CONDUCT OF REGIONAL ANAESTHESIA

Dr.Charulatha.R MDAssistant ProfessorMGMCRI

August Bier 1885

SPINAL CORD

Flow of CSF

Where Spinal Cord Ends

Cauda Equina

BLOOD SUPPLY TO SPINAL CORD

100% Sterile

Spinal Anaesthesia

Holding for Spinal

Sitting Position

Flexion

Structures Pierced

Spinal Needle

Factors Influence The Level Of Anaesthesia The level of

Injection The volume of

drug Tilt of Table Speed of

Injection

Advantages of spinal anaesthesia

• Full and complete anaesthesia• Prolonged block: Pain free postoperatively• Alternative to GA for certain poor risk patients esp.:- Difficult airway- Respiratory disease• Contracted bowel• Good muscle relaxation• Suitable for certain surgical procedures:-

Caesarian section (awake patient, bonding)

-Lower limb surgery

-Lower abdominal surgery

- Urological & gyneacological procedures.

SITTING / LYING

Reason For the Patho physiological Changes

Blockade of the Sympathetic Systems

Cardivascular Changes Hypotension

Tachycardia

Bradycardia

Sympathetic Blockade

Marys law/Mayos Reflex

Bainbridge Reflex

Drug for Spinal Anaesthesia Lignocaine Bupivacaine

Hyperbaric Stay in the

lowest area as per gravity

5% with Glucose

0.5% with Glucose

Does not mix up with CSF

Complications On Table

Delayed

On Table Complication Hypotension IV Isotonic

Fluids Vasopressors Oxygen by

mask Atropine-

Bradycardia

Pregnancy & Spinal Aortocaval

Occlusion Pre loading

with IV Fluids Left lateral

Position Vasopressors Oxygen therapy

Delayed Complication Head ache Sixth Cranial

nerve palsy Infection

How to prevent Delayed Complication

Use Thin Spinal needles

Sterile Precaution

Indication Economical Pulmonary Diseases Full Stomach Lower Abdominal Surgery Ischemic Heart Diseases for Lower

Abdominal Surgery

Relative Contraindication Hypotensive Patients Cardiac failure Raised ICT Spinal Deformity Refusing Patients Bleeding Diathesis Skin Infection

Introduction to Epidural Anesthesia Epidural anesthesia produces a reversible

loss of sensation and motor function much like a spinal with the exception that local anesthetic is placed within the epidural space.

Larger doses of local anesthetic are required to produce anesthesia when compared to a spinal anesthetic.

Doses must be monitored to avoid toxicity.

Introduction to Epidural Anesthesia An epidural catheter allows the

versatility to extend the duration of anesthesia beyond the original dose by the administration of additional local anesthetic.

Epidural catheters may be left in place for postoperative analgesia.

Epidural Anesthesia Indications Cesarean section Procedures of the uterus, perineum* Hernia repairs Genitourinary procedures Lower extremity orthopedic procedures Excellent choice for elderly or those who

may not tolerate a general anesthetic

Epidural Anesthesia Should NOT be used in patients who are

hypovolemic or severely dehydrated. Patients should be pre-hydrated with .5 –

1 liter of crystalloid solutions (i.e. ringers lactate) immediately prior to the block.

Epidural Anesthesia Higher failure rate for procedures of the

perineum. Lower lumbar and sacral nerve roots are

large and there is an increased amount of epidural fat which may affect local anesthetic penetration and blockade.

This is known as sacral sparing.

Epidural Anesthesia Advantages Easy to perform (though it takes a bit

more practice than spinal anesthesia) Reliable form of anesthesia Provides excellent operating conditions The ability to administer additional local

anesthetics increasing duration The ability to use the epidural catheter

for postoperative analgesia

Epidural Anesthesia Advantages Return of gastrointestinal function

generally occurs faster than with general anesthesia

Patent airway Fewer pulmonary complications compared

to general anesthesia Decreased incidence of deep vein

thrombosis and pulmonary emboli formation compared to general anesthesia

Epidural Anesthesia Disadvantages Risk of block failure. The rate of failure is

slightly higher than with a spinal anesthetic. Always be prepared to induce general anesthesia if block failure occurs.

Onset is slower than with spinal anesthesia. May not be a good technique if the surgeon is impatient or there is little time to properly perform the procedure.

Epidural Anesthesia Disadvantages Normal alteration in the patient’s blood pressure

and potentially heart rate (generally slower onset with less alteration in blood pressure and heart rate than with a spinal anesthetic). It is essential to place the epidural block in the operating room/preoperative area with monitoring of an ECG, blood pressure, and pulse oximetry. Resuscitation medications/equipment should be available.

Risk of complications as outlined in Introduction to Neuraxial Blockade chapter. There is an increase in the complication rate compared to spinal anesthesia.

