Bag-Mask Ventilation

Robert F. Reardon

Brian E. Driver

INTRODUCTION

Bag-mask ventilation (BMV) is a fundamental airway skill. BMV is the initial mode of ventilation for patients with unexpected respiratory failure and the first line of rescue for failed rapid sequence intubation (RSI). Disposable self-inflating resuscitation bags are ubiquitous and often the only available equipment in the initial moments of an unexpected airway emergency. Difficult face mask ventilation is relatively common in critically ill patients, so it is important to learn the best technique for BMV. Although BMV is widely recognized as the most important airway skill, this critical task is often delegated to personnel who are neither the most experienced airway manager nor ultimately responsible for the patient. Responsible clinicians must know how to perform optimal BMV and be able to recognize when it is being performed poorly. BMV devices are designed for hypopneic or apneic patients, not for delivering oxygen to spontaneously breathing patients.

BAG-VALVE-MASK DEVICES

This chapter will focus on the use of disposable bag-valve-mask devices with self-inflating resuscitation bags (Fig. 21.1). The first self-inflating resuscitation bag was invented by Henning Ruben and Holger Hesse in Copenhagen, Denmark, in 1956, and manufactured by Testa Laboratory. They named the device “AMBU” (Air mask bag unit) and later changed the name of the company to Ambu; the name “AMBU” became synonymous with the self-inflating resuscitation bag. Self-inflating resuscitation bags are distinct from free-flow or flow-inflating “anesthesia” bags used in operating rooms, which require high-flow oxygen to inflate. Self-inflating resuscitation bags can be used to deliver room air when no oxygen source is available or can deliver 100% oxygen when attached to an oxygen source. Exhaled gas is simply “exhausted” into the room through a series of one-way valves.

Figure 21.1: Modern adult bag-valve-mask unit.

(From Reardon RF, Carleton SC. Bag-mask ventilation. In: Brown CA III, ed. The Walls Manual of Emergency Airway Management. 6th ed. Wolters Kluwer; 2023:109-123. Figure 12.1.)

Self-inflating bags often perform poorly when used to “assist” spontaneously breathing patients. There have been several studies showing that self-inflating bags often fail to deliver high-concentration oxygen to spontaneously breathing patients.¹^,²^,³^,⁴^,⁵^,⁶^,⁷ Unless there is a perfect mask seal (which is unlikely), spontaneously breathing patients inhale room air around the mask and end up getting a low concentration of oxygen. In the operating room setting, a face mask is commonly used to deliver 100% FIO₂ using an anesthesia machine, which allows delivery of flush-rate oxygen (≥40 L/min). This compensates for a poor mask seal. This does not work well with a self-inflating bag device and a poor mask seal results in delivery of low-concentration oxygen.⁸^,⁹ In addition, several studies show that using a self-inflating bag for spontaneously breathing patients increases the work of breathing, especially with increasing minute ventilation and the addition of PEEP.¹⁰^,¹¹^,¹² When spontaneously breathing patients need high-concentration oxygen, it is best to use bilevel positive airway pressure (BiPAP), continuous positive airway pressure (CPAP), high-flow nasal oxygen (HFNO), or a nonrebreather (NRB) mask with flush-rate oxygen.⁹^,¹²^,¹³^,¹⁴

When reoxygenating is difficult and mask seal does not appear to be the major limitation, PEEP valves may be helpful. They may help open the upper airway in cases of difficult BMV. Although it is common practice to use a PEEP valve with self-inflating bag, there is little evidence to guide the practice. A closed system is needed to maintain PEEP, and it is rare for the mask seal to be 100% leak free. Several studies show that when a disposable PEEP valve is added to a neonatal self-inflating resuscitation bag, the results are inconsistent.¹⁵^,¹⁶^,¹⁷^,¹⁸ With some setups, PEEP valves work properly, but with others, the PEEP pressure is rapidly lost, and desired pressures are not accurately delivered.¹⁵^,¹⁶^,¹⁸ The 2010 International Liaison Committee for Resuscitation (ILCOR)
recommendations for newborn resuscitation suggest that self-inflating bags with PEEP valves “often deliver inconsistent end-expiratory pressures.”¹⁹ There is no published evidence to guide the practice of using PEEP valves with self-inflating bag devices in adults. At the same time, PEEP valves are unlikely to cause harm and should be used when mask ventilating, especially in the context of difficult BMV.

