Airway/review articlePreoxygenation and Prevention of Desaturation During Emergency Airway Management
Introduction
Maintaining hemoglobin saturation during airway management is critical to patient safety. Desaturation to below 70% puts patients at risk for dysrhythmia, hemodynamic decompensation, hypoxic brain injury, and death.1, 2 The challenge for emergency physicians is to secure a tracheal tube rapidly without critical hypoxia or aspiration. In patients without pulmonary pathology, adequate hemoglobin, or low metabolic demands and an initial pulse oximetry reading of 100% on room air, there is a low risk of desaturation after adequate preoxygenation. Conversely, in a septic patient with multilobar pneumonia who is already hypoxemic (oxygen saturation ≤90%) despite 100% oxygen at high flow, there is an immediate risk of critical tissue hypoxia during tracheal intubation.
This article reviews preoxygenation and peri-intubation oxygenation techniques to minimize the risk of hypoxemia during emergency tracheal intubation of adult patients. It introduces a risk-stratification approach based on initial pulse oximetry level in response to oxygen administration and provides recommendations about specific techniques based on periprocedural risk. Techniques reviewed include positioning, preoxygenation and denitrogenation, use of positive pressure devices to increase mean airway pressure, and passive apneic oxygenation during tracheal intubation efforts.
Section snippets
What is the Rationale for Providing Preoxygenation Before Tracheal Intubation?
Preoxygenation allows a safety buffer during periods of hypoventilation and apnea. It extends the duration of safe apnea, defined as the time until a patient reaches a saturation level of 88% to 90%, to allow for placement of a definitive airway. When patients desaturate below this level, their status is on the steep portion of the oxyhemoglobin dissociation curve and can decrease to critical levels of oxygen saturation (<70%) within moments (Figure 1).3
The standard anesthesia induction of
What is the Best Source of High FiO2 for Preoxygenation?
The duration of safe apnea times in most of the preoxygenation literature is predicated on anesthesia circuits that are capable of delivering 90% to 100% FiO2 when used with a well-fitting mask. However, the usual source of oxygen during ED preoxygenation is a facemask with an oxygen reservoir. This device is erroneously referred to as the nonrebreather mask despite an absence of 1-way valves covering all of its ports. True nonrebreather masks set at 15 L/minute for patients with normal
For What Period of Time Should the Patient Receive Preoxygenation?
Ideally, patients should continue to receive preoxygenation until they denitrogenate the functional residual capacity of their lungs sufficiently to achieve greater than 90% end-tidal oxygen level.14 Although the mass spectrometers in many EDs allow the measurement of end-tidal oxygen levels, in practice this is rarely performed. Instead, expediency often demands an empiric timing of preoxygenation.
Three minutes' worth of tidal-volume breathing (the patient's normal respiratory pattern) with a
Can Increasing Mean Airway Pressure Augment Preoxygenation?
Mean airway pressure may be increased during preoxygenation through the use of techniques such as noninvasive positive-pressure ventilation. If patients have not achieved a saturation greater than 93% to 95% before tracheal intubation, they have a higher likelihood of desaturation during their apneic and tracheal intubation periods.2, 16, 18, 22, 23 If patients do not achieve this saturation level after 3 minutes of tidal-volume breathing with a high FiO2 source, it is likely that they are
In What Position Should the Patient Receive Preoxygenation?
Supine positioning is not ideal to achieve optimal preoxygenation. When one is placed flat, it is more difficult to take full breaths and more of the posterior lung becomes prone to atelectatic collapse,3 which reduces the reservoir of oxygen contained within the lungs and therefore reduces safe apnea time.
Lane et al42 performed a randomized controlled trial of patients preoxygenated in a 20-degree head-up position versus a control group that was left supine. After 3 minutes of preoxygenation,
How Long Will it Take for the Patient to Desaturate After Preoxygenation?
