2.6 Human Factors Engineering and Ergonomics

Introduction to Human Factors Engineering (HFE)

Human factors engineering (HFE) and ergonomics are scientific disciplines concerned with understanding interactions among humans and other elements of a system. HFE applies theoretical principles, data, and methods to design systems that optimize human well-being and overall system performance. In healthcare, HFE seeks to make medical devices, software systems, and clinical workflows user-friendly and error-tolerant.

Rather than attempting to train clinicians to overcome poorly designed systems, HFE focuses on redesigning systems to match human cognitive and physical capabilities. By understanding human limitations, we can design environments that make it easy to do the right thing and difficult (or impossible) to do the wrong thing. The goal is to design out hazards and build safeguards that acknowledge the fallibility of human memory and vigilance.

Cognitive Load Theory and Clinical Decision-Making

Human performance is constrained by cognitive and physical limitations. Cognitive load refers to the total amount of mental effort being used in the working memory. Working memory has a limited capacity (often cited in cognitive psychology as 7 plus or minus 2 items of information). When a clinician is placed in a high-stress environment with multiple distractions, alarms, and complex clinical tasks, their cognitive load can easily exceed this limit, leading to cognitive overload.

Cognitive load is classified into three types:

1. Intrinsic load: The effort associated with a specific clinical topic or task itself (e.g., calculating a complex pediatric drug dose or interpreting an unusual ECG pattern).
2. Extraneous load: The mental effort imposed by the way information is presented or the environment (e.g., a poorly designed electronic health record user interface, loud alarms, or chaotic unit layouts).
3. Germane load: The work put into creating a permanent store of knowledge, or a "schema" (e.g., learning a diagnostic heuristic or internalizing a clinical rule).

To reduce errors, healthcare organizations must focus on minimizing extraneous cognitive load by designing intuitive medical equipment interfaces and reducing administrative distractions. When extraneous load is high, it consumes working memory capacity that is desperately needed for complex clinical reasoning, resulting in omission errors and diagnostic blind spots.

Fatigue and Stressors

Physical and mental fatigue dramatically impairs cognitive performance. Sleep deprivation disrupts attention, slows reaction times, and compromises executive function, leading to diagnostic errors and failures in procedural execution. Bedside clinicians working extended shifts of over 24 hours exhibit cognitive deficits equivalent to a blood alcohol concentration of 0.05% to 0.10%. Resident physicians working these extended shifts commit 36% more serious medical errors than those working shorter shifts.

Chronic fatigue also leads to burnout, which is strongly associated with an increase in self-reported medical errors. Systems-level solutions, such as implementing strict shift length limits (e.g., maximum 12-hour shifts) and providing designated nap areas, are required to manage fatigue-related risks. Relying on clinicians to 'stay alert' or 'work harder' ignores physiological realities and represents a critical failure in system design.

The Hierarchy of Controls (Patient Safety Interventions)

In HFE, safety interventions are categorized by their reliability and effectiveness. For the CPPS exam, it is critical to distinguish between weak, medium, and strong interventions. Weak interventions rely on human vigilance, whereas strong interventions utilize design features to prevent errors.

Forcing Functions and Constraints

A forcing function is a design feature that prevents an action from being completed unless a specific condition is met. For example, enteral feeding tubes now use ENFit connectors that physically cannot connect to intravenous lines, preventing fatal tube-feeding misconnections. A physical constraint makes it difficult or impossible to perform an incorrect action. For example, medical gas outlets in hospital walls are keyed specifically to match only the corresponding gas hose (oxygen vs. nitrous oxide), preventing the administration of the wrong gas.

Standardization and Simplification

Standardization involves structuring processes to follow a uniform sequence. For example, standardizing the location of emergency medications on a crash cart across an entire hospital system ensures that a nurse can find epinephrine immediately, even under stress. Simplification involves removing unnecessary steps from a workflow to reduce opportunities for error. Both strategies reduce the cognitive load on the clinician.

Weak Interventions

Interventions such as education, training, and policy memos are the most common but the least effective. They assume that errors are caused by lack of knowledge or carelessness, rather than system failures. They do not change the underlying system design and fail when clinicians are fatigued or distracted. Similarly, double-checks are weak because they are highly susceptible to confirmation bias (where the second checker assumes the first checker was correct) and diffusion of responsibility.

Usability Testing and Design

HFE emphasizes user-centered design, where end-users are actively involved in the design and testing of devices and software. Usability testing involves observing clinicians interacting with a system (such as an EHR or infusion pump) in simulated settings to identify design flaws before clinical deployment. Key evaluation techniques include:

• Heuristic evaluation: Comparing a user interface design against established usability principles (heuristics) to identify potential issues (e.g., checking if error messages are clear and helpful).
• Formative evaluation: Iterative usability testing conducted during the design phase to identify user interface problems and guide design modifications.
• Summative evaluation: Testing conducted at the end of the development cycle to verify that the final product meets safety and performance standards before widespread release.