Pragmatic Trial Examining Oxygenation Prior to Intubation

BACKGROUND:

Clinicians frequently perform tracheal intubation of critically ill patients in the emergency department (ED) or intensive care unit (ICU). Complications of intubation, including hypoxemia and cardiovascular instability, occur in nearly half of intubations performed in these settings. Preventing complications during tracheal intubation is a key focus of clinical care and airway management research.

HYPOXEMIA DURING INTUBATION OF CRITICALLY ILL PATIENTS:

Life-threatening hypoxemia occurs in 1-in-10 cases of emergency tracheal intubation. Severe hypoxemia during intubation is associated with increased risk of cardiac arrest and death. Severe hypoxemia may be associated with worse outcomes in survivors. For example, neurologic recovery from traumatic brain injury may be worse after hypoxemia due to secondary ischemic insult.

ROLE OF PREOXYGENATION IN PREVENTING HYPOXEMIA DURING INTUBATION:

In current clinical practice, emergency tracheal intubation involves the nearly simultaneous administration of a sedative agent and a neuromuscular blocking agent to optimize the anatomic conditions for intubation. Following medication administration, patients rapidly become hypopneic and then apneic until invasive mechanical ventilation is initiated through the newly-placed endotracheal tube. The oxygen contained in the lungs at the time of neuromuscular blockade (i.e., the patient's functional residual capacity) is the reservoir of oxygen available to the patient's body to prevent hypoxemia and tissue hypoxia during the intubation procedure. For a patient breathing ambient air (i.e., room air), only 21% of the gas in the functional residual capacity is oxygen; 78% is nitrogen. Administering 100% oxygen to a patient prior to induction of anesthesia and tracheal intubation, referred to as "preoxygenation," can replace the nitrogen in the lung with oxygen, increasing up to five-fold the reservoir of oxygen available to the body during the procedure and prolonging the period during which intubation can be performed safely without encountering hypoxemia. In current clinical practice, the two most common methods of providing preoxygenation are:

1. Non-invasive positive pressure ventilation - a tight-fitting mask connected to either an invasive ventilator or non-invasive mechanical ventilator.
2. Facemask oxygen - with either a non-rebreather mask or a bag-mask device.

PREOXYGENATION WITH NON-INVASIVE POSITIVE PRESSURE VENTILATION:

Preoxygenation with non-invasive positive pressure ventilation is common during emergency tracheal intubation of critically ill adults in current clinical practice. During preoxygenation with non-invasive positive pressure ventilation, a tight-fitting mask is connected to a machine capable of providing positive pressure ventilation. Non-invasive positive pressure ventilation delivers up to 95-100% oxygen and can be provided by either a conventional invasive mechanical ventilator or a dedicated non-invasive ventilation machine, commonly referred to as a Bilevel Positive Airway Pressure (BiPAP) machine. In addition to providing high concentrations of oxygen, non-invasive positive pressure ventilation increases mean airway pressure and delivers breaths at a set rate during the period of hypopnea/apnea after induction. Because a mechanical ventilator is always required following intubation of a critically ill adult, no specialized equipment is required to use non-invasive positive pressure ventilation for preoxygenation of critically ill adults undergoing tracheal intubation.

PREOXYGENATION WITH FACEMASK OXYGEN:

In current clinical practice, preoxygenation with facemask oxygen is commonly performed using one of the following two types of facemask: [1] a non-rebreather mask or [2] a bag-mask device. Both a types of facemask (a non-rebreather and a compressed bag-mask device) deliver supplemental oxygen without increasing airway pressures or providing assistance with ventilation.

• A non-rebreather mask is a type of facemask with a loose-fitting mask that sits over a patient's nose and mouth and is connected to an oxygen reservoir. It delivers at least 15 liters per minute of 100% oxygen, but it may not reliably deliver flows of oxygen greater than 15 liters per minute and may allow entrainment of ambient air. Studies show that the while the oxygen content for healthy and calm volunteers may approach 100%, the oxygen content received by critically ill patients with tachypnea may be as low as 50%. It does not provide positive pressure.
• A bag mask device is a type of facemask with a mask that forms a tight seal over the mouth and nose when held in place by the operator, an exhalation port, and a self-inflating bag that serves as a reservoir for oxygen and can be compressed to provide positive pressure ventilation. If the bag of this device is compressed, this device delivers oxygen without providing positive pressure ventilation and can deliver more than 90% oxygen with an ideal mask seal. However, in the setting of emergency intubation leaks may result in the entrainment of ambient air and reduced oxygen delivery.

