Martinu Tereza, Menzies Dick, Dial Sandra
Respiratory Epidemiology Unit, Montreal Chest Institute, McGill University, Montreal, Quebec, Canada.
Can Respir J. 2003 Sep;10(6):311-5. doi: 10.1155/2003/818404.
The prediction rules for the evaluation of the acid-base status in patients with chronic respiratory acidosis, derived primarily from an experimental canine model, suggest that complete compensation should not occur. This appears to contradict frequent observations of normal or near-normal pH levels in patients with chronic hypercapnia.
Linear regression analysis was used to estimate the relationships between arterial pH, bicarbonate and partial pressure of carbon dioxide (PCO2) from 18 separate arterial blood gas measurements in 18 clinically stable outpatients with chronic hypercapnic respiratory failure from chronic obstructive lung disease, and without clinical conditions or medications likely to cause a primary metabolic alkalosis.
The PCO2 ranged from 45 mmHg to 77 mmHg, and pH ranged from 7.37 to 7.44. In only three of the arterial blood gas measurements were the pH values lower than 7.38. From the regression equations derived from these measurements, the pH decreased by 0.014 for each 10 mmHg increase in the PCO2, and the bicarbonate level increased by 5.1 mmol/L. These values are quite different from a decrease in pH of 0.03 and an increase in bicarbonate of 3.5 mmol/L predicted using the rules derived from the canine model.
In patients with chronic stable hypercapnia, acid-base compensatory mechanisms appear to be more effective than would be predicted using the classic rules.
评估慢性呼吸性酸中毒患者酸碱状态的预测规则主要源自实验犬模型，该规则表明不应出现完全代偿情况。这似乎与慢性高碳酸血症患者pH值正常或接近正常的常见观察结果相矛盾。
采用线性回归分析，对18例患有慢性阻塞性肺疾病所致慢性高碳酸血症呼吸衰竭且临床稳定的门诊患者的18次独立动脉血气测量结果进行分析，以估计动脉pH值、碳酸氢盐和二氧化碳分压（PCO2）之间的关系，这些患者无可能导致原发性代谢性碱中毒的临床状况或用药情况。
PCO2范围为45 mmHg至77 mmHg，pH范围为7.37至7.44。仅在3次动脉血气测量中pH值低于7.38。根据这些测量结果得出的回归方程显示，PCO2每升高10 mmHg，pH值下降0.014，碳酸氢盐水平升高5.1 mmol/L。这些值与使用犬模型得出的规则所预测的pH值下降0.03及碳酸氢盐升高3.5 mmol/L有很大差异。
在慢性稳定高碳酸血症患者中，酸碱代偿机制似乎比使用经典规则预测的更为有效。
