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