KEY CONCEPTS:
Upon completion of this topic, it is expected that the reader will understand these following concepts:
• The benefits of preoxygenation for any patient in need of active airway management or ventilatory support
• The use of cricoid pressure during manual ventilation
• Simple airway maneuvers that can make all the difference
• Understanding ventilatory pressure and reducing gastric inflation
• Indications and application of continuous positive airway pressure (CPAP)
• Assessing the adult and pediatric patient for appropriate oxygenation and ventilation
CASE STUDY:
The Paramedics were called to the home of Mrs. Tedesco, an elderly woman with a lengthy history of congestive heart failure. When they arrived, Mrs. Tedesco’s breathing appeared worse than usual. One Paramedic placed her on a nonrebreather mask but she continued to labor.
OVERVIEW
Knowledge and skill in basic airway management is mandatory. Often some of the most basic techniques are the most critical and fundamental airway management skills a Paramedic can perform. This topic addresses a number of skills and simple devices the Paramedic can utilize to effectively ventilate patients through simple face-mask techniques. In addition, continuous positive airway pressure (CPAP) and other advances in airway technology allow critically ill patients to be managed without the need for intubation.
Basic Airway Management
Basic airway management is one of the most critical and fundamental skills an emergency medicine provider can possess.1-3 Whether that provider is an EMT, a Paramedic, a nurse, or a physician, knowledge and skill in basic airway management is critical. As stated succinctly in the 1994 EMT national standard curriculum, "a patient without an airway is a dead patient." Although the knowledge and skill to perform intubations and other advanced airway maneuvers, as described in the next topic, are a critical part of the Paramedic’s practice, the non-invasive, basic skills are truly the most critical to master.
Using the Non-Intubating Airway Management Algorithm (Figure 22-1) as a guide, this topic will review the fundamentals of basic airway skills. In addition, techniques to avoid intubation, such as CPAP and assisted ventilation, will be discussed.
STREET SMART
Correct positioning of the patient and the airway is the most basic airway maneuver.
Figure 22-1 Non-intubating airway management algorithm.
The Basic Airway Management Algorithm
By the time the Paramedic enters the basic algorithm, the decision has already been made to provide airway and ventilatory support to the patient. Once that decision has been made, the Paramedic must proceed in an orderly manner through the steps of care.
Preoxygenation
Any patient in need of active airway management or ventila-tory support is in need of supplemental oxygen. Providing a patient with supplemental oxygen serves a number of purposes. Supplemental oxygen replaces nitrogen in the dead space of the lungs with oxygen, referred to as nitrogen washout. Not only does this increase the diffusion gradient, causing more oxygen to dissolve into the plasma, but it also provides a "reservoir" of oxygen in the lungs in the event the patient becomes apneic.4,5 Oxygen can often decrease the patient’s respiratory distress, in turn decreasing catecholamine release and myocardial oxygen demand.
Oxygen Delivery Devices
Oxygen equipment includes oxygen storage devices, regulators, and delivery devices (i.e., masks, nasal cannula). It is important that the Paramedic be skilled in the use of these devices.
Oxygen is stored as either a compressed gas, in steel or aluminum tanks, or as a liquid. Common compressed gas cylinders in the prehospital environment include D cylinders, which hold 400 L of oxygen when completely filled; E cylinders, which hold 660 L of oxygen; and M cylinders, which hold 3,450 L.6,7 Since the cylinders contain oxygen at high pressure (1,800 PSI), it is important that they be handled with care to prevent damage to the valve.
Oxygen can also be chilled or compressed at high pressures and stored in a liquid form. Although liquid oxygen (LOX), concentrated oxygen in liquid form, systems permit large volumes of oxygen to be stored in a relatively small space, there are several disadvantages to these systems. The tanks must be stored upright and special equipment is required for storage and cylinder transfer. Additionally, anecdotal reports suggest that, due to system leakage, unless the oxygen is used in a high volume agency, oxygen losses may exceed usage. Therefore, compressed oxygen cylinders are the most common method of storing oxygen in the prehospital environment.
Oxygen cannot safely be administered at the high pressure at which it is stored (500 to 1,800 PSI). Instead, a regulator is used to decrease the pressure to a tolerable level.
