[Intraoperative changes in arterial end tidal CO2 partial pressure difference in interventions with constant...

During general anaesthesia, the endtidal CO2 pressure serves as an estimate of the arterial CO2 pressure to regulate the ventilator setting. Important arterial to end-tidal carbon dioxide tension differences (P(a-et)CO2) have been observed among patients undergoing procedures which have substantial impact on the ventilation-perfusion ratio (V/Q). Data on the P(a-et)CO2 for procedures in which the V/Q-ratio remains constant are lacking. Repeated measurements of P(a-et)CO2 in twelve patients with chronic obstructive lung disease (COLD) and nine pulmonary healthy patients undergoing jaw surgery were performed. The P(a-et)CO2 in the pulmonary healthy subjects (5.96 +/- 1.68 mmHg) was lower than in the COLD patients (9.05 +/- 3.49 mmHg) (p < 0.01). A clinically significant P(a-et)CO2 > or = 8 mmHg was observed in 52% of the measurements in patients with COLD compared with 11% in the pulmonary healthy subjects (p < 0.01). Both patient groups showed only minimal intraoperative changes of P(a-et)CO2. The deviation of all subsequent P(a-et)CO2 values from the initial P(a-et)CO2 was 2.17 +/- 1.52 mmHg in the pulmonary healthy patients and 2.02 +/- 1.49 mmHg in the patients with COLD (p = 0.76). Intraoperative changes of the P(a-et)CO2 are small during procedures with no major alterations of the V/Q ratio. For these procedures an initial measurement of the P(a-et)CO2 in patients with lung disease should be sufficient. In pulmonary healthy subjects the P(a-et)CO2 seems to be negligible.