Epidural Anesthesia Disadvantages Continuous epidural catheters should not

be used on the ward if the patient’s vital signs are NOT closely monitored.

Risk for infection, resulting in serious complications.

Absolute Contraindications Epidural Patient refusal Infection at the site of injection Coagulopathy Severe hypovolemia Increased Intracranial pressure Severe Aortic Stenosis Severe Mitral Stenosis Ischemic Hypertrophic Sub-aortic

Stenosis

Relative Contraindications Sepsis Uncooperative patients Pre-existing neuro deficits/neurological

deficits Demylenating lesions Stenotic valuvular heart lesions (mild to

moderate Aortic Stenosis/Ischemic Hypertrophic Sub-aortic Stenosis)

Severe spinal deformities

Controversial Prior back surgery Inability to communicate with the patient Complicated surgeries that may involved

prolonged periods of time to perform, major blood loss, maneuvers that may complicate respiration

Mechanism/Site of Action Administered at a physiologic distance

when compared to spinal anesthesia. The intended targets are the spinal nerves and associated nerve roots.

Several barriers to the spread of local anesthetic to the intended site of action results in the requirement of larger volumes of local anesthetic when compared to spinal anesthesia.

Barriers Dura mater between the epidural space

and spinal nerve and nerve roots act as a modest barrier.

The majority of the solutions is absorbed systemically through the venous rich epidural space.

Epidural fatty tissue acts as a reservoir. The remainder reaches the spinal nerve

and nerve roots.

Spread of Local Anesthetic in the Epidural Space Local anesthetic injected into the

epidural space moves in a horizontal and longitudinal manner.

Theoretically the longitudinal spread could reach the foramen magnum and sacral foramina if enough volume was injected.

Spread of Local Anesthetics- Longitudinal

Spread of Local Anesthetics- Horizontal Horizontally the local anesthetic spreads

through the intervertebral foramina to the dural cuff.

Local anesthetics spread through the dural cuff via the arachnoid villa and into the CSF.

Blockade occurs at the mixed spinal nerves, dorsal root ganglia, and to a small extent the spinal cord.

Spread of Local Anesthetics- Horizontal

Spread of Local Anesthetics- Local anesthetics gain access to CSF via arachnoid granules

Distribution, Uptake & Elimination Takes 6-8 times the dose of a spinal

anesthetic to create a comparable block.

This is due to: Larger mixed nerves are found in the

epidural space when compared to the subarachnoid space.

Local anesthetics must penetrate arachnoid and dura mater.

Local anesthetics are lipid soluble and will be absorbed by tissue and epidural fat.

Epidural veins absorb a significant amount of local anesthetic with blood concentrations peaking in 10-30 minutes after a bolus.

Distribution, Uptake & Elimination Local anesthetics absorbed in the

epidural veins will be diluted in the blood.

The pulmonary systems acts as a temporary buffer and protects other organs from the toxic effects of local anesthetics.

Distribution occurs to the vessel rich organs, muscle, and fat.

Distribution, Uptake & Elimination Long acting amides will bind to alpha-1

globulins which have a high affinity to local anesthetics but become rapidly saturated.

Amides are metabolized in the liver and excreted by the kidneys.

Esters are metabolized by pseudocholinesterase so rapidly that there are rarely significant plasma levels.

Factors Affecting Height of Epidural Blockade Volume of local anesthetic Age Height of the patient Gravity

Volume Can be variable General rule: 1-2 ml of local anesthetic

per dermatome i.e. epidural placed at L4-L5; you want a

T4 block for a C-sec. You have 4 lumbar dermatomes and 8 thoracic dermatomes. 12 dermatomes X 1-2 ml = 12-24 ml

Big range! Stresses importance of incremental dosing!

Volume If you require only segmental anesthesia

than the dose would be less. Volume of local anesthetic plays a

critical role in block height. Dose of local anesthetics administered in

thoracic area should be decreased by 30-50% due to decrease in compliance and volume.

Age As age increases the amount of local

anesthetic to achieve the same level of anesthesia decreases. A 20 year old vs 80 year old

This is due to changes in size and compliance of the epidural space

Height The shorter the patient the less local

anesthetic required. A patient that is only 5’3” may require 1

ml per dermatome while someone who is 6’3” may require the full 2 ml per dermatome

Gravity Position of patient does affect spread and

height of local anesthetic BUT not to the point of spinal anesthesia.

i.e. lateral decubitus position will “concentrate” more local anesthetic to the dependent side will a weaker block will occur in the non-dependent area.

A sitting patient will have more local anesthetic delivered to the lower lumbar and sacral dermatomes

Gravity L5-S2 sometimes will have ‘patchy’

anesthesia due to sparing. By having the patient “sitting” or in a semifowlers position one can concentrate local anesthetic to this area.

