Principles of ultrasound-guided regional anesthesia

CHAPTER 7 Principles of ultrasound-guided regional anesthesia



The ability to use ultrasound guidance for regional anesthesia is achieved by systematic learning and maintained by regular practice. Knowledge of anatomy is paramount for the successful practice of regional anesthesia. In order to visualize this anatomy, one has to know how to use an ultrasound machine. We hope this chapter will give the reader the knowledge and impetus to make better use of their ultrasound equipment, but it takes learning from more experienced colleagues, practice, self-discipline and reflection to get one’s skills to an adequate level.



Introduction to ultrasound


Ultrasound is a mechanical wave with frequencies over 20 000 Hz. Ultrasound used in medicine is generated and sensed by piezoelectric crystals. The ultrasound transducer incorporates a battery of piezoelectric crystals. When scanning, the transducer switches quickly between transmitter and receiver modes. When in transmitting mode, the piezoelectric crystals are stimulated by electrical energy, vibrate and emit ultrasound waves. In the receiver mode the crystals are hit by the ultrasound waves reflected from the tissues (Fig 7.1). The resultant mechanical stimulation of the crystals is converted to electrical signals, which are processed and ultimately create the image we see on the screen.




Why understanding ultrasound physics and how to use an ultrasound machine is important


Here are some examples:












Ultrasound physics












Table 7.1 The acoustic impedances of selected body tissues
























Tissue Acoustic impedance (g/cm2 sec × 100)
Air 0.0004
Fat 1.3
Water 1.5
Blood 1.6
Muscle 1.7
Bone 7



The ultrasound machine


The ultrasound machine consists of a transducer (acting as transmitter and receiver), main unit (generating pulses for the transmitter, processing the impulses from the receiver, control unit, memory) and a display.




Jul 28, 2016 | Posted by in ANESTHESIA | Comments Off on Principles of ultrasound-guided regional anesthesia
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