test 2 GP B Flashcards
Epidural Anesthesia history
Popularized epidural anesthesia in the 1950’s
Touhy Needle introduced in 1949
Lidocaine available in 1950’s
By the 1960’s it was popular amongst the obstetric population
epidural technique and safety
Neuraxial techniques have proven to be safe when well managed
There is still a risk of complications: ranges from self limited back soreness to debilitating permanent neurological deficits and even death
Practitioners must: have expert knowledge of anatomy; pharmacology and toxic dosages of agents
Epidural Anesthesia - today
Today neuraxial blocks are widely used for labor analgesia; caesarian section; orthopedic procedures; perioperative analgesia and chronic pain management
These blocks provide alternatives to general anesthesia or be used simultaneously with general or afterward for postoperative analgesia
Epidural - Benefits of neuraxial blocks - Reduces incidence of?
venous thrombosis & pulmonary embolism
cardiac complications in high-risk patients
bleeding & transfusion requirements & vascular graft occlusion
pneumonia & respiratory depression following upper abdominal or thoracic surgery in patients with chronic lung disease
earlier return of Gastrointestinal function
Epidural - Block benefits Rationale: (Proposed Mechanisms)
avoidance of larger doses of anesthetics and opioids
amelioration of the hypercoagulable state
sympathectomy-mediated increases in tissue blood flow
improved oxygenation from decreased splinting
enhanced peristalsis
suppression of neuroendocrine stress response to surgery
In patients with CAD, a decreased stress response results in less perioperative ischemia and reduced M & M
Reduction of parenteral opioid requirements – decrease atelectasis, hypoventilation, aspiration pneumonia and reduction of ileus duration
Postoperative epidural analgesia reduces time to extubating; preserves immunity thus reduces cancer spread according to some studies
Epidural Blocks in the Obstetric Patient
Epidural anesthesia is widely used for analgesia in women in labor and during vaginal delivery
Caesarean section- most commonly performed under epidural or spinal anesthesia- both blocks allow a mother to remain awake for the birth of her child
Studies also show Blocks = less maternal M & M than GETA (largely d/t incidence of aspiration and failed intubation)
Definition of Epidural Anesthesia
It is the reversible chemical blockade of neuronal transmission produced by the injection of a LA drug into the epidural space
It interrupts transmission of sensory, autonomic, and motor nerve fiber transmission in the anterior and posterior nerve roots
Disadvantages of Epidural
Time consuming to perform
May require 10-20 minutes to establish a level
Sympathetic blockade
Surgeon complains “It takes to long”
Advantages of epidural
Predictable
Pt can remain fully conscious
Analgesia can be extended into the post-operative period
Can provide a segmental blockade
Ideal for lower abdomen, pelvis/perineum, or lower extremities
Reduce risk of thrombosis
Anatomy spinal cord
Vertebral column is made up of 33 Vertebrae
Cervical: 7 (C1-C7)
Thoracic: 12 (T1-T12)
Lumbar: 5 (L1-L5)
Sacral: 5 fused (S1-S5)
Coccygeal: 4 fused to form coccyx
Vertebrae differ in shape and size at the various levels
1st cervical vertebra (atlas)- lacks a body and has unique articulations with the base of the skull
2nd cervical vertebra (axis)- has atypical articular surfaces
All 12 thoracic vertebrae- articulate with their corresponding rib
Lumbar vertebrae- have large anterior cylindrical body
When all stacked vertically the hollow rings become the spinal canal (where the cord and its coverings sit)
Individual vertebral bodies are connected by intervertebral disks
Spinal Ligaments- (superficial to deep)
Interspinous ligament
Ligamentum flavum
Posterior longitudinal ligament
Anterior longitudinal ligament
spinal cord anatomy cont. what it contains; 3 layers; where is CSF?
Spinal canal contains the cord with coverings (meninges) fatty tissue, and venous plexus
Meninges- 3 layers: pia mater, arachnoid mater and dura mater (contiguous with cranial counterparts)
Pia mater- closely adherent to the spinal cord
Arachnoid mater- closely adherent to the thicker and denser dura mater
CSF- contained between the pia and arachnoid mater in the subarachnoid space
The Spinal Cord cont. anatomy - epidural space?
