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August 1, 2013
Manual ventilation in EMS: A primer
Bag valve ventilation, whether through a mask or connected to an airway device, is not an easily mastered skill. Despite the assertions of EMT textbooks and the American Heart Association (AHA) Guidelines 2010 that bag valve mask (BVM) ventilation is a two-person task1, many EMS educational programs test BVM ventilation as a single rescuer skill, negating the difficulty of performing it properly on a live patient. Positive pressure ventilation is not without potential complications. You may be surprised how much harm can result from bag valve ventilation when improper techniques are applied.
There are people who cannot be ventilated, just as there are people who can’t be intubated, no matter how skilled the provider. No one knows for certain what portion of the population has this most troublesome trait, but it is very likely about 1 percent2. Anesthesiologists appreciate this and exercise a great deal of cautious preplanning to avoid catastrophe.
ALS providers don't always have the time for this level of preparation. The unfortunate complication, should you encounter a patient you cannot ventilate, could result in a significant hypoxic brain injury, or death.
Recognizing the need
Beginning with the basics, the first step is recognizing a need to ventilate a patient. Certain ominous signs require prompt action: altered level of consciousness (decreased or, alternatively - combative), inability to maintain respiratory effort, cyanosis or bradycardia3. Bradycardia is a very late sign, which can suggest imminent cardiopulmonary arrest.
Providers occasionally fail to consider respiratory insufficiency when a patient on cardiac monitoring develops bradycardia; don’t get caught with tunnel vision.
Two important BLS tools for monitoring and assessing the adequacy of ventilation are respiratory rate and pulse oximetry. A progressively increasing respiratory rate suggests deterioration. Patients with near normal oxygen saturations who progressively desaturate are decompensating.
The role of capnography cannot be overemphasized in monitoring ventilation. Whether or not an advanced airway is in place and whether or not the patient is spontaneously breathing, capnography provides accurate reading of respiratory rate and important information about ventilation.
During bag valve ventilation, capnography can help a provider fine tune tidal volume and respiratory rate18. While previously considered an ALS tool, capnography is now included in the EMS Educational Standards for EMTs.
One important caveat to keep in mind when using capnography is the influence of cardiac output on end tidal values. Increases and decreases in cardiac output will be reflected in similar changes to exhaled carbon dioxide values.
The use of airway adjuncts
No study to date has demonstrated significant advantages of an oral or nasal airway to facilitate BVM ventilation1. Hence, you won’t find BLS airways recommended in the AHA Guidelines since 2005.
Lastly, proponents of transport ventilators argue that mechanical ventilators are better for patients than manual ventilation using a bag valve device. Such benefits to patients are unsupported by prehospital studies6-8.
However, use of a mechanical or automatic ventilator has been shown to free up a provider to perform other tasks. For hospitalized patients, mechanical ventilators have been show in studies to provide more reliable ventilation during intra-facility transports (i.e., trips to CAT scan, the cath lab, OR, etc) when compared to manual ventilation8.
Mechanics of bag valve mask ventilation
To properly provide BVM ventilation, you need a BVM with a non-rebreathing valve and an oxygen reservoir (allowing a spontaneously breathing patient to draw oxygen from the bag and reservoir) and a clear mask (allowing you to visualize any regurgitation) that permits a tight seal over both the mouth and nose. BVMs should not have operational “pop-off” or pressure relief valves as adequate ventilation in some patients may require very high pressures.
Each breath should be delivered over 1 second with the minimum volume needed to produce chest rise. Initial ventilation rate for an adult should be 10 to 12 breaths per minute1. Optimally two rescuers should perform this task, one creating an effective mask seal and head position, while the other focuses on correct tidal volume and rate.
Spontaneously breathing patients are more challenging to ventilate and require greater eye-hand coordination coupled with intense reassurance and coaching for the patient. The best way to learn and refine your ability to track respirations and ventilate a spontaneously breathing patient is to practice on a coworker. It is not a simple skill to learn.
The primary goal in ventilation is to maintain oxygenation9. This is best evidenced by a pulse oximeter oxygen saturation of 90% or greater. If BVM ventilation is not achieving this result, consider mask size, adequate mask seal, positioning (ideal is aligning the ear canal with the sternal notch), use of a jaw thrust, and insertion of an oral pharyngeal or nasal airway (OPA or NPA).
Suction the airway if necessary, minimizing interruptions in CPR and using correct technique. If the saturation cannot be maintained minimally in the high 80’s, this is an airway emergency and requires prompt placement of a supraglottic airway and, if unsuccessful, an immediate surgical airway10-11.
Adults require an average 600 mL tidal volume to maintain ventilation and oxygenation. A typical 1 liter bag valve should be squeezed about two thirds, and a 2 liter bag about one third its volume to produce chest rise1.
During CPR without an advanced airway in place, compressions should be interrupted during ventilations to reduce airway pressures.
The message for any level provider in dealing with an airway emergency is, “get help!” Depending on your resources, help may be at the closest ED. An interesting case report12 from Survival Flight in Michigan used a S.A.L.T. airway (EcoLab, Columbus, MS) to improve oxygen saturations from the mid 60’s to mid 90’s in a 74 year-old trauma patient the crew was unable to intubate in the field.
From a physiologic perspective, bag valve ventilation is completely opposite normal ventilation. Spontaneously breathing patients use negative pressure created by chest muscles, including the diaphragm, to draw air into the lungs.
While positive pressure ventilation forces air into the airways, it is not without negative consequences. The most significant and immediate consequence is decreased cardiac output13. The pressure in the chest cavity from bag valve ventilation decreases venous blood return to the right side of the heart, reducing blood flow to the lungs and potentially from the left ventricle. This effect is worsened in hypovolemia. This impairment of cardiac output is the primary reason for emphasis on limiting ventilatory rates during CPR.
A second and equally significant complication of bag valve ventilation is barotrauma, or injury caused by the pressure being applied to the airways, lungs, and other organs. Higher than necessary tidal volumes (the air squeezed out of the bag with each ventilation), respiratory rates fast enough to not allow complete exhalation between breaths and very high pressures used to deliver air into the airways all have potential to damage structures in the body14.
In the prehospital environment, barotrauma resulting from delivery of higher volumes than needed to achieve chest rise commonly lead to pneumothoraces (especially in infants and adults with lung disease), and gastric distention. Gastric distention can interfere with ventilation by inhibiting downward displacement of the diaphragm and is also associated with aspiration of stomach contents from regurgitation.
Worse yet, case reports and one large review of the literature suggest that perforation of the stomach during bag valve mask ventilation may be much more common than previously believed15-17. These complications can be limited by close attention to positioning the airway (which will reduce the pressure needed to deliver breaths), gently squeezing the bag, and immediately releasing when chest rise is visible.
Bag valve ventilation is a common skill, yet one that takes considerable practice to master. When providing bag valve ventilation, the goal is to sustain oxygen levels in the body as evidenced by a saturation of at least 90%.
The consequences of bag valve ventilation are numerous, ranging from brain injury or death from inability to ventilate a patient to decreased cardiac output from properly delivered breaths. Complications resulting from bag valve ventilation induced barotrauma including ruptured stomach and pneumothorax may be underreported and can be limited by practiced and skillful delivery of ventilations.