Overview
Definition:
Bronchiolitis is a common viral lower respiratory tract infection in infants and young children, characterized by inflammation and obstruction of the bronchioles
Mechanical ventilation is often required for severe cases with respiratory failure
Permissive hypercapnia is a ventilatory strategy that accepts elevated arterial carbon dioxide levels (PaCO2) to reduce ventilator-induced lung injury by minimizing peak airway pressures and tidal volumes.
Epidemiology:
Bronchiolitis affects approximately 10-30% of infants annually, with Respiratory Syncytial Virus (RSV) being the most common causative agent
Hospitalization rates range from 1-2% of affected infants
Mechanical ventilation is reserved for the most severe cases, typically less than 5% of hospitalized patients
Premature infants, those with underlying cardiac or pulmonary conditions, and infants with congenital abnormalities are at higher risk for severe disease.
Clinical Significance:
Severe bronchiolitis can lead to significant respiratory distress, hypoxemia, and respiratory failure, necessitating mechanical ventilation
Understanding and applying permissive hypercapnia is crucial for optimizing ventilatory support, preventing barotrauma and volutrauma, and improving outcomes in these vulnerable patients
This knowledge is vital for pediatric residents and DNB/NEET SS candidates preparing for critical care scenarios.
Clinical Presentation
Symptoms:
Initial symptoms often mimic a common cold: rhinorrhea, cough, and mild fever
Progression to wheezing, tachypnea, retractions, and grunting respirations
In severe cases: progressive dyspnea, cyanosis, apneic episodes, lethargy, and feeding difficulties.
Signs:
Tachypnea (>60 breaths/min in infants)
Retractions (subcostal, intercostal, suprasternal)
Nasal flaring
Grunting
Auscultation reveals diffuse expiratory wheezing, crackles, and diminished breath sounds
Tachycardia
Hypoxemia (SpO2 < 90%)
Altered mental status in severe illness.
Diagnostic Criteria:
Clinical diagnosis based on age (typically < 2 years), prodromal URI symptoms, diffuse wheezing, and characteristic radiographic findings (hyperinflation, peribronchial thickening, atelectasis)
Viral studies (e.g., RSV antigen detection) can confirm etiology but do not alter management
Arterial blood gas (ABG) is crucial for assessing severity and guiding ventilation, revealing hypoxemia, and often hypercapnia.
Diagnostic Approach
History Taking:
Age of onset
Duration of symptoms
Prodromal URI symptoms
Fever
Cough characteristics
Feeding status and tolerance
Birth history (prematurity, gestational age)
History of prematurity, congenital heart disease, lung disease, or neuromuscular disorders
Exposure to sick contacts, especially in daycare or family members
Prior episodes of bronchiolitis or wheezing.
Physical Examination:
General appearance (activity, alertness, comfort level)
Respiratory rate, pattern, and work of breathing (retractions, nasal flaring, grunting)
Auscultation of lung fields for air entry, wheezing, crackles, and other adventitious sounds
Assessment of cardiovascular status (heart rate, rhythm, perfusion)
Evaluation for signs of dehydration or fluid overload
Neurological assessment (level of consciousness).
Investigations:
Arterial Blood Gas (ABG): Essential for assessing gas exchange, identifying hypoxemia (PaO2), hypercapnia (PaCO2), and acid-base status
Typical findings in severe bronchiolitis requiring ventilation include hypoxemia and varying degrees of hypercapnia and respiratory acidosis
Chest X-ray: May show hyperinflation, peribronchial thickening, and atelectasis
however, it is often normal or non-specific
Viral studies (nasopharyngeal swab for RSV and other common viruses): Primarily for epidemiological purposes and infection control
rarely changes immediate management
Complete Blood Count (CBC) and Electrolytes: Generally not indicated unless there are specific concerns for secondary bacterial infection or electrolyte disturbances.
Differential Diagnosis:
Asthma exacerbation (less common in < 1 year)
Pneumonia (focal consolidation on X-ray)
Bronchopulmonary dysplasia
Congenital airway anomalies
Gastroesophageal reflux with aspiration
Foreign body aspiration
Cystic fibrosis
Bacterial tracheitis.
Management
Initial Management:
Supportive care: Supplemental oxygen to maintain SpO2 > 90%
Humidified air
Hydration (oral or IV fluids if poor oral intake)
Nasal suctioning to clear secretions
Bronchodilators (e.g., albuterol) are generally not effective and not routinely recommended, but may be tried in selected cases with a positive response.
