Dispatch sends you to the home of a 79-year-old male with chronic obstructive pulmonary disease (COPD) who is complaining of “shortness of breath.” He sits upright, leaning forward and supporting his weight with both arms. His head seems to be attached directly to his shoulders. He appears drowsy, and replies to your questions about medical history with single-word answers only. His wife relates that he has grown increasingly short of breath during the past three days. After he refused to see his doctor, his wife called 9-1-1.
You palpate a pulse of 98 beats per minute (bpm) and measure his blood pressure at 180/90. His respiratory rate is 30. Breath sounds are diminished and wheezy bilaterally, but there’s little chest movement with each breath. The pulse oximeter reveals an oxygen saturation (SpO2) level of 93% and an end-tidal carbon dioxide (EtCO2) level of 35. He grows more somnolent. Narcan doesn’t improve his level of arousal.
This patient is on the verge of acute respiratory failure. Level of arousal (wakefulness) is a sensitive and reliable indicator of brain function. The patient is drowsy and growing more so because of the buildup of CO2 from a lack of effective ventilation. An easily reversible cause (opiate effect) for his lethargy isn’t present. The pulse oximeter indicates borderline hypercapneic respiratory failure. It can often be misleading, as in this case, with the EtCO2 number indicating adequate ventilation; however, it likely represents an increase of expired partial pressure of carbon dioxide (PCO2) with ineffective ventilation.
Noninvasive positive pressure ventilation, such as continuous positive airway pressure (CPAP), may be considered to decrease the work of breathing in hypercapneic respiratory failure. But this patient is unlikely to be cooperative because of his somnolence, and his respiratory drive is failing rapidly. The likeliest clinical course is continued deterioration.
You and your partner attempt to augment the patient’s ventilation with a bag-valve mask (BVM). You maintain a tight seal with two hands on the mask while your partner squeezes the bag. The patient becomes apneic. His SpO2 drops to 80%. Your partner places an oropharyngeal airway (OPA) device, which allows ventilation with continued high fraction of inspired oxygen (FIO2) rate via the BVM.
Maintaining a rate of eight to 10 to avoid hyperventilation, you see the SpO2 climb to 95% over the next three minutes. Addition of a disposable positive end-expiratory pressure (PEEP) valve to the exhalation port of the BVM results in improvement of the SpO2 to 100%.
Just prior to becoming apneic, his SpO2 was the brink of the steep portion of the hemoglobin desaturation curve (see Figure 1, p. 35). Further desaturation, even if brief, indicates a precipitous fall in arterial oxygen content and will place the brain and other vital organs at risk for anoxic damage. A further rise in CO2 diminishes the affinity of hemoglobin for oxygen further worsening oxygen delivery to organs. Note that there’s a lag time between the SpO2 registered by the pulse oximeter and the real-time arterial saturation. This delay can range from a few to 30 seconds depending on the etiology (e.g., heart failure vs. septic shock) and severity of illness. Unfamiliarity with this characteristic of the pulse oximeter may cause mistaken concern that the patient isn’t improving with BVM therapy. Conversely, false confidence may result when the patient is “desaturating,” yet the pulse oximeter continues to read 100%.
The urban myth persists that providing high-flow oxygen to COPD patients will cause respiratory arrest and should be avoided. This phenomenon is much talked about but seldom seen. The greater danger to this patient is persistent hypoxemia untreated. Deterioration in oxygen saturation with apnea occurs at a rate determined by factors including age, severity of illness and the presence of obesity. Figure 1, shows the rate of SpO2 decline in patients initially 100% saturated who are paralyzed prior to elective intubation. This is a “best case” scenario, and the times to desaturation should not be generalized to EMS patients. However, one does see how rapidly ill or pediatric apneic patients will become hypoxemic. For types of patients made apneic by RSI, see Figure 1.
