Basic Airway Management and Decision Making

Chapter 3


Basic Airway Management and Decision Making



Basic airway procedures are often overlooked in favor of more exciting intubation devices and techniques, but basic procedures are critically important and often lifesaving. Establishment of a patent airway, oxygenation, and bag-mask ventilation (BMV) remain the cornerstones of good emergency airway management.1,2 These techniques can be used quickly and in any setting. They allow practitioners to keep apneic patients alive until a definitive airway can be established.3


Extraglottic devices, such as laryngeal mask airways (LMAs) and the King Laryngeal Tube (LT), have also become important for the initial resuscitation of apneic patients and for rescue ventilation when intubation fails.4–6 Another commonly used device is the esophageal-tracheal Combitube, which will be discussed and compared with the King LT. Noninvasive positive pressure ventilation (NPPV) is widely available in both prehospital and emergency department (ED) settings and can be used to optimize oxygenation before intubation or to avoid intubation in carefully selected patients.7,8


This chapter describes basic airway skills, including opening the airway, O2 therapy, BMV, and extraglottic airway (EGA) devices. These are the skills that providers can rely on when other airway techniques are difficult or impossible. Mastery of these skills and use of an airway algorithm help providers manage difficult, anxiety-provoking emergency airways.


Pulse oximetry (Spo2) has greatly improved our ability to monitor the oxygenation of patients at risk for airway or ventilatory compromise.9 These monitors are accurate under most conditions10 and allow clinically subtle deterioration to be recognized quickly (see Chapter 2). Spo2 monitors are standard equipment in all emergency airway settings. The use of waveform capnography in the emergency setting is rapidly increasing but is not yet universally available or applied. This trend should be encouraged because capnography can improve patient safety by rapidly detecting hypoventilation, impending airway obstruction, and risk for apnea before these conditions occur.11



The Challenge of Emergency Airway Management


Although other specialists are sometimes available, most emergency airways are managed by emergency medicine providers.12 Airway management in the ED is quite unique and much different from airway management in the controlled setting of an operating room. Likewise, conventional airway management tools may be ineffective in the uncontrolled emergency environment. Major challenges include an incomplete historical database, hypoxia, shock, full stomach, and the presence of vomit, blood, or excessive secretions in the airway. Many patients are uncooperative and combative, thus making it impossible to properly examine their airway before choosing an intubation technique. Medical history, allergies, and even the current diagnosis are often unknown before emergency airway management begins. Time constraints, lack of patient cooperation, and risk for vomiting limit the use of some techniques, such as awake intubation. In trauma patients, the risk for cervical spine injury limits optimal head and neck positioning for BMV and laryngoscopy. All these factors increase the risk for complications from emergency airway management,12,13 and about 1% of all emergency airways require a surgical approach.14 The popularity of video laryngoscopy and other video airway devices may further reduce the incidence of emergency surgical airways.



Basic Airway Management Techniques



Opening the Airway


The first concern in the management of a critically ill patient is patency of the airway. Upper airway obstruction most commonly occurs when patients are unconscious or sedated. It can also be due to injury to the mandible or muscles that support the hypopharynx. In these situations, the tongue moves posteriorly into the upper airway when the patient is in a supine position (Fig. 3-1A). Upper airway obstruction caused by the tongue can be relieved by positioning maneuvers of the head, neck, and jaw; the use of nasopharyngeal or oropharyngeal airways; or the application of continuous positive airway pressure (CPAP).




Manual Airway Maneuvers


Airway obstruction in unconscious patients may be due to posterior displacement of the tongue, but research in patients with obstructive sleep apnea using CPAP supports the concept that the airway collapses like a flexible tube.3,15 Upper airway obstruction may cause obvious snoring or stridor, but it may be difficult to appreciate in some patients. All unconscious patients are at high risk for upper airway obstruction.


More than 35 years ago, Guildner16 compared different techniques for opening obstructed upper airways and found that the head-tilt/chin-lift and jaw-thrust techniques were both effective (Fig. 3-1B and C). Modern airway textbooks still describe the head-tilt/chin-lift and jaw-thrust maneuvers but also use the term “triple airway maneuver,” which is a combination of head tilt, jaw thrust, and mouth opening.3,17 Many airway experts believe that the jaw-thrust maneuver (anterior mandibular translation to bring the lower incisors anterior to the upper incisors) is the most important technique for opening the upper airway (Fig. 3-1C).3,18,19


It is widely accepted that the jaw-thrust-only (without head tilt) maneuver should be performed in patients with suspected cervical spine injury,17 but there is no evidence that it is safer than the head-tilt/chin-lift maneuver.20 In 2005, the American Heart Association (AHA)21 concluded that airway maneuvers are safe during manual in-line stabilization of the cervical spine but highlighted evidence that all airway maneuvers cause some spinal movement. Both the chin-lift and the jaw-thrust maneuvers have been shown to cause similar substantial movement of the cervical vertebrae.22–26 The AHA recommended that “in a victim with a suspected spinal injury and an obstructed airway, the head-tilt/chin-lift or jaw-thrust (with head-tilt) techniques are feasible and may be effective for clearing the airway” and emphasized that “maintaining an airway and adequate ventilation is the over-riding priority in managing a patient with a suspected spinal injury.”21


Importantly, the addition of CPAP may relieve airway obstruction when simple manual positioning maneuvers fail. Meier and colleagues15 showed that adding CPAP to the chin-lift and jaw-thrust maneuvers decreased stridor and improved the nasal fiberoptic view of the glottic opening in anesthetized children.



