Spinal Anesthesia Flashcards
What is spinal anesthesia?
Reversible chemical blockade of neuronal transmission produced by the injection of a local anesthetic drug into the CSF contained within the subarachnoid space
What nerve fibers transmission are temporarily inhibited with spinal anesthesia?
Sensory
Autonomic
Motor
How might a spinal anesthetic speed the patients recovery?
Surgical stress is reduced by the afferent block
How might spinal anesthesia decrease the occurrence of venous thrombosis and blood loss?
Reduction of arterial and venous pressure
What postoperative complications can the incidence be lowered with spinal anesthesia?
Nausea/Vomiting
Sedation
Cognitive impairment
Wound pain
Why is it important to cycle the blood pressure cuff immediately after administering spinal anesthesia?
Sympathetic blockade accompanies spinal anesthesia virtually 100% of the time
What are some complications often associated with spinal anesthesia?
Urinary retention
Post-dural puncture headache
Intense motor blockade
Why do many patients fear having a SAB?
Fear of being awake, educate the patient that sedation will be provided
Why might a SAB be a safer option in a patient with a full stomach?
Vomiting and pulmonary aspiration is less likely (unless over sedated)Patients with difficult airways may be easier to manage
Why might a SAB be useful in patients undergoing a TURP procedure?
The conscious patient is able to tell if bladder perforation has occurred, CHF can be monitored and electrolyte disturbances could be assessed
What are the benefits of a laboring mother receiving SAB?
Somatic motor function loss can be minimized when the level is kept lowMother remains awake and can see the child
Why is a SAB beneficial for metabolic diseases?
It has minimal effect on metabolism, beneficial for
- Liver disease
- Kidney disease
- Diabetes
What are some absolute contraindications to a SAB?
Patient refusal Infection at the injection site Coagulopathy or other bleeding diathesis Severe hypovolemia Severe aortic or mitral valve stenosis Increased ICP
Why is a SAB contraindicated if a patient has an infection at the injection site?
Risk of skin core introducing infection into the CSF
What is a SAB contraindicated in aortic or mitral valve stenosis?
It causes a decrease in after load which causes a decrease in CO which can’t keep up with the vasodilation a SAB causes
What can occur if a SAB is performed on a patient with an increased ICP?
It can cause the patient to herniate
Why might it not be a good idea to give a patient with a demyelinating disease spinal anesthesia?
It could potentially cause an exacerbation of the disease if it was in remission
Why wouldn’t a provider choose to give a patient a SAB if they had a history of metastatic CA of the lumbar vertebrae?
There is a potential for neurologic deficit in these patients
How can HIV effect a providers choice in giving a patient spinal anesthesia?
There is a potential for neurologic disorder and there is a thought that you could potentially be introducing the virus to the CSF
What local anesthetic would patients have an allergy to and why?
Esters, preservative PABA
What might the provider expect if they gave spinal anesthesia to a patient with uncontrolled HTN?
Massive HoTN due to a low tank and a sympthomectomy
What is the thought behind administering 1000-1500mL of a balanced crystalloid solution prior to spinal anesthesia?
It is supposed to help prevent against HoTN however, likely not effective
What must the provider have available and functioning prior to spinal anesthesia and why?
A patent IV, anticipate giving vasoactive agents to treat the sympathomectomy
How many total vertebrae are present in the spinal column?
33 vertebrae
How many cervical vertebrae are present in the spinal column?
C1-C7 = 7
How many thoracic vertebrae are present in the spinal column?
T1-T12 = 12
How many lumbar vertebrae are present in the spinal column?
L1-L5 = 5
How many sacral vertebrae are present in the spinal column?
5 Fused
How many vertebrae are present in the coccyx of the spinal column?
4 Fused
What two spinal regions have a lordosis curvature?
CervicalLumbar
What two spinal regions have a kyphosis curvature?
ThoracicSacral
What is the laymen’s term for the coccyx?
Tailbone
What is the typical shape of a lumbar vertebrae?
Kidney shaped
What are the structures called where vertebrae come into contact with each other?
Superior articular processInferior articular process
What is the typical shape of the body of a thoracic vertebrae?
Heart shaped
What is the order from skin to the subarachnoid space does a need pass to get spinal anesthesia?
Skin Subcutaneous tissue and fat Supraspinous ligament Interspinous ligament Ligamentum flavum Epidural space Dura Subarachnoid space
What is the tip of the spinal cord called and what is its function?
Conus Medullaris, it stabilizes the spinal cord
What is the name of the structure that extends beyond the conus medullaris as multiple nerves?
