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.
What is Absorption?
-Conversion of US into heat
-This is where majority goes
-Using modern US machines there has never been any documented biological risk to Pts
What is Attenuation?
-Degradation of US wave in tissue
-Higher frequency US energy degrades more quickly
Clinical significance:
-Higher frequency probes (Only for superficial structures)
-Lower Frequency probe (Better for deep structures)
Attenuation is high in muscle and skin, and low in fluid-filled structures. High-frequency waves are attenuated to a greater extent than low-frequency waves.
What is Frequency?
-How many sound waves per sec
-2 – 15 MHz commonly used in US
-Human ear 20Hz – 20 kHz
Higher frequency, shorter wavelength
What is Wavelength?
-Distance between wave peaks
-Inversely related to Frequency (higher frequency = shorter wavelength)
-Primary determinant of lateral and axial resolution
-Temporal resolution is related to frame rate (typically 30 frames/sec)
-Shorter wavelength typically has more detail (better resolution)
What is the Linear Probe used for?
-Higher Frequency Probe
-Better resolution of superficial structures
-Up to 6 cm deep
-For superficial nerve blocks and Vascular access: IJ line, ISB, Femoral, etc.
5-10 MHz
What is the Curvilinear Probe used for?
-AKA – Phase Array
-Lower Frequency probe
-Visualize deeper structures
-To 14 cm deep
-For deeper structure Nerve blocks and Musculoskeletal assessment: Sciatic nerve, TAPs, Neuraxial assessment
2-5 MHz
What is the US mode we typically use (2D mode)?
B-Mode (Brightness)
What is M-Mode?
-Image of Movement over Time
-Useful in assessment of specific tissues
-Heart valves, Lung
What is Doppler Mode?
-Doppler Effect - The change in sound waves resulting from relative motion between source and receiver
Moving Toward Receiver:
-Higher Pitch (frequency)
-Flow coming toward probe
-Red Color
Moving Away from receiver:
-Lower Pitch (frequency)
-Flow moving Away from probe
-Blue Color
Useful for Vascular identification
Flow moving towards the probe/receiver is what pitch and what color?
-Higher pitch
-Red
Flow moving away from the probe/receiver is what pitch and what color?
-Lower pitch
-Blue
What are the 3 ways nerves can appear on an US?
-Hyper echoic (white, shiny)
-Hypo echoic (black)
-Honeycomb (fascicles within the nerve themselves)
What is Shadowing? (Review Regional Anesthesia ppt for pictures)
Significant reduction of image below solid objects.
-Ex: Bone
What is Enhancement? (Review Regional Anesthesia ppt for pictures)
-Overly intense echogenicity behind an object
-Ex: Blood vessel, cyst
What is Reverberation? (Review Regional Anesthesia ppt for pictures)
Equally spaced bright linear echoes below an object
What is Mirror Image? (Review Regional Anesthesia ppt for pictures)
Objects appearing on both sides of a highly reflective interface
What is Velocity Error? (Review Regional Anesthesia ppt for pictures)
Visual displacement of interface due to difference in actual US velocity versus calibrated speed.
-1540 m/sec
What view is the Short Axis?
-Cross sectional
-Transverse
What view is the Long Axis?
Longitudinal view
What does In Plane mean?
-The needle is parallel to the probe
-Can see the whole needle length
-Can be easy to fall off to one side or the other
-US beam is about 2 mm wide (credit card width)
What does Out of Plane mean?
Needle is perpendicular to probe
-Can only see bright shiny needle tip
-Easy to lose track of tip
What are the benefits of Single Shot?
-Easier to perform
-Fewer risks
-Effects generally limited <24 Hrs
Which has more risks, single shot vs continuous perineural catheter?
Continuous perineural catheter
What are the risks associated with a continuous perineural catheter?
More Difficult to perform and maintain than SS.
More risks:
-Infection
-Leaking
-Dislodgement/migration
-Knotting and kinking
-Neural injury
-Equipment goes home with Pt
Pt selection is critical
What are the benefits of a continuous perineural catheter?
-Longer/better pain control (Can remain in up to 72hrs)
-Facilitates early discharge
-Reduce narcotic use
-Also reduced side effects of narcotics
-Improved PT satisfaction (Will play big part in future reimbursement)
-Allows more invasive procedures to be outpatient
What is the Triad of Safety?
-Nerve Stimulator: negative test. If you don’t have a twitch AND you’re above 0.3 mA, you cannot be inside of a nerve.
-Injection monitoring: Pressure, pain, and paresthesia. Do not inject! Does it hurt? Numbness/tingling?
-Ultrasound Guidance
