Analgesia Prof J

EPIDURAL AND INTRATHECAL ANALGESIA

Terminology

• Analgesia: Relief of pain without loss of consciousness.

• Anesthesia: Loss of feeling or awareness without loss of vital function.

• Intraspinal: Refers to procedures conducted within the spinal area, specifically includes epidural and intrathecal.

• Epidural Anesthesia: Produced by injecting an anesthetic into the lumbar area of the spine, specifically in the space between the ligamentum flavum and-dura mater. This procedure results in a loss of sensation and some motor function while effectively managing pain. The onset for epidural anesthesia typically takes about 20 minutes until it becomes effective.

• Intrathecal Anesthesia (also known as Spinal Anesthesia): This involves the introduction of a therapeutic substance directly into the cerebrospinal fluid via an injection into the subarachnoid space within the spinal cord. This method is used to bypass the blood-brain barrier.

Epidural Space Anatomy

• Location: The epidural space is situated between the ligamentum flavum and the dura mater.

• Length: Extends from the foramen magnum to the sacrococcygeal membrane.

• Composition: The space contains blood vessels, fat, lymphatics, and spinal nerve roots, providing support for nerve structures.

Intrathecal Space Anatomy

• Location: The intrathecal space is found between the arachnoid membrane and the pia mater, specifically in the subarachnoid space.

• Composition: This space is filled with cerebrospinal fluid, which plays a role in protecting the spinal cord and enabling the delivery of medications.

Pain Pathways and Receptors

• Pain Transmission Mechanism:
    - Involves ascending input from peripheral nociceptors to the dorsal horn and via the spinothalamic tract.
    - Descending modulation pathways help modulate pain by influencing those ascending signals.

• Receptor Sites:
    - Mu Receptor Sites: Located within the brainstem and spinal cord along the ascending pain pathway, these sites interact with opioid medications to inhibit transmission of pain impulses, effectively decreasing the perception of pain.
    - Local Anesthetics: They block pain signals by affecting the dorsal root ganglions that traverse the epidural space, leading to peripheral pain blockage.

Dermatomes

• Definition: Areas of skin innervated by specific spinal nerves, showing that there is overlapping between adjacent dermatomes.

• Significant Dermatomes:
    - C8: Lower spinal nerve roots exit below the corresponding vertebral body.
    - T4: Roughly corresponds to the nipple line; innervates cardioaccelerators above this level.
    - T6: Corresponds to the lower sternum.
    - T10: Relates to the umbilicus.
    - T12: At the pubic bone level.
    - Lumbar spinal nerve roots relate sensory innervation primarily to the legs.

Indications/Contraindications for Intraspinal Therapy

• Indications:
    - Postoperative pain management for thoracic, intra-abdominal, orthopedic, and/or cardiovascular surgeries.
    - Severe burns, trauma, sickle cell crisis.
    - Labor: Vaginal or cesarean delivery.
    - Chronic debilitating pain, both malignant and nonmalignant, requiring long-term management.
    - Conditions such as COPD and other lung or cardiac diseases.

• Contraindications:
    - Patient refusal to undergo the procedure.
    - History of true allergic reactions to narcotics.
    - Abnormal hemostasis or bleeding disorders.
    - Patients currently receiving anticoagulants or antiplatelet therapy.
    - Presence of systemic or localized infections.
    - Increased intracranial pressure.

Benefits of Epidural Analgesia

• Advantages:
    - Fewer side effects compared to systemic analgesic routes.
    - Provides more constant pain relief with fewer peaks and valleys in analgesia.
    - Targets opioid receptors within the spinal cord, enhancing effectiveness.
    - Requires a smaller dosage of medication to achieve pain relief.

• Respiratory and Gastrointestinal Benefits:
    - Improved pulmonary and gastrointestinal function.
    - Longer duration of analgesic effects alongside opioids and local anesthetics that work synergistically to enhance patient comfort and satisfaction.
    - Shortened length of hospital stays.

Epidural Opioid Medications

• Fentanyl (Sublimaze):
    - Solubility: Lipid
    - Onset: 10-15 minutes
    - Duration: 4-8 hours

• Hydromorphone (Dilaudid):
    - Solubility: Lipid
    - Onset: 15-30 minutes
    - Duration: Up to 18 hours

• Morphine (Duramorph):
    - Solubility: Hydrophilic
    - Onset: 30-90 minutes
    - Duration: Up to 24 hours

• Common Side Effects of Opioids:
    - Respiratory depression.
    - Hypotension.
    - Nausea and vomiting.
    - Pruritus (itching).
    - Urinary retention.

Local Anesthetic Medications

• Bupivacaine (Marcaine):
    - Solubility: Lipid
    - Onset: 3-5 minutes
    - Duration: 3-6 hours.

