Ultrasound-guided regional anaesthesia

Abstract

Diagnostic medical ultrasound (US) uses high-frequency sound waves (2–15 MHz), in real-time visualization of both superficial and deep structures. From its early application in obstetrics, it has now developed into the most commonly used imaging technique accounting for .40% of all radiological examinations. Technological advances in piezoelectric materials, electronics, and software have enabled improved probe design and software capability; this has led to the development of small, portable 2D machines with good resolution and penetration available for bedside ‘point-of-care’ use. High-frequency probes (5–15 MHz) with improved resolution now allow visualization of superficial structures including arteries, veins, muscles, tendons, and nerves. This, with the incorporation of Doppler technology, has led to an expansion in the use of US in anaesthesia and intensive care. Following the introduction of NICE 49 (2002) guidelines recommending the use of US for the placement of central venous catheters, the availability of portable US machines within anaesthetic departments has significantly increased. US is now used routinely for cardiac imaging and cardiac output monitoring, vascular access and simple diagnostics, and aspiration in ICU (pleural effusion, abscesses). Regional anaesthesia is another developing area of US use. Portable 2D US allows the clinician to place needles with precision, guided by a real-time image of the patient’s actual anatomy and not that implied by surface anatomical landmarks. Such techniques offer potential advantages over established techniques including: improved success rates; reduced complications; and enhanced teaching. In order to benefit from these advantages, clinicians require training in this new technique as well as access to appropriate equipment and consumables. US is a dynamic technique and, as such, very operator-dependent. In the last 10 yr, ultrasound has been used sporadically by enthusiasts to perform a variety of regional techniques. The machines employed initially were inadequate to obtain the images of sufficient quality to sustain both reliability and interest. However, the use of modern higher specification cart-based machines have confirmed the potential of US in regional anaesthesia, and the presence of smaller portable laptop-type machines (e.g. Sonosite demands) have now made US-guided regional anaesthesia a reality.