MR Safety: Infusion PumpsWhat are the specific MR precautions with implanted infusion pumps?
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Surprising fact: During the last decade, the leading cause of MRI-related deaths has not been from projectiles, burns, or pacemaker failures, but infusion pump malfunction.
At least a half-dozen such cases were reported in the USA alone, a situation so significant that the Food and Drug Administration (FDA) issued a special safety communication in 2017 to address this issue. Life-threatening effects of the magnetic field on implanted infusion pumps include:
- Increased rate of drug delivery, including discharge of the entire pump contents as a single lethal dose
- Decreased rate of drug delivery or cessation of pump operation while in the scanner; delayed restart of pumping after removal from the scanner
- Permanent device failure due to demagnetization of the pump magnet
"MR Conditional" SynchroMed® II infusion pump
Implantable infusion pumps are internally powered devices surgically placed subcutaneously in the upper chest or abdominal wall. They consist of a titanium-encased pump assembly (containing a drug reservoir and refilling port) connected to a small-gauge plastic catheter. The catheter tip may be placed intravenously, intra-arterially, subcutaneously, intraperitoneally, intrathecally, or epidurally.
Typical drugs administered via implantable infusion pumps include chemotherapeutic agents for cancer, opioids for pain control, and baclofen for spasticity.
Typical drugs administered via implantable infusion pumps include chemotherapeutic agents for cancer, opioids for pain control, and baclofen for spasticity.
Implantable infusion pumps have been used clinically for 30 years, but today only three companies manufacture all such devices used worldwide: Medtronic, Flowonix, and Tricumed (the latter's offerings not available in the USA). Additionally, several "legacy" pumps, produced up until the mid-2010's may occasionally be encountered, including the Codman® 3000, Isomed®, and SynchroMed® EL. Implanted infusion pumps can be divided into two types based on their mechanism of fluid propulsion.
"MR Conditional" Codman® 3000 implantable infusion pump.
Propellant-driven Pumps
The simplest types of implantable infusion pumps do not contain a motor, but rely on thermal expansion of a gaseous propellant to force drug delivery into the catheter. Examples of such pumps include the legacy Codman® 3000 (Johnson & Johnson) and Isomed® (Medtronic) pumps and those currently manufactured by Flowonix (Prometra®) and Tricumed (LENUS Pro®, IP2000V, and Siromedes®). As shown in the schematic right, such pumps have two compartments: 1) a collapsible titanium bellows serving as the drug reservoir, and 2) a surrounding chamber containing a flurochlorocarbon propellant in gas-vapor equilibrium. As the device heats to body temperature, the propellant expands, compressing the bellows and driving drug delivery into the catheter. Various valves and filters control the flow.
The devices listed above are all considered MR Conditional at 1.5 and/or 3.0T. Because RF-heating of the pump may occur during scanning, the possibility of increased drug flow (related to temperature-induced propellant expansion) should be considered and high SAR protocols avoided. Prometra® pumps have an additional unique limitation in that their drug reservoirs must be emptied before entering the MR environment. This requirement resulted from a 2017 incident where the strong magnetic field opened inlet and outlet valves resulting in a complete discharge of pump contents and patient death.
The simplest types of implantable infusion pumps do not contain a motor, but rely on thermal expansion of a gaseous propellant to force drug delivery into the catheter. Examples of such pumps include the legacy Codman® 3000 (Johnson & Johnson) and Isomed® (Medtronic) pumps and those currently manufactured by Flowonix (Prometra®) and Tricumed (LENUS Pro®, IP2000V, and Siromedes®). As shown in the schematic right, such pumps have two compartments: 1) a collapsible titanium bellows serving as the drug reservoir, and 2) a surrounding chamber containing a flurochlorocarbon propellant in gas-vapor equilibrium. As the device heats to body temperature, the propellant expands, compressing the bellows and driving drug delivery into the catheter. Various valves and filters control the flow.
The devices listed above are all considered MR Conditional at 1.5 and/or 3.0T. Because RF-heating of the pump may occur during scanning, the possibility of increased drug flow (related to temperature-induced propellant expansion) should be considered and high SAR protocols avoided. Prometra® pumps have an additional unique limitation in that their drug reservoirs must be emptied before entering the MR environment. This requirement resulted from a 2017 incident where the strong magnetic field opened inlet and outlet valves resulting in a complete discharge of pump contents and patient death.
