Thoracic Epidural Anesthesia

Thoracic Epidural Anesthesia

• Thoracic epidurals are more difficult to insert due to the angled spinous processes which makes midline access more challenging.
• The spinal canal is shallower, increasing the risk of dural puncture or spinal cord injury.
• A paramedian approach is preferred to avoid the steep angulation of the spinous processes.
• Thoracic Epidural Anesthesia Risks:
  • Hypotension due to proximity to cardiac accelerator fibers T1-T4.
  • False loss of resistance (LOR) is more common.
  • Respiratory depression if the block extends too high.
  • Epidural hematoma risk due to proximity to vascular structures.

Epidural Additives

• Opioids (Fentanyl, Morphine): Increases sensory block duration but don't enhance motor block.
• a2 Agonists (Clonidine, Dexmedetomidine): Prolong analgesia and reduce LA requirements.
• Epinephrine: Prolongs LA effect by vasoconstriction, slowing systemic absorption.
• Bicarbonate: Speeds onset by alkalinizing the solution.

Local Anesthetics for Epidural Anesthesia:

• Chloroprocaine (2-3%): Fastest onset (5-10 min), short duration (45-60 min). Good for short procedures.
• Lidocaine (1.5-2%): Onset 10-15 min, duration 60-90 min. Can cause tachyphylaxis.
• Mepivacaine (1-1.5%): Onset 10-15 min, duration 60-90 min. Similar to Lidocaine, slightly longer action
• Bupivacaine (0.0625%-0.75%): Onset 15-20 min, duration 120-140 min. Sensory > motor block, risk of cardiotoxicity.
• Ropivacaine (0.2-0.75%): Onset 15-20 min, duration 120-140 min. Less motor block and cardiotoxic than Bupivacaine.

SAB vs. Epidural Blockade

• SAB (Spinal Anesthesia):
  • Faster onset
  • Complete sensory and motor block
  • More profound hypotension due to greater sympathetic blockade
• Epidural:
  • Slower onset, can be titrated
  • Sensory block occurs first, followed by motor (depending on LA)
  • Sympathetic block spreads 2 levels higher than sensory

Laboratory Values for Epidural Insertion

• INR: <1.5 (preferably <1.3)
• Platelets: >100,000
• LMWH:
  • Low dose: Wait 4-6 hours
  • Intermediate dose: Wait 12 hours
  • High dose: Wait 24 hours
• NOACs (Apixaban, Rivaroxaban): Wait 72 hours
• Clopidogrel: Discontinue 7 days prior

Epidural Blood Patch Procedure

• Used to treat post-dural puncture headache (PDPH).
• 10-15 mL autologous blood is injected into the epidural space at or one level below the dural puncture.
• Patient should lie flat for 1-2 hours post-procedure.

Characteristics of the Epidural Space

• Boundaries:
  • Anterior: Posterior longitudinal ligament
  • Posterior: Ligamentum flavum
  • Lateral: Pedicles & intervertebral foramina
  • Rostral: Foramen magnum
  • Caudal: Sacral hiatus
• Identification via:
  • Loss of Resistance (LOR) Technique (air or saline).
  • Test dose (1.5% lidocaine + epinephrine) to confirm placement.

Test Dose Significance

• 3 mL of 1.5% lidocaine + 1:200,000 epinephrine
• Positive Test Dose:
  • Intrathecal (subarachnoid): Rapid sensory/motor block in <3 min
  • Intravascular: HR increases by >20% within 30 sec
• Negative Test Dose: Epidural placement confirmed.

Anatomical Structures Encountered During Epidural Catheter Administration:

• Skin → SubQ → Supraspinous Ligament → Interspinous Ligament → Ligamentum Flavum → Epidural Space

Potential Complications of Epidural Insertion:

• High Spinal:
  • Symptoms: Severe hypotension, bradycardia, apnea
  • Treatment: ABCs, vasopressors
• Intravascular Injection:
  • Symptoms: Seizures, tachycardia
  • Treatment: Lipid emulsion therapy
• Epidural Hematoma:
  • Symptoms: Severe back pain, paralysis
  • Treatment: Emergency MRI, decompression
• PDPH (Post Dural Puncture Headache:
  • Symptoms: Headache worse when upright
  • Treatment: Epidural blood patch
• Inadequate Pain Relief:
  • Symptoms: Unilateral block
  • Treatment: Reposition or replace catheter

Epidural Catheter Insertion Depth

• Insert 3-5 cm inside epidural space to prevent unilateral block

Sensory Block Height for Procedures

• Upper abdominal and C-Section = T4
• Intestinal, gynecological, and urologic = T6
• Vaginal delivery, hip surgery, TURP = T10
• Thigh surgery and lower leg amputations = L1
• Foot and ankle surgery = L2
• Perineal and anal surgery = S1
• Surgery with tourniquet = T8-10
  • Higher level d/t pain associated w/ tourniquet is sympathetically mediated
• Inguinal hernia, lower abd sx, traction on peritoneum and abd viscera, and testicles perceived higher bc derived from same tissue embryologically as kidneys → higher level needed

Recognizing an Effective Epidural

• Sympathetic block (warm legs, slight BP drop)
• Sensory block (cold test, pinprick test)
• Motor block (Bromage scale)

Dermatome Levels

• C4 = clavicle
• T4-5 = nipples
• T6-8 = xiphoid
• T7 = inferior border of scapula (lower tip)
• T10 = umbilicus
• L4 = superior iliac crest
• S2-S5 = perineum

Epidural Catheter Removal

• Pull slowly with patient flexed forward.
• If resistance is felt, reposition patient. If resistance continues, discontinue removal and get imaging to ensure complete removal.
• Ensure catheter tip is intact after removal.

