Central Neuroxial blockage ( Spinal and Epidural block ) By Dr Sachin Gaikwad

Central Neuroaxial Blockade

Dr Sachin Gaikwad

Applied Anatomy

Vertebral column consist of 33 vertebra 7 cervical , 12 thoracic , 5 lumbar , 5 fused

sacral and 4 fused coccygeal vertebra.

Vertebral column curves

4 curves Kypotic curves-

Thoracic and sacral

Lordotic curves- lumbar and cervical

Vertebral canal boundaries

Surface landmarks

Epidural Space ( Extradural or Peridural space)

It lies outside duramater. Extends from foramen magnum to sacral hiatus. It is triangular in shape with apex dorsomedial

Contents of epidural space Anterior and posterior nerve root Epidural veins Spinal arteries Lymphatics Fat

Epidural Veins Venous plexus of Batson Valveless veins connecting pelvic veins to

cranial veins directly Accidental injection of air or LA can directly

ascend to cranium These veins directly drains into IVC so

whenever there is obstruction to vena caval flow as in pregnancy ,abdominal tumours these veins are engorged reducing the size of epidural space and less dose is required.

Anatomy of Spinal Cord Extend from medulla oblongata to lower border

of L1 in adults. In infants and neonates it ends at the lower

border of L3 Adult level is achieved by 2 yr of age So in infancy spinal anaesthesia is given at L4-

L5 space. Below L1 vertebral canal is occupied by

lumbar,sacral and coccygeal nerve roots in oblique and downward direction forming cauda equina (horse tail).

Divides into 31 pairs of spinal nerves 8 cervical ,12 thoracic,5 lumbar,5 sacral and 1

coccygeal. Each spinal nerve has anterior and posterior

root.

Important dermatological segment levels

T4 – Nipples T6 - Xiphisternum T10 – Umbilicus L1- Inguinal ligament S1 to S4 - Perineum

Segmental levels of Spinal reflexes T7,8 – Epigastric T9-T12- Abdominal L1,2- cremasteric L2,3,4- Knee jerk S1,2 – Ankle jerk S4,5- Anal sphincter S1,2- Planter

Meninges Inside to outside by piamater ,arachnoid and

duramater. Duramater extends up to S2 in adults and up to

S4 in infants while piamater extends as filum terminale up to coccyx.

Cerebrospinal Fluid CSF is present between pia and arachnoid

mater ie subarachnoid space that is why spinal anaesthesia is also called as subarachnoid block.

Secreted by choroid plexus of 3rd

, 4th

and lateral ventricles and is absorbed into venous sinuses via arachnoid villi

500 ml in 24 hours. Volume of CSF at one time is 140ml , half of

which is present in cramium and half in spinal canal.

Sp.gravity = 1.003 to 1.009 ( avg 1.004) .pH – 7.35 CSF pressure – 100- 150 mm of H2O

Advantage over GA Cheap Less risk of pulmonary aspiration Respiratory complications are obviated like

bronco-spasm,post op atelectasis Systemic effect of GA drugs not seen Consequences failed intubation avoided Disturbances of body chemistry are avoided Bleeding is less because of low mean arterial

pressure Decreased incidence of thromboembolism due

to increased vascularity of lower limbs.

Physiological alteration of central Neuroaxial blocks

Cardiovascular System Most prominent effect is hypo tension Venodilation because of sympathetic block Dilatation of post arteriolar capillaries Decreased cardiac output Decreased venous return Bradycardia Decreased catecholamine release due

paralysis of nerve supply of adrenal glands Supine hypotension syndrome- compression of

IVC and aorta by pregnant uterus,abdominal tumours.

Bradycardia is due to Bainbridge reflex – decreased arterial

pressure because of decreased venous return. Direct inhibition of cardioacceletor fibres T1 to

T4.

Nervous system Sequence of blockage of nerve fibres Autonomic-> Sensory -> Motor Recovery in reverse order Autonomic level is 2 segment higher than

sensory which is 2 segment higher than motor This is called as differential blockage . Autonomic level is tested by temp.,sensory by

pin prick and motor by toe movement.

Respiratory system Tidal volume , minute volume, arterial oxygen

tension are well maintained Apnea may occur due to severe hypotension

causing medullary ischemia. Other causes are High spinal (C3,C4,C5),Total spinal,Accidental injection of LA in systemic circulation

Gastrointestinal system Contracted gut with relaxed sphincters due to

sympathetic block with parasympathetic over activity

Nausea Vomiting Liver – no impairment

Excretory system and reproductive system

Renal function not impaired unless MAP falls below critical pressure of Kidney for auto-regulation ( 55 mm of Hg)

Urinary retention due blockage of sacral parasympathetic fibres (S2,3,4)

Engorgement of penis

Endocrine system Stress response to surgery is inhibited Hypoglycaemia due to augmented response to

insulin Increased in ADH is supressed during surgery

Thermoregulation Vasodilatation causes hit loss which is

compensated by vasoconstriction above the block and shivering

Spinal Anaesthesia Subarachnoid block Intrathecal block

Indications Orthopaedic surgery of lower limb and pelvis General surgery – all pelvic and perineal

surgeries , hernia,hydrocele, appendix,testicular surgeries.

