Pianosi P, Hochman J
Department of Pediatrics and Child Health, Children's Hospital of Winnipeg, Manitoba, Canada.
Pediatr Pulmonol. 1996 Sep;22(3):154-60. doi: 10.1002/(SICI)1099-0496(199609)22:3<154::AID-PPUL3>3.0.CO;2-P.
We set out to determine the effects of various estimates of arterial PCO2 (PaCO2) on calculation of cardiac output (Q) by the indirect Fick (CO2) method in healthy children and children with cystic fibrosis (CF), and to develop a prediction equation for children for PaCO2, based on end-tidal PCO2 (PetCO2). The study had 3 parts: 1) Twenty-three healthy children exercised lightly and moderately while arterialized capillary blood gases and PetCO2 were measured simultaneously so that a prediction equation for PaCO2 could be derived from PetCO2. Cardiac output was measured by CO2 rebreathing at each workload; different values for PaCO2 (measured in arterialized capillary blood, end-tidal, and PaCO2 derived from the Bohr equation assuming normal dead space) were used to calculate Q; 2) our equation PaCO2 = 0.647 PetCO2 + 12.4 was tested prospectively to measure Q in 9 healthy children; and 3) cardiac output based on arterialized capillary PaCO2 was compared with that based on Jones-corrected PetCO2 during light and moderate exercise in 16 CF patients whose forced expiratory volume in 1 second (FEV1), range from normal to 37% predicted. Our results have shown that in healthy children end-tidal based-estimates of PaCO2 tended to overestimate Q, whereas PaCO2 values derived by the Bohr equation and assuming normal dead space tended to underestimate Q, compared with Q calculated from directly measured PaCO2. Our prediction equation resulted in good agreement compared with directly measured PaCO2 when used to calculate Q (mean difference, +1.3%; range, +9% to -13%). CF patients with little or no airway obstruction had results similar to healthy controls, but those with severe airway obstruction had lower values for Q when PetCO2 was used instead of directly measured PaCO2. We conclude that estimates of PaCO2 from PetCO2 are not reliable in patients with moderately severe pulmonary disease due to CF. In healthy children, the prediction equation for PaCO2 from PetCO2 derived in the present study gives results superior to other bloodless methods currently in use for computation of Q by the indirect Fick (CO2) method.
我们着手确定在健康儿童和囊性纤维化（CF）患儿中，采用间接菲克（二氧化碳）法计算心输出量（Q）时，动脉血二氧化碳分压（PaCO2）的各种估算值所产生的影响，并基于呼气末二氧化碳分压（PetCO2）建立一个针对儿童PaCO2的预测方程。该研究分为三个部分：1）23名健康儿童进行轻度和中度运动，同时测量动脉化毛细血管血气和PetCO2，以便从PetCO2推导出PaCO2的预测方程。在每个工作量下通过二氧化碳重呼吸测量心输出量；使用不同的PaCO2值（在动脉化毛细血管血中测量、呼气末以及根据假设正常死腔的玻尔方程得出的PaCO2）来计算Q；2）前瞻性地测试我们的方程PaCO2 = 0.647 PetCO2 + 12.4，以测量9名健康儿童的Q；3）在16名1秒用力呼气量（FEV1）范围从正常到预测值的37%的CF患者进行轻度和中度运动期间，比较基于动脉化毛细血管PaCO2的心输出量与基于琼斯校正的PetCO2的心输出量。我们的结果表明，在健康儿童中，基于呼气末的PaCO2估算值往往高估Q，而与根据直接测量的PaCO2计算出的Q相比，由玻尔方程得出并假设正常死腔的PaCO2值往往低估Q。当用于计算Q时，我们的预测方程与直接测量的PaCO2相比结果吻合良好（平均差异为 +1.3%；范围为 +9%至 -13%）。气道阻塞很少或没有的CF患者结果与健康对照相似，但当使用PetCO2而非直接测量的PaCO2时，气道阻塞严重的患者Q值较低。我们得出结论，对于因CF导致中度严重肺部疾病的患者，从PetCO2估算PaCO2并不可靠。在健康儿童中，本研究中从PetCO2得出的PaCO2预测方程在通过间接菲克（二氧化碳）法计算Q时，其结果优于目前使用的其他无血方法。