BVM Ventilation & Oxygenation
EMS providers are overconfident in their skills and knowledge in how to use BVMs. Multiple studies of prehospital resuscitations have documented compression rates that are too rapid, inspiratory pressures generated by bag compression that’s too great and volumes of air per compression that are too large for optimal outcomes. These factors strongly predict patient harm in the patients with severe obstructive lung disease, such as COPD or asthma. Rapid large-volume bagging exacerbates existing high intrathoracic pressures and may cause pneumothorax or significant cardiovascular strain.(1)
Proper BVM technique presupposes proper positioning. Correct positioning is achieved when a line from the ear canal to the sternal notch is parallel to the floor or reverse Trendelenburg position, in which the patient’s head are placed about 15—30 degrees higher than their head, for patients immobilized on spine boards.(1) Proper positioning prevents atelectasis and improves oxygenation. Effective BVM use requires a tight seal between face and mask; in practice, this requires two operators. With an adequate seal, a bag-valve mask with an oxygen reservoir and one-way exhalation port will deliver an FIO2 greater than 90%.(1) Bag compression rates greater than eight to 10 per minute cause decreased cerebral perfusion and contribute to increased intrathoracic pressure. Field interventions have attempted to control BVM ventilation rates. Examples are metronomes and timing lights–standalone and attached to BVMs. These provide convenient guidance without changing the BVM process.
Sufficient self-discipline under the high stress of an actual field response is difficult. Less important is the duration of each compression of the bag. Breaths should be administered over two seconds; shorter breath times result from higher airway pressures. The peak airway pressure possible from manual compression of a standard adult-size BVM easily exceeds 20 cm of water, the pressure at which air is forced past the lower esophageal sphincter into the stomach.(1) Gastric distention, regurgitation and aspiration result.
BVMs with built-in “variable resistance” valves are helpful in limiting both ventilation rate and peak airway pressure. The harder one squeezes these bags, the harder they are to compress. The provider controls both ventilation rate and peak airway pressure without conscious thought or calculation. The potential for hyperinflation of the lungs and dangerously high peak airway pressure is thereby reduced.
In practice, sufficient pressure needs to be applied to the bag to create rise and fall of the chest wall. More force applied to the BVM bag will be required to expand the less-compliant lungs of patients with COPD. However, a common error is interpretation of the back pressure felt from attempting to force gas too quickly through the larynx as “stiff lungs” and applying even more force to the BVM. Try compressing the bag less forcefully to see if airflow improves. Consider also upper airway obstruction and re-check patient positioning. Don’t administer a BVM breath while the patient is still exhaling.
Patients who don’t reach SpO2 of 100% saturation with a standard BVM treatment will benefit from attachment of a disposable PEEP valve to the exhalation port of the BVM.
Note: CPAP alone should not be used in apneic or intermittently apneic patients.
Gastric insufflation isn’t generally created by overinflation of the lungs but by short breath times and high inspiratory flows creating high upper airway pressures. As these high flows are restricted from immediately entering the lungs by the larynx, gas is diverted into the stomach. Cricoid pressure produces laryngeal/tracheal compression in many patients and doesn’t reduce the risk of regurgitation and aspiration.
Preoxygenation
In the apneic patient, more oxygen is absorbed in the alveoli than carbon dioxide is released. This creates a negative pressure in the lungs relative to the oropharynx, allowing gas flow into the lungs. A high concentration of oxygen delivered via nasal cannula at a flow rate of 15 L per minute will provide a continuous flow of oxygen to the alveoli. This is called “apneic oxygenation” and has been demonstrated to maintain oxygen saturation for longer periods in patients paralyzed in the operating room and emergency department (ED) for endotracheal (ET) tube placement.(1) The duration of safe apnea after the administration of sedatives and muscle relaxants is prolonged. A nasal cannula is the most readily available and effective means of providing apneic oxygenation during ET tube attempts.
Given the unique variables involved in each emergency tracheal intubation, it’s impossible to predict the exact duration of safe apnea for any given patient. Those with high initial saturation levels on room air or after adequate oxygenation are at lower risk and may maintain adequate saturation for as long as eight minutes of apnea. Critically ill patients and those with saturations just above the steep portion of the oxyhemoglobin dissociation curve are at high risk of rapid-onset hypoxemia with prolonged tracheal intubation efforts.
Endotracheal Intubation
Of course, endotracheal intubation (ETI) by paramedics in the field is controversial–with or without rapid sequence intubation (RSI) medications, which paralyze the patient’s airway.(2,3) Like any complex psycho-motor skill, ETI must be performed frequently, or a reasonably accurate simulation repeated frequently, to maintain a high level of skill. Including ETI in the scope of practice is a local decision based on frequency of intubations, available alternative airways and training resources.