"MR Conditional" SynchroMed® II implantable infusion pump
Motor-driven Peristaltic Pumps
These pumps, typified by the Medtronic SynchroMed® series, contain a battery, electric motor, and rollers on a rotating wheel that serially compress the internal tubing for drug propulsion. Electric pumps are more complex than propellant-driven ones, containing microelectronics for precise control over infusion rates, remote programming, and interrogation. SynchroMed® pumps are all rated as MR Conditional, so the usual limits on field strength, spatial field gradient, etc. apply. But due to their sophisticated design several additional conditions must be followed:
These pumps, typified by the Medtronic SynchroMed® series, contain a battery, electric motor, and rollers on a rotating wheel that serially compress the internal tubing for drug propulsion. Electric pumps are more complex than propellant-driven ones, containing microelectronics for precise control over infusion rates, remote programming, and interrogation. SynchroMed® pumps are all rated as MR Conditional, so the usual limits on field strength, spatial field gradient, etc. apply. But due to their sophisticated design several additional conditions must be followed:
- Palpation of the implanted pump should be performed to ensure that it has not rotated into a position perpendicular to the long axis of the body (and Bo field). This orientation may demagnetize the pump motor, rendering it permanently inoperable.
- The shunt is expected to stop operating when the patient is placed in the scanner, resulting in temporary cessation of drug delivery. This may be dangerous for some patients, particularly those receiving intrathecal baclofen, where a life-threatening withdrawal reaction may occur.
- Upon removal from the scanner the pump must be interrogated to make sure it is no longer stalled. On rare occasions the pump may take several hours to restart.
References
Chappel E. Implantable drug delivery devices. In: Chappel E (ed). Drug Delivery Devices and Therapeutic Systems. Academic Press, 2021: 129-156. Google Books preview available at this link.
Food and Drug Administration. Safety concerns with implantable infusion pumps in the magnetic resonance (MR) environment: FDA Safety Communication. Silver Spring, MD, 2017.
Metronic. MRI guidelines for Medtronic implantable infusion systems. Medtronic, 2020-05-01. Downloaded from this site 4/21. (Be sure and recheck the Medtronic site for the most up-to-date MR safety information about this line of products).
Mohammed I, Hussain A. Intrathecal baclofen withdrawal syndrome- a life-threatening complication of baclofen pump: A case report. BMC Clinical Pharm 2004; 4:6 [DOI LINK]
Pons-Faudoa FP, Ballerini A, skamoto J, Grattoni A. Advanced implantable drug delivery technologies: transforming the clinical landscape of therapeutics for chronic diseases. Biomed Microdevices 2020; 21:47. [DOI LINK]
Prometra® Programmable Pumps MRI Safety Information. (PL-21604-03). Flowonix. 2020. Downloaded from this site 4/21. (Be sure and recheck the Flowonix site for the most up-to-date MR safety information about this line of products).
Chappel E. Implantable drug delivery devices. In: Chappel E (ed). Drug Delivery Devices and Therapeutic Systems. Academic Press, 2021: 129-156. Google Books preview available at this link.
Food and Drug Administration. Safety concerns with implantable infusion pumps in the magnetic resonance (MR) environment: FDA Safety Communication. Silver Spring, MD, 2017.
Metronic. MRI guidelines for Medtronic implantable infusion systems. Medtronic, 2020-05-01. Downloaded from this site 4/21. (Be sure and recheck the Medtronic site for the most up-to-date MR safety information about this line of products).
Mohammed I, Hussain A. Intrathecal baclofen withdrawal syndrome- a life-threatening complication of baclofen pump: A case report. BMC Clinical Pharm 2004; 4:6 [DOI LINK]
Pons-Faudoa FP, Ballerini A, skamoto J, Grattoni A. Advanced implantable drug delivery technologies: transforming the clinical landscape of therapeutics for chronic diseases. Biomed Microdevices 2020; 21:47. [DOI LINK]
Prometra® Programmable Pumps MRI Safety Information. (PL-21604-03). Flowonix. 2020. Downloaded from this site 4/21. (Be sure and recheck the Flowonix site for the most up-to-date MR safety information about this line of products).
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