How to Measure Peak Cough Flow with a Tracheostomy
Measure peak cough flow (PCF) in tracheostomy patients by connecting a peak flow meter directly to the tracheostomy tube and having the patient perform a maximal cough effort, with the measurement taken at the tube rather than at the mouth.
Measurement Technique
The fundamental principle is that PCF measurement location matters critically—values obtained through a tracheostomy tube are substantially lower than those measured at the mouth. When measuring through a tracheostomy:
- Connect a portable peak flow meter directly to the tracheostomy tube 1
- Have the patient perform a maximal voluntary cough effort
- Record the highest value from at least 3 attempts
- Ensure the cuff is deflated if measuring spontaneous cough capacity (unless contraindicated)
Alternative Methods
For patients on mechanical ventilation: You can measure CPF using the ventilator's built-in flow meter without disconnecting the patient. This method shows good correlation with handheld peak flow meters (correlation coefficient 0.63), though ventilator-measured values are approximately 2.3 times higher than handheld meter values 2.
For assisted cough techniques: The measurement can be performed after lung volume recruitment (air stacking) or with manually assisted cough to assess maximum achievable flows 1, 3.
Critical Threshold Values
The threshold values differ dramatically based on measurement location:
Through the Tracheostomy Tube:
- >60 L/min suggests adequate cough for successful extubation/decannulation 4
- >100 L/min (measured with speaking valve in place) indicates sufficient cough capacity for safe decannulation 5
- 29 L/min has been identified as a cutoff for successful decannulation in neurosurgical patients 6
At the Mouth (with capped tracheostomy):
- >160 L/min indicates effective airway clearance capability 1
- Values measured at the mouth with a capped tracheostomy are typically 35-43 L/min higher than measurements through the tube 3
Important Technical Considerations
Cuff status matters: For spontaneous cough assessment, deflate the cuff to allow airflow through the upper airway, which more accurately reflects real-world function 7. However, if measuring assisted cough with positive pressure, an inflated cuff may be necessary.
Speaking valve option: Measuring with a speaking valve (one-way valve) in place provides values closer to post-decannulation function and may be more predictive of success 5.
Avoid using suction catheters for assessment: While passing a suction catheter confirms tube patency, it does not measure cough effectiveness 8.
Common Pitfalls
- Don't confuse measurement locations: A value of 60 L/min through the tube is adequate, but the same value at the mouth would be concerning
- Don't measure during acute illness: Respiratory muscle function deteriorates during infections, so baseline measurements may not reflect capacity during illness 1
- Don't rely solely on spontaneous cough: Assisted cough techniques (lung volume recruitment + manual assistance) can generate flows 34-43 L/min higher than spontaneous efforts and may better predict post-decannulation success 3
Clinical Context
PCF measurement is particularly valuable for:
- Assessing decannulation readiness
- Evaluating need for assisted cough techniques
- Monitoring patients with neuromuscular weakness
- Predicting extubation success
The measurement should be part of a comprehensive assessment that includes secretion volume, mental status, and upper airway patency, but PCF provides objective data that correlates with successful outcomes 5, 4, 6.