Grenier B, Verchère E, Mesli A, Dubreuil M, Siao D, Vandendriessche M, Calès J, Maurette P
Department of Anesthesiology 3, University Hospital, Bordeaux, France.
Anesth Analg. 1999 Jan;88(1):43-8. doi: 10.1097/00000539-199901000-00009.
In neurosurgery, estimation of PaCO2 from PETCO2 has been questioned. The aim of this study was to reevaluate the accuracy of PETCO2 in estimating PaCO2 during neurosurgical procedures lasting >3 h and to measure the effect of surgical positioning on arterial to end-tidal CO2 gradient (P[a-ET]CO2) over time. One hundred four neurosurgical patients classified into four groups (supine [SP], lateral [LT], prone [PR], sitting [ST]) were included in a prospective study. PaCO2, PETCO2, and P(a-ET)CO2 were measured after induction of anesthesia (T0), after positioning (T1), each following hour (T2, T3, T4), and at the end of the procedure after return to the SP position (T5). Data are expressed as the mean +/- SD, and statistical analysis used linear regression, the Bland-Altman method, and analysis of variance. The mean durations of positioning and surgery were 4.1+/-1 h and 3.7+/-1.3 h, respectively. We performed 624 simultaneous measurements of PaCO2 (33+/-5 mm Hg) and PETCO2 (27+/-4 mm Hg), leading to a mean P(a-ET)CO2 of 6+/-4 mm Hg. P(a-ET)CO2 of the LT group (7+/-3 mm Hg) was larger (compared with the SP, PR, and ST groups) because of a lower PETCO2 (26+/-4 mm Hg). Negative P(a-ET)CO2 (PETCO2 > PaCO2) occurred 22 times, only in the SP (n = 9) and ST groups (n = 13). Changes in opposite directions of PETCO2 and PaCO2 between two successive measurements were found in 26% of the cases. Correlation coefficients in the four groups (PaCO2 versus PETCO2) were not in good agreement (0.46 to 0.62; P < 0.001). The mean bias was between 5 and 7 mm Hg. The superior (13-15 mm Hg) and inferior (-5 to 0 mm Hg) limits of agreement were too large to expect PETCO2 to replace PaCO2. In conclusion, during neurosurgical procedures of >3 h, capnography should be performed with regular analysis of arterial blood gases for optimal ventilator adjustment.
This study, which aimed to reevaluate the ability of PETCO2 to estimate PaCO2 during neurosurgical procedures according to surgical position, indicates that PETCO2 cannot replace PaCO2 for the following reasons: scattering of individual values; occurrence of negative arterial to end-tidal CO2 gradient (P[a-ET]CO2; PaCO2 and PETCO2 variations in opposite directions; large changes in P(a-ET)CO2 between two samples; and instability of P(a-ET)CO2 over time.
在神经外科手术中，通过呼气末二氧化碳分压（PETCO2）来估算动脉血二氧化碳分压（PaCO2）一直受到质疑。本研究的目的是重新评估在持续时间超过3小时的神经外科手术过程中，PETCO2估算PaCO2的准确性，并测量手术体位随时间对动脉血与呼气末二氧化碳分压差（P[a - ET]CO2）的影响。一项前瞻性研究纳入了104例神经外科患者，这些患者被分为四组（仰卧位[SP]、侧卧位[LT]、俯卧位[PR]、坐位[ST]）。在麻醉诱导后（T0）、体位摆放后（T1）、随后的每小时（T2、T3、T4）以及手术结束回到仰卧位后（T5）测量PaCO2、PETCO2和P(a - ET)CO2。数据以平均值±标准差表示，统计分析采用线性回归、布兰德 - 奥特曼方法和方差分析。体位摆放和手术的平均持续时间分别为4.1±1小时和3.7±1.3小时。我们同时进行了624次PaCO2（33±5 mmHg）和PETCO2（27±4 mmHg）测量，得出平均P(a - ET)CO2为6±4 mmHg。LT组的P(a - ET)CO2（7±3 mmHg）更大（与SP、PR和ST组相比），这是因为其PETCO2较低（26±4 mmHg）。负的P(a - ET)CO2（PETCO2 > PaCO2）出现了22次，仅在SP组（n = 9）和ST组（n = 13）中出现。在26%的病例中发现连续两次测量之间PETCO2和PaCO2呈相反方向变化。四组中（PaCO2与PETCO2）的相关系数不一致（0.46至0.62；P < 0.001）。平均偏差在5至7 mmHg之间。一致性的上限（13 - 15 mmHg）和下限（ - 5至0 mmHg）太大，无法期望PETCO2取代PaCO2。总之，在持续时间超过3小时的神经外科手术过程中，应进行二氧化碳监测，并定期分析动脉血气以进行最佳通气调整。
本研究旨在根据手术体位重新评估神经外科手术过程中PETCO2估算PaCO2的能力，结果表明PETCO2不能取代PaCO2，原因如下：个体值分散；出现负的动脉血与呼气末二氧化碳分压差（P[a - ET]CO2）；PaCO2和PETCO2呈相反方向变化；两个样本之间P(a - ET)CO2变化大；以及P(a - ET)CO2随时间不稳定。
