Always scan the whole area of interest to locate structures and identify anatomical variations.
- Visualize nerves or plexus
- Visualize structures to avoid: blood vessels, pleura
- Visualize needle
- Visualize local anesthetic spread:
- Limit volume, as injection can be stopped when spread deemed adequate
- Avoid intravascular injection; risk of complication when needle tip in a compressed, poorly visualized vein, and when no spread is seen when injecting as a result
- Confirm position of catheter:
- Inject fluid, agitated fluid, or air
- Color Doppler can be used
- Sterile conductive gel and sterile protective cover for ultrasound (US) probe should be used
- Ideally, a telescopic probe cover, fixed in place by an elastic band, should be employed
- After use, probe should be sterilized or disinfected, rinsed, dried, and kept in a clean environment
Transducer shape (Figure 127-1):
- Straight (linear) transducers yield an image as wide as the probe
- Curvilinear transducers yield a semicircular picture, allowing visualization of structures not directly underlying the probe
- Probes with special shapes are used to minimize probe “footprint,” especially in small patients or children (e.g., “hockey stick” probe)
Figure 127-1. Straight, Curvilinear, and “Hockey Stick” Probes
(A and B) Straight probe and ultrasound picture obtained with the probe. (C and D) Curvilinear probe and ultrasound picture obtained with the probe. (E) “Hockey stick” probe. Reproduced with permission from Hadzic A. The New York School of Regional Anesthesia Textbook of Regional Anesthesia and Acute Pain Management. New York: McGraw-Hill; 2006. Figure 52-1. Copyright © The McGraw-Hill Companies, Inc. All rights reserved.
- Pick a transducer based on frequency (usually between 3 and 15 MHz)
- High-frequency transducer (8–12 or 15 MHz):
- Less penetration into deeper structures
- Best for target depth up to 3–4 cm
- Higher resolution (picture quality)
- Low-frequency transducer (3–5 MHz):
- More penetration into deeper structures
- Best for targets deeper than 5 cm
- Lower resolution (picture quality)
- After picking the appropriate transducer, fine-tune the frequency of the wave by selecting the upper, mid, or lower frequency range of that specific transducer
Identify which side of transducer corresponds to which side of the image on the US monitor:
- Most transducers have a fixed label (i.e., palpable notch/groove) corresponding to an indicator on the screen
- If in doubt, tap on side of transducer to identify orientation
- Affects brightness (hyperechoic) or darkness (hypoechoic) characteristics of the ...
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