Indication
- Has a pain diagnosis classified into neuropathic, nociceptive, or mixed.
- Pain is chronic or both chronic and progressive in nature owing to either a malignant or non-malignant cause.
- Pain should be present throughout nearly the entire day.
- Patients have failed to achieve analgesia with conservative nonpharmacologic modalities.
- Patient is refractory or intolerant to orally administered analgesics.
- Corrective treatment addressing the pain generator is not warranted.
- Surgical contraindications to implanting prosthetic hardware and accessing the intrathecal space are absent (e.g. bacteraemia, anticoagulation).
Route
Intraventricular narcotics
- Indications
- May be used for cancer pain (especially head and neck) unresponsive to other methods in patients with a life expectancy < 6 mos.
- For managing pain above the diaphragm/umbilicus
- Technique
- An intraventricular catheter is connected to a ventricular access device (p.1616). 0.5–1mg of intrathecal morphine is injected via the VAD and usually provides ≈ 24 hrs of analgesia.
- Complications
- Side effects.
- Common ones include dizziness, N/V.
- The risk of respiratory depression is minimized by using correct dosing.
- Complications in a series of 52 patients:
- Bacterial colonization of reservoir (4%),
- Dislodged catheter (2%),
- Blocked catheter (6%),
- Postoperative meningitis (2%).
- Outcome
- Pain is successfully controlled in 70% at 2 mos,
- But thereafter the effectiveness diminishes as a result of tolerance to the narcotics
Intraspinal
- Two routes
- Epidurally
- Epidural catheters commonly develop problems with scarring → less effective sooner than intrathecal catheters.
- Intrathecally
- Temporal
- One time injection
- Continuous Infusion
- Intermediate-term basis (< 60 days) with the use of a subcutaneous reservoir
- Long-term basis with an implantable drug infusion pump10 (e.g. Infusaid® or Medtronic® pump).
- For managing pain below the neck
Pros & Cons
- Pros
- Over systemic narcotics
- Less sedation and/or confusion,
- Less interference with GI motility (constipation), and possibly less N/V.
- Cons
- The effectiveness is usually limited to ≈ 1 year
- Not indicated for chronic benign pain.
- With time, increased doses are required because of the development of tolerance and/or progression of disease
- This will also increase the development of the usual narcotic side effects.
Agents
- Types
- Morphine
- Ziconotid
- Is exclusively intrathecal form of ω-conotoxin MVIIa
- Blocks a N-type calcium channel on small myelinated and unmyelinated nociceptive afferents that are primarily localized in the superficial Rexed laminae (I and II).
- Must be preservative-free
- For either intrathecal or epidural use
- Where to get
- Pharmacist prepared
- (e.g. add enough preservative free 0.9% saline to 1 or 3 gm morphine sulfate powder to yield a total of 100ml produces 10 or 30mg/ml solution respectively, and then filter this through a 0.22 mcm filter).
- Commercially available preparations include
- Duramorph® (available as 0.5 or 1mg/ml)
- Infumorph® (available in 20ml ampules of 10 or 25mg/ml),
- Any of which may be diluted to a lower strength with preservative free diluent (normal saline).
- Cross tolerance to systemic narcotics does occur
- Spinal narcotics are more effective in patients who have not been on continuous high-dose IV opiates (patients on high-dose IV narcotics need higher initial intraspinal narcotic doses).
Side effects
- Pruritus
- Often diffuse
- May be experienced most intensely in the nose
- Respiratory depression
- The respiratory depression with spinal narcotics is usually very gradual,
- Detected by monitoring respiratory rate q 1 hr
- Taking action if the rate decreases
- Urinary retention
- N/V.
Trial injection
- Before implanting
- Test injection to
- Verify pain relief
- Tolerance for medication.
- Done via an external pump connected to a
- Percutaneously inserted epidural OR
- Intrathecal catheter
- Doses for intrathecal catheters are usually ≈ 5– 10 times lower than those for epidural catheters.
- Technique:
- Use no other narcotics for ≈ 24 hrs
- With a continuous infusion additional narcotics should be withheld until the effect of the spinal narcotics has been determined
- 2 ampules (0.4mg each) of naloxone and syringe taped to patient’s bed
- (For the first 24 hrs after a single injection; at all times with continuous infusion)
- Head of bed elevated ≥ 10° for 24 hrs
- Record respiratory rate q 1 hr for 24 hrs;
- If asleep and respiratory rate < 10 breaths/min, awaken patient.
