3. LOCAL ANAESTHETICS
Basic function
• These drugs act by blocking voltage-gated sodium channels in axons,
preventing action potential.
Local effect
• Block is most effective in smaller, myelinated fibers that fire at high
frequency.
• Pain and temperature fibers are much more sensitive than pressure fibers,
which are more sensitive than motor and proprioceptive fibers.
4. Toxicity
Central nervous system (CNS)
• Results from intravenous (IV) absorption or injection and high plasma
levels
• They block inhibitory pathways, leading to unopposed excitatory
components.
• Signs and symptoms include dizziness, tongue numbness, nystagmus,
and seizures (tonic–clonic).
Cardiovascular-depressive effects
• Weaker contraction and arteriolar dilatation occur.
• High doses can result in ventricular fibrillation.
Neurotoxicity
5. Lidocaine: rapid, potent, high penetration
• Short acting
• Most widely used local anesthetic: local anesthesia, regional, spinal, epidural
Bupivacaine: slower, potent
• Longer duration than lidocaine
• Can separate motor and sensory block by altering concentration
• Increased cardiac toxicity when injected intravascularly
Ropivacaine
• “Safer” version of bupivacaine with same analgesic characteristics considered to be
• associated with a lower incidence of significant cardiac toxicity
Maximal dose of commonly used local anesthetics
Lidocaine: 5 mg/kg (7 mg/kg if combined with epinephrine)
Bupivacaine: 2 mg/kg (3 mg/kg with epinephrine)
6. VASOCONSTRICTORS
Allow for longer lasting blockade (decreased blood flow, less drug leaves
area)
They may also decrease local blood loss.
Epinephrine
• Most widely used, diluted to 1/200,000
• Should not be used for a digital block, Bier block, or ankle block
• Mnemonic for areas not to use epinephrine: nose, hose (penis), fingers,
toes
Phenylephrine is occasionally used in spinal anesthesia.
7. OPIODS
They are derived from the seed of the opium poppy, Papaver somniferum.
Morphine and codeine are directly from the plant; others are synthesized.
They act by binding to specific opioid receptors in the CNS (μ, δ, κ).
• The μ receptor is the one most responsible for the analgesic effect.
• The action is both presynaptic and postsynaptic.
Central action/pain modulation
• When activated, the μ receptor inhibits γ-aminobutyric acid (GABA)-ergic
neurons that would otherwise inhibit pain inhibitory neurons.
• They may also affect neurons in the thalamus and midbrain to modulate
pain stimuli.
8. CNS effects
• Analgesia, euphoria, sedation, respiratory depression, cough suppression,
miosis, nausea
Cardiovascular: bradycardia
Gastrointestinal: decreased motility, constipation, constriction of biliary tree
Genitourinary: decreased renal function and increased sphincter tone
Morphine
• Naturally occurring, oldest member of this drug class
• Dosing for adults : Loading dose of 0.05 to 0.10 mg/kg IV followed by 0.8 to 10.0
mg/hour IV titrated to pain
• Onset: 5 minutes
• Relatively long lasting: 3 to 4 hours
• Better for continuous dull pain rather than sharp/severe pain
• Used for postoperative patient-controlled analgesia (PCA). Basal rates tend to
increase episodes of hypoxia.
