Implantable Pumps for Spinal Infusion of Drugs

An implantable pump is a specialized device that delivers precise amounts of concentrated drug into the intrathecal space through a small catheter. The intrathecal space contains the cerebrospinal fluid. Spinal infusion is also called intrathecal infusion.

Implantable pumps are intended for patients with severe chronic pain that has not responded to other treatments. Some examples of diagnoses for which an implantable pump may be effective are: low back pain after failed surgery, cancer pain, sympathetic-reflex dystrophy, neuropathic pain, and severe pain from vertebral fractures.

These are patients who do not respond to pharmacological treatments or who suffer intolerable side effects.

The spinal infusion pump continuously administers small amounts of concentrated analgesic drugs, thus bathing the pain receptors located in the spinal cord. This provides pain relief and reduces or eliminates the need for oral or transdermal (patch) medication. As the medication is deposited directly into the nervous system, the doses required for most drugs are much lower.

Since it is impossible to know a priori whether or not a particular patient will benefit from continuous spinal infusion, it is very important to perform a preliminary test, which may consist of an injection of the drug to be used in the intrathecal space, or a temporary continuous infusion with an external pump for a few days. In the latter case, since there is a risk of infection, the control by the physician must be very close.

The implantation of the infusion system is performed in an operating room. It is not necessary to use general anesthesia, although it can be done depending on the characteristics and general state of health of each patient. Generally, deep sedation and local anesthesia are used.

The implant consists of two parts: the insertion of a fine catheter into the intrathecal space through a puncture in the lumbar or dorsal spine, and the placement of the implantable pump under the skin, generally in the abdominal region.

It is advisable to remain under observation for at least 24 hours in order to administer adequate analgesia and antibiotics.

Once the pump is implanted, it is filled with morphine or with the drugs to be used for the infusion. The infusion rate is programmed electronically with remote control.

These are some of the drugs frequently used for implantable pumps:

• Morphine: This is a potent opioid analgesic. It is the most commonly used drug in spinal infusions for the treatment of pain. As short-term side effects, it can cause nausea, vomiting, itching, leg swelling, drowsiness and urinary retention. These effects usually disappear within one to three days. A side effect to be taken into account is also the development of tolerance, i.e. the need to use higher and higher doses to achieve the same results.
• Bupivacaine: This is a long-acting local anesthetic which, together with morphine or other opioid drugs, enhances their action, significantly improving the analgesia provided by continuous spinal infusion.
• Clonidine: This is a drug with antihypertensive effects, which has high analgesic properties, especially if combined with other drugs. Among other side effects, it can produce a decrease in blood pressure, which sometimes prevents its use.
• Ziconotide: It is a new drug, extracted from a species of snail. It has been shown to be effective in many forms of neuropathic pain. It is used only by the spinal route.
• Baclofen: A muscle relaxant drug used in patients suffering from muscle stiffness or spasticity as a result of cerebral vascular accident, spinal cord injury, or other types of neurological disease. When therapeutic levels (effective in relieving symptoms) are reached, they generally remain stable for a long time.

The medication inside the pump lasts from one to three months, depending on the concentration and infusion rate that is programmed. Each time the medication in the pump runs out, it must be refilled by puncturing the pump implanted under the skin with a small needle. At each revision, the infusion rate and drug concentration parameters can be modified to improve pain control.

The pump battery runs out after a few years. The duration depends on the use of the pump. The battery cannot be replaced; the entire pump must be replaced. This requires a simple surgical procedure in which the site where the pump is located is incised, removed and replaced with a new one.

It is not advisable to perform an MRI on a patient with an implanted programmable pump. However, if absolutely necessary, it can be done following protocols that will be provided to radiologists and radiology technicians.

All patients will be provided with special identification indicating that a device has been implanted, in order to avoid going through security checks at airports.

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