How should sputum induction be performed safely in an adult patient who cannot expectorate spontaneously and requires lower‑airway samples for microbiologic or cytologic diagnosis (e.g., suspected tuberculosis or interstitial lung disease)?

How to Perform Sputum Induction

Sputum induction should be performed by having the patient inhale nebulized hypertonic saline (3-7% concentration) for 15-20 minutes via ultrasonic nebulizer after premedication with a short-acting bronchodilator, with the procedure conducted in a negative-pressure room and healthcare workers wearing N95 respirators. 1, 2

Pre-Procedure Preparation

Patient Preparation:

• Administer a short-acting bronchodilator (e.g., salbutamol/albuterol) before starting the procedure to prevent bronchospasm 3
• Have the patient fast for at least 2 hours before the procedure to reduce nausea and retching risk 3
• Instruct the patient to rinse their mouth thoroughly with water and perform rigorous cleaning of teeth, gums, and cheeks to remove oral debris that could contaminate the specimen 3, 1
• Remove any dentures 3

Environmental Safety Requirements:

• Perform the procedure in a negative-pressure room or booth relative to adjacent areas 2, 4
• Ensure air is expelled directly outside, away from all windows and air intake vents 2, 4
• In resource-limited settings without environmental containment, perform collection outdoors 2
• Allow sufficient time between patients for elimination of droplet nuclei 2

Healthcare Worker Protection:

• All personnel must wear protective respirators (N95 or equivalent) during the procedure 1, 2
• Workers should receive proper training in respirator use and disposal 2

Induction Protocol

Nebulization Technique:

• Use a high-output ultrasonic nebulizer (e.g., UltraNeb 99m or DP100) 3
• Load the reservoir with 20-30 mL of hypertonic saline solution 3, 1
• Use 3-7% concentration hypertonic saline (commonly 3%, 4%, and 5% in sequence) 3, 2, 4
• Administer for 15-20 minutes total duration 3, 1, 5
• When using sequential concentrations, have the patient inhale each concentration (3%, 4%, 5%) for 5 minutes each 3

Expectoration Process:

• Instruct the patient to cough deeply from the chest at the end of each 5-minute inhalation period 1
• Discard the first sputum sample as it is frequently unrepresentative of the lower respiratory tract 3
• Collect subsequent material for microbiological and cytological analysis 3
• The success rate of obtaining adequate specimens is approximately 68-80% 1, 6

Monitoring During Procedure

Safety Monitoring:

• Monitor oxygen saturation continuously with a transcutaneous oximeter, as unpredictable arterial oxygen desaturation may occur and persist after the procedure 3
• Monitor for bronchospasm, particularly in patients with airway hyperresponsiveness 5
• The mean fall in FEV1 during saline inhalation is typically 5.3%, with maximum falls up to 20% 7
• Do not perform exercise testing immediately after this procedure 3

Post-Procedure Management

Patient Care:

• Have patients remain in the treatment booth/room (or go outside if weather permits) until coughing has decreased 2
• Do not allow patients to return to common waiting areas until coughing subsides 2
• Advise patients not to eat or drink for about 1 hour after treatment if local anesthetics were used 3

Specimen Processing

Quality Assessment:

• Screen all specimens microscopically before processing to ensure they represent lower respiratory secretions, not saliva 1
• Acceptable specimens must have ≥25 polymorphonuclear cells per low-power field (100x) and <10 squamous epithelial cells per low-power field 1
• Reject specimens with >10 squamous cells per field as they indicate significant oral contamination 1

Laboratory Processing:

• Disperse expectorated sputum using a mucolytic agent 3
• Filter through 48-μm mesh gauze to remove excess mucus 3
• Centrifuge the filtrate to produce a cytospin 3
• Perform differential cell count by counting 400 nonsquamous cells 3
• Process specimens on the same day for cell quantification and viability 3

Clinical Advantages and Yield

Diagnostic Performance:

• Sputum induction has equal or superior diagnostic yield compared to bronchoscopy, with detection rates of 91-98% by smear and 99-100% by culture for tuberculosis 1, 2, 4
• The overall diagnostic yield for community-acquired pneumonia is approximately 20% 8
• In patients unable to expectorate spontaneously, induction is successful in obtaining specimens in 68.75% of cases 6

Cost-Effectiveness:

• Sputum induction costs approximately $22 Canadian dollars versus $187 for bronchoscopy 4
• The most cost-effective strategy is obtaining 3 induced sputum samples without bronchoscopy 2, 4

Critical Pitfalls to Avoid

Common Errors:

• Never accept specimens with >10 squamous epithelial cells per low-power field, as they represent saliva contamination and yield unreliable results 1
• Do not rely on negative AFB smears to exclude tuberculosis, as only 63% of culture-confirmed TB cases have positive smears 1, 2, 4
• Avoid performing induction after antibiotics have been started, as this significantly reduces diagnostic yield 8
• Do not skip bronchodilator premedication, as there is significant risk of bronchospasm 3

When to Proceed to Bronchoscopy:

• If sputum induction fails to yield adequate specimens after proper attempts 3, 4
• In patients with high clinical suspicion of tuberculosis or other serious infections despite negative induced sputum results 3, 2
• When rapid diagnosis is essential and initial induced sputum is negative 3