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Approach to the Critical Patient
Immediate priorities
Immediate priorities
Airway risk
GCS 8 or less
Recurrent seizures
Loss of protective reflexes
Severe agitation needing deep sedation
Breathing
SpO2 target 94 to 98 percent
End tidal CO2 monitoring if intubated
Circulation
Two large bore IV
Hypotension trigger for sepsis pathway
MAP target 65 mmHg or higher
Glucose
Point of care glucose
If hypogly.reqia then dextrose per protocol
Temperature
Hyperthermia control
Hypothermia evaluation
Exposure and safety
Toxic ingestion screening triggers
Restraint only if immediate danger
Time critical disease control
Time critical disease control
Empiric antiviral and antibacterial coverage
If encephalitis suspected then acyclovir without delay
If meningitis cannot be excluded then add empiric antibiotics
Seizure control
If convulsive seizure then benzodiazepine first line
If status epilepticus then second line antiseizure medication
Raised intracranial pressure risk
Head of bed 30 degrees
Neck midline
Avoid hypotension
Avoid hypoxia
Isolation
Droplet precautions until meningococcal excluded
Consultation and escalation
Consultation and escalation
Early ICU involvement
Declining mental status
Refractory seizures
Shock
Respiratory failure
Infectious diseases
All suspected encephalitis admissions
Immunocompromised hosts
Neurology
Seizures
Focal deficits
Suspected autoimmune encephalitis
Public health triggers
Suspected arboviral encephalitis
Cluster cases
Travel related exposure
History
Core syndrome features
Core syndrome features
Altered mental status timeline
Hours to days
Subacute weeks
Fever
Peak temperature
Antipyretic response
Seizures
First time seizure
Focal onset features
Headache
Severe or progressive
Thunderclap trigger for SAH workup
Focal neurologic symptoms
Aphasia
Hemiparesis
Cranial nerve findings
Psychiatric or behavioral change
New paranoia
New hallucinations
Catatonia
Exposures and risks
Exposures and risks
Infectious exposures
Sick contacts
Childcare exposure
Institutional living
Travel and vectors
Recent travel region
Mosquito exposure
Tick exposure
Animal exposures
Bat exposure
Raccoon or skunk exposure
Sexual exposure
New partners
HIV risk
Immunocompromise
Transplant
Steroids
Biologics
Cancer therapy
Vaccination status
Varicella
MMR
Meningococcal
Japanese encephalitis if relevant
Medical context and pitfalls
Medical context and pitfalls
Recent infection
URI prodrome
Gastroenteritis prodrome
Recent rash
Vesicular rash
Dermatomal pain
Medication and toxin risks
Anticholinergics
Serotonergic agents
Withdrawal risk
Autoimmune clues
New cancer diagnosis
Ovarian teratoma risk symptoms
Personal autoimmune disease
Cardiorespiratory symptoms
Chest pain
Dyspnea
Palpitations
Physical Exam
Neurologic exam focus
Neurologic exam focus
Mental status
Orientation
Attention
Language
Memory
Focal deficits
Motor asymmetry
Sensory asymmetry
Visual field deficit
Gaze preference
Meningeal signs
Nuchal rigidity
Photophobia
Movement disorders
Orofacial dyskinesia
Chorea
Myoclonus
Autonomic instability
Labile BP
Tachycardia
Hyperthermia
General and systemic exam
General and systemic exam
Vitals and perfusion
Fever
Hypotension
Hypoxia
Skin and mucosa
Petechiae or purpura
Vesicles
Eschar
HEENT
Otitis or mastoid tenderness
Sinus tenderness
Cardiopulmonary
Murmur
Endocarditis stigmata
Abdomen
Hepatosplenomegaly
Trauma
Head trauma signs
PITFALLS
PITFALLS
Normal neck exam does not exclude encephalitis
Afebrile presentation in elderly or immunocompromised
Focal deficits may mimic ischemic stroke
Agitation may be misattributed to intoxication
Differential Diagnosis
