Roemer V M
Institute for Fetal-Maternal Medicine, Detmold, Germany.
Z Geburtshilfe Neonatol. 2011 Jun;215(3):115-24. doi: 10.1055/s-0031-1271756. Epub 2011 Jul 13.
Besides actual pH, base excess [ctH (+)(B) (mmol/l)] is of major importance since it is meant to reflect lactate acidosis due to foetal hypoxia; In vivo BE (B) is not independent from pCO (2). Independence is achieved by using the extended extracellular fluid (Ecf) for dilution of haemoglobin (cHb (B)) thus reducing cHb (B) to cHb (B)/3 (in the foetus to cHb (B)/4). Correction of ctH (+)(B) from the normally low foetal oxygen saturation by reoxygenation of Hb increases ctH (+)(B), resulting in 4 different variables: ctH (+)(B,act) (=BE (B)), ctH (+)(Ecf,act) (standard BE), ctH (+)(B,ox.) and ctH (+)(Ecf,ox). 3 questions arise: (i) which variable is most appropriate for perinatal acid-base studies? (ii) are there clinical advantages for using BE when compared with actual pH (UA), and (iii) what are the thresholds of the BE parameters?
The Apgar 1 min and the WAS score were used thus measuring neonatal vigour and FHR characteristics during the last 30 min of 475 foetuses all delivered by the vaginal route. FHR was evaluated by computation of the WAS index . The WAS index refers to (FHMW1)(OZFW2)(OZA*W3)(-1) where fhm is mean heart frequency (bpm), ozf denotes the number of turning points (N/min) and oza refers to the oscillation amplitude/min (bpm). The weighting functions W1, W2 and W3 were computed using optimizing software. The WAS score denotes the mean of the WAS indices of the last 30 min of delivery. BE was computed according to the van Slyke/Henderson-Hasselbalch equation using pH and pCO (2) measurements; sO (2) (%) for HbF was determined according to Ruiz et al. .
In vivo foetal ctH (+)(B,act) (UA) is closely correlated with pCO (2). UA: r=-0.288, P<10 (-4), N=475: whereas ctH (+)(Ecf,act) (standard BE) becomes independent from pCO (2): r=-0.0068, P=0.881. In UA blood there is no independence of the 2 blood gases pCO (2) and pO (2): both are inversely correlated: r=-0.291, P<<10 (-4). pO (2) shows no correlation with ctH (+)(B,act) (r=-0.074, P=0.105) but correlates well with ctH (+)(Ecf,act): r=-0.1722, P=0.0002. The Apgar score (1 min) is best correlated with pH (UA) (r=0.4078, P<10 (-4)(,) Spearman's rho=0.307, P<10 (-4)). Correction of ctH (+)(B,act) or ctH (+)(Ecf,act) to 100% oxygen saturation always leads to higher coefficients. Using: ctH (+)(B,ox), ctH (+)(B,act), ctH (+)(Ecf,ox) and ctH (+)(Ecf,act): rho=0.2597, 0.2394, 0.1838 and 0.1763, respectively; P all <10 (-4). The same holds true for Apgar 5 min: rho=0.2307, 0.2168, 0.1811 and 0.1771, respectively (P<10 (-4) for all). The WAS score is closely correlated with pH (UA): r=0.656, P<<10 (-4), N=475. The correlation with the 4 variables under investigation: ctH (+)(B,ox), ctH (+)(B,act), ctH (+)(Ecf,ox) and ctH (+)(Ecf,act) leads to r=-0.587, r=-0.565, r=-0.437 and r=-0.427, respectively (P<10 (-4) for all). The threshold of standard BE (ox.)(=ctH (+)(Ecf ox)) in 390 acidotic term infants with still good outcomes is -14.0 mmol/l.
Actual pH (cH (+)) offers the closest correlation with 2 essential clinical parameters: FHF and Apgar scores; the advantages of ctH (+)(B) and ctH (+)(Ecf), are not self-evident; if determination of the metabolic component becomes necessary standard BE, (ctH (+)(Ecf)) should be used with correction to 100% oxygen saturation (ctH (+)(Ecf,ox.)) of haemoglobin (HbF), because this quantity (after pH (UA)) correlates best with clinical indices. However if the 'correction' is omitted the difference seems clinically irrelevant.
