This was a single-centre case series study that took place at an academic hospital in Toronto, Canada and was approved by our institution's Research Ethics Board (No. 3456). The ED is a regional trauma centre, the primary residency training site for emergency medicine POCUS, hosts a POCUS fellowship program, and receives over 60,000 patients annually.

Resuscitative TEE was performed by a staff emergency physician, or by a senior emergency medicine resident or POCUS fellow under direct supervision of that staff emergency physician. The emergency physician has completed advanced training in resuscitative TEE including four hours of guided practice on a high-fidelity simulator (Vimedix, CAE Healthcare), 16h of training in the operating room under the supervision of a credentialled TEE expert, and ongoing clinical practice. The emergency physician is the ultrasound fellowship director. At least one POCUS machine and an immediately accessible TEE probe were available in the ED.

The study population was a convenience sample of patients who underwent resuscitative TEE during the study period when the study physician was available in the ED. Indications for ED resuscitative TEE were cardiac arrest, shock, and post-cardiac arrest. Contraindications included an unprotected airway, a history of known esophageal surgery, esophageal varices, or other anatomic abnormalities including strictures.

TTE was considered in all patients before TEE and attempted before TEE whenever possible to obtain subxiphoid cardiac, parasternal long axis, apical four chamber, and inferior vena cava views. If TEE was performed before TTE, TTE was abandoned. TEE (Zonare P8-3TEE, Mindray Medical Systems, Shenzhen, China) views included mid-esophageal four-chamber (ME4C), mid-esophageal long axis (MELAX), trans-gastric short axis (TGSAX), mid-esophageal bicaval (MEBicaval), mid-esophageal descending aorta (MEDescAo), mid-esophageal aortic root, and mid-esophageal inflow-outflow using a standardized approach. ME4C, MELAX, TGSAX, MEBicaval, MEDescAo TEE views were obtained in a standardized fashion for each patient in the order listed. Subsequent views were obtained at the discretion of the resuscitation team and TEE operator.

The quality of each TTE and TEE view was classified as adequate, limited, or inadequate. Adequate images were defined as those with sufficienct visualization to be used for clinical decision-making purposes, as judged by the operator prospectively at the time of resuscitation. Images did not undergo a post-hoc review. POCUS and resuscitative data consisted of both categorical and written text recorded on data sheets collected prospectively at the time of resuscitation and stored in a secure location in the emergency department (“Appendix”). Pre- and post-TEE working diagnoses were recorded in real time by the resuscitation clinician and TEE operator in order to minimize recall bias.

The primary outcome of this study is a descriptive analysis of the management of critically ill patients who underwent resuscitative TEE in the ED. During the resuscitation of each patient, initial diagnoses and management were recorded in real time on data sheets before and after TEE was performed. After each TEE examination during each resuscitation, the diagnosis and management were recorded on data sheets. A change in management was reported if there was a difference between pre- and post-TEE therapeutic recommendations. Secondary outcomes included the descriptive analyses of working diagnoses, complications (immediate and delayed), patient disposition, survival to hospital discharge, and the most utilized and the quality of sonographic TEE views produced. Therapeutic recommendations were made in collaboration with the TEE operator and the resuscitation clinician. The insertion of the TEE probe was defined as easy or difficult. A difficult insertion was defined as one that required airway and/or neck manipulation, was prolonged (> 30 s) or where multiple insertion attempts were required. Probable reasons for difficult insertion and troubleshooting maneuvers were recorded prospectively during the time of resuscitation.

Immediate complications were identified and recorded at the time of resuscitation. The complete medical record for each patient who survived to hospital admission were reviewed comprehensively for any delayed complications as well as patient disposition and survival. Post-mortem reports were not reviewed for evidence of complications for patients who died in the ED. The authors assessed for complications as they have been previously defined in the literature in categories of oropharyngeal (lip laceration, loose or chipped tooth, displaced dentures, pharyngeal laceration, tongue necrosis), esophageal (odynophagia, dysphagia, laceration, perforation, Mallory Weiss tear, gastric perforation, hemorrhage), and other (splenic laceration, compression of mediastinal structures, laryngospasm, endotracheal tube displacement, airway obstruction, immediate dysrhythmias, and thermal injury or burn) [9]. Immediate complications were lip lacerations, loosened or chipped teeth, displaced dentures, pharyngeal bleeding, upper gastrointestinal bleeding, laryngospasm, endotracheal tube displacement, airway obstruction, and immediate dysrhythmias.

Descriptive statistics were used to report study outcome data. Data was collected in password protected software and analyzed using commercial software (Microsoft Excel V16.43 20110804).