1. Local Anesthetic Techniques
Prepared by Dr. Mahmoud Abdel-Khalek Jan 2015

2. Local Anesthetic Techniques
Local Anesthetic Drugs
Regional Anesthesia
Spinal Anesthesia
Epidural Anesthesia
Brachial Plexus Block
Bier’s Block

3. Local Anesthetic Drugs

4. Definition and Mode of Action
LA are drugs that block the generation and propagation of impulses in excitable tissues: nerves, skeletal muscle, cardiac muscle, brain
LA substances bind to a Na+ channel receptor on the cytosolic side of the Na+ channel (i.e. must be lipid soluble), inhibiting Na+ flux and thus blocking impulse conduction
LA must convert to an ionized form to properly bind to receptor
Different types of nerve fibres undergo blockade at different rates

5. Mechanism of Action
Un-ionized local anesthetic diffuses into nerve axon & the ionized form binds the receptors of the Na channel in the inactivated state

6. Local Anesthetics Esters Metabolism Amides Metabolism Procaine
Chloroprocaine
Tetratcaine
Cocaine
Metabolism
Hydrolysis by pseudo- cholinesterase enzyme
Amides
Lidocaine
Mepivacaine
Bupivacaine
Etidocaine
Prilocaine
Ropivacaine
Metabolism
Liver

7. Local Anesthetics & Baracity
Hyperbaric
Typically prepared by mixing local with dextrose
Flow is to most dependent area due to gravity
Hypobaric
Prepared by mixing local with sterile water
Flow is to highest part of CSF column
Isobaric
Neutral flow that can be manipulated by positioning
Very predictable spread
Increased dose has more effect on duration than dermatomal spread

8. Absorption, Distribution, Metabolism
LA readily crosses the blood-brain barrier (BBB) once absorbed into the blood stream
Ester-type LA (procaine, tetracaine) broken down by plasma and hepatic esterases; metabolites excreted via kidneys
Amide-type LA (lidocaine, bupivicaine) broken down by hepatic mixed function oxidases (P450 system); metabolites excreted via kidney

9. Choice of LA depends on
Onset of action –influenced by pKa (lower the pKa, the higher the concentration of the base form of the LA and the faster the onset of action)
Duration of desired effects – influenced by protein binding (long duration of action when the protein binding of LA is strong)
Potency – influenced by lipid solubility (agents with high lipid solubility will penetrate the nerve membrane more easily)
Unique needs (e.g. sensory blockade with relative preservation of motor function, for pain management)
Potential for toxicity

10. Maximum Dose of LA
Always be aware of the maximum dose for the particular LA used
Maximum dose usually expressed as (mg of LA) per (kg of body weight) and as a total maximal dose (adjusted for young/elderly/ill)
lidocaine maximum dose: 5 mg/kg (with epinephrine: 7mg/kg)
chlorprocaine maximum dose: 11 mg/kg (with epinephrine: 14 mg/kg)
Bupivacaine maximum dose: 2.5 mg/kg (with epinephrine: 3 mg/kg)

11. Systemic Toxicity
Occurs by accidental intravascular injection, LA overdose, or unexpectedly rapid absorption
Systemic toxicity manifests itself mainly at CNS and CVS
CNS effects first appear to be excitatory due to initial block of inhibitory fibres; subsequently, block of excitatory fibres
CNS effects (in approximate order of appearance):
Numbness of tongue
Tremors
Perioral tingling
Convulsions
Disorientation
Seizures
Drowsiness
Generalized CNS depression
Tinnitus
Coma
Visual disturbances
respiratory arrest
Muscle twitching

12. Systemic Toxicity

14. Treatment of LA systemic toxicity
Use the A, B, C’s for the management of local anesthetic toxicity
A= airway Maintain a patent airway, administer 100% oxygen
B= breathing May need to be assisted with positive pressure ventilation or intubation
C= circulation Check for a pulse If no pulse, initiate CPR
Seizures Diazepam in doses of 5 mg, or alternatively sodium pentothal in doses of mg will decrease or terminate seizures

15. Treatment of LA systemic toxicity
Hypotension:
Rapid infusion of IV fluids
Place the patient in a head down position (Trendelenburg)
Phenylephrine shots or infusion
Ephedrine (typically 5 mg shots)
If refractory treat the patient with epinephrine (5-10 mcg shots)
Repeat and escalate the dose as necessary
The use of lipids in the treatment of local anesthetic toxicity has shown promise There are currently no established methods and research continues

