Airway Management of Respiratory Failure

Patients in respiratory distress often require airway management, including endotracheal intubation. It takes a methodical approach to transition from an unstable patient in distress with an unsecured airway, to a stable, sedated patient with a definitive airway. Through a deliberate course of advanced preparation, the emergency physician can tailor the approach to the individual clinical situation and optimize the chance of first-pass success. Sedation of the intubated patient confers physiologic benefits and should be included in the plan for airway control.

Key points

  • The decision to intubate a patient in respiratory distress is based on the physician’s judgment as to whether the patient can maintain the airway, if ventilation and oxygenation are inadequate, and consideration of the expected clinical course.

  • A careful evaluation of the patient’s suitability to undergo the intubation process should occur before administration of sedative and neuromuscular blocking agents.

  • Several distinct steps are followed in safely transitioning the awake, often unstable patient in need of an airway, to a sedated, stable patient with a secure airway.

  • The key action in management of the airway is anticipation. Physicians should consider the barriers to airway control in advance, and be facile with the many techniques and technologies to rescue the airway should an unforeseen challenge arise.

Video showing Demonstration of the reduction in anatomic deadspace with high flow nasal oxygen accompanies this article at


Diseases of the respiratory system are the reason for 1 in 10 emergency department visits, second only to injury and poisoning. Further, nonrespiratory diagnoses, including overdose, cerebrovascular accident, shock, trauma, altered mental status, or upper airway compromise, may result in significant airway compromise or gas exchange derangements that require advanced airway management. Although the proportion of these patients who require active airway management is unknown, this subset requires disproportionately more resources, skill, and expertise to correct a deteriorating course.


Diseases of the respiratory system are the reason for 1 in 10 emergency department visits, second only to injury and poisoning. Further, nonrespiratory diagnoses, including overdose, cerebrovascular accident, shock, trauma, altered mental status, or upper airway compromise, may result in significant airway compromise or gas exchange derangements that require advanced airway management. Although the proportion of these patients who require active airway management is unknown, this subset requires disproportionately more resources, skill, and expertise to correct a deteriorating course.

The decision to intubate

Patients in respiratory distress may describe heaviness, tightness, or squeezing sensation in the chest, or simply dyspnea at rest. Clinical signs of respiratory distress include tachypnea, accessory muscle use, intercostal retractions, paradoxic abdominal muscle use, wheezing, diaphoresis, tachy-dysrhythmias or brady-dysrhythmias, altered mental status, and hypoxia. Progression from respiratory distress to respiratory failure can evolve over minutes, and is characterized by the patient’s inability to accomplish adequate gas exchange to maintain oxygenation and carbon dioxide elimination. That notwithstanding, there are likely no precise blood gas parameters that define the moment of intervention in respiratory failure. The decision to secure the airway in respiratory distress is rooted in 3 basic clinical questions :

  • 1.

    Is the patient able to maintain the airway?

  • 2.

    Is ventilation or oxygenation inadequate?

  • 3.

    What is the anticipated clinical course?

Is the Patient Able to Maintain the Airway?

What tools does the emergency physician have to evaluate the patient’s ability to protect the airway? Several options exist, although none seem to provide clear answers as to when intervention is warranted. The Glasgow Coma Scale (GCS) is a time-honored, reproducible tool that does afford some guidance with extreme scores. The loss of the patient’s gag reflex has been promoted as another indicator for the need to secure the airway. Despite the intellectual attractiveness of this notion, the presence or absence of the gag reflex has little to do with important outcomes, like aspiration pneumonia.

Since its introduction by Teasdale and Jennette in 1974, the GCS has been widely used for prognostication in patients with altered mental status. It allows a quick assessment of altered patients and demonstrates good interrater reliability. Increasingly, it is widely used throughout a range of pathology to promote consistent communication across specialties, standardize observations, and suggest anticipated clinical course. In the setting of trauma, a GCS of 8 or lower signifies coma. Eizadi-Mood et al demonstrated aspiration pneumonitis was more likely in patients with low GCS (<6) in a population of poisoned patients undergoing gastric lavage. It is widely accepted that comatose patients are unable to maintain their airway and need definitive airway management.

