Mask ventilation may save lives, particularly during difficult intubation. Numerous papers have discussed various methods for improving mask ventilation. This article summarizes the known literature and theories on challenging mask ventilation. According to the etiology, we classify problematic mask ventilation into three major categories: insufficient mask seal, increased airway resistance, and reduced respiratory compliance. The solutions for overcoming difficulties that have been published are provided and sorted by etiology.
Introduction
Maintaining enough oxygenation is critical for patient safety in an apneic patient. Failure to oxygenate, not intubate, results in brain damage and cardiopulmonary collapse. 1 Even when intubation is ineffective, mask ventilation is the most important approach for preserving oxygenation and may avert disastrous consequences. Developing abilities in optimizing mask ventilation is critical for caregivers who discover or render patients apneic, including anesthesia physicians, emergency medicine clinicians, emergency medical service employees, and respiratory therapists.
Despite the critical nature of mask ventilation and the association between difficult mask ventilation and difficult intubation,1 the mechanism of failed mask ventilation has received less attention than the cause of failed intubation.
The bulk of the literature on approaches for improving mask ventilation is out of date, and there are fewer equipment available for mask ventilation than for intubation. While difficult intubation may be less demanding than in the past owing to the availability of video laryngoscopes, the frequency of serious airway management issues has not diminished. Based on the current research, this study establishes a conceptual framework for the etiologies of problematic mask ventilation. It then discusses relevant treatment techniques for each cause. We concentrate on clinicians’ easily accessible expertise and resources. While it is unlikely that all difficult mask ventilation will be eliminated, we hope that this working framework will help clinicians take a more simplified approach to difficult mask ventilation situations, expand their repertoire of techniques for optimizing mask ventilation, and help reduce the impact of difficult mask ventilation and its associated complications.
Epidemiology and Definition
There is currently no universally recognized objective definition of problematic mask ventilation, and application of existing criteria is confounded by interoperator variability. These difficulties hinder patient history communication, epidemiologic data reporting, and the conduct of objective investigations on difficult mask breathing. The majority of published definitions are binary in nature (ie, difficult or not difficult) and include multiple facets of insufficient oxygenation and/or ventilation. Similarly to intubation, patients often fall between between simple and difficult mask ventilation. As a result, a graded definition, such as the one we frequently use for intubation, is likely to be more therapeutically relevant. Although none of these categorization systems have acquired general recognition, some have been suggested. Han et al3 developed a classification and description scale in 2004 that suggests grades 0–4: grade 0 no attempt at mask ventilation, grade 1 mask ventilation, grade 2 mask ventilation with adjuvant, grade 3 difficult mask ventilation (inadequate, unstable, or requiring two practitioners), and grade 4 unable to ventilate.
According to reported epidemiologic data, problematic mask breathing occurs in 1.4 percent (range, 0.9–7.8 percent) of patients having general anesthesia and 4–11% of emergency department patients.
4,5 The true incidence of difficult mask breathing during field resuscitation is unclear but is almost certainly greater than that observed in the hospital due to the inferior settings. High body mass index, edentulous and/or bearded patients, and a high Mallampati class are all predictive markers. With estimates ranging from 0.07–0.16%, impossible mask ventilation is less predictable. 2 With over 21 million general anesthetic operations conducted each year in the United States, this corresponds to around 15,000–34,000 impossible mask ventilations every year. It is fair to assume that as the obese and severely obese populations rise, these numbers will increase, and problematic mask ventilation will remain a challenge for health-care practitioners.
Framework Conceptualization for Difficult Mask Ventilation
Difficult mask ventilation might be a result of patient- or non-patient-specific causes. While they are critical, variables unrelated to the patient, such as operator inexperience or defective equipment, will not be the focus of this assessment.
Mask ventilation is a technique that successfully transfers gas from a positive-pressure source to the patient’s lungs through a mask-patient interface, such as a face mask. Gas flow is inversely proportional to resistance and directly proportional to the drop in pressure along that channel.
As a result, difficult mask ventilation must be caused by one or more of the following: (1) a low-resistance alternative path caused by an inadequate seal, (2) an increase in air-flow resistance along the path to the lungs, or (3) a decrease in lung and/or chest wall compliance resulting in increased distal pressure. It is critical to understand the etiology of difficult mask breathing in order to make the accurate diagnosis and treat the patient appropriately in an emergency scenario.
On the basis of this concept, we present a method to challenging mask ventilation below. Tables 1 and 2 summarize the underlying reasons and suggested strategies addressed below.
At the Mask-Patient Interface, an insufficient seal exists.
A gas will flow preferentially along less-resistance routes.
A leaky seal at the mask-patient interface allows for a reduced resistance escape during positive-pressure breaths.