9. Meperidine (Demerol)
• One-tenth as potent as morphine
• Dosing for adults :15 to 35 mg/hour slow IV infusion or 50 to 150 mg
subcutaneously/intramuscularly every 3 to 4 hours as needed
• Poorly titrated: 5- to 10-minute onset and 2- to 3-hour duration
• Potential for CNS stimulation
• Concern about bad interactions with monoamine oxidase (MAO) inhibitors
Fentanyl
• 100 times more potent and 7,000 times more lipophilic than morphine
• Rapid uptake: 30 to 60 seconds with peak analgesia in 2 to 3 minutes
• Duration: 20 to 30 minutes
• Dose: 1 μg/kg slowly, with sedation often at 3 to 4 μg/kg
• Risks: “tight chest syndrome,” bradycardia, respiratory depression
10. Hydromorphone
• 7 to 10 times more potent than morphine but with a shorter half-life
• Semisynthetic opioid analogue with perceived analgesic action within 15 minutes after IV
administration
• PCA dose of 0.2 to 0.4 mg IV with 6 to 10 minutes lockout in opioid-naive patients
Naloxone, naltrexone
• Opioid antagonist
• Strong affinity for μ receptor
• Binds to receptor but does not activate it, rapidly reversing the opioid effect within 1 to 3
minutes
• Usual dose: 0.1 to 0.4 mg IV (0.01 mg/kg in children)
• Shorter half-life than most agonists, so multiple doses may be necessary
11. SEDATIVES
Benzodiazepines
• In general, they produce anxiolysis and sedation and encourage sleep.
• They are metabolized in the liver and excreted in the urine.
• Mechanism
They act centrally, bind to, and activate the GABA-A receptor.
GABA is major inhibitory neurotransmitter in the CNS.
The GABA receptor is the chloride channel.
When activated, they hyperpolarize the membrane, making it less excitable.
• Effects
Sedation, hypnosis, anesthesia, amnesia (anterograde), anticonvulsant effects,
muscle relaxation, respiratory depression (especially in pulmonary patients)
Often increased when combined with opioids
12. Midazolam
• Peak effect: 2 to 3 minutes
• Water-soluble, hepatic metabolization
• Easily titrated with doses every 5 to 7 minutes
• 1 to 2 mg per dose (0.1 mg/kg per dose in children)
Flumazenil
• Blocks the effect of benzodiazepines at the GABA receptor level
• It has a much shorter half-life than most benzodiazepines that are
used clinically.
• The dose is 0.1 to 0.2 mg IV (0.02 mg/kg in children).
• Use with caution because it may precipitate seizures.
13. Ketamine
• Dissociative anesthetic
• Catatonic, amnestic, without loss of consciousness or loss of protective
reflexes
• Blockade of glutamic acid at the NMDA receptor subtype
• May stimulate cardiovascular system and increase blood flow
• Dose: 1 mg/kg IV
• Rapid onset: 1 to 3 minutes
• Duration: 15 to 20 minutes
• Occasional hallucinations on emergence: can be avoided with a small
dose of midazolam
• May increase salivation: atropine, 0.01 mg/kg, given before ketamine
14. Propofol
• Isopropylphenol compound
• Rapid onset, short duration (half-life 30 minutes but lipid soluble so clinical
duration is less)
• Minimal gastrointestinal side effects or nausea
• Provides general anesthesia: sedation, hypnosis, without analgesia or
amnesia
• Complications: respiratory depression, hypotension, pain at injection site
• Need for anesthesia/emergency department assistance with airway
• Dose: 0.5 to 1.0 mg/kg for induction of sedation
• Highly titratable: 25 to 100 μg/kg/minute infusion after initial bolus
15. NITROUS OXIDE
• Inhaled agent
• Given in varying 50/50 to 70/30 mixture with oxygen
• Provides analgesia and anxiolysis, some sedation
• Rapid onset and offset
• Short duration: resolves within 5 minutes of removing mask
• Often used as an adjunct with other forms of anesthesia or for short
procedures
• Very safe for brief procedures
17. HEMATOMA BLOCK
This replaces the fracture hematoma with local anesthetic.
It provides analgesia for closed reductions.
It provides postreduction analgesia.
Technique
• Sterile preparation of the fracture site is indicated.
• Enter the fracture hematoma with a large-bore needle, aspirating hematoma fluid.
• Replace the hematoma with 10 to 15 mL of 1% lidocaine without epinephrine.
Bupivacaine may be added to help with postreduction pain. Give in safe dose such as 10
mL of 0.25%.
• Wait 5 to 7 minutes and then perform the reduction maneuver.
