Background

External insulin infusion devices are becoming increasingly popular since their introduction in 1974. As of 2007, more than 375,000 external insulin infusion pumps are in use.³

Anatomy

An external insulin infusion pump device consists of a portable, programmable infusion pump connected to a subcutaneously implanted catheter maintained in place with adhesive tape (Fig. 71-1). The implanted catheter site varies, but it is commonly placed on the abdomen in adults and on the buttocks in young children. The thighs, hips, and upper part of the arms are other sites. It is recommended that the implanted catheter be replaced every 2 to 3 days.

Device Complications

In 2010, the Food and Drug Administration (FDA) published a panel report that highlighted problems associated with insulin infusion devices.³ From the top five device manufacturers, the FDA noted 16,640 adverse events, including 310 deaths, 12,093 injuries, and 4,294 malfunctions. Box 71-1 lists the most frequently reported problems with devices in descending frequency. Box 71-2 lists the most frequently reported patient-oriented adverse reactions, which include hyperglycemia and hospitalization.

Of the 310 deaths reportedly related to insulin infusion pumps, the vast majority of problems with the device were not known to the patient or providers at the time and the root cause of failure of the device was not identified by the manufacturer. In 29 deaths, problems with the device identified included overinfusion, bent cannulas, disconnection, pump alarming, failure to deliver, suspected electromagnetic interference, and display failure.

Procedure

As with all patients seen in the emergency department, consider device malfunction as part of the differential diagnosis in patients with insulin infusion devices. In addition to medical management, troubleshoot the device and remove it in cases of uncertainty or emergency.

To remove the catheter, simply peel off the adhesive and embedded catheter together to discontinue the flow of injected medication into the patient. There are a variety of proprietary pump manufacturers, each with their own device programming. Call the appropriate manufacturer to troubleshoot the device, visit the manufacturer’s website for an online troubleshooting manual, or simply instruct the patient to discontinue use of the device and return to a standard calculated insulin schedule by manual injection until the device-related complication is investigated and resolved.

Background

Intrathecal drug delivery systems (IDDSs) have been in clinical use since the 1980s. Although data are accumulating, very few robust clinical studies of IDDSs have been published.⁴ The FDA approved the use of intrathecal baclofen in 1992 for severe spasticity secondary to spinal cord injury, multiple sclerosis, cerebral palsy, or stroke. In addition, the FDA approved the use of intrathecal morphine in 1995 for chronic pain refractory to traditional medical therapies. An IDDS is also used for the delivery of chemotherapeutic medications for specific oncologic conditions. Moreover, there are numerous off-label uses of various intrathecal medications.

Anatomy

Currently, Medtronic is the only IDDS manufacturer in the United States. Medtronic’s SynchroMed II Programmable Infusion Pump consists of an infusion pump connected to an intrathecal catheter (Fig. 71-2A). The infusion pump is available with a refillable reservoir of either 20 or 40 mL. The pump is powered by a permanent lithium battery that cannot be recharged. The battery must be surgically replaced every 4 to 7 years. Normal refill intervals are usually between 2 and 3 months.

The pump is placed in a subcutaneous pocket, generally in the right lower abdominal region. The intrathecal catheter is inserted slightly lateral to the spinous process into an appropriate lower lumbar interspace and connects to the pump via a subcutaneous tract that wraps around the abdominal wall (see Fig. 71-2B).

Interrogation and programming of the device are conducted with a magnetic field–induced, external programming wand connected to a handheld computer.

Device Complications

Several studies have shown a significant rate of adverse effects in IDDS patients ranging anywhere from 2% to 50%.5,6

The most frequent and serious adverse events related to the device and implant procedures are catheter dislodgement from the intrathecal space, catheter fracture, implant site infection, and meningitis. Internal device programming errors that cause underdosing or overdosing are less common. If the drug supply is depleted, systemic symptoms related to acute drug withdrawal will occur. This is characteristic for the specific drug being delivered and should be anticipated. Opioid and baclofen withdrawal syndromes are unlikely.

Medications currently in use via IDDSs include clonidine, bupivacaine, morphine, hydromorphone, fentanyl, ziconotide, and baclofen.⁷ Of these, bupivacaine and morphine have specific antidotes (Intralipid and naloxone, respectively). Medication overdoses, aside from standard emergency management, can also be treated by accessing the infusion pump reservoir.

A unique complication related to IDDSs that was identified by the FDA and issued as a warning is the formation of a granuloma at the tip of the intrathecal catheter. This can obstruct infusion of the medication and lead to withdrawal symptoms.8,9

Common adverse effects related to intrathecal baclofen include hypotonia, somnolence, headache, convulsions, dizziness, urinary retention, nausea, and paresthesias. Acute intrathecal baclofen withdrawal, which may resemble alcohol or benzodiazepine withdrawal, is also possible in cases of underdosing or inability to deliver medication.

With regard to intrathecal opioids, the degree of lipophilicity of the intrathecal opioid affects its pharmacokinetics. Fentanyl, with its high lipophilicity, is absorbed rapidly by the spinal cord and little is left to ascend in cerebrospinal fluid (CSF). Thus, it has a rapid onset and shorter duration with fewer adverse effects. Morphine, with its high hydrophilicity, penetrates the spinal cord slowly, which allows a considerable amount of the drug to ascend in CSF. This, in turn, results in a slower onset and longer duration with a higher incidence of adverse effects, including pruritus, nausea and vomiting, urinary retention, changes in mental status, and respiratory depression.10,11