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Local Anesthesia

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Decrease cardiovascular depression associated with general anesthesia ... After one minute intubation occurs without laryngospasm. Local Infiltration ... – PowerPoint PPT presentation

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Title: Local Anesthesia


1
Local Anesthesia
Megan McQuade CVM 2005
2
Local Anesthesia
  • Local Anesthetics
  • Why provide local anesthesia?
  • Pharmacology
  • Mechanism of Action
  • Toxicity
  • Agents
  • Applications
  • Topical
  • Infiltration
  • Regional

3
Local Anesthesia
  • Why provide local anesthesia?
  • Better control of pain (multi-modal analgesia)
  • Lower analgesic dose requirements
  • Minimize incidence of chronic pain
  • Decrease cardiovascular depression associated
    with general anesthesia
  • Provide pre-emptive analgesia
  • Inexpensive
  • Minimal side effects
  • Fast onset
  • Ability to use with other analgesics

4
Preemptive Analgesia
  • Long-term changes occur within the peripheral and
    central nervous systems following noxious input.
  • These changes have been termed peripheral
    sensitization and central sensitization.
  • Peripheral sensitization reduction in the
    threshold of nociceptor afferent peripheral
    terminals
  • Central sensitization an activity-dependent
    increase in the excitability of spinal neurons

5
Preemptive Analgesia
  • They contribute to the post-injury pain
    hypersensitivity found post-operatively.
  • This manifests as an increase in the response to
    noxious stimuli and a decrease in the pain
    threshold, both at the site of injury and in the
    surrounding uninjured tissues.
  • Recent evidence suggests that preoperative
    regional administration of local anesthetics can
    preempt postoperative pain by preventing the
    establishment of central sensitization.

6
Local Anesthetics
  • Desirable Characteristics
  • Good penetration into body tissues
  • High potency so that low concentrations can be
    used
  • Rapid onset
  • Long duration of action
  • Low systemic toxicity
  • Not irritating to nerves or other tissues
  • Reversible action

7
Pharmacology
  • Local anesthetic molecules consist of three parts
  • Lipophilic aromatic group
  • allows penetration into nerve
  • Intermediate alkyl chain
  • Hydrophilic tertiary amine
  • provides water-solubility

8
Mechanism of Action
  • Local anesthetics are membrane stabilizing agents
  • They enter and occupy the membrane channels
    through which ions normally flow
  • The most immediate and apparent effect is the
    prevention of the inflow of Na which blocks
    subsequent ionic flow
  • Nerve cell depolarization is prevented, slowing
    or stopping the conduction of nerve impulses

9
Site of Action
  • The drug must diffuse through several physical
    barriers before it reaches individual neurons
    within a peripheral nerve
  • Small fibers are affected more rapidly than large
    fibers.
  • The larger the nerve, the longer it will take to
    diffuse into the center of the nerve fiber and
    complete the blockade
  • Non-myelinated fibers are blocked more rapidly
    than myelinated.
  • In myelinated nerves the areas of penetration are
    limited to the nodes of Ranvier

10
Types of Nerve Fibers
  • Myelinated A-fibers
  • a motor, proprioception 12-20mm
  • b motor, touch 5-12mm
  • g muscle spindles 3-6mm
  • d pain, temperature 2-5mm
  • Myelinated B-fibers lt3mm
    (preganglionic sympathetic)
  • Non-myelinated C-fibers
  • Pain 0.4-1.2mm
  • Temperature 0.3-1.3mm

11
Priority of Blockade
  • Nerve fibers
  • 1. B-fibers and C fibers
  • 2. Ad -fibers
  • 3. Aa fibers
  • Sensation
  • 1. Pain
  • 2. Cold
  • 3. Warmth
  • 4. Touch
  • 5. Joint
  • 6. Deep pressure

(sensation returns in the reverse order of
blockade)
12
Absorption
  • Poor absorption through intact skin
  • Variable absorption from
  • Injured skin
  • Mucous membranes
  • Serosal surfaces
  • Respiratory epithelium
  • Intramuscular deposition
  • Subcutaneous deposition
  • Intravenous administration

13
Toxicity
  • Usually due to inadvertent rapid intravenous
    injection or excessive extravascular dose.
  • Biphasic response of excitation followed by
    depression
  • Vasodilation
  • Cardiovascular depression
  • Clinical signs
  • Hypotension
  • Cardiovascular collapse
  • Seizures
  • Methemoglobinemia
  • Allergic reaction

14
Lidocaine and Bupivicaine
 
15
Applications
  • Topical anesthesia
  • Local infiltration
  • Peripheral nerve blocks
  • Head
  • Forelimb
  • Thorax
  • Hindlimb
  • Intra-articular

16
General Considerations
  • Use sterile solutions and equipment
  • Do not inject into inflamed areas
  • Use as small a gauge needle as practical
  • Aspirate for blood before injecting
  • Use lowest effective concentration
  • Use smallest possible amount

17
Topical Anesthesia
  • Lidocaine is effective when placed topically on
    mucous membranes (not on intact skin).
  • Mouth
  • Tracheobronchial tree
  • Esophagus
  • Genitourinary tract
  • Proparacaine, a very short acting local
    anesthetic is used to desensitize the cornea.

18
Splash Block
  • After induction of anesthesia one drop of 2
    Lidocaine is dripped directly over the arytenoids
    in cats
  • After one minute intubation occurs without
    laryngospasm.

