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Updated: Jun 24, 2026

Expired CO2 Measurement in Intubated or Spontaneously Breathing Patients from the Emergency Department
Published on: January 30, 2011
Decrease in spectral entropy by low tidal volume ventilation-associated severe hypercapnia: a case report
Junggun Ann1, Sung Mee Jung1, Sang-Jin Park1
1Department of Anesthesiology and Pain Medicine, Yeungnam University School of Medicine, Daegu, Korea.
Abstract:
Severe hypercapnia can be predicted by a decrease in cerebral electrical activity. The authors describe a sudden decrease in spectral entropy due to severe hypercapnia-induced respiratory acidosis in a patient with chronic pulmonary obstructive disease during lung resection. After two and a half hours of low tidal volume ventilation in the lateral position, the state entropy suddenly dropped from 45 to 7, without any changes in the effect-site concentration of propofol, end-tidal carbon dioxide (CO2) tension, oxygen saturation, or arterial pressure. However, arterial blood gas analysis showed severe respiratory acidosis (pH 7.01, PaCO2 115 mmHg and PaO2 246 mmHg with FIO2 of 0.5). Immediate hyperventilation improved the state entropy and acid-base balance. Electroencephalography-based spectral entropy can detect severe hypercapnia in chronic pulmonary obstructive disease patients with a large arterial to end-tidal CO2 difference due to prolonged hypoventilation during thoracic surgery.
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