But is a low GCS specifically reliable enough to guide the emergency physician in the decision to intubate? Rotheray and colleagues, studied a Chinese population without predominance of intoxicants or trauma, and demonstrated a wide response of airway reflexes throughout a range of GCS scores, suggesting that patients with altered mental status have significant risk of airway complications even with moderate or high GCS scores .

In considering whether to intervene, should the emergency physician be reassured by an intact gag reflex? Maybe not. In 111 patients presenting with altered mental status, Moulton and colleagues found absent gag reflexes at all GCS scores. The investigators emphasized that an absent gag reflex is a poor indicator of the need to intervene to prevent aspiration injury (ie, intubation), but should raise concern for “at-risk” airways.

In aggregate, the answer to the question, “Can this patient maintain the airway?” is not so straightforward. The emergency physician should be aware of the limitations of any single aspect of a patient’s presentation. The ultimate answer to this first question will be informed by a careful evaluation of GCS, an assessment of the patient’s gag reflex, and consideration of the entire clinical picture.

Is Ventilation or Oxygenation Inadequate?

The emergency physician is expected to recognize dangerous scenarios and intervene to reverse the downward spiral with strategies that often involve positive-pressure ventilation. For example, congestive heart failure worsens with pulmonary edema, anxiety, work of breathing, and hypoxia, and devolves into demand ischemia, catecholamine surge, hypertension, increased myocardial oxygen demand, and progressively poorer cardiac performance, ultimately resulting in circulatory arrest. Similarly, the dyspnea in bronchospasm (as in asthma) results in anxiety, increased work of breathing with concomitant worsening air trapping, ineffective alveolar ventilation, and hypercarbia with hypoxia, ultimately ending in fatigue and hypoventilatory cardiorespiratory arrest. In these scenarios, earlier intervention is favored while the patient can still tolerate hypoxia, acid-base disturbances, and hemodynamic instability, which often accompany the significant physiologic hurdle that is rapid sequence intubation (RSI).

What Is the Anticipated Clinical Course?

Emergency physicians may not be pressed to intubate a patient for airway protection or optimization of pulmonary function, but may consider intubation given what lies ahead. For example, a patient with altered mental status after a fall from height may have no trouble with airway protection, oxygenation, or ventilation. But this patient may not cooperate with c-spine protection, or have a need to travel away from the emergency department for long periods of time, or possibly require sedation for painful procedures. For any of these reasons, definitive airway management should strongly be considered. Similarly, specific disease entities that threaten the upper airway, such as trauma to the chest or neck (eg, expanding neck hematoma), infectious processes involving the oropharyngeal structures (eg, Ludwig angina), or late-developing airway compromise (eg, smoke inhalation), warrant contemplation of early airway intervention.

What Is the Role of Arterial Blood Gas Values in the Decision to Intubate?

Although the emergency provider may find it alluring to obtain arterial blood gas (ABG) measurements to inform the decision of whether or not to intubate, it is a temptation to be resisted. Oxygenation (S a O 2 ) can often be reliably obtained with pulse oximetry (S p O 2 ) and even in hypoxic or shock states, oximetry remains clinically accurate. Similarly, end-tidal carbon dioxide (P ET CO 2 ) can be used as a noninvasive tool to evaluate arterial carbon dioxide (P a co 2 ) with good correlation. Further, continuous capnography can produce waveform morphologies that can shine light on the underlying pathology (eg, bronchospasm), as well as trend impact of interventions (eg, noninvasive ventilation).

If obtained, the emergency physician must be cautious regarding apparently reassuring ABG values. These values are simply a snapshot of the patient’s physiologic condition, and cannot reflect dynamic improvement or deterioration like other bedside data. For example, poor air movement, fatigue, and worsening hypoxia mandate an escalation of efforts despite recent reassuring ABG values. Similarly, improved respiratory mechanics, less anxiety, and stabilizing S p O 2 values indicate the success of interventions regardless of ABG values. In conclusion, despite the appeal of ABG values, the patient is better served by considering the entirety of the clinical picture in the decision to proceed with intubation.