The Head-Tilt/Chin-Lift Maneuver


To perform the head-tilt/chin-lift maneuver, place the tips of the index and middle fingers beneath the patient’s chin (Fig. 3-1B). Lift the chin cephalad and toward the ceiling. The upper part of the neck will naturally extend when the head tilts backward during this maneuver. Apply digital pressure on only the bony prominence of the chin and not on the soft tissues of the submandibular region. The final step in this maneuver is to use the thumb to open the patient’s mouth while the head is tilted and the neck is extended.



The Jaw-Thrust Maneuver


To perform the jaw-thrust maneuver, place the tips of the middle or index fingers behind the angle of the mandible (Fig. 3-1C). Lift the mandible toward the ceiling until the lower incisors are anterior to the upper incisors. This maneuver can be performed in combination with the head-tilt/chin-lift maneuver or with the neck in the neutral position during in-line stabilization.



The Triple Airway Maneuver


The “triple airway maneuver” is described by many authors as the best manual method for maintaining a patent upper airway.3,17 The most common description of this maneuver is head tilt, jaw thrust, and mouth opening.3,17 Other authors describe the triple maneuver differently—as a combination of upper cervical extension (head tilt), lower cervical flexion, and jaw protrusion (jaw lift).19 The triple airway maneuver has been described as a technique for providers with advanced airway skills.17 No studies exist to support the assertion that this technique is more effective than the head-tilt/chin-lift or jaw-thrust maneuvers, but the triple maneuver is commonly mentioned in the anesthesia literature as a valuable technique.



Patient Positioning


The best way to position a patient’s head and neck for opening the upper airway is to mimic how patients position themselves when they are short of breath, with the neck flexed relative to the torso and with atlanto-occipital extension.2 This is known as the “sniffing position” and was described by Magill almost 100 years ago.27 In normal-sized supine adults, this is accomplished by elevating the head about 10 cm while tilting the head back so that the plane of the patient’s face tilts slightly toward the provider at the head of the bed (see Chapter 4, Fig. 4-8).2,3,28–30 Morbidly obese patients require much more head elevation to achieve the proper sniffing position. This can be accomplished by building a ramp of towels and pillows under the upper torso, head, and neck or by using a Troop Elevation Pillow (Mercury Medical, Clearwater, FL) or similar device (Fig. 3-2).31–34 Horizontal alignment of the external auditory meatus with the sternum is the best position for opening the upper airway in morbidly obese patients.33–36



The sniffing position is contraindicated in patients with cervical spine injuries. The best technique for opening the airway in this situation is a simple jaw-thrust maneuver with anterior mandibular translation to bring the lower incisors anterior to the upper incisors (Fig. 3-1C).3,18,19


In young children, this position is often achieved without lifting the head because the occiput of a child is relatively large, so the lower cervical spine is normally flexed when the child is lying supine on a flat surface.


Airway management is usually easiest when patients are in the supine position, but the lateral position may be best for patients who are actively vomiting and those with excessive upper airway bleeding or secretions. Some evidence suggests that rotating patients to the lateral position may not prevent aspiration.37 Patients with suspected cervical spine injury should have their head immobilized with in-line stabilization if they need to be rolled to the lateral position. Airway management maneuvers may be limited or difficult when patients are in the lateral position.



Foreign Body Airway Obstruction


Awake patients with partial airway obstruction can usually clear a foreign body on their own. Intervention is required when the patient is not moving air or has altered mental status. Some patients with upper airway obstruction can be ventilated and oxygenated with aggressive high-pressure BMV, so always try this if standard BMV fails. Massive aspiration of vomitus, however, is often a fatal event because of inability of the patient and clinician to adequately clear the airway.



Abdominal Thrusts (Heimlich Maneuver), Chest Thrusts, and Back Blows (Slaps)


The 2010 International Consensus Conference on Cardiopulmonary Resuscitation and Emergency Cardiopulmonary Care4 evaluated the evidence for different techniques to clear foreign body airway obstruction. They found good evidence for the use of chest thrusts, abdominal thrusts, and back blows or slaps. Insufficient evidence exists to determine which technique is the best and which should be used first. Some evidence indicates that chest thrusts may generate higher peak airway pressure than the Heimlich maneuver does.