Internal valve configurations are important to understand and vary by manufacturer. Generally, there is a duck-bill inspiratory valve that is forced open by squeezing the bag. This valve can also be opened by patient inhalation, but this may require more inspiratory force than a critically ill patient can generate. In addition, the valve configuration of self-inflating bag devices allows inhalation of room air (rather than oxygen from the bag) in patients with spontaneous respirations.

Disposable self-inflating bag devices are available in adult (1,500 to 2,000 mL), pediatric (450 to 900 mL), and neonatal (220 to 320 mL) sizes. The volume of these bags is much more than the tidal volume required for most patients. The difference between bag volume and desired tidal volume has implications depending on the clinical circumstances. For patients undergoing ventilation with a face mask, the volume delivered during facemask ventilation is often much lower than intended due to air leak from a poor mask seal. Conversely, for those already intubated (where air leak is not possible), the bag volume may be four to five times greater than the patient’s optimal tidal volume.

OPTIMAL FACE MASK VENTILATION TECHNIQUE (

Video 21.1)

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Video 21.1. Mask Ventilation

Many clinicians initially learn mask ventilation techniques in the operating room, where the incidence of difficult mask ventilation is low and one-handed techniques are common and sufficient to meet the patient’s need. This does not always translate well to the critical care setting, where difficult mask ventilation is the rule, rather than the exception, and one-handed techniques often fail. Critical components of optimal facemask ventilation create a perfect mask seal, open the airway, and deliver adequate oxygenation and ventilation. These components include:

optimizing the face mask seal
using a grip that allows for maximal anterior mandibular advancement
head and neck positioning (sniffing position) to open the upper airway
using oral and/or nasal airways
neuromuscular blockade when needed
application of positive end-expiratory pressure (PEEP)
ongoing assessment of BMV adequacy (with capnography)

Optimizing Face Mask Seal

Creating an adequate mask seal without leaks involves using the correct mask size and ensuring continuous contact between the mask and facial structures. The air-filled mask cuff allows it to conform to the contours of the patient’s face. It is intended to make contact on the bridge of the
nose the malar eminences of the maxillae, the maxillary, and mandibular teeth, the anterior body of the mandible, and the groove between the chin and the alveolar ridge of the mandible. Using the appropriate size mask makes it easier to create a good mask seal (Fig. 21.2). This ensures that the mouth and nose will be covered entirely and that the cuff will be supported by bony structures thereby limiting mask leak.

Figure 21.2: Proper face mask placement.

Spreading the cuff of the mask before seating it on the face to improve the mask seal. Using the proper mask size is important, but it is better to use a mask that is too large than one that is too small.

(From Reardon RF, Carleton SC. Bag-mask ventilation. In: Brown CA III, ed. The Walls Manual of Emergency Airway Management. 6th ed. Wolters Kluwer; 2023:109-123. Figure 12.2.)

In general, the seal between the mask and the face is least secure laterally over the cheeks. This is particularly true in edentulous patients, whose unsupported soft tissue of the cheeks may incompletely contact the cuff. In this circumstance, leaving dentures in place during bagging can help ensure adequate contact between the face and cuff during BMV. In addition, excess facial tissue outside of the mask can be compressed into the mask to improve the seal. Shifting the mask such that the lower edge of the cuff rests above or inside the lower lip may improve the seal between the mask and the face in edentulous patients.

The patient’s face should be pulled upward into the mask—rather than the mask pushed onto the face. This has significant implications for the most effective method of holding the mask. As discussed in the following section, a two-handed and two-person technique employing a thenar mask grip should be used whenever possible.

Face Mask Grip for Maximal Mandibular Advancement (Jaw Thrust)

In obtunded or pharmacologically paralyzed patients it is common for the tongue to move posteriorly and occlude the airway (Fig. 21.3). Advancing the mandible forward overcomes this occlusion by pulling the tongue anteriorly and off the posterior pharyngeal wall and is the best way to open the upper airway in an unconscious or paralyzed patient (Fig. 21.4).

Figure 21.3: Occlusion of the upper airway caused by posterior displacement of the tongue in an unconscious or paralyzed patient.

Figure 21.4: Mandibular advancement (or jaw thrust).

A, B: This eliminates upper airway obstruction by moving the tongue out of the posterior oropharynx. It is useful to think of this maneuver as “creating an underbite,” with the bottom incisors placed anterior to the upper incisors. This is the best way to open the upper airway and can be safely performed without cervical spine movement in blunt trauma patients.

