Tang W, Modi N, Clark P
Royal Postgraduate Medical School, Queen Charlotte's and Chelsea Hospital, London.
Arch Dis Child. 1993 Jul;69(1 Spec No):28-31. doi: 10.1136/adc.69.1_spec_no.28.
The aim of this study was to determine the kinetics of H(2)18O equilibration and elimination in preterm babies for the estimation of total body water. Thirteen, clinically stable, preterm babies of less than 32 weeks' gestation were studied in the first week after birth. Blood and urine samples were obtained for baseline measurement of 18O:16O ratio and 1 ml/kg of 10% H(2)18O (0.1 g/kg isotope) administered orally. Eleven blood samples were obtained over the next six hours and between one and four over the next 18 hours. During the same 24 hour period between three and eight urine samples were also obtained. The dilution space at zero time (volume of distribution or total body water) was estimated using double exponential curve fitting using all available points, from single samples and from linear regression on the log data using two or three samples. Equilibration time was variable and showed a significant correlation with percentage change in body weight from birth. For blood samples, the median time to equilibrium was 81 minutes (range 2 to 191). A plateau phase was not detected, with H(2)18O enrichment declining after the point of maximum enrichment. The median volume of distribution at time 0, based on double exponential curve fit analysis, was 859 ml/kg (range 755 to 995). The volume of distribution, estimated from linear regression on the log data using two serum samples obtained at three and six hours, approximated most closely to that based on exponential curve fit analysis with a median difference of -4 ml/kg (range -41 to 73). It was concluded that in most situations blood sampling at three and six hours may be acceptable. However, as equilibration time is variable and influenced by the state of expansion or depletion of body water compartments, when studying overhydration states, multiple sampling is advised in order to be certain that the elimination phase has been reached.
本研究的目的是确定早产婴儿体内H₂¹⁸O的平衡及消除动力学，以估算全身水含量。对13例出生后第一周临床状况稳定、孕周小于32周的早产婴儿进行了研究。采集血样和尿样用于基线时¹⁸O:¹⁶O比值的测定，并口服给予1ml/kg的10% H₂¹⁸O（0.1g/kg同位素）。在接下来的6小时内采集11份血样，在随后的18小时内采集1至4份血样。在同一24小时期间，还采集3至8份尿样。利用所有可用点通过双指数曲线拟合来估计零时的稀释空间（分布容积或全身水含量），也可根据单一样本以及利用两或三个样本对对数数据进行线性回归来估计。平衡时间存在差异，且与出生后体重的百分比变化显著相关。对于血样，达到平衡的中位时间为81分钟（范围为2至191分钟）。未检测到平台期，H₂¹⁸O富集在达到最大富集点后下降。基于双指数曲线拟合分析，零时的中位分布容积为859ml/kg（范围为755至995ml/kg）。根据在3小时和6小时采集的两份血清样本对对数数据进行线性回归估算的分布容积，与基于指数曲线拟合分析估算的结果最为接近，中位差异为 -4ml/kg（范围为 -41至73ml/kg）。得出的结论是，在大多数情况下，在3小时和6小时采集血样可能是可以接受的。然而，由于平衡时间存在差异且受身体水室的扩张或消耗状态影响，在研究水合过多状态时，建议进行多次采样，以确保已进入消除阶段。