The technique of subdiaphragmatic abdominal thrusts to relieve a completely obstructed airway was popularized by Dr. Henry Heimlich and is commonly referred to as the “Heimlich maneuver.”38 The technique is most effective when a solid food bolus is obstructing the larynx. In a conscious patient, stand behind the upright patient. Circle the arms around the patient’s midsection with the radial side of a clenched fist placed on the abdomen, midway between the umbilicus and xiphoid. Then grasp the fist with the opposite hand and deliver an inward and upward thrust to the abdomen (Fig. 3-3A). A successful maneuver will cause the obstructing agent to be expelled from the patient’s airway by the force of air exiting the lungs. Abdominal thrusts are relatively contraindicated in pregnant patients and those with protuberant abdomens. Potential risks associated with abdominal thrusts include stomach rupture, esophageal perforation, and mesenteric laceration, thus compelling the rescuer to weigh the risks and benefits of this maneuver.39–44 Use a chest position for pregnant patients (Fig. 3-3B).



If a choking patient loses consciousness, use chest compressions in an attempt to expel the obstructing agent (Fig. 3-3C).4 The theory is the same as the Heimlich maneuver, with high intrathoracic pressure created to push the obstruction out of the airway. Some data suggest that chest compressions may generate higher peak airway pressure than the Heimlich maneuver.45 After 30 seconds of chest compressions, remove the obstructing object if you see it, attempt 2 breaths, and then continue cardiopulmonary resuscitation (CPR; 30 compressions to 2 breaths). Every time you open the airway to give breaths, look for the object and remove it if possible, and then continue CPR if necessary.


Back blows are recommended for infants and small children with a foreign body obstructing the airway. Some authors have argued that back blows may be dangerous and may drive foreign bodies deeper into the airway, but there is no convincing evidence of this phenomenon.46,47 As with the other techniques, anecdotal evidence suggests that back blows are effective.48–50 No convincing data, however, indicate that back blows are more or less effective than abdominal or chest thrusts. Back blows may produce a more pronounced increase in airway pressure, but over a shorter period than with the other techniques. The AHA guidelines suggest back blows in the head-down position (Fig. 3-3D) and head-down chest thrusts in infants and small children with foreign body airway obstruction (Fig. 3-3E).4 The AHA does not recommend abdominal thrusts in infants because they may be at higher risk for iatrogenic injury. From a practical standpoint, back blows should be delivered with the patient in a head-down position, which is more easily accomplished in infants than in larger children.


Any patient with a complete airway obstruction may benefit from chest compressions, abdominal thrusts, or back blows. It is important to realize that more than one technique is often required to clear obstruction of the airway by a foreign body, so multiple techniques should be applied in a rapid sequence until the obstruction is relieved.21 Perform a finger sweep of the patient’s mouth only if a solid object is seen in the airway. It is recommended that suction be performed on newborns rather than giving them back blows or abdominal thrusts.51


Perform CPR on all unconscious patients with airway obstruction. Try aggressive high-pressure BMV in this setting. In cases in which obstructive foreign bodies cannot be removed under direct visualization and aggressive positive pressure ventilation has failed, practitioners with advanced airway skills and proper equipment can try to push a subglottic foreign body beyond the carina.



Suctioning


Patient positioning and airway-opening maneuvers are often inadequate to achieve complete airway patency. Ongoing hemorrhage, vomitus, and particulate debris frequently require suctioning. Several types of suctioning tips are available. A large-bore dental-type suction tip is the most effective in clearing vomitus from the upper airway because it is less likely to become obstructed by particulate matter. The tonsil tip (Yankauer) suction device can be used to clear hemorrhage and secretions. Its rounded tip is less traumatic to soft tissues, but the tonsil tip device is not large enough to effectively suction vomitus.


A large-bore dental-type tip device, such as the HI-D Big Stick suction tip, should be readily available at the bedside during all emergency airway management (Fig. 3-4). The large-bore tip allows rapid clearing of vomitus, blood, and secretions.



A limiting feature of many suction catheters is the diameter of the tubing. Vomitus may obstruct the standard image-inch-diameter catheter.52 A image– or image-inch-diameter suction tube (Kuriyama Tubing, image-inch inner diameter, 0.44-inch outer diameter, clear; www.grainger.com) has been shown to significantly decrease suction time for viscous and particulate material (see Fig. 3-4).53


Keep suctioning equipment connected and ready to operate. Everyone participating in emergency airway management should know how to use it. Interposition of a suction trap close to the suction device prevents clogging of the tubing with particulate debris. A trap that fits directly onto a tracheal tube has been described, and use of this device allows effective suctioning during intubation.54


No specific contraindications to airway suctioning exist. Complications of suctioning may be avoided by anticipating problems and providing appropriate care before and during suctioning maneuvers. Nasal suction is seldom required, except in infants, because most adult airway obstruction occurs in the mouth and oropharynx.


Avoid prolonged suctioning because it may lead to significant hypoxia, especially in children. Do not exceed 15 seconds for suctioning intervals and administer supplemental O2 before and after suctioning. Naigow and Powasner55 found that suctioning consistently induced hypoxia in dogs and that it was best avoided by hyperventilation with high-concentration O2 before and after suctioning.