Trendelenberg or reverse trendelenberg may help spread local anesthetic cephalad or alternatively limit the spread.

Local Anesthetics used for Epidural Anesthesia

Considerations in choosing Understanding of local anesthetic

potency & duration Surgical requirements and duration of

surgery Postoperative analgesic requirements

Local Anesthetics for Epidural Anesthesia Use only preservative free solutions Read the labels, ensure that it is

preservative free or prepared for epidural/caudal anesthesia/analgesia

Categories according to duration of action Short Acting: 2-chloroprocaine Intermediate Acting: lidocaine and

mepivacaine Long Acting: bupivacaine, etidocaine,

ropivacaine, levobupivacaine

Intermediate Acting Lidocaine Prototypical amide local anesthetic 1.5-2% concentrations used for surgical

anesthesia Epinephrine will prolong the duration of

action by 50% Addition of fentanyl will accelerate the

onset of analgesia and create a more potent/complete block

Intermediate Acting Lidocaine

Lignocaine Dose 3mg /kg

7mg/kg with adrenaline

Prolong action/reduces the toxicity

Long Acting Bupivacaine Long acting amide local anesthetic 0.5-0.75% concentrations used for

surgical anesthesia 0.125-.25% used for epidural analgesia Epinephrine will prolong duration of

action but not to the extent of lidocaine, mepivacaine, and 2-chloroprocaine

Long Acting Bupivacaine 0.75% concentration should not be used in OB In 1983 the FDA came out with this

recommendation There were several cardiac arrests due to

inadvertent intravascular injection in OB patients

Bupivacaine (as well as etidocaine) are more likely to impair the myocardium and conduction system with toxic doses than other local anesthetics

Long Acting Bupivacaine Bupivacaine has a high degree of protein

binding and lipid solubility which accumulate in the cardiac conduction system and results in the advent of refractory reentrant arrhythmias

Long Acting Bupivacaine

Bupivacaine Longacting 4-6 hours Deferential blockers

-Sensory more than Motor-Dose- 1-1.5 mg/kg-Cardiac Toxic-No Tachyphylaxis- Repeat drug

Long Acting Levobupivacaine S isomer of bupivacaine Used in the same concentrations Clinically acts just like bupivacaine with

the exception that it is less cardiac toxic

Long Acting Levobupivacaine

Long Acting Ropivacaine Long acting amide local anesthetic Mepivacaine analogue Used in concentrations of 0.5-1% for surgical

anesthetic Used in concentrations of 0.1-0.3% for

analgesia Ropivacaine is unique among local

anesthetics since it exhibits a vasoconstrictive effect at clinically relevant doses

Long Acting Ropivacaine Similar to bupivacaine in onset, duration,

and quality of anesthesia Key differences include: in doses for

analgesia there is excellent sensory blockade with low motor blockade and it is less cardiotoxic than bupivacaine

Long Acting Ropivacaine

Local anaesthetic systemic toxicity Tingling sensation around mouth Drowsiness Hypotension seizures Treatment ABC Midazolam /thiopentone intralipid

Epidural Additives Epinephrine will increase the duration of action

of all epidurally administered local anesthetics. There is a large variability among local

anesthetics as to the degree of increase The greatest effect is found with lidocaine,

mepivacaine, 2-chloroprocaine. Lesser effects found with bupivacaine,

levobupivacaine, etidocaine Minimal effects have been found with

ropivacaine

Epidural Additives Epi vs phenylephrine Epi is more effective in reducing peak

blood levels Phenylephrine does not appear to

reduce the peak blood levels

Epidural Additives Carbonation of local anesthetics has been

touted to improve the quality of epidural blocks due to increased penetration of connective tissue and intraneural diffusion

Studies are ambivalent Carbonation may not improve quality or

onset; may lead to increased blood levels of local anesthetic; result in a higher incidence of hypotension when compared to non carbonated local anesthetics

Epidural Additives Sodium bicarbonate can be added to

lidocaine, mepivacaine, and 2-chloroprocaine

Addition will increase the amount of free base which increases rate of diffusion and speeds onset

Studies have found that when added to 1.5% lidocaine speeds onset of blockade and results in a more solid block

Epidural Additives Generally 1 meq of bicarbonate is added

to 10 ml of local anesthetic (i.e. lidocaine, mepivacaine, 2-chloroprocaine)

The addition of bicarbonate to bupivacaine is not as popular. Usually 0.1 ml of bicarbonate is added to 10 ml of bupivacaine

Bupivacaine precipitates occurs at a pH > 6.8

Epidural Additives Mixing long acting and short acting local

anesthetics may not have much advantage for epidural anesthesia

Many choices for local anesthetics and additives

Thank you