Increase the liter flow when a nonrebreathing mask reservoir collapses to ensure adequate oxygen delivery.

A patient is receiving O2 through a nonrebreathing mask set at 8 L/min. What should you do if the mask's reservoir bag collapses completely before the end of each inspiration?

• A. Decrease the liter flow
• B. Increase the liter flow
• C. Change to a nasal cannula
• D. Replace the mask

Answer: (B)

When a patient is using a nonrebreathing mask and the reservoir bag collapses completely before the end of each inspiration, it indicates that the flow of oxygen is insufficient to meet the patient's inspiratory needs. A nonrebreathing mask is designed to provide a higher concentration of oxygen, and the reservoir bag serves as a source of oxygen that the patient can draw upon during inhalation. Increasing the liter flow will ensure that the reservoir bag remains inflated, allowing the patient to inhale a consistent and adequate supply of oxygen. This is crucial in situations where a patient may have significantly increased oxygen demands due to various factors such as respiratory distress, hypoxemia, or increased work of breathing. Decreasing the liter flow would worsen the situation by further collapsing the reservoir bag and leaving the patient at risk for inadequate oxygenation. Switching to a nasal cannula would not provide the same concentration of oxygen needed for the patient, and replacing the mask may not effectively address the issue of oxygen flow. Thus, increasing the liter flow is the appropriate response to maintain proper oxygen delivery.

Oxygen therapy often feels like a little science experiment in a busy room. When things click, patients breathe easier and the air inside the room seems to brighten a bit. One common tool for delivering high-concentration oxygen is the nonrebreathing mask. It’s designed to keep a reservoir of oxygen ready for each inhalation, so the patient can pull in a lot of oxygen quickly, especially in distress. But what happens when that reservoir bag collapses completely before the end of each breath? That’s a red flag—and a moment to act.

Let me explain what’s going on

A nonrebreathing mask has a mask, a one-way valve, and a small bag—the reservoir—that fills with oxygen. During exhalation, the bag is meant to refill so it’s ready for the next inhale. If the bag deflates or collapses during inspiration, it means the flow of oxygen from the source isn’t meeting the patient’s inspiratory demand. The patient can’t pull in enough oxygen because the bag isn’t supplying a sufficient pool of oxygen to draw from. In other words, the mask is not delivering the concentration it’s supposed to.

This is especially important in cases of respiratory distress, hypoxemia, or when a patient is working hard to breathe. The whole point of the NRB is to deliver a high FiO2 (fraction of inspired oxygen) quickly and reliably. If the bag collapses, you’re losing that therapeutic edge. So the natural question follows: what should you do to fix it?

Increase the liter flow—the straightforward move

When the reservoir bag collapses during inspiration, the most appropriate response is to increase the liter flow. Why? Because raising the flow rate helps ensure the bag stays inflated and maintains a steady reservoir of oxygen for each inhale. In practical terms, you’re boosting the oxygen that’s available to the patient on every breath, reducing the work of breathing and helping to maintain adequate oxygenation.

Think of it like a person drawing water from a well. If the pump isn’t delivering enough water, the bucket you dip for each scoop runs dry. Turn up the pump and you fill the bucket again. With oxygen therapy, this “pump” is the flow from the oxygen source through the regulator and tubing into the mask. If the bag collapses, the pump isn’t keeping up with the demand.

A note on typical flow ranges

Nonrebreathing masks are designed to deliver relatively high concentrations of oxygen, often requiring about 10 to 15 L/min (and sometimes more) to keep the reservoir bag inflated. If you’re starting at 8 L/min and the bag collapses, that’s a clear indication to increase the flow. Of course, you’ll tailor the exact setting to the patient’s needs, monitoring their oxygen saturation, heart rate, and overall work of breathing as you go.

Why not just switch to a nasal cannula?

A nasal cannula is great for comfortable, low-flow oxygen delivery, but it simply can’t meet the oxygen concentration demands of a nonrebreathing scenario. When the goal is high FiO2, the NRB is the right tool. If you’re seeing a collapsed bag, the problem isn’t a mismatch of technique; it’s an undersupply. Switching to a nasal cannula would deprive the patient of the oxygen concentration they’re depending on in an urgent moment. The right move is to boost the flow, reassess, and watch the bag re-inflate.

What to check first, in a calm, effective sequence

• Verify the setup. Is the mask properly fitted? A loose mask or a torn reservoir bag can allow air to leak and defeat the purpose of increasing the flow.