In the field, every airway is a “difficult airway.” For example, the patient in the scenario is obese with a short neck and pharyngeal anatomy that makes visualizing the glottis–a key step in successful ETI–a challenge. He also verges on respiratory failure with deteriorating oxygenation and hypoventilation. He has been working hard to breathe and will soon tire out. Definite indications for endotracheal intubation are present. And although ETI remains the best method of advanced airway management–providing better (not perfect) airway protection, higher FIO2 and more reliable ventilation of the lungs than other airway management techniques, it remains difficult for many paramedics to maintain an adequate level of skill. That’s where devices that assist the provider in visualizing necessary anatomy to successfully intubate patients can be beneficial.
Extraglottic Airways & RSI
Extraglottic airways are alternate airway devices that are inserted blindly into the esophagus and don’t pass through the vocal cords into the trachea. Inflated balloons obstruct the oropharynx and esophagus to create a path for ventilation into the trachea. Because of this, they don’t require visualization of the glottis. They’re designed to support both ventilation and oxygenation in combination with a BVM. A variety of them are in widespread EMS use.
The Combitube, King Airway and Laryngeal Mask Airway (LMA) device have proven useful where ALS isn’t available, where the frequency of ET tube placement per paramedic is low, and where local medical direction judges the balance between risk and benefit better than that of endotracheal intubation. There’s a significant history and body of medical literature on their use as a primary airway or rescue device after unsuccessful ETI attempts.
Administration of RSI medications in the field, like ETI itself, requires knowledge of patient selection, opportunities for skills maintenance, a preconstructed backup plan in case of unsuccessful intubation and meticulous review of each event for quality assurance. The use of sedating and paralyzing medications in the ED improves the rate of successful and atraumatic endotracheal intubation. In the field, successful endotracheal intubation in other than unconscious unresponsive patients without RSI is possible but improbable.(4)
In some awake, conscious patients–notably those with significant airway burns and expanding neck hematomas, the predictable clinical course indicates intubation to prevent imminent total airway occlusion. The probability of successful endotracheal tube placement with less trauma and fewer attempts is increased with the use of RSI medications.(5)
Video Laryngoscopy
Successful ETI with direct laryngoscopy (DL), which includes all the prementioned methods and devices, requires the alignment of the oral cavity, pharynx and tracheal axes to permit a direct line of sight from the operator to the vocal cords. Despite the optimal positioning, (e.g., horizontal line from ear to sternal notch), visualization is often difficult or impossible.
Video laryngoscopes improve this view by incorporating a micro video camera on the undersurface of the laryngoscope blade that projects magnified images onto a monitor screen. This allows the operator to indirectly view the glottic inlet.6 During the past 10 years, video laryngoscopes, as well as optical devices using mirrors and prisms, have become common in operating rooms, EDs and critical care units for routine and difficult airways. Multiple studies have shown improved success with video laryngoscope (VL) compared with direct laryngoscopes in a variety of settings, including prehospital and novice trainees.(7—9)
Optimizing first-attempt success is of paramount importance, especially in critically ill patients with difficult airways. Three or more unsuccessful attempts at ETI are associated with a higher incidence of complications (e.g., unrecognized esophageal intubation, airway trauma, aspiration and hypoxemia).(10) Recent research from several EDs and at least one EMS system demonstrates that video laryngoscopes result in better visualization of the glottis, higher proportion of successful ETIs and shorter placement times without an increase in complications (see Table 1).(3,7,11)
Prehospital video laryngoscopes come in a variety of configurations. Several factors will determine the best choice for a particular jurisdiction. The initial capital investment and recurring cost of use differ widely among video laryngoscopes currently available on the market. Some available video laryngoscopes may be reused if properly disinfected. Others are completely disposable. Economically speaking, there’s a point when the number of intubations make reusable laryngoscopes a better economic proposition than disposable ones.
Early VLs that were portable enough to be used in the field contained internal rechargeable battery packs. These needed either charging devices or wall plugs. Increasingly available are ones powered by AA or AAA alkaline batteries. Video laryngoscopes vary significantly in the shape of blade. Some are comparable to Macintosh and Miller blades and may be used in the same way. Little retraining is necessary, and in some cases these blades may be used to perform conventional direct laryngoscopy.
Other video blades differ from standard direct laryngoscope blades incorporating a hyper-angulated curvature. They require additional training and, in some cases, the addition of specialized stylets.
