Mod IV: Regional Anesthesia Part 5 Flashcards by Olivier Mba

_{Regional Anesthesia - Locating Nerves}

How to find what your looking for?

Apply that Anatomy

Knowledge of nerve path, surrounding structures, and surface landmarks is of paramount importance

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_{Regional Anesthesia - Locating Nerves}

Techniques used to localize nerves

Landmarks - Paresthesia - Nerve Stimulator

Ultrasound - Fluoroscopy

CT guided

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_{Regional Anesthesia - Locating Nerves}

Nerve localization technique that provides both still and live x-ray views:

Fluoroscopy

Used primarily in pain blocks

Expensive

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_{Regional Anesthesia - Locating Nerves}

Nerve localization technique that provides still and live Ct images:

Ct guided

Used rarely in pain blocks

Extremely expensive!!!

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_{Regional Anesthesia - Locating Nerves}

Techniques for locating nerves that use surface landmarks and knowledge of anatomical relationships:

Landmark Techniques

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_{Regional Anesthesia - Locating Nerves}

Using Landmarks alone can help anesthetized which structures?

Ankle

Digits

Cervical plexus

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_{Regional Anesthesia - Locating Nerves}

Landmark Techniques can be combined with:

Paresthesia

Nerve Stimulator

Ultrasound

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_{Regional Anesthesia - Locating Nerves}

The feeling of tingling, tickling, burning, prickling, or buzzing felt is also known as:

Paresthesia

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_{Regional Anesthesia - Locating Nerves}

What’s the goal of Paresthesia technique?

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 nerves distribution

Old technique still used by some practitioners

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_{Regional Anesthesia - Locating Nerves}

What are disadvantages of the Paresthesia technique?

Risk of neural injury

Higher block failure rates when compared to newer techniques

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_{Regional Anesthesia - Locating Nerves}

Nerve localization technique that uses electricity to produce a response of a target nerve:

Nerve Stimulator Technique

Used in combination with anatomical and surface landmark knowledge

Motor –Target nerve muscles twitch

Sensory – paresthesia over target nerve distribution

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_{Regional Anesthesia - Locating Nerves}

Membrane potentials - What’s Resting MP?

– 90 mV

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_{Regional Anesthesia - Locating Nerves - Membrane potentials}

What’s Threshold Level? what happens when it’s reached by a stimulus?

– 55mV

Depolarization occurs

Propagation of Action potential

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_{Regional Anesthesia - Locating Nerves}

How does Nerve Stimulator work?

Negative Polarity Impulse

Neutralizes positive current outside nerve dropping MP

Black lead attached to needle

Red positive lead is attached to skin

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_{Regional Anesthesia - Locating Nerves}

Which nerves have Lowest Threshold of Ext Stim to generate AP? why?

Motor nerves

B/c Highly myelinated nerves

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_{Regional Anesthesia - Locating Nerves}

Which nerves have Higher Threshold for External Stim to generate AP? why?

Sensory nerves

B/c Unmyelinated nerves – slower

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_{Regional Anesthesia - Locating Nerve - Generating a Action Potential}

Which characteristics of a stimulus determine generation of an Action Potential?

Stimulus Strength and Duration

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_{Regional Anesthesia - Locating Nerves}

Generating a Action Potential - Strength of electrical stimulus is also known as:

Current Amplitude

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_{Regional Anesthesia - Locating Nerves}

The amount of time a stimulus must be applied to generate an Action Potential is known as:

Current Duration

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_{Regional Anesthesia - Locating Nerves}

Generating a Action Potential - Impulses of which duration are better discriminator of distance?

Short duration impulses

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_{Regional Anesthesia - Locating Nerves}

Motor impulse duration:

0.1 ms

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_{Regional Anesthesia - Locating Nerves}

Sensory impulse duration:

0.3 ms

Longer duration needed to reach threshold level

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_{Regional Anesthesia - Locating Nerves}

Nerve stimulator - Frequency:

1-2 Hz

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_{Regional Anesthesia - Locating Nerves}

Nerve stimulator - Duration:

1ms Motor
3 ms Sensory

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_{Regional Anesthesia - Locating Nerves} Nerve stimulator - Amplitude - Start stimulator at which mA?

