Background and Objective: Lung ultrasound has been the most impactful new bedside diagnostic tool in modern emergency medicine during the last 15–20 years, together with the advent of troponins, with the difference that lung ultrasound has a broad spectrum of applications while troponin has only very few specific. This narrative review aims to describe the multiple fields of application of ultrasonography, to improve the diagnostic process and allow to make a differential diagnosis among the various pathologies that have led the patient to the emergency area. We summarized the use of immediate and fast-focused point-of-care ultrasound (POCUS) for a rapid and real-time evaluation of pathologies at the patient’s bedside and its clinical applications, including goal-directed echocardiography (GDE), echocardiography during cardiac arrest, thoracic ultrasonography, evaluation for deep vein thrombosis (DVT) and pulmonary embolism, screening abdominal, ocular, neck, obstetric and musculoskeletal ultrasonography, as well as fluid balance assessment. Methods: A systematic literature search was conducted on PubMed/Medline databases. Related MeSH: ultrasound, emergency department, shock, dyspnea. We included English-language publications from January 1995 to December 2023. Key Content and Findings: In the emergency department, it is crucial to evaluate and triage patients. The use of POCUS allows doctors to make differential diagnoses of life-threatening conditions (shock, dyspnea, heart failure) and guide an appropriate treatment. It is also a valid tool during invasive procedures as it increases accuracy and reduces the risk of errors. Conclusions: We provided a comprehensive overview on the application of ultrasound (US) in critical care and emergency departments. According to the existing literature, US use seems to allow physicians to make quick diagnoses and to recognize early life-threatening conditions which require prompt interventions. US is also frequently adopted for real-time invasive procedures such as thoracentesis, drainage positioning, etc. to increase accuracy in the technique. Furthermore, ultrasonographic approach has been recently used to evaluate fluid tolerance and intolerance and to guide de-escalation therapy in acute decompensated heart failure (ADHF). In conclusion, US should be considered as an invaluable tool when used in the clinical context in the hand of a skilled emergency physician.