Medical Management:
Mechanical Ventilation: Indicated for respiratory failure, severe hypoxemia (refractory to oxygen), apnea, or inability to protect airway
Modes: Volume-controlled or pressure-controlled ventilation
Initial Settings: Low tidal volumes (4-6 mL/kg) to minimize volutrauma
Respiratory rate (20-30 breaths/min, depending on CO2 levels and patient age)
Inspiratory time (Ti): 0.3-0.5 seconds
Positive End-Expiratory Pressure (PEEP): 5-8 cm H2O to maintain alveolar recruitment
Permissive Hypercapnia Strategy: Accept PaCO2 levels above normal (e.g., up to 60-80 mmHg or higher) as long as pH remains above 7.20-7.25 and hemodynamic stability is maintained
This strategy reduces peak airway pressures and driving pressures, minimizing ventilator-induced lung injury (VILI)
Adjust ventilator to maintain adequate oxygenation (PaO2 > 50-60 mmHg) while allowing controlled hypercapnia
Frequent ABG monitoring is essential
Sedation and analgesia are often required to synchronize the patient with the ventilator and reduce oxygen consumption.
Surgical Management:
Rarely indicated for bronchiolitis itself
May be considered for complications such as severe pneumothorax requiring chest tube insertion or for addressing underlying congenital anomalies contributing to respiratory compromise.
Supportive Care:
Continuous cardiorespiratory monitoring
Strict intake and output monitoring
Enteral feeding (nasogastric or orogastric) to maintain nutritional status, with breaks for airway care if needed
Suctioning of endotracheal tube as necessary to clear secretions
Careful fluid management to avoid overload
Monitoring for secondary bacterial infections.
Complications
Early Complications:
Ventilator-associated pneumonia (VAP)
Pneumothorax
Atelectasis
Acute respiratory distress syndrome (ARDS)
Secondary bacterial infections
Sepsis
Hemodynamic instability
Electrolyte abnormalities.
Late Complications:
Bronchiolitis obliterans (rare)
Recurrent wheezing or asthma-like symptoms
Prolonged mechanical ventilation and intensive care unit stay
Neurological sequelae from hypoxic insults.
Prevention Strategies:
Judicious use of mechanical ventilation
Employing lung-protective ventilation strategies, including permissive hypercapnia and low tidal volumes
Strict adherence to VAP prevention bundles (head elevation, oral care, sedation vacations)
Early recognition and management of complications
Adequate hydration and nutrition.
Prognosis
Factors Affecting Prognosis:
Severity of initial illness
Presence of underlying comorbidities (prematurity, cardiac/pulmonary disease)
Development of complications (e.g., VAP, pneumothorax)
Age at presentation (younger infants generally have worse outcomes)
Etiology of the infection (RSV remains common).
Outcomes:
Most infants with bronchiolitis recover fully with supportive care
Mortality rates are low in otherwise healthy infants but increase with severity and comorbidities
Long-term sequelae, such as recurrent wheezing, can occur in a significant proportion of survivors
Successful application of permissive hypercapnia can mitigate some risks of mechanical ventilation and improve short-term outcomes.
Follow Up:
Follow-up is recommended for infants with severe bronchiolitis or those with underlying risk factors
Assessment of pulmonary function, recurrent wheezing, and developmental milestones may be indicated
Education for parents on signs of recurrent respiratory distress and preventive measures is important.
Key Points
Exam Focus:
Permissive hypercapnia is a strategy to minimize VILI by accepting higher PaCO2 and lower peak pressures
Target pH > 7.20-7.25
Low tidal volumes (4-6 mL/kg) are crucial
Indications for ventilation: respiratory failure, severe hypoxemia, apnea
Bronchodilators are generally ineffective
RSV is the most common cause.
Clinical Pearls:
Always assess pH before adjusting ventilation for hypercapnia
Monitor for signs of increased intracranial pressure if hypercapnia is severe or prolonged
Consider non-invasive ventilation (CPAP/BiPAP) in select cases before intubation
Differentiating bronchiolitis from asthma in infants can be challenging
focus on age and prodromal symptoms
Aggressive airway clearance and hydration are paramount.
Common Mistakes:
Over-reliance on bronchodilators
Using excessively high tidal volumes, leading to volutrauma
Incorrect interpretation of ABGs, leading to unnecessary hyperventilation or ventilation changes that worsen lung injury
Failure to adequately monitor for complications of intubation and ventilation
Delaying ventilation in infants with true respiratory failure.