Similarly, higher airway resistance increases the likelihood that alternate pathways (e.g., the mask-patient interface or the esophagus) may receive flow. Improper mask size, shape/design, or placement, facial hair, edentulism, micrognathia, maxillomandibular abnormalities, and foreign items all lead to a poor seal at the mask-patient interface (eg, nasogastric tubes). 6
Independent of the reason of the insufficient seal, increasing fresh gas flows may assist in compensating for the leak (when employing valveless systems [Mapleson] or anesthetic ventilators).
Increased flow does not compensate for a leak in the more usual bag-valve-mask system unless a PEEP valve is used. Even when correction is feasible, it is restricted by the fact that the majority of operating room ventilators give a maximum of 12 L/min. This may be enhanced by using the oxygen flush function included on all ventilators. 6 Although they are not routinely accessible in the operating room, using a ventilator intended for noninvasive ventilation or ICU ventilators with leak compensation may significantly enhance ventilation. Numerous these ventilators are capable of compensating for leakage of up to 60 liters per minute. 7,8
Face masks come in a variety of forms, and some may be molded to suit the patient’s face optimally. The usually advised face mask location fits superiorly over the bridge of the nose, laterally over the nasolabial folds, and inferiorly over the mental crease. To minimize dead space and ocular constriction, the smallest acceptable mask is advised. To minimize leakage into the eyes, the top of a well installed mask should be slightly inferior to the bridge of the nose. Numerous techniques for adequately sealing a face mask have been documented, including the widely used C-E clamp, in which the thumb and index finger make a C shape over the mask and the third, fourth, and fifth fingers (the E) draw the mandible into the mask. The double C-E method involves forming a C shape with the thumb and index finger on either side of the mask, while lifting the mandible toward the mask with the third, fourth, and fifth fingers of both hands. Another two-handed method, the V-E, employs a thumb and thenar eminence on either side of the mask, while the second through fifth fingers pull the jaw upward (Fig. 1). Another one-handed approach, referred to as the V (or N) technique, involves rotating the hand such that the caregiver’s wrist is at the mental protuberance. The thumb is put on one side of the mask, the second through fourth fingers on the opposing side, and the fifth finger is used to raise the jaw at the mental protuberance.
In comparison to one-handed ventilation, two-handed techniques generate a superior seal9,10 and yield larger tidal volumes11,12, but need an extra provider or equipment to administer the positive-pressure breaths.
13 Although it is often misused, programming a mechanical ventilator to give positive-pressure breaths while masking may be beneficial. It frees up both hands for mask application and gives extra diagnostic information (for example, pressure tracing from a single breath might distinguish a circuit leak from a resistance or compliance issue). By limiting peak pressures to 20 cm H2O, the possibility of unintentional gastric insufflation is reduced. While recent data shows that 15 cm H2O may result in reduced stomach insufflation, it may not be sufficient to achieve successful mask ventilation when challenging mask ventilation is encountered. 14,15
Inadequate seals are often caused by facial hair and edentulism. While shaving facial hair is possible, it is often unwelcome by patients and may not be viable in emergency cases. Alternatively, big occlusive dressings may be put over facial hair to provide a sufficient area for sealing. Clear adhesive tape (such as Tegaderm, 3M, St Paul, Minnesota), plastic wrap, gel, gauze, and even defibrillator pads have been used to accomplish this. 16,17 Additionally, it has been reported to place the inferior aspect of the mask within the lower lip near the alveolar ridge. 16
Edentulism results in bone and buccinator muscle atrophy. This structural breakdown results in a space between the cheeks and the mask. 18,19 During mask ventilation, using two hands to pull the patient’s cheeks in opposition to the mask often helps decrease leak. Restoring structure may be accomplished by leaving dentures in place18 or by packing the patient’s cheeks with gauze20, albeit the latter carries the risk of foreign object blockage or aspiration.
When an insufficient face-mask seal remains after optimization efforts, other mask-patient interfaces may be beneficial. If the patient’s mouth is blocked with a hand or dressing, a nasal mask or a toddler-sized mask with the bottom border lying over the patient’s top lip may offer an acceptable seal. 21 As discussed in the next section, the nasal mask may also be used to alleviate airway blockage.
Although the double nasopharyngeal tube22 that delivers positive pressure directly to the pharyngeal cavity is no longer commercially available, successful use of an ordinary nasopharyngeal airway connected to an endotracheal tube adapter while compressing the contralateral nostril has been described.