除实际pH值外，碱剩余[ctH(+)(B)(mmol/L)]也很重要，因为它旨在反映胎儿缺氧导致的乳酸酸中毒；体内碱剩余（B）并非独立于pCO₂。通过使用扩展细胞外液（Ecf）稀释血红蛋白（cHb(B)）来实现独立性，从而将cHb(B)降低至cHb(B)/3（胎儿为cHb(B)/4）。通过血红蛋白再氧合纠正胎儿正常低氧饱和度时的ctH(+)(B)会增加ctH(+)(B)，从而产生4个不同变量：ctH(+)(B,act)(=BE(B))、ctH(+)(Ecf,act)（标准碱剩余）、ctH(+)(B,ox.)和ctH(+)(Ecf,ox)。出现3个问题：（i）哪个变量最适合围产期酸碱研究？（ii）与实际pH值（UA）相比，使用碱剩余有哪些临床优势？（iii）碱剩余参数的阈值是多少？
使用1分钟阿氏评分和WAS评分来衡量475例经阴道分娩胎儿最后30分钟的新生儿活力和胎心率特征。通过计算WAS指数评估胎心率。WAS指数指(FHMW1)(OZFW2)(OZA*W3)(-1)，其中fhm是平均心率（bpm），ozf表示转折点数量（次/分钟），oza指振荡幅度/分钟（bpm）。加权函数W1、W2和W3使用优化软件计算。WAS评分表示分娩最后30分钟WAS指数的平均值。根据范斯莱克/亨德森-哈塞尔巴尔赫方程，使用pH和pCO₂测量值计算碱剩余；根据Ruiz等人的方法测定HbF的sO₂(%)。
体内胎儿ctH(+)(B,act)（UA）与pCO₂密切相关。UA：r = -0.288，P < 10⁻⁴，N = 475；而ctH(+)(Ecf,act)（标准碱剩余）与pCO₂无关：r = -0.0068，P = 0.881。在UA血中，两种血气pCO₂和pO₂不独立：两者呈负相关：r = -0.291，P << 10⁻⁴。pO₂与ctH(+)(B,act)无相关性（r = -0.074，P = 0.105），但与ctH(+)(Ecf,act)相关性良好：r = -0.1722，P = 0.0002。1分钟阿氏评分与pH（UA）相关性最佳（r = 0.4078，P < 10⁻⁴，斯皮尔曼等级相关系数rho = 0.307，P < 10⁻⁴）。将ctH(+)(B,act)或ctH(+)(Ecf,act)校正至100%氧饱和度总是导致更高的系数。使用：ctH(+)(B,ox)、ctH(+)(B,act)、ctH(+)(Ecf,ox)和ctH(+)(Ecf,act)时：rho分别为0.2597、0.2394、0.1838和0.1763；P均 < 10⁻⁴。5分钟阿氏评分情况相同：rho分别为0.2307、0.2168、0.1811和0.1771（所有P < 10⁻⁴）。WAS评分与pH（UA）密切相关：r = 0.656，P << 10⁻⁴，N = 475。与所研究的4个变量的相关性：ctH(+)(B,ox)、ctH(+)(B,act)、ctH(+)(Ecf,ox)和ctH(+)(Ecf,act)导致r分别为 -0.587、-0.565、-0.437和 -0.427（所有P < 10⁻⁴）。390例结局良好的酸中毒足月儿中，标准碱剩余（ox.）（=ctH(+)(Ecf ox)）的阈值为 -14.0 mmol/L。
实际pH值（cH(+)）与两个重要临床参数：胎心率和阿氏评分相关性最密切；ctH(+)(B)和ctH(+)(Ecf)的优势并不明显；如果需要测定代谢成分，应使用标准碱剩余（ctH(+)(Ecf)）并将血红蛋白（HbF）校正至100%氧饱和度（ctH(+)(Ecf,ox.)），因为该量（仅次于pH（UA））与临床指标相关性最佳。然而，如果省略“校正”，差异在临床上似乎无关紧要。
