Regional Anesthesia Flashcards
The spinal cord extends from the foramen magnum to ___ in the adult and ranges from ____ cm, and to ___ in the newborn.
L1
42-45 cm
L3
The spinal cord terminates at conus medullaris and the ________ extends down and anchors in the lower sacral region.
Filum terminale
How many vertebrae?
How many pairs of spinal nerves?
33 vertebrae (7 cervical, 12 thoracic, 5 lumbar, 5 sacral, 4 coccygeal) 31 pairs of spinal nerves
What is the nerve group in the lower dural sac (L1 to S5)?
Cauda equina
List the structures traversed to arrive at the subarachnoid space.
- Skin
- Subcutaneous
- Supraspinous ligament (C7 to sacrum)
- Interspinous ligament
- Ligamentum flavum
- Epidural space
- Dura
- Arachnoid
- Subarachnoid space
Which ligament binds the epidural space posteriorly? Anteriorly?
Ligamentum flavum
Dura
Where is the ligamentum flavum the widest? Narrowest?
Wides at L2
Narrowest at C5
List the 3 spinal meninges.
- Dura mater
- Arachnoid
- Pia mater
Where is CSF found?
Subarachnoid space
Between the arachnoid and pia mater
What is the principle site of action for neuraxial blockade?
Nerve root
LA act on nerve rootlets, nerve roots, and the spinal cord
Factors with proven effects on distribution of drug include:
- Site of injection
- Anatomical shape of spinal column
- Patient height
- Angulation of needle
- Volume of CSF
- Characteristics of LA (baracity)
- Dose of LA
- Volume of LA
- Position of patient during injection
- Position of patient after injection
Uptake of LA occurs by ____ down a concentration gradient.
Diffusion
Uptake is greatest where the concentration of LA is the greatest
Elimination occurs by ______ via subarachnoid and epidural _______.
Vascular absorption
Blood vessels
The predominant action of sympathetic blockade due to LAs is ________.
Venodilation
Reduces VR, SV, CO, BP
What happens if sympathetic outflow from T1 to T4 is blocked by LAs?
Unopposed vagal stimulation
Bradycardia
Bradycardia following spinal injection is a result of what 2 things?
- Blockade of cardioaccelerator fibers (T1-T4)
2. Bainbridge reflex (decreased VR)
The best means for treating hypotension during spinal anesthesia is ________, not pharmacologic.
Physiologic
- Give IV fluids if not normovolemic (5 mL/kg)
- If normovolemic, give ephedrine or neo
When giving a fluid bolus for hypotension following a spinal injection, why avoid glucose containing solutions?
Glucose can act as a diuretic - worsen the situation
Explain why the patient may feel dyspneic under subarachnoid or epidural block.
As the sensory block reaches the level of T2-T4 - loss of perception of intercostal and abdominal wall movement
Apnea, if it occurs, under subarachnoid or epidural block is due to what?
Hypoperfusion of the respiratory centers in the medulla
Secondary to severe hypotension
Spinal or epidural: ability to control the spread of the anesthetic by controlling the specific gravity of the solution and the position of the patient.
Spinal
With cut-bevel needles (Quinke)ā¦the bevel should face what in the sitting position? Lateral position?
Sitting position - face either R or L
Lateral position - face up or down
(to minimize trauma to the dura)
Anticoagulants and Neuraxial Anesthesia NSAIDS? Aspirin? Herbals? SubQ or minidose Heparin? IV Heparin? Chronic Warfarin? Ticlodipine? Clopidogrel? Abciximab? Eptifibatide and tirofiban? GPIIb/IIIa antagonists?
NSAIDS, Aspirin - OK Herbals - OK if alone SubQ or minidose Heparin - OK IV Heparin - NO, unless a normal PTT Chronic Warfarin - 4 days Ticlodipine - 14 days Clopidogrel - 7 days Abciximab - 24-48 hours Eptifibatide and tirofiban - 4-8 hours GPIIb/IIIa antagonists - 4 weeks
When a central nerve block is used and intra-op anticoagulation is initiated, it is recommended that heparin dosing be held for a least ___ hour after placement of the neuraxial anesthetic.
1 hour
Indwelling catheters should be removed ___ hours after the last heparin dose and the patientās heparin status is known.
2-4 hours
Heparinization can occur ___ hour after catheter removal.
1 hour
Neuraxial block may be administered IF the perioperative INR is less than what?
INR < 1.5
Indwelling catheters should be removed at a minimum of ____ hours after last LMWH dose is given.
10-12 hours
Initiate any subsequent LMWH dosing a minimum of ___ hours after the catheter has been removed.