- If unable to awaken, administer naloxone 0.4mg IV and notify physician. Repeat naloxone 0.4mg IV q 2min PRN
- Optional: pulse oximeter for 24 hrs
- Diphenhydramine 25mg IV q 1 hr PRN itching
- Droperidol 0.625mg (which is 0.25 ml of the 2.5 mg/ml standard concentration available) IV q 30–60mins PRN nausea
- PRN supplemental pain medication:
- Narcotic agonist/antagonist: e.g. nalbuphine 1–4mg IV q 3 hrs, OR
- Ketorolac tromethamine 15mg IV or IM or 30mg IM q 6 hrs (use lower dose for weight < 50 kg, age > 65 yrs, or reduced renal function)
Implantable drug delivery pumps
Indication
- Pumps should only be implanted if patients have successful pain control with test injection of
- Spinal epidural (5–10mg) OR
- Intrathecal (0.5–2mg) morphine.
- Patient life expectancy of >3 months is recommended for implantable pumps (if shorter longevity is anticipated, an external pump may be used).
- One such series of commonly used implantable drug delivery pumps is manufactured by Infusaid Inc.
- The only needle that should be used with their devices are special 22 gauge Huber (non-coring) needles.
- Delivery rates
- Increase with body temperature 10–13% per °C above 37 °C,
- Decrease with body temperature 10–13% per °C below 37 °C
- Become inaccurate at ≤ 4ml of reservoir fluid.
- Pumps should never be allowed to run until empty, as this may permanently affect accuracy and reliability of drug delivery.
- In addition to the pump reservoir port, most models have one or more side “bolus” ports that deliver injected fluid directly to the outlet tubing.
- One should not aspirate when accessing either port.
- Medtronic produces a programmable pump.
Technique
- Lateral position
- Similar to the insertion of a lumbar-peritoneal shunt
- The pump is inserted into a subcutaneous pocket, created with a slightly curved 8–10cm skin incision.
- The pump may be sutured to the fascia of the abdomen (in obese patients, it may be sutured to the subcutaneous tissue).
- Excess tubing should be coiled underneath the pump to prevent inadvertent puncture when accessing either reservoir.
- The spinal catheter is inserted through
- Indirectly via a Tuohy needle inserted between lumbar spinous processes either percutaneously or via a small incision 2–3mm lateral to the spinous processes. OR
- Directly via a hemilaminectomy.
- Fluoroscopy may be used intraoperatively to verify rostral placement of the catheter; radiographic visualization of the catheter may be aided by filling it with iodinated contrast, e.g. Omnipaque-300 (p.236).
- All bends in the tubing should be very gradual to avoid kinking.
Post-op pain management
- Although the pump will be infusing when the patient leaves the operating room, unless they have been on intraspinal narcotics up until the time of surgery, it will usually take several days for the drug to reach equilibrium in the CSF before the level of pain control will be adequate.
- This can be mitigated by a bolus infusion (3–4mg morphine for epidural catheters, or 0.2–0.4mg for intrathecal catheters).
Complications
- Meningitis and respiratory failure are rare complications.
- CSF fistula and spinal H/A may occur.
- Disconnection or dislodgment of catheter tip may result in failure to control pain
- Inflammatory mass (granuloma)
- Associated with Intrathecal morphine and increasingly hydromorphone, with high drug concentrations combined with low flow rate increase the risk of granuloma development.
- Presents as
- Loss on pain control
- New-onset pain complaints
- Progressive myelopathy.
- CT myelography or MRI + C of the catheter tip region is necessary to confirm the diagnosis.
- Management
- In asymptomatic and nonprogressive patients, weaning of intrathecal medications and initiation of saline infusion can produce spontaneous disintegration of the mass.
- In patients with progressive or severe neurologic compromise, urgent surgical decompression and excision are recommended.
Outcome
- Cancer pain: improved in up to 90%.
- Neuropathic pain (e.g. postherpetic neuralgia, painful diabetic sensory neuropathy): 25–50%.
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