What does a shark‑fin pattern on a capnography waveform indicate?

Shark Fin Pattern on Capnography Indicates Airway Obstruction

A shark fin pattern on capnography represents airway obstruction, most commonly from bronchospasm (asthma, COPD exacerbation) or other causes of expiratory flow limitation, and requires immediate intervention to relieve the obstruction.

What the Pattern Looks Like

The shark fin waveform shows a sloped, gradual rise during the expiratory phase (Phase 2) instead of the normal steep vertical rise. This creates a characteristic triangular or "shark fin" appearance. The slope ratio between Phase 1 and Phase 2 is significantly increased—research shows obstructed airways have a mean slope ratio of 31.9 compared to 7.57 in normal airways 1.

Clinical Significance and Immediate Actions

When you see this pattern, think airway obstruction first:

• Bronchospasm (asthma, severe COPD exacerbation, anaphylaxis)
• Mucus plugging or secretions
• Endotracheal tube obstruction (kinked tube, mucus plug in intubated patients)
• Foreign body or other mechanical obstruction

Critical Management Algorithm

1. Assess the patient immediately - Don't just watch the monitor

   • Check for wheezing, increased work of breathing, accessory muscle use
   • Verify oxygen saturation
   • In intubated patients: Use the DOPE mnemonic 2, 3:
     • Displacement of tube
     • Obstruction of tube (remove inner cannula if present, suction)
     • Pneumothorax
     • Equipment failure

2. For bronchospasm (most common cause):

   • Administer bronchodilators immediately (albuterol)
   • Consider corticosteroids
   • Optimize oxygenation
   • If severe/status asthmaticus: May require intubation with careful ventilator management 3

3. For intubated patients with sudden shark fin appearance:

   • Remove any obstructing devices (speaking valves, caps, humidifiers) 4
   • Remove and inspect inner cannula if tracheostomy 4
   • Suction the airway
   • Consider fiberoptic inspection if partial obstruction suspected 5
   • Verify tube position hasn't changed

Important Caveats

The shark fin pattern is highly specific for expiratory obstruction - when present with clinical wheezing, it confirms airway obstruction 1. However, remember:

• Loss of waveform entirely suggests complete obstruction, tube displacement, or cardiac arrest with no pulmonary blood flow 2
• The pattern can worsen with interventions that increase auto-PEEP in mechanically ventilated patients 3
• In severe obstruction (status asthmaticus), the pattern may be present even with proper tube placement and requires aggressive bronchodilator therapy 2

Monitoring Recommendations

Continuous waveform capnography should be used for:

• All intubated patients (Class I recommendation) 6, 5
• All patients on mechanical ventilation 4
• During procedural sedation to detect early respiratory compromise 7
• Non-intubated patients with respiratory distress as a continuous monitoring tool 1

The shark fin pattern provides real-time visual feedback that obstruction is present and allows you to monitor response to treatment—as bronchodilators work, the waveform should normalize toward a more vertical Phase 2 slope.