flow oxygen can be delivered using four main devices: a flow-inflating bag with a mask, a T-piece resuscitator, oxygen tubing held near the face (blow-by), and, with some important caveats, a self-inflating bag with a reservoir attached. Each device delivers oxygen differently, and the concentration that actually reaches the patient varies widely depending on technique and distance.
Flow-Inflating Bag
A flow-inflating bag (also called an anesthesia bag) is one of the most reliable devices for delivering free-flow oxygen. Because it requires a compressed gas source to inflate, oxygen flows continuously through the system. To give free-flow oxygen, you hold the mask loosely over the infant’s face without creating a tight seal. The oxygen source should deliver at least 5 liters per minute, and holding it close to the face maximizes the concentration the patient breathes in.
The flow-inflating bag’s main advantage is that it provides a consistent, high-concentration oxygen stream as long as the gas source is connected. It also gives the provider tactile feedback: if the bag stays inflated, gas is flowing properly. The tradeoff is that it requires a compressed oxygen source and some practice to use correctly.
T-Piece Resuscitator
A T-piece resuscitator connects to a gas source and delivers a controlled flow of blended oxygen through a patient circuit. For free-flow delivery, the mask is held near the face without a tight seal, allowing the infant to breathe the oxygen passively. T-piece devices are commonly used in delivery rooms because they allow precise control over both oxygen concentration and pressure. When you simply want to provide free-flow oxygen without positive pressure, you leave the pressure cap open or hold the mask slightly away from the face.
Blow-By Oxygen Tubing
Blow-by is the simplest method: oxygen tubing or a mask is held near the patient’s nose and mouth, directing a stream of oxygen toward the airway. The technique is straightforward, but the oxygen concentration that reaches the patient drops off dramatically with distance.
A laboratory study using a pediatric non-rebreather mask at 10 liters per minute measured this effect precisely. When the mask was placed directly at the face (0 cm distance), the delivered oxygen concentration averaged about 87%. At just 5 cm away, it plummeted to roughly 29%, and at 10 cm it dropped further to about 24%, barely above room air. Only the 0 cm distance maintained concentrations above 40% throughout the study. This means that blow-by oxygen works well only when the device is held very close to the face. Cupping your hand around the tubing near the infant’s face can help funnel the oxygen and reduce dilution with room air.
Other devices that can serve as the delivery end of a blow-by setup include an aerosol mask, face tent, or tracheostomy collar, all connected to an oxygen source via corrugated tubing.
Self-Inflating Bag With a Reservoir
Standard self-inflating bags were traditionally considered unable to deliver free-flow oxygen because of their internal valve design. When the bag is not being squeezed, only a small fraction of the incoming gas passes through. Research found that outflow from an unsqueezed self-inflating bag was only 18 to 24% of the gas flowing in, because an internal valve between the bag and reservoir opens only at very low pressures.
However, studies have shown that a self-inflating bag can deliver free-flow oxygen when a reservoir is attached, 100% oxygen flows into the bag at a minimum of 5 liters per minute, and the mask is held close to (but not tightly sealed against) the face. Under these conditions, the device provides high oxygen concentrations to a spontaneously breathing infant. Without the reservoir, the self-inflating bag does not reliably deliver meaningful free-flow oxygen, so this detail matters.
What Does Not Work for Free-Flow Oxygen
A self-inflating bag without a reservoir does not deliver adequate free-flow oxygen. The valve mechanism inside the bag blocks most of the gas from reaching the patient unless the bag is actively squeezed. If you only have a self-inflating bag available and no reservoir, you cannot count on it as a free-flow device.
Blow-by tubing held more than a few centimeters from the face also fails to deliver clinically useful oxygen concentrations. As the data above show, even 5 cm of distance cuts the delivered concentration by more than two-thirds.
Practical Considerations
Regardless of which device you use, the oxygen source should flow at a minimum of 5 liters per minute for neonatal applications. Higher flow rates (up to 10 liters per minute) are used in pediatric settings, particularly during transport.
Free-flow oxygen does not generate positive pressure in the airway. That means it supports a patient who is already breathing on their own but cannot substitute for ventilation in a patient who is not breathing adequately. It also does not provide the kind of continuous airway pressure that keeps the lungs open between breaths.
Temperature is another factor. Unheated, unhumidified oxygen can cool an infant and contribute to cold stress. In clinical settings, oxygen is often warmed and humidified before delivery, especially for premature or very small babies. Prolonged exposure to high oxygen concentrations also carries risks: lung injury in any infant, and in very premature babies, potential damage to the brain and eyes. The goal is to use the lowest concentration needed to maintain adequate oxygen levels, guided by pulse oximetry.