Management of Regional Anesthesia and Spinal Block Flashcards
T/F: Local anesthetics are weak bases?
True
Structures consists of an aromatic moiety connected to a substituted amine through an _____ or _____ linkage.
Ester, Amide
How can you tell whether a local anesthetic is an ester or amide?
Amides will contain two “i” within the name.
What was the first anesthetic to be used?
Cocaine
Who was the first person to administer a local anesthetic and what was the time?
August Beer, 1884
Does a molecule have to unionized or ionized to cross the lipophilic barrier to get into a cell.
Unionized
What does pKa mean?
The pH at which 50% of the local anesthetic is in the charged form and 50% is in the uncharged form.
What is the mechanism of action for local anesthetic?
- Block nerve conduction by impairing propagation of the action potential in axons.
- Decrease the rate of rise of the action potential such that the threshold potential is not reached
- Interact directly with specific receptors on the Na+ ion influx.
What increases potency and allows local anesthetics more easily cross nerve membrane?
Lipid Solubility
Agents with a high degree of _______ binding will have a prolonged duration of effect.
protein
What does pKa do?
Determines speed of onset of neural blockade.
Blockade of Nerve Fibers (Size): ______ fibers are more easily blocked than _______ fibers.
thin, thick
Blockade of Nerve Fibers (myelinated): _______ fibers are more readily blocked than _________ fibers.
UnMyelinated, myelinated
Myelinated nerve fibers are blocked only at __________.
Node of Ravier
What will be the sensory lost in a spinal block?
Sympathetic
What is the sequence of clinical anesthesia to be lost.
- Sympathetic block with peripheral vasodilation and skin temperature elevation.
- Loss of pain and temperature sensation.
- Loss of proprioception (loss of body orientation)
- Loss of touch and pressure sensation.
- Motor paralysis
What are esters metabolized by?
- Cleaved by plasma cholinesterase. Half life in circulation is short (about 1 minute)
- Degradation product of ester metabolism is a metabolite related to p-aminobenzoic acid.
What are amides metabolized by?
Amides linkage is cleaved through N-dealkylation followed by hydrolysis. This occurs in the liver.
(Elimination half life is 2-3 hours)
What does baricity mean?
Classification of local anesthetic solution as hypobaric, isobaric, or hyperbaric based on their density relative to the density/specific gravity of cerebral spinal fluid.
What is the specific gravity of spinal fluid?
1.009 to 1.004
What are adjuvants for local anesthetic?
Epinephrine, phenylephrine, sodium bicarb, and opioiods
What effect will epinephrine have on site with local anesthetic?
- Prolong duration
- Decrease systemic toxicity by decreasing rate of absorption
- increase intensity of block
- decreases surgical bleeding
- assist in evaluation of test dose
When should epinephrine not be used with local anesthetics?
- Peripheral nerve clocks in areas with poor collateral circulation
- IV regional technique (bier block)
- Hx of uncontrolled HTN, CAD arrhythmia, hyperthyroid, utero-placental insufficiency.
- phenylephrine
What effect will sodium bicarb do with local anesthetic?
- raises pH and raises concentration of non-ionized base.
- increases the rate of diffusion across thenerve membrane and speeds onset of neural blockade.
- 1 meq added to each 10 mL of lidocaine or mepivacaine.
- 0.1 mEq added to each 10 mL of bupivicaine (to avoid ppt of the drug)
What effect will opioid have with local anesthetic?
- Addition of 50-100ug of fentanyl to the local anesthetic shortens the onset, increases the level and prolongs the duration of a regional block.
- A selective action at the dorsal horn of the spinal cord modulates pain transmission.
- Action is synergistic with the action of the local anesthetic.
Amides may have what in them to cause an allergic reaction?
Methyl-paraben (PABA) a preservative
Esters may have what in them to cause an allergic reaction?
- Metabolite similar to PABA
- pt. sensitive to sulfonamides or thiazide diuretics.
