Dependence of the gradient between arterial and end-tidal P-CO2 on the fraction of inspired oxygen

作者：Yamauchi H^*; Ito S; Sasano H; Azami T; Fisher J; Sobue K

来源：British Journal of Anaesthesia, 2011, 107(4): 631-635.

DOI：10.1093/bja/aer171

• pulmonary gas exchange
• respiratory dead space
• respiratory physiological phenomena
• ventilators, mechanical

Background. End-tidal P-CO2 (PECO2') is routinely used in the clinical assessment of the adequacy of ventilation because it provides an estimate of Pa-CO2. How well PECO2' reflects Pa-CO2 depends on the gradient between them, expressed as Delta Pa-E-CO2'. The major determinant of Delta Pa-E-CO2' is alveolar dead space (V-Dalv). The fraction of inspired O-2 (F-IO2) is not thought to substantially affect Delta Pa-(ECO2)' in anaesthetized patients. We hypothesized that a high F-IO2 may indeed increase Delta Pa-(ECO2)' by preferentially vasodilating well-perfused alveoli, resulting in the redistribution of blood flow to these alveoli from poorly perfused alveoli and an increase in V-Dalv. We therefore investigated the effects of changes in F-IO2 on Delta Pa-(ECO2)' and V-Dalv.
Methods. With Institutional Review Board approval and informed consent, we studied 20 ASA I-II supine patients undergoing elective lower abdominal surgery under combined general and epidural anaesthesia. At constant levels of ventilation, F-IO2 levels of 0.21, 0.33, 0.5, 0.75, and 0.97 were applied in a random order and Delta Pa-(ECO2)' and V-Dalv were calculated.
Results. The Delta Pa-(ECO2)' values were, in order of ascending F-IO2, {mean [standard error of the mean (SEM)]} 0.13 (0.04), 0.28 (0.08), 0.29 (0.09), 0.44 (0.11), and 0.53 (0.09) kPa. The corresponding values of V-Dalv were 25.5, 33.8, 35.8, 48.9, and 47.4 ml. Each successive hyperoxic level showed a significant increase in Delta Pa-(ECO2)' except between the 0.33-0.5 and 0.75-0.97 F-IO2 levels.
Conclusions. These data demonstrate that Delta Pa-(ECO2)', in anaesthetized patients depends on F-IO2.

• 出版日期2011-10