RT-24 · Analysis & Monitoring

Capnography & Bedside Monitoring

Waveform capnography, the PaCO2–EtCO2 gradient, pulse oximetry limits, and the monitors that tell you the truth before the gas does.

~18 min read3 concept sections·2 questions with rationale

What you'll be able to do

  • Read the four phases of a normal capnogram and name the abnormal shapes
  • Use the PaCO2–EtCO2 gradient to separate dead space from hypoventilation
  • State the confirmed uses and limits of pulse oximetry
  • Select co-oximetry when saturation cannot be trusted
Concept breakdown
01

The capnogram, phase by phase

Shape names the problem; height names the ventilation. Read both on every waveform question.

  • Phase I: anatomic dead space, no CO2. Phase II: rapid upstroke as alveolar gas arrives. Phase III: alveolar plateau, nearly flat. Phase IV: inspiratory downstroke to zero.
  • Normal EtCO2 is 35–43 mm Hg with a plateau that returns to a zero baseline.
  • A sloping, shark-fin phase III is obstruction — bronchospasm, COPD, a kinked or partially blocked tube.
  • A baseline that never returns to zero means rebreathing: exhausted absorber, incompetent expiratory valve, or inadequate expiratory time.
  • A sudden drop to zero is a disconnect, esophageal placement, or an obstructed tube. A sudden drop to a low but present value is a fall in cardiac output or pulmonary embolism.
  • Curare cleft (a notch in the plateau) is returning spontaneous effort against the ventilator.
At the bedside

Sustained waveform capnography is the standard confirmation of tube placement and the highest-quality feedback loop in CPR — EtCO2 under 10 mm Hg means compressions are not perfusing.

Practice quiz

Check yourself before you read the rationale.

Question 1 of 1

A ventilated patient's EtCO2 drops abruptly from 38 to 14 mm Hg while the ABG PaCO2 is 42 mm Hg. Breath sounds are equal and the tube is at depth. The most likely cause is:

Practice questions

Answer first, then read why the distractors fail.

Question 1

A ventilated patient's EtCO2 drops abruptly from 38 to 14 mm Hg while the ABG PaCO2 is 42 mm Hg. Breath sounds are equal and the tube is at depth. The most likely cause is:

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2 more concept sections, 1 more question, and the exam-day playbook for this module.

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