In addition, since oxygen is usually delivered in a continuous flow rather than on-demand, regulators are coupled with flow meters to deliver a fixed flow, measured in liters per minute (LPM). For portable regulators, the regulator and flow meter are integrated, while for fixed (on-board) oxygen systems, the flow meter is generally separate from the regulator. Oxygen flow rates range from 0.5 to 25 LPM. In addition, many regulators can deliver a 50 PSI source of oxygen for various devices (e.g., ventilators, continuous and bilevel positive airway pressure, and trans-tracheal jet ventilation equipment).
Oxygen is delivered to the patient from the regulator through a number of devices. The most commonly used devices are the nasal cannula, the simple face mask, and the nonrebreather mask. In addition, demand valve devices also provide a method for providing high concentration oxygen but are less commonly used.
The nasal cannula is a pronged device designed for nasal oxygen delivery (Figure 22-2). With oxygen flows from 0.5 to 6 LPM, these devices can deliver up to a 40% FiO2. They are generally well tolerated and do not require a patient to breathe through his nose to be effective. Only complete bilateral nasopharyngeal obstruction would prevent oxygen delivery. Indications include the need for supplemental oxygen. Contraindications include severe hypoxia, apnea, and intolerance of the device.
The high-flow nasal cannula (HFNC) is an advance in nasal cannula technology. By humidifying and warming the oxygen, and using membrane technology, the device is able to comfortably deliver up to 40 LPM to the patient through a nasal cannula. Although this technology has not yet been applied in the prehospital environment, it does offer some promise.
The simple face mask is a low- to mid-concentration oxygen delivery device. The mask seals over the mouth and nose, delivering oxygen through an input port and drawing air through an open side port. At 10 LPM, a 40% to 60% FiO2 is attained.8 Unfortunately, increasing the oxygen flow above 10 LPM does not significantly increase FiO2 since the same amount of room air will still be drawn through the side port on inspiration. Additionally, leaks around the mask will decrease the FiO2. These masks are not used as commonly as the next class, the nonrebreather mask.
Figure 22-2 Nasal cannula.
Figure 22-3 Nonrebreather face mask.
Nonrebreather face masks (Figure 22-3) are designed to overcome the issue of room air dilution by adding a reservoir to the oxygen supply system. While oxygen flows, it simultaneously supplies oxygen into the mask and into a reservoir bag. When the patient exhales, a one-way valve seals and the oxygen is directed into the reservoir. When the patient inhales, the one-way valve opens and the patient breathes the oxygen from the reservoir.
Although a normal adult male may have a minute ventilation of 6 to 8 LPM, this ventilation occurs during inhalation and airflow is not continuous. The flow during inhalation may approach 50 LPM!9 Oxygen delivery from a regulator, on the other hand, is continuous and limited to the liter flow settings on the regulator. The reservoir bag on the nonrebreather mask supplies the additional liter flow required during inhalation by storing oxygen during exhalation. This is why it is important that the liter flow is set high enough that the reservoir bag does not collapse during inhalation. Most nonrebreather face masks have two exhalation ports, at least one of which is left open. If the reservoir bag is collapsing during inhalation, room air is drawn through the side port to prevent rebreathing of carbon dioxide.
Nonrebreather face masks (NRFM), oxygen masks with an oxygen reservoir, can deliver up to 80% FiO2; they do not deliver 100% FiO2 because there will always be some room air mixing through the open side port.
A demand valve regulator is a device available that will provide 100% FiO2 at appropriate liter flows. When attached to a 50 PSI oxygen source, this device delivers high LPM flows of 100% oxygen when the patient inhales. When the patient is exhaling, the valve closes and oxygen flow stops. This device is different from a manually triggered ventilation device in that it is the patient’s inspiratory effort that triggers the device. Therefore, the risk of over pressurization injury is minimized. However, the device cannot be used in apneic patients.
Venturi masks, special masks with a restricted intake that permits an exact percentage of oxygen, can also be used to deliver oxygen, although their use in the prehospital environment is generally limited to specialty care services. These devices use a face mask connected to a specially designed adapter. These adapters have small holes in the sides and are designed so that when a specific oxygen liter flow is delivered to the adapter, a specific amount of room air is drawn into the adapter as well, called the venturi effect. This mixing provides a very specific oxygen concentration. Generally speaking, unless a patient is already using a venturi mask and is not hypoxic or is on a fixed FiO2 during a specialty transport, there are no indications for the prehospital use of the venturi mask.