Risks
• Systemic toxicity : Potential risk of the local anesthetics entering the bloodstream directly via the
bones blood supply
• Infection : Theoretically converting a closed fracture to an open one; single case report in
orthopaedic literature
18. REGIONAL BLOCKS
• They provide anesthesia to a certain area of the body, without general
whole-body effects.
• They are useful in fracture-dislocation reduction as well as minor and
major surgical procedures on the extremities.
• They are also beneficial for postprocedure analgesia.
• Local anesthetic is injected around the peripheral nerves or plexi.
• Length of block depends on the choice of anesthetic as well as the use of
epinephrine.
19. Digital Block
Indications include
• Finger fracture,
• Laceration,
• Nail bed injury, and
• Finger/nail bed infection.
Do not use epinephrine.
Technique :
• Pronate the hand (skin on the dorsum is
less sensitive).
• Use two injection sites, at each side of
the metacarpophalangeal.
• Use about 2 mL per nerve.
20. Wrist Block
Median nerve
Indications include multiple finger fractures and
finger/nail bed lacerations.
Technique
• Supinate the forearm.
• The needle is placed between the palmaris
longus and the flexor carpi radialis, 2 cm
proximal to the wrist flexion crease.
• If paresthesia is elicited, inject 3 to 5 mL at this
site.
• If no paresthesia occurs, then inject 5 mL in fan-
shaped fashion.
21. Radial nerve
Indications include thumb and dorsum of hand lacerations.
Technique
• Field block is performed on the pronated hand at the level of the snuff box.
• This is superficial to the extensor palmaris longus tendon.
• Start at the snuff box and continue over the entire dorsum of the hand.
• A dose of 5 to 8 mL is required.
Ulnar nerve
Indications: ulnar-sided lacerations, reductions of
boxer’s fracture (if anesthesia is required)
Technique: supinated hand, 6 cm proximal to wrist
crease, just radial to flexor carpi ulnaris, 8 to 10 mL
(more distal block will miss the dorsal branch, which
can be blocked by a wheal ulnar to the flexor carpi
ulnaris)
22. Elbow Block
• Indications include procedures of the hand and wrist.
• Four nerves are involved: median, ulnar, radial, and lateral antebrachial cutaneous.
Median nerve
• Draw a line between the medial and lateral condyles of the humerus.
• The skin wheal is just medial to the brachial artery.
• Advance the needle until paresthesia is obtained.
• Inject 3 to 5 mL of lidocaine.
Ulnar nerve
• The elbow is flexed.
• Inject 1 cm proximal to the line that connects the medial epicondyle and the olecranon.
• Use 3 to 5 mL of lidocaine.
• Inject very superficially.
• Too much fluid can cause “compartment syndrome.”
Radial/musculocutaneous (lateral antebrachial cutaneous nerve)
• At the intercondylar line, inject 2 cm lateral to the biceps tendon.
23. Axillary Block
Indications
• These include hand and forearm procedures and some elbow procedures.
Technique
• The patient is supine with the shoulder abducted and externally rotated.
• Palpate the axillary artery in the distal axilla.
• Some advocate going through the artery, depositing two-thirds of the total anesthetic (20
to 30 mL) behind the artery and one-third superficial to it.
• Others suggest going on either side of the palpable artery.
• Think of three nerves around the artery (clock):
Median: 12 to 3 o’clock
Ulnar: 3 to 6 o’clock
Radial: 6 to 9 o’clock
• Other techniques include ultrasound-guided blocks and nerve stimulation techniques.
24.
25. Ankle Block
Indications include any foot and ankle procedure.
The block must include all five nerves: tibial, deep peroneal, superficial
peroneal, saphenous, and sural nerves.
• Tibial : Posterior to the posterior tibial artery, halfway between the medial
malleolus and the calcaneus
• Deep peroneal : Just lateral to the anterior tibial artery and the extensor
hallucis longus
• Superficial peroneal and saphenous : Field block medially and laterally
from a deep peroneal site
• Sural : Lateral border of the Achilles tendon, halfway between the lateral
malleolus and the calcaneus
26.
