Regional Exam I Flashcards
What nerves compose the Brachial Plexus?
Mostly C5-C8 and T1
- some contributions from C4 and T2
Where do C5 and C6 rami unite?
medial border of the middle scalene
- forms the superior trunk of the plexus
What makes up the roots of the brachial plexus?
ventral rami
What nerve becomes the middle trunk of the brachial plexus?
C7
Which nerves make up the inferior trunk of the brachial plexus?
C8 and T1
What facilitates the US identification of the C7 nerve root?
C7 transverse process lacks an anterior tubercle
Where do the roots and trunks of the Brachial Plexus pass through?
interscalene groove
When do the 3 trunks of the brachial plexus undergo the first anatomic separation?
lateral border of the first rib
- anterior (flexor)
- posterior (extensor)
What parts form the lateral cord of the Brachial Plexus?
anterior divisions of the superior and middle trunks
What parts form the posterior cord of the Brachial Plexus?
posterior divisions of all 3 trunks
What parts form the medial cord of the Brachial Plexus?
anterior division of the inferior trunk
How many branches do the cords separate into?
2 major terminal branches and a variable number of minor intermediary branches
Innervation of lateral cord of the Brachial Plexus
musculocutaneous nerve and lateral component of median nerve
Innervation of posterior cord of the Brachial Plexus
dorsal aspect of the upper extremitiy
- via radial and axillary nerves
Innervation of medial cord of the Brachial Plexus
ulnar nerve and the medial component of the median nerve
Important intermediary branches of the medial cord of the Brachial Plexus
medial antebrachial cutaneous nerve and the medial cutaneous nerve
- these join the intercostobrachial nerve (T2) to innervate the skin over the medial aspect of the arm
Endoneurium
connective tissue around the myelin sheath of each myelinated nerve fiber
Perineurium
covers fascicles
Epineurium
covers groups of fascicles
- as the nerve travels away from the spinal cord, the density diminishes, but its total volume increases
- Amount of neural tissue remains constant
- 1:1 in proximal plexus to 2:1 in distal plexus
Why are peripheral nerves more difficult to block than distal nerves?
greater proportion of connective tissue compared to nerve/fascicle
Where is local anesthetic first absorbed by the nerve?
mantle fibers on the nerve’s periphery
- blockade manifests proximal to distal
- block resolution goes from distal to proximal
What may explain the relatively longer block onset times with distal compared to proximal?
increased ratio of nonneural to neural tissue as one moves away from the spinal cord
Response of superior trunk stimulation
deltoid motor response
Response of musculocutaneous nerve stimulation
arm to flex at elbow
Response of median nerve stimulation
forearm pronation, wrist flexion, and thumb opposition
Response of ulnar nerve stimulation
ulnar deviation at the wrist, little-finger flexion, thumb adduction, and flaring of fingers
Response of radial nerve stimulation
wrist and finger extension
What method is used to assess the extent of the brachial plexus blockade?
4 P’s
- push the arm (radial nerve)
- pull of the arm (musculocutaneous nerve)
- pinch at base of index finger (median nerve)
- pinch at base of little finger (ulnar nerve)
Origin of verteral artery
subclavian artery
C6
Where does the external jugular vein usualy lie?
over the interscalene groove at C6
Where does the subclavian artery usually lie?
alongside the brachial plexus over the first rib
Supraclavicular nerves
branches of the superficial cervical plexus (C3-C4)
- provide cutaneous innervation of the cape of the shoulder
- NOT part of the brachial plexus
- still may be blocked with interscalene
(3) Accessory Upper Extremitiy Nerve Blocks
- supraclavicular
- suprascapular
- intercostobrachial
Suprascapular Nerve
C5 and C6
- provides sensory innervation to posterior/superior 70% of the shoulder joint, acromioclavicular joint, and to the anterior axilla
- typically blocked by interscalene
Suprascapular Nerve Block
usually done as an adjunct to general anesthesia or a rescue block for an incomplete ISB
- approaching from a cephalad to caudad direction reduces risk of pneumothorax
Intercostobrachial nerve
T2
- medial upper arm or axilla
- branch of second intercostal nerve
Ultrasound in Regional Blocks
- 4-5 minutes faster
- faster onset and longer duration of block
- fewer needle passes
- less patient discomfort
Continuous Catheter settings for Brachial Plexus
- 5-10 mL/hour basal rate
- 2-5 mL/hour bolus volume
- 20-60 minutes lockout
What determines how long a block should last?
- hos much the patient desires a numb extremitiy
- ability to protect insensate arm from injury
- surgeon’s need to assess neurovascular function
Epinephrine in Local Anesthetics
- prolongs duration and intensity
- 1:200,000 (5 ug/mL) increases the mean duration of lidocaine almost 1.5x
- causes vasoconstriction
- prolongs nerve’s exposure by limiting clearance
- limits systemic local anesthetic toxicity
- intravascular marker
Clonidine and Local Anesthetics
- prolongation of anesthesia and analgesia
- best when mixed with intermediate acting LA
- best used in brachial plexus blockade
What may cause peripheral nerve injury within the first 24 hours?
hematoma, intraneural edema, or a lesion of axons
Mechanical Trauma of Regional
- mechanical trauma
- needle type
- injury occurance is higher in long-beveled needles
- elicitation of paresthesia
- high injection pressure
High injection pressures and Ischemic Nerve injury
- infrascicular injection can result in compressive nerve sheath pressures that exceed 600mmHg for up to 15 min
- axonal degeneration and dystrophy
- fibroblast proliferation
Which block has the highest rate of hemidiaphragmatic paresis?