Generally speaking, patients can be thought of as being at minimal risk for hypoxia, at moderate risk for hypoxia, or hypoxic. Patients at minimal risk for hypoxia may benefit from a nasal cannula, depending on the patient’s clinical condition. Patients at moderate risk for hypoxia or who are hypoxic should receive high-concentration oxygen (i.e., a nonrebreather mask). Any patient who requires active airway management should be preoxygenated with a nonrebreather mask. Once the patient is being oxygenated, the remainder of the basic airway management equipment should be prepared to address ventilations.
Equipment for Basic Airway Management
There are multiple methods for opening the airway and ventilating a patient who is in respiratory distress or respiratory arrest. A number of techniques can be used to manually open the airway. Devices, such as oropharyngeal and nasopharyn-geal airways, can be used to help maintain an open airway. The most commonly used device for providing ventilatory assistance is the bag-valve-mask assembly. When used properly, these devices can effectively be used to ventilate most patients. Other devices such as the pocket mask, the manually triggered oxygen-powered ventilator, and the automatic transport ventilator are also available to provide ventilation. Furthermore, suction is an important and frequently overlooked adjunct to airway management.
Oropharyngeal and Nasopharyngeal Airways
Some of the most fundamental and easiest to use devices for airway management are the oropharyngeal and nasopharyngeal airways.
Figure 22-4 Oropharyngeal airway.
Since the epiglottis is attached to the hyoid bone by the hyoepiglottic ligament, anterior displacement of the hyoid opens the airway. The hyoid is indirectly attached to the tongue, and anterior displacement of the tongue facilitates anterior displacement of the hyoid. Additionally, the tongue can increase airway turbulence by narrowing the upper airway. The oropharyngeal airway is designed to address this issue.10,11 The nasopharyngeal airway helps to displace the soft palate anteriorly, improving airflow through the upper airway. Neither the oral airway nor the nasopharyngeal airway provide protection against aspiration.12
Oral airways come in a number of sizes, from neonatal to large adult (Figure 22-4). Preparation of an oropharyn-geal airway involves measuring the appropriate size for the patient. Two common methods are used. The first is to measure the airway from the midline of the lips to the angle of the jaw. The second is to measure the airway from the corner of the mouth to the inferior tip of the ipsilateral earlobe. Either method is appropriate.
An airway that is too small will not displace the tongue and jaw anteriorly and is at risk of being lost in the airway. An oral airway that is too large will tend to rise out of the mouth and during ventilation, may actually displace the tongue posteriorly. Therefore, it is important to only use an oral airway if the appropriate size is available.
It is important to note that the oral airway may stimulate a gag reflex and should not be used in patients with an intact gag reflex.13,14 If an oral airway is to be used, suction must be immediately available in the event that the patient vomits during placement.
While the oropharyngeal airway is made of hard plastic, the nasopharyngeal airway is made of soft silicone with a beveled tip (Figure 22-5). The nasopharyngeal airway is useful in patients with an altered mental status but with an intact gag reflex.
Figure 22-5 Nasopharyngeal airway.
Although the nasopharyngeal airway is less likely to stimulate a gag reflex, patients may vomit or sneeze after nasopharyn-geal airway placement. Therefore, suction must be immediately available when a nasopharyngeal airway is placed.
There are a number of advantages to the placement of the nasopharyngeal airway. These include the ability to place them in patients with trismus or in those who are otherwise unable to open their mouths. Nasopharyngeal airways can also be used in patients who have an intact gag reflex.
The only true contraindication to the placement of the nasopharyngeal airway is the patient’s inability to tolerate the airway. Care must be taken if it is being used in someone with a head injury. Make sure that there is no evidence of a basilar skull fracture, as there is some risk, although very slight, of placing the airway into the cranium.15-20 In addition, patients with bleeding disorders or who are on blood thinners are at risk of significant epistaxis from nasopharyngeal airway placement.
Like the oropharyngeal airway, the nasopharyngeal airway must be measured before placement to assure good sizing. The most common method for measuring the nasopharyngeal airway is to place the airway against the face, measuring from the nare to the ipsilateral inferior tip of the earlobe. Unlike the oral airway, the nasal airway should be lubricated before use. In addition, pretreatment of the nare with an inhaled vasoconstrictor (e.g., neosynephrine) and topical anesthetic (e.g., spray or viscous lidocaine) before placement may improve patient tolerance and decrease bleeding.
