Microscopy Special Techniques in Microscopy: Immunohistochemistry.
6. Special Techniques
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Transcript of 6. Special Techniques
1Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Local Anesthesia Assisted and Controlled Ventilation Neuromuscular Blocking Agents
Special Techniques
Chapter 6
2Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Local Anesthesia
Use of a chemical agent on sensory neurons to disrupt nerve impulse transmission leading to temporary loss of sensation
Indications: Tractable animal General anesthesia is undesirable or high risk Means to deliver general anesthesia are not
available
3Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Local Anesthesia (Cont’d)
Advantages Low cardiovascular toxicity Inexpensive Excellent pain control immediately postoperatively Minimum patient recovery time
Uses Ruminant obstetric and abdominal procedures Complement standing sedation in horses In conjunction with general anesthesia for pain
control
4Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Local Anesthetic Agents
Skin infiltration and mucous membrane application: Lidocaine
• Administer at 0.5% to 2%• Dilute with sterile saline if necessary
Bupivacaine• Administer at 0.25% or 0.5%• Slower onset of action; long duration
Mepivacaine Procaine
Ophthalmic use: tetracaine, proparacaine
5Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Characteristics of Local Anesthetics
Not general anesthetics Don’t affect the brain and have no sedative effect
Few cardiovascular or respiratory effects Better for high-risk patients
Exert action close to site of injection Not distributed throughout the body
Don’t normally cross the placenta Used for cesarean sections and obstetric
manipulations
6Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Local Anesthetic Mechanism of Action
Drugs that affect primarily sensory neurons Drug must be placed in proximity to the neuron Blocks sodium channels and prevents generation
of electrical impulses (stops depolarization) Reversal occurs as drug is absorbed into the local
circulation Metabolized in liver
7Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Local Anesthetic Mechanism of Action (Cont’d)
Drugs that affect primarily motor neurons Cause temporary local paresis or paralysis Seen in conjunction with sensory neuron loss of
sensation• e.g., Epidural block
8Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Local Anesthetic Mechanism of Action (Cont’d)
Drugs that affect the autonomic nervous system Not always desirable Affect sympathetic neurons between the brain and
blood vessels and internal organs Sympathetic blockade = temporary loss of function Sympathetic blockade may affect the heart if local
anesthetic diffuses into the thoracic spinal cord Peripheral effect: vasodilation leading to local
flushing and increased skin temperature Vasodilation may lead to hypotension
9Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Routes of Administration of Local Anesthetics: Topical
Applied directly to intact skin Drug molecules can penetrate the epidermis to
reach the dermis Less pain relief and shorter duration of effect than
if administered by infiltration Clinical applications
Lidocaine patches Ethyl chloride spray Eutectic mixture Splash block Bupivacaine instilled through a chest tube Mucous membrane application
10Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Routes of Administration of Local Anesthetics: Infiltration
Drug injected into tissues in proximity to the target nerve
Lidocaine with or without epinephrine is most common
Intradermal, subcutaneous, or intramuscular administration
Provides analgesia for surgery involving superficial tissues
11Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Routes of Administration of Local Anesthetics: Infiltration (Cont’d)
Procedure Surgical prep Small-gauge needle (20- or 25-gauge) Amount of drug used varies with species and
procedure location Onset of action (lidocaine) = 3-5 minutes Test effectiveness prior to surgery: gently prick
skin with a 22-gauge needle
12Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Infiltration of Local Anesthetics
Effectiveness of local anesthetics Deep tissues are not affected if injection is
superficial Scar tissue, fibrous tissue, fat, edema, and
hemorrhage impede diffusion of drug Inflammation or infection decrease effectiveness
Duration of effect depends on drug used and
rate of absorption by local blood vessels Epinephrine may be added to local anesthetic to
affect rate of absorption Use of lidocaine without epinephrine
13Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Infiltration Techniques: Nerve Blocks
Injecting local anesthetic in proximity to a nerve
Desensitizes a particular anatomic site Decreases amount of general anesthesia
needed Provides short-term analgesia postoperatively
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Infiltration Techniques: Nerve Blocks (Cont’d)
Most commonly used in large animals Lameness examinations in horses Cornual blocks for dehorning cattle Paravertebral blocks for abdominal or obstetric
procedures in cattle Dental blocks in dogs and cats Intercostal nerve blocks for chest surgery Limb amputations Cat declaws
15Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Infiltration Techniques: Line Blocks
A continuous line of local anesthetic placed between the target area and the spinal cord
Ring block: line of local anesthetic completely encircles an anatomic part
Used in food animal and equine surgery Teat surgery or wound repair
L-block: a line block used for laparotomy surgery in ruminants
16Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Infiltration Line Blocks (Cont’d)
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Other Infiltration Techniques
Intraarticular administration Local anesthetics injected directly into a joint
Regional anesthesia Local anesthetic injected into a nerve plexus or in
proximity to the spinal cord Affects a larger area such as an entire limb or
caudal portion of the body
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Other Infiltration Techniques (Cont’d)
Paravertebral anesthesia (ruminants only) For standing laparotomies as an alternative to an
L-block Local anesthetic blocks the dorsal and ventral
branches of spinal nerves T13-L2 Provides wide, uniform area of anesthesia May produce hind limb weakness or scoliosis
19Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Infiltration Techniques: Epidural Anesthesia
A regional anesthetic procedure used in small and large animals
Blocks sensation and motor control of the rear, abdomen, pelvis, tail, pelvic limbs, and perineum
Uses: Tail amputation Anal sac removalPerianal surgery UrethrostomiesObstetric manipulations Cesarean sectionsSome rear limb operations
20Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Infiltration Techniques: Epidural Anesthesia (Cont’d)
Drug choice determined by procedure Local anesthesia
• 2% lidocaine or 0.5% bupivacaine Postoperative pain control
• Opioid (morphine) Opioid and local anesthetic mixture
• Anesthesia and analgesia Opioid and alpha2-agonist mixture
• Epidural anesthesia in horses and cattle
21Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Epidural Anesthesia (Cont’d)
Location Drug deposited in epidural space between spinal
cord and vertebrae Spinal nerves pass through this space and are
affected by drugs placed here Dogs: between the last lumbar vertebra (L7) and
the sacrum
22Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Epidural Anesthesia (Cont’d)
Effects: Local anesthetics block sensory and motor
neurons Sensory block controls pain Motor block may affect tail and limb mobility Opioids have minimal effect on motor neurons
23Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Infiltration Techniques: Bier Block
Intravenous regional anesthesia Provides short-term local anesthesia to a limb Lidocaine only Tourniquet applied to proximal superficial vein Lidocaine injected into distal superficial vein Effect lasts less than 1 hour
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Systemic Constant Rate Infusion
Lidocaine administered to healthy anesthetized animals
Reduces dose of general anesthesia or analgesic required
Used in dogs, cats, and horses
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Adverse Effects of Local Anesthetics
Loss of motor neuron function Loss of nerve function with direct injection Tissue irritation Paresthesia during recovery Allergic reactions from rash or hives to
anaphylactic shock Systemic toxicity Trauma to spinal cord or cauda equina Serious toxicity and death with infiltration into the
cranial portion of the spinal cord Sympathetic nerve block with infiltration into the
cervical or thoracic spinal cord
26Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Assisted and Controlled Ventilation
Positive-pressure ventilation (PPV) Assisted ventilation
Anesthetist delivers an increased volume of air or oxygen/anesthetic gases to the patient
Patient initiates inspiration Controlled ventilation
Anesthetist delivers all air required by the patient No spontaneous respiratory effort by the patient Anesthetist controls respiratory rate and volume
and pressure of gas inhaled
27Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Normal Ventilation
Physical movement of air into and out of the lungs and upper respiratory passageways
Active phase Inhalation Initiated by increased PaCO2 detected by
respiratory center in the brain Thoracic muscles (diaphragm and intercostals)
movement causes thoracic cavity to expand Air is pulled into the breathing passages and goes
to the alveoli When lungs are “full” the respiratory center stops
inhalation
28Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Normal Ventilation (Cont’d)
Passive phase Exhalation No active muscle movement PaCO2 begins to rise until respiratory center starts
inhalation again Normally twice as long as inspiration Normal tidal volume = 10-15 mL/kg
29Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Ventilation in Anesthetized Animals
Differs from ventilation in awake animals Reduced amount of air entering and leaving
the lungs Tranquilizers and general anesthetics
Decrease responsiveness of breathing center to carbon dioxide levels so inhalation doesn’t occur as often
Relax intercostals muscles and diaphragm so the chest doesn’t fully expand (VT is reduced)
30Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Potential Problems
Hypercarbia Related to the breakdown of carbon dioxide to
bicarbonate ions and hydrogen ions, which can lead to respiratory acidosis
Hypoxemia Related to less oxygen entering the lungs to be
absorbed into the blood Atelectasis
Related to decreased VT so alveoli don’t fully expand on inhalation, which can lead to partial collapse of the alveoli in some sections of the lung
31Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Types of Controlled Ventilation (PPV)
Patient is intubated and connected to anesthetic machine
Manual ventilation or bagging Anesthetist bags patient every 2-5 minutes
Intermittent mandatory ventilation Patient requires bagging throughout the anesthetic
period Mechanical ventilation
Lungs are filled with oxygen by pressure of gas from a ventilator
32Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Manual Ventilation
Lungs are filled with oxygen by pressure of gas entering airways Anesthetist is squeezing the reservoir bag Pop-off valve is fully or partially closed Exhalation is passive and occurs when positive
pressure is discontinued and pop-off valve is fully opened, which allows the lungs to empty
Bag one to two breaths every 2-5 minutes (sighs) Bag is squeezed for 1-1.5 seconds (inhalation
time) Pressure manometer reading: <20 cm H2O (small
animals); <40 cm H2O (large animals)
33Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Intermittent Mandatory Manual Ventilation (Cont’d)
Periodic bagging doesn’t provide enough ventilation
Animals with preexisting heart or lung disease; diaphragmatic hernias Patients show shallow breaths and respiratory rate
<6 bpm May be used prior to placing animal on the
ventilator Bagging superimposes positive pressure over
patient’s spontaneous breathing efforts, which will stop in about 1 minute
34Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Intermittent Mandatory Manual Ventilation (Cont’d)
Assisted ventilation rate Initially 8-20 bpm depending on size of the patient 6-12 bpm after control of respiration has been
established Wean patient off assisted ventilation near the
end of the surgical procedure
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Mechanical Ventilation
Similar to intermittent mandatory manual ventilation
Breathing is controlled by the ventilator, which replaces the reservoir bag and becomes part of the breathing circuit Ventilator bellows automatically compresses and
forces oxygen and anesthetic into the patient’s airways
Gases delivered on inspiration: pressure cycle, volume cycle, or time cycle ventilators
36Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Mechanical Ventilation (Cont’d)
Normal beginning settings RR = 6-12 bpm Duration of inspiration = 1-1.5 seconds Duration of expiration = 2-6 seconds Inspiratory/expiratory ratio = 1:2 to 1:3
Ventilator settings vary with the needs of the patient
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Ventilators
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Risks of Controlled Ventilation
Ruptured alveoli Decreased cardiac output Respiratory alkalosis Ventilator delivers more inhalant anesthetic to
patient Anesthetist monitoring
39Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Neuromuscular Blocking Agents
Muscle-paralyzing agents Animals remain conscious and feel pain
Limited use in veterinary medicine Animals on mechanical ventilation Orthopedic surgery and ophthalmic surgery Cesarean sections Facilitate difficult intubation Balanced anesthesia techniques
Administered when animal is unconscious and respiration is controlled by intermittent mandatory mechanical ventilation
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Neuromuscular Blocking Agents: Depolarizing
Interrupt normal impulse transmission from motor neuron to muscle synapse
Succinylcholine Single surge of activity at neuromuscular
junction Followed by period when the muscle end
plate is refractory to further stimulation Fast onset; short duration of effect Useful for rapid intubation
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Neuromuscular Blocking Agents: Nondepolarizing
Interrupt normal impulse transmission from motor neuron to muscle synapse
Gallamine, pancuronium, atracurium besylate, cisatracurium
Block receptors at end plates No initial surge of activity
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Neuromuscular Blocking Agents
Concurrent use with other drugs may affect potency
Administered by slow IV injection Effect seen within 2 minutes and lasts
10-30 minutes Repeated doses or continuous infusion can
be used with some agents Makes assessment of anesthetic depth
difficult Only voluntary skeletal muscles are affected
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Neuromuscular Blocking Agents: Reversal Drugs
Nondepolarizing agents reversed with a anticholinesterase agent Edrophonium, neostigmine, pyridostigmine Maintain at light anesthesia until reversal is
complete Make sure spontaneous breathing has started or
support respiration Pretreat patient with atropine or glycopyrrolate to
prevent adverse effects Depolarizing agents have no effective
reversal drugs