Intro to Regional Flashcards
1
Q
What advantages does a block room provide?
A
- Initially, regional anesthesia was conducted in the operating room
- Now, typically conducted in a designated “block room”
- More efficient
- Quicker turnover
- Allows “soak time” or “set-up”
- Requires dedicated/ knowledgeable staff
- Proper equipment/monitors
- Access to medication
2
Q
What resuscitation equipment is necessary to have in setup for regional anesthesia?
A
-
Resuscitation Equipment
- Oxygen supply, nasal airway, and O2 masks
- Oral airways of different sizes, laryngeal masks, and endotracheal tubes
- Laryngoscopes (Macintosh and Miller blades)
- Bag-mask ventilation device
- Suction
- Selection of various size intravenous cannulas
- Defibrillator
3
Q
What supplies are needed to perform regional anesthesia?
A
- Antiseptic solution for skin disinfection
- Sterile towels or drapes
- Marking pen
- Sterile gauze
- 20-mL syringes for local anesthetic solution
- One 1-ml syringe with a 25-gauge needle for skin wheal (optional)
- One 5-cm, short-bevel 22-gauge “B” bevel insulated needle
- most commonly used with single shot PNB
-
Balance b/w patient comfort and bending of the needle as it punctures through the skin
- Surface electrode to be used with nerve stimulator
- Nerve stimulator
- Ultrasound
-
selection of sedatives:
- midazolam 0.5-3 mg IV
- Short acting opioids such as fentanyl 50-100 mcg IV
- propofol 20-100 mg for more uncomfortable nerve blocks that require deeper sedation
-
LA and normal saline for drug diluation
- kept in separate compartment to avoid drug error
-
patient must have IV catheter before regional anesthesia started
*
4
Q
What to consider when choosing larger versus smaller gauge needles?
A
- longer needles bend easier during advancement and may be difficult to steer with deeper blocks, which may require a larger-gauge needle
- larger gauge needles are associated with
- increased severity of tissue injury and
- hematoma
-
smaller gauge needles carry more serious risk of the tip being inserted intra-fascicular
- resistance also increased with smaller gauge needles
- takes longer for blood to be aspirated back should the tip be intravascular
5
Q
Structure of local anesthetics?
What are local anesthetics characterized by?
A
- Contain an aromatic ring and an amine at opposite ends of the molecule, separated by a hydrocarbon chain, and either an ester or amide bond
- described by their potency, duration of action, speed of onset, and tendency for differential sensory nerve block
6
Q
What causes increase in potency of LA?
A
- Larger (increasing molecular weight) and more lipid soluble LA have increased potency
- larger, lipophilic molecules permeate the nerve membrane easier and bind to the Na channels with greater affinity
- for example, bupivacaine has greater lipid solubility and potency than lidocaine and mepivacaine
- lipid soluble LA are relatively water insoluble, and highly protein bound in blood.
- this makes the LA less readily removed by the blood stream
- therefore, increased lipid solubility is associated with increased protein binding in blood, increased potency and longer DOA
7
Q
What other factors influence the ability of the LA to produce adequate regional anesthesia?
A
dose
site of administration
additives
temperature
pregnancy
8
Q
What are examples of long acting local anesthetics?
A
- Ropivacaine -0.5% (most common)
- Bupivacaine 0.25- 0.5% (sensory >motor; longest latency of onset)
- liposomal bupivacaine (Exparel)- infiltration; ISB
9
Q
What is an example of intermediate acting LA?
A
Mepivacaine 1.5% (intense motor block)
10
Q
Example of short acting LA?
A
Lidocaine 1-2% (most versatile)
11
Q
What are some examples of adjuncts to regional anesthesia?
A
-
Adjuncts
- Epinephrine
- 1:200,000
- 1:400,000
- A2 agonist
- Clonidine 100 mcg
- Steroids
- Dexamethasone 8 mg
- Opioids
- Buprenorphine 300 mcg
- Mixed opioid agonist & antagonist
- Buprenorphine 300 mcg
- Epinephrine
-
Others
- Sodium bicarbonate
- Increase speed of onset
- Neostigmine
- Magnesium
- Ketamine
- Fentanyl
- Morphine
- Sodium bicarbonate
12
Q
Why are adjuncts added to regional anesthesia technique?
A
- Speed onset, prolong effect, and reduce total required dose.
- can enhance postoperative analgesia without prolonging adverse effects of local anesthetics.
- optimizing analgesia while minimizing CNS side effects.
13
Q
What are some benefits to regional anesthesia?
A
- Regional anesthesia has become commonplace in many practices worldwide due to the increasing evidence of patient benefits, such as:
- a reduction in pulmonary and thromboembolic complications
- reduction in opioid consumption
- reduced pain and time to discharge
- better quality of life in the immediate postoperative period.
