Comparison of Three Point-of-care Ultrasound Techniques to Confirm Endotracheal Tube Placement: a Randomized Clinical Trial

In emergency medicine, endotracheal intubation (ETI) is commonly performed for patients who require airway management due to acute respiratory failure, inadequate oxygenation or ventilation, or an inability to protect the airway resulting from altered consciousness. When ETI is performed outside of a cardiac arrest scenario, a series of steps are followed to optimize the procedure. These steps aim to prevent hypoxia, maintain hemodynamic stability, reduce the risk of aspiration, and increase the success rate of ETI. This methodical approach is known as Rapid Sequence Intubation (RSI). RSI involves preparing the necessary and auxiliary equipment, administering premedication, ensuring oxygenation, and applying anesthetic and neuromuscular blocking agents, followed by the placement of the endotracheal tube (ETT). The procedure concludes with confirming the ETT's placement and providing post-intubation care.

The primary goal of ETI is to position the ETT through the vocal cords into the trachea, ensuring that both lungs are ventilated effectively. Incorrect or unrecognized endobronchial intubation can result in hypoventilation and collapse of the non-ventilated lung, while the over-ventilated lung may suffer barotrauma or pneumothorax. Unrecognized esophageal intubation, on the other hand, can lead to failure in ventilation, resulting in hypoxia and subsequent complications, including brain damage and other morbidities. Therefore, ensuring the correct placement of the ETT is crucial to avoid serious adverse outcomes.

Various methods have been described to confirm correct ETT placement, including direct visualization during intubation, observation of chest wall movements, bilateral auscultation of lung sounds, end-tidal carbon dioxide (EtCO2) monitoring, fiberoptic bronchoscopy, and chest X-ray. Among these, capnography is considered the gold standard. However, in specific clinical situations, EtCO2 monitoring may be unreliable. Patients in cardiac arrest, patients with severe hypotension, pulmonary embolism, or poor pulmonary reserve may present lower than expected EtCO2 values. Similarly, gastric insufflation, using antacids, or consuming carbonated beverages may result in false-positive readings.

The American College of Emergency Physicians (ACEP) guidelines recommend the use of additional confirmation methods after ETT placement. Ultrasound (US) has emerged as a relatively new technique for confirming ETI. Its advantages include being non-invasive, portable, rapid, and capable of providing real-time, accurate results. Additionally, the US is unaffected by environmental noise, which can be challenging in noisy environments such as the emergency department. It is also not influenced by changes in pulmonary blood flow.

Several ultrasound techniques have been described to confirm ETT placement. The most commonly used methods include direct visualization of the ETT during intubation (tracheal ultrasound), detection of the "lung sliding" sign via lung ultrasound to indicate lung aeration and bilateral identification of diaphragmatic movement. Tracheal ultrasound can detect esophageal intubation before ventilation begins, preventing unnecessary gastric insufflation and its associated complications. The lung sliding sign and bilateral diaphragmatic movement techniques can help identify endobronchial intubation by visualizing pleural and diaphragmatic movement, respectively, thereby complementing tracheal ultrasound and reducing the risk of missed endobronchial intubation.