Interscalene 100%
a patient with ____% reduction in pulmonary function should not recieve an upper extremity block
30%
Pneumothorax due to a regional block is most likely to occur ____ hours afterwards
6-12 hours
- concern for outpatients without medical followup
Convulsant doses after carotid or vertebral artery injection of lidocaine and bupivacaine
Lidocaine 14.4mg and bupivacaine 3.6mg
When should local anesthetics peak after a single injection?
10 to 30 min
(up to an hour if using Epinephrine)
Which approach has the greatest seizure risk?
vertical infraclavicular
Seizures and Peripheral blocks
5x more likely than epidural
- test dose
- aspiration
- fractioned dosing with continuous observation
Horner Syndrome
(oculosympathetic palsy)
local anesthetic diffuses to sympathetic cervical ganglion chain
- ptosis, miosis, and anhydrosis
- may cause hoarseness due to blockade of recurrent laryngeal nerve
What blocks may cause damage to recurrent laryngeal nerve?
Interscalene and supraclavicular
(has not been reported with infraclavicular)
Tourniquet pressures should never exceed
400 mmHg
How long does it take to return to normal metabolic status after 3hrs of tourniquet?
40 minutes
Ischemic nerve or muscle damage is unlikely in the noncompressed area if flow is re-established within ____
6 hours
Peripheral Nerve Anatomy
Cutaneous Sensory Distribution
Axillary Block
Interscalene Block
Supraclavicular
Infraclavicular
Difference between Pneumothorax and Tension Pneumothorax
- Pneumothorax
- puncture of a lung that releases air into the chest
- one time injury
- Tension Pneumothorax
- current injury of the lung that is continuously releasing gas from bronchial tree into pleural space
Which lasts longer: anesthesia or analgesia?
Analgesia
Organize from roots to branches
Root - Trunk - Divisions - Cords - Branches
Which nerve often contributes to tourniquet pain because it is difficult to block?
T2
- can give 5-10cc in upper arm between bicep and tricep to take care of anesthetic
Shoulder bones
The brachial plexus is responsible for all innervation of the upper limb except:
the trapezius muscle and an area of axilla skin
- Trapezius (CN XI)
- skin near axilla (intercostobrachial)
TRI
Transient Radicular Irritation
- pain in the lower limbs and butt
- “Transient neurologic symptoms”
Organize the rate of absorption by site
- Intercostal
- Paracervical
- caudal
- lumbar epidural
- brachial plexus
- subarachnoid
- subcutaneous
Onset
pKa
Duration
protein binding
Potency
lipid solubility
ineffectiveness of local
pKa or pH
Why would you add bicarbonate to epi/lidocaine?
to decrease pH and increase the onset time
Which LA has a high incidence of PONV?
procaine
Class 1 - Antiarrhythmics
Flecainide, Phenytoin (dilantin), Procainamide, and Propafenone
Max dose of 2-Chloroprocaine
800 mg
(1,000 with epi)
Max dose of Procaine
500 mg
Max dose of Bupivacaine
175 mg
(225 mg with epi)
Max dose of Lidocaine
300 mg
(500 mg with epi)
Lipid Emulsion Therapy
- infuse 20% lipid emulsion
- bolus 1.5 mL/kg IV bolus (repeat 2x)
- maintenance
- 0.25-0.5 mL/kg/min
Max dose 10mL/kg over 30 minutes
Exparel
bupivacaine mixture
- used in infiltration bunionectomy and colorectal infiltration
- not approved for peripheral nerve blocks
Hyperechoic
stronger reflection on US
(white on the screen)
- nerves, bones, muscles
Anechoic
no reflection on US
(black on the screen)
- arteries and veins
B.A.R.T
blue away, red toward
Hyper/Hypo-echoic nerves
- proximal nerves are hypoechoic
- distal nerves are hyperechoic
- degree reflects the amount of connective tissue within the nerve
P.A.R.T
Pressure, Alignment, Rotation, and Tilt
Muscles of Scapula
(insertion on scapula, moves scapula)
- trapezius
- rhomboids
- pectoralis major
- serratus ventralis
- levator scapulae
Muscles of Scapula
(origin on scapula, moves arm)
teres major and latissimus dorsi
Rotator Cuff
baseball pitcher
- originate on fossae of scapula
- medial and lateral rotation of upper limb
Anatomy of Brachial Plexus
(brachial)
Sensory Supply Areas
- supraclavicular
- axillary
- musculocutaneous
- radial
- medial cutaneous (arm)
- medial cutaneous (forearm)
- median
- ulnar