Cauda equina
What sensation can occur is the cauda equina is struck by a needle when attempting spinal anesthesia?
Paresthesis, however should resolve because they are floating structures
What is the outermost layer of the menenges that is tough, fibrous and runs longitudinally?
Dura mater
Where does the dura mater extend?
From the foramen magnum to S2-3
What is the name of the middle layer of the menenges that is delicate and nonvascular?
Arachnoid mater
When does the arachnoid mater end?
S2
What is the name of the innermost layer of the menenges that is delicate, highly vascular and covers the spinal cord?
Pia mater
Where is the subarachnoid space located?
Between the pia and arachnoid mater which is where CSF resides
What is the function of the CSF?
Mechanical buffer to protect the brain and spinal cord
What is the specific gravity of CSF and how does that relate to water?
1.003-1.009 slightly greater than that of water (1)
What is the total amount of CSF in an adult and how much of that is in the subarachnoid space?
150mL in an adult, 20-35mL is present in the subarachnoid space
How much CSF is produced in a day?
21mL/hr which is equivalent to about 500mL/day
What dermatome is represented at the little finger?
C8
What dermatome is represented at the nipple line at the 4-5th intercostal space?
T4
What dermatome is represented at the level of the xyphoid process?
T6
What dermatome is represented at the level of the umbilicus?
T10
What dermatome is represented at the level of the posterior medial thigh?
S2
How can the dermatome C7 be easily identified?
Find the most prominent cervical process
How can the dermatome T7 be easily identified?
Find the inferior tip of the scapula
How can the dermatome L4 be easily identified?
Find the superior aspect of the iliac crest
How can the dermatome S2 be easily identified?
Posterior superior iliac spine
What is the function of A-alpha nerve fibers?
Motor and proprioception
What is the diameter and level of myelination in A-alpha nerve fibers?
Heavy myelination and 6-22um in diameter
What is the function of A-beta nerve fibers?
Motor, proprioception, touch and pressure
What is the diameter and level of myelination in A-beta nerve fibers?
Moderate myelination and 6-22um in diameter
What is the function of A-gamma nerve fibers?
Muscle tone
What is the diameter and level of myelination in A-gamma nerve fibers?
Moderate myelination and 4-6um in diameter
What is the function of A-delta nerve fibers?
Pain, touch and cold
What is the diameter and level of myelination in A-delta nerve fibers?
Light myelination and 1-4um in diameter
What is the function of Beta nerve fibers?
Preganglionic and Sympathetic
What is the diameter and level of myelination in Beta nerve fibers?
Light myelination and 0.5-2um in diameter
What is the function of the C nerve fibers?
Pain, touch, warm and cold
What is the diameter and level of myelination in C nerve fibers?
No myelination and 0.5-1.3um in diameter
In what order do nerve fibers become blocked?
B, C, A-delta, A-gamma, A-beta and A-alpha
When can a dural puncture be accomplished?
At any level between L2 and S1
What is the most common interspaces for a spinal anesthetic?
L2-3 or L3-4
What direction would a hyperbaric solution tend to favor in a female patient?
Cephalad due to wider hips and narrow shoulders
What direction would a hyperbaric solution tend to favor in a male patient?
Caudal due to wider shoulders and smaller hips
What direction would a hyperbaric solution tend to favor in a pregnant female patient?
Cephalad, due to wider hips and an increase in abdominal circumference
Why shouldn’t the person helping position hold the shoulders?
It can rotate the spinal column making it more difficult to insert the needle at an appropriate angle
What is the landmark generally located at L4?
Intercrestal line “tuffiers line”
If using a hypobaric technique for anesthesia of the anus how can the provider tell if they are in the right place since CSF won’t freely flow out?
Ask the patient to valsava and the provider should see CSF bubble up through the needle
What is a hyperbaric solution?
Local anesthetic solution is heavier than CSF
How can the provider make a LA hyperbaric?
Add glucose to the local anesthetic
What is an isobaric solution?
Local anesthetic solution has the same specific gravity as the CSF
How can the provider make a LA isobaric?
Mix LA with CSF (aspirate and allow it to mix)
What is a hypobaric solution?
Local anesthetic solution is lighter than CSF
How can the provider make a LA hypobaric?
Mix LA with sterile water
What is the specific gravity of CSF?
1.003-1.009
What is the baricity of plain 0.5% bupivacaine?
Hypobaric to isobaric (0.9990-1.0058)
What is the baricity of plain 2% Lidocaine?
Hyperbaric
What is the baricity of plain 10% procaine?