When feasible, perform suctioning under direct vision or with the aid of the laryngoscope. Forcing a suction tip blindly into the posterior pharynx can injure tissue or convert a partial obstruction to a complete obstruction.



Oropharyngeal and Nasopharyngeal Artificial Airways






Artificial Airway Placement


The simplest and most widely available artificial airways are the oropharyngeal and nasopharyngeal airways (Fig. 3-5). Both are intended to prevent the tongue from obstructing the airway by falling back against the posterior pharyngeal wall. The oral airway may also prevent teeth clenching. In cases of severe upper airway edema, such as angioedema caused by an angiotensin-converting enzyme inhibitor, these devices may not function properly or be able to adequately bypass the obstruction. The oropharyngeal airway may be inserted by either of two procedures. One approach is to insert the airway in an inverted position along the patient’s hard palate (Fig. 3-5, step 2). When it is well into the patient’s mouth, rotate the airway 180 degrees and advance it to its final position along the patient’s tongue, with the distal end of the artificial airway lying in the hypopharynx (Fig. 3-5, step 3). A second approach is to open the mouth widely, use a tongue blade to displace the tongue, and then simply advance the artificial airway into the oropharynx (Fig. 3-5, step 4). No rotation is necessary when the airway is placed in this manner. This technique may be less traumatic, but it takes longer.



The nasopharyngeal airway is very easy to place. It may be easiest to place it on the patient’s right so that the bevel is facing the septum on insertion. Be sure to lubricate the device before insertion (Fig. 3-5, step 6). Some clinicians use a nasopharyngeal airway to dilate the nasal passages for 20 to 30 minutes before nasotracheal intubation. Simply advance it into the nostril and direct it along the floor of the nasal passage in the direction of the occiput, not cephalad (Fig. 3-5, step 7). Advance it fully until the flared external tip of the airway is located at the nasal orifice (Fig 3-5, step 8).


Both oropharyngeal and nasopharyngeal airways are available in multiple sizes. To find the correct size of either device, estimate its size by measuring along the side of the patient’s face before insertion. An oropharyngeal airway of the correct size will extend from the corner of the mouth to the tip of the earlobe (Fig. 3-5, step 1); a nasopharyngeal airway of the correct size will extend from the tip of the nose to the tip of the earlobe (Fig. 3-5, step 5).


Both oropharyngeal and nasopharyngeal airways provide airway patency similar to that achieved with the head-tilt/chin-lift maneuver. The nasal airway is better tolerated by semiconscious patients and is less likely to induce vomiting in those with an intact gag reflex.




Oxygen Therapy


Adequate O2 delivery depends on the inspired partial pressure of O2, alveolar ventilation, pulmonary gas exchange, oxygen-carrying capacity of blood, and cardiac output. The easiest factor to manipulate is the partial pressure of inspired O2, which is accomplished by increasing the fraction of inspired oxygen (Fio2) with supplemental O2.



Indications and Contraindications


Resuscitate all patients in cardiac or respiratory arrest with 100% O2. The most certain indication for supplemental O2 is the presence of arterial hypoxemia, defined as a Pao2 lower than 60 mm Hg or arterial oxygen saturation (Sao2) less than 90%.56 Normal subjects will begin to experience memory loss at an arterial oxygen partial pressure (Pao2) of 45 mm Hg, and loss of consciousness occurs at a Pao2 of 30 mm Hg.57–59 Chronically hypoxemic patients can adapt and function with a Pao2 of 50 mm Hg or lower.60


When tissue hypoxia is present or suspected, give O2 therapy.56,61 Shock states resulting from hemorrhage, vasodilatory states, low cardiac output, and obstructive lesions can all lead to tissue hypoxia and benefit from supplemental O2. Whatever the cause of the shock state, administration of O2 is indicated until the situation can be thoroughly evaluated and cause-specific therapy instituted.


Respiratory distress without documented arterial hypoxemia is a common indication for O2 administration, although no evidence exists to support this practice.62 Oxygen therapy is often recommended for acute myocardial infarction, but there is no difference in outcomes between patients receiving O2 and those receiving room air after myocardial infarction. The AHA has given a class I recommendation for O2 only in patients with hypoxemia, cyanosis, or respiratory distress.56,61,63–65


Although O2 is routinely administered to acute stroke patients, there is no convincing evidence that this practice is beneficial without documented hypoxia, and it is not recommended by current guidelines.66–68 It is reasonable to administer O2 to hypotensive patients and those with severe trauma until tissue hypoxia can definitively be excluded.62


Administer 100% O2 to patients with carbon monoxide poisoning. The half-life of carboxyhemoglobin is 4 to 5 hours in a subject breathing room air but can be decreased to approximately 1 hour by the administration of 100% O2 by non-rebreather face mask at atmospheric pressure.69


There are no contraindications to O2 therapy when a definite indication exists. The risks associated with hypoxemia are grave and undeniable. Never withhold oxygen therapy from a hypoxemic patient for fear of complications or clinical deterioration. Carbon dioxide retention is not a contraindication to O2 therapy. Rather, it demands that the clinician administer O2 carefully and recognize the potential for respiratory acidosis and clinical deterioration. Although the mechanism for the development of respiratory acidosis in patients with chronic obstructive pulmonary disease (COPD) who are administered O2 is debated, its occurrence is not.70,71 Use caution when administering supplemental O2 to hypoxic patients with arterial carbon dioxide pressure (Paco2) higher than 40 mm Hg, but do not withhold it.



