Regional AnaesthesiaAn introduction to peripheral nerve

blocks

Dr Aasifa TredrayConsultant Anaesthetist

Clinical Governance meeting July 11th 2013

Aim of presentation

• Equipment

• Anatomy of an axillary block

• Practical aspects of an axillary block

• Complications

Peripheral Nerve BlocksDistribution of local anaesthetic around nerves causing them to become numb and allow surgical procedures to be done. •Advantages

patient factors-analgesia, no GA, short starvation times, quicker recovery, long term benefitshospital factors-more efficient lists, more DSU patients, financial savings

Disadvantages patient suitability-contraindications logistics-time, list order, equipment, location

Overall high patient satisfaction rate so we should encourage and facilitate its use

Peripheral Nerve Stimulators and Ultrasound Machine

Principle of Ultrasound Transducer contains Piezo electric crystals - convert electric signal into sound waves

• Sound waves are then either absorbed or reflected back as they pass through structures in the body

• Reflected waves are then convert by machine into a digital 2D image seen on screen

• High frequency linear probes(5-12MHz) allows higher resolution but poor penetration so good for superficial structures

• Low frequency curvilinear probes (2-5MHz) will allow greater penetration but poorer resolution but good for deeper structures

Knobology!!

Depth

GainAmplification of received ultrasound information which will lighten whole image

Noise and artefacts are also amplified so best kept at lowest level that allows clear distinction of desired structures.

Latest machines offer complex computer controlled auto- gain buttons

Doppler Describes apparent change in sound frequency as source moves towards or away from probe

Away from probe as blue and flow towards probe as red (i.e. not necessarily corresponding to arterial and venous)

If Flow is perpendicular to probe then there will be Doppler shift and there will be no coloured flow on screen

Needling

• Out of plane

• In plane

Peripheral Nerve Stimulators

Peripheral Nerve Stimulators

• PNS is useful adjunct to USM as it increases safety of block

• Settings are pulse duration 0.05-0.1ms, frequency 2Hz and current starting at 0.5-1mA

• Current – distance of needle to nerve and which nerve is being stimulated

If twitches seen current is then reduced until no motor response is seen Ideal is for twitches to disappear by 0.2/0.3mA

If twitches disappear at a current > 0.5mA usually needle is too far away from nerve, so block will have a very slow onset or be unsuccessful

If twitches still present at current < 0.2mA,or increased resistance or pain on injection may suggest intraneural needle placement

Pulse width

Pulse width is the duration the current needs to be applied to a nerve to cause a stimulus/contractionDifferent nerves have different pulse widthsPossible to stimulate motor nerves but not sensory or pain nerves by using a short pulse width of 0.05-0.1ms.

Nerves Chronaxie time

Unmyelinated C 0.40

Myelinated Aδ 0.17

Myelinated Aα 0.05-0.10

Frequency Rate at which the twitches/contractions are seen

Ideal comfortable stimulation is 1 to 2 Hz

Higher frequency will give more frequent feedback to operator, but can cause greater discomfort to patient

• Not all nerves twitch as demonstrated when using the USMwhere you can see that your needle is in close proximity tonerve and no motor responses elicited even at currents 1.5mA

• Patients with neuropathy do not respond normally to PNS

Common St George’s Blocks

• Brachial plexus blocksInterscalene blockSupraclavicular and Infraclavicular blocksAxillary block

• Nerve blocks at the elbow

• Nerve blocks of the lower limb

Axillary Blocks

Axillary Blocks

Axillary Blocks• Anaesthetic pre-operative assessment• Consent• Plan B• Anaesthetic room

WHO sign in

Full monitoring and 1 BP measurement takenEstablish IV accessEmergency/anaesthetic drugs available

Position patient with arm out at 90 degrees

Axilla and whole arm exposed

Make sure they are comfortable

Axillary Blocks

Equipment Ultrasound machine – M turbo/Micromax/S nerve

50mm insulated nerve stimulating needle+/- Peripheral Nerve StimulatorECG and needle connectionsSterile gel and sheath for probe

•Local Anaesthetic mixture

Set up of block

Sit down and get comfortable

•Select appropriate probe •US machine set for nerve examination •Use adequate US gel to provide an air free interface•Gel applied to probe, then covered with sterile sheath•Skin cleaned with antiseptic spray -2% chlorhexidene is OK for peripheral blocks but not for spinals or epidurals•Sterile Gel applied to skin•Place probe on patient and orientate image (blue dot)•Assess anatomy and look for key landmarks

White / hyperechoic Black / hypoechoic Nerves close to spinal cord appear hypoechoicNerves pick up connective tissue as they move away from the spinal cord so change and become hyperechoic

• Local Anaesthetic to skin• Remove all air from LA syringe and flush needle- air really distorts the

ultrasound image• Connect needle to PNS if being used• Choose entry point with PAJUNK needle• Recheck settings of PNS• When needle is in correct position for nerve, anaesthetist will ask you to

ASPIRATE gently then inject 0.5ml- 1ml LA• STOP injection if too hard- high pressure may suggest intra neural

placement• We will assess spread of LA- if good will ask you to repeat• Ideal is for spread to surround entire nerve

Step by Step procedure Axillary Block

•Post block- keep monitoring patient and cycle BP every 3-5mins•Don’t rush and allow time for it to work•Assess numbness using cold spray-looking for a temperature difference. •Keep questions simple with yes/no answers for patient so that it is easy to see whether block is working or top up necessary• Keep equipment sterile and do not throw away remaining LA in case a top up is needed• Sedation? Oxygen?• Fluids?• Antibiotics?• Transfer to theatre- keep fully monitored, make sure comfortable

Blocks at the elbow

• Indications- hand surgery– to augment incomplete B.P.B– post-operative analgesia following GA – to expedite B.P.B

• Problems- – varying nerve distribution and wide overlap– no anaesthesia for upper arm tourniquet– no relaxation of upper arm muscle

Nerve blocks at elbow

Radial nerve block in the upper arm

Radial nerve block

4-5 cms above the elbow At the elbow

Median and ulnar blocks at the elbow

Complications of Blocks

Technique

Direct trauma to nerves, blood vessels and other nearby structuresBleeding, haematoma, infection at injection site

Intra neural injection leading to nerve damage

Drug related intravascular injection

systemic toxicityanaphylaxis

ALS protocols and location of INTRALIPID