Although breathing at a high FiO2 level will slightly increase the bloodstream stores of oxygen, the primary benefit of preoxygenation is the creation of a reservoir of oxygen in the alveoli. When a patient is breathing room air, 450 mL of oxygen is present in the lungs; this amount increases to 3,000 mL when a patient breathes 100% oxygen for a sufficient time to replace the alveolar nitrogen. A patient breathing room air will have a total oxygen reservoir in the lungs and bloodstream of
Can Apneic Oxygenation Extend the Duration of Safe Apnea?
Alveoli will continue to take up oxygen even without diaphragmatic movements or lung expansion. In an apneic patient, approximately 250 mL/minute of oxygen will move from the alveoli into the bloodstream. Conversely, only 8 to 20 mL/minute of carbon dioxide moves into the alveoli during apnea, with the remainder being buffered in the bloodstream.53 The difference in oxygen and carbon dioxide movement across the alveolar membrane is due to the significant differences in gas solubility in the
When and How Should We Provide Manual Ventilations During the Apneic Period?
Practitioners should not initiate laryngoscopy before full muscle relaxation to maximize laryngeal exposure and to avoid triggering the patient's gag reflex and active vomiting just before apnea. Ventilation provides 2 potential benefits during the onset phase of muscle relaxation: ventilation and increased oxygenation through alveolar distention and reduction in shunting.
The first benefit is minimal in most clinical scenarios. On average, PaCO2 increases 8 to 16 mm Hg in the first minute of
What Positioning and Maneuvers Should the Patient Receive During the Apneic Period?
Apneic oxygenation requires a patent airway for oxygen to reach the hypopharynx and be entrained into the trachea; once the patient is sedated and paralyzed, it is imperative to keep the posterior pharyngeal structures and tongue from occluding the passage of gas. Head elevation, chin lift, and jaw thrust will accomplish this in most patients; a jaw thrust alone should be used if there is risk for cervical spine injury. In some patients, a nasal trumpet or oral airway may also be required.
Does the Choice of Paralytic Agent Affect Preoxygenation?
The choice of paralytic agent may influence the time to desaturation during airway management. In a study of operative patients, the time to desaturation to 95% was 242 seconds in patients receiving succinylcholine versus 378 seconds in a group given rocuronium.95 Similarly, in obese patients undergoing surgery, the succinylcholine group desaturated to 92% in 283 seconds versus 329 seconds in the rocuronium group.96 When used at a dose of greater than or equal to 1.2 mg/kg, rocuronium provides
Risk Stratification and Conclusions
Patients requiring emergency airway management can be risk stratified into 3 groups, according to pulse oximetry after initial application of high-flow oxygen. The recommended techniques to use for patients in each group are shown in Table 2, and a logistic flow of preoxygenation steps is shown in Figure 3.
Head-elevated positioning is simple and easy to apply in all patients; in the patient immobilized for cervical spine injury, it is beneficial to tilt the foot of the bed downward.
Patients at
References (97)
The incidence and risk factors for cardiac arrest during emergency tracheal intubation: a justification for incorporating the ASA guidelines in the remote location
J Clin Anesth
(2004)- et al.
Monitoring preoxygenation
Br J Anaesth
(1994) - et al.
Preoxygenation
- et al.
Comparison of eight deep breaths and tidal volume breathing preoxygenation techniques in morbid obese patients
Ann Fr Anesth Reanim
(2004) - et al.
Noninvasive positive-pressure ventilation versus conventional oxygen supplementation in hypoxemic patients undergoing diagnostic bronchoscopy
Chest
(2002) - et al.
Inflation pressure, gastric insufflation and rapid sequence induction
Br J Anaesth
(1987) - et al.
Prevention of atelectasis during general anaesthesia
Lancet
(1995) - et al.
Pre-oxygenation in the obese patient: effects of position on tolerance to apnoea
Br J Anaesth
(2005) - et al.
Laryngeal exposure during laryngoscopy is better in the 25 degrees back-up position than in the supine position
Br J Anaesth
(2007) - et al.