Oxygen Administration during Cardiac Arrest and Neonatal Resuscitation


The 2010 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care4 address the potential harm of oxygen therapy and hyperoxemia following cardiac arrest and during neonatal resuscitation. Excerpts from this document are shown in Box 3-1. Although it is still prudent to administer oxygen in the prehospital and ED setting as discussed earlier, additional research may alter current recommendations. See also “Complications of Oxygen Therapy” in this chapter. As a general guideline, fear of oxygen toxicity should not prevent the use of O2 when there is an indication but should encourage the clinician to use the minimum concentration of O2 necessary to achieve the therapeutic goals.



Box 3-1   Potential Adverse Effects of Oxygen Administration during Adult and Neonate Resuscitation


Excerpts from the 2010 Guidelines of the American Heart Association



Overview of Post-Cardiac Arrest Care and the Use of Supplemental Oxygen


Although 100% oxygen may have been used during initial resuscitation, providers should titrate inspired oxygen to the lowest level required to achieve an arterial oxygen saturation of ≥94%, so as to avoid potential oxygen toxicity. It is recognized that titration of inspired oxygen may not be possible immediately after out-of-hospital cardiac arrest until the patient is transported to the emergency department or, in the case of in-hospital arrest, the intensive care unit (ICU). The optimal FIO2 during the immediate period after cardiac arrest is still debated. The beneficial effect of high FIO2 on systemic oxygen delivery should be balanced with the deleterious effect of generating oxygen-derived free radicals during the reperfusion phase. Animal data suggests that ventilations with 100% oxygen (generating PaO2 > 350 mm Hg at 15 to 60 minutes after ROSC) increase brain lipid peroxidation, increase metabolic dysfunctions, increase neurological degeneration, and worsen short-term functional outcome when compared with ventilation with room air or an inspired oxygen fraction titrated to a pulse oximeter reading between 94% and 96%.82–87* One randomized prospective clinical trial compared ventilation for the first 60 minutes after ROSC with 30% oxygen (resulting in PaO2 = 110 ± 25 mm Hg at 60 minutes) or 100% oxygen (resulting in PaO2 = 345 ± 174 mm Hg at 60 minutes).88* This small trial detected no difference in serial markers of acute brain injury, survival to hospital discharge, or percentage of patients with good neurological outcome at hospital discharge but was inadequately powered to detect important differences in survival or neurological outcome.


Once the circulation is restored, monitor systemic arterial oxyhemoglobin saturation. It may be reasonable, when the appropriate equipment is available, to titrate oxygen administration to maintain the arterial oxyhemoglobin saturation ≥94%. Provided appropriate equipment is available, once ROSC is achieved, adjust the FIO2 to the minimum concentration needed to achieve arterial oxyhemoglobin saturation ≥94%, with the goal of avoiding hyperoxia while ensuring adequate oxygen delivery. Since an arterial oxyhemoglobin saturation of 100% may correspond to a PaO2 anywhere between ~80 and 500 mm Hg, in general it is appropriate to wean FIO2 when saturation is 100%, provided the oxyhemoglobin saturation can be maintained ≥94% (Class I, LOE C)



Assessment of Oxygen Need and Administration of Oxygen in the Neonate


There is a large body of evidence that blood oxygen levels in uncompromised babies generally do not reach extrauterine values until approximately 10 minutes following birth. Oxyhemoglobin saturation may normally remain in the 70% to 80% range for several minutes following birth, thus resulting in the appearance of cyanosis during that time. Other studies have shown that clinical assessment of skin color is a very poor indicator of oxyhemoglobin saturation during the immediate neonatal period and that lack of cyanosis appears to be a very poor indicator of the state of oxygenation of an uncompromised baby following birth.


Optimal management of oxygen during neonatal resuscitation becomes particularly important because of the evidence that either insufficient or excessive oxygenation can be harmful to the newborn infant. Hypoxia and ischemia are known to result in injury to multiple organs. Conversely there is growing experimental evidence, as well as evidence from studies of babies receiving resuscitation, that adverse outcomes may result from even brief exposure to excessive oxygen during and following resuscitation.



