Mechanisms of Collapse in Influenza Patients
Influenza can cause collapse through multiple mechanisms including severe respiratory failure from primary viral pneumonia, cardiovascular complications like myocarditis, and neurological involvement leading to altered consciousness.
Primary Respiratory Mechanisms
Primary Viral Pneumonia
- Occurs within the first 48 hours of fever onset 1
- Characterized by:
- Rapid progression to respiratory failure
- Initially dry cough becoming productive with blood-stained sputum
- Cyanosis and tachypnea
- Bilateral crepitations and wheezing on examination
- Bilateral interstitial infiltrates on chest radiography
- High mortality rate (>40%) despite intensive care 1
- Death typically occurs within seven days of hospital admission
Secondary Bacterial Pneumonia
- More common than primary viral pneumonia (up to four times more frequent) 1
- Typically develops during early convalescent period (4-5 days after initial symptoms)
- Common pathogens include S. pneumoniae, S. aureus, and H. influenzae
- Mortality rates range from 7% to 24% 1
- Staphylococcal pneumonia carries particularly poor prognosis (mortality up to 47%) 1
Mixed Viral-Bacterial Pneumonia
- Shows features of both primary viral and secondary bacterial pneumonia
- Chest radiograph may show lobar consolidation superimposed on bilateral diffuse infiltrates
- High mortality rate (>40%) similar to primary viral pneumonia 1
Cardiovascular Mechanisms
Myocarditis and Pericarditis
- Can occur in severe influenza illness 1
- ECG abnormalities (ST segment deviation, T wave changes, rhythm disturbances) reported in up to 81% of hospitalized patients 1
- Necrotizing myocarditis has been found on postmortem examination even without clinically significant antemortem symptoms 1
- Can lead to cardiac dysfunction and circulatory collapse
Neurological Mechanisms
Encephalitis/Encephalopathy
- Manifests as decreased consciousness and seizures
- Typically occurs about three days after onset of respiratory symptoms 1
- Can lead to altered mental status and collapse
- May be accompanied by focal neurological signs 1
- Abnormal CT/MRI findings associated with poor outcomes 1
Acute Necrotizing Encephalopathy
- Rare but fulminant syndrome associated with multifocal brain lesions 1
- Can lead to rapid neurological deterioration and collapse
Other Contributing Mechanisms
Myositis
- Typically develops after subsidence of acute respiratory symptoms
- Usually affects gastrocnemius and soleus muscles 1
- Rarely associated with myoglobinuria and renal failure, which can contribute to circulatory collapse 1
Reye's Syndrome
- Characterized by encephalopathy and acute fatty liver
- Associated with aspirin use and high mortality (~40%) 1
- More common in children but can occur in adults
Toxic Shock Syndrome
- Can occur in conjunction with secondary S. aureus infection 1
- Leads to systemic vasodilation and circulatory collapse
Risk Factors for Collapse
- Pre-existing chronic cardiac and respiratory conditions 1
- Age >65 years or very young children 1
- Immunocompromised status 2
- Pregnancy 2
Clinical Pearls
- The risk of collapse is highest in the first week of illness, particularly in patients with primary viral pneumonia 1
- Rapid clinical deterioration with respiratory failure can occur within days of symptom onset 1
- ECG monitoring is important as cardiac involvement may be subclinical but can contribute to collapse 1
- Early recognition of neurological symptoms is crucial as they may herald impending collapse 1
- Patients with mixed viral-bacterial pneumonia are at particularly high risk for collapse and should be monitored closely 1
Warning Signs of Impending Collapse
- Persistent high fever
- Severe cough
- Progressive dyspnea
- Altered mental status
- Cyanosis
- Tachypnea
- Hemoptysis
- Hypotension
- Decreased level of consciousness 2
Early recognition of these mechanisms and prompt intervention are essential to prevent collapse in influenza patients, particularly those with risk factors for severe disease.