How can I safely and systematically induce sputum in an adult respiratory‑medicine ward patient who can follow instructions, has no contraindications (e.g., severe airflow obstruction, recent myocardial infarction, uncontrolled hypertension, active haemoptysis, saline hypersensitivity), and needs a specimen for suspected tuberculosis, atypical pneumonia, or interstitial lung disease?

Systematic Protocol for Sputum Induction in a Respiratory Medicine Ward

Sputum induction using nebulized hypertonic saline (3–7%) over 15–20 minutes in a negative-pressure room is the preferred initial method for obtaining respiratory specimens in adults who cannot expectorate spontaneously, with pre-treatment bronchodilation mandatory to prevent bronchospasm. 1

Pre-Procedure Patient Preparation

Bronchodilator Administration (Critical—Never Skip)

• Administer a short-acting beta-agonist (e.g., salbutamol/albuterol) immediately before starting the procedure to prevent bronchospasm during hypertonic saline inhalation 1
• This step is non-negotiable; omitting bronchodilator pre-medication markedly increases the risk of acute bronchospasm 1

Patient Preparation Steps

• Require the patient to fast for at least 2 hours prior to the procedure to minimize nausea and vomiting risk 1
• Instruct the patient to rinse the mouth thoroughly with water and clean teeth, gums, and cheeks to eliminate oral debris that could contaminate the specimen 1, 2
• Remove dentures before the procedure to avoid saliva contamination 1

Environmental and Safety Requirements

Room Setup

• Perform sputum induction in a negative-pressure room or booth relative to adjacent areas 3, 1
• Ensure room air is exhausted directly to the outside, away from all windows and air intake ducts 3, 1
• Allow adequate time between patients for droplet nuclei clearance; this varies by ventilation efficiency 3

Healthcare Worker Protection

• All personnel must wear N95 respirators (or equivalent protective respirators) throughout the procedure if they must be in the room with the patient 3, 1
• This is particularly critical when tuberculosis is suspected 3

Nebulization Protocol

Equipment and Solution

• Use a high-output ultrasonic nebulizer (e.g., UltraNeb 99m or DP100) 1
• Load the nebulizer reservoir with 20–30 mL of hypertonic saline 1

Saline Concentration and Timing

• Employ hypertonic saline concentrations of 3%–7% 3, 1, 4
• The common sequential approach uses 3%, then 4%, then 5% saline 1
• Deliver aerosol for a total duration of 15–20 minutes 1, 5
• When using sequential concentrations, have the patient inhale each concentration for 5 minutes before advancing to the next 1

Expectoration and Specimen Collection

Collection Technique

• Discard the first expectorated sample because it frequently represents upper-airway secretions rather than lower-respiratory material 1
• Collect all subsequent samples for microbiological and cytological analysis 1
• Aim to collect at least 3 specimens for tuberculosis evaluation, with optimal volume of 5–10 mL per specimen (minimum 3 mL) 4, 2

Diagnostic Yield

• Sputum induction has equal or superior diagnostic yield compared to bronchoscopy, with detection rates of 91–98% by AFB smear microscopy and 99–100% by mycobacterial culture when 3 or more specimens are obtained 3, 1, 4
• The success rate of obtaining adequate specimens is approximately 80% in adults 3, 2, 6

In-Procedure Monitoring

Continuous Surveillance

• Continuously monitor oxygen saturation with a transcutaneous oximeter throughout the procedure, as unpredictable desaturation can occur and may persist after the session 1
• Monitor for excessive coughing that may culminate in vomiting 3
• The greatest fall in FEV₁ typically occurs in the second stage of induction and can predict the maximum fall 7

When to Stop

• Discontinue if the patient develops significant bronchospasm (>20% fall in FEV₁), though this occurs in less than 2% of patients even with moderate-to-severe airflow obstruction 7

Post-Procedure Patient Management

Immediate Care

• Patients must remain in the booth or treatment room (or go outside if weather permits) and not return to common waiting areas until coughing has subsided 3, 1
• Advise patients to refrain from eating or drinking for approximately 1 hour after the procedure if a local anesthetic was used 1
• Do not schedule exercise testing immediately after sputum induction 1

Laboratory Processing of Specimens

Same-Day Processing Protocol

• Process specimens on the same day to preserve cell viability and allow accurate quantification 1
• Disperse the expectorated sputum with a mucolytic agent (dithiothreitol/DTT) before further handling 1, 8
• Filter the dispersed sputum through a 48-µm mesh gauze to remove excess mucus 1
• Centrifuge the filtrate to obtain a cytospin preparation 1
• Perform a differential cell count by evaluating 400 nonsquamous cells per slide 1
• Report total cell count, cell viability, and squamous cell contamination 3

Quality Assessment

• Acceptable specimens should have ≥25 polymorphonuclear cells per low-power field (100×) and <10 squamous epithelial cells per low-power field 2
• Specimens with >10 squamous cells indicate significant oral contamination and should be rejected 2

Cost-Effectiveness Considerations

Sputum induction is significantly more cost-effective than bronchoscopy, with direct costs of approximately $22 CAD versus $187 CAD for bronchoscopy 3, 1, 4. The most cost-effective diagnostic strategy is to obtain 3 induced sputum samples without proceeding to bronchoscopy 3, 1, 4.

Critical Pitfalls to Avoid

• Never omit bronchodilator pre-medication—this is the single most important safety measure 1
• Never rely on a negative AFB smear to exclude tuberculosis, as only 63% of culture-confirmed TB cases have positive smears 4, 2
• Approximately 14% of confirmed pulmonary TB cases have negative cultures, so clinical suspicion must guide management regardless of laboratory results 4, 2
• Do not accept specimens with excessive squamous cells (>10 per field), as they represent saliva contamination and yield unreliable results 2

Indications for Escalation to Bronchoscopy

Proceed to flexible bronchoscopy if:

• Sputum induction fails to yield adequate specimens after 3 attempts 1
• There is high clinical suspicion of tuberculosis or other serious infections despite negative induced sputum results 1, 4
• Rapid diagnosis is essential and initial induced sputum is negative 1

However, recognize that five of six comparative studies demonstrated higher yield from induced sputum than bronchoscopy 3, making sputum induction the preferred first-line approach for both diagnostic yield and safety 3, 1.