US Flashcards
Resolution is defined as
ability to clearly distinguish 2 structures lying beside one another
Focus is defined as
focus should be placed at level of object being assessed
Gain is defined as
intense or decrease the signal intensity (brightness)
what frequency does ultrasound use? MHz when US travels into the body and has contact with various tissues- what can it do?
Uses high frequency (1-20 MHz) sound waves emitted from multiple piezoelectric crystals inside a transducer rapidly vibrate in response to an alternating electric current… US then travels into the body where, on contact with various tissues, can be reflected, refracted, and scattered
High frequency
transducers provide a high-resolution picture with a relatively clear image but offer poor tissue penetration, thus used for more superficial nerves
Lower frequency
transducers provide an image of poorer quality but have better tissue penetration, thus used for deeper structures
Modes:
amplitude (A) mode brightness (B) mode (most commonly used for ultrasound guided regional anesthesia) motion (M) mode
for superficial structures use what frequency
high frequency greater than or equal to 7MHz
for peripheral nerve blocks frequencies range from
3-15MHz
transducers with a range of 10-15MHZ- what is their negative attribute
you become limited to what is 2-3cm below the skin- penetration is limited.
Transducer movement ART
A= alignment (side longitudinally) R= rotation (rotate clockwise/counter clockwise) T=tilting (tilting or angling the transducer
<2.0cm field depth=which block
wrist, ankle block
2-3cm field depth= which blck
interscalene, axillary, brachial plexus block
3-4cm field depth
femoral, supraclavicular, transverses abdomens plane block
4-7cm field depth
infraclavicular, popliteal, subgluteal, sciatic nerve blocks
7-10cm block
pudendal, gluteal sciatic nerve, lumbar plexus block
>10cm
anterior approach to sciatic nerve
use of a peripheral nerve stimulator
this concept will be on the exam.
mode most commonly used for ultrasound guided regional anesthesia
brightness (B) mode
field depth for placing interscalene, brachial plexus block?
2-3 cm
field depth for placing femoral block?
3-4 cm
field depth for placing gluteal sciatic nerve block?
7-10 cm
field depth for placing popliteal block?
4-7 cm
screen brightness can be adjusted manually by TWO function buttons:
Gain Time-gain compensation (TGC)
Excessive or inadequate gain can cause both a blurring of
tissue boundaries loss of information
optimal gain for scanning peripheral nerves is typically the gain at which the best contrast is obtained b/w the
muscles and the adjacent connective tissue
PNB set up: (keep in mind)
-Ultrasound machine -Transducer covers -Nerve block kit -Peripheral nerve stimulator -Sterile work station -Local anesthetic drawn up and labeled -Sedation medications drawn up and labeled -Connect the ultrasound machine to the power outlet -Comfortable patient position -The ultrasound machine should be set up on the opposite side of the patient -Tray should be positioned close -Ambiance-set room settings: Adjust the lights in the room in order to view the ultrasound machine
to ease visualization, what needle selection should be made?
large bore needles (17G) -preferred for deep blocks
for more superficial blocks, what size needles would be ok?
smaller bore needles (22G) -also more comfortable for awake pts
An _____ needle concentrates electrical current at the needle tip while a wire attached to the needle hub connects to a nerve stimulator
insulated
PNS are used to:
accurately identifiy specific nerves/improve adequacy of block
PNS grounding electrode is attached to
the pt “to complete the circuit”
when an insulated needle is placed in proximity to a motor nerve…. what happens?
muscle ctx are induced
Needle placed inline with and parallel to
the transducer (ultrasound beam). Both the needle shaft and tip are visualized
PNB technique - Set up: fyi/review
-2-person technique (find an assistant) -Standard monitors (B/P, ECG, Pulse ox) -Have O2, suction, resuscitative -medications & equipment readily available -Locate crash cart and intralipid -Before starting the procedure, check for the proper functioning of the nerve stimulator and the connecting cables -Pre-medicate (but don’t “over sedate”) —>Short acting benzodiazepine and opioid titrated for comfort –>Patient should always respond to verbal cues -Position patient properly (favorable for clinician and comfortable for patient) -negative pole should be connected to the stimulating electrode (needle) and the positive pole to the patient’s skin -Time-out -Disinfect the skin/create sterile field -Connect the nerve stimulation needle to the nerve stimulator (which should be turned on once in the subcutaneous tissue), and adjust PNS to deliver 2 mA after introduced into subcutaneous tissue (turning it on sooner will cause the patient pain) -Apply sufficient amount of gel to transducer -Position transducer (always stay within sterile field)/ place transducer on skin and adjust settings -Introduce needle/begin procedure
-negative pole should be connected to the ______ and the positive pole to the _____.
-stimulating electrode (needle) -patient’s skin —-Negative-needle —-Positive-skin
When would you turn on the PNS?
once in the Subcutaneous tissue -adjust to deliver 2mA AFTER introduced into subq tissue (any sooner, cause pain to pt)
PNS technique continued - from needle penetration on… (fyi/review)
-As needle approaches sheath, continuously reduce the mA so that the muscle response to the stimulation is maintained -Once the sought-after muscle response is obtained, the current intensity amplitude is gradually reduced and the needle is advanced further SLOWLY -Advancement of the needle and current reduction are continued until the desired motor response is achieved with a current of 0.2-0.5 mA stimulus duration ***** Optimal LA injection is when muscle contraction/response is maintained at a current between 0.2-0.5 mA ***** If muscle contraction is elicited < 0.2 mA, there could be increased risk of intraneural injection (neural damage)
***-Advancement of the needle and current reduction are continued until the desired motor response is achieved with a current of
0.2-0.5 mA stimulus duration
***** Optimal LA injection is when muscle contraction/response is maintained at a current
between 0.2-0.5 mA
***** If muscle contraction is elicited < 0.2 mA, there could be increased risk of
intraneural injection (neural damage) ** we want LA AROUND the nerve, not IN the sheath.
Once a proper motor response is obtained with a current of 0.2-0.5 mA (most nerve blocks), the needle is
positioned correctly for an injection of local anesthetic
***When the needle is in confirmed position, what do you do next?
- ASPIRATE! - A small test dose of local anesthetic is injected, which abolishes the muscle twitch **STAY STILL!! now blocked and you won’t get muscle twitch again**
If the motor twitch is lost during needle advancement, the stimulus intensity first should be
increased to regain the muscle twitch rather than move the needle blindly
insert PNS image
Black - to needle Red - to pt for grounding
charting considerations for block:
-twitch elicited -sustained up to -where you placed -how much LA you gave -insertion? …. etc.
