BVM: 3 tips to avoid over-ventilating your patient
The bag-valve-mask can save your patient’s life; ensure you’re using it properly with these tools
By Jake Mellor
The bag-valve mask (BVM) is arguably one of the simplest tools we carry in our bags as EMS providers. That simplicity, however, undercuts how significant this piece of equipment can be – it is sometimes the only lifeline for a patient, but it can also cause harm if used incorrectly.
One of the biggest mistakes providers make is over-ventilation. In order to cut down on over-ventilation, it helps to remember a few simple ideas that can get lost during a high-stress call:
1. Focus on ventilation rate
Providers both in and out of the hospital can fail to maintain the correct ventilation rate, and more often than not, we ventilate too quickly At the core of the over-ventilation problem is the simple mechanics of the lungs. Air goes in, and air goes out. When the ventilation rate is high, we interrupt that second step. Air goes in and keeps going in until a new exit route must be created.
While conscious, humans have a safeguard against over-inflation called the Hering-Breuer reflex, which is why it is impossible to breathe enough air in to pop your lungs. When patients are unresponsive, however, we cannot rely on this reflex to protect the lungs, which is why a steadily increasing air pressure can lead to a rupture, creating a pneumothorax. Because of the excess air pressure in and now around the lungs, the great vessels that rest between the lungs can be squeezed, resulting in diminished blood flow to and from the heart.
In two-rescuer CPR with asynchronous ventilation and in the case of endotracheal intubation/supraglottic airway device placement, the AHA recommends 10 breaths per minute, or one every six seconds. Know what six seconds feels like as well as you know 100 beats per minute.
2. Apply and monitor capnography
Capnography is an essential piece of equipment when it comes to ventilating patients. Not only can we get a good idea of the ratio of oxygen to CO2 in our patient’s system, but by looking at the waveform, we can see the quality of each breath. When we are breathing for our patient, it is vital that we have hard data to give us feedback on how we’re doing, rather than using a continuous general impression.
Capnometry is also important to monitor because of the impact an improper oxygen/CO2 ratio can have on cerebral perfusion. The fact that a hyperoxic/hypocapnic blood gas level causes cerebral vasoconstriction has been well documented, so maintaining the correct range of ET CO2, 35-45 mmHg, is essential for protecting the brain (among other things) in ventilated patients.
Common waveform patterns can tell us:
- If we are ventilating too quickly or too slowly.
- If we are leaving too much air in the lungs before we give another breath.
- If there is a blockage in the airway.
- If a patient that was in cardiac arrest has reached ROSC.
3. Know how much air to give
A normal adult BVM holds about 1.5 L of air – almost three times the American Heart Association’s recommended 600 mL tidal volume for an adult patient. However, one patient will very greatly from the next. The magic number we’re looking for isn’t actually a number at all; we need enough air to see adequate chest rise and fall with each ventilation, and the corresponding waveform. This is a standard we can easily apply to any patient.
Large and forceful ventilations can result in significant damage to the lungs. In a patient with already damaged alveoli (patients with COPD, ARDS, etc.), a healthy alveolus is the path of least resistance for the incoming air. It accepts its normal share of air, plus the air of the diseased alveoli that cannot take it in. This extra burden stresses the healthy alveoli, putting them at risk of rupture.
The BVM and supplemental oxygen are capable of saving our patient’s life, but only if we can recognize and overcome the common errors in their use. As with much of our equipment, the BVM has the inherent ability to hurt someone as much as help them; it is up to us as providers to ensure we’re helping.
About the author
Jake Mellor is a firefighter/paramedic student intern with the Town of Madison (Wis.) Fire Dept.