16. Neuraxial Blocks

17. Anatomy
The vertebrae are 33 number, divided by structural into five region: cervical 8, thoracic 12, lumber5, sacral 5, coccygeal3

18. Anatomy
The vertebrae are joined together by strong anterior and posterior longitudinal ligaments

19. Anatomy
The spinal cord lies within the spinal canal surrounded by meninges; Dura mater, subarachnoid space, then pia matter, end by Cauda equina (Hoarse tail)
The spinal cord receives blood supply from anterior and posterior spinal arteries
Spinal cord extends to L2, Dural sac to S2
Nerve roots (Cauda equina) from L2 to S2
Needle inserted below L2 should not encounter cord, thus L3-L4 and L4-L5 interspace are commonly used for spinal anesthesia

20. Spinal Meninges Dura Mater Arachnoid Sub Arachnoid Space Pia
Outer most layer
Fibrous
Arachnoid
Middle layer
Non-vascular
Sub Arachnoid Space
Lies between the arachnoid and pia
Pia
Inner most layer
Highly vascular

21. Indications of Spinal/ Epidural
Full stomach
Anatomic distortions of upper airway
TURP surgery
Obstetrical surgery (T4 Level for CS)
To relieve post-operative pain

22. Absolute Contraindications to Spinal/ Epidural Anesthesia
Lack of proper equipment or properly trained personnel
Patient refusal
Lack of IV access
Allergy to LA
Infection at puncture site or underlying tissues
Uncorrected hypovolemia
Coagulation abnormalities
Raised ICP

23. Relative Contraindications to Spinal/ Epidural Anesthesia
Bacteremia
Preexisting neurological disease
Aortic/mitral valve stenosis
Previous spinal surgery
Back problems
Severe/unstable psychiatric disease or emotional instability (Uncooperative)

24. Spinal Anesthesia Technique
Preparation & Monitoring
EKG
NBP
Pulse Oximeter
Patient Positioning
Lateral decubitus
Sitting
Prone (hypobaric technique)

25. Spinal Anesthesia Technique
Midline Approach
Skin
Subcutaneous tissue
Supraspinous ligament
Interspinous ligament
Ligamentum flavum
Epidural space
Dura mater
Arachnoid mater
Paramedian or Lateral Approach
Same as midline excluding supraspinous & interspinous ligaments

26. Spinal Anesthesia Levels
Spinal Injection
Sympathetic block is 2-6 dermatomes higher than sensory block
Motor block is 2 dermatomes lower than sensory block

27. Complications of Spinal Anesthesia
Failed block
Backache
Hypotension, bradycardia if block reaches T2-T4 (sympathetic nervous system block)
Post-spinal headache
More common in women ages 13-40
Larger needle size increase severity (use G23 or smaller)
Onset typically occurs first or second day post-op
Treatment: Bed rest, Fluids, Caffeine, Blood patch

28. Complications of Spinal Anesthesia
Extensive spread of anesthetic ("high spinal")
Persistent paresthesia (usually transient)
Epidural or subarachnoid hematoma
Spinal cord trauma
Infection

29. Complications of Spinal Anesthesia
Failed block
Back pain (most common)
Spinal headache
More common in women ages 13-40
Larger needle size increase severity
Onset typically occurs first or second day post-op
Treatment:
Bed rest
Fluids
Caffeine
Blood patch

30. Blood Patch Effective treatment for postspinal headache
Increase pressure of CSF by placing blood in epidural space
If more than one puncture site, use lowest site due to rostral spread
May be done more than one time
95% success with first patch
Second patch may be done 24 hours after first

31. Epidural Anesthesia Larger dose of LA used (12- 20 mL)
LA deposited in epidural space (potential space between ligamentum flavum and dura)
Widest at Level L2 (5-6mm)& Narrowest at Level C5 (1-15mm)
Safest point of entry is midline lumbar

32. Epidural Anesthesia
Solutions injected spread in all directions of the potential space; SG of solution does not affect spread
Initial blockade is at the spinal roots followed by some degree of spinal cord anesthesia as LA diffuses into the subarachnoid space through the dura

33. Epidural Anesthesia
Test Dose: 1.5% Lidocaine with Epinephrine 1:200,000
Tachycardia (increase >30bpm over resting HR)
High blood pressure
Light headedness
Metallic taste in mouth
Ring in ears
Facial numbness
Note: if beta blocked will only see increase in BP not HR
Bolus Dose: Preferred Local of Choice
10 mL for labor pain
20-30 mL for C-section

