It is very important to ensure the tube placement in patients with cardiac arrest and unrecognized misplacement of endo-tracheal tube can lead to morbidity and mortality. In recent pandemic situations such as COVID-19 (Coronavirus disease-19), the number of cases of cardiopulmonary resuscitation with personal protective equipment (PPE) have increased. In those cases, existing methods such as auscultation and chest uprising have to be limited. Quantitative waveform capnography is recommended as the gold standard for confirming correct endotracheal tube placement in the 2010 American HeartAssociation (AHA) Guidelines for Cardiopulmonary resuscitation (CPR) and Emergency Cardiovascular Care (ECC), but it has some well-known limitations in cardiac arrest patients.

Ultrasonography is a non-invasive, real-time diagnostic tool commonly used during resuscitation. Especially, tracheal ultrasonography can be performed in real-time when the tube is passed through the trachea or esophagus. Previous prospective studies revealed that tracheal ultrasonography could feasibly and rapidly confirm tracheal intubation during emergency intubation.

There have already been several studies comparing the accuracy of tracheal ultrasound and capnography, but there was no study comparing the two tools under the constraints of PPE that is essential in pandemic situations as in this study. This study aimed to determine the accuracy of tracheal ultrasonography in assessing endotracheal tube position during CPR with PPE.

When patients in cardiopulmonary arrest enter a emergency room (ER) or patients staying in a ER have a cardiopulmonary arrest, participants perform intubation and CPR. When it is judged as a high-risk group with a high probability of droplet infection, all participants in resuscitation team should wear personal protective equipment. Tracheal ultrasound and end-tidal carbon dioxide are used to confirm the placement of tube. The gold standard is the direct visualization using laryngoscope. The time it takes to confirm the placement of tube is also measured.

Inclusion Criteria:

• 1. cardiopulmonary arrest patients receiving emergency intubation and CPR
• 2. patients judged to need to wear PPE according to the judgement of the clinician

Exclusion Criteria:

• 1. sign for "do not resuscitate (DNR)"
• 2. patients unable to perform tracheal ultrasound due to trauma of the site
• 3. patients unable to perform tracheal ultrasound due to oropharynx cancer
• 4. patients unable to perform tracheal ultrasound due to placement of tracheal cannula
• 5. patients not used tracheal ultrasound for checking tube placement