Life threatening and treatable causes
Life threatening and treatable causes
HSV encephalitis
ICD 10 B00.4
Temporal lobe features
Bacterial meningitis with encephalopathy
ICD 10 G00.9
Rapid decline
Brain abscess
ICD 10 G06.0
Focal deficit with fever
Subarachnoid hemorrhage
ICD 10 I60.9
Thunderclap headache
Intracerebral hemorrhage
ICD 10 I61.9
Ischemic stroke with delirium
ICD 10 I63.9
Nonconvulsive status epilepticus
SNOMED CT concept status epilepticus
Toxic metabolic encephalopathy
Hypoglycemia
Hyperammonemia
Hypoxia
Hyponatremia
Mimics and related syndromes
Mimics and related syndromes
Autoimmune encephalitis
Anti NMDA receptor encephalitis
Limbic encephalitis
Acute disseminated encephalomyelitis
Post infectious
Viral meningitis
Enterovirus
CNS vasculitis
Primary angiitis of CNS
Wernicke encephalopathy
Thiamine deficiency
Thyroid storm or myxedema coma
Heat stroke
Serotonin syndrome
Neuroleptic malignant syndrome
Laboratory Tests
Initial blood tests
Initial blood tests
CBC with differential
Leukocytosis support for infection
Leukopenia risk in immunocompromise
Electrolytes and renal function
Sodium for seizure risk
Creatinine for acyclovir dosing
Liver panel
Hepatic encephalopathy context
CRP or ESR
Inflammatory signal support
Blood cultures
Before antibiotics if feasible
Serum glucose
Concurrent with CSF glucose interpretation
Targeted infectious labs
Targeted infectious labs
HIV testing
If risk factors or severe infection
Syphilis serology
If subacute neuropsychiatric syndrome
Respiratory viral PCR
If influenza like illness
Arboviral serology region dependent
West Nile virus IgM serum
CSF studies
CSF studies
Opening pressure
Elevated support for ICP risk
Cell count and differential
Lymphocytic predominance typical viral
Neutrophilic early viral possible
Protein g/L
Elevated common in infection
Glucose mmol/L
Low support for bacterial or TB or fungal
CSF to serum glucose ratio
Low ratio support for bacterial
Gram stain and culture
Highest yield before antibiotics
HSV 1 and 2 PCR
High sensitivity after 24 hours symptoms
VZV PCR
If rash or immunocompromised
Enterovirus PCR
More common in children
Cryptococcal antigen
HIV or immunocompromised
TB NAAT and AFB smear and culture
Subacute meningitis features
Oligoclonal bands and IgG index
If autoimmune demyelinating concern
Autoimmune encephalitis panel
If psychiatric dominant or dyskinesias
Diagnostic Tests
Scoring Systems
Scoring Systems
Glasgow Coma Scale use
Trend for airway and ICU triggers
Limitation sedation confounds
qSOFA sepsis screen
Altered mentation
RR 22 or higher
SBP 100 mmHg or lower
Graus criteria autoimmune encephalitis framework
Subacute onset less than 3 months
Working memory deficit or altered mental status or psychiatric symptoms
At least one supportive feature
New focal CNS findings
New seizures
CSF pleocytosis
MRI suggestive encephalitis
Exclusion of alternative causes
MRI
MRI
MRI brain with and without gadolinium
Preferred for encephalitis localization
Limbic system involvement support for HSV or autoimmune
Sequences
DWI for infarct
FLAIR for edema
SWI for hemorrhage
Contraindications
Non compatible implant
Severe instability
Evidence notes
Higher sensitivity than CT for early encephalitis patterns
CT
CT
Noncontrast CT head
Rule out hemorrhage
Mass effect screening before LP
CT angiography head and neck
If stroke mimic concern
If vasculitis or RCVS consideration
CT chest abdomen pelvis
If malignancy search for paraneoplastic syndrome
ACEP evidence framing
CT head before LP if focal deficit or immunocompromised or new seizure or papilledema or altered level of consciousness
ACEP Level B recommendation common practice pattern for imaging triggers before LP