Administration of Supplementary Oxygen in Neonatal Resuscitation


Two meta-analyses of several randomized controlled trials comparing neonatal resuscitation initiated with room air versus 100% oxygen showed increased survival when resuscitation was initiated with air.44,45† There are no studies in term infants comparing outcomes when resuscitations are initiated with different concentrations of oxygen other than 100% or room air. One study in preterm infants showed that initiation of resuscitation with a blend of oxygen and air resulted in less hypoxemia or hyperoxemia, as defined by the investigators, than when resuscitation was initiated with either air or 100% oxygen followed by titration with an adjustable blend of air and oxygen.46†


In the absence of studies comparing outcomes of neonatal resuscitation initiated with other oxygen concentrations or targeted at various oxyhemoglobin saturations, it is recommended that the goal in babies being resuscitated at birth, whether born at term or preterm, should be an oxygen saturation value in the interquartile range of preductal saturations measured in healthy term babies following vaginal birth at sea level (Class IIb, LOE B). These targets may be achieved by initiating resuscitation with air or a blended oxygen and titrating the oxygen concentration to achieve an SpO2 in the target range as described above using pulse oximetry (Class IIb, LOE C). If blended oxygen is not available, resuscitation should be initiated with air (Class IIb, LOE B). If the baby is bradycardic (HR <60 per minute) after 90 seconds of resuscitation with a lower concentration of oxygen, oxygen concentration should be increased to 100% until recovery of a normal heart rate (Class IIb, LOE B).



*Citations 82-88 are from Peberdy MA, Callaway CW, Neumar RW, et al. Part 9: post-cardiac arrest care: 2010 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care. Circulation. 2010;122(18 suppl):S768. Available at http://circ.ahajournals.org/content/122/18_suppl_3.toc. Accessed November 3, 2012.


†Citations 44-46 are from Kattwinkel, J, Perlman JM, Aziz, K, et al. Part 15: neonatal resuscitation: 2010 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care. Circulation. 2010;122(18 suppl):S909. Available at http://circ.ahajournals.org/content/122/18_suppl_3.toc. Accessed November 3, 2012.



Oxygen Delivery Devices


High-flow delivery systems provide an Fio2 that is relatively constant despite changes in the patient’s respiratory pattern. The Venturi mask is the high-flow delivery device that is most widely available (Fig. 3-6). Room air is entrained into the system through entrainment ports and mixes with the O2 provided from the O2 source. The proportion of entrained air—and therefore Fio2—is constant and determined by the velocity of the O2 jet and the size of the entrainment ports. Because the total gas flow (O2 plus air through the entrainment ports) meets or exceeds the patient’s inspiratory flow rate, no additional entrainment of air occurs around the mask, thereby minimizing changes in Fio2 as the patient’s respiratory pattern changes.72,73 The mask is continuously flushed by the high flow of gas, which prevents the accumulation of exhaled gas in the mask. Venturi masks are packaged with multiple inserts, each with a different size orifice for O2 inflow. Fio2 is determined by selecting the appropriate colored insert and O2 flow rate according to the manufacturer’s instructions. The inspiratory flow rate for a resting adult is about 30 L/min, a rate matched by the total gas flow provided by the Venturi mask at all settings. A patient in respiratory distress may have an inspiratory flow rate of 50 to 100 L/min.73 If the inspiratory flow rate exceeds the total gas flow delivered by the mask, additional air will be entrained around the mask, and Fio2 will decrease. Masks with higher Fio2 ratings entrain less outside air and therefore provide less total flow. Caution should be used with masks rated above 35% in patients with respiratory distress because Fio2 may be significantly reduced with high inspiratory flow rates.



Low-flow delivery devices provide gas flow that is less than the patient’s inspiratory flow rate. The difference between the patient’s inspiratory flow and the flow delivered by the device is met by a variable amount of room air being drawn into the system. Patients with normal respiratory rates and tidal volumes will require less outside air than those in respiratory distress, who typically receive a higher Fio2. As a patient’s inspiratory flow changes, so will the Fio2 that they receive from a low-flow device.72,73


The prongs of a nasal cannula deliver a constant flow of O2 that accumulates in the nasopharynx and provides a reservoir of oxygen-enriched air for inspiration. The Fio2 delivered by nasal cannulas is determined by many factors, including the respiratory rate, tidal volume, pharyngeal geometry, and O2 flow. Most importantly, at a constant O2 flow rate, Fio2 varies inversely with the respiratory rate. Despite this limitation, nasal cannulas are very comfortable for patients and are the most common low-flow O2 delivery device. Although it may seem intuitive, patients using a nasal cannula should be reminded that they should not smoke while oxygen is being delivered (Fig. 3-7).



Simple masks receive a constant flow of O2 from the O2 source and have multiple vent holes. During inspiration, the oxygen-enriched air that has accumulated in the mask, along with room air entrained through the vent holes, is inhaled. During expiration, 200 mL (the approximate volume of the mask) of exhaled gas is deposited in the mask with the rest exiting through the vent holes. The continuous flow of O2 then partially washes out the mask before the next inspiration. The mask itself provides the reservoir of oxygen-rich gas for inhalation. A complex interplay between mask volume, tidal volume, respiratory rate, and O2 flow determines the Fio2 delivered to the patient.


