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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