23 Supraglottic airways give an additional patient interface, which will be addressed in further detail later.
Increased Resistance of the Airway
Increased resistance is most often caused by supraglottic problems, although infraglottic contributions to airflow resistance (which are generally more difficult to overcome) are covered at the conclusion of this section. 6 The upper airway is mostly formed of soft tissue and is bounded proximally by the nose’s bones and cartilage and distally by the inflexible trachea. The transitional region of unsupported soft tissue or pharyngeal tube is particularly prone to collapse, particularly when the upper-airway dilator muscles, such as the genioglossus, are depressed owing to loss of consciousness or pharmacologic paralysis. This is exacerbated by tonsillar and adenoidal hypertrophy, redundant soft tissue (e.g., morbid obesity or obstructive sleep apnea), a large tongue or epiglottis, airway edema (e.g., following repeated intubation attempts, trauma, or angioedema), oropharyngeal tumors, external compression (e.g., large neck masses or hematoma), or laryn To mask-ventilate in the presence of an upper-airway blockage, the produced positive pressure must exceed the compressed pharynx’s critical closure pressure,24 or the blocked airway may be bypassed with the installation of an airway adjuvant or supraglottic airway device.
Positioning movements may be used to alleviate blockage of the upper airway. By increasing longitudinal tension in the pharyngeal soft tissue, the sniffing position (lower cervical flexion and upper cervical extension) and chin lift stent open the pharyngeal soft tissue.25-27 Jaw thrust displaces the mandible,25-27 increasing the retrolingual and retropalatal spaces by pulling the tongue anteriorly, although this benefit may be diminished in the obese patient. 26 In the reverse Trendelenburg position, gravity pushes down on the diaphragm and trachea, extending and lowering the collapsibility of the pharyngeal tube. 28 CPAP maintains the outward pressure gradient in the pharyngeal cavity, hence increasing airway patency. 29 Additionally, CPAP enhances lung capacity, which improves oxygenation and puts longitudinal strain on the pharyngeal tube. 30 Nasal mask ventilation generates pressure that displaces the tongue and palate anteriorly, and it may be more successful than combined oronasal ventilation, which may displace the tongue and palate posteriorly and exacerbate blockage (Fig. 2). It allows for greater tidal volumes while maintaining lower peak inspiratory airway pressures31,32, but has not been systematically examined in individuals with documented difficulties with mask ventilation.
When active pharyngeal tube closure is the source of airway obstruction (e.g., mild anesthesia, laryngospasm, opioid-induced vocal cord closure),33 deeper anesthesia or pharmacologic paralysis is beneficial.
34-36 Of course, suitable airway apparatus and a practitioner knowledgeable in advanced airway care should be present before paralyzing a patient. Historically, muscle relaxants were withheld until sufficient mask ventilation was confirmed, owing to their putative capacity to restore spontaneous breathing. 37 Many now feel that individuals may be unable to resume spontaneous breathing prior to developing life-threatening hypoxia. The third, and perhaps more significant, aspect of this disagreement is that neuromuscular blockade often aids in mask breathing problems, and delaying its delivery may bring unneeded danger. Currently, the use of muscle relaxants in suspected instances of difficult or impossible mask ventilation is debatable.
Adjuvant devices such as an oral or nasal airway or supraglottic devices should always be considered first. A properly sized oral or nasal airway often stretches from the mouth or nose’s corner to just above the mandible’s angle. In fact, obtaining the ideal fit is often difficult, even for experienced hands. 38 Adjuvant airways that are too tiny might posteriorly shift the tongue, resulting in worsened blockage, while those that are too lengthy may mistakenly intubate the esophagus or posteriorly displace the epiglottis. 38 Dental injury is a possibility with oral airway insertion (particularly in the context of weak dentition), and epistaxis is a possibility with nasal airways, complicating an already problematic airway. 6 These problems may be avoided with gentle insertion and proper nasal airway lubrication. The most often used supraglottic device is the laryngeal mask airway. Only around 45–60% of the time does optimal placement, which excludes the esophagus and epiglottis, occur. 39 Although inadvertent placement may result in partial restriction, gas flow is often adequate. Complete occlusion of the laryngeal mask airway by the epiglottis, a twisted laryngeal mask airway, or an accidentally bent laryngeal mask airway tip been recorded in 0.4–6% of instances. In individuals with tiny mouths, big tongues, large tonsils, or posterior larynges, laryngeal mask airways are more difficult to position. In some instances, a laryngoscope may aid in implantation. When a laryngeal mask airway is unavailable or ineffective, inserting an endotracheal tube into the supraglottic region and then hyperinflating the cuff with 50–60 mL (the poor man’s laryngeal mask airway) has been reported as a successful rescue procedure. 40-42
Although infraglottic causes of increased air-flow resistance are uncommon, they must be considered since therapy is etiology-specific. Airway secretions or mucous plugs, foreign substances, high cricoid pressure, bronchospasm, tracheomalacia, tracheal stenosis, and airway or mediastinal mass are some of the possible causes.