VLs also vary in sizes and although not all VLs can be used in children, manufacturers continue to introduce separate pediatric-sized devices or laryngoscope blades for existing devices. Channel guides are another innovation that vary among video laryngoscopes. They are fittings that are attached to the laryngoscope where an endotracheal tube may be placed. After visualization of the glottis, the ET tube is advanced through the guide and the cords. Guides limit the size ET tube that can be used.
Acceptable image size and quality is a matter of user preference. VLs suitable for field use generally provide images of sufficient quality for successful endotracheal intubation. In general, an inverse relationship between image quality and cost exists, meaning the higher the device costs, the better the image quality. Finally some VLs can be connected to an external monitor. This permits a trainer or observer to simultaneously view the picture available to the endotracheal tube operator.
Challenges
Note that children aged 4 years or younger are particularly challenging. The epiglottis is at the level of C-1, not C-4 as in adults; there’s a relatively large amount of adenoidal tissue in the airway that’s friable and prone to bleeding with minimal trauma. In addition, small children have a rapid metabolic rate and are therefore prone to rapid desaturation (see Figure 1). Thus, there’s virtually no time of safe apnea for small children because they begin to desaturate immediately on becoming apneic for any reason.
Therefore, an approach de-emphasizing ETI in small children is more medically prudent. The majority of children, who are without trauma to the face or facial abnormalities may be adequately oxygenated and ventilated with a bag valve mask and oropharyngeal or nasopharyngeal airway device.
This approach, “uninterrupted ventilation,” should be stopped only if there’s no movement of the chest with bagging. “Quick-look” laryngoscopy with pediatric Magill forceps at the ready to remove any possible foreign bodies may then be performed–but then only long enough to visualize the foreign body.
Summary
Since 2000, many studies of advanced emergency airway management have appeared in the medical literature. Although most described patients in the operating room, intensive care unit or emergency department, studies of video laryngoscopy in the field are in progress and beginning to appear in the literature.
Video laryngoscopy provides better views of the glottis, and it permits more successful intubations with fewer attempts. Price reductions as more devices, some specifically intended for EMS, enter the market will lower the entry costs for adoption. It is my prediction that in five years, video laryngoscopy will be the method of choice for endotracheal intubation in the field.
References
1. Weingart SD, Levitan RM. Preoxygenation and prevention of desaturation during emergency airway management. Ann Emerg Med. 2012;59(3):165—175.
2. Wang HE, Szydlo D, Stouffer JA, et al. Endotracheal intubation versus suproglottic airway insertion in out-of-hospital cardiac arrest. Resusciation 2012;83(9):1061—1066.
3. Dunford JV, Davis DP, Ochs M, et.al. Incidence of transient hypoxia and pulse rate reactivity during paramedic rapid sequence intubation. Ann Emerg Med. 2003;42(6):721—728.
4. Lawner BJ. RSI without paralytics: Just don’t do it. In: Avoiding Common Prehospital Errors. Lawner BJ, Slovis CM, Fowler R, et al (Eds). Lippincott Williams & Wilkins: Philadelphia, 2013.
5. Nagib M, Samarkandi AH, El-Din ME, et al. The dose of succinylcholine required for excellent endotracheal intubating conditions. Anesth Analg 2006;102(1)151—155.
6. Sakles JC, Brown CA, Bair AE. Video laryngoscopy. In: Manual of Emergency Airway Management. 4th ed. Lippincott Williams & Wilkins: Philadelphia, 2012:140—157.
7. Wayne MA, McDonnell M. Comparison of traditional vs. video laryngoscopy in out-of-hospital tracheal intubation. Prehosp. Emerg Care. 2010;14(2):278—282.
8. Sakles JC, Tolby N, VanderHeyden TC, et al. Ability of emergency medicine residents to use alternative optical airway devices. Presentation at April 2003 Western Society for Academic Emergency Medicine meeting; Phoenix.
9. Kaplan MB, Hagberg CA, Ward DS, et al. Comparison of direct and video-assisted views of the larynx during routine intubations. J Clin Anesth. 2006;18(5):357—362.
10. Hasegawa K, Shigemitsu K, Hagiwara Y, et al. Association between repeated intubation attempts and adverse events in emergency departments: An analysis of a multicenter prospective observational study. Ann Emerg Med. 2012;60(6):749—754.e2.
11. Sakles JC, Mosier J, Chiu S, et al. A comparison of the C-MAC video laryngoscope to the Macintosh direct laryngoscope for intubation in the emergency department. Ann Emerg Med. May 4 2012. [Epub ahead of print].
