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Lesson

Reading Capnography Waveforms

12 min Airway & Breathing Skip to quiz

Objective: Read four waveform shapes: square, shark fin, rising baseline, and sudden flat. Say the next action for each.

Why this matters

A waveform that is present tells you carbon dioxide is coming from the lungs. The shape tells you how that breath got out.

A square wave, a shark fin, a baseline that will not fall, and a line that goes flat are four different problems. They do not get the same next move.

Confirming that the tube is in the trachea is the first job of capnography. This lesson is the next job. Read the shape, then change the ventilation or the circuit.

Key points
  • No waveform and no chest rise means failed ventilation until you find the disconnect, the obstruction, or the displaced tube.
  • A shark fin means slow, obstructed exhalation. Think bronchospasm, and give the patient time to exhale.
  • A baseline above zero means the patient is rebreathing carbon dioxide. A low number during cardiopulmonary resuscitation (CPR) is about perfusion and CPR quality. It is not a reason to stop.
Verbalize
  • The wave is square and the chest is rising. I am ventilating.
  • The wave is a shark fin. I am giving a longer time to exhale, and I am treating bronchospasm per protocol.
  • The line is flat. I am checking the patient, the tube, and the circuit before I trust the monitor.
Four capnography shapes and a curare cleft A square wave, a shark-fin upstroke, a baseline that does not return to zero, and a sudden flat line. A dip in the plateau is a curare cleft. Square Chest is rising. You are ventilating. Shark fin Slow upstroke. No plateau. Obstructed exhalation. Allow time. Baseline stays up The waves never return to zero. The patient is rebreathing CO2. Sudden flat line A wave, then nothing. Check the patient, tube, and circuit. Curare cleft A dip in the plateau. The patient may be starting to breathe. Recheck sedation per protocol. It is not a drug order.
A square wave with chest rise means ventilation is happening. A shark fin is slow, obstructed exhalation, so allow time to exhale. A baseline that stays above zero means the patient is rebreathing carbon dioxide. A sudden flat line is failed ventilation until you find the cause. A dip in the plateau, sometimes called a curare cleft, is a reason to recheck sedation per protocol. It is not a drug order.

Clinical sequence

  1. Confirm you are looking at a waveform, not only a number. A number without a wave can be wrong.
  2. If the wave is square and the chest is rising, ventilation is happening. Then look at the height and the rate against the patient’s condition. Protocol owns the target.
  3. If the wave rises slowly, like a shark fin, slow the rate and allow exhalation. This pattern is common in severe asthma and chronic obstructive pulmonary disease (COPD). Use the asthma and COPD ventilation lesson.
  4. If the baseline climbs and never returns to zero, the patient is rebreathing carbon dioxide. Check the circuit, the expiratory valve, and whether the rate is too fast.
  5. If the wave disappears, run DOPE-S. Check the patient, the tube, and the circuit. A flat line after intubation is an esophageal or displaced tube until you prove otherwise. If the tube is in the esophagus, take it out and oxygenate. Do not talk yourself out of a flat line with breath sounds.

Teaching points

  • AHA 2025 uses continuous waveform capnography to confirm and monitor an advanced airway. A single color change on a detector is not the same thing.
  • A curare cleft is a dip in the plateau. It can mean the patient is starting to breathe against the ventilator, or that a paralytic is wearing off. Reassess sedation and the ventilator per protocol. It is not a drug order.
  • A sudden rise in end-tidal carbon dioxide during CPR can mean return of spontaneous circulation (ROSC). Confirm with a pulse. Do not stop compressions for the number.

Common errors

  • Calling a shark fin a calibration error when the chest is silent and tight.
  • Stopping resuscitation because the end-tidal number is low while a waveform is still present.
  • Ignoring a flat line because the tube fogged once.

Practice

One-minute check

Draw four shapes in the air: square, shark fin, rising baseline, and flat. For each shape, say one action. Then open waveform capnography if you need the confirmation rules again.

Sources & Further Study

Named guidelines for further study. They are not clinical orders and do not replace your protocol or medical direction.

Education only. Apply learning within your protocols and medical direction. This is not clinical care guidance.

Check Your Understanding

Questions drawn only from this lesson. After you check, the key is highlighted. Education practice — not a certification exam.

1. A waveform that is suddenly flat, with no chest rise, means:
2. A shark-fin waveform is a teaching sign of:
3. A baseline that does not return to zero suggests:
4. During CPR, a low end-tidal number is:
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