Ultrasound (or US)
Ultrasound (or US)
POCUS for shock states
IVC assessment
Cardiac function
Pericardial effusion
Optic nerve sheath diameter
Elevated ICP support in experienced hands
Limitation operator dependent
Lung ultrasound
Aspiration pneumonitis
Pulmonary edema
Disposition
Level of care
Level of care
ICU admission criteria
GCS 12 or less
Recurrent seizures
Need for ventilatory support
Vasopressor requirement
Concern for elevated ICP
Ward admission criteria
Stable airway
No shock
Controlled seizures
Clear diagnosis and improving course
Transfer criteria
Need for neuro ICU
Need for continuous EEG not available
Need for neurosurgical capability
Follow up planning
Follow up planning
Infectious diseases follow up
Antiviral duration planning
Pending culture review
Neurology follow up
Seizure plan
Cognitive rehab referral
Public health reporting
Arboviral suspected or confirmed
Treatment
Empiric antimicrobials
Empiric antimicrobials
Acyclovir IV
Initiate immediately if encephalitis suspected
Dose 10 mg per kg IV every 8 hours
Use ideal body weight for obesity
Renal adjustment required
Hydration to reduce nephrotoxicity
Isotonic fluids if not contraindicated
Duration
HSV confirmed 14 to 21 days
If initial HSV PCR negative but high suspicion then repeat PCR 24 to 48 hours
Empiric bacterial meningitis coverage when not excluded
Ceftriaxone IV 2 g every 12 hours
If meningococcal risk continue droplet precautions until 24 hours effective therapy
Vancomycin IV weight based dosing
Target trough per local protocol
Ampicillin IV 2 g every 4 hours
Add if age 50 or older
Add if immunocompromised
Listeria coverage
If severe beta lactam allergy then alternative per local antibiogram
Dexamethasone for suspected pneumococcal meningitis
Initiate with or before first antibiotic dose
Dose 10 mg IV every 6 hours for 4 days
Stop if non pneumococcal etiology confirmed
Seizure management
Seizure management
Benzodiazepine first line for active seizure
Lorazepam IV 0.1 mg per kg
Maximum 4 mg per dose
Repeat once if needed
Midazolam IM 10 mg if no IV access
Second line antiseizure medication
Levetiracetam IV 60 mg per kg loading
Maximum 4500 mg
Maintenance 1000 to 1500 mg every 12 hours
Valproate IV 40 mg per kg loading
Maximum 3000 mg
Avoid in pregnancy and severe liver disease
Fosphenytoin IV 20 mg PE per kg loading
Cardiac monitoring
Refractory status epilepticus pathway
Continuous EEG
ICU sedation protocol per local guideline
Intracranial pressure and cerebral edema
Intracranial pressure and cerebral edema
Supportive measures
Head elevation 30 degrees
Normocapnia target PaCO2 35 to 40 mmHg
Normoxia target PaO2 80 mmHg or higher
Normoglycemia target 4 to 10 mmol/L
Hyperosmolar therapy if herniation concern
Mannitol IV 0.5 to 1 g per kg
Avoid hypotension
Monitor osmolality
Hypertonic saline 3 percent IV 2 mL per kg bolus
Sodium monitoring
Avoid rapid correction in chronic hyponatremia
Neurosurgery involvement triggers
Mass lesion
Hydrocephalus
Refractory elevated ICP
Autoimmune encephalitis immunotherapy
Autoimmune encephalitis immunotherapy
First line immunotherapy after exclusion of uncontrolled infection
Methylprednisolone IV 1 g daily for 3 to 5 days
Glucose monitoring
GI prophylaxis if high risk
IVIG 0.4 g per kg daily for 5 days
Thrombosis risk assessment
Renal function monitoring
Plasma exchange 5 to 7 exchanges
Central access planning
Second line therapies specialist directed
Rituximab
Cyclophosphamide
Tumor screening and treatment
Ovarian teratoma evaluation
Age appropriate malignancy screening
Supportive care
Supportive care
Fever management
Acetaminophen dosing per weight