Epidural space (potential space)- within the spinal canal bounded by the dura and the ligamentum flavum
Extends from the foramen magnum to the level of L1 in adults
In children the spinal cord ends at L3 and moves up with age
Lower spinal nerves form the cauda equine (horse’s tail)
*Performing lumbar (subarachnoid) puncture below L1 in adults and L3 in children usually avoids potential needle trauma to the cord; damage to the cauda equine unlikely*
epidural Mechanism of Action
Interruption of efferent autonomic transmission at the spinal nerve roots =
Sympathetic Blockade
The physiological responses of neuraxial blockade =
decreased sympathetic tone/ unopposed parasympathetic tone
Sign and Symptoms:
drop in BP
decrease in HR
arterial vasodilation- decreased SVR
Clinical Considerations
As a primary anesthetic, neuraxial blocks are most useful:
As a primary anesthetic, neuraxial blocks are most useful:
lower abdominal
inguinal
urogenital
rectal
lower extremity surgeries
Upper abdominal procedures such as gastrectomy have been performed with spinal or epidural anesthesia- can be difficult to safely achieve adequate sensory level for patient comfort
epidural Pre-op Preparation
Discuss plan with the surgeon
Good choice for pt.’s with coexisting pulmonary disease
Discuss the proposed surgery and explain the epidural technique in detail
Interview must be unhurried
Answer all questions
Do not coerce the patient into an epidural anesthetic
Do a full pre-operative assessment and interview
Informed consent
epidural?
and Preop meds
Informed consent
Make sure you document that you have discussed the advantages & disadvantages of the anesthetic
Discuss risk
GA is plan B
Document
Pre-op meds
Pt should be NPO
Do not over sedate the patient
OB patients are not sedated
Midazolam (titrate to effect)
Opioids
Epidural Indications
An epidural can be employed as a component of a “balanced” regional/general anesthetic
Pt has a full stomach
Upper airway anomalies
Urological procedures
TURP
Lower limb surgery
Post-op pain relief
Obstetrics
Absolute contraindications epidural
Patient refusal
Severe psychiatric disease
Aortic/mitral stenosis or asymmetric septal hypertrophy
Preexisting CNS disease
Herpetic infection
Increased ICP
Coagulopathy
Infection at the site
Septicemia or bacteremia
Allergy to LA
Absolute contraindications spinal
Patient refusal
Severe psychiatric disease
May not cooperate
Cardiovascular disease
Severe aortic/mitral stenosis and septal hypertrophy
Severe hypovolemia
Can be corrected before the spinal
CNS disease
MS or nerve injury
Herpetic infections
Increased ICP- brain herniation
Blood clotting anomalies
Anticoagulant therapy
ASRA guidelines
Infection at the site
Septicemia or bacteremia
Allergy to LA
Ester LA
Reaction to the preservatives
Relative contraindications to epidural
HIV infections
Surgery of unknown duration
Untreated chronic HTN
Surgical procedures above the umbilicus
Obesity/ deformities of the spinal column
Chronic HA or backache
Multiple attempts
Minor blood clotting abnormalities
ASA or mini heparin doses
Check coags
Relative contraindications spinal
HIV
Associated with neurological manifestations
Surgery of unknown duration
Untreated chronic HTN
Unstable BP after spinal
Greater drop in BP than normal pt.
Procedures above the abdomen
Obesity
Deformities of the spinal column
Chronic HA or backache
Bloody tap
Multiple attempts
Minor abnormalities in blood clotting
ASA therapy
Small dose of heparin
Check coags before spinal insertion and document
Platelet count
Patient Preparation Epidural
Baseline VS & Pt must have an IV
Standard monitors
BP & ECG
Pulse-ox & Stethoscope
Suction
Equipment to provide positive pressure ventilation
O2 & ambu-bag
Mask & airway equipment
Supportive meds
Versed & Succinylcholine
Ephedrine, atropine, & IV fluids (Resuscitation drugs)
Patient Preparation Epidural
Baseline VS & Pt must have an IV
Standard monitors
BP & ECG
Pulse-ox & Stethoscope
Suction
Equipment to provide positive pressure ventilation
O2 & ambu-bag
Mask & airway equipment
Supportive meds
Versed & Succinylcholine
Ephedrine, atropine, & IV fluids (Resuscitation drugs)
Procedure Epidural technique
Can be done in the sitting or lateral position
Make sure the patient is on an adjustable bed
Make sure someone is there to support the patient
Not the spouse or family member
Inform the patient of what to expect throughout the procedure
Make sure pt. has an IV, monitors, and O2
