sub arachnoid block.ppt

7/30/2019 SUB ARACHNOID BLOCK.ppt

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SUB ARACHNOID BLOCK( SAB )


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Definition :

Injecting local anaesthetic into CSF. The injection is usually made in the lumbar

spine below L2.

Spinal anaesthesia is easy, excellent forsurgery below the umbilicus.


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The Advantages of Spinal Anaesthesia :

Cost.The costs are minimal.

Patient satisfaction.

Majority of patients are very happy andappreciate the rapid recovery and absence of sideeffects.

Respiratory disease.Produces few adverse effects on the respiratory

system Patent airway.

Reduce risk of airway obstruction or aspirationof gastric contents.


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Diabetic patients.

Little risk of unrecognised hypoglycaemia,usually return to their normal food andinsulin regimen soon after surgery

Muscle relaxation.

Provides excellent muscle relaxation forlower abdominal and lower limb surgery.

Bleeding.

Blood loss during operation is less thandone under general anaesthesia.


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Splanchnic blood flow.

Reduce the incidence of anastomoticdehiscence.

Visceral tone.

Normal gut function rapidly returnsfollowing surgery.

Coagulation.

Post-operative deep vein thromboses andpulmonary emboli are less common


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Disadvantages of Spinal Anaesthesia :

Sometimes it can be difficult to find thedural space.

Hypotension may occur .

Some patients are not psychologicallysuited to be awake, even if sedated, duringan operation.


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not suitable for surgery lasting longer

than approximately 2 hours. When an anaesthetist is learning a new

technique, it will take longer to perform

Infection into the sub-arachnoid spaceand causing meningitis.

A postural headache


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Indications :

1. Operations below the umbilicus

2. Older patients and those with systemicdisease such as chronic respiratorydisease, hepatic, renal and endocrine

3. caesarean section.


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Contra-indications :

1.Inadequate resuscitation drugs andequipment.

2.Clotting disorders.

3.Hypovolaemia

4.Patient refusal.

5.Children.

high specialised technique


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6.Sepsis7.Septicaemia.

8.Anatomical deformitiesa relative contraindication

9.Neurological disease. The advantages anddisadvantages of spinal anaesthesia in the

presence of neurological disease need carefulassessment.10.Raise intracranial pressure,

precipitate coning of the brain stem.
http://www.nda.ox.ac.uk/wfsa/html/u12/u1208_01.htm


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Physiology of Spinal Anaesthesia :

1. Local anaesthetic blocks conduction of impulsesalong all nervesThere are three classes of nerve: motor, sensoryand autonomic.

a) Stimulation of the motor nerves causes musclesto contract and when they are blocked, muscleparalysis results.

b) Sensory nerves transmit sensations such as touchand pain to the spinal cord and from there to the

brain,c) Autonomic nerves control the calibre of blood

vessels, heart rate, gut contraction and otherfunctions not under conscious control.


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2. Generally, autonomic and sensory fibres

are blocked before motor fibres. Thishas several important consequences. Forexample, vasodilation and a drop in blood

pressure may occur when the autonomicfibres are blocked


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Anatomy :
http://www.nda.ox.ac.uk/wfsa/html/u12/u1208f01.htm


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The spinal cord usually ends at the level of L2

in adults and L3 in children. Dural puncture above these levels is

associated with a slight risk of damaging thespinal cord and is best avoided.

An important landmark to remember is that aline joining the top of the iliac crests is at L4to L5.

Remember the structures that the needle will

pierce before reaching the CSF (figure 1).


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Local Anaesthetics :

Local anaesthetic agents are :1. Hyperbaric solutions

Tend to spread down2. Isobaric solutionsnot influenced in this way. may be madehyperbaric by the addition of dextrose.

3. Hypobaric solutionsRarely used.


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1. Bupivacaine (Marcaine). 0.5% hyperbaric (heavy)

Bupivacaine lasts longer than most other spinalanaesthetics: usually 2-3 hours.2. Lidocaine/Lignocaine (Xylocaine).

Which lasts 45-90 minutes.

2% lignocaine can also be used but it has a shorterduration0.2ml of adrenaline 1:1000 is added to thelignocaine, it will prolong its duration.it is said to be potentially neurotoxic despite ithaving been used uneventfully for over forty years..

