Regional Anesthesia Basic Overview (pt 2) Flashcards
When is Fluoroscopy used?
-Provides both still and live x-ray views
-Used primarily in pain blocks
-expensive
When do you use CT do guide nerve location?
-Provides still and live Ct images
-Used rarely in pain blocks
-Extremely expensive
Describe the Paresthesia technique of locating a nerve.
Goal is to place the needle in direct contact with the desired nerve to produce a Paresthesia.
-This tells the practitioner they are very close or in the target nerve, then withdraw slightly until paresthesia stops and inject LA
-NEVER inject LA if pt has sharp PAIN or PARESTHESIA!!!
-The elicited paresthesia should follow the target nerve’s distribution
-Old technique still used by some practitioners
-Risk of neural injury
-Higher block failure rates when compared to newer techniques
What is a paresthesia?
The feeling of tingling, tickling, burning, prickling, or buzzing
Describe the nerve stimulator technique.
-Used in combination with anatomical and surface landmark knowledge
-Use of electricity to produce a response of a target nerve.
-Motor –Target nerve muscles twitch
-Sensory – paresthesia over target nerve distribution
How does a Nerve Stimulator create a response? (Clarify this in textbook)
-Normal RMP is -90 mV (according to ppt)
-Threshold is about - 55 mV
-The nerve stimulator emits a negative polarity impulse that neutralizes positive current outside the nerve, dropping the membrane potential.
-Needle tip provides negative polarity to reach the threshold
Which nerves have the lowest threshold of external stimulation to generate an AP?
Highly myelinated nerves (motor)
Which nerves have the highest threshold of external stimulation to generate an AP?
Unmyelinated nerves (slower, sensory)
What is Current Amplitude?
The strength of an electrical stimulus.
What is Current Duration?
How long the stimulus is applied.
-Short duration impulses are better discriminator of distance
-Motor = 0.1 msec
-Sensory = 0.3 msec (longer duration needed to reach threshold)
How do you perform the Nerve Stimulator technique?
-Frequency: 1-2 Hz
-Duration: 0.1 ms motor and 0.3 ms sensory
-Start stimulator at 1-1.5 mA
-Adjust needle position to elicit twitch
-Decrease mA and adjust needle position further
-Goal is to loss of motor response at 0.3-0.5 mA. Indicates that the tip of the block needle is in the correct position.
What about if you have a twitch at <0.3 mA?
Never inject <0.3 mA!!!!
-Issue with reliability of the nerve stimulator
-You are ALWAYS intraneural if a twitch is present at 0.2 - 0.3 mA.
What is SENSe Mode?
Sequential Electrical Nerve Stimulation
-Series of 3 pulses (3Hz frequency)
-2 short: 0.1ms
-1 longer: duration increases with Amplitude
-0.2ms @ 0.3mA
-0.42ms @ 1mA
-0.84ms @ 2mA
-Longer pulse reaches further in tissue (can target a nerve further away)
Use:
-Single twitch achieved
-Needle optimized until 3 twitches present
-Goal: current 0.3 – 0.5mA with 3 twitches
What are Insulated needles?
Needles that are coated to where just the needle tip is exposed.
-Current is directed at the tip for precise needle location
-Allows for the discharge of electricity to be more exact.
How do ultrasound probes work?
-There is Piezoelectric material in the probe.
-Electricity -> material (tissue) -> sound waves -> material (tissue) -> electricity -> picture.
-100 - 300 crystals in a Probe
-Send out cyclical pulses of US energy and measures reflected energy that travels back to the probe
-Reflected energy produces the US image you see
-Probe talks (2%) and listens (98%)
-The sum of all the crystals creates the US beam.
What is Reflection?
-This is what we see
-When US encounters boundaries some energy is reflected back at the probe and the rest transmitted.
What is Scatter?
Degradation of US by rough surfaces and heterogeneous material.
-Ex: bone, striations in muscle, etc.
