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OverviewAetiologyPathophysiologyClinical features and red flagsInvestigationsDifferential diagnosisManagementComplicationsMonitoring and follow-upSpecial situationsCommon pitfallsQuestionsSources
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Educational draft · awaiting clinical reviewThe full textbook explains uncertainty but does not replace live national or local guidance, specialist advice, or current prescribing information.

Mental illness in critical and acute medical care

Psychiatry · UK scope · Sources checked 7 Sept 2026 · Clinical review pending

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Do not miss a physical cause or medicine emergency

New confusion, rigidity, severe agitation, suicidal intent, marked sedation or abrupt loss of function during acute admission can reflect life-threatening illness or psychotropic toxicity.

Action: Reassess physiology and medicines immediately, obtain senior medical and liaison input together, and treat urgent causes while making a specific plan for safety and essential medication.

Overview

Integrate psychiatric and physical assessment during acute illness, protect continuity of essential treatment and identify psychological and cognitive needs throughout recovery from critical care.

A general hospital admission can expose the interaction between mental illness, physiological stress and treatment. A patient may arrive with established bipolar disorder and develop delirium from infection, or experience panic and nightmares after ventilation without a previous psychiatric diagnosis. The clinical task is to establish the time course and meaning of symptoms, examine physical contributors and arrange coordinated treatment. Responsibility should be shared explicitly so that neither team assumes the other has dealt with a problem.

Begin with the person's usual function and treatment. Clarify existing diagnoses, previous admissions, early relapse signs, helpful approaches and communication needs. Medication reconciliation must capture what was actually taken, not only what appears on a repeat list. Ask about depot antipsychotics, clozapine supply and monitoring, lithium, benzodiazepine dependence and substance use. A patient who is nil by mouth or too unwell to request medication can develop withdrawal, relapse or an avoidable treatment interruption.

Aetiology

01

Pre-existing psychiatric illness

Established mood, psychotic or anxiety disorders may complicate admission through relapse, treatment interruption or distress, alongside rather than instead of the physical illness.

02

Illness and treatment effects

Inflammation, organ failure, intensive-care experiences, drug interactions and altered sleep can generate new cognitive or emotional symptoms during the acute episode and recovery.

Pathophysiology

  1. 1
    Changing drug exposure

    Acute renal or hepatic dysfunction and altered enzyme activity can change psychotropic concentrations, so a previously tolerated maintenance dose may produce adverse effects.

  2. 2
    Brain and bodily stress

    Severe illness disrupts attention and sleep while pain, breathlessness and invasive treatment create threat, with interacting cognitive, autonomic and emotional consequences.

  3. 3
    Recovery and memory

    Fragmented recollection, weakness and loss of control may shape later anxiety or trauma symptoms, particularly when frightening experiences remain unexplained after physiological stabilisation.

Clinical features and red flags

Acute cognitive change

Fluctuating attention, disorientation or altered arousal favours delirium and requires medical investigation rather than immediate attribution to psychiatric relapse.

Relapse pattern

A familiar sequence of reduced sleep, increased activity, fixed beliefs or mood change may indicate recurrence, particularly after missed treatment.

Treatment-related syndrome

New tremor, ataxia, dysphagia, rigidity, severe constipation or excess sedation may signal adverse effects that worsen during physical illness.

Post-critical-care distress

Nightmares, intrusive memories, avoidance, low mood or persistent anxiety can impair rehabilitation and deserve assessment in their own right.

Red flags requiring action

  • Fever with rigidity, clonus, a falling level of consciousness or autonomic instability requires urgent assessment for toxicological syndromes, infection and neurological disease.
  • Clozapine treatment interrupted for more than forty-eight hours must not be restarted at the previous maintenance dose; arrange specialist retitration.

Investigations

  1. 01
    Joint timeline and collateral historyFirst step
    Why
    Separate baseline mental illness from changes linked to the admission, treatment and recovery.
    Interpretation and limitations
    Align symptoms with infection, procedures, sedation, missed medication and sleep disruption; several mechanisms can coexist rather than compete for one diagnosis.
  2. 02
    Physiological and delirium assessment
    Why
    Identify acute brain dysfunction and reversible physical contributors to altered behaviour.
    Interpretation and limitations
    Use critical-care instruments in ICU and setting-appropriate assessment elsewhere; mental-health referral does not remove the need to investigate deterioration.
  3. 03
    Psychotropic reconciliation and pharmacy review
    Why
    Verify doses, last administration, interactions and whether formulations remain suitable.
    Interpretation and limitations
    Look beyond electronic repeat lists for specialist-supplied medicines; swallowing difficulty, feeding tubes and treatment breaks may change administration and restart requirements.
  4. 04
    Targeted safety tests and concentrations
    Why
    Investigate toxicity or altered exposure when symptoms and illness create a specific concern.
    Interpretation and limitations
    Select ECG, electrolytes, organ function, relevant blood counts and drug concentrations with timing documented; results need interpretation against the clinical picture and last dose.