Palpate the back
Superior aspects of the iliac crest and the spinous process
L4 or L4-5
May be difficult to palpate in the obese patient
Use the largest and most superficial interspace you can find
L2-3
Set up equipment
Sterile technique
Draw up the LA to be used for the skin wheal in a 3 ml plastic syringe
Draw 2-3 ml of preservative free saline into the 5 ml glass syringe
Check integrity of epidural catheter
Loading and maintenance dose should be drawn up in separate syringes
Cleanse the patient skin
Place fenestrated drape over the proposed site of injection
Full or half drape
Make sure you remove all chemicals from the injection site
ID the spinous process of L3-4
Midline approach
Loss of resistance technique
Raise a skin wheal with the 27-gauge needle
Raise a small intradermal skin wheal of LA
Recheck overall position of the patient
Grasp the Touhy needle with stylet, between the thumb and index finger of your dominant hand and place it over the middle of your thumbnail and through the skin wheal
As you advance through the ligaments you will notice an increase in resistance as you pass the ligamentum flavum
Ligamentum flavum is normally 4 cm from the skin
Remove the stylet and attach the 5ml glass syringe
Loss of resistance technique
Air vs saline
Midline approach epidural layers:
Technique: Midline Approach
Layers you will penetrate with needle:
Skin
Subcutaneous tissue and fat
Supraspinous ligament
Interspinous ligament
Ligamentum flavum
Epidural space
Paramedian Approach - epidural layers and technique for paramidian
Technique: Paramedian Approach
Layers you will penetrate with needle:
Skin
Subcutaneous tissue and fat
Paraspinous muscle
Ligamentum flavum
Epidural space
Technique: Make a skin wheal 1-2 cm lateral to the midline directly opposite the upper edge of the spinous process below the selected interspace
Direct needle medially and cephalad
additional technique: epidural :
Once you have identified the epidural space:
Gently aspirate to verify you are not in the subarachnoid space or intravascular
Test dose
One shot technique or insert an epidural catheter
Equipment Epidural - Touhy Needle
Epidural needle
3.5 inches long
17-18 gauge
Has an inner stylet that prevents occluding the lumen with tissue
Rounded tip to prevent puncture of the dura and easier to thread the catheter
Equipment epidural Epidural Catheter
1st marking= 5 cm
Each marking after that is 1 cm
2nd double marking= 10 cm
Thick mark is 11 cm (tip of needle)
When inserted to this point you are at the tip of the needle in the epidural space
3rd triple mark= 15 cm
Single hole at the end vs multiple ports on its distal side
Skin to epidural space
4-6 cm in 60% of patients
2-4 cm in 25% of patients
6-8 cm in 10% of patients
>8 cm in 5% of patients
Will usually leave 3-4 cm of catheter in the epidural space
Dr Havenstein’s Anecdotes:
Epidural
When advancing the catheter the patient may feel transient paresthesia’s
May not aspirate CSF in the needle but the catheter may puncture dura and you will get CSF
Be careful when removing the needle after the catheter is placed
An antibacterial filter is attached to the end of the catheter
Epidural Test dose
A negative aspiration does not ensure you are not in a vessel or the subarachnoid space
Test dose
3 ml of 1.5-2% Lidocaine with 1:200,000 epinephrine
This dose will only produce a T10 block if injected in the CSF
1.5% is 15mg per ml 45; and 1:200,000 epi is 5mcg per ml = 15 mcg of epi
Epidural test dose symptoms
Observe the patient
Ask the patient to report symptoms “feeling different, ringing in the ears or metallic taste in the mouth”
Intravascular injection
Increase in HR of 15-20 bpm for 2-3 minutes
Systemic toxicity- numb tongue, dizziness, ringing in the ears
Subarachnoid injection (3-5 minutes)
Immediate onset of sensory and motor block in the buttocks and lower extremities (T10 block)
Subdural
Produce a high block
if epidural test dose is negative
Administer the pre-calculated volume in 3-5 ml increments every 60 seconds
Tape the catheter in place
Document the marking of the catheter at the skin
Evaluation of epidural
Onset is slower than a spinal
After repositioning evaluate patient for 10-30 minutes
Evaluate BP, ECG, and pulse ox
Measure BP every minute for the first 3-5 minutes then every 2-3 minutes until the block is set
Determine the level of blockade every 2-3 minutes with an alcohol sponge and then a sharpened device until the level is set.
