Fluctuating Capacity in Healthcare (Delirium, Dementia & Decision-Making)

A patient might appear able to make decisions during one part of the day but seem confused or unable to understand information later. This situation is known as fluctuating capacity.

In healthcare, a person’s ability to make decisions can sometimes change over time, particularly when conditions affect how the brain is functioning. This is commonly seen in patients experiencing delirium, infection, medication effects or certain stages of dementia.

 

In England and Wales, decision-making and capacity assessments are governed by the Mental Capacity Act 2005. In Scotland, similar protections exist under the Adults with Incapacity (Scotland) Act 2000, which provides the legal framework for supporting and protecting adults who may have difficulty making decisions (Department of Health and Social Care, 2005; Scottish Government, 2000).

 

Both frameworks emphasise that capacity must always be assessed at the time a specific decision needs to be made. This means someone may have capacity at one moment but lack capacity later. For student nurses, this can feel confusing at first, because capacity is often mistakenly thought of as something a person either has or does not have.

In reality, capacity is decision-specific and time-specific.

 

Why Capacity Can Fluctuate

Some medical conditions affect the brain in ways that cause changes in attention, understanding and reasoning. One of the most common examples is delirium. Delirium is a sudden disturbance in mental functioning that can occur due to infection, dehydration, medication effects or acute illness. Patients with delirium may appear alert and coherent at certain times but become confused, disoriented or unable to concentrate at other times.

Similarly, people living with dementia may experience periods where their ability to understand information varies during the day. Many individuals with dementia are more alert earlier in the day and may become increasingly confused later in the evening, a pattern often referred to as “sundowning.”

Because of this, decision-making ability may change throughout the day or over the course of an illness.

 

The Evidence-Based “Decision Window”

Research and clinical guidance suggest that cognitive functioning in patients with dementia or delirium often follows a daily pattern, where attention and clarity are stronger earlier in the day and decline as fatigue increases. Guidance from NICE Guideline NG108 on decision-making and mental capacity emphasises that clinicians should consider timing assessments to coincide with the patient’s best cognitive performance whenever possible (NICE, 2018).

In practice, this means that healthcare professionals may try to assess capacity or discuss important decisions during periods when the patient is most alert. Some clinicians refer to this as the patient’s “decision window.”

 

The Decision Window Strategy

Although every patient is different, clinicians often notice patterns that can help guide when important discussions take place.

 

Morning (higher alertness)

Morning hours are often when patients with delirium or dementia are most alert. This can be the best time for complex decisions, such as discussions about treatment options, discharge planning or consent for procedures.

 

Afternoon (increasing fatigue)

Later in the day, fatigue may begin to affect concentration. At this stage, patients may still be able to make simpler decisions, such as choices about meals or personal care.

 

Evening (possible sundowning)

Many patients with cognitive impairment become more confused or agitated in the evening. Because of this, clinicians usually avoid conducting major assessments or complex discussions at this time unless absolutely necessary.

 

This approach helps ensure that patients are given the best possible opportunity to understand and participate in decisions about their care.

 

Supporting Patients During Fluctuating Capacity

When capacity fluctuates, healthcare professionals may take additional steps to support decision-making. This might include choosing a quieter environment for discussion, explaining information slowly and clearly or allowing extra time for responses. Providing support before concluding that someone lacks capacity is a key principle of both the Mental Capacity Act 2005 and the Adults with Incapacity (Scotland) Act 2000, which emphasise helping individuals participate in decisions wherever possible (Department of Health and Social Care, 2005; Scottish Government, 2000).

 

When Capacity Cannot Be Established

In some situations, even with support and careful timing, a patient may still be unable to make a decision. If the person cannot understand, retain, weigh up or communicate information relevant to the decision, they may be considered to lack capacity for that specific decision.

When this happens, healthcare professionals must follow the best interests decision-making process in England and Wales or the appropriate decision-making framework outlined under the Adults with Incapacity (Scotland) Act 2000.

 

What Student Nurses Might See on Placement

Student nurses may notice fluctuating capacity in many clinical settings.

For example, a patient with delirium may appear confused during an evening assessment but much clearer the following morning. Similarly, a patient living with dementia may have periods where they are able to participate fully in discussions about care.

Understanding fluctuating capacity helps explain why healthcare professionals sometimes repeat discussions or reassess decisions at different times.

Final Thoughts

Fluctuating capacity reminds us that decision-making ability is not always constant. Illness, infection, medication effects and cognitive conditions can all influence how well someone is able to understand and process information.

For healthcare professionals, the goal is always to support patients to make their own decisions whenever possible and to assess capacity carefully, fairly, and at the right time.

 

References

Department of Health and Social Care. (2005).

Mental Capacity Act 2005.

Scottish Government. (2000).

Adults with Incapacity (Scotland) Act 2000.

NICE. (2018). Decision-making and mental capacity (NG108).

NICE. (2010). Delirium: prevention, diagnosis and management in hospital and long-term care

 

Disclaimer:This resource is designed for educational purposes for UK student nurses and healthcare professionals. While we strive for clinical accuracy, it does not constitute medical advice. Always refer to your specific Trust’s local policies, NICE guidelines and the NMC Code in clinical practice. Clinical scenarios can change rapidly; when in doubt, escalate to your mentor or senior clinician.