The Thenar Grip

The face mask grip that allows maximal anterior mandibular advancement is the thenar grip. The thenar grip is performed by aligning the fingers toward the floor and placing the tips of the middle fingers behind the angle of the mandible (Fig. 21.5). It is referred to as the thenar grip because the body of the mask is held in place by the strong thenar eminence of the hands, which frees up four fingers to perform mandibular advancement. This technique can be performed from the head of the bed or from the patient’s side. This technique is significantly different from the face mask grips that are traditionally taught, and multiple studies have shown that the thenar grip results in larger ventilation volumes and a lower risk of ventilation failure. In a study of anesthetized apneic patients in the operating room setting, the two-handed thenar eminence mask grip was shown to result in substantially

greater ventilation volumes and fewer failed breaths compared to the traditional two-handed CE technique for mask ventilation by novices.²⁰ Comparing the two-handed CE and thenar grips on anesthetized obese apneic patients with more experienced providers showed similar results.²¹^,²²

Figure 21.5: Thenar mask grip.

This grip allows maximal anterior mandibular advancement and should be the “go-to” face mask grip in emergency settings. It can be performed from the head of the bed or from the bedside.

Traditional Single-Hand Mask Grip

This is a suboptimal technique and is generally not appropriate in critical or emergency situations. In the one-handed technique, the operator’s dominant hand is used to hold and compress the bag, whereas the nondominant hand is placed on the mask, with the thumb and the index finger partially encircling the mask connector, as if making an “OK” sign. This grip is also referred to as the “EC grip,” because the third through fifth fingers form the letter “E” and grasp the patient’s mandible, whereas the thumb and index finger form the letter “C” while grasping the mask (Fig. 21.6A). With a one-hand mask grip, it is virtually impossible to perform adequate mandibular advancement. It was developed for anesthesiologists providing inhalational anesthesia to spontaneously breathing patients and does not perform well for providing positive pressure ventilation to patients with hypoventilation or apnea. For this reason, the traditional one-hand face mask grip technique should not be used during emergency airway management unless there is no other choice (no assistant available to squeeze the bag). In this scenario, it may be better to place an extraglottic device (EGD) and attach the patient to a ventilator (see Chapter 22, ‘Extraglottic airway devices’), rather than perform suboptimal BMV.

Figure 21.6: A: Single-handed mask hold with the “EC” grip. B: Two-handed mask hold with the conventional, double “EC” grip. These techniques are suboptimal since maximal mandibular advancement is not achieved.

Traditional Two-Handed Mask Grip

This technique has been shown to be inferior to the thenar technique but is superior to the single-hand grip. Holding the mask with two hands allows the provider to make a better mask seal and perform proper anterior mandibular advancement. However, this technique is not optimal because this is simply a two-handed CE technique (Fig. 21.6B), and with this technique, the operator’s fingers are on the body of the mandible and cannot perform maximal mandibular advancement. Multiple studies have shown that the thenar grip is better and results in higher ventilation volumes and a lower risk of ventilation failure.

Neuromuscular Blockade to Facilitate BMV

BMV is usually the initial rescue technique for critically ill patients with acute respiratory arrest. BMV can be difficult in these patients because the upper airway can have muscle tone or the patient can have dyssynchronous respiratory effort—both of these can significantly interfere with BMV. Using an NMBA relaxes the upper airway musculature and removes the patient’s unhelpful respiratory efforts. Traditional dogma, however, stipulates that an NMBA should not be given to someone who is or could be difficult to ventilate. Using an NMBA, however, improves BMV. In many instances, BMV will be unsuccessful until an NMBA is given.

The decision to give an NMBA to improve the ease of bagging is distinct from the decision to administer NMBAs in spontaneously breathing patients who require emergency airway
management, in whom RSI might be initially contraindicated if rescue mask ventilation is predicted to fail. There are several studies showing that paralysis with a neuromuscular blocker improves BMV.²³^,²⁴^,²⁵^,²⁶^,²⁷^,²⁸ None of the patients became more difficult to BMV after administration of an NMBA. Soltesz et al. conducted an interesting study of patients at high risk for or known to have difficult BMV. They found that median tidal volumes increased from 350 to 600 mL after complete neuromuscular blockade. Modern difficult airway algorithms recommend that a neuromuscular blocker be administered when difficult BMV is encountered.²⁹^,³⁰ In addition, unless related to an immediately reversible overdose (i.e., heroin), patients compromised to the extent of needing BMV are inevitably going to undergo either placement of an EGD or a tracheal tube and would receive an NMBA in the course of completing those procedures.

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