14
Q
Historical and common techniques for nerve block placement?
A
-
Historical
- Topical
- Compression
- Paresthesia
-
Common
- Nerve stimulation
- Ultrasound imaging
The combined use of ultrasound and nerve stimulation creates a more objective method of achieving accurate and safe blocks while allowing monitoring and visualization of the block needle and targets in real-time.
15
Q
Use of nerve stimulation for PNB placement?
A
- First described by von Perthes in 1923
- Didn’t gain widespread acceptance until late 1990’s
- Low current electrical impulse applied to a peripheral nerve produces stimulation of motor fibers and can theoretically identify distal nerves.
- Low-intensity (up to 5mA) and short duration (0.05-1ms) electrical stimulus (at 1-2 Hz repetition rate) to obtain defined response (muscle twitch or sensation) in order to locate a peripheral nerve/nerve plexus with an insulated needle before injection LA
- use of nerve stimulator can locate an intraneural or intrafascicular needle placement, prevent further needle advancement intraneurally and help reduce risk of nerve injury
- Less nerve damage than with paresthesia techniques
- Still very inconsistent results
- dual monitoring (concurrent use of US) has become common practice to guide needle placement and robust medicolegal documentation of nerve block procedures
16
Q
Features on a nerve stimulator?
A
- Hz- frequency - cycles/second
- 2 – 2.5 Hz
- ms – pulse width
- 100 – 200 ms
- Matches chronaxies of Aa fibers
- Minimal sensory nerve stimulation
- mA - Intensity
- 0.01 – 5 mA
- What we really want to control
- large, readable display of actual current delievered
-
selectable pulse duration (width)
- motor fibers are stimulated more easily with currents of shorter duration (0.1 ms) while sensory fibers require longer stimulus duration (1.0 ms)
- A display of the circuit impedance (kΩ) is recommended to allow the operator to check the integrity of the electrical circuit and to detect a potential intraneural or intravascular placement of the needle tip.
- An automatic self-check process of the internal functioning of the unit with a warning message if something is wrong with the circuit.
17
Q
Safety features of a nerve stimulator?
A
- Easy and intuitive use.
- A large and easy-to-read display.
- Limited current range (0–5 mA) because an amplitude that is too high may be painful or uncomfortable for the patient.
- A display of all relevant parameters, such as amplitude (mA) (alternatively stimulus charge [nC]), stimulus duration (ms), stimulus frequency (Hz), impedance (kΩ), and battery status.
- Clear identification of output polarity (negative polarity at the needle).
- Meaningful instructions for use, with lists of operating ranges and allowed tolerances.
- Battery operation of the nerve stimulator, as opposed to electrical operation, provides intrinsic safety; there is no risk of serious electric shock or burns caused by a short circuit to the main supply of electricity.
- The maximum energy delivered by a nerve stimulator with 5 mA and 95-V output signal at 1-ms impulse duration is only 0.475 mWs.
- Combined units for peripheral (for peripheral nerve blockade) and transcutaneous (for muscle relaxation measurement) electrical nerve stimulation should not to be used because the transcutaneous function produced an unwanted high energy charge.
18
Q
Practical guidelines for nerve stimulator use?
(Attachement, starting settings?) process for using NS?)
What is the Raj test?
A
-
Attachment
- Negative – needle
- Positive – patient
-
Set to 1 mA
- sufficient amplitude for most superficial nerves
- for deeper nerves, it may be necessary to increase initial current amplitude between 1.5-3 mA until motor response elicited at a safe distance from the nerve.
- too high current intensity can lead to direct muscle stimulation or discomfort for the patient
-
Advance needle to get the desired movement
- if motor twitch is lost during needle advancement, stimulus intensity should be increased first to regain muscle twitch, rather than move the needle blindly
-
After you obtain desired movement, decrease current to 0.3 -0.5 mA, (at 0.1 ms stimulus duration) while advancing the needle
- < 0.2 mA increase chance of intraneural injection
- Inject 1 – 3 ml’s local anesthetic
-
Loss of twitch (after injection of local anesthetic)
- Positive Raj test
- Inject local in 3-5 ml increments
- It should be remembered that the absence of the motor response with a stimulating current of up to 1.5mA does not rule out intraneural needle placement (low sensitivity)
-
however, the presence of a motor response with a low-intensity current (<0.2 mA, 0.1 mS) occurs only with intraneural and possibly, intrafascicular needle placement)
- if motor response still present at 0.2mA or less, needle should be withdrawn slightly to avoid risk of intrafascicular injection.
19
Q
What are insulated needles?
A
- B – Beveled
- 30 – 45 degrees
- 22 – 24 gauge
- Non-conductive coating
- Focus current at the tip of the needle- provide more accurate localization of neural structures
- Allows for stimulating of target nerve with low current (0.2 – 0.5 mA)
20
Q
Advantages to ultrasound use?
