01Approach to the Critical Patient/attcp63

Immediate threats

›Resuscitation priorities

›Airway risk

›Stridor

›Inability to protect airway

›Altered mental status

›Breathing failure

›SpO2 persistently low despite supplemental oxygen

›Rising work of breathing

›Exhaustion

›Circulatory shock

›Hypotension

›Mottling

›Lactate elevation with hypoperfusion concern

›High consequence complications

›Severe pneumonia

›Myocarditis

›Encephalopathy

›Secondary bacterial sepsis

Infection control

›Transmission controls

›Droplet precautions

›Surgical mask for staff and patient

›Eye protection for close contact

›Airborne precautions triggers

›Aerosol generating procedures

›Intubation

›Nebulized therapy

02History/hx65

Symptom pattern and timing

›Illness timeline

›Symptom onset date and time

›Under 48 hours

›Over 48 hours

›Fever pattern

›Persistent fever over 3 days

›Recurrent fever after improvement

›Respiratory symptoms

›Cough

›Sore throat

›Rhinorrhea

›Dyspnea

›Pleuritic pain

›Systemic symptoms

›Myalgias

›Headache

›Profound fatigue

›Gastrointestinal symptoms

›Vomiting

›Diarrhea

Risk and exposure

›Exposure context

›Household influenza like illness

›High risk household members

›Outbreak setting

›Long term care

›Shelter

03Physical Exam/exam43

Vitals and general

›Severity markers

›Temperature

›Persistent fever

›Hypothermia

›Heart rate

›Tachycardia out of proportion to fever

›Blood pressure

›Hypotension

›Respiratory rate

›Tachypnea

›SpO2 on room air

›Hypoxemia

›Mental status

›Delirium

›Lethargy

›Hydration status

›Dry mucous membranes

›Capillary refill

›Orthostasis

Respiratory

›Lung assessment

›Work of breathing

›Accessory muscle use

›Inability to speak full sentences

›Auscultation

›Focal crackles

›Diffuse wheeze

04Differential Diagnosis/ddx26

Viral and atypical respiratory

›Respiratory viral syndromes

›COVID-19

›Overlapping influenza like illness

›RSV infection

›Parainfluenza

›Human metapneumovirus

›Atypical pneumonias

›Mycoplasma pneumonia

›Chlamydophila pneumonia

Bacterial and high risk mimics

›Bacterial infections

›Community acquired pneumonia

›Streptococcus pneumoniae

›Staphylococcus aureus including MRSA

›Haemophilus influenzae

›Streptococcal pharyngitis

›Pertussis

›Life threatening mimics

›Sepsis syndrome

›Pulmonary embolism

›Acute coronary syndrome

›Meningitis

Coding aligned problem list

›Influenza coding anchors

›ICD-10 J09 influenza due to identified zoonotic or pandemic influenza virus

›ICD-10 J10 influenza due to other identified influenza virus

›ICD-10 J11 influenza due to unidentified influenza virus

05Laboratory Tests/lt23

Core labs by severity

›Baseline assessment

›Complete blood count for severe illness

›Leukocytosis secondary bacterial infection concern

›Leukopenia immunosuppression marker

›Electrolytes and renal function for dehydration and dosing

›Creatinine clearance estimation for oseltamivir adjustment

›Hyponatremia in severe infection concern

›Liver enzymes for systemic illness

›Hepatic dysfunction for differential and medication safety

›Sepsis and organ dysfunction

›Lactate for shock concern

›Serial trend for resuscitation response

›Blood cultures for pneumonia or sepsis concern

›Before antibiotics when feasible

›Venous blood gas for respiratory failure assessment

›pCO2 in mmHg

›Targeted labs for complications

›Troponin for myocarditis concern

›Serial testing if ongoing symptoms

›Creatine kinase for myositis or rhabdomyolysis concern

›Kidney injury risk linkage

›Pregnancy test when status uncertain

›Antiviral and imaging planning

06Diagnostic Tests/dt54

Scoring Systems

›Risk stratification tools

›NEWS2 for clinical deterioration risk

›Escalation thresholds per local protocol

›qSOFA for sepsis risk screen

›Altered mentation

›Respiratory rate 22 per minute or higher

›Systolic blood pressure 100 mmHg or lower

›CURB-65 for pneumonia disposition support

›Confusion

›Urea

›Respiratory rate 30 per minute or higher

›Blood pressure low threshold

›Age 65 years or older

›IDSA ATS severe CAP criteria for ICU consideration

›Major criteria

›Minor criteria count

MRI

›Neurologic complications imaging

›MRI brain indications

›Encephalitis concern

›Persistent altered mental status without alternative explanation

›MRI brain findings

›Temporal lobe signal abnormalities

›Diffuse inflammatory changes

›MRI limits

›Not a primary influenza diagnostic test

›Time and stability requirements

07Disposition/dispo30

Discharge criteria

›Safe outpatient pathway

›Clinical stability

›Normal mentation

›No respiratory distress

›SpO2 stable on room air or baseline oxygen

›Hydration adequacy

›Oral intake tolerated

›No persistent vomiting

›Follow up feasibility

›Reliable access within 24 to 48 hours

›Return precautions understood

›Antiviral plan

›High risk and treatment initiated or arranged

Admission criteria

›Inpatient indications

›Hypoxemia requiring supplemental oxygen