27. Popliteal Block
Indications include foot and ankle surgery.
Technique
• The patient is prone, with the knee flexed.
• Identify the popliteal fossa.
• Inject 7 cm superior to the skin crease, 1 cm lateral to the midline, lateral
to the artery.
• Advance in an anterosuperior direction.
Add a field block of the saphenous distal to the medial tibial plateau for a
more complete block (covers sensation to the medial portion of the foot).
Ultrasound-guided and nerve stimulation techniques can be used for this
block.
28. Bier Block
It is also known as regional IV anesthesia.
This was developed by August Bier in 1908.
Indications include hand/wrist procedures and fracture reductions.
Technique
• Start the IV infusion in the hand. Place IV catheter. Do not run IV fluid.
• Place double tourniquets around the upper arm.
• Exsanguinate the upper extremity.
• Inflate the more proximal tourniquet.
• Inject lidocaine without epinephrine (1.5 mg/kg dilute solution or 3 mg/kg, ~50 mL 0.5%) and without any
preservative.
• The tourniquet must stay inflated for 25 to 30 minutes. If the patient has tourniquet pain, the distal
tourniquet may be inflated followed by deflation of the proximal tourniquet.
Risks
• Tourniquet pain
• Length of block most often limited by the ability to tolerate the tourniquet
• Systemic toxicity
• Theoretic risks: severe cardiovascular and CNS side effects with early release of the tourniquet and a
large intravascular bolus of lidocaine
29. MODERATE SEDATION
Alteration in consciousness
• Decreased anxiety
• Pain relief
Patient able to maintain patent airway and has intact protective airway reflexes
Patient able to respond to verbal or physical stimuli
Sedation a continuum
• Awake/light sedation
• Anxiolysis, patient essentially responding normally
• Conscious sedation
• Response requiring verbal or physical stimuli, airway maintained
• Deep sedation : Repeated or painful stimuli necessary for response, airway patency
• General anesthesia : Unarousable, airway not protected
30. When to use it?
• Anytime a potentially painful procedure needs to be
performed in the outpatient setting
• For procedures not requiring general anesthesia and
that are reasonably short in duration
• When appropriate monitoring equipment is available
• When patient is appropriately nothing by mouth
(NPO)
Contraindications
• Clinically unstable patient requiring other more
urgent procedures
• Refusal by a competent patient
Relative contraindication: long-lasting
procedures, likely to require general anesthetic for
success
Appropriate
equipment
IV access
Pulse oximetry
Electrocardiographic monitor
Blood pressure cuff
Airway management
equipment
Supplemental oxygen
Reversal medications
(naloxone, flumazenil)
31. Technique
• This typically involves combining an opioid (morphine or fentanyl) for analgesia and a
benzodiazepine (midazolam) for sedation, relaxation, and amnesia.
• Titrate dosing to achieve appropriate level of sedation while minimizing the risk of adverse
outcome.
• The patient should at all times be responsive to physical or verbal stimuli (therefore should
have protective airway reflexes intact).
• Remember that these patients have likely already had large doses of opioids for pain
control.
• Be aware of “dose stacking,” giving additional doses of narcotics before waiting to see the
effects of the prior doses.
Risks
• Respiratory depression/hypoventilation
• Risk of respiratory depression potentiated by a combination of opioids and
benzodiazepines
• Moderated by appropriate dosing, monitoring, and presence of reversal agents
• Aspiration
![PHARMACOLOGY : CLASSES OF DRUGS
• Local anesthetics
• Vasoconstrictors
• Opioids
• Sedatives (benzodiazepines)
• Others (nonsteroidal anti-inflammatory drugs [NSAIDs],
acetaminophen, dexamethasone, gabapentinoids, N-methyl-D-
aspartate [NMDA] receptor antagonists)UGS](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)