Importance of first-pass success

After the decision to intubate is made, the priority in adults is to optimize the chances to place a cuffed endotracheal tube through the vocal cords on the first attempt. That is, focus on first-pass success.

That first-pass success is associated with fewer adverse events is axiomatic. Adverse events in the peri-intubation period are defined in Table 1 . An overall adverse event rate of 11% to 15% is reported, meaning that the emergency physician should expect complications in the peri-intubation period once in every 8 patients. Sakles and colleagues noted that the adverse event rate triples when more than one attempt is needed (1 attempt: 14.2% vs >1 attempt: 53.1%). A similar relationship was noted by Hasegawa and colleagues. This should inform the mindset as preparations are made to intubate the emergency patient.

Table 1

Definitions of adverse events during intubation

Adverse Event Definition
Oxygen desaturation a Decrease in oxygen saturation ≥10% or <90%
Esophageal intubation Improper placement of ETT in esophagus, reintubation required
Mainstem intubation Radiographic identification of the tip of the ETT in a mainstem bronchus
Hypotension Decrease in systolic blood pressure <90 mm Hg, unexplained by ongoing disease process or trauma
Aspiration Presence of vomit at the glottis inlet visualized during intubation in a previously clear airway
Cardiac arrest Pulseless dysrhythmia occurring during intubation
Cuff leak Air leak around a cuffed ETT, controlled reintubation may be required
Accidental extubation Accidental removal of endotracheal tube, immediate reintubation required
Laryngospasm Adduction of the vocal cords preventing passage of the ETT through the glottis inlet
Dental trauma Fracture or avulsion of a tooth during laryngoscopy
Dysrhythmia b Bradycardia or any ventricular dysrhythmia
Pneumothorax Radiographic identification of air in the pleural space, unexplained by ongoing disease process or trauma

In descending order of occurrence, based on frequency reported in Walls et al.

Abbreviation: ETT, endotracheal tube.

Adapted from Sakles JC, Chiu S, Mosier J, et al. The importance of first pass success when performing orotracheal intubation in the emergency department. Acad Emerg Med 2013;20:73; with permission.

a Various investigators define desaturation differently, and was not originally reported in Walls et al.

b Tachycardia is not considered an adverse event.

To ensure first-pass success, a careful evaluation must be undertaken to establish the patient’s suitability for RSI. In some cases, RSI may not be the most appropriate technique to secure the airway. For example, if the physician anticipates a difficult airway and has both time and a cooperative patient, awake intubation may be pursued. On the other hand, in case of respiratory arrest, the patient may not need or tolerate RSI, and a crash airway is undertaken. But there is a broad expanse of patients between those extremes that require intervention to transition rapidly and safely to a controlled airway. It is this patient population that benefits from an expeditious and competent march through the process culminating in a safely intubated patient. Careful preintubation evaluation and a well-conceived plan for securing the airway are the key elements in the management of patients who require intubation.

What Can Be Done to Improve Success When Securing the Airway?

Anticipation of the any difficulty ahead is the first priority. The typical patient requiring emergent airway intervention is physiologically marginalized. Once the physician administers sedative and paralytic agents, the risks to the patient increase. As protective airway reflexes are taken away, can the patient be readily intubated? When the patient’s respiratory drive is suppressed, can the patient be ventilated using bag-mask ventilation (BMV)? If the patient cannot be intubated, can an extraglottic device (EGD) be placed to provide airway protection and oxygenation temporarily? If the patient cannot be intubated and cannot be oxygenated (ie, a “CICO” situation), can the physician provide a surgical airway to rescue the patient? It is wise then to evaluate the patient in light of these questions so as to anticipate difficulties before they arise?

Evaluation of Airway Difficulty

Some may consider evaluating the patient and simply assigning a Mallampati score for quick airway assessment before RSI, but this is likely not sufficient. An association between an increased Mallampati score and airway obstruction, limited mobility, or difficult intubation has not been established. A systematic review of published literature found the sensitivity and specificity of the isolated Mallampati score to be inadequate for reliably predicting a difficult airway.