Accidental intravascular injection or overdose of local anesthetic can be minimized by:
Aspiration prior to injection
Use of epi-containing solutions for test dose
Use of small incremental volumes to establish the block
Use of proper technique during IV regional
What are the clinical feature of central nervous system toxicity of local anesthetics?
Lightheadedness
Tinnitus
Metallic taste
Visual disturbance
Numbness of tongue and lip
May progress to:
- Muscle twitching
- Loss of consciousness
- Grand mal seizure
- Coma
Starting from low to high local anesthetic toxicity name the clinical signs.
1 Numbness of tongue 2 Light headedness 3 Visual disturbance 4 Muscular twitching 5Unconsciousness 6 Convulsions 7 Coma 8 Respiratory arrest 9 CVS depression
What is the treatment of local anesthetic CNS toxicity?
Administer O2
Seizure activity
Midazolam 1-2 mg
Thiopental 50-200mg
Propofol
What are the signs of local anesthetic cardiovascular toxicity?
Clinical presentation
Decreased contractility
Decreased conduction
Loss of peripheral vasomotor tone
Cardiovascular collapse
Intravascular injection of bupivacaine or etidocaine may
result in cardiovascular collapse that is refractory to
therapy because of the high degree of tissue binding of
these agents
What is the treatment for local anesthetic cardiovascular toxicity?
Administer O2
Support the circulation with volume, vasopressors, and inotropes
ACLS if indicated
Treat V-tach with cardioversion
Prolonged cardiopulmonary resuscitation may be required until the cardiotoxic effects subside with drug redistribution.
T/F: Research suggests that post-op morbidity and possibly mortality may be reduced when neuraxial blockade is used, either alone or in combination with general anesthesia.
True
When a neuraxial blockade is used what are the reduced incidences of:
venous thrombosis
pulmonary embolism
cardiac complications
vascular graft occlusion
respiratory depression and pneumonia
blood loss and transfusion
allows earlier return of GI function
How is a neuraxial blockade done?
Accomplished by injecting local anesthetic solution into the cerebral spinal fluid within the subarachnoid/intrathecal space
What are the pros of doing a neuraxial blockade?
Easy to perform
Uses less local anesthetic
Causes less discomfort during placement
Produces more intense sensory and motor block
What are the indication for doing a spinal?
Surgery of lower abdomen
Surgery of lower extremities
Surgery on perineum
What are the general consideration for pre-op care before doing a spinal?
Note specific baseline neuro deficits
Bacteremia - abscess
Current meds
Cardiac disease
What is an absolute contraindication for doing a spinal?
Aortic Stenosis
What are the clinical signs for a spinal or epidural hematoma?
New onset weakness to lower limbs and sensory deficit
New onset back pain
New onset bowel or bladder dysfunction
Must diagnose and surgically decompress hematoma within 8 hours for best outcome
What is the risk of permanent neurologic injury for spinal anesthesia?
1 to 4.2 : 10000
what are the risk of permanent neurologic injury for epidural anesthesia?
0 to 7.6 : 10000
Suggested minimum cutaneous levels for spinal anesthesia are:
Lower extremities / T12 Hip / T10 Vagina/uterus / T10 Bladder/prostate / T10 Lower extremitie(TQ)/ T8 Testis/ovaries / T8 Lower intraabdominal/T6 Other intraabdominal /T4
What is the anatomy of the vertebral column:
7 cervical vertebra 12 thoracic 5 lumbar 5 sacral 4 coccygea
What are the intralaminar ligaments?
three intralaminar ligaments bind the vertebral processes together
Name the intralaminar ligaments?
Supraspinous ligament
Interspinous ligament
Ligamentum flavum
What does the supraspinous ligament do?
– connects apices of spinous processes.
What does the interspinous ligament do?
connects the spinous processes.
connects the spinous processes.
What does the ligamentum flavum do?
connects the caudal edge of the vertebra above to the cephalad edge of the lamina below.