Check level every 30-45 minutes
Distribution of Local Anesthetics
Epidural
The distribution of the LA in the epidural space is dependent on the volume injected
Positioning will not aide in distribution of the local (per book but it helps in clinical)
*The primary objective of the epidural is to block the afferent fibers located in the dorsal roots
Site of Action of Local epidural
Ultimate target are the spinal nerves & roots
The dura serves as a barrier to diffusion of Local
Most is absorbed into the circulatory system some will stay in the epidural space and the rest will enter the spinal nerves and nerve roots
The Local will spread horizontally and longitudinally once in the epidural space
Blockade of fibers occurs quickly
Blockade is 2 dermatomes higher than sensory
Effects accentuated in the hypovolemic patient
A quick drop in BP may be an early sign that a “spinal” is setting up
Rapid decrease in BP- nausea or dizziness
Cardioaccelator fibers
physiology Temperature & Light Touch
Unmyelinated C & myelinated A-delta fibers
Follows autonomic blockade
Alcohol sponge
Correlates with sensory loss
May report lower extremity feels warm
Initial Motor Impairment & Touch
Myelinated A-beta & A-gamma
Onset of motor weakness and impaired perception of strong tactile stimulation
Follows loss of temperature and touch (sharpened device)
Profound Motor & Proprioception
Myelinated A-alpha fibers
Profound motor block develops with loss of proprioception
Feel “Phantom Limb”
Assess motor block
Dorsiflex feet (S1-S2)
Flex toes (L4-L5)
Raise knees (L2-3)
Lift shoulders of the bed (T6-T12)
Assess motor block if there then they cant do action
Desired Level of Block
epidural
Will be determined by the volume and concentration of drug and the level of the epidural catheter placement
Injection of 10-15 ml of LA into the epidural space in the lumbar area will produce a T7-9 level in the average sized patient
Inadequate Block epidural
The concentration or volume of the drug may have been too weak to penetrate spinal nerves
If the block does not reach the desired level, you can give a top off dose
One-half of the initial volume can be reinjected
Wait 10-15 minutes before reinjection
Dosing Epidural
Volume is the key factor in the height of the block
The guideline for dosing an epidural in adults is 1–2 ml per segment to be blocked.
Adjust the guideline for shorter patients (< 5 ft. 2 in.) or taller patients (> 6 ft. 2 in.).
Example: T10 block from L3-4 injection: 6-12 ml of local anesthetic.
Local anesthetic epidural
The type, volume, and total dose administered will vary with the level and duration of block desired
LA drugs reversibly interrupt nerve impulse conduction by interfering with sodium ion conductance
The membrane is unable to depolarize, preventing propagation of impulses
Local anesthetic Epidural
potency
Potency
Equal to lipid solubility
Higher lipid soluble, the more readily it penetrates neuronal membranes
Better able to penetrate A-alpha motor fibers
Local Anesthetic Epidural
Rate of onset
Rate of onset
Determined by pKa
Weak bases
pKa near physiologic ph will move more readily into nerve membranes
The neutral (non-ionized) form is most readily able to penetrate the neuronal membrane
Local anesthetic: duration of action
Determined by potency and protein binding
Highly protein bound agents are less available for systemic absorption
Equipment - spinal needle
Spinal Needles
Single use
Has a stylet to prevent occluding lumen
Most are 3-3.5 inches (7.5-9cm) long
In obese pt.’s you may need a longer needle (5 inches)
Classified as cutting or spreading
Quincke, Whitacre, & Sprotte
Pharm pic of the spinal local anesthetics
Local anesthetic long winded method of action
Nerve fibers classified according to their size, conduction velocity and function
Large nerve size+ myelin sheath=fast conduction velocity
Myelin-electrical insulation of nerve fibers and rapid impulse transmission
Transmission of electrical impulses along nerve membrane=signal transduction along nerve fibers
Resting membrane potential -60-70 mV by active transport and passive diffusion of ions
Na+/K+ pump; Transport of 3 Na+ ions out of the cells for every 2 K+ into cells
Na+ channels are membrane bound proteins that composed of one large alpha subunit and two smaller beta subunits
LA bind a specific region of alpha subunit and inhibits voltage gated sodium channel, preventing channel activation, inhibiting Na+ influx=membrane depolarization
Action potential can no longer be generated and impulse propagation is abolished
Conduction is blocked and anesthesia is created
Sensitivity of nerve fibers to LA is determined by axonal diameter, myelination and other factors
Onset of action of LA depends on lipid solubility and pKa
pKa is pH at which fraction of ionized and nonionized drug is equal
Less potent less lipid-soluble agent have faster onset then more potent more lipid-soluble agents
SUMMARY
Summary of Method of Action
Membrane stabilizing medications
Slow down speed of AP/stop AP generation
Inhibit Na+ influx in the neuronal cells
Bind to Na+ channels
DOA correlates with potency and lipid solubility
***Must know max doses of LAs***
LA spinal pic choice
Epidural vs spinal pic