The “LEMON” mnemonic emphasizes a systematic evaluation of patient characteristics that improve the physician’s ability to predict difficult laryngoscopy and intubate with success. Elements of the prediction tool are illustrated in Fig. 1 and include Look at the external features to form an impression of the difficulty; evaluate the anatomy of the airway using the 3-3-2 rule; assign a Mallampati score to the view of the posterior pharynx; identify airway obstruction , and degree of neck mobility. Identifying at least one difficult airway criterion predicts adverse events in 1 of every 4 intubations. Overall, utilization of tools, like the LEMON mnemonic, may encourage a more detailed presedation evaluation of the airway and identify barriers to successful airway management before problems arise.

Fig. 1

LEMON mnemonic for airway assessment.

( From Reed MJ, Dunn MJ, McKeown DW. Can an airway assessment score predict difficulty at intubation in the emergency department? Emerg Med J 22(2):100; with permission.)

Evaluation of Difficulty in Ventilating with Bag-Mask Ventilation

Evaluation of the patient appropriateness for bag-mask ventilation (BMV) is the next important consideration before undertaking RSI. Frequently, BMV is the rescue strategy after a failed intubation attempt. Not only is it critical for the emergency provider to master this skill, but also to ensure any assistants are skilled in the technique as well. Several patient characteristics can impede effective BMV and should be sought as part of a routine preparation for definitive airway management. In an observational study of nearly half a million adult patients undergoing general anesthesia, Kheterpal and colleagues demonstrated 13 patient characteristics that predict difficulty in BMV ventilation and direct laryngoscopy. “MOANS” is a simplified mnemonic that incorporates many predictive patient characteristics. The MOANS tool has been promoted to help identify patients likely to be difficult ventilate via BMV techniques ( Table 2 ).

Table 2

The MOANS mnemonic to evaluate ease of BMV

MOANS Element Description
Mask seal/Mallampati Higher Mallampati (>2) should raise suspicion of difficulty in BMV
Facial hair can jeopardize the mask seal and can be overcome by applying water-soluble gel to the patient’s beard.
Obesity Defined as BMI >30 kg/m 2 and correlates with difficulty in BMV.
Age a With advanced age (>46 y old), the inferior pharyngeal sphincter muscles weaken and allow air to pass into the stomach during aggressive BMV attempts.
No teeth Adequate seal is difficult when the patient is edentulous. Dentures should remain in place to support the facial tissues and maintain the oropharyngeal geometry.
Snoring Laxity and redundancy of upper airway tissues leads to snoring and can hamper attempts at BMV. Elicit the history from patient or family before induction.

The MOANS mnemonic is described by Walls and Murphy and incorporates many of the elements described by Kheterpal et al.

Abbreviations: BMI, body mass index; BMV, bag mask ventilation.

a Walls et al report the age cutoff to be >49.

Technique of Bag-Mask Ventilation

Delivering slow, deliberate breaths to minimize insufflation of the stomach cannot be overemphasized. Slow flow rates minimize gastric insufflation, reducing risk of vomiting. Often, in an effort to maximize ventilation, the well-intentioned assistant delivers BMV with rapid, staccatolike action. Given that the correct approach in adults emphasizes a slow positive-pressure breath delivered over 2 seconds, a single respiratory cycle can last 5 seconds or more, making the maximum respiratory rate 12 to 15 breaths per minute.

Improvement in the effectiveness ventilation while bagging is typically accomplished through better positioning. Aligning the oral tracheal axis to effect a “sniffing position” is often achieved with a slight chin lift or a pad behind the shoulders. Consideration should be given to placement of an oral or nasopharyngeal airway to keep the posterior pharynx patent. The jaw thrust maneuver is a well-recognized technique to provide airway patency when a second person is trained in the technique.