Gynaecological and obs – hysterectomy,myomectomy, C section, tubectomy,tuboplasty,ovarian surgeries,cervical surgeries

Urology- bladder and ureteric stone,prostate

Procedure Position – lateral ,sitting, prone Approach – mid-line, paramedian, lumbosacral

(Taylor) Under AAP spinal needle is inserted in Sub

arachnoid space and after confirmation of free and clear flow CSF LA is injected.

LA mainly act on spinal nerves and dorsal ganglion.

In the horizontal supine position ,hyperbaric local anesthetic solutions injected at the height of the lumbar lordosis (circle) flow down the lumbar lordosis to pool in the sacrum and in the thoracic kyphosis. Pooling in the thoracic kyphosis is thought to explain the fact that hyperbaric solutions produce blocks with an average height of T4-6.

Drugs used for SA

1) Xylocain – 5% made hyperbaric by addition of 7.5% dextrose.

2)Bupivacaine – 0.5% made hyperbaric by addition of 8% dextrose.

3)Tetracaine - 1% made hyperbaric by addition of 5% dextrose.

4)Procaine - 10% made hyperbaric by addition of 5 % dextrose.

5)Opioid-

Drug Concentration Specific gravityLignocaine 5% in 7.5% in D 1.0333Bupivacaine o.5% in 8% in D 1.0273Tetracaine 1% in 5% in D 1.0203Procaine 10 % in 5% in D 1.0203

Spinal Needles Dura cutting and dura separating

Dura cutting- Quincke- bobcock ,Greene Dura separating – these are pencil tip

point end. Whitre ,sporte and pitkin Incident of Post spinal puncture headache

and cost

Factors affecting the height of the block

1)Volume of drug- greater volume higher level2) Baricity – it is the ration of sp. Gravity of an

agent at body temperature to sp. Gravity of CSF at same temperature.

Hyperbaric technique- common ,outcome is govern by position of patient

Hypobaric technique- less common,agent used is tetracaine 0.3% which is made hypobaric by addition of sterile water. Useful in colorectal surgery and applied in prone position where head is lower than buttocks ( Jack Knife position.

Isobaric technique- commonly used bupivacaine 0.5% plain.settled at the same level of injection

3) Position of patient- very important factor eg if Trendelenburg position is given then same volume will produce a much higher block

4)Intra Abdominal pressure – in ascities,pregnancy,abdo tumours decreases volume of subdural space and increases CSF pressure producing higher blocks

5)Spinal curvature- by affeccting contour of sub arachnoid space can affect the level of block

6) Patient factors – 7)Age -in old age due to reduced spinal and

epidural space chances of higher block 8)Obesity – affects block due to increase in intra

abdo pressure9)Height- taller patient have long spine so require

more drug and vice versa.

Factores affecting duration of block

1.Dose 2.Increased concentration of agent3.Pharmacological profile of drug like protien

binding ,metabolism4.Type of drug used .Bupivacaine vs lignocaine5.Addetives- Adrenaline,opiod.

Complications of SAB

1 Hypotension Most common complication Mild hypotenison do occure in all patients but in

1/3rd patient BP may fall < 90 systolic Treatment-

I. Prophylactic- preloading with 1 to 1.5 L of crystalloidII.Curative-

a) Head low position to increase venous return up to 15 %b) Fluids- colloids are better than crystalloidsc) Vasopressors –

ephedrine,mephenteramine,methoxamine( sympatho memetic actin

d)I notropes- Dopamine ,dobutamine improve cardiac output

e) Oxygen inhalation – prevent hypoxia of brain

2 Bradycardia Treatment – IV atropine

3. Respiratory paralysis Apnea – it usually because of hypotension so

treat hypotension .if high or total spinal then give IPPV

Slight respiratory difficulty is treated with oxygenation and reassurance

4. Nausea and vomitting Because of central hypoxia due to hypotension Treatment – treat hypotension,oxygenation,

antiemetics

5. Difficulty in phonation Due to high spinal block involving cervical level Treatment – IPPV

6.Restlessness,anxiety,apprehension Ruleout hypoxia then reassure and sedate

7 LA toxicity Due to intra vascular injection Treat symptomatically

8.Cardiac arrest

May be due to total / High spinal,severe hypotension,LA toxicity/ anaphylaxis

Start CPCR

9 .High spinal /Total spinal If involving lower inter costal then patient will

complain of dysnea, give oxygenation and reassurance

If high to block cardioaccelerator fibres then sever bradycardia & hypotension

If too high to involve cervical fiber then IPPV may required

10. Miscellaneous Pain during injection Bloody tap Broken needle

Post OP complications

1) Urinary retention – due to blockage of S2,S3 S4 .Catheterisation may require

2)Post spinal headache-Post dural puncture headache

3)Meningitis- chemical ,infective 4)Cauda equina syndrome- due direct injury to

nerve fibres by needle or LA agent. Mostly seen with continuous spinal with small bore catheter.