Suctioning of airway secretions is possible. Foreign bodies may be removed by flexible or rigid bronchoscopy or may need to be pushed distally into a branch in the event of full airway blockage. Bronchospasm is treated with agonists such as albuterol, by increasing volatile anesthetic concentrations, or by increasing PEEP. Intravenous epinephrine might also be tried, since inhaled medicines may be ineffective in severe bronchospasm. Traditionally, tracheomalacia, tracheal stenosis, and airway or mediastinal malignancies have been handled by preserving spontaneous breathing and suitable posture, however CPAP may also be beneficial by raising luminal pressure and lung capacity. Increased driving pressure and prolonged inspiratory duration aid in ventilating past fixed blockages in the event of a fixed obstruction. These patients often have little trouble breathing prior to anesthetic induction, but when lung capacity decreases, partial blockage of the lower airway progresses to total obstruction. Preoperative evaluation should establish the patient’s most comfortable breathing posture. If difficult ventilation occurs after induction, the patient should be put in this rescue posture. A hard bronchoscope may be necessary in certain circumstances to circumvent the clogged section. In extreme situations, an emergency sternotomy and mass elevation may be required to prevent death from inability to breathe. 43
If the chance of difficult mask ventilation and intubation is high, referral to a tertiary care hospital equipped with extracorporeal membrane oxygenation should be explored.
Reduced proximal compliance
By raising distal pressure, which reduces the driving-pressure gradient, decreased compliance of the lungs and chest wall results in difficult mask breathing. Contributing factors include insufficient depth of anesthesia or paralysis (ie, ventilation asynchrony), a large body habitus, restrictive lung disease (which can be chronic, as with kyphoscoliosis, or acute, as with ARDS), intra-abdominal hypertension, external compression (eg, a compressing orthotic), and tension pneumothorax. 6 Treatment options include maintaining an acceptable depth of anesthesia or paralysis and administering pressures sufficient to breathe correctly or tolerating the existence of hypercapnia, as is often done in the context of ARDS. The required pressures will be high, which may aggravate leakage at the maskpatient interface and increase the danger of stomach insufflation. However, until lung compliance is diminished independently, the transpulmonary pressures will remain normal (eg, ARDS). When feasible, externally compressing equipment should be removed, and tension pneumothorax should be treated quickly with needle decompression, since positive pressure may exacerbate the disease.
Summary of Emergency Recommendations
We arrange the main ideas into an etiology-based approach to problematic mask ventilation in this section.
As previously described and summarized in Table 2, some circumstances may be better suited to different techniques. These suggestions are designed to simplify and maximize mask ventilation in emergency settings, but not to replace the American Society of Anesthesiologists’ algorithm for difficult airways. Most critically, the advice above should not be used to postpone asking for assistance, trying intubation, or planning for an urgent invasive airway.
(1) Identify and compensate for substantial leaks: immediately use two-hand mask ventilation using either a bag or a ventilator with pressure mode ventilation. A different mask size or shape should be used to compensate for the observed mismatch between the mask and the patient. When utilizing a ventilator, the operator may verify whether the mask seal is insufficient by watching for collapse of the bellows (or a single-breath pressure trace if using a ventilator without visible bellows). If an insufficient seal cannot be repaired, increase both oxygen and air flow to at least 20 L/min. If ventilation adequacy is improved, oxygenation will increase regardless of the decreased FIO2. Consider switching to one of the several mask-patient interfaces outlined above. (2) Optimize airway patency by placing the patient in the sniffing posture, using jaw thrust and chin lift, and repositioning the patient in the reverse Trendelenburg position. Adjuvant devices (nasal or oral airway, for example) should be used. Consider paralytics, particularly if spontaneous breathing is unlikely to resume. For people with tiny mouths and big tongues, the nasal airway may be more successful than the oral airway. Ascertain that the face mask does not obstruct the nose, since this commonly happens during emergency mask ventilation, and continue CPAP if feasible, as greater lung capacity improves airway patency.
(3) Overcome distal rigidity: typical distal rigidity-reducing procedures include reverse Trendelenburg posture, pharmacologic sedation or paralysis, and greater driving pressures (if not previously attempted).
Summary
Despite technological advancements in intubation, problematic airways exist. Mask ventilation is an essential lifesaving skill that doctors should understand, and a systematic algorithmic approach to mask ventilation may be important for oxygenation and vitality maintenance.
This paper presents a rational approach to mask ventilation optimization based on a thorough examination of the extant difficult-airway literature and theory (summarized in Table 2). Incorporating this sort of methodology into difficult-airway recommendations, training courses, and crisis checklists may result in decreased morbidity and death due to failure to ventilate.