34. Epidural Anesthesia Distances from Skin to Epidural Space
Average adult: 4-6cm
Obese adult: up to 8cm
Thin adult: 3cm
Assessment of Sensory Blockade
Alcohol swab
Most sensitive initial indicator to assess loss of temperature
Pin prick
Most accurate assessment of overall sensory block

35. Complications of Epidural Anesthesia
Inadvertent dural puncture
Inadvertent IV administration
Hypotension (nausea & vomiting)
Headache
Backache
Infection

36. Caudal Epidural Anesthesia
Anatomy
Sacrum
Triangular bone
5 fused sacral vertebrae
Needle Insertion
Sacrococcygeal membrane
No subcutaneous bulge at site of injection after 2-3ml

37. Caudal Epidural Anesthesia
Dosages
S5-L2: 15-20ml
S5-T10: 25ml
Post Operative Problems
Pain at injection site is most common
Slight risk of neurological complications
Risk of infection

38. Brachial Plexus Block Musculocutaneous Nerve Median Nerve Ulnar Nerve
Radial Nerve

39. Axillary approach of BPB
Advantages
Provides anesthesia for forearm & wrist
Fewer complications than a supraclavicular block
Limitations
Not for shoulder or upper arm surgery
Musculocutaneous nerve lies outside of the sheath and must be blocked separately
Complications
Intravascular injection
Elevated bleeding time increases risk for hematoma

40. Axillary Approach Position
Head turned away from arm being blocked
Abduct to 90º
Forearm is flexed to 90º
Palpate axillary artery for pulse
The needle is inserted adjacent to the artery

41. Axillary Block Dosing Note 40mL is most common vollume
Lidocaine 1% ml
Etidocaine 1% ml
Bupivacaine 0.5% 30-40ml
Note 40mL is most common vollume

42. Local Intravenous Anesthesia (Bier’s Block)
Suitable for upper limb below elbow& lower limb below knee surgeries
Advantages: Easy to administer, rapid onset, muscle relaxation and rapid recovery
Limitation
Time!
Ideal for procedures lasting minutes
Maximum time limit is 90 minutes
Tourniquet pain generally starts after minutes

43. Contraindications
Raynaud’s disease
Sickle cell disease
Crush injuries
Young Children
Must have a reliable/operative tourniquet! If this can not be guaranteed then this technique should not be used due to risk of toxicity!

44. Mechanism of Action
Not clearly understood
Local anesthetics, ischemia, asphyxia, hypothermia, and acidosis all may play a role

45. Equipment Operative and reliable double tourniquet
Running IV in non-operative arm
Resuscitation equipment
Eschmarch bandage

46. Local Anesthetic Choice
0.5% lidocaine or 0.5% prilocaine
Max dose is 3 mg/kg for either
NEVER USE EPINEPHRINE CONTAINING SOLUTIONS
Complication of prilocaine is methemoglobinemia in doses of > 10 mg/kg
Treat with 1-2 mg/kg of 1% methylene blue given over 5 minutes

47. Technique
IV catheter in operative arm as distally as possible

48. Technique IV catheter in operative arm as distally as possible
Double tourniquet on the operative arm
Proximal Cuff
Distal Cuff

49. Technique Have patient hold arm up
Use Eschmark bandage to exsanguinate the arm
Exsanguinate the arm from distal to proximal

50. Inflate the proximal tourniquet to 150 mmHg over the patients systolic pressure
Proximal Cuff
Distal Cuff

51. Confirm the absence of a radial pulse

52. Inject your local (0.5% lidocaine or prilocaine in a dose of 3 mg/kg)

53. Remove IV catheter, hold pressure and have OR staff prepare arm Onset of anesthesia should occur in 5 minutes

54. When the patient complains of pain you can inflate the distal tourniquet and then deflate the proximal tourniquet
2nd
Proximal Cuff
1st
Distal Cuff

55. Minimum time for tourniquet inflation
The tourniquet should be up for at least 25 minutes…releasing it before this may result in toxicity
Releasing the tourniquet in cyclic deflations (10 second intervals) will decrease peak levels of local anesthetic

56. Complications Tourniquet discomfort
Rapid return of sensation after tourniquet release and subsequent surgical pain
Toxic reactions from malfunctioning tourniquets or deflating the tourniquet prior to the 25 minute limit

57. Thank You