• Inspect the bag. If the reservoir bag is damaged or pinched, it won’t inflate properly, no matter how much flow you push through. Replace it if needed.

• Look for leaks in the tubing or at connection points. A leak is a sneaky way to “lose” oxygen before it reaches the patient.

• Confirm the oxygen source and regulator are delivering what you set. Sometimes the flowmeter or regulator has a misread or a kinked, blocked line.

• Check that the bag inflates at the start of inspiration and remains inflated throughout the breath. If it deflates again, reassess the rate and the seal.

• Don’t forget the patient’s needs. If a patient has increased oxygen demand due to fever, agitation, or an escalating respiratory drive, the rate may need continuous adjustment.

If increasing flow still doesn’t keep the bag inflated

There are a few reasons why you might not see the bag stay filled even after nudging the flow higher:

• The patient’s inspiratory effort is very high. You may be dealing with acute respiratory distress that needs more aggressive support.

• The mask fit remains imperfect, or there are leaks that you haven’t fully identified yet.

• The oxygen source is unreliable or the tubing has a hidden kink.

• Consider other devices selectively. If you’re unable to sustain adequate oxygen delivery with an NRB, a high-flow system or a Venturi mask that can precisely set FiO2, or in some settings a noninvasive positive-pressure device, may be more appropriate. The key is to tailor the choice to the patient’s oxygen needs and clinical status.

Real-world tips that help in the moment

• Keep the airflow steady. Don’t chase a number with rapid, erratic adjustments. Small, incremental increases are safer and more effective.

• Watch the patient, not just the numbers. Oxygen saturation is important, but signs like reduced work of breathing, improved color, and stabilized heart rate are also valuable.

• Maintain the gear. A clean, intact mask with fresh straps is easier to seal. If the mask is constantly slipping or tearing, replace it.

• Document what you changed. If you’re in a busy setting, a quick note about the new flow rate and the patient’s response helps the next clinician pick up where you left off.

A little context for broader understanding

High-concentration oxygen delivery isn’t a one-size-fits-all play. Some patients tolerate high FiO2 well, while others may become uncomfortable or experience dryness. It’s not just about cranking up the number; it’s about ensuring a stable, adequate oxygen reservoir that the patient can draw from with each breath. The nonrebreathing mask is a tool for urgent, sometimes dramatic improvement in oxygenation, but it requires careful attention to flow, fit, and the patient’s evolving needs.

Common pitfalls to avoid

• Assuming more flow is always better. Too much flow can cause nasal dryness or discomfort if the mask isn’t well-tolerated. Start with a measured increase and reassess.

• Forgetting to reassess after a change. The patient’s status can change quickly, especially in acute care. Recheck vital signs and oxygenation after you adjust.

• Ignoring leaks. A leak undermines even a higher flow. If you can’t seal the mask, switch to a different size or style.

• Overlooking alternative devices. If the NRB isn’t delivering as intended, a targeted FiO2 device or a high-flow system might be a better fit.

Putting it all together

Here’s the gist: when a nonrebreathing mask’s reservoir bag collapses during inspiration, the patient isn’t getting enough oxygen from the current flow. The simplest, most effective response is to increase the liter flow so the bag stays inflated and the patient can take in consistent, adequate oxygen with each breath. Check for leaks, ensure a proper fit, verify the equipment’s accuracy, and keep in mind that some patients may require different delivery methods as their condition evolves.

If you’ve ever watched a tense moment in a hospital room, you know oxygen delivery is more than just numbers on a screen. It’s about reading the scene: the patient’s effort, the equipment’s behavior, and the small adjustments that keep a life on track. With a clear plan—confirm the setup, increase the flow, monitor closely—you can navigate that moment with confidence and provide real relief where it’s most needed.

A final note from the front lines

Oxygen therapy sits at the intersection of art and science. The science is straightforward: supply enough oxygen to meet the patient’s demand. The art is in how you implement that plan—how you communicate with the patient and the team, how you balance comfort with effectiveness, and how you stay alert to changes that demand a new approach. The nonrebreathing mask is a powerful ally in moments of crisis, and knowing when to increase flow—and when to pivot to a different device—can make all the difference in those critical breaths.

If this topic sparked questions for you, you’re not alone. The true value lies in understanding the mechanism, recognizing the signals, and applying a calm, methodical response. After all, every breath is a small victory—and the way we support it matters.