• Ropivacaine (Naropin):
    - Solubility: Lipid
    - Onset: 5-20 minutes
    - Duration: Up to 6 hours.

• Signs & Symptoms of Systemic Absorption of Local Anesthetic:
    - Circumoral paresthesia (tingling around the mouth).
    - Cardiac dysrhythmias.
    - Tremors.
    - Irritability.
    - Metallic taste.
    - Seizures.
    - Tinnitus.

Precautions for Intraspinal Procedures

• All intraspinal injections and infusions must remain sterile and preservative-free.

• Anesthesiologist or CRNA’s order is necessary for the administration of additional opioids or sedatives.

• Use of additional opioids or sedatives should be executed with caution to minimize adverse events.

• Notify the anesthesiologist/CRNA before starting any anticoagulant therapies.

Obstetric Patient Selection

• Advantages:
    - The mother remains alert and cooperative retaining some motor control.
    - Airway reflexes remain intact with reduced gastric emptying times.
    - Excessive blood loss is avoided.

• Disadvantages:
    - Need for IV access.
    - Potential leg weakness.
    - Difficulty in bladder emptying.

Obstetric Patient Protocols

• Pre-load Fluid Administration:
    - Administer 500-1000 cc of Lactated Ringer’s (LR) solution 20-30 minutes prior to epidural placement if possible.
    - Encourage the patient to void before the epidural procedure.

• Monitoring During Procedure:
    - Check baseline vital signs; including temperature, O₂ saturation, and fetal heart rate.
    - Assist the patient into the desired position as arranged by the anesthesiologist.
    - Continuously monitor blood pressure every 2 minutes for the initial 15 minutes, then extend monitoring every 15 minutes until complete.
    - Position patient on one side for about 20 minutes, then shift to the other side for an additional 20 minutes before Foley catheter insertion.

General Assessment & Care for Epidural Patients

• Catheter Management:
    - The catheter may remain in place for up to 96 hours but must be properly managed and secured.
    - Instruct the patient not to drag their back against the bed while moving or turning to prevent dislodging.
    - In cases of accidental disconnection, stop the infusion immediately without reconnecting, apply a sterile dressing over the line, and notify the anesthesiologist for guidance.

Assessment for Labor Patients

• Monitoring Parameters:
    - Monitor FHR, blood pressure, pulse, respiratory rate, O₂ saturation, and fetal heart rate initially every 2 minutes for the first 15 minutes, then every 15 minutes until discontinued.
    - If rebolused, monitor every 2 minutes for an additional 15 minutes.

• Pain and Labor Progression:
    - Assess for pain relief and monitor the progression of labor, taking appropriate measures to prevent supine hypotension and related issues.

Post-Spinal Anesthetic Assessment

• Vital Signs Monitoring:
    - Obtain respiratory rates every hour for 24 hours if duramorph was administered.
    - Elevate and record vital signs regularly, alongside motor and sensory function evaluations, sedation levels, and pain ratings as per protocols.
    - Notify anesthesiologist immediately for any significant changes such as decreased ability to move or feel limbs, reduced anesthesia level, more than 20% drop in blood pressure, respiratory rates dropping below 8, decreased consciousness, or sudden back pain.

Managing Hypotension in OB Patients

• Definition: Hypotension characterized by systolic blood pressure (SBP) below 100 or a more than 20% drop.

• Management Steps:
    - Open the IV line to a full rate bolus.
    - Reposition the patient onto their side.
    - Notify the anesthesiologist immediately for further instructions regarding treatment, including administering ephedrine per the anesthesia order while the patient is on a cardiac monitor.
    - Awareness of decreased perfusion to the placenta that may result in late decelerations.

Catheter and Tubing Safety Protocols

• Identification: Yellow cassette/yellow-striped tubing should be distinctly marked to prevent confusion with PCA tubing.

• Labeling: Clearly label all catheter and tubing with "Epidural Infusion" for accurate identification.

• Prevention of Misconnection: Require two nursing staff to confirm the correct connection of epidural tubing to the epidural catheter, thoroughly tracing the catheters to the point of origin prior to connecting new devices or at shift changes.

Key Points for Safe Administration

• Always verify with the anesthesiologist/CRNA before starting any sedatives, opioids, or anticoagulants.

• Remove catheters only after confirming that no anticoagulants were administered.

• Registered Nurses (RNs) are not authorized to administer bolus doses through the epidural catheter.

• Blocking sensory function at T4 and above can result in severe bradycardia, hypotension, cardiovascular collapse, or even cardiac arrest.

• Provide comprehensive education to patients and their families regarding the procedure and any potential risks involved, including referencing reliable resources like Lippincott Procedures.