A
- Visualize anatomical features and block needle (tip of needle) in real time.
- Small, portable
- Multiple uses
- Doppler scan (arterial vs venous flow)
- Photo documentation of final block with local spread.
- May decrease time to perform block
- May Use less volume of local anesthetic
- No clear advantage in block effectiveness compared to nerve stimulator technique.
- Improves the success rate of the block
- Decreases placement time and onset of block
- Reduces the volume of LA required for successful block
- Is associated with decreased vascular puncture and local anesthetic systemic toxicity (LAST)
- Reduces incidence of pneumothorax and phrenic nerve block
21
Q
Disadvantages to ultrasound use?
A
- Expensive ($20-$60 K)
- Anesthesia provider experience required
- Learning curve
- Superior understanding of anatomy
- Eye and hand coordination and dexterity
22
Q
What are ultrasound waves?
A
- Mechanical energy transmitted longitudinally through a medium by vibration of particles in the medium
-
in most cases, ultrasound transducers are made of special ceramic crystal materials called piezoelectrics
- these materials are able to produce sound waves when an electric field is applied to them, but can also work in reverse, producing an electric field when a sound wave hits them.
-
in most cases, ultrasound transducers are made of special ceramic crystal materials called piezoelectrics
- Ultrasound: non-audible sound wave with frequencies above 20 kHz
- piezoelectric in US probe send out sound waves, which are reflected back by tissues in the path of the beam.
-
using speed of sound and time of each echo’s return, the scanner calculates the distance from the transducer to the tissue boundary
- these distances generate 2D images of tissues and organs
30
Q
What is the ultrasound probe?
A
- An ultrasound transducer, also called a probe, is a device that produces sound waves that bounce off body tissues and make echoes.
- The transducer receives the echoes and sends them to a computer that uses them to create an image called sonogram.
- essential element of each ultrasound transducer is a piezoelectric crystal.
- It serves to generate as well as receive ultrasound waves.
- You can find ultrasound transducers in different shapes, sizes, and with diverse features. That is because you need different specifications for maintaining image quality across different parts of the body.
31
Q
What is a linear probe?
A
- Typically: 4 – 13 MHz (high frequency transducer)
- Crystals in a single row
- Evenly spaced beams and the best resolution
- Excellent for vascular and superficial structures
- 6 – 8 cm’s
- general rule of thrumb- use this probe for anything under 8 cm. if >8 cm, then the linear probe limits visualization
- 6 – 8 cm’s
- Most commonly used in regional anesthesia
32
Q
What is a curved array?
A
- Typically: 2 -5 MHz (low-frequency probe)
- Ideal for deep structures
- has larger/wider footprint allowing for better lateral resolution
- Crystals in a curved pattern
- Best resolution in center
- Edges loose resolution
- Wide field and deep field of view
- Most commonly used for abdomen and deep structures like the sciatic nerve
- also can be used for cardiac and thoracic US exams, but limited by large footprint and difficulty with scanning b/w rib spaces
33
Q
What is a phased array probe?
A
- Typically 1.7 – 4 MHz
- “cardiac probe”
- Just a few crystals
- Pie shaped image
- Has good resolution in center
- Excellent for looking through small windows -
- I.E. between ribs at the heart
- advantage to this probe is that the crystals are layered and packed in the center of the probe, making it easier to get into small spaces (such as ribs)
34
Q
What are the planes of view?
A
- In plane
- View shaft and tip of needle
- With the in-plane approach, the needle enters the skin at the side of the probe. The needle traverses the plane of ultrasound and the whole shaft is visualized as it progresses towards the target.
- View shaft and tip of needle
- Out of plane
- Only single cross section of the needle
- With the Out-of-Plane approach, the needle enters the skin away from the probe, and is aimed at the plane of sound. With this approach just the needle tip is visualized and the remainder of the needle is off screen.
- Only single cross section of the needle
36
Q
What are the various echogenicty of different structures in the body? bones? tendon? nerves? far? arteries and veins?
A
- Bones- hyperechoic, with acoustic shadowing
- Tendon- hyperechoic
- Nerves- variable
- hyperechoic in upper extremity
- hypoechoic in lower extremity
- Fat- hypoechoic; comrpessible
- Arteries and Veins- anechoic
- veins- anechoic/hypoechoic, non-pulsatile, compressible
- Muscle- heterogenous (mixture of hyperechoic lines with a hypoechoic tissue background)
- Pleura- hyperechoic line
- local anesthetic- hypoechoic, expanding hypoechoic region
37
Q
What are various terms to describe echogenicity?
