Decrease in spectral entropy by low tidal volume ventilation-associated severe hypercapnia: a case report

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.

Keywords: Electroencephalography; Entropy; Hypercapnia; Hypoventilation.