19
Local Infiltration
  • The solution is injected extravascularly using a
    22 to 25 gauge needle.
  • It is slowly injected, after aspirating for
    blood, advancing the needle along the proposed
    incision line.
  • This technique is used for removal of small
    superficial tumors, debridement and suturing of
    wounds, laparotomies, and cesarean sections.

20
Field Block
  • A diamond-shaped block for removal of small
    tumors or lesions.

21
Ring Block
  • A field block in which the soft tissues around an
    extremity are infiltrated to induce anesthesia
    distally.
  • Onychectomies
  • Tail amputations
  • Caution with volume of local used in puppies
  • Do not use lidocaine combined with epinephrine.
    Vasoconstriction can lead to necrosis

22
Radial-Median-Ulnar Nerve Block
  • 0.1-0.3ml of local anesthetic at each site
  • Medial to the accessory carpal pad on the palmar
    surface
  • Medial and palmar branch of the ulnar nerver
  • Lateral and proximal to the accessory carpal pad
    on the palmar surface
  • Dorsal branch of the ulnar
  • Dorso-medial aspect of the proximal carpus
  • Radial nerve

23
Regional Anesthesia of the Head
  • Infraorbital B. Maxillary C. Ophthalmic
  • D. Mental E. Mandibuloalveolar

24
Anesthesia of the Upper Lip and Nose
  • Blocking the infraorbital nerve provides
    anesthesia to the upper lip and nose, roof of
    nasal cavity and skin ventral to the infraorbital
    foramen.
  • The needle is inserted either intraorally or
    extraorally 1 cm cranial to the bony lip of the
    infraorbital foramen. It is then advanced to the
    infraorbital foramen.
  • The infraorbital foramen can be palpated between
    the dorsal border of the zygomatic process and
    the gum of the canine tooth.

25
Anesthesia of the Maxilla
  • Blocking the maxillary nerve provides anesthesia
    to the maxilla, upper teeth, nose, and upper lip.
  • The needle is inserted through the skin at a 90
    degree angle ventral to the border of the
    zygomatic process and approximately 0.5cm caudal
    to the lateral canthus of the eye.

26
Anesthesia of the Lower Lip
  • Blocking the mental nerve provides anesthesia to
    the lower lip.
  • The needle is inserted over the mental nerve,
    rostral to the middle mental foramen at the level
    of the second premolar tooth.

27
Anesthesia of the Eye
  • Blocking the lacrimal, zygomatic, and ophthalmic
    nerves provides anesthesia to eye, orbit,
    conjunctiva, eyelids, and forehead skin.
  • The needle is inserted ventral to the border of
    the zygomatic process at the lateral canthus of
    the eye. It should be approximately 0.5 cm
    cranial to the anterior border of the vertical
    portion of the ramus of the mandible. The needle
    is advanced medial to the ramus in a mediodorsal
    and somewhat caudal direction until it reaches
    the orbital fissure.

28
Anesthesia of the Mandible
  • Blocking the inferior alveolar branch of the
    mandibular nerve provides anesthesia to the cheek
    teeth, canine, incisors, skin, and mucosa of the
    chin and lower lip.
  • The needle is inserted at the lower angle of the
    jaw approximately 1.5 cm rostral to the angular
    process. It is advanced 1.5 cm dorsally against
    the medial surface of the ramus of the mandible
    to the palpable lip of the mandibular foramen.

29
Anesthesia of the Forelimb
  • Brachial Plexus Block
  • Blocking the radial, median, ulnar, and axillary
    nerves provides anesthesia within or distal to
    the elbow.
  • The needle is inserted at the point of the
    shoulder, medial to the shoulder joint and
    directed toward the costochondral junction, and
    parallel to the vertebral column. The anesthetic
    is injected slowly as the needle is withdrawn.
  • Anesthesia occurs within 20 minutes and can last
    for up to 2 hours.

30
Brachial Plexus Block
31
Anesthesia of the Thorax
  • Intercostal nerve blocks are performed after
    lateral thoracotomies.
  • A minimum of two adjacent intercostal spaces both
    cranial and caudal to the incision must be
    blocked due to overlap of nerve supply.
  • The needle is inserted at the caudal border of
    the rib near the intervertebral foramen.

32
Anesthesia of the Thorax
  • Intrapleural block
  • A splash block of the pleura can be performed
    during thoracotomies.
  • Local anesthetic can also be injected into a
    chest tube post-op. The animal is then often
    positioned so that the side with the incision is
    dependent.

33
Anesthesia of the Hindlimb
  • Selective blockade of the saphenous, common
    peroneal, and tibial nerves will provide
    anesthesia distal to the hip.

34
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35
References
  • Atchinson, W. (2002) Pharmacology of Local
    Anesthesia. Veterinary Pharmacology PHM 556.
    Michigan State University.
  • Greene, S. A. (2003) Local Anesthetic
    Techniques. Proceedings of the Western
    Veterinary Conference. www.vin.com
  • Ilkiw, J. (2001) Local Anesthesia and Local
    Anesthetic Techniques. World Small Animal
    Veterinary Association World Congress
    Proceedings. www.vin.com
  • Lumb, W. V., Jones, E. W. (1984). Veterinary
    Anesthesia. Philadelphia Lea Febiger.
  • Muir, W. W., Hubbell, J. A., Skarda, R. T.,
    Bednarski, R. M. (2000). Handbook of Veterinary
    Anesthesia, Third Edition. St. Louis Mosby.
  • Stein, R. (2003) Ring Blocks. Veterinary
    Anesthesia Support Group. http//www.vasg.org/ring
    _blocks.htm
  • Warren, R. G. (1983). Small Animal Anesthesia.
    St. Louis Mosby.

36
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