How should induced sputum be collected in children—including indications, contraindications, pre‑procedure preparation (fasting, bronchodilator), hypertonic saline nebulization protocol, monitoring, and post‑procedure care?

Induced Sputum Collection in Pediatric Patients

Induced sputum using nebulized hypertonic saline is a safe, feasible, and highly effective method for obtaining respiratory specimens in children with suspected pulmonary tuberculosis or lower respiratory tract infections, with superior diagnostic yield compared to gastric lavage and should be the preferred initial sampling method in pediatric cases. 1, 2

Indications for Induced Sputum in Children

• Primary indication: Children hospitalized with suspected pulmonary tuberculosis who cannot spontaneously expectorate sputum 1
• Children with severe or very severe pneumonia requiring microbiological confirmation 3
• Infants and young children (as young as 1 month of age) in whom gastric lavage would traditionally be considered 2, 4
• The diagnostic yield in children is 20-30% for tuberculosis, with culture positivity rates reaching 87% when multiple specimens are obtained 1, 2

Absolute Contraindications

While the guidelines do not explicitly list contraindications, the PERCH study advisory group recommended that sputum induction should only be performed "provided no contraindications exist," suggesting clinical judgment regarding severe respiratory distress or hemodynamic instability 3

Pre-Procedure Preparation

Fasting Requirements

• Require a minimum 2-hour fast before the procedure to reduce risk of nausea, vomiting, and aspiration 5
• For gastric lavage comparison studies, a minimum 4-hour fast was used, though this may be excessive for sputum induction alone 4

Bronchodilator Administration

• Administer a short-acting bronchodilator (e.g., salbutamol) before starting to prevent bronchospasm 5
• This step is critical and should never be omitted, as skipping bronchodilator premedication markedly increases the risk of bronchospasm during saline inhalation 5

Oral Hygiene

• Instruct the patient (or perform for younger children) to rinse the mouth thoroughly with water to eliminate oral debris and reduce contamination 5, 6
• Remove any dentures if applicable 5

Hypertonic Saline Nebulization Protocol

Equipment and Solution

• Use a high-output ultrasonic nebulizer (e.g., UltraNeb 99m or DP100) for optimal aerosol delivery 5
• Load the nebulizer reservoir with 20-30 mL of hypertonic saline 5
• Hypertonic saline concentration: 3-7%, with common sequential protocol using 3%, 4%, then 5% saline 7, 5

Nebulization Timing

• Total nebulization duration: 15-20 minutes 7, 5
• When using sequential concentrations, have the child inhale each concentration for 5 minutes before advancing to the next 5
• Multiple protocols exist; the PERCH study selected nebulization with hypertonic saline over chest/abdomen massage techniques 3

Environmental Safety Requirements

• Perform in a negative-pressure room or booth with air expelled directly outside, away from windows and air intake vents 7, 5, 6
• In resource-limited settings without environmental containment, collection is safer when performed outdoors 5
• All healthcare personnel must wear N95 or equivalent respirators throughout the procedure 5, 6

Specimen Collection Technique

Sample Handling

• Discard the first expectorated sample as it frequently represents upper-airway secretions rather than lower-respiratory material 5
• Collect all subsequent samples for microbiological analysis 5
• Optimal number: 2-3 specimens collected on consecutive days or at intervals of at least 4 hours 8, 2
• One induced sputum specimen has similar yield to three gastric lavages, making it highly efficient 2

Quality Assessment

• Process specimens on the same day to preserve cell viability 5
• Disperse sputum with a mucolytic agent and filter through 48-µm mesh gauze 5
• Perform differential cell count evaluating 400 nonsquamous cells per slide 5

Monitoring During the Procedure

Vital Sign Monitoring

• Continuously monitor oxygen saturation with transcutaneous oximetry throughout the procedure 5
• The median drop in oxygen saturation during sputum induction is typically 1%, which is clinically insignificant 8
• Unpredictable desaturation can occur and may persist after the session, requiring ongoing observation 5

Clinical Observation

• Record clinical signs and symptoms before and for 30 minutes after sputum induction 8
• Healthcare workers should supervise and observe patients during collection when possible 5

Post-Procedure Care

Immediate Post-Procedure

• Patients should remain in the treatment booth/room (or go outside if weather permits) and not return to common waiting areas until coughing has decreased 5
• Advise patients to refrain from eating or drinking for approximately 1 hour after the procedure if local anesthetic was used 5
• Do not schedule exercise testing immediately after sputum induction 5

Specimen Processing

• Submit specimens for comprehensive testing including AFB smear microscopy, mycobacterial culture, and nucleic acid amplification testing (e.g., Xpert MTB/RIF) 7, 6
• Culture remains the gold standard with results typically available within 28 days 7

Safety Profile and Adverse Events

Common Side Effects

• Epistaxis (nosebleeds): Most common, occurring in approximately 19% of procedures 8
• Wheezing: Occurs in approximately 1% of procedures 8
• Other minor effects include increased coughing and occasional vomiting 2, 4
• All adverse events are typically mild and self-limited 8, 9, 2

Overall Safety

• Sputum induction has been demonstrated safe in children as young as 1 month of age 2, 4
• The procedure is well tolerated across all age groups, including HIV-infected children 8, 2, 4
• Success rate of obtaining adequate specimens is approximately 80-97% 6, 8

Critical Pitfalls to Avoid

Technical Errors

• Never omit bronchodilator premedication—this is the single most important step to prevent bronchospasm 5
• Do not accept specimens with excessive squamous cells (>10 per low-power field), as they represent saliva contamination 6
• Never rely on a negative AFB smear to exclude tuberculosis, as only 63% of culture-confirmed TB cases have positive smears 7, 5, 6

Clinical Judgment Errors

• Approximately 14% of confirmed pulmonary TB cases have negative cultures, so clinical suspicion must guide management regardless of laboratory results 7, 5, 6
• Do not assume induced sputum is inferior to gastric lavage—studies demonstrate superior or equal yield with induced sputum (87% vs 65% positivity) 2
• The diagnostic yield does not differ between HIV-infected and HIV-uninfected children, so apply the same protocol regardless of HIV status 2, 4

When to Escalate to Bronchoscopy

Indications for Bronchoscopy

• Proceed to flexible bronchoscopy if sputum induction fails to yield adequate specimens after recommended attempts 5, 6
• Consider bronchoscopy when there is high clinical suspicion of tuberculosis despite negative induced sputum results 5, 6
• Use bronchoscopy when rapid diagnosis is essential and initial induced sputum is negative 5
• However, bronchoscopy in children has lower yield (10-22% for BAL) compared to induced sputum 1

Cost-Effectiveness Considerations

• Induced sputum is significantly less expensive than bronchoscopy ($22.22 vs $187.60 Canadian dollars) 1, 7
• The most cost-effective strategy is obtaining 3 induced sputum samples without bronchoscopy 1, 7, 5

Special Pediatric Considerations

Age-Specific Success Rates

• Sputum induction is feasible in infants as young as 1 month, with median age of successful procedures at 9-13 months 2, 4
• Success rates are consistently high (91-97%) across all pediatric age groups 8, 9, 4
• The technique is more convenient and better tolerated than gastric lavage in young children 2, 4

Comparison to Gastric Lavage

• Induced sputum is superior to gastric lavage for microbiological confirmation, with one induced sputum specimen yielding similar results to three gastric lavages 2
• The difference in yield between induced sputum and gastric lavage is 5.6% in favor of induced sputum (p=0.018) 2
• Induced sputum should be the preferred method over gastric lavage in both HIV-infected and HIV-uninfected children 2, 4