Local Anesthetics for Procedures (Duration)

• Short: Chloroprocaine (Onset: 5 min, DOA: 45-60 min)
• Intermediate: Lidocaine or mepivacaine (Onset: 10-15 min, DOA: 60-90 min)
• Long: Bupivacaine or ropivacaine (Onset: 15-20 min, DOA: 120-140 min)

Airway Block Objectives:

• Risk factors for difficult intubation:
  • Previous difficult intubation
  • Upper lip bite test (poor result)
  • Hyomental distance <3 cm
  • Retrognathia (posteriorly positioned mandible)
  • Mallampati (MP) score >3
• Patients NOT candidates for an airway block:
  • High risk of vomiting/aspiration (e.g., full stomach, severe GERD, bowel obstruction)
  • Uncooperative patients (e.g., severe anxiety, agitation)
  • Active bleeding in the airway
  • Infection at the block site

Medications for Airway Blocks and Awake Intubations:

• Topical anesthetics:
  • Cocaine (5-10% solution, max 1.5 mg/kg)
  • Lidocaine (1%, 2%, 4%, or 10% solutions)
  • Benzocaine (20% spray, max dose 200 mg)
• Sedation options:
  • Ketamine (dissociative anesthesia, preserves respiration)
  • Dexmedetomidine (alpha-2 agonist, mild sedation)
  • Remifentanil (short-acting opioid for analgesia)
  • Midazolam (benzodiazepine for anxiolysis)
  • Fentanyl (opioid for pain relief and sedation)
• Other adjuncts:
  • Glycopyrrolate (0.1-0.2 mg IV) – antisialogogue to reduce secretions
  • Afrin/phenylephrine nasal spray – vasoconstriction for nasal intubation
  • Ondansetron (4 mg IV) – antiemetic to reduce gag reflex

Equipment for Fiberoptic Laryngoscopy and Endotracheal Tube Insertion:

• Fiberoptic bronchoscope
• Endotracheal tube (ETT)
• Atomizers or nebulizers (for local anesthetics)
• Nasal trumpets (for nasal intubation preparation)
• Syringes with local anesthetic (for nerve blocks)
• Suction (to clear secretions)
• Yankauer suction tip
• Bag-valve-mask (BVM)
• Bite block

Topical Anesthetics for Airway Anesthesia:

• Cocaine: Local anesthetic + vasoconstrictor (5-10% solution, max dose 1.5 mg/kg)
• Lidocaine: Amide local anesthetic, slow systemic absorption, max dose varies (>4 mg/kg)
• Benzocaine: Ester local anesthetic, rapid onset (<1 min), max dose 200 mg (risk of methemoglobinemia)
• Moffett's Solution: Combination of 10% cocaine, epinephrine, sodium bicarbonate, and saline

Airway Blocks:

• Glossopharyngeal Nerve Block: Reduces gag reflex, used for oral intubation.
• Superior Laryngeal Nerve Block: Anesthetizes base of tongue, epiglottis, aryepiglottic folds.
• Recurrent Laryngeal Nerve (Translaryngeal) Block: Anesthetizes vocal cords and trachea, reduces coughing.
• Sphenopalatine Ganglion Block: Assists with nasal intubation.

Nerve Innervation for Airway Anatomy:

• Recurrent laryngeal nerve (CN X-Vagus): Sensory below vocal cords, motor to all intrinsic laryngeal muscles (except cricothyroid).
• Glossopharyngeal nerve (CN IX): Sensory to posterior 1/3 of tongue, pharynx, tonsils, epiglottis.
• Superior laryngeal nerve (CN X- Vagus): Sensory to base of tongue, epiglottis, aryepiglottic folds, and arytenoids.
• Sphenopalatine ganglion (Trigeminal V2): Sensory to nasal mucosa.

Implications of Topical Anesthetic Sprays

• Risk of methemoglobinemia with benzocaine
• Risk of toxicity if exceeding max doses (e.g., lidocaine > 4 mg/kg)
• Need for adequate drying of mucosa for better absorption
• Some patients may require additional nerve blocks for complete anesthesia

Performance of Airway Blocks:

• Glossopharyngeal Block:
  • 2-5 mL of 2% lidocaine injected into anterior/posterior tonsillar pillar
  • 22-25 gauge needle after negative aspiration
• Superior Laryngeal Nerve Block:
  • 2 mL of 2% lidocaine injected near the hyoid
  • Supine position, neck extended
• Recurrent Laryngeal (Translaryngeal) Block:
  • 5 mL of 4% lidocaine injected through cricothyroid membrane
  • Produces cough to distribute anesthetic
• Sphenopalatine Ganglion Block:
  • Lidocaine-soaked pledgets placed in the piriform fossa

Expected Results from Laryngeal and Tracheal Block:

• Reduced cough reflex
• Reduced sensation in the larynx and trachea
• Facilitates awake fiberoptic intubation

Dosage of Benzocaine Spray to Prevent Toxicity

• Max dose: 200 mg, which is like 1-2 seconds of spray
• Excess use may cause methemoglobinemia

Gag Reflex Suppression

• Will suppress the gag reflex:
  • Glossopharyngeal nerve block
  • Superior laryngeal nerve block (partial effect)
• Will NOT fully suppress gag reflex:
  • Recurrent laryngeal nerve block (only affects vocal cords/trachea)
  • Sphenopalatine ganglion block (affects nasal mucosa, not pharynx)

Nerves of the Airway

• Trigeminal (V1, V2, V3): Nose, tongue, pharynx
• Glossopharyngeal (IX): Posterior tongue, oropharynx
• Vagus (X): Larynx, trachea (via SLN and RLN)