What are some key points of the spinal cord?
Extends the length of the vertebral canal during fetal life, ends at L3 at birth.
Spinal cord moves progressively cephalad eventually reaching the adult position of L1 by 2 years of age.
The conus medularis, lumbar, sacral, and coccygeal nerve roots branch out distally to form the cauda equina.
Spinal needles are placed below L2 as the mobility of spinal nerves reduces the danger of needle trauma.
What are the three meninges that cover the spinal cord?
Pia mater (inner)
Arachnoid – lies between the dura and the pia mater. (middle)
Dura mater – tough fibrous sheath running the length of the cord. (outer)
What are the characteristics of cerebrospinal fluid?
Clear
Colorless
Fills the subarachnoid
What is the total volume of CFS in the CNS?
~140 mL
What is the volume of CNS in the spinal canal?
30 - 80 mL
CNS fluid is continuously formed at _____ mL day.
500
Where is the CFS predominantly formed at?
Choroid plexuses of the cerebral ventricles.
Where is the CNS absorbed at?
arachnoid granulations along the sagittal sinus.
What is optimal CSF pressure?
10-20 cm H2O pressure
What factors affect the level of a spinal blockade?
- Drug dose
- Drug volume
- Turbulence of CSF
- Increased intra-abdominal pressure
- Pressure against the inferior vena cava causes epidural venous engorgement, and reduces the volume of CSF. (Local anesthetic spreads farther.
- Spinal curvature (lordosis and kyphosis)
- Baricity of local anesthesia
What is baricity of local anesthesia?
– local anesthetic solutions are hyperbaric, hypobaric, or isobaric in relation to the baricity of CSF. (Specific gravity of CSF 1.003-1.009)
How is a hyperbaric solution obtained for local anesthetic?
adding 5-8% dextrose (glucose)
Which way will the hyperbaric solution of a local anesthetic flow?
flow to the most dependent part of the CSF column due to gravity.
Hyperbaric has a baricity of greater than _____.
1.0015
How is a hypobaric solution obtained?
Adding sterile water
Which way will a hypobaric solution flow?
Highest part of the CSF column
When might a hypobaric solution be used?
Perineal procedures in prone-jackknife
Hypobaric has a baricity less than ____?
0.999
What are the benefit of using a isobaric solution?
Predictable spread
Increased dose will only prolong anesthetic
Position of pt. can be changed to augment dermatone spread of anesthetic.
Isobaric has a baricity of _____.
1
T/F:It is not possible to prepare a solution that is precisely isobaric, near isobaric sol’n remain and act in the same location in which it was injected.
True
What is a touhy needle use for?
Epidural
A Quicke-babcock will _____ more tissure.
incise
What is the pt. postion in lateral position for an epidural?
Spine is horizontal and parallel to the edge of the table.
Knees drawn up to chest and chin flexed downward to chest to obtain maximal flexion of spine.
Affected side up if using hypobaric technique, affected side down if hyperbaric technique.
What is the pt. position in sitting positon for an epidural?
Head and shoulders are flexed downward onto the trunk with patients back close to the edge of the table.
Assistant in attendance to stabilize the patient.
Patient should not be over sedated
Often useful with obese patients to assist in identification of midline.
Used in conjunction with hyperbaric anesthetics
What is the pt. position in a prone postion for an epidural?
Patient placed in prone jackknife position while awake.
Used in conjunction with hypobaric anesthesia.
Useful for procedures on rectum, perineum and anus
What is the approach of the needle for a midline epidural?
Needle is advanced through the skin in the same plane as the spinous processes with a slight cephalad angulation toward the intralaminar space.
What is the approach of the needle for a paramedian epidural?
Useful in patients who cannot be maximally flexed or whose intraspinous ligaments are ossified.
Spinal needle is placed 1-1.5 cm lateral to midline of selected interspace.