3. Cinchocaine


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4. Tetracaine5. Mepivacaine

6. Pethidine/Meperidine.The 5% solution (50mg/ml) has localanaesthetic properties and is a versatileagent.

The standard intravenous preparation ispreservative-free and is isobaric. A dose of0.5-1mg/kg is usually adequate for spinalanaesthesia.

7. Ropivacaine (Naropin)long-acting local anaesthetic, similar tobupivacaine.


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Preoperative Visit :

Tell about their anaesthetic procedure

Premedication

benzodiazepine such as 5-10mg orally 1hour before the operation.

narcotic agents may also be used.

Anticholinergics such as atropine orscopolamine (hyoscine) are not routinelyrequired.


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Intravenous Pre-loading :

Must have a large IV canule. Give intravenous fluids immediately

before the spinal preventhypotension

The volume of fluid is vary 500mls 1500 mls.

Dextrose 5% should be avoided as it isnot effective for maintaining the bloodvolume.


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Positioning the Patient for LumbarPuncture :

Easily performed when there is maximumflexion of the lumbar spine (figure 2).

The patient sitting on the operating tableand placing their feet on a stool.

The patient lying on their side with theirhips and knees maximally flexed.


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http://www.nda.ox.ac.uk/wfsa/html/u12/u1208f03.htmhttp://www.nda.ox.ac.uk/wfsa/html/u12/u1208f02.htm


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An assistant may help to maintain theposition.

The sitting position is preferable in theobese

The lateral is better for uncooperative or

sedated patients.


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Factors Affecting the Spread of theLocal Anaesthetic :

1. The baricity of the local anaestheticsolution

2. The position of the patient

3. The concentration and volume injected

4. The level of injection

5. The speed of injection

6. If a patient is kept sitting for severalminutes after the injection "saddleblock"


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7. Increased abdominal pressure (pregnancy,

ascites etc.) can lead to engorgement of theepidural veins, compression of the dura andhence a reduction in the volume of the CSF.


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Quantities of Local Anaesthetics :

Type of Block Hyperb Bupivac Plain Bupivac Hyperb Lidoc

Sadle block(genetalia,perineum)

1 ml 2 ml 1 ml

Lumbar Block(legs,groin,hernia)

2 3 ml 2 3 ml 1,5 2 ml

Mid thoracic(Hysterect) 2

4 ml 2

4 ml 2 ml


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Preparation for Lumbar Puncture :

A spinal needle.

27-29 gauge with a pencil point tip

An introducer, 5ml syringe

2ml syringe for.


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antiseptic e.g. chlorhexidine, iodine, ormethyl alcohol.

Sterile gauze

plaster to cover the puncture site. The local anaesthetic to be injected

intrathecally should be in a single useampoule.


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Performing the Spinal Injection :

1. Scrub and glove up carefully.2. Check the equipment on the sterile trolley.3. Draw up the local anaesthetic to be

injected intrathecally into the 5ml syringe,4. Draw up the local anaesthetic to be usedfor skin infiltration into the 2ml syringe.Read the label.

5. Clean the patient's back with the swabsand antiseptic


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6. Locate a suitable interspinous space.7. Inject local anaesthetic under the skin8. Insert the spinal needle (through the

introducer, if applicable).9. An increased resistance the needle enters

the ligamentum flavum, loss of resistance

enter epidural space CSF flow from theneedle

10. Aspirate gently slowly inject the local

anaesthetic.11. Apply a sticking plaster to the puncturesite.
http://www.nda.ox.ac.uk/wfsa/html/u12/u1208_01.htmhttp://www.nda.ox.ac.uk/wfsa/html/u12/u1208_01.htm


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Practical Problems :

The spinal needle feels as if it is in the right positionbut no CSF appears.Wait at least 30 seconds try rotating the needle 90degrees and wait again. If no CSF inject 0.5-1ml of air toensure the needle is not blocked then use the syringe to

aspirate .Stop as soon as CSF appears in the syringe. Blood flows from the spinal needle. Wait a short time. If

the blood becomes pinkish and finally clear, all is well. Ifblood only continues to drip, then it is likely that the needletip is in an epidural vein and it should be advanced a littlefurther to pierce the dura.

The patient complains of sharp, stabbing leg pain. Theneedle has hit a nerve root because it has deviated laterally.Withdraw the needle and redirect it more medially awayfrom the affected side.

sub arachnoid block.ppt

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