Differential diagnosis

01

Delirium

An acute fluctuating attention disorder should be assessed as medical brain dysfunction, even when hallucinations or a prior psychiatric diagnosis dominate the initial account.

02

Medication toxicity or withdrawal

The timing of symptoms relative to missed treatment, organ dysfunction or new prescriptions may identify a reversible cause of sedation, agitation or neurological change.

03

Depressive or trauma-related disorder

Persistent low mood, hopelessness, avoidance or intrusive recollections need assessment beyond immediate physiological stress, with attention to duration, impairment and safety.

Management

01Acute admissionBuild a joined treatment planFirst stepA patient with mental illness or psychotropic treatment is admitted to a medical or critical-care service.+
  1. 1Document usual function, essential treatment, contact details and reasonable adjustments, obtaining collateral information and pharmacy input early.
  2. 2Review immediate medical threats, delirium, withdrawal and self-harm risk, with a named clinician responsible for each active problem.
  3. 3AlternativeDecide explicitly which medicines continue, pause or require an alternative route, and specify review, monitoring and restart criteria in the record.
02New psychiatric symptomsAssess the whole clinical contextFear, withdrawal, unusual beliefs, agitation or low mood emerges during physical treatment.+
  1. 1Check oxygenation, glucose, pain, attention, sleep, infection and new drug effects before attributing the change to a primary psychiatric syndrome.

Complications

01

Preventable relapse

Interrupted essential treatment or poorly coordinated transfer may precipitate a psychiatric deterioration that delays physical recovery and increases readmission risk.

02

Toxicity and interactions

Changes in metabolism, clearance and co-prescribing can cause hypotension, sedation, arrhythmia or neurological injury unless medication plans adapt to the acute illness.

03

Impaired rehabilitation

Cognitive difficulty, fear, depression and weak continuity of care can limit participation, prolong dependence and place additional strain on patients and families.

Monitoring and follow-up

  • Review medication changes at every transfer and daily during rapidly changing organ function, infection or sedation requirements; document the reasons for ongoing holds.
  • Follow attention, sleep, mood, psychotic symptoms and participation in rehabilitation alongside physiological recovery, and obtain the patient's account when communication improves.
  • Monitor for withdrawal or relapse after missed medicines and for toxicity when interacting treatment or smoking status changes during admission.
  • Ensure discharge prescriptions, specialist monitoring responsibilities and the actual available medicine supply match the agreed plan before the patient leaves.
  • Reassess psychological and cognitive recovery after discharge, including family strain, work, driving questions and practical support needs that may not have been evident in hospital.

Special situations

Specialist medicines can disappear

Clozapine supplied outside primary care may be absent from a routine prescription list, so the patient, monitoring service and treating team may be essential sources.

A belief may outlast delirium

A frightening memory formed during critical illness can remain emotionally powerful after attention returns, requiring explanation and support rather than dismissive correction.

Capacity changes with the decision

A person may understand a simple blood test while struggling to weigh a complex discharge plan, especially with fatigue, delirium or communication barriers.

A treatment break is clinical

Missed doses caused by supply, swallowing or administrative problems can alter restart safety; the duration of interruption must be treated as prescribing information.

Common pitfalls

  1. 01

    Using a psychiatric diagnosis to explain breathlessness, confusion or abnormal observations without a fresh physical assessment.

  2. 02

    Continuing the home psychotropic doses unchanged despite new renal impairment, serious infection or cessation of smoking.

  3. 03

    Stopping every psychiatric medicine during admission without considering withdrawal, relapse, formulation alternatives or safe retitration.

  4. 04

    Interpreting inability to speak while intubated as inability to understand or participate in decisions.

  5. 05

    Discharging with a list of medicine changes but no explanation, specialist contact or plan for the monitoring needed to maintain them.

Practice

Two practice questions

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Question 1 of 2
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PsychiatryOriginal SBA

Clozapine after missed treatment

A medical inpatient usually takes clozapine 350 mg nightly. Supply difficulties mean the last dose was three days ago. The patient can now swallow and the old dose is copied onto the chart. What should happen?

Choose one answer, then submit
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Sources and review status4 sources · checked 7 Sept 2026 · clinical review pending+
Sources

Sources and review status

National guidance is shown before implementation-dependent detail. Typical adult dose examples remain subject to patient factors, contraindications and the live BNF or specialist protocol. Source check completed 7 Sept 2026; clinical approval remains outstanding.