Needle is aimed medially and slightly cephalad and passed lateral to the supraspinous ligament.
If lamina is contacted, the needle is redirected and walked off in a medial and cephalad direction.
Nurse Anesthesia pg.1056
What are the identifying landmarks for the spine?
A line connecting the upper borders of the ileac crests intersects the spinous process of L4, or the L3-L4 interspace
Where is spinal anesthesia usually administered?
interspace L2-L3, L3-L4, or L4-L5
What preparation is done for a epidural?
Prepare a large area of skin with antiseptic solution.
Avoid contamination of spinal kit with antiseptic solution – this is potentially neurotoxic.
Check integrity of stylet and spinal needle.
Infiltrate skin at intended spinal puncture site with 1% lidocaine solution. (25 gauge needle
How will you insert the needle on a spinal?
Insert the needle so that its bevel is parallel to the fibers that run longitudinal to reduce the incidence of post – dural puncture headache.
Advance the needle until increased resistance is felt as it passes through the ligamentum flavum.
A sudden “Pop” or loss of resistance is felt as the needle is advanced beyond this ligament
Remove the stylet from the needle.
Correct placement is confirmed by free flow of CSF into the hub of the needle.
Paresthesia occurring with placement of the needle requires immediate withdrawal of the needle and repositioning.
The hub of the needle may be rotated in 90-degree increments until good flow is established.
How do you administer anesthetic in a spinal?
Syringe containing calculated dose of local anesthetic is connected to the needle.
Aspiration of CSF confirms free flow.
Drug is slowly injected.
Re-aspiration of CSF at end of injection confirms the needle tip is still in the subarachnoid space.
The needle is gently removed and patient is placed in desired position.
Describe the onset of the blockade?
The ascending anesthetic level is assessed using pinprick or alcohol swab.
Blood pressure, heart rate and respirations are closely monitored (at least once a minute) until patient is deemed stable.
Fixation of local anesthetic takes approximately 20 minutes.
What is a differential neural blockade?
- smaller c nerve fibers conveying autonomic impulses are blocked than larger sensory and motor fibers
- The level of autonomic blockade therefore extends two or three segments above the sensory blockade.
Fibers conveying sensation are more easily blocked than larger motor fibers.
Sensory blockade therefore extends two or three segments above motor blockade.
In a differential neural blockade the autonomic blockade are ___ segment _____ than the ______ blockade.
2, higher, sensory
In a differential neural blockade the sensory blockade are ___ segment ______ than the ______ blockade.
2, higher, motor
In a differential neural blockade the motor blockade are ___ segment _____ than the ______ blockade.
2, lower, sensory
When a sympathetic block is achieved what is the cardiovascular response?
- hypotension proportional to the degree of the block
- Dilation of vascular bed…both arteries and veins.
Decreased SVR with subsequent decreased venous return.
May be profound in the hypovolemic patient.
Heart rate does not change significantly in most patients.
Significant bradycardia does occur in 10-15% of patients.
Risk of bradycardia increases with increasing sensory levels of anesthesia.
Block of cardio-accelerator fibers T1-T4
What is the treatment of a sympathetic block?
Fluid load with 500-1000cc IV prior to spinal blockade if history allows. (15mL/kg min. prior to the start of the spinal anesthetic)
Oxygen mask
Vasopressors
Atropine
Epinephrine
CPR
What are the most important factors that affect the level of anesthesia for neuraxial block?
Baricity of anesthetic solution
Position of the patient during injection and immediately after injection
Drug dosage
Site of injection
What are other factors affecting the level of anesthesia for a neuraxial block?
Age Cerebrospinal fluid Curvature of spine Drug volume Intra-abdominal pressure Needle direction Patient height Pregnancy
What happens if neuraxial block does not work?
Either try again with half the dose or go to general anesthesia
What are the complication of spinal anesthesia?
Nausea – (pg. 1062)
Urinary retention – (pg. 1062)
Hypoventilation
Backache