Evaluation of Suitability for Extraglottic Device

The spirit of anticipating airway management difficulties has generated a mnemonic for evaluating the suitability of extraglottic devices (EGDs) as alternative techniques for establishing an airway. Briefly “RODS” represents 4 factors that may influence ease of EGD use: Restricted mouth opening, preventing introduction of the EGD; Obstruction or Obesity may lead to inability to properly seat the device for an adequate seal (especially a laryngeal mask airway); Disrupted or Distorted airway, may prevent adequate seal, as in cases of epiglottitis, hematoma, or malignancy; and Stiff , refers to anatomy requiring inspiratory pressures that may exceed the seal pressure. It is important to remember that the RODS screening aid is based on expert opinion and the presence of one or more of the criteria would not necessarily prevent the use of an EGD.

Evaluation of Difficulty in Performing Cricothyrotomy

Surgical cricothyrotomy is rare, with a frequency of 2 in 1000 airways requiring it as an initial method of airway management, rising to 6 in 1000 airways when performed as a rescue alternative to RSI in civilian and military populations. This infrequent exposure to cricothyrotomy as a definitive technique can lead to unfamiliarity and indecision. Although this may be understandable given the rarity of task performance and prevalence of improved rescue airway adjuncts (eg, EGDs), hesitation and deliberation can be fatal. For these reasons, emergency physicians must give some advance thought to surgical airway management before a patient deteriorates to the point of requiring one.

Experts have devised a systematic way to evaluate for anticipated difficulty in establishing a surgical airway. Consideration should be given to any recent Surgery , whereby the anatomy is distorted; presence of a Mass , such as a hematoma that may conceal landmarks; impaired Access , which may result from obesity, restricted movement, or external fixation; changes from previous Radiation may similarly distort landmarks; and airway Tumors may present challenges from identification of landmarks, to passage of the tube, to bleeding complications. Thus, the “SMART” mnemonic will remind practitioners of patient attributes that can complicate cricothyrotomy, and should be considered in advance of the need to act.

The process of rapid sequence intubation

After assessment of the patient’s need for an airway and evaluation of expected difficulties, the technique of RSI is most often used to provide ideal intubating conditions in most patients. In preparation for RSI, 7 distinct steps are recognized, from preparation through intubation and on to postintubation care, known as the “Seven Ps of RSI” ( Table 3 ).

Table 3

The 7 P’s of rapid-sequence intubation

Time Course Step Details
−10 min Preparation Assemble team, equipment, medications, monitors
−8 min Preoxygenation Maximize oxygen saturation and stores to maximize apnea time
−3 min Pretreatment Administer medications to provide smooth transition through RSI
Time = 0 Paralysis with induction Sedative and paralytic medications administered in rapid sequence to provide optimal intubating conditions
+15–30 s Positioning Ready patient for optimal laryngoscopy
+45 s Pass the tube with verification Intubate the airway and prove correct ETT placement with adjuncts
+90 s Postintubation care Prompt titration of sedation, close monitoring for arrhythmias and hypotension, chest radiography

Abbreviations: ETT, endotracheal tube; RSI, rapid-sequence intubation.

From Walls RM. Rapid sequence intubation. In: Walls RM, Murphy MF, editors. Manual of emergency airway management. 4th edition. Philadelphia: Lippincott Williams and Wilkins; 2012. p. 228; with permission.


After the assessment of the patient’s airway and suitability for RSI, prepare the patient, the equipment, and the team. Ensure the patient is monitored with pulse oximetry, 3-lead electrocardiogram rhythm, and blood pressure by using a noninvasive cuff cycling frequently. P ET CO 2 should be monitored and should be readily available after the endotracheal tube (ETT) is placed. Intravenous access should be reliable with 2 peripheral intravenous (IV) lines. In all but a few select cases (congestive heart failure), a fluid bolus will support the patient through the hemodynamic changes associated with intubation.