A partial rebreathing mask incorporates a bag-type reservoir to increase the amount of O2 available during inspiration, thereby requiring less outside air to be entrained. Non-rebreathing masks are similar to partial rebreathing masks but have a series of one-way valves. One valve lies between the mask and the reservoir and prevents exhaled gas from entering the reservoir. Two valves in the side of the mask permit exhalation while preventing the entry of outside air. In practice, one of these valves is often removed to permit inhalation in the event of interruption of flow of O2 to the mask. A variable amount of air can still leak around the mask. This outside air and the exhaled gas remaining in the mask dilute the O2 from the reservoir and prevent the mask from providing 100% O2. Oxygen flow to the mask should be sufficient to prevent collapse of the bag during inspiration. As with all low-flow devices, the Fio2 delivered varies with the patient’s respiratory pattern. Many clinicians have the misconception that a non-rebreathing mask can provide an Fio2 near 100%. In practice, a non-rebreathing mask usually delivers an Fio2 of about 70%.



Procedure


In selecting the proper delivery device, consider the clinical condition of the patient and the amount of O2 needed. High-flow systems should generally be used for patients who need precise control of Fio2, such as COPD patients with chronic respiratory acidosis. Low-flow masks are appropriate for patients who need supplemental O2 but do not require precise control of Fio2. Nasal cannulas are traditionally used in patients who do not require a high Fio2 and will not be harmed by the lack of precise control. An oxygen flow rate of 1 to 3 L/min by nasal cannula will result in an Fio2 of 23% to 35%. Patients with significant hypoxemia, end-organ dysfunction, or respiratory distress require a higher Fio2 delivery system.


An initial Fio2 of 24% to 28% delivered by Venturi mask is indicated for patients with hypoxemia and chronic respiratory acidosis.62,70


Frequent clinical assessment and Spo2 monitoring are needed in all patients receiving O2 therapy. Periodic blood gas analysis or capnography is imperative for those at risk for respiratory acidosis.74–76 Equilibration of Sao2 after changes in supplemental O2 occurs within 5 minutes.77


Fio2 should be titrated to achieve therapeutic goals while minimizing the risk for complications. An Sao2 of 90% to 95% (Pao2 ≈ 60 to 80 mm Hg) is an appropriate target for most patients receiving supplemental O2.62 Increases above these levels do not add appreciably to the O2 content of blood and are unlikely to confer an additional benefit. One may exceed these parameters in patients with shock and end-organ dysfunction, but the added risk and small potential benefit should be considered on an individual basis. In patients with COPD-associated hypercapnia, an Sao2 of 90% (Pao2 ≈ 60 mm Hg) should be the goal of O2 therapy.74–76 Mechanical ventilation should be considered when oxygenation goals cannot be achieved without progressive respiratory acidosis.



Preoxygenation for Rapid-Sequence Intubation


Preoxygenation is one of the most important aspects of emergency airway management. Preoxygenation before rapid-sequence intubation (RSI) provides much more time for intubation before desaturation occurs and thus significantly increases the chance of successful intubation on the first attempt. Failure to preoxygenate before RSI is often a critical factor when a straightforward emergency airway becomes an airway disaster. Preoxygenation is usually accomplished by providing the maximal Fio2 with a non-rebreather mask for 3 to 5 minutes before intubation. Alternatively, eight vital capacity breaths from a maximal Fio2 system, such as a non-rebreather mask or a bag-valve-mask device, is acceptable when there is no time for standard preoxygenation.78 When using a bag-valve-mask device for preoxygenation, it is important that the exhalation port have a one-way valve so that room air is not drawn into the mask when the patient inhales.


The purpose of preoxygenation is not just to maximize oxygen saturation but to wash out nitrogen from the patient’s lungs and replace it with oxygen. This provides the maximum safe apneic time during RSI. Those at greatest risk for rapid desaturation include obese, pregnant, critically ill, and pediatric patients, and they will benefit the most from good preoxygenation. Most studies addressing preoxygenation have been conducted under ideal conditions in relatively healthy individuals. It is far more challenging to effectively preoxygenate critically ill patients.79


Morbidly obese patients are best preoxygenated in a 25-degree head-up position because significantly higher oxygen tension can be achieved in this position.80 Patients who are hypoxic despite maximal oxygen delivery have been shown to benefit from 3 minutes of NPPV (with 100% O2) just before intubation.81,82


Sometimes patients who need preoxygenation the most are uncooperative with a face mask because of delirium from hypoxia, hypercapnia, or other factors. These patients may benefit from delayed-sequence intubation—careful sedation without blunting of respirations to allow oxygenation with a face mask or NPPV for 2 to 3 minutes before administering a paralytic agent.82 Ketamine (1 to 1.5 mg/kg by slow intravenous push) has been suggested for this technique. Delayed-sequence intubation is a practical way to deal with a difficult problem, but it has not been well studied, and providers using this method should be prepared for clinical deterioration, hypoventilation, or apnea.



