Improving Cough Efficiency and Strength After Extubation (While on HFNC)

1. Understand the Problem First: Assess Cough Adequacy

• PCF > 270 L/min: effective, self-clearance likely adequate
• PCF 160-270 L/min: borderline - augmentation techniques indicated
• PCF < 160 L/min: ineffective cough - secretion retention highly likely; active intervention essential

2. Maximize Inspiratory Volume First (Pre-Cough Phase)

A. Breath Stacking / Lung Volume Recruitment (LVR)

• Patient takes several successive deep breaths in, holding each inhaled volume before exhaling
• Builds up to maximal insufflation capacity (MIC) - significantly higher than normal tidal volume
• Perform 10-15 stacks, 3 times per day
• Increases PCF by providing a larger lung volume from which to cough
• HFNC does not prevent this - the patient actively stack-breathes while maintaining the cannula

B. Bag-Valve Mask (BVM) Assisted Breath Stacking

• If patient cannot self-stack (too weak), therapist delivers several positive pressure breaths via BVM/resuscitator bag
• Patient holds glottis closed between breaths to stack air
• Raises lung volume, then patient coughs from this increased volume

C. Non-Invasive Ventilation (NIV/BiPAP) Augmented Inspiration

• Short NIV sessions (mask BiPAP) can supplement inspiratory volume pre-cough even when patient is otherwise maintained on HFNC
• The BTS/ACPRC guideline recommends considering NIV/airway clearance strategies when SpO2 falls below 95%, and maximal insufflation strategies when VC <1500 mL or <50% predicted

3. Augment the Cough Itself (Expiratory Phase)

A. Manually Assisted Cough (MAC)

1. Anterior chest compression ("costophrenic compression") - therapist places hands over lower rib cage and pushes inward and upward as patient coughs
2. Abdominal thrust (Heimlich-type) - hands placed below the xiphoid/above the navel; sharp upward-inward thrust timed precisely to the start of cough
   • Displaces the diaphragm upward, rapidly increasing intrathoracic pressure and expiratory flow
   • Most effective in patients without bulbar dysfunction
3. Combined approach (maximal insufflation + MAC): Trebbia et al. showed this combination produced significantly greater PCF than either technique alone

B. Mechanical Insufflation-Exsufflation (MI-E) - "Cough Assist" Device

• Delivers a positive pressure breath (insufflation, typically +40 cmH2O, 2-3 seconds) followed by rapid switch to negative pressure (exsufflation, -40 cmH2O, 2-3 seconds)
• Generates a high expiratory flow that mimics and augments a natural cough
• Can be applied via face mask (patient on HFNC - simply apply mask over face, remove HFNC briefly per cycle)
• Protocol: 8 cycles per session, 3 sessions per day in the post-extubation period (morning, afternoon, evening)
• Combining MI-E with a simultaneous abdominal thrust produces the highest peak cough flow (Fishman's Pulmonary Diseases)
• Evidence from case series shows 91-95% extubation success in neuromuscular patients when MI-E combined with lung volume recruitment

C. Expiratory Muscle Training (EMT)

• Threshold-loaded expiratory devices (e.g., Threshold PEP/EMT device) provide resistance training for expiratory muscles
• Patient exhales forcefully against an adjustable threshold load
• Builds expiratory muscle strength over days-weeks
• Start at 30-40% of maximal expiratory pressure (MEP), progress every 3-5 days

4. Role of HFNC in Supporting the Process

• Dead-space washout of the nasopharynx - improves efficiency of each breath, reducing CO2 rebreathing and improving alveolar ventilation per breath
• Reduced work of breathing - conserves respiratory muscle energy so more is available for cough effort
• Maintained PEEP effect (~0.5-1 cmH2O per 10 L/min flow) - maintains end-expiratory lung volume, preventing atelectasis which would reduce available lung volume for cough
• Optimal heated humidification (37°C, ≥33 mg H2O/L) - keeps secretions less viscous and easier to mobilize
• Mucociliary clearance is improved by adequate humidification (compared to dry low-flow oxygen)

5. Secretion Mobilization Adjuncts (Loosen Before Coughing)

6. Active Rehabilitation

7. Practical Stepwise Protocol Post-Extubation on HFNC

1. Assess PCF and SpO2 every shift
2. Ensure adequate analgesia (pain kills cough effort, especially post-thoracic/abdominal surgery)
3. Position upright (≥30-45° head of bed; ideally sitting at edge of bed)
4. Nebulize saline or prescribed bronchodilator if indicated
5. Perform 10-15 breath stacks (or BVM-assisted if too weak)
6. Apply MI-E via mask (if available) OR perform MAC technique 
7. Have patient huff 2-3 times to centralize secretions, then full cough
8. Suction only if cough inadequate to clear visible/audible secretions
9. Repeat 3x daily; reassess PCF after each session

8. When to Escalate

• PCF persistently <160 L/min despite techniques
• Increasing respiratory rate, SpO2 drop on HFNC
• Unable to clear secretions despite augmentation - consider NIV trial or temporary return to higher support
• Signs of aspiration or bulbar dysfunction - bulbar patients cannot glottis-close, limiting breath stacking effectiveness; MI-E is preferred in this group

• Fishman's Pulmonary Diseases and Disorders (Cough augmentation, NMD section) - MI-E + MAC combination achieves highest PCF
• BTS/ACPRC Guidelines for Physiotherapy Management (Thorax 2009;64:i1-i51) - PCF thresholds, maximal insufflation, breath stacking protocols
• Cochrane systematic review - cough augmentation for extubation in critically ill patients - MI-E + lung volume recruitment yielded 91-95% extubation success in neuromuscular patients
• HFNC mechanisms - secretion clearance and dead space washout