2 hours
Dermatomes Anterior C4 T4 T6 T8 T10 L1 L2-L3 S2-S5
C4 - clavicle T4 - nipples T6 - xiphoid T8 - lower border of ribcage T10 - umbilicus L1 - inguinal ligament L2-L3 - knee and below S2-S5 - perineal
Dermatomes Posterior C7 T7 L4 S2
C7 - most prominent cervical spinous process
T7 - inferior border of scapula
L4 - superior iliac crest
S2 - posterior superior iliac spine
Absolute Contraindications of Spinal Anesthesia
Patient refusal or uncooperative Lack of skill of provider Operation > DOA of spinal Infection at the site of injection Severe hypovolemia Increased ICP, brain tumor Spinal cord disease Abnormal coagulation
Abruptio placentae
Severe aortic stenosis
Severe mitral stenosis
IHSS
Relative Contraindications of Spinal Anesthesia
Surgical procedure above umbilicus Deformity of spinal column Chronic headache or backache Neurologic defect 3 failed attempts Extreme patient age Mobitz type I, II, and CHB w/o PM
Controversial: prior back surgery, complicated surgery
Cardiac disease, whether myocardial, valvular, or ischemic, is considered a major contraindication to spinal anesthesia if sensory levels of ____ or above are required.
T6
Spinal anesthesia is indicated in patients with even severe cardiac disease if only ____ levels of anesthesia are required.
Perineal
The lateral approach to a neuraxial block will not pass through which 2 structures?
- Supraspinous ligament
2. Interspinous ligament
Complications of Spinal Anesthesia
Infection (fever, nuchal rigidity, severe headaches)
Backache
Headache - PDPH
Failed block
What is the common infectious agent seen with spinal meningitis?
Alpha hemolytic steptococci
What is the most common causative organism in epidural abscess?
Staphylococcus aureus
Hematomas with neurologic deficits are best diagnosed with?
MRI
What is the most common complication of spinal block?
Backache
What is the second most common complication of spinal block?
Headache
PDPH
Frequency?
Location?
Aggravated by what position?
0.2-24% Highest incidence in obstetrics
Bifrontal and occipital
Aggravated in upright position
Describe what is happening with a PDPH.
Decrease in the amount of CSF
Causes the medulla and brainstem to drop into the foramen magnum - stretching the meninges, vessels, and nerves
CN palsy d/t decreased blood supply to nerves
Epidural Blood Patch
How many mL for injection?
First blood patch resolves ____ of headaches.
May repeat after how many hours?
10-30 mL of aseptically-drawn blood
1st - 89-95%
May repeat in 24 hours
In the supine position, the highest point of the spinal column lies at the level of which vertebrae? Where is the lowest point?
Highest point - L3
Lowest point - T6
The largest space in the spinal canal is found where?
The epidural space is largest at what level?
L5-S1
L2-L3
What is the major inhibitory NT in the spinal cord?
Glycine
Is the hydrostatic pressure in the subarachnoid space positive or negative?
Positive (5-15 mmHg)
fluid should leak out of a needle when its tip is placed in this space
Does the epidural space have a negative or positive pressure?
What does the epidural space contain?
Negative
Loose connective tissue, adipose tissue, nerve roots, blood vessels, lymphatics
A line drawn between the L and R iliac crest crosses the spine of what lumbar vertebra?
L4
As the needle is being inserted for subarachnoid block, you feel a pop. What has occurred?
The dura has been penetrated
The clinical progression of differential nerve block by LAs, from first blocked to last blocked, isā¦
Autonomic fibers
Sensory fibers
Motor fibers
What is the order of nerve fiber blockage during a spinal and epidural?
B fibers
Preganglionic sympathetic efferents
C and A-delta fibers
Postganglionic sympathetic neurons
Pain + temp + touch
A-gamma
A-beta
A-alpha *most difficult to block
What level of spinal block would be appropriate for a patient with kidney pain?
T10-L1
What level of spinal block would be appropriate for a TURP?
T10
What level of spinal block would be appropriate for lower abdominal surgery?
T6
What level of spinal block would be appropriate for upper abdominal surgery?
T4
The surgical procedure requires a tourniquet on the LE. What is the min sensory level required for cutaneous anesthesia in this case?
T8
What is the specific gravity of CSF?
1.003-1.008
What factor most influences the level of block achieved with a hyperbaric spinal?
Position
Which LA produces the most profound motor block?
Tetracaine
What is the DOA of lidocaine used for spinal anesthesia w/ and w/o epinephrine?
W/ epinephrine - 60-90 min
W/o epinephrine - 45-60 min
You should assess subarachnoid block after how many minutes?
5 min
Subarachnoid block usually reaches its highest level ____ minutes after spinal injection.
20 min
Describe the differential block with epidural anesthesia.
Sympathetic is at the same level as sensory block
Motor block is 4 segments lower
The half-life of a LA is longer when injected intrathecally or epidurally?
Intrathecally