Oxygen Therapy during Apnea


Another method to delay desaturation during RSI is nasopharyngeal oxygen insufflation during apnea. Many studies have shown that providing oxygen therapy during apnea is much more beneficial than one might imagine.83–86 During apnea, oxygen continues to be absorbed through the alveoli, and air with a low oxygen concentration is left in the lower airways. Supplying oxygen to the nasopharynx during apnea allows air with a higher oxygen concentration to passively replenish oxygen in the alveoli. Multiple studies, in normal and morbidly obese patients, have shown that nasopharyngeal oxygen insufflation results in a significant delay in desaturation after the onset of apnea.83,86,87 In these studies, nasopharyngeal oxygen insufflation was accomplished by inserting a 10-Fr catheter into the nasopharynx to a distance equal to the distance from the mouth to the tragus of the ear and delivering oxygen at a flow rate of 5 L/min when apnea occurred.83 Using a standard nasal cannula with a nasopharyngeal airway is simpler and would probably provide the same benefit. Also, it is important to keep the upper airway open by using a jaw thrust or artificial airway for this technique to be most beneficial.



Nasal High-Flow Oxygen


High-flow nasal oxygen is a relatively new concept that may have some utility for optimizing oxygenation in critically ill children and adults.88 At lower flow rates, Fio2 is somewhat dependent on the patient’s respiratory rate, but at very high flow rates, Fio2 is consistently very high. In one study, the Fio2 delivered by nasal cannula ranged from about 25% at 1 L/min to 70% to 80% at 15 L/min.89 Commercially available humidified high-flow nasal cannula (HHFNC) systems use flow rates of 5 to 40 L/min and deliver an Fio2 of close to 100%. High-flow oxygen by nasal cannula is not well tolerated unless it is humidified, so commercially available systems (Vapotherm 2000i, Fisher and Paykel Nasal High Flow, AquinOx) deliver oxygen with nearly 100% humidity. HHFNC devices are popular in neonatal and pediatric intensive care units and are commonly used for respiratory support after extubation and for management of respiratory disease.90,91 Some evidence suggests that high-flow nasal oxygen may provide low-grade CPAP.92,93 Several adult studies have shown that high-flow nasal oxygen systems are well tolerated and deliver a higher Fio2 than a high-flow mask in patients with respiratory failure or simulated respiratory failure.94–96



Complications of Oxygen Therapy


Worsening of CO2 retention leading to progressive respiratory acidosis and obtundation in patients with COPD is the complication most likely to be seen in the ED. This phenomenon is well documented and was first described by Barach in 1937.97 It has been attributed to several mechanisms, including loss of hypoxic respiratory drive, ventilation-perfusion (image) mismatch, and decreased hemoglobin affinity for CO2 (Haldane effect). This avoidable complication is best prevented by administering O2 to chronic CO2 retainers only when there is an indication, administering it at the smallest effective dose, and carefully monitoring clinical, capnographic, and arterial blood gas parameters.


Exposing the brain and lung to excessive concentrations of O2 can lead to toxicity and, in severe cases, can cause acute respiratory distress syndrome. Injury to the pulmonary parenchyma occurs as a result of the formation of reactive oxygen species. Oxygen toxicity is of special concern in premature neonates, in whom prolonged hyperoxemia can lead to retinopathy. No data describe what concentration or duration of exposure to O2 leads to toxicity, but presumably both these factors and individual patient characteristics determine the likelihood of toxicity. The benefits of O2 therapy in the ED usually outweigh the risk for O2 toxicity. Fear of toxicity should not prevent the use of O2 when there is an indication but should encourage the clinician to use the minimum concentration of O2 necessary to achieve therapeutic goals. High concentrations of O2 are well tolerated over short periods and may be lifesaving.


In patients receiving high concentrations of supplemental O2, nitrogen in the alveoli is largely replaced by O2. If this O2 is then absorbed into the blood faster than it can be replaced, the volume of the alveoli will decrease and absorptive atelectasis can occur. Airway obstruction potentiates this problem by preventing the rapid replacement of absorbed gas.



Bag-Mask Ventilation



BMV is the single most important technique for emergency airway management.1,19,98 Bag-mask devices are widely available and are standard equipment in all patient care settings. Although the bag-mask method of ventilation appears to be simple, it can be difficult to perform correctly. Having good BMV skills is a prerequisite to more advanced methods of emergency airway management.1 Manually opening the airway, properly positioning the head and neck, placing an oropharyngeal airway device, and achieving a tight face mask seal are the keys to good BMV.



Indications and Contraindications


BMV is the most common initial technique for ventilation of apneic patients and for rescue ventilation after failed intubation.1,2 Many authors note that BMV is relatively contraindicated in patients with a full stomach, those in cardiac arrest, and those undergoing RSI.2,3 These patients have a high risk for stomach inflation and subsequent aspiration. Unfortunately, these are the patients for whom ED providers most commonly use BMV. In ED situations, the need for ventilation and oxygenation always takes priority over potential aspiration.2


The only contraindication to attempting BMV is when application of a face mask is impossible. It is often impossible to achieve an effective face mask seal on patients with significant deforming facial trauma and those with thick beards. An intermediate ventilation device, such as an LMA, is a better choice for initial ventilation in such patients.

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Sep 6, 2016 | Posted by in EMERGENCY MEDICINE | Comments Off on Basic Airway Management and Decision Making

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