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March 2, 2015
How to improve your bag-valve mask technique
Before EMS providers can deliver effective ventilation, they must control the airway. It is the single most important prehospital intervention. Although this sounds like a simple step, it is not always easy to do. Many experts attribute inadequate control of the airway as a major cause of preventable death in the prehospital environment.
Manual airway maneuvers
The most basic category of all techniques used to insure a patent airway is manual airway maneuvers. These techniques form the foundation for all airway control maneuvers both in the field and hospital.
Following unconsciousness in most patients, the muscles of the throat relax. In a supine position, this loss of muscle tone allows a portion of the tongue to shift from the oral cavity into the oropharynx. Tilting the head back and lifting the chin displaces the jaw toward the front of the body and pulls the tongue out of the patient’s airway. When properly performed, the head tilt/chin lift maneuver has no complications and is the preferred method of manual airway control in unconscious patients.
However, proper execution of this maneuver requires manipulation of the head, which moves the patient’s neck. If a neck injury is present, the head tilt/chin lift maneuver could worsen the injury. For this reason, EMTs and paramedics suspecting the presence of spinal injury should use an alternative manual airway maneuver, such as the jaw thrust.
Although manual airway maneuvers are effective at establishing a patent airway, rescuers often find them difficult to maintain for prolonged periods. Many find it useful to add the assistance of some type of mechanical airway maneuver, or airway adjunct to maintain airway patency. These include oropharyngeal and nasopharyngeal airways.
Bag-valve mask ventilation
One critical skill all EMS providers must master is effective bag-valve mask ventilation (BVM). Unfortunately, BVM ventilation by out-of-hospital (OOH) care providers often results in inadequate ventilation and may be potentially dangerous for both intubated and non-intubated patients.
Manikin studies demonstrate that EMTs using a standard BVM deliver mean tidal volumes significantly lower than those recommended by the American Heart Association). In the same study, EMTs achieved recommended ventilation volumes in only 27 percent of the ventilation attempts.
One problem associated with ineffective ventilation is the inability of EMS personnel to provide effective mask seal on the BVM[3,4] (The American Heart Association (AHA) recommends use of EC clamp as a technique for sealing the face mask to the patient’s face during assisted ventilation. However, attempting to provide an effective BVM seal using a single-hand EC clamp often tilts the mask to the left and allows air leakage from under the right side of the air-cushion.
Some argue that replacing the EC clamp with a rotated mask hold may provide a more effective seal. This hold combined with a “chin lift grip” and a newly designed ergonomic face mask may help improve mask seal when performed by a single rescuer.
Two-person BVM technique
Side by side comparisons demonstrate that a BVM technique that utilizes two rescuers instead of one provides consistently more effective ventilation than a single person technique[9,10,11,12]. In this two-person technique, one rescuer can deliver the recommended tidal volume by squeezing the bag while the second rescuer can use both hands to provide an effective mask seal on the patient’s face. For the rescuer holding the seal, replacing the two-handed EC clamp with the thenar eminence grip improves ventilation efficacy.
The thenar eminence grip is achieved by using muscles at the base of the thumb to place downward pressure on the mask while using the other four fingers of each hand to pull the jaw into the mask. However, given the personnel restrictions that often accompany EMS responses, two person BVM techniques are not always feasible.
Avoiding gastric insufflation
During BVM-assisted ventilation, rescuers must use caution to avoid generating high airway pressures. In general, inspiratory pressures greater than 20 cm H2O in the adult patient increases the risk of forcing air through the esophagus and into the stomach, a condition known as gastric insufflation. Gastric insufflation increases the risk of regurgitation and subsequent aspiration of stomach contents.
Although a number of factors contribute to high airway pressures, EMS personnel who ventilate patients slowly, deliver smaller tidal volumes, and reduce the inspiratory period decrease the risk of gastric insufflation. In addition, ventilation using a bag-valve device equipped with a pressure-responsive, flow-limiting valve reduces mean airway pressure and the likelihood of gastric insufflation compared to using a standard BVM. An inspiratory pressure of 15 cm H2O provides the reasonable balance between effective ventilation and the risk of gastric insufflation.
Use of pressure manometers and filters
One simple tool to monitor inspiratory pressure is a manometer, which EMS personnel can place within the breathing circuit between the BVM and the patient. Pressure manometers allow the EMS provider to see exactly how much pressure is being created in the patient’s airway with each ventilation attempt. EMTs and paramedics can then adjust ventilation techniques to avoid unwanted pressures. The use of an in-line manometer during BVM ventilation of a simulated infant has been shown to decrease peak inspiratory pressure.
Some BVM devices have an option to install an inline bacterial/viral filter to reduce pathogen introduction into the patient’s airway and contamination of the healthcare provider by the patient’s exhaled breath. The filters are small but do introduce an increase in dead space volume by about 25 to 50 mL, not thought to be clinically relevant. The devices have a filtering efficiency greater than 99.99 percent and are effective against a number of pathogens including viruses that cause hepatitis, influenza, and SARS[18,19].
It is important to note however, that filtering efficiency is highly dependent upon how the device is tested. Viruses and bacteria are smaller than water droplets. Any testing method that utilizes pathogens nebulized in an aqueous medium will likely appear more efficient than they really are. This is because the filter is actually trapping water droplets that contain the pathogens.
It is possible a testing method that utilized dry air as the transport medium for the pathogen would yield different results. Pathogen transmission is still possible even when utilizing these filters. EMTs and paramedics must take additional protective measures such as the use of personal protective equipment that include taking droplet precautions.
In some cases, paramedics may need to begin inhaled drug therapy while simultaneously providing assisted ventilation, especially following endotracheal intubation. Unfortunately, the efficiency of drug delivery via nebulizer during mechanical ventilation varies from 0 to 42 percent. Case reports in an adult and two infants suffering from bronchoconstriction refractory to nebulized beta-agonists report almost immediate improvement in aeration and lung compliance following the endotracheal instillation of undiluted bronchodilators.
For acute exacerbations of asthma requiring endotracheal intubation, the AHA recommends endotracheal administration of undiluted beta-agonists as soon as tube placement is confirmed rather than continued use of nebulizers.
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