1-1.5 mA Position needle =\> twitch ↓ mA, and adjust needle position …

_{Regional Anesthesia - Locating Nerves} Nerve stimulator - Amplitude - What's the goal?

**Goal is loss of motor response 0.3-0.5mA** Indicates that the tip of the block needle is in correct position **Never inject \<0.3mA** (0.2mA by some sources)

_{Regional Anesthesia - Locating Nerves} Nerve stimulator - Why is Reliability a Problem?

**74.5% sensitivity** for needle to nerve contact **25% NO muscle twitch** ^{even when needle actually touching nerve!!}

_{Regional Anesthesia - Locating Nerves} Nerve stimulator - Reliability is a Problem. However Twitch present at:

0.2-0.3mA ## Footnote **ALWAYS INTRANURAL!!**

_{Regional Anesthesia - Nerve stimulator} Technique of Locating Nerves with Series of 3 pulses (3Hz frequency), also known as:

**Sequential Electrical Nerve Stimulation** | (SENSe Mode)

_{Regional Anesthesia - Nerve stimulator} Sequential Electrical Nerve Stimulation aka SENSe Mode - Technique:

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

_{Regional Anesthesia - Nerve stimulator} Use of Sequential Electrical Nerve Stimulation aka SENSe Mode:

Single twitch achieved Needle optimized until 3 twitches present Goal: current 0.3 – 0.5mA with 3 twitches

_{Regional Anesthesia - Locating Nerves} Stimulating Needles:

**Insulated** Direct current at the tip for precise nerve location **Blunt Bevel**

_{Regional Anesthesia - Locating Nerves} Technique of locating nerves that provides real time imaging of target nerves, related structures, LA injection

**Ultrasound Guidance** 1978 1st case report of using US for regional

_{Regional Anesthesia - Locating Nerves} US guidance has greatly improved as evidenced by:

Block success Speed of onset Anesthetic quality of block **Becoming the gold standard in block placement!!!**

_{Regional Anesthesia - Locating Nerves} What are arguments againts US guidance?

Steep learning curve Adds to much time to blocks Cost of machine No need, “…my blocks don’t fail”

_{Regional Anesthesia - Locating Nerves} How is US image generated?

**Piezoelectric Material in Probe** ^{Electricity => material => sound waves} ^{Sound waves => material => electricity} **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**

_{Regional Anesthesia - Locating Nerves} US probe talks (_xx%) and listens (_yy%)

Talks (**2%**) Listens (**98%**)

_{Regional Anesthesia - Locating Nerves - Ultrasound Guidance} When US encounters boundaries some energy is reflected back at the probe and the rest transmitted. What you see is called:

**Reflection** This is what we see

_{Regional Anesthesia - Locating Nerves - Ultrasound Guidance} Degradation of US by rough surfaces and heterogeneous material is also known as:

**Scatter**

_{Regional Anesthesia - Locating Nerves - Ultrasound Guidance} Conversion of US into heat; This is where majority goes and it is also known as:

**Absorption**

_{Regional Anesthesia - Locating Nerves - Ultrasound Guidance} Does Absorption of US waves using modern US machines poses any risk to pts?

There has never been any documented biological risk to Pts

_{Regional Anesthesia - Locating Nerves - Ultrasound Guidance} Degradation of US wave in tissue is also known as:

**Attenuation** Higher frequency US energy degredates more quickly

_{Regional Anesthesia - Locating Nerves - Ultrasound Guidance} Higher frequency US energy degredates more quickly. What's the clinical significance of this?

Use **Higher frequency** probes only for **superficial structures** **Lower Frequency** probe are Better for **deep structures**

_{Regional Anesthesia - Locating Nerves - Ultrasound Guidance} The number of sound waves per sec is also known as:

**Frequency** 2 – 15 MHz commonly used in US Human ear 20Hz – 20 kHz

_{Regional Anesthesia - Locating Nerves - Ultrasound Guidance} Distance between wave peaks:

**Wavelength** Inversely related to Frequency Primary determinant of lateral and axial resolution Temporal resolution is related to frame rate (typically 30 frames/sec)

_{Regional Anesthesia - Ultrasound Guidance - Probe Selection} Higher Frequency Probes are also known as:

**Linear Probes** Better resolution of superficial structures Up to 6 cm deep For superficial nerve blocks and Vascular access. ^{IJ line, ISB, Femoral, etc}

_{Regional Anesthesia - Ultrasound Guidance - Probe Selection} Lower Frequency probes are also known as:

**Curvilinear Probes** AKA – Phase Array Visualize **deeper structures** **_{To 14 cm deep}** For deeper structure Nerve blocks and Musculoskeletal assessment ^{Sciatic nerve, TAPs, Neuraxial assessment}

_{Regional Anesthesia - Ultrasound Guidance - US Modes} The US mode that displays the 2D imaging we see today is also known as"

**B-Mode** ^(Brightness) What you will typically use

_{Regional Anesthesia - Ultrasound Guidance - US Modes} The US mode that displays Image of Movement over Time is also known as:

**M-Mode** Useful in assessment of specific tissues Heart valves, Lung

_{Regional Anesthesia - Ultrasound Guidance - US Modes} The change in sound waves resulting from relative motion between source and receiver is also known as:

**Doppler Effect**

_{Regional Anesthesia - Ultrasound Guidance - Doppler Mode} **Red** Color indicates flow moving in which direction?

Flow coming **toward** probe Moving Toward Receiver Higher Pitch *Useful for Vascular identification*

_{Regional Anesthesia - Ultrasound Guidance - Doppler Mode} **Blue** Color indicates flow moving in which direction?

Flow moving **Away** from probe Moving Away from receiver Lower Pitch *Useful for Vascular identification*

_{Regional Anesthesia - Ultrasound Machine} Knob that allows for optimal **depth adjustment** important for **focusing** image

**Depth** knob Limited to probe selected

_{Regional Anesthesia - Ultrasound Machine} Knob on Newer machines that can automaticaly focus

**Focus knob** May have to set depth to focus on

_{Regional Anesthesia - Ultrasound Machine} Knob that allows to adjust **Brightness** of image on screen

**Gain** knob Some machines allow for gain to be adjusted at different depths independently

_{Regional Anesthesia - Ultrasound Machine} Knob used to aid in detecting vascular structures

**Doppler knob**

_{Regional Anesthesia - Ultrasound Guidance} What Nerves Look Like? Nerve shapes:

Round, oval, triangular

_{Regional Anesthesia - Ultrasound Guidance} Images from US could have which three appearances?

Hyper-**echoic** **Hypo**-echoic **Honeycomb**

_{Regional Anesthesia - Ultrasound Guidance} What are possible US Image Artifacts?

Shadowing Enhancement Reverberation Mirror image Velocity Error

_{Regional Anesthesia - Ultrasound Guidance - Image Artifact} A significant reduction of image below solid objects is known as:

**Shadowing**

_{Regional Anesthesia - Ultrasound Guidance - Image Artifact} Overly **intense echogenicity** behind an object (Blood vessel, cyst) is known as:

**Enhancement**

_{Regional Anesthesia - Ultrasound Guidance - Image Artifact} Equally spaced bright linear echoes below an object is known as:

**Reverberation**

_{Regional Anesthesia - Ultrasound Guidance - Image Artifact} Objects appearing on both sides of a highly reflective interface represents which artifact?

**Mirror image**

_{Regional Anesthesia - Ultrasound Guidance - Image Artifact} Visual displacement of interface due to difference in actual US velocity versus celebrated speed (1540 m/sec) is known as:

**Velocity Error**

_{Regional Anesthesia - Ultrasound Guidance} What are the two axial options for maping a structure?

Short Axis Long Axis

_{Regional Anesthesia - Ultrasound Guidance - Imaging a structure} A Cross sectional or Transverse view represents which axis?

**Short Axis view**

_{Regional Anesthesia - Ultrasound Guidance - Imaging a structure} A Longitudinal view represents which axial view?

**Long Axis view**

_{Regional Anesthesia - Ultrasound Guidance} Needle Approaches:

In Plane Out of Plane

_{Regional Anesthesia - Ultrasound Guidance} Professor's Practice using US - Nerve Block:

Short axis View Needle In Plane Injection of LA under direct visualization Placement of Catheter directly visualized

_{Regional Anesthesia - Ultrasound Guidance} Professor's Practice using US - Vascular Access:

Short Axis Out of Plane