Equipment should be reviewed for availability and function. Video laryngoscopy picture and power source should be verified. Direct laryngoscope handles with an assortment of blade sizes and shapes (eg, Mac and Miller) should be checked for function . And ETT should be tested for balloon integrity and fitted with a stylet, with an additional smaller ETT (eg, 0.5 mm smaller internal diameter) within reach if a difficult airway is anticipated. It is prudent to have airway rescue devices close at hand (eg, laryngeal mask airway, gum-elastic bougie, and esophageal tracheal tube). The physician should also confirm suction is nearby and functioning.

Team preparation includes assembling appropriate nurses, respiratory therapists, and a pharmacist, depending on local custom. Further discussion of the physician’s assessment of the need for intubation, the initial plan for RSI, including medications, postintubation sedation plan, and alternate/rescue airway management strategies, should take place. Much of this preparation can occur while the patient is undergoing a period of preoxygenation.

Evolving emphasis on checklists to standardize the approach to routine health care procedures is gaining acceptance in the care of surgical and intensive care unit (ICU) patients. Development of a preintubation checklist for trauma patients intubated in the emergency department (ED) based on accepted safety elements undertaken by Smith and colleagues, demonstrated substantial risk reduction in intubation-related complications. Clinicians may find checklists increasingly useful as a tool to organize the health care team’s efforts in the preparation for intubation.


In preparation for intubation, the importance of preoxygenation cannot be overstated. Through the natural course of RSI, respiratory musculature is paralyzed and airway protective mechanisms are suppressed. The time to desaturation for a patient breathing room air can be shorter than the peak effect of RSI medications (ie, <90 seconds). Therefore, the physician should endeavor to extend the period of safe apnea in every intubation. These strategies include improved positioning, preoxygenation for a period of 3 to 5 minutes, nitrogen washout, and administration of high-flow nasal oxygen simultaneous with laryngoscopy.

How is preoxygenation accomplished?

Preoxygenation and nitrogen washout can be accomplished in most cases with high fraction of oxygen (Fi o 2 ) applied to the airway of the awake, spontaneously breathing patient over several minutes. Nasal cannulae alone at typical flow rates (2–6 lpm) are inadequate. Widely used “non-rebreather” (NRB) masks only supply up to 70% Fi o 2 when supplied with traditional oxygen flow rates (ie, 15 lpm) and self-inflating bag-mask devices can supply only 80%+ Fi o 2 if a tight seal is maintained and if equipped with a 1-way valve to limit entrainment of room air. In most cases, Fi o 2 approaching 90% can be achieved only with typical NRB masks if the flow delivers 30 lpm, or in some situations, set to “flush.”

Various approaches are reported, including “3 minutes” of breathing high Fi o 2 . In a review of preoxygenation strategies, Tanoubi and colleagues describe the general superiority of 3 minutes of tidal breathing Fi o 2 = 1.0 over either 4 or 8 rapid deep breaths of Fi o 2 = 1.0. The investigators note that if time is limited, 4 or 8 maximal breaths over 30 to 60 seconds may be advantageous in emergent situations, but this approach requires a cooperative patient and high oxygen flow rates. In more difficult cases, consider a short period of noninvasive positive pressure ventilation (NIPPV) on Fi o 2 of 100% to accomplish goals of nitrogen washout and optimization of preintubation oxygen saturations.

How long is the time to desaturation?

Benumof and colleagues produced a useful model to illustrate differences in time to desaturation across various patient populations ( Fig. 2 ) based on earlier theoretic work on oxyhemoglobin desaturation by Farmery and Roe. The message is clear: unless successful intervention to support oxygenation is accomplished, most patients will desaturate before recovery from short-acting paralytic agents occurs. Additionally, this model vividly demonstrates the heterogeneity of patient responses despite the apparently reassuring S a O 2 at the onset of apnea. Over the past 2 decades, these concepts have been repeatedly supported by subsequent studies.

Fig. 2

Time to hemoglobin desaturation with initial FAO2 = 87%. S a O 2 versus time of apnea for various types of patients. The mean times to recover from 1 mg/kg IV succinylcholine are depicted on the lower right-hand corner.