5)Paraplegia- epidural hematoma, abscess6)Spinal cord ischemia -severe prolong

hypotension, use of vasocontrictors

7)Local toxicity of LA like chloro procaine can injure spinal cord and can cause paraplegia

8)Anterior spinal artery syndrome- Epidural haematoma,abscess, epidermoid tumour can lead to compression of anterior spinal artery causing anterior spinal artery syndrome manifested by motor deficit without involving posterior column.

Contraindications Absolute1) Raised intra cranial pressure2)Patient refusal3)Severe hypo volumic shock4)Patient on anti coagulant5)Thrombolytic / fibrinolytic therapy6)Bleeding disorders / coagulopathies7)Septicemia and bacteremia8)Infection at local site

Relative1) Fixed cardiac output lesions( AS , MS)2)Mild to moderate hypo volemia or hypotension3)Uncontrolled hyper tension4) H/o recent MI,severe ischemic heart disease5)Heart blocks and patient on beta blockers6)Patients on aspirin7)Patients on low dose heparin8)Spinal deformity9)Previous spinal surgery

10) History of headache11) GIT perforation12)Neuropathies13)CNS disorders14)

Spinal anaesthesia in children Should be given in low space L4-L5 Preloading is not require as children less than 8

years are virtually free of heamodynamic side effects

Use of narcotics is contra indicated Chances of systemic toxicity is high

EPIDURAL ANAESTHESIA

Indications All surgeries under spinal block can be

performed under epidural block. Mainly used for controlling post op pain Painless labour To control chronic pain To control pain due to cancer Acute occlusive vascular conditions Blood patch for post spinal headache

Epidural needle Most common is Tuophy’s needle It is blunt bevel with curve of 15 to 30 degree at

tip. This curve is called as Huber Tip. Weiss – is winged Crawford – straight blunt bevel with no curve

Technique Like in spinal it can be given in sitting or lateral. Usually epidural space is encountered 4 to 5

cm from skin and it has negative pressure .

Methods to locate epidural space Loss of resistance technique – after piercing

ligamentum flavum there is loss of resistance. Hanging drop technique ( Guttierrez’s sign)-

drop of saline in hub sucked in due to negative pressure .

MacIntosh extradural space indicator Movement of bubble on Odom’s indicator

Confirmation Test dose of 1ml of hyperbaric lignocaine with

adrenaline is given if in 5 min there is no evidence of either spinal block or intravascular injection further dose can be given

Then epidural catheter is passed through the needle

and 3 to 4 cm of catheter should be in epidural space. Microfilter is attached to prevent contamination

Onset of action – 15 to 20 min Successful block is assessed by absence of

knee jerk and pain by pin prick

Site of action of drug Mainly Anterior and posterior nerve roots Mixed spinal nerve Drug diffuses through dura and arachnoid and

inhibits descending pathways in spinal cord

Drugs used

NO Drugs concentration1 Lignocaine 1-2 %

2 Bupivacaine 0.25- 0.5 %

3 Chloroprocaine 2-3 %

4 Mepivacaine 1-2 %

5 Prilocaine 2-3 %

LA

Opioids Morphine- 4 to 6 mg Fentanyl- 100 mcg ( diluted in 10ml NS) onset

within 10 min last for 2 to 3 hours Fentanyl + bupivacaine – for post op analgesia

and painless labour.

Advantage of opioid Only sensory block Long lasting effect No sympathetic block

Disadvantage Respiratory depression Urinary retention Pruritus Nausea and vomiting Sedation

Factors affecting level Volume of drug Age Gravity Intra abdominal tumours, pregnancy Speed of injection Level of injection Length of vertebral column Conc of LA

Complications

Inadequate block Hypotension Apnea Total Spinal Dural puncture Subdural block Intravascular injection LA toxicity Horners syndrome Epidural heamatoma Epidural abscess Anterior spinal artery syndrome Direct injury to cord Brocken catheter Meningitis

Advantage of epidural anaesthesia Less hypotension No post spinal headache Level of block can be changed Any duration of surgery can be performed

Comparison

Spinal Epidural1 cost Cheaper Expensive 2 onset of action Early Delayed 3 Technically Easier Difficult 4 Duration of action Less Prolonged5 Quality of block Excellent May be patchy6 Change of level Not possible after fixation Can be possible7 Block failure rate Less High 8 Post dural puncture headache

Seen Not seen

9 epidural Heamatoma less High incidence10 Total spinal rare High 11 intravascular inj rare High chance12 drug toxicity less high13 Catheter complications Not seen present

Thank you