Cooling measures if severe hyperthermia
Delirium and agitation
Lowest effective sedation
Avoid anticholinergic burden
VTE prophylaxis
Mechanical until bleeding risk clarified
Pharmacologic per inpatient protocol when safe
Nutrition and aspiration prevention
Swallow assessment if extubated and dysphagic
Renal protection
Avoid nephrotoxins with acyclovir
Special Populations
Pregnancy
Pregnancy
Diagnostic considerations
MRI preferred when feasible
CT acceptable if emergent
Medication considerations
Acyclovir generally considered acceptable when indicated
Avoid valproate if possible
Obstetric involvement
Fetal monitoring if viable gestational age
Pre eclampsia mimic evaluation
Geriatric
Geriatric
Atypical presentations
Afebrile infection
Delirium predominant
Pathogens
Listeria risk higher
VZV reactivation higher
Medication risk
Renal dosing for acyclovir
Higher delirium sensitivity to sedatives
Pediatrics
Pediatrics
Age specific pathogens
Enterovirus common
HSV in neonates
Weight based dosing
Acyclovir 10 to 20 mg per kg IV every 8 hours by age and protocol
Ceftriaxone 50 mg per kg IV every 12 hours
LP considerations
Lower threshold for rapid viral PCR panels
Early pediatric ICU involvement for seizures
Background
Epidemiology
Epidemiology
Incidence
Encephalitis rare but high morbidity
Common infectious causes
HSV 1 leading sporadic cause in many regions
Arboviruses region and season dependent
Autoimmune encephalitis recognition increasing
Anti NMDA receptor common in young patients
Pathophysiology
Pathophysiology
Infectious encephalitis mechanisms
Direct viral neuronal invasion
Immune mediated injury
HSV tropism
Limbic and temporal lobe predilection
Hemorrhagic necrosis risk
Autoimmune encephalitis mechanisms
Synaptic receptor antibodies
Paraneoplastic immune activation
Complications
Cerebral edema
Seizures
SIADH and hyponatremia
Therapeutic Considerations
Therapeutic Considerations
Time dependence
Early acyclovir associated with improved outcomes in HSV encephalitis
Empiric strategy rationale
High consequence of missing HSV
Early bacterial meningitis overlap
Immunotherapy timing
Delay worsens autoimmune encephalitis outcomes in many cohorts
Evidence framing
Class I recommendation expert consensus for immediate acyclovir in suspected HSV encephalitis
Class I recommendation sepsis bundles for shock physiology
ACEP Level C support for CT before LP in high risk features
Patient Discharge Instructions
copy discharge instructions
copy discharge instructions
Discharge eligibility uncommon
Alternative diagnosis established
Normal neuro exam
Stable vitals
Reliable follow up within 24 to 72 hours
Home care
Hydration
Rest and sleep hygiene
Avoid alcohol and recreational drugs
Return to ED now
New or worsening confusion
New seizure
Severe or worsening headache
Fever or rigors
Neck stiffness
New weakness or trouble speaking
Persistent vomiting
Follow up
Primary care or neurology as arranged
Review pending test results plan
References
Guidelines and key sources
Guidelines and key sources
Infectious Diseases Society of America encephalitis guidance
Empiric acyclovir for suspected encephalitis
CSF HSV PCR testing
American Academy of Neurology guidance on status epilepticus management
Benzodiazepine first line
Second line antiseizure options
Graus et al clinical approach to autoimmune encephalitis criteria
Subacute psychiatric or cognitive syndrome framework
CDC resources on arboviral encephalitis testing and reporting
West Nile virus IgM guidance
Source instructions file
SymptomDx is an educational tool for medical professionals. It does not replace clinical judgment. Verify all clinical data and drug dosages with authoritative sources.