( From Benumof JL, Dagg R, Benumof R. Critical hemoglobin desaturation will occur before return to an unparalyzed state following 1 mg/kg intravenous succinylcholine. Anesthesiology 1997;87(4):980; with permission.)

Maximizing preintubation oxygen saturation is of paramount importance. Davis and colleagues demonstrated an accelerating desaturation curve for young, comatose trauma patients intubated by prehospital providers. Although a minority of patients (6%) with beginning S p O 2 of 95% or higher desaturated during the intubation attempt, all patients with initial S p O 2 of 93% or lower had critical desaturation.

Further complicating attempts at preoxygenation may be the predisposing pathology that initially indicated the need for intubation. Mort observed that the critically ill, unstable patient does not preoxygenate adequately and desaturates rapidly. The complication of hypoxemia (simply to an S p O 2 <90%) during emergent intubation causes a fourfold risk of cardiac arrest.

Obese patients present a challenge for multiple reasons. Given anatomic factors, like reduced functional residual capacity (FRC) and physiologic constraints, such as increased oxygen consumption rate (V o 2 ), hypoxemia develops rapidly in the apneic period. Placing obese patients in reverse Trendelenburg position of 25 to 30° and applying continuous oropharyngeal oxygen prolongs the safe apnea period in obese patients considerably.

What is the physiologic basis for apneic oxygenation?

Frumin and colleagues, provided an elegant discussion of the outstanding mechanism of apneic oxygenation in 1959. Assuming an apneic adult has a respiratory quotient of 1.0, and an FRC of 2000 mL filled with oxygen during the preoxygenation phase, and an average V o 2 of 300 mL/min, all of the oxygen would be consumed in 7 minutes. Holmdahl demonstrated that carbon dioxide is partitioned in the buffering systems within the tissues and blood and only about 10% of evolved CO 2 crosses the alveolar interface to be exhaled. In this example, 300 mL O 2 is absorbed from the alveolar space and only 30 mL CO 2 replaces it each minute. If alveolar volume remains constant, pressure must decrease. In aggregate, there is net reduction in alveolar pressure compared with ambient pressure at the upper airways, resulting in a driving force down the respiratory tree. Frumin and colleagues observed in 8 human subjects who remained sedated, intubated, and apneic on a closed-loop circuit with Fi o 2 = 1.0, the S a O 2 remained ≥98% for a duration of 18 to 55 minutes. They interpreted the gradual volume loss in the circuit’s reservoir bag as “semi quantitative confirmation,” of this process at work.

Such observations have led various investigators over the ensuing decades to recommend nasal cannula oxygen during apneic oxygenation at rates of 5 lpm or 15 lpm just as induction medications are administered. Aside from the mass transport of oxygen into the lungs described previously, recent work by Möller and colleagues elegantly demonstrated the reduction in anatomic deadspace with high-flow nasal oxygen (15–45 lpm nasal flow). Interested readers are directed to the accompanying [CR] .


Pretreatment agents in the critically ill patient

Critically ill patients with status asthmaticus, acute coronary syndrome (ACS), or elevated intracranial pressure (ICP) can deteriorate while undergoing laryngoscopy. Repeated manipulation of the pharynx routinely causes a hyperdynamic response, which may worsen the blood pressure–heart rate product in patients with ACS, escalate ICP in the setting of impaired cerebral blood flow autoregulation, or precipitate catastrophic hemorrhage in vascular emergencies. Laryngeal stimulation can have profound respiratory effects (eg, laryngospasm, cough, and bronchospasm). Ideally, traditional agents like fentanyl or lidocaine ( Table 4 ) used to mitigate injurious responses during intubation attempts would demonstrate a clear therapeutic benefit. However, unequivocal evidence showing improved outcomes using pretreatment medications in the emergency patient population does not exist. It had been proposed that lidocaine may have some impact on bronchospasm, but again this benefit is not supported by the literature.

