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

Northern Ireland note: The Mental Capacity Act (Northern Ireland) 2016 is being implemented in phases. Phase One covers deprivation of liberty, research, and money and valuables. Do not assume the full Act is in force for every healthcare decision.

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.

Finding the person’s best time

There is no universal “morning window” for capacity. Some people are clearer earlier in the day, while others are not. The useful approach is to learn the person’s pattern, address reversible factors such as pain, infection, dehydration, medication effects or sensory barriers, and choose a time and setting that gives them the best chance to decide. If a non-urgent decision can safely wait until capacity is likely to improve, delaying it may be the least restrictive option.

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).

Sources and further reading

• NICE: Decision-making and mental capacity (NG108)
• Mental Capacity Act 2005 Code of Practice
• Adults with Incapacity (Scotland) Act 2000

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