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.
