Cause of Device-Related Incident
Device factors

Clinical Specialty or Hospital Department
Clinical/Biomedical Engineering; Nursing; Pharmacy / IV therapy

Device Factors
Design / labeling error

Document Type
Hazard Reports

External Factors
*Not stated

Mechanism of Injury or Death
Failure to deliver therapy; Underdose

Support System Failures
*Not stated

Tampering and/or Sabotage
*Not stated

User Errors
*Not stated

UMDNS
Infusion Pumps [16-495]; Infusion Pumps, General Purpose [13-215]

Undetected Upstream Occlusions in Volumetric Infusion Pumps



Hazard [Health Devices Jun 1986;15(6):182-4]

Problem

After a member hospital evaluated its infusion pumps, it found that several pumps could not detect an occlusion in the upstream (bottle-side or proximal) IV line. This problem can result when hospital personnel fail to release the upstream manual clamp (if one is present) after activating the pump. Other mechanisms that can cause an upstream occlusion are a clogged upstream filter or a nonvented bottle used with a nonvented IV set. In these situations, some pumps will continue to operate, but the patient will not receive the infusion.

Discussion

When the downstream (patient-side or distal) IV line is occluded, most pumps alarm when the downstream line pressure exceeds a preset value. However, this mechanism cannot detect an upstream occlusion. In this case, the pump not only can continue to operate without infusing the solution, but it can also display an erroneous value for the accumulated volume infused. This inaccurate record of total fluid volume infused to the patient could result in an inappropriate clinical decision when prescribing further IV therapy. It may also delay the administration of critical medications, which can include both fast-acting drugs (e.g., dopamine, oxytocin, nitroprusside) and slower-acting drugs whose effects are not immediately recognized (e.g., heparin, insulin, lidocaine). The hospital reported that this situation has occurred with several patients and has caused complications.

ECRI believes that undetected upstream occlusions may have other adverse effects, although we have no documented reports of such occurrences. If a pump operates without infusing any solution, the IV needle could become occluded by blood clots. In addition, removing an IV set from the pump when an upstream vacuum pressure is present may cause the vein at the infusion site to collapse due to the induced negative pressure. These situations may sacrifice valuable venous infusion sites and complicate further IV therapy.

Some currently sold infusion pumps can detect an upstream occlusion. The most common detection mechanism is a drop (or flow) sensor. When the upstream IV line is occluded and causes flow to cease, the absence of drops falling in the drip chamber causes the unit to alarm. In addition to confirming fluid flow, drop sensors also can alert the user to an empty IV container before the upstream IV line is depleted. This feature eliminates the need for the user to prime a new IV set when replacing the IV solution container.

Other mechanisms that can detect an upstream occlusion are also acceptable and eliminate the problems associated with drop sensors (e.g., breakage, mispositioning, nuisance alarms during patient transport). In cassette pumps that apply a negative pressure to fill a cassette chamber, an upstream occlusion can be detected in one of two ways: by monitoring for excessive negative pressure or by allowing the pump to stall when the filling pressure exceeds the maximum pumping capability of the motor. (The latter method is reliable only in pumps that alarm when the motor mechanism stalls.) In pumps that passively fill a cassette chamber (i.e., by gravity flow), a sensor detects an upstream occlusion by monitoring the presence of fluid in the filling chamber.

Another mechanism that can detect an upstream occlusion is an air-in-line alarm. Residual air (e.g., minute air bubbles) may increase in volume significantly as the negative pressure increases during an upstream occlusion; in some cases, enough air may pass through the pumping mechanism to be detected by the alarm. Although most pumps are equipped with an air-in-line detector, this mechanism's ability to detect upstream occlusions is often unreliable.

The upstream occlusion detection performance (e.g., time to alarm at different flow rates, maximum occlusion pressures, time to detect gradual occlusion formation) may vary greatly with any of these different detection methods. For example, the time to detect an upstream occlusion for those units with drop sensors may depend on the set flow rate and the infusion pump alarm software. We will consider upstream occlusion detection performance in a future evaluation of infusion devices. (See our evaluation of infusion pumps in Health Devices 13:31-62.)

After investigating this problem and surveying available infusion pumps, we found that six volumetric infusion pumps lack a mechanism designed to detect an upstream occlusion. The probability that an upstream occlusion will occur in such pumps depends on factors other than their intrinsic design. For example, some IV sets are packaged with the roller clamp located just below the drip chamber, which may increase the likelihood that the upstream occlusion will not be detected when used with certain pumps. However, on other  IV sets, the manual clamps, which are located near the patient connection, will allow the upstream IV line to occlude only if they are moved.

Although some pumps do not have an upstream detection mechanism, their supplier states that its IV set product lines are nonetheless designed to be effective in overcoming the upstream occlusion problem. All the manual clamps, except for burette and blood administration IV sets, are located downstream of the cassette and cannot be moved to the upstream IV line. The IV sets that do have upstream manual clamps have a drip chamber below the clamps. An upstream occlusion due to a clamp that is inadvertently left closed or to other mechanisms will be detected when the air in the drip chamber expands and is pumped downstream to trigger the air-in-line alarm. Thus, IV set design in this case may also be effective in preventing undetected upstream occlusions.

Some pumps can operate when the drop sensors are disconnected. Most such pumps have a visual display that indicates when the drop sensor is not in use. Although this feature allows the pumps to operate without being interrupted by nuisance alarms during patient transport, manufacturers who incorporate this feature into their pump design, as well as ECRI, believe that drop sensors on pumps so equipped should always be used except during patient transport or when froth in the drip chamber obscures drop detection.

When using infusion pumps that cannot detect upstream occlusions, it is important to take proper precautionary measures. The risk of undetected occlusions is greatly reduced by purchasing IV sets that have manual clamps on the downstream IV line (and that cannot be repositioned to the upstream IV line). We recommend that upstream manual clamps be moved to the downstream IV line and that IV sets with upstream manual clamps that cannot be moved to the downstream IV line not be used unless they are required by the pump manufacturer. However, these measures do not eliminate the need to provide in-service training to emphasize this problem because several types of IV sets require upstream clamps (e.g., primary set clamps for use with secondary lines, burette sets, blood administration sets), and occlusions may be caused by other mechanisms.

Recommendations

  1. Using the information provided in this report, determine whether any pumps that are unable to detect an upstream occlusion by their intrinsic design are in use at your hospital.
  2. While this problem does not justify removing these pumps from service, thorough training sessions focusing on undetected upstream occlusions should be provided for all users. Although failing to release a manual clamp is the most likely cause of upstream occlusions, inform users that an upstream occlusion can also occur when an upstream filter becomes clogged or a nonvented IV bottle is used with a nonvented IV set.
  3. Provide periodic in-service training to remind staff of this problem as well as all other aspects of pump operation.
  4. When possible, use IV sets that have downstream manual clamps for all pumps, and instruct users to position manual clamps on the downstream IV line.
  5. If the manufacturer does not provide a cautionary label, prominently place a notice such as the following on all infusion pumps: Check fluid flow after activating the pump and hourly thereafter. While labels cannot guarantee that accidental upstream occlusions will not occur, but they may help reduce their frequency.
  6. In selecting new pumps, keep the advantages of detecting upstream occlusions in perspective along with other safety concerns, pump performance, and economic factors.

UMDNS Terms

  • Infusion Pumps [16-495]
  • Infusion Pumps, General Purpose [13-215]

Cause of Device-Related Incident

Device factor: Design/labeling error

Mechanism of Injury or Death

Failure to deliver therapy; Underdose


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