When a closed reservoir bag is used, a connector with 2 one-way valves is interposed between them (Figures 3 and 4). The valve that opens outward acts as a vent (positive pressure relief valve) if the reservoir bag is overinflated by excessive oxygen flow, and the valve that opens inward acts as an inlet to draw air in (negative pressure relief valve) if the oxygen supply fails to inflate the reservoir bag.
The BVM is primarily designed to provide positive pressure ventilation in the following situations.
- Intra- or interhospital transfer of a patient needing ventilator support.
- Ventilation before intubation of a patient in respiratory distress.
- Emergency ventilation during malfunction of the anesthesia machine.
CHECKING THE BVM
As for any equipment used in anesthesia, the BVM should be checked before use.
- Visual examination of the BVM
The bag, when squeezed with the patient port occluded, should feel tight and not empty completely (Figure 5A). If it does empty, it either suggests a leak or a malfunctioning valve. Note: The BVM meant for neonates has a 40 mm Hg pressure relief valve, which can be overridden by the locking mechanism (Figure 4).
Squeeze the bag completely and close the inlet valve. The bag should stay deflated when the pressure on the bag is released (Figure 5B).
- a. Ensure that there is no damage or deformity of the bag
- b. Visually confirm that the valve is correctly seated and opens when the bag is squeezed.
SOME COMMON QUESTIONS AND MISCONCEPTIONS ABOUT BVM
Can 100% Oxygen Be Given Through a BVM?
Although the BVM was intended for resuscitation with air, most modern resuscitation bags have an attachment for oxygen enrichment. The percentage of oxygen within the bag will depend on the oxygen flow, the volume of the reservoir, and the minute ventilation (a lower respiratory rate would give more time for the reservoir to be filled with oxygen). An oxygen flow of above 15 L/min is needed to attain close to 100% oxygen.8
Can the BVM Be Used to Preoxygenate?
Spontaneously breathing patients can get high inspired oxygen from the resuscitation bag only if they generate sufficient negative pressure to open the inspiratory valve. A patient in respiratory distress may not allow the facemask to be applied firmly around the mouth and nose. It may also be difficult to get an air-tight seal in patients with long facial hair or edentulous gums.
The type of inspiratory valve also affects the concentration of oxygen delivered to a spontaneously breathing patient. In the absence of the expiratory unidirectional valve, atmospheric air can be entrained and dilute the oxygen-enriched gas from the bag.9 , 10 It has been shown that resuscitation bags with a disk valve or a “duck-bill” valve with expiratory unidirectional valve can deliver >90% oxygen.8–11
An oxygen source with a reservoir bag should be connected to the inlet of the BVM. If the mask cannot be held tightly over the face, then the bag must be repeatedly squeezed to open the inspiratory valve and permit oxygen to flow from the bag on to the patient. This should preferably be synchronized to the inspiratory phase of a spontaneously breathing patient. It may be prudent to leave the nasal cannula with oxygen flowing while preoxygenating. In a patient who is breathing inadequately, positive pressure ventilation with the mask held firmly over the face would be needed.
How to Ventilate an Intubated Patient Having Inspiratory Effort?
If the bag is squeezed as the patient tries to exhale, it would create a significant expiratory pressure. This dyssynchrony could be uncomfortable and cause hemodynamic impairment but, more seriously, can lead to barotrauma. Therefore, while ventilating a patient with an invasive airway, it would be prudent to synchronize the squeezing of the bag to the inspiratory effort of the patient. This synchrony would also ease the work of breathing for a patient inhaling through an endotracheal tube.
Can a BVM Be Used to Provide Continuous Positive Airway Pressure?
When the bag is squeezed, the higher pressure in the bag opens the valve to force the air into the patient, but as the pressure equalizes, the valve shuts even if the bag is kept squeezed. Therefore, unlike when using the breathing circuit attached to a continuous flow anesthesia machine, where squeezing the reservoir bag against a tight-fitting mask can provide continuous positive airway pressure, BVM cannot be used to provide continuous positive airway pressure.
Can a BVM Be Used to Provide Positive End-Expiratory Pressure?
An adjustable, spring-loaded disk valve attached at the expiratory port can provide positive end-expiratory pressure (PEEP) up to 20 cm of H2O (Figure 1). However, this is only effective with a tight-fitting facemask or a cuffed endotracheal tube. Unlike in the circle system, where the bag feels tight when the adjustable pressure limiting valve is tightened to provide PEEP, the self-inflating bag will not feel any different whether the PEEP is applied or not. This is because, in a BVM, the PEEP valve is in the expiratory section and the bag is in the inspiratory limb, while in a circle system, both the bag and the PEEP valve are in 1 “circle.”
How Does One Measure the End-Tidal CO2 While Ventilating With a BVM?
The simplest way to measure end-tidal CO2 is to attach a “side-stream” capnography connector between the patient port and the facemask, the laryngeal masks, or the endotracheal tube (Figure 6). This sample line may also be used to measure the fraction of inspired oxygen.
Some BVMs have a port opening into the NRV (Figure 2). This is to measure the peak inspiratory pressure or the inflating pressure, and not to measure end-tidal CO2 or to administer oxygen. A spring-loaded manometer is provided in most “neonatal” BVMs (Figure 4). This port should be capped while ventilating to avoid a leak.
Please familiarize yourself with this life-saving equipment!
Name: Carolyn S. Sivco, BS.
Contribution: This author helped review the literature and write the manuscript.
Name: Verghese T. Cherian, MD, FFARCSI.
Contribution: This author helped conceive and plan the article, review the literature, create the figures, and write the manuscript.
This manuscript was handled by: BobbieJean Sweitzer, MD, FACP.
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© 2018 International Anesthesia Research Society
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