Regional Intro/US Flashcards
Nerve-blocking potency of LAs increases with
increasing molecular weight and increasing lipid solubility.
Larger, more lipophilic molecules permeate nerve membranes more readily and bind Na+ channels with greater affinity.
Increased lipid solubility [in LAs] is associated with
Increased protein binding in blood, increased potency, and longer duration of action
Regional anesthesia has become commonplace in many practices worldwide due to the increasing evidence of patient benefits such as:
- reduction in pulmonary and thromboembolic complications
- reduction in opioid consumption
- as well as reduced pain and time to discharge
- better quality of life in the immediate post-op period
the use of nerve stimulation can recognize
- an intraneural or intrafasicular needle plaecment injection
- prevent further needle advancement intraneurally and help reduce teh risk of nerve injury
Nerve stimulator control: Hz
Hertz - measure of frequency
cycles per seond/pulses per second.
Usually 1 - 3 Hz, best compromise = 2 Hz
Nerve Stimulator Control: Ms
Ms: pulse width, the pulse duration.
Usually between 0.1 and 1.0 milliseconds,
motor fibers are stimulated more easily with current of shorter duration (0.1 Ms)
starting milliamps for superficial nerves
1 milliamp to start in most cases
starting milliamps for deepr nerves
Although results differ for different blocks, in general the use of US guidance compared with nerve stimulator technique:
- improves the success rate of blocks
- decreases the placement time and onset of blocks
- reduces the volume of LA required for successful block
- Is associated with decreased vascular puncture and LAST
- reduces incidence of pneumothorax and phrenic nerve block
useful applications for “M” mode US:
- assessment of the IVC for intravascular volume
- estimating wall movement and cardiac contractility
- evaluation of pneumothorax
“M” mode is used extensively in
cardiac and fetal cardiac imaging, not used in regional anesthesia
color flow doppler US colors:
red: high frequency, movement toward transducer
cold: low frequency flow, movement away from transducer
Color power doppler identifies
the amplitude or power of the Doppler signals rather than the frequency sfhits. More sensistive than pulse wave doppler to detect blood flow in organs with typically low flow states, such as ovaries or testicles.
Particularly useful in evaluation or ovarian or testicular torsion.
Linear Probe specs:
- typically 4-13 mHz - considered “high frequency”
- crystals in a single row
- evenly spaced beams and the best resolution
- excellent for superficial structures (<8cm)
- most commonly used in regional anesthesia
linear probe -> high frequency, linear footprint, shallow structures
Curved Array Probe:
- typically 2-5 Hz
- ideal for deep structure
- best resolution in center
- edges loose resolution
- wide and deep field of view
- most commonly used for abdomen and deep structures like the sciatic nerve
“Curvilinear US probe has a frequency range of 2-5 mHz. It is considered a low-frequency probe and has a large/wide footprint.”
often used for abdomenal US, can be used for thoracic.
Phased Array Probe:
- Phased array/sector array/ aka cardiac probe
- typically 1.7 - 4 mHz
- just a few crsytal
- pie shaped image
- has good resolution in the center
- excellent for looking through small windows -> heart, ribs
- 1-5mHz
- Similar frequency tot he curvilinear porbe but has a smaller and flat footprint.
- Crystals are layered and stacked in the center of the probe.
hyperehoic =
more dense (white) than surrounding tissue
hypoehoic
less dense (darker) than surrounding tissue
anechoic
devoidof tissue - fluids/blood/cysts
bones and tendons are
hyperechoic
nerve echogenicity
is variable
- upper extremity: nerves are HYPERECHOIC
- lower extremitity: nerves are HYPOechoic
Gain
- gain is related to brightness
- allows compensation for attentuation of signals due to absorption
- does not impact how energy is transmitted to patient
“how bright or dark you want your image to appear”
TGC
time gain compensation:
- most machines will allow you to further adjust the gain in even more specific areas of your US screen. This is called time gain compensation.
- Adjusting the TGC allows you to adjust the gain at almost any depth of your US image, not just near and far fields.
4(+) cardinal US movements
- Slide
- Rock
- Tilt “Fan”
- rotate
- compression
Anisostropy:
Echongenicity changes based on the angle of the probe
Dependent ont he angle of the insonating beam. Maximum return of echo occurs when the US beam is perpendicular to tendon,
Bayonet Artifact
When beam passes through two adjacent areas with different density and needle appears to bend
Reverberation
Repeated reflection between strongly refecltive surfaces
posterior shadowing
dropout of singal behind poorly conducting tissue like bone/air
longer gauge needles for regional anesthesia are
associated with increased severity of tissue injury and hematoma.
smaller gauge needles carry the risk of
“More serious risk of” being inserted into intra-fasciular.
motor fibers are stimulated more easily with
currents of shorter than 0.1 ms duration,
sensory fibers requires a longer stimulus duration (1.0ms)
starting amplitude for PNS
for superficial nerves 1 mA is fine, for deeper nerves: 1.5 to 3mA
“B” mode
B = best for regional
also “brightness”
2d images.
