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What Every Anesthesiologist Should Know About the Manual Resuscitation Bag

Sivco, Carolyn S., BS*; Cherian, Verghese T., MD, FFARCSI

doi: 10.1213/XAA.0000000000000839
Educational Tool

The bag-valve-mask or the manual resuscitation bag is life-saving equipment. This article explains its construction, functioning, and limitations. This article also attempts to clarify some common misconceptions such as whether a resuscitation bag can be used to preoxygenate or provide continuous positive airway pressure or positive end-expiratory pressure and the highest percentage of oxygen that it can deliver.

From the *Department of Anesthesiology & Perioperative Medicine, Penn State Health College of Medicine

Department of Anesthesiology & Perioperative Medicine, Penn State Health College of Medicine, Hershey, Pennsylvania.

Accepted for publication May 31, 2018.

Funding: None.

The authors declare no conflicts of interest.

Address correspondence to Verghese T. Cherian, MD, FFARCSI, Department of Anesthesiology & Perioperative Medicine, Penn State Health MS Hershey Medical Center, 500 University Dr, Hershey, PA 17033. Address e-mail to vcherian@pennstatehealth.psu.edu.

Figure 1

Figure 1

Figure 2

Figure 2

A Bag-Valve-Mask (BVM) consists of a “self-inflating” bag and a “nonrebreathing” valve (NRV)1 (Figure 1). The NRV houses a unidirectional valve that allows air within the bag to pass to the patient while simultaneously blocking the expiratory port. It then returns to its resting state and allows the exhaled gas from the patient to be vented out through the expiratory port (Figure 2). These valves are lightweight and can be opened by the inspiratory effort of a spontaneously breathing patient.2 The patient port connects to an endotracheal tube connector (15 mm) or a facemask (22 mm). The expiratory port has a unidirectional flap valve that prevents the intake of atmospheric air. The self-inflating bag is filled with air that enters through the unidirectional inlet valve (Figure 2).

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HISTORY AND EVOLUTION

In 1954, Henning Ruben, a Danish anesthesiologist invented the first self-inflating resuscitator. He inserted an oval frame, made from 4 bicycle spokes, into an anesthesia bag that kept the bag expanded and helped it spring back into shape after compression. The tail of the bag was fitted with an air inlet valve and, at the patient end, a Ruben valve, a NRV that he had invented in 1952.3–5 Holger Hesse, a German engineer, improved on Ruben’s design by replacing the bicycle spokes for a foam rubber lining to maintain the shape of the bag. In 1964, the American Medical Association declared the Artificial Manual Breathing Unit or the “AMBU” as “one of the most significant medical advances in anesthesiology of the last 25 years.”4 , 5

The NRV used for resuscitation did not have the expiratory relief valve, while those used to provide anesthesia did. The thought was that if a “dying” patient were to make an inspiratory effort not strong enough to open the inspiratory valve, a NRV without an expiratory valve would allow atmospheric air to be inhaled, while during anesthesia this air dilution would lighten the anesthesia.6 However, with the use of more pliable materials for the construction of resuscitation bags and the valves, the inspiratory effort needed to open the valve is minimal. Most modern BVMs have a 1-way valve at the expiratory port, which would prevent air entrainment. However, neonatal resuscitation bags do not have this valve, and so an infant can get a breath of “fresh air” with minimal effort!

Over the years, a major advancement to the BVM has been the modes of oxygen enrichment of the air mixture within the bag.1 , 7 One mechanism was to deliver oxygen around the air inlet valve. This system was simple and did not increase the pressure within the bag because the oxygen flow did not enter the bag directly. However, the resulting percentage of oxygen within the bag could only be raised to about 40%. Another mechanism was to deliver oxygen directly into the bag. This allowed a higher concentration of oxygen, without making the unit cumbersome. However, there was a likelihood of buildup of pressure within the bag that could force the inspiratory valve open and transmit excessive pressure to the patient’s lungs. The third mechanism delivered oxygen into a reservoir (a bag or an open-ended tube) that surrounds the air inlet valve (Figures 1 and 3). The self-inflating bag is filled with the oxygen-enriched gas from the reservoir. This system provides the maximum oxygen concentration and is used in nearly all currently available resuscitation bags.

Figure 3

Figure 3

Figure 4

Figure 4

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.

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FUNCTION

The BVM is primarily designed to provide positive pressure ventilation in the following situations.

  1. Resuscitation.
  2. Intra- or interhospital transfer of a patient needing ventilator support.
  3. Ventilation before intubation of a patient in respiratory distress.
  4. Emergency ventilation during malfunction of the anesthesia machine.
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CHECKING THE BVM

Figure 5

Figure 5

As for any equipment used in anesthesia, the BVM should be checked before use.

  1. Visual examination of the BVM
    • 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.
  2. 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).
  3. Squeeze the bag completely and close the inlet valve. The bag should stay deflated when the pressure on the bag is released (Figure 5B).
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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

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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.

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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.

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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.

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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.”

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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.

Figure 6

Figure 6

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!

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DISCLOSURES

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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REFERENCES

1. Franco de Godoy AC, Vieira RJ, Vieira Neto RJ. Oxygen outflow delivered by manually operated self-inflating resuscitation bags in patients breathing spontaneously. J Bras Pneumol. 2008; 34: 212–216.
2. Khoury A, Hugonnot S, Cossus J, De Luca A, Desmettre T, Sall FS, Capellier G. From mouth-to-mouth to bag-valve-mask ventilation: evolution and characteristics of actual devices – a review of the literature. Biomed Res Int. 2014. Article ID 762053. Available at: http://dx.doi.org/10.1155/2014/762053. Accessed March 14, 2018.
4. Baskett P, Zorab J, Lim A. Obituary: Henning Ruben MD, FFARCS(I), FFARCS: 1914–2004. Resuscitation. 2005;64:253–256.
5. Ruben H. Rupreht J, van Lieburg MJ, Lee JA, Erdmann W. Anesthesia and resuscitation equipment I happened to be involved with. In: Anaesthesia Essays on Its History. 1998:Berlin, Germany: Springer, 65–68.
6. Dorsch JA, Dorsch SE. Dorsch JA, Dorsch SE. The Breathing system III. Systems employing non-rebreathing valves. In: Understanding Anesthesia Equipment. 1984:2nd ed. Philadelphia, PA: Williams & Wilkins, 197–209.
7. Carden E, Hughes T. Evaluation of manually operated self-inflating resuscitation bags. Anesth Analg. 1975;54:133–138.
8. Mills PJ, Baptiste J, Preston J, Barnas GM. Manual resuscitators and spontaneous ventilation–an evaluation. Crit Care Med. 1991;19:1425–1431.
9. Khoury A, Sall FS, De Luca A, Pugin A, Pili-Floury S, Pazart L, Capellier G. Evaluation of bag-valve-mask ventilation in manikin studies: what are the current limitations? Biomed Res Int. 2016. Article ID 4521767. Available at: http://dx.doi.org/10.1155/2016/4521767. Accessed February 4, 2018.
10. Kwei P, Matzelle S, Wallman D, Ong M, Weightman W. Inadequate preoxygenation during spontaneous ventilation with single patient use self-inflating resuscitation bags. Anaesth Intensive Care. 2006;34:685–686.
11. Nimmagadda U, Salem MR, Joseph NJ, et al. Efficacy of preoxygenation with tidal volume breathing. Comparison of breathing systems. Anesthesiology. 2000;93:693–698.
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