  • NICE CG83 rehabilitation after critical illnessIntegrated physical, psychological and cognitive recovery and follow-up.
  • NICE CG103 delirium assessmentRecognition of acute cognitive change and critical-care instruments.
  • NHS SPS clinical considerations for clozapineTreatment breaks, infection, smoking and specialist liaison.
  • Clozaril 100mg tablets UK SmPCSpecific restart regimen and precautions after treatment interruption.

Editorial contact: Doctor’s Passport editorial team. Source-check date is separate from clinical approval. Report a content problem · Content changes

Authoring stateComplete draftClinical stateAwaiting reviewJurisdictionUnited Kingdom
Pharmacokinetic changes are especially important during infection and organ failure. Dehydration and reduced renal function can increase lithium exposure; infection and stopping tobacco smoking can raise clozapine concentrations. New antimicrobials, opioids, antiemetics and anaesthetic drugs may introduce interactions, QT effects or sedation. The correct response is an individual medicine review with pharmacy and the specialist team, including clear hold, restart and monitoring instructions rather than either automatic continuation or indiscriminate cessation.

Psychological assessment should be possible even when speech is limited. Use writing, picture boards, interpreters or supported yes/no communication and allow time for fatigue. Check pain, breathlessness and delirium before concluding that apparent withdrawal represents depression. Ask directly about fear, hopelessness and suicidal thoughts when appropriate. Unusual memories of intensive care can remain vivid after delirium resolves; explain what happened without dismissing the distress associated with those experiences.

Recovery involves more than survival of the acute episode. Weakness, altered appearance, disturbed sleep, cognitive difficulty, anxiety, depression and trauma symptoms can affect relationships and return to work. NICE recommends coordinated rehabilitation with goals and information transferred between teams, and review at two to three months after critical-care discharge for people with rehabilitation needs. Earlier assessment is required for urgent symptoms rather than waiting for a routine clinic.

Key points

  • Mental illness and acute physical illness require joint care; psychiatric history must not lower the standard of physical assessment.
  • New inattention or fluctuating consciousness is a possible delirium syndrome even when a patient already has psychosis or dementia.
  • Reconcile psychotropic medicines, actual last doses, depot dates, dependence-forming drugs and over-the-counter products early.
  • Acute infection, renal or hepatic dysfunction, smoking changes and interacting prescriptions can turn a stable psychotropic regimen into a toxic one.
  • Distinguish understandable fear and transient distress from persistent depressive, trauma-related, psychotic or catatonic syndromes.
  • Support communication for intubated, sensory-impaired or fatigued patients and assess capacity for each relevant decision.
  • Plan rehabilitation across critical care, the ward and discharge, including cognitive, psychological, family and practical needs.
  • 05
    Psychological and functional assessment
    Why
    Identify mood, trauma, cognitive and practical barriers to participation in recovery.
    Interpretation and limitations
    Distress may evolve after transfer or discharge; assess chosen goals and actual daily function rather than assuming a normal physiological recovery has resolved all needs.
  • 2Offer an adapted interview and supportive explanation, then seek liaison assessment for persistent symptoms, diagnostic uncertainty, capacity questions or safety concerns.
  • 3Agree a proportionate management plan combining physical treatment, psychological support, environmental adjustments and specific psychiatric therapy when indicated.
    • 03Recovery and transferPreserve continuity after critical careThe patient is moving to the ward, rehabilitation service or community after significant acute illness.+
    1. 1Reassess physical, cognitive and psychological function with the patient and family, setting achievable rehabilitation goals and explaining likely difficulties.
    2. 2Provide a medicines reconciliation with reasons for changes, outstanding tests, specialist contacts and arrangements for supply and blood monitoring.
    3. 3Arrange appropriate early follow-up and the NICE two- to three-month critical-care recovery review where rehabilitation needs exist, with urgent referral for worsening mental health.
    Key medicines and prescribing safety1 treatment · regimens, roles and cautions+
    Restore essential antipsychotic treatment safely after a significant interruption rather than restarting the full previous maintenance regimen.

    Clozapine after a treatment interruption

    When more than two days have elapsed since the last Clozaril dose, the cited UK SmPC requires re-initiation at 12.5 mg orally once or twice on the first day, followed by specialist-directed retitration according to tolerance and the clinical situation.

    Contact the treating clozapine team and monitoring service, confirm blood monitoring and supply, and assess infection, smoking change, hypotension, sedation and interactions. A prior history of serious cardiorespiratory reactions requires particular caution.