›Moderate to severe respiratory distress

›Hemodynamic instability

›Altered mental status

›Severe dehydration or unable to maintain intake

›Significant comorbidity decompensation

›Complication concern

›Pneumonia

›Myocarditis

›Encephalitis

ICU criteria

›Critical care indications

08Treatment/t90

Supportive care

›Symptom and physiologic support

›Oxygen therapy

›Nasal cannula for mild hypoxemia

›High flow nasal oxygen for escalating needs

›Noninvasive ventilation for selected patients

›Intubation if failing noninvasive support

›Fluids

›Oral rehydration for mild dehydration

›IV crystalloids for significant dehydration or shock

›Antipyretics and analgesia

›Acetaminophen per local formulary

›NSAID per renal and GI risk

›Antiemetics

›Persistent vomiting with dehydration risk

Antiviral therapy

›Neuraminidase and endonuclease inhibitors

›Timing and priority

›Initiate as soon as possible for hospitalized and high risk

›Most benefit when started within 48 hours in uncomplicated outpatient illness

›Longer duration for severe or immunocompromised may be needed

›Oseltamivir oral

›Adults treatment

›75 mg twice daily for 5 days

›Extend duration for severe illness per clinical judgment

›Children treatment

›Under 1 year

›3 mg/kg per dose twice daily for 5 days

09Special Populations/sp29

Pregnancy

›Maternal fetal considerations

›Higher risk of severe influenza and complications

›Lower threshold for treatment and admission

›Antiviral selection

›Oseltamivir preferred in pregnancy

›Most safety data among antivirals

›Chemoprophylaxis after close contact

›Oseltamivir 75 mg once daily for 7 days after last exposure

›Breastfeeding

›Oseltamivir compatible

›Less than 1% excreted in breast milk

Geriatric

›Older adult risks

›Atypical presentation

›Minimal fever

›Delirium as primary symptom

›Antiviral prioritization

›Treat regardless of time since onset when hospitalized or high risk

›Vaccination preference age 65 years or older

›High dose inactivated vaccine option

›Recombinant vaccine option

›Adjuvanted inactivated vaccine option

Pediatrics

›Child specific considerations

›Higher dehydration risk

›Early oral rehydration strategy

›Antiviral age thresholds

10Background/b29

Epidemiology

›Seasonal patterns and prevention

›Annual vaccination recommendation

›Canada vaccine offered annually to age 6 months and older without contraindication

›2025 to 2026 vaccine composition

›Trivalent formulation

›A H1N1 component

›A H3N2 component

›B Victoria lineage component

Pathophysiology

›Disease mechanism

›Influenza A and B viral replication in respiratory epithelium

›Epithelial injury

›Cytokine mediated systemic symptoms

›Complication pathways

›Viral pneumonia with diffuse alveolar damage

›Secondary bacterial pneumonia from mucociliary dysfunction

›Myocarditis from inflammatory injury

›Encephalopathy from systemic and direct effects

Therapeutic Considerations

›Evidence framework

›Antivirals shorten illness and reduce complications in high risk populations when started early

›Treatment recommended for uncomplicated ambulatory illness

›Oseltamivir 5 days

›IDSA A-I

›Zanamivir 5 days

›IDSA A-I

›Peramivir single dose

11Patient Discharge Instructions/pdi27

copy discharge instructions

›Home care plan

›Hydration

›Frequent oral fluids

›Oral rehydration solution if vomiting or diarrhea

›Fever and pain control

›Acetaminophen per label directions

›NSAID per label directions if safe for kidneys and stomach

›Infection prevention

›Mask around others when symptomatic

›Hand hygiene

›Avoid close contact with high risk people until improving

›Antiviral adherence when prescribed

›Complete full course

›Return to ED immediately

›Trouble breathing

›Blue or grey lips

›Chest pain

›New confusion

›Fainting

›Signs of dehydration

›No urination for 8 hours

›Unable to keep fluids down

›Fever or symptoms improving then suddenly worsening

›Severe weakness preventing normal activity

›Follow up

›Primary care within 24 to 48 hours if high risk

›Earlier follow up for worsening cough or dyspnea

12References/r13

Clinical guidelines and public health

›Key sources

›CDC influenza antiviral medications summary for clinicians

›CDC antiviral dosing table for treatment and chemoprophylaxis

›IDSA seasonal influenza clinical practice guideline

›CDC rapid influenza diagnostic tests clinician guidance

›CDC ACIP influenza vaccine recommendations summary

›NACI statement on seasonal influenza vaccines 2025 to 2026

›ACOG influenza in pregnancy prevention and treatment practice advisory

›Ontario Health recommendations for antiviral therapy of seasonal influenza

Evidence grading notes

›Grading notes

›IDSA uses graded recommendations including A-I strength and quality

›ACEP Level A B C policy statements not identified for seasonal influenza antiviral selection

›Class I IIa IIb terminology not routinely used in influenza guidelines

Evidence & Review

Evidence & Review