Miniature intravascular pCO2 sensors in neurosurgery

In this study the authors compared PaCO2 measurements from a newly developed miniature intravascular pCO2 sensor for continuous on-line monitoring with those from a Radiometer bench instrument. In 10 patients undergoing craniotomy procedures, 84 paired comparisons were made. At the same time it was possible to follow continuously the trend of PaCO2 during deliberate hyperventilation, during the apneic period following hyperventilation, and during spontaneous respiration in the postoperative period. The comparisons showed an average difference in pCO2 of 1.62 +/- SE 0.15 torr. The apneic threshold for PaCO2 after passive hyperventilation was lower than in the awake patient. After the period of apnea no hypoxemia occurred. In the recovery room the PaCO2 increased and the PaO2 decreased. The latter decreased to subnormal levels in two patients more than an hour postoperatively.