Flow Rate and Volume Input Errors in Infusion Pumps: A Usability Engineering Perspective

The usability of medical equipment in clinical settings is a critical factor directly affecting patient safety. A medication error incident involving an infusion pump at a healthcare facility starkly illustrates this importance. In this case, a drug that should have been administered at 30 mL/h was mistakenly entered as 900 mL/h, resulting in overdose and subsequent respiratory arrest—a severe medical accident.

The root cause of this accident lay in the device’s user interface design. The infusion pump in question employed a single switch to toggle between flow rate and volume settings for input, a specification prone to causing user confusion. In the high-stress, time-constrained environment characteristic of clinical settings, such design significantly increases the risk of inducing human error.

Considerations from Usability Engineering Standards

From the perspective of usability engineering based on IEC 62366-1:2015+AMD1:2020, operating different functions through the same interface can be identified as a design that fails to consider human cognitive characteristics. This international standard specifies a process for manufacturers to analyze, specify, develop, and evaluate the usability of medical devices as it relates to safety, requiring them to assess and mitigate risks associated with normal use and use errors.

Human attentional resources are limited, and the ability to process multiple pieces of information simultaneously diminishes particularly under stress. Research in cognitive psychology has shown that error rates increase exponentially when attention is divided and working memory load increases. Therefore, it is desirable to provide physically separate, dedicated controls for critical settings. This represents a fundamental principle of “error-prevention design” and is a design approach recommended in both IEC 62366-1 and IEC 60601-2-24:2012 (the particular standard for infusion pumps).

IEC 60601-2-24:2012 specifies particular requirements for the basic safety and essential performance of infusion pumps and volumetric infusion controllers. This standard applies to enteral nutrition pumps, infusion pumps, infusion pumps for ambulatory use, syringe pumps, volumetric infusion controllers, and volumetric infusion pumps. The second edition conforms to the structure of IEC 60601-1:2005+AMD1:2012 and incorporates the new collateral standards for usability (IEC 60601-1-6) and alarms (IEC 60601-1-8).

Use Errors in Infusion Pumps: Insights from the FDA MAUDE Database

The U.S. Food and Drug Administration’s Manufacturer and User Facility Device Experience (MAUDE) database contains numerous reports of use errors related to infusion pumps. Analysis of these cases reveals the following common error patterns:

Dose-setting errors due to unit confusion (mixing up μg/h and mL/h), setting mistakes caused by confusion between flow rate and total volume input fields, overlooking incorrect inputs due to skipping confirmation screens, confusion arising from operational differences between pumps from different manufacturers, and continued use due to misinterpretation or dismissal of alarms.

These errors are not merely operational mistakes but systemic issues arising from the interaction between device design and human factors. The FDA MAUDE database receives approximately 2,000 new reports annually, with infusion pumps representing one of the medical device categories with particularly high adverse event reporting rates.

Specific Improvement Measures

The following multi-layered approaches can be derived as specific improvement measures from this case:

Design-Stage Countermeasures: Position flow rate and volume settings on physically different switches and screen areas, reducing the risk of misoperation from the design stage. Introduce multi-sensory distinction methods such as color coding, shape differentiation, and tactile feedback. These measures are based on the principle of “foolproof design.”

Enhanced Confirmation Process: Always display a confirmation screen during numerical input, explicitly showing input values in large characters. Visually emphasize input values and units, providing opportunities to reconfirm settings. Implement features that support the independent double-check process.

Intelligent Warning System: When values significantly outside the normal usage range are entered, display clear warning messages and prompt for confirmation. Appropriately set soft limits (warnings) and hard limits (input rejection). Consider features that reference safe administration ranges for each drug by linking with a drug database.

Implementation of Usability Evaluation: Usability testing that considers actual use environments is essential. IEC 62366-1 requires both formative evaluation and summative evaluation. It is necessary to verify operability under various conditions, including nighttime and emergency situations, to identify potential risks. This includes field evaluations with actual healthcare professionals participating and operational tests in simulated emergency situations.

Integration with Risk Management: Usability engineering must work closely with ISO 14971 (Risk Management for Medical Devices). It is required to identify use error scenarios, conduct risk assessments for each scenario, and implement risk reduction measures to achieve acceptable risk levels.

Latest Trends in International Standards

Amendment 1 was issued to IEC 62366-1:2015 in 2020, introducing the concept of User Interface of Unknown Provenance (UOUP). This allows manufacturers of existing devices to reduce the burden of re-evaluation for user interface elements that have been appropriately evaluated in the past.

Additionally, IEC 62366-1 is recognized as an FDA recognized consensus standard, allowing manufacturers to satisfy part of premarket review requirements by submitting a declaration of conformity. The FDA provides guidance on Human Factors Engineering, specifying detailed requirements for usability evaluation.

The EU Medical Device Regulation (MDR) and In Vitro Diagnostic Regulation (IVDR) also specify usability requirements in Annex I Section 5. Manufacturers are required to adopt designs that consider use by intended users and minimize the risk of use errors.

The Essence of Medical Device Usability

What is important in improving medical device usability is not merely enhancing operability but adopting an essential design approach to ensure safety. This includes a deep understanding of human cognitive and behavioral characteristics, grasping constraints in actual use environments, and implementing appropriate countermeasures against reasonably foreseeable misuse.

Usability engineering is an activity related to the entire product realization process, particularly Section 7.3 “Design and Development” of ISO 13485. Information obtained through Post-Market Surveillance activities is utilized for updating use environments and risk management, forming a continuous improvement cycle.

In defining use environments, it is necessary to consider all aspects: physical environment (lighting, noise, temperature, etc.), social environment (teamwork, communication), and organizational environment (workload, training). Particularly in clinical settings, special conditions such as time pressure, multitasking, and frequent interruptions exist, which become factors inducing errors.

Information Provision and Training

Usability engineering applies not only to the device’s user interface itself but also to the information provided (including displays, labeling, and instructions for use) and training provided to users (or trainers of users). Critical safety information must be perceivable, understandable, and actionable.

Instructions for use are considered part of the user interface, and IEC 62366-1 explicitly requires evaluation of safety information. In particular, emergency response procedures, error recovery procedures, and warnings/cautions must be described clearly and concisely.

Conclusion

Medical device usability engineering is thus positioned as an important technical foundation for protecting patients’ lives. Manufacturers are required to adopt design approaches that consider usability from the early stages of development and to implement continuous improvement. This is an essential initiative to fulfill the social responsibility of improving medical safety.

The infusion pump case demonstrates that a lack of usability can lead to fatal consequences. However, through appropriate design principles, systematic usability engineering processes, and continuous post-market surveillance, these risks can be significantly reduced. As the medical device industry as a whole, deeply understanding and practicing the philosophy of user-centered design will become increasingly important in the future.