Table 4

Pretreatment medication summary

Agent Dose Onset Duration of Action Elimination Drug Interactions Indications
Lidocaine 1.5 mg/kg
45–90 s 10–20 min Hepatic (90%); Renal excretion Dofetilide (Dysrhythmia)
Monoamine oxidase inhibitors (Hypotension)
Amiodarone (Bradycardia)
Elevated ICP
Fentanyl 3 μg/kg
2–3 min 30–60 min Hepatic (90%) and small intestine; Renal excretion Cytochrome
P-450 (CYP-3A4) inhibitors (macrolides, azoles, protease inhibitors) can prolong action.
To blunt hypertensive response, as in increased ICP, ACS, AAA or dissection.

Abbreviations: AAA, abdominal aortic aneurysm; ACS, acute coronary syndrome; ICP, intracranial pressure; IV, intravenous.

From Daro DA, Bush S. Pretreatment agents. In: Walls RM, Murphy MF, editors. Manual of emergency airway management. 4th edition. Philadelphia: Lippincott Williams and Wilkins; 2012. p. 235; with permission.

If pretreatment agents are deemed necessary, they should be given 3 to 5 minutes before initiation of RSI; however, rapid progression through the discrete steps leading to definitive airway management should not be delayed to incorporate pretreatment medications. Further, the real possibility of introducing unnecessary complexity or delay into the preintubation routine is a significant drawback. When weighed against the absent evidence of actual benefit, routine pretreatment with these agents during RSI in the emergent patient population cannot be uniformly recommended.

Paralysis with induction

The safe transition from an awake, spontaneously breathing patient in need of an airway to a sedated, stable patient with a secure airway is accomplished through a well-choreographed induction sequence. The pharmacologic agents facilitate this safe transition and need to rapidly meet several requirements, described in the following sections.

Provide Ideal Intubating Conditions

Rapid onset of both sedation and paralysis prevents aspiration, hypoxia, and hypercapnea. Within a narrow window, agents should facilitate excellent laryngoscopy with relaxation of laryngeal musculature, reduction in laryngospasm, and suppression of the gag reflex.

Prevent Hemodynamic Instability

Sedation with paralysis is often undertaken in unstable patients with poor cardiovascular reserve. Ideally, induction medications would have no impact on blood pressure, heart rate, cardiac contractility, and cerebral perfusion pressure.

Promote Analgesia and Amnesia

Reports of patient awareness during intubation and anesthesia do appear in the literature. An induction regime should prevent pain, provide sedation, and facilitate amnesia to the event.

Although no single agent identified to date can meet all of the idealized characteristics, it is possible for the emergency physician to select agents that function in concert to accomplish the previously described goals. A decade ago, Sagarin and colleagues reviewed frequencies of induction agents in a survey of 4513 intubations and found that etomidate was used in 69% of intubations, midazolam in 16%, fentanyl in 6%, and ketamine in 3%. It is unlikely that these proportions continue to represent physician practice today, as physician awareness of advantages of some agents (eg, ketamine or propofol) is rising while other medications fall out of favor (eg, fentanyl or midazolam). A summary of commonly used induction agents is provided in Table 5 .

Table 5

Common medications in rapid sequence intubation

Medication Dose Indication Modification in Shock States
Induction agents Etomidate 0.3 mg/kg IV RSI 0.1 mg/kg IV
Propofol 0.5–1.5 mg/kg IV May use for RSI in hemodynamically stable patients Not indicated
Ketamine 1–2 mg/kg IV Hypotension
Status asthmaticus
0.5 mg/kg IV
Methohexital 1.5 mg/kg IV Largely supplanted by etomidate, caution in hypotensive patients 0.5–0.75 mg/kg IV
Midazolam 0.2–0.3 mg/kg IV Considered too slow in onset for RSI Not favored in hemodynamic instability
Paralytic agents Succinylcholine 1.5–2.0 mg/kg RSI in most cases
Pregnancy Class C
Rocuronium 1 mg/kg RSI if succinylcholine contraindicated
Pregnancy Class B
Vecuronium 0.15 mg/kg RSI if succinylcholine contraindicated
Pregnancy Class C

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Dec 14, 2017 | Posted by in Uncategorized | Comments Off on Airway Management of Respiratory Failure

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