Intro to Regional Flashcards
1
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
2
Q
What other factors influence the ability of the LA to produce adequate regional anesthesia?
A
dose
site of administration
additives
temperature
pregnancy
3
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
4
Q
What is an example of intermediate acting LA?
A
Mepivacaine 1.5% (intense motor block)
5
Q
Example of short acting LA?
A
Lidocaine 1-2% (most versatile)
6
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.
7
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.
8
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)
9
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
10
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
11
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.
12
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.
13
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
14
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
15
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)
16
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
