How do you perform a cuff leak test on a patient with an endotracheal tube (ETT)?

How to Perform the Cuff Leak Test

The cuff leak test should be performed with the patient in semi-recumbent position on assist-control ventilation, measuring the difference between inspired tidal volume (with cuff inflated) and the average of the three lowest expired tidal volumes among six measurements after cuff deflation. 1

Patient Preparation and Positioning

• Position the patient semi-recumbent before beginning the test 1
• Perform thorough oral and tracheal suctioning to remove secretions that could interfere with measurements 1
• Set the ventilator to assist-control mode (volume control) 1
• Ensure adequate sedation to prevent coughing during the test, as coughing significantly reduces measurement reliability 1

Step-by-Step Measurement Technique

Baseline Measurement

• Verify that inspired and exhaled tidal volumes (Vt) are equal with the cuff inflated 1
• Record the inspired tidal volume as your baseline reference 1

Cuff Deflation and Measurement

• Completely deflate the endotracheal tube cuff 1
• Record six consecutive expired tidal volumes after cuff deflation 1
• Calculate the average of the three lowest values among these six measurements 1

Calculating the Leak Volume

• Absolute leak volume = Inspired Vt (cuff inflated) minus average expired Vt (cuff deflated) 1
• Relative leak volume = (Absolute leak volume ÷ Inspired Vt) × 100% 1

Interpreting Results

Positive Test (High Risk for Laryngeal Edema)

• Absolute leak volume < 110 mL indicates high risk 1, 2
• Relative leak volume < 10% indicates high risk 1, 2
• A positive test has excellent specificity (87-92%) but only moderate sensitivity (56-66%), meaning it effectively identifies low-risk patients but misses many who will develop complications 1, 3

Clinical Implications

• The test has a positive predictive value of only 12-15%, meaning most patients who fail the test will NOT develop post-extubation stridor 3, 4
• The negative predictive value is excellent (97-98%), so a passed test reliably indicates low risk 5, 4

Alternative Qualitative Method

When quantitative measurement is impractical, use a qualitative approach: obstruct the endotracheal tube with your finger while the patient breathes normally and listen for audible air leak around the tube 1. This simplified method is less precise but can be used when ventilator measurements are unreliable 1.

Important Technical Considerations

Factors That Affect Accuracy

• Inspiratory flow rate: Lower flows increase the measured leak volume, particularly the inspiratory component 6
• Respiratory system compliance: Lower compliance increases measured leak 6
• Timing of cuff deflation: Deflating at end-inspiration (measuring only expiratory leak) gives lower values than conventional method that includes both inspiratory and expiratory components 6
• Patient cooperation: Coughing during measurement invalidates results 1

When to Perform the Test

• Conduct the test immediately before planned extubation in patients who have successfully completed spontaneous breathing trials 1
• The test should be reserved for high-risk patients including: those intubated >6 days, traumatic/difficult intubation, large endotracheal tube relative to patient size, female gender, or previous reintubation 1, 2, 3

Management Based on Results

If Test is Positive (Failed)

• Administer systemic corticosteroids (prednisolone 1 mg/kg/day or equivalent) at least 4-6 hours before extubation 1, 3
• Proceed with extubation 4-12 hours after steroid administration rather than delaying indefinitely 3
• Have equipment ready for high-flow oxygen, nebulized epinephrine, and potential reintubation 3

If Test is Negative (Passed)

• Proceed with extubation as planned 1
• Continue standard post-extubation monitoring, as the moderate sensitivity means some patients will still develop complications 1

Common Pitfalls to Avoid

• Don't delay extubation indefinitely for a failed cuff leak test—give steroids and proceed within 4-12 hours 3
• Don't rely solely on the test in unselected low-risk patients, as its sensitivity is only moderate 1, 3
• Don't perform the test without adequate suctioning first, as secretions interfere with measurements 1
• Don't interpret the test during active coughing, as this invalidates measurements 1