Management of the airway remains a major contributor to death and brain damage in anesthesia, emergency medicine, and intensive care settings. The ability to recognize and understand the difficult airway is not a redemptive grace in clinical practice. Successful interventions with good outcomes are based on an excellent knowledge of airway anatomy and physiology, equipment familiarity and variety, fluidity of thinking, improvisational skills, and sound judgment.
Ultrasound-guided techniques are increasingly used in anesthetic practice. Ultrasonography (US) has many potential advantages– it is safe, quick, repeatable, portable, widely available, and gives real-time dynamic images. sonography of the upper airway may be a useful adjunct to clinical methods of bedside airway assessment. US must be used dynamically in direct conjunction with the airway procedures for maximum benefit in airway management. For these, ultrasound can be used for airway assessment and imaging.
Ultrasound physics refers to sound beyond 20,000 Hz and frequencies from 2 MHz to 15 MHz are normally used for medical imaging. Ultrasound transducers act as both transmitters and receivers of reflected sound. Tissues exhibit differing acoustic impedance, and sound reflection occurs at interfaces between different types of tissues. The impedance difference is greatest at interfaces of soft tissues with bone or air. Some tissues give a strong echo (fat and bone, for example); these structures are called hyper echoic structures and appear white. Other tissues let the ultrasound beam pass easily (fluid collections or blood in vessels, for example), and thus create only little echo; they are called hypo echoic and appear black on the screen.
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