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By Captain Steve LeCroy, MA, CRT, EMTP
Human beings by nature are creatures of routine. This is especially true for those that practice medicine. Even the most open-minded practitioners seem to stick with routines and habits that are not supported by current evidence. It’s extremely challenging to unfreeze old behaviors and introduce new ones especially when it comes to basic skills such as manual ventilation.
The first manual resuscitator with the current design, commonly known as the Artificial Manual Breathing Unit or Ambu, was introduced to the market in 1956. The patent for the original device does not mention the size of the bag, so where does the size come from?
Most likely the volume was a holdover from the second world war where the U.S. military was supplied with a hand-operated bellows for manual ventilation with an approximate volume of 1600 milliliters I was unable to find any explanation as to why the device had such a high-volume capacity. In the late 1970s, when I graduated from respiratory therapy school, the standard for setting mechanical ventilation tidal volume was 10 to 12 milliliters per kilogram.
As an example, for a 100-kilogram patient, the tidal volume would be 1000 to 1200 milliliters which come close to the stroke volume of a 1500 – 1600 milliliter bag. How does the standard of the 1970s compare to the standards of today? Standards today for tidal volume outlined by the American Heart Association is 5 – 7 milliliter per kilogram. With the current standard, why are clinicians still using a device that was designed over 50 years ago using a standard (not scientifically supported) from World War II?
Bag-valve mask ventilation (BVM) is a basic skill but not an easy skill. When using a basic BVM the user gets no feedback on the volume other than watching the chest rise. The question with chest rise is do you stop squeezing when the chest starts to rise? Or, do you squeeze to get full chest expansion? During the excitement of an emergency, I believe it’s the latter. Hyperventilation can not only be achieved with too many breaths per minute but by too large of a breath that exceeds the patient’s natural lung capacity.
What are the negative effects when a patient is ventilated with too much volume? The following list outlines what may happen when the lungs are overdistended with too much volume.
- Barotrauma or injury to lung tissue caused by too much pressure.
- An increase in intrathoracic pressure can reduce pre-load to the heart reducing blood pressure.
- Volutrauma or injury through alveolar overdistension causing alveolar rupture leading to cell death.
- The additional volume also increases the possibility of air entering the stomach encouraging the patient to vomit and possibly aspirate.
The question now is: Which one of these side effects are you ok with? I hope the answer is none.
In a study by Kane, it was reported that lung-protective ventilation reduces morbidity and mortality and that EMS professionals over-ventilated using an adult size BVM (1500 – 1600 milliliters). So, just what is lung-protective ventilation or LPV? LPV is often used with mechanical ventilation where the peak airway pressure is kept below 30 centimeters H2O and tidal volumes are based on predicted lean body weight (not actual body weight) or using the patient’s height and sex. This type of ventilation has been shown to reduce ventilation associated lung injury. Research has shown that the same type of injuries can occur with manual ventilation, even with short transport times.
Lung protective ventilation strategies can include:
- Limiting the tidal volume by using a small adult bag (1000 milliliter)
- Limiting peak inspiratory pressure (PIP) by using a manometer
- Providing adequate Positive End Expiratory Pressure (PEEP) to keep the lungs open and prevent alveolar collapse
- Using a timing device to maintain the appropriate rate
A recent study by Spaite through the University of Arizona indicated that hyperventilation also can be devastating to patients with Traumatic Brain Injury (TBI). Part of the recommended guideline for the study was to prevent hyperventilation by using age-appropriate ventilation rates and ventilation adjuncts. What I believe is missing from the study is a mention of tidal volume. An increase in tidal volume can have the same effect on minute volume as an increase in ventilation rate. After reading the paper I contacted the author of the study, Daniel Spaite, Virginia Piper Distinguished Chair of Emergency Medicine Director and EMS Research Collaboration. I asked him what he thought about using smaller BVMs to reduce hyperventilation in addition to controlling the ventilation rate for TBI patients. Here’s his response:
“Yes, we recommend a flow-controlled bag with ventilation rate timer (the timing light 10 BPM for adults and 20 BPM for kids). This helps decrease volume. Some are getting rid of the adult bag altogether and going with the peds bag only. No need to have more than 1000 milliliter volumes. Yes...lung-protective volumes should be used from the very beginning of care...even in the field.”
So, unfreeze old habits. The evidence is clear, and the cost is neutral. Evaluate what you are using and implement the current standard for better outcomes.
References
Kane, E., Siegler, J., & Hafez, Z. (2019). Assessing tidal volumes delivered by an adult and pediatric BVMs when using chest rise as an end-point. Retrieved from www.itrauma.org/wp-content/uploads/2018/11/2-Comparing-Tidal-Volumes-Delivered-by-Adult-and-Pediatric-BVMs-When-EMS-Use-Chest-Rise-as-an-End-Point-for-Ventilation-Erin-Kane.pdf.
Kreiselman J. A new resuscitation apparatus. Anesthesiology 1943; 4:608-611.
US Patent No. 3,009,459. Apparatus for artificial respiration. Filed 12th September 1957. H Ruben, applicant
About the Author
Steven LeCroy is the Director of EMS Sales for Mercury Medical. He has a Master’s degree in disaster management and has been a paramedic for over 35 years and a Respiratory Therapist for over 40 years. He retired as a Captain from St. Petersburg Fire & Rescue after 30 years.