A
- Hyperechoic
- More dense than surrounding tissue
- bone
- tendone
- UE nerves
- More dense than surrounding tissue
- Hypoechoic
- Less dense than surrounding tissue
- LE nerves
- Fat
- Less dense than surrounding tissue
- Isoechoic
- Same density as surrounding tissue
- Anechoic
- Devoid – fluids (moving blood, cysts, bile, etc)
- ex- arteries, veins
- Devoid – fluids (moving blood, cysts, bile, etc)
- Reflective
- Creating a shadow
38
Q
What is depth on a ultrasound?
A
- one of the first US setting adjusted
- rule of thmb- only use as much depth as necessary to see structure of interest
- if depth is too high, wasted US real estate
- right side of screen has dots/lines correlated to depth in cm
- increase depth- numbers increase on right side of screen to correspond to depth of penetration
39
Q
What is focus?
A
- When adjusting focus, you are concentrating your US waves at a specific depth of the image to maximize resolution at that depth
- some machines, like sonosite, don’t allow for adjusting focus since the machine has auto-focus built in
40
Q
What is gain?
A
- Is related to image “brightness”
- how light/dark you want your image to appear
- increases or decreases strength of the returning US signal that you visualize on the screen
- Allows compensation for attenuation of signals due to absorption
- Does not impact how much energy is transmitted to patient
- Can affect image interpretation
- excessive or inadequate gain can cause blurring of tissue boundaries and loss of info
- optimal gain for peripheral nerves is typically the gain at which the best contrast b/w muscle and adjacent connective tissue
- Most ultrasound machines will allow you to further adjust the gain in even more specific areas of your ultrasound screen. This ultrasound setting is called “Time Gain Compensation” or TGC.
- Adjusting the Time Gain Compensation (TGC) allows you to adjust the gain at almost any depth of your ultrasound image, not just the near and far-fields.
Pic- top left- not enough gain, top right- too much gain. middle bottom- just right
41
Q
What are the 4 basic movements of the ultrasound probe?
A
- Slide
- Rock
- Tilt (Fan)
- Rotate
- 5th is compression
43
Q
What is anisotropy
A
- dependent on angle of the insonating beam
- maximum return echo occurs when US beam is perpendicular to the tendon
- decreasing the insonating angle on the normal tendon, will cause it to change from brightly hyperechoic (actual echo from tightly bound tendon fibers) to darkly hypoechoic
44
Q
What is the bayonet effect?
A
- Virtual bending of a needle caused by faulty image processing
- caused by reflected US beam from different parts, but the same depth of the needle arrives back at difference times
- to show an object at the correct place, the echo return time (measured) is multiplied by the US speed (assumed)
- software assumes constant US speed 1540m s-1 in soft tissues
- however, this is an average value and actual speed can be difference
- when the needle goes through or under tissue with varying characteristics, the reflected US beam from different parts, but same depth of the needle, arrives back to the probe at slightly different times
45
Q
What is reverberation effect?
A
- Occurs when an US beam encounters two strong parallel reflectors
- when US beam reflects back and forth b/w the reflectors, the US transducer interprets the sound waves returning as deeper structures since it took longer for wave to return to the transducer
- reverberation artifacts can be improved by changing the angle of insonation so reverberation b/w strong reflectors cannot occur
46
Q
What is shadowing?
A
- The ratio of reflected and transmitted ultrasound is determined by the difference in acoustic impedances of tissues on either side of the interface: the larger the difference, the more ultrasound is reflected back
- acoustic impedance of soft tissue is every similar to each other
- bone has larger acoustic impedance
- consequently, bone and tissue interfaces give a very strong echo
- unfortunately, this makes examination of underlying objects impossible as only a small percentage of original US energy remains for underlying planes
- consequently, bone and tissue interfaces give a very strong echo
47
Q
What is injection pressure monitoring?
A
- Intraneural injections may lead to nerve damage
- monitoring injection pressure can help distinguish needle-tip location in perinerual tissue versus the needle-nerve contact or intrafasciular needle placement
-
high pressure injection, even with small volumes, into the intraneural space, can be a major contributor to mechanical injury of neurological tissue during PNB
- combo of mechanical injury from preaching of the perineurium, leading to interference with endoneural microcirculation, and chemical injury from neurotoxicity of LA
- Damage
- Cut perineurium
- Compression of microcirculation
- Chemical injury from neurotoxicity
- Inflammatory response/scaring
- Monitoring
- Initial - < 15 mmHg (psi? slide says mmHg but picture shows psi)
- Injection - < 20 mmHg
- The inline pressure monitor is placed proximal to the needle and in line with the non-distensible tubing. The other end of the pressure monitor is attached directly to the syringe.
- The critical opening pressure necessary to inject local anesthetic when the needle is in contact with the nerve or is intrafascicular has been estimated in several studies to be more than 15 psi