Arterial oxygen saturation before intubation of the tracheaAn assessment of oxygenation techniques
Br J Anaesth
(1984)
A model to describe the rate of oxyhaemoglobin desaturation during apnoea
Br J Anaesth
Apneic oxygenation during prolonged laryngoscopy in obese patients: a randomized, controlled trial of nasal oxygen administration
J Clin Anesth
Effects of face mask ventilation in apneic patients with a resuscitation ventilator in comparison with a bag-valve-mask
J Emerg Med
Effects of decreasing peak flow rate on stomach inflation during bag-valve-mask ventilation
Resuscitation
Head-elevated laryngoscopy position: improving laryngeal exposure during laryngoscopy by increasing head elevation
Ann Emerg Med
Cricoid pressure in emergency department rapid sequence tracheal intubations: a risk-benefit analysis
Ann Emerg Med
The effect of cricoid pressure application on airway patency
J Clin Anesth
Rate of decline in oxygen saturation at various pulse oximetry values with prehospital rapid sequence intubation
Prehosp Emerg Care
Nunn's Applied Respiratory Physiology
Anaesthetic deaths due to regurgitation or vomiting
Anaesthesia
Polarographic study of arterial oxygenation during apnea in man
N Engl J Med
Apneic oxygenation in man: polarographic arterial oxygen tension study
Anesthesiology
Oxygen delivery systems, inhalation therapy, and respiratory therapy
Delivery of high FiO2
Efficacy of preoxygenation with tidal volume breathingComparison of breathing systems
Anesthesiology
Manual resuscitators and spontaneous ventilation—an evaluation
Crit Care Med
Anesthesiology
End-tidal oxygraphy and safe duration of apnoea in young adults and elderly patients
Anaesthesia
A study of denitrogenation with some inhalation anesthetic systems
Anesthesiology
Preoxygenation: comparison of maximal breathing and tidal volume breathing techniques
Anesthesiology
Oxygenation using tidal volume breathing after maximal exhalation
Anesth Analg
Single vital capacity breath for preoxygenation
Can J Anaesth
Total oxygen uptake with two maximal breathing techniques and the tidal volume breathing technique: a physiologic study of preoxygenation
Anesthesiology
Preoxygenation: best method for both efficacy and efficiency
Anesthesiology
Noninvasive bilevel positive airway pressure for preoxygenation of the critically ill morbidly obese patient
Can J Anaesth
Noninvasive ventilation improves preoxygenation before intubation of hypoxic patients
Am J Respir Crit Care Med
Applied Respiratory Physiology
The effectiveness of noninvasive positive pressure ventilation to enhance preoxygenation in morbidly obese patients: a randomized controlled study
Anesth Analg
Noninvasive ventilation and alveolar recruitment maneuver improve respiratory function during and after intubation of morbidly obese patients: a randomized controlled study
Anesthesiology
Effectiveness of continuous positive airway pressure to enhance pre-oxygenation in morbidly obese women
Anaesthesia
Positive end-expiratory pressure during induction of general anesthesia increases duration of nonhypoxic apnea in morbidly obese patients
Anesth Analg
The effect of positive airway pressure during pre-oxygenation and induction of anaesthesia upon duration of non-hypoxic apnoea
Anaesthesia
An intervention to decrease complications related to endotracheal intubation in the intensive care unit: a prospective, multiple-center study
Intensive Care Med
Face mask resuscitation: does it lead to gastric distension?
Arch Dis Child
Gas leak and gastric insufflation during controlled ventilation: face mask versus laryngeal mask airway
Can J Anaesth
Gastric inflation in relation to airway pressure
Acta Anaesthesiol Scand
Right atrial pressure predicts hemodynamic response to apneic positive airway pressure
Crit Care Med
Optimizing preoxygenation in adults
Can J Anaesth
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Supervising editors: Gregory W. Hendey, MD; Donald M. Yealy, MD
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Publication date: Available online November 2, 2011.