POTENTIAL ADVANTAGES OF PREOXYGENATION WITH NON-INVASIVE POSITIVE PRESSURE VENTILATION OR PREOXYGENATION WITH FACEMASK OXYGEN:

Preoxygenation with non-invasive positive pressure ventilation has been proposed to offer the following potential advantages compared to preoxygenation with facemask oxygen:

• Entrainment of ambient air: The tight-fitting mask used to deliver non-invasive ventilation entrains less ambient air than a non-rebreather or bag-mask device. The higher flow rates of oxygen gas with non-invasive ventilation may also help prevent entrainment of ambient air and increase the fraction of inspired oxygen.
• Atelectasis and alveolar recruitment: Preoxygenation and induction of anesthesia rapidly results in the development of atelectasis in both healthy patients and critically ill patients. This atelectasis increases shunt fraction and increases the risk of peri-procedural hypoxia. By delivering positive pressure during both inspiration and expiration, non-invasive ventilation raises mean airway pressure, recruiting alveoli and preventing the development of atelectasis.
• Hypopnea and Apnea. Administration of sedation and neuromuscular blocking agents reduces or eliminates spontaneous respiratory effort. This hypoventilation leads to accumulation of alveolar carbon dioxide and reductions in alveolar oxygen, contributing to hypoxemia. Use of non-invasive ventilation before induction and between induction and laryngoscopy provides continuous oxygen to the alveoli, increases the size of breaths taken in the setting of hypopnea, and delivers controlled breaths when patients are apneic.

Preoxygenation with facemask oxygen (via a non-rebreather or compressed bag-mask device) has been proposed to offer the following potential advantages compared with preoxygenation with non-invasive positive pressure ventilation:

• Simplicity of use: Preoxygenation with facemask oxygen (using either a non-rebreather or compressed bag-mask device) is simpler to set up than non-invasive positive pressure ventilation.
• Low risk of gastric insufflation: Although no clinical evidence exist to suggest that preoxygenation with non-invasive positive pressure ventilation increases the risk of gastric insufflation or aspiration of gastric contents, use of facemask oxygen (without any positive pressure) avoids this hypothetical concern.

PRIOR EVIDENCE FROM CLINICAL TRIALS:

Two small clinical trials have compared preoxygenation with non-invasive ventilation to preoxygenation with facemask oxygen during the tracheal intubation of critically ill adults. The first trial compared non-invasive ventilation to a facemask among 53 critically ill ICU patients in two hospitals and found that non-invasive ventilation increased the lowest oxygen saturation (93% vs. 81%, p<0.001) with no difference in incidence of aspiration (6% vs. 8%). The second trial compared non-invasive ventilation to a facemask oxygen with regard to severity of illness in the 7 days after intubation among 201 critically ill ICU patients. This trial found no significant difference in the severity of illness between groups and no significant difference in the rate of severe hypoxemia (18.4% vs 27.7%, p=0.10). This trial did not have adequate statistical power to detect clinically important differences between groups in the risk of hypoxemia. No large, multicenter trials have compared preoxygenation with non-invasive positive pressure ventilation to preoxygenation with facemask oxygen for critically ill adults undergoing tracheal intubation. Based on the available data from these small randomized clinical trials, preoxygenation with non-invasive positive pressure ventilation and preoxygenation with facemask oxygen both represent acceptable approaches to emergency tracheal intubation. Both approaches are considered standard-of-care and are used commonly in current clinical practice.

RATIONALE FOR A LARGE MULTICENTER TRIAL OF PREOXYGENATION:

Because of the imperative to optimize emergency tracheal intubation in clinical care, the common use of both preoxygenation with non-invasive positive pressure ventilation and preoxygenation with facemask oxygen in current clinical practice, and the lack of existing data from randomized trials to definitively inform whether preoxygenation strategy effects the rate of hypoxemia, examining the approach to preoxygenation during emergency tracheal intubation represents an urgent research priority. To address this knowledge gap, the investigators propose to conduct a large, multicenter, randomized clinical trial comparing preoxygenation with non-invasive positive pressure ventilation versus preoxygenation with facemask oxygen with regard to hypoxemic during tracheal intubation of critically ill adults in the ED or ICU.