Pump flip. CT image of a complete flipped pump. (a) The CT was performed after a failed pump refill with needle unable to identify the reservoir entry; fluoroscopic image performed in the pain clinic showed reservoir closer to skin consistent with pump flip. (b) Images from Dr. Anitescu’s personal library
29.4 Expired Pump
All programmable intrathecal pumps can stop functioning properly due to a natural, expected decline in battery function if the pump continues to run past the lifespan of the battery. Medtronic and Prometra pumps utilize batteries to drive function of their respective devices. The Codman pump utilizes a battery-free design that depends solely on pressured gas to promote flow.
There are currently no commercially available rechargeable battery-operated intrathecal pumps. Most battery-powered pumps have a life span of 3–9 years, primarily dependent upon how intensively the pump is used (i.e., rate of delivery). In a study by Flückiger et al., the average time to pump replacement due to battery exhaustion was 55 months . Battery exhaustion was the most common indication for exchange or revision of an intrathecal pump in this study. After this point in time, the pump will be expected to stop functioning properly. Surgical replacement is usually scheduled several months before anticipated battery failure and alerts, and alarms are generated well in advance of this date to inform the patient and medical practitioner that replacement is necessary.
Perhaps less-known complications are the ones related to catheters. In majority of cases, the commercially available intrathecal drug delivery systems (IDDS) offer lifetime warranty for their products, meaning that upon placement of an intrathecal catheter, unless it breaks through trauma, develops granuloma via high opioid concentration, or migrates out of the intrathecal space, the device ensures stable and continued delivery of medication to treat patients’ pain. However, it is unclear if those implants maintain their original properties during the years. In many situations, a malfunction of an intrathecal catheter may be encountered during an intrathecal reservoir change and requires changing the entire IDDS. During this operation, defective (friable, broken, punctured) catheters can be encountered although clinical reports are sparse. Special attention should be taken with replacement of intrathecal catheters that have been implanted more than 10 years as coating of the catheter may sheer from its body; in those situations, catheters become friable and can easily break, sometimes with irretrievable pieces in the intrathecal space or abdominal wall (Fig. 29.2). multidisciplinary collaboration with neurosurgeons and/or plastic surgeons may be needed in these situations to ensure complete explant of the system. In very rare cases when risks outweigh the benefits, catheter parts may be left in place (e.g., abdominal wall) with careful monitoring of the patient.
Intrathecal pump malfunction . The original IDDS was placed 10 years ago, with replacement after 6 years. During the second replacement occurring after sudden pump stop, the catheter was unable to produce CSF upon aspiration. A complete revision of the system showed a significantly damaged catheter whose coating sheered from the catheter body. The catheter was friable but was easily removed from the intrathecal space. The picture shows the finding of the catheter during removal surgery. The entire system was removed but was not replaced with a new system as patient was weaned off intrathecal opioids during the period before surgery and tolerated it well with minimal pain and side effects
29.5 Pump Stall
There are several potential causes of mechanical failure of intrathecal pumps. In the retrospective study by Flückiger et al.  of 100 patients in Switzerland with implanted intrathecal pumps, the annual rate for complications requiring surgical intervention was 10.5%, with 35% of complications being pump-related and the remaining-catheter related. Pump complications included pump defect, battery exhaustion, pump repositioning, and infection.
In June 2013, a class I recall was issued for the Medtronic SynchroMed® II and SynchroMed® EL Implantable Drug Infusion Pumps . This recall mentioned a potential for electrical shorting within the pump that could present as a motor stall and potentially lead to loss of or reduction in therapy. Another set of case reports by Rigoli et al. discussed two patients with symptoms of acute baclofen withdrawal with supposedly functional pumps in place . In these two cases, each patient had pump reservoirs that were near empty when withdrawal symptoms presented. These cases brought attention to the concept that intrathecal drug delivery may be unreliable in some pump systems at low reservoir volumes.
Combining multiple drugs to elicit their synergistic effects at lower drug doses is common in intrathecal pump management . Drug polytherapy is recommended as second-line therapy in the consensus treatment guidelines . Despite these recommendations, intrathecal pumps may stall when several medications, especially “off-label” medications, are compounded for intrathecal therapy. Morphine, baclofen, and ziconotide as sole agents are the only FDA-approved intrathecal medications. None of the drugs that are FDA approved for IT administration are approved for mixing with any other drug. In clinical practice, other “off-label” medications, such as local anesthetics, opioids other than morphine, and clonidine, are routinely used in intrathecal therapy.
Combinations of intrathecal medications can contribute to internal corrosion within some intrathecal pumps. Information published by Medtronic indicates that corrosive agents (e.g., chloride ion, sulfate ion) originating from drug formulations may be to blame . This report notes that some unapproved drug formations show chloride permeation rates orders of magnitude higher than those for approved drugs. Other postulated causes of internal corrosion may be due to antimicrobial and antioxidant preservatives (e.g., sodium metabisulfite), drug additives to maintain solubility, drug formulations with a pH ≤ 3, and hydrophobic drugs (e.g., fentanyl, bupivacaine).
A case report by Sgouros et al. discussed the sequela of the stall of an intrathecal pump filled with baclofen . When the pump restarted after the stall, the patient received a large bolus of baclofen. The patient subsequently was unable to move her legs and later lapsed into a coma requiring intubation and ventilation. After 17 h, the patient awoke gradually from the coma with no new neurological deficits. The pump was subsequently explanted and underwent forensic examination by the manufacturer who identified no technical problems with the device.
Although a spontaneous pump stall is possible with any system at any time due to structural dysfunction (e.g., mechanical failure), these instances are very uncommon due to the high reliability of available systems. The most common time for a pump to stall is during an MRI when the mechanism for drug delivery relies upon magnetic components, as it does with the Medtronic ITP. In this instance, the pump will stop due to the magnetic field of the MRI scanner and should resume spontaneously after the patient is removed from the MRI and associated magnetic field . Permanent stall, although unlikely, is possible, which is why a pump should be interrogated approximately 20 min after an MRI to determine whether the pump has resumed normal function. The event log should show messages indicating that a motor stall and subsequent motor recovery have occurred. If a recovery has not occurred or alarms have not been triggered, the patient is at risk for a withdrawal syndrome related to cessation of intrathecal therapy, especially baclofen. In this instance, it is recommended to wait another 20 min and interrogate the pump again to address delays in event logging due to electromagnetic interference from the MRI. The pump manufacturer representative should be contacted if the pump has not restarted, and appropriate care should be taken to prevent the development of withdrawal symptoms.