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Always scan the whole area of interest to locate structures and identify anatomical variations.
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- 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
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- 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
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Transducer shape (Figure 127-1):
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- 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)
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- 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
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Identify which side of transducer corresponds to which side of the image on the US monitor:
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- 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
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- Affects brightness (hyperechoic) or darkness (hypoechoic) characteristics of the displayed image
- Adjust gain to obtain clear image
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