End-Tidal Oxygen for Intubation in the Emergency Department

BACKGROUND AND INTRODUCTION

Rapid Sequence Intubation (RSI) is a common procedure in Emergency Departments (ED). However, it is a high-risk procedure and is associated with significant complications including hypoxia, failed intubation, hypotension, trauma and aspiration. (1-3) Specifically, hypoxia during intubation can lead to poor outcomes such as dysrhythmias, haemodynamic compromise, hypoxic brain injury and death and therefore oxygen desaturation is of primary concern during any intubation procedure. (4, 5) In order to prevent desaturation events during intubation, a number of steps are taken by clinicians. These include optimal patient positioning, adequate preoxygenation, assessment of airway anatomy and development of a detailed airway plan as well as the use of apnoeic oxygenation.(6)

Effective preoxygenation is vital to ensure that the patient does not develop hypoxia during the period between induction (administration of sedative and paralytic agents) and restoration of ventilation by successful endotracheal intubation or rescue breathing. Various methods of preoxygenation have been developed to wash the nitrogen out of the lungs (denitrogenation) which allows the functional residual capacity (FRC) to act as an oxygen reservoir during intubation, which prolongs safe apnoea time, therefore, preventing desaturation whilst an endotracheal tube (ETT) is placed.

Adequate preoxygenation is especially important for those patients at highest risk of hypoxia during the RSI. This patient group includes those with underlying lung pathology e.g. pneumonia, patients with increased metabolic demand e.g. sepsis, patients with an oxygen requirement prior to RSI, or patients with underlying conditions that predisposes to hypoxia e.g. obesity.

For many years anaesthetists have used end-tidal oxygen (ETO2) levels to guide the effectiveness of preoxygenation. ETO2 measures the exhaled oxygen concentration and is a marker of the oxygen concentration in the alveoli. Prior to induction, anaesthetists most commonly preoxygenate with a face-mask seal via either a circle circuit, Mapleson circuit, or bag valve mask. ETO2 provides an objective measurement of preoxygenation efficacy. The Difficult Airway Society guidelines suggest aiming for an ETO2 of ≥87% prior to commencing RSI.(7) ETO2 levels are not routinely measured in Emergency Departments.

Currently, it is not possible to measure the effectiveness of preoxygenation in the ED. Pulse-wave oximetry reflects peripheral oxygen saturation and not the pulmonary oxygen concentration. Therefore, to attempt to optimize preoxygenation the emergency clinician currently can only use time as a surrogate. The typically recommended duration of preoxygenation is > 3 minutes.

Recently, the investigators conducted two multi-site studies (Ethics identifier: 2019/ETH06644) that investigated the use of ETO2 in the ED.(8, 9) The first study was conducted with clinicians blinded to the ETO2 result (8). The investigators demonstrated that preoxygenation was uniformly poor with only 26% of patients achieving the required target ETO2 of ≥85%. The investigators then completed a second study where clinicians had access to ETO2 values and found that the proportion of patients reaching levels ≥85% was improved to 67% of patients. (9) The prevalence of hypoxemia (SpO2 <90%) in the group blinded to ETO2 was 18% (n=18, 95% CI: 11% to 27%) and was 8% in the group where ETO2 was available (n = 8, 95% CI: 4% to 15%). These studies indicate that the use of ETO2 may substantially improve preoxygenation in the ED and therefore reduce the risk of hypoxia.

These studies, however, were focused on preoxygenation practices and not patient-oriented outcomes (hypoxia) and were limited in design and resources. Consequently, it is still unclear whether the use of ETO2 in the ED leads to improved clinical outcomes.

RATIONALE FOR PERFORMING THE STUDY

The aim of this study is to determine the effectiveness of ETO2 monitoring in preventing desaturation for patients with a high risk of hypoxia undergoing RSI in ED.

HYPOTHESIS

The investigators hypothesise that the use of ETO2 monitoring leads to reduced rates of oxygen desaturation during the peri-intubation period compared to when it is not used.