Hyperbaric
How do hyperbaric solutions disperse when injected?
They migrate to the most dependent area of the spine
What are the most important factors that influence the level of the spinal?
Baricity
Positioning (during injection and immediately after)
Drug dose
Site of injection
What is the most easily identifiable interspace?
L2-3
At what gauge needle and smaller requires an introducer before insertion?
25 gauge or smaller
Where should the needle be placed within the interspace?
Midline of the lower third of the interspace
When inserting the needle what two layers are being passed when pops may be felt?
Ligamentum flavum (entering the epidural space) Dura (entered the subarachnoid space)
Why is it important to turn the needle once you have entered the subarachnoid space?
To ensure your needle has passed completely through the dura
When aspirating the CSF what is a clear indicator it is entering the syringe?
You will see a swirl in the syringe demarcating a different substance has entered
Why is it important to elevate the patients head after insertion of local anesthetic into the subarachnoid space?
To prevent a total spinal
What type of spinal needle has a higher rate of postdural headaches?
Quincke, or a cutting needle
What three scenarios may be occurring if bone is being struck while inserting a spinal needle?
Needle is touching the superior crest of the spinous process below the interspace
Needle is touching the interior surface of the spinous process above the interspace
Repeatedly encountering bone is probably striking lamina
What should the provider do if they encounter paresthesia while inserting a spinal needle and it goes away after a minute?
Continue with the injection
What should the provider do if they encounter paresthesia while inserting a spinal needle and it does not go away after a minute?
Remove and reposition the needle
If no CSF flow through the catheter and paresthesia occurs where is the needle most likely located?
Extradural
What has occurred if there is no CSF, no paresthesia and no bone?
May have transversed both the dorsal and anterior surfaces of the dura
Gently aspirate the syringe as you pull the needle back
What has occurred if frank red blood that does not clear up is seen when the stylet is pulled from the catheter
The tip is likely in an epidural vein
What fibers are our goal to block in spinal anesthesia?
A-delta and C fibers
At what level can the cardio-acclerator center be blocked?
T4 resulting in bradycardia
How often should the degree of the block be checked when initially setting up?
Every 2-3m
What sensation should be used to assess dermatome level?
Cold temperature
Where is the upper limit of the autonomic block in relation to level of sensory block?
Two dermatomes higher
Where is the upper limit of the motor block in relation to level of sensory block?
Generally two dermatomes below
What is generally the level of a saddle block?
S2-5
What is typically the desired level of a low spinal?
T10
At what level would a tourniquet be able to be used with spinal anesthesia?
T4
What is considered a high spinal?
C8 proper (remember little finger) However jargon for anything higher than a T2 block
What two ligaments does the paramedian approach avoid?
Supraspinous and Interspinous ligaments
Where does the needle pass in order to bypass the interspinous and supraspinous ligaments?
Needle passes through the paraspinal muscles to the ligamentum flavum
What type of patients is the paramedian approach beneficial in?
When patients cannot flex the lumbar spine : back surgeries, rheumatoid arthritis and hip/leg trauma
What opening does the Lumbosacral approach utilize?
Uses the largest opening to the spinal canal L5-S1
Where should the skin wheal be made for the paramedian approach?
1cm lateral and 1cm caudad to the spinous process above the selected interspace
Where should the skin wheal be made for the lumbosacral approach?
1cm medial and 1cm caudad to the spine
what is another name for the lumbosacral approach?
Taylor approach
How does adding epinephrine effect a block?
Prolongs the duration and possibly the intensity of the LA effect
How much epinephrine can be added to LA?
0.1-0.2mL of 1:1000
What LA do vasoconstrictors have the greatest impact on?
Tetracaine
How much phenylephrine can be added to LA for vasoconstrictive effects?
0.05-0.2mL of 1% solution
When is clonidine useful to use in spinal anesthesia?
Prolong the duration of SAB when epi is contraindicated
What central effects can clonidine have when given in SAB?
Appears to help prevent tourniquet pain
How can the best analgesia be achieved with spinal anesthesia?
Combination of preservative FREE opioid and local anesthetic agents
What are the most common opioids used in SAB?
Fentanyl
Morphine
Sufentanil
Meperidine
What is the dose of fentanyl mixed with LA?
12.5-25mcg
Why is morphine more likely to cause respiratory depression in SAB compared to fentanyl?
Highly polarized not highly bound to lipid elements in the spinal cord and feely drifts into CSF
What is the dose of Morphine with LA?
0.25-0.5mg
What complication are seen with opioids used in SAB?
Urinary retention
Itching
Respiratory depression
