A person is judged to have mental capacity if they can understand and retain information for long enough to consider its meaning and merits and can then communicate their decision to others.

In order to protect people who are deemed to lack capacity and to enable them in so far as is possible to be a part of their health‐related decision making, the following statutory principles apply:

Within the environment of a busy hospital, emergencies can be challenging to manage. The nature of the emergency may be such that there is insufficient time to conduct all necessary investigations and to consult with all the relevant people; as a result, there is the potential for capacity to be misjudged. The Mental Capacity Act ([176]) states that in these situations, when a nurse or other healthcare professional has acted in the best interests of the patient, they will not be liable for that decision and the following actions. These actions can include restraint if it is judged to be proportionate and necessary to prevent harm (Section 6), and even ‘a deprivation of liberty’ if this is necessary for ‘life sustaining treatment or a vital act’ while a court order is sought if need be (Section 4B).

The Mental Capacity Act ([176]) and the Mental Capacity Act Code of Practice ([177]) apply to people aged 16 years or older in England and Wales. Nurses must have due regard for the legislation and statutory guidance and apply this appropriately in their practice.

The Mental Capacity Act ([176]) provided the legal framework for the creation of the Independent Mental Capacity Advocate (IMCA). The IMCA helps vulnerable people who lack capacity and are facing important decisions, including serious healthcare treatment decisions, and who have nobody to speak for them. Local IMCA services and organization safeguarding leads can advise when the involvement of the IMCA may be appropriate, for example when a patient who lacks capacity has no appropriate person to speak on their behalf with respect to a serious medical treatment or a change in accommodation.

It is prudent to identify patients who lack capacity, or who are likely to lack capacity in the future, and ascertain whether they have communicated or delegated their decision making in advance. Declarations (some of which are legally binding and some of which are not) can inform best interests decisions and care plans (Box 5.25).

Assessment of capacity involves a two‐stage test (Figure 5.22). Before assessing a person's capacity to make a decision, it is important to be clear about what decision the patient is required to make, so that the capacity decision is specific. Capacity is a fluctuating state and must therefore be assessed each time a decision is made:

If someone is assessed as lacking capacity and is therefore unable to consent to or refuse a medical test or treatment, then nurses and their colleagues need to act in the patient's best interests. This is best achieved by working with the patient, other healthcare staff and, where applicable and appropriate, the patient's carers (Box 5.26).

Following an assessment of capacity and any best interest decisions, nurses must consider the tasks of confidentiality, communication, record keeping (Box 5.27) and reporting. Nurses must follow local policies and procedures, and seek guidance from their manager as appropriate.