To the Editors:
I read with interest the article by Rees等。1。他们关于40例慢性肺病患者的数据支持使用外周静脉血来估计动脉氧张力(pa,O2) in a vast majority of patients. They also address this issue in a similar study2。他们发现这意味着pa,O2was not clinically larger than the peripheral venous oxygen tension (0.83±4 mmHg or 0.11±0.53 kPa). They also showed that peripheral venous carbon dioxide tension and pH correlate very well with arterial values, with the arterial values being slightly lower and clinically negligible compared with venous values for carbon dioxide tension (-0.7±2.1 mmHg or -0.09±0.28 kPa) and pH (-0.001±0.013)1。
我想提出两点findin评论gs. First, the authors describe accuracy (bias) as the mean difference between the two samples. However, true mean bias is best taken as the mean absolute difference between the two samples. Suppose, for example, that one subject has apa,O2那比静脉样品高5 mmHg,另一个受试者有一个pa,O2that is 5 mmHg less. In such a case, if one uses mean difference instead of absolute mean difference, one would erroneously conclude that the accuracy of peripheral venous blood to predictpa,O2是完美的(平均偏见是0 mmHg),而实际上不是。作者计算出其样品的偏置为0.83 mmHg(0.11 kPa)。但是,如上示例所示,绝对偏差可能会更大。
Secondly, the findings are of no surprise. A recent meta-analysis of 29 studies indicates that the accuracy of predictingpa,O2来自静脉样品取决于动脉样品3。尽管荟萃分析将耳垂和指尖毛细管样品与动脉样品进行了比较,但由于在两种情况下都评估了静脉采样,因此荟萃分析的发现仍然适用。荟萃分析清楚地表明,作为pa,O2下降,例如海拔或其他病理生理学(IE。肺部病),预测的准确性pa,O2改进3。因此,荟萃分析阐明了为什么珠穆朗玛峰研究4,,,,and any study using diseased patients with lowpa,O2((例如Dar等。5), supports the use of capillary blood to representpa,O2,以及使用正常受试者的任何其他研究pa,O2values does not. The data of Rees等。1支持外周静脉血反射的观念pa,O2因为患者的平均水平很低pa,O2((67 mmHg or 9 kPa) to begin with, and a lowpa,O2最小化氧气张力的动脉差异,提高了其预测的准确性pa,O2。在荟萃分析的表7中,回归方程表明当动脉pa,O2is 67 mmHg, the mean difference between arterial and earlobe oxygen tension is small (0.79 mmHg; r2 = 0.86, mean square error 4.8 mmHg)3。This difference is nearly identical to the 0.83 mmHg mean difference from Rees等。1当使用相同的平均值pa,O2。
Consistent with the recent work of Rees and co-workers1,,,,2,荟萃分析表明,来自耳垂或指尖的静脉采样可以准确反映动脉pH或动脉二氧化碳张力(pa,CO2) over a wide range of values3。Therefore, sampling either peripheral venous blood, arterialised capillary blood from the earlobe, or fingertip capillary blood for predictingpa,CO2在广泛的临床值中,动脉pH值非常健壮。如果只想预测动脉pH或pa,CO2。
用于预测pa,O2,从外周静脉或耳垂样品(比指尖样本更好)的静脉血液采样仅适用于条件pa,O2低。当然,难题是一个人不知道是否pa,O2低 (IE。<70 mmHg) unless it is actually measured from an arterial sample. As the residual standard error in predictingpa,O2从静脉样品中,从耳垂采样(类似于其外周静脉抽样数据)预测到15 mmHg时,从6 mmHg进行预测。3,,,,I would recommend against using venous blood to predictpa,O2或患者或研究受试者中的肺泡到动脉氧张力差异。
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