Chauhan S P, Cowan B D, Meydrech E F, Magann E F, Morrison J C, Martin J N
Department of Obstetrics and Gynecology, University of Mississippi Medical Center.
Am J Obstet Gynecol. 1994 Jun;170(6):1705-9; discussion 1709-12.
Sampling of the umbilical artery for determination of acid-base status is performed within 60 minutes of birth, but is not feasible in all hospitals on a 24-hour basis. A desirable alternative would be to perform the arterial cord blood gas analysis hours after the sample was obtained at delivery with reliable identification of whether the newborn was acidotic.
After 19 deliveries multiple umbilical arterial blood samples were withdrawn into five preheparinized syringes, and these were analyzed at 0.5, 15, 30, 45, and 60 hours after delivery. On the basis of observed changes in pH and base deficit over 60 hours, two separate regression equations were generated. These two equations permit calculation of the original pH and base deficit if the following are known: (1) the time interval from delivery to blood gas analysis and (2) the values of the remote pH and remote base deficit. The regression models were validated among 23 subsequent deliveries to assess how accurately they identified newborn acid-base status at birth.
The original pH and base deficit can be calculated with two separate equations from linear regression models if two variables are known: the results of the remote umbilical arterial blood gas analysis and time intervals from delivery to analysis. Of 23 newborns during the validation phase of the study, 16 were not acidotic, one had respiratory acidosis, and six had metabolic acidosis. The second umbilical arterial blood gas analysis was performed at a mean (+/- SD) interval of 53.8 +/- 41.5 hours (range 7.5 to 138 hours). The remote gas analysis inaccurately identified 68.7% (11/16) of nonacidotic newborns as being acidotic at birth. However, insertion of these data into these equations produced results with none of the newborns predicted to have normal acid-base when they were acidotic at birth or predicted to be acidotic when the cord pH was normal.
Use of these mathematic models allows the clinician to perform an umbilical arterial blood pH analysis < or = 60 hours after delivery yet with accurate estimation of true acid-base status at birth.
出生后60分钟内采集脐动脉血以测定酸碱状态，但并非所有医院都能24小时随时进行。一个理想的替代方法是在分娩时采集样本数小时后进行动脉脐血气分析，并能可靠地确定新生儿是否酸中毒。
19例分娩后，将多份脐动脉血样本采集到5个预肝素化注射器中，并在分娩后0.5、15、30、45和60小时进行分析。根据60小时内观察到的pH值和碱缺失变化，生成了两个独立的回归方程。如果已知以下两点，则可通过这两个方程计算原始pH值和碱缺失：（1）从分娩到血气分析的时间间隔；（2）远程pH值和远程碱缺失值。在随后的23例分娩中对回归模型进行验证，以评估其在确定出生时新生儿酸碱状态方面的准确性。
如果已知两个变量，即远程脐动脉血气分析结果和从分娩到分析的时间间隔，则可通过线性回归模型的两个独立方程计算原始pH值和碱缺失。在研究的验证阶段的23例新生儿中，16例无酸中毒，1例有呼吸性酸中毒，6例有代谢性酸中毒。第二次脐动脉血气分析的平均（±标准差）间隔时间为53.8±41.5小时（范围7.5至138小时）。远程血气分析将68.7%（11/16）的非酸中毒新生儿错误地鉴定为出生时酸中毒。然而，将这些数据代入这些方程得出的结果是，没有一个新生儿在出生时酸中毒时被预测为酸碱正常，或在脐血pH值正常时被预测为酸中毒。
使用这些数学模型可使临床医生在分娩后≤60小时进行脐动脉血pH分析，同时准确估计出生时的真实酸碱状态。
