Coulthard M G, Hey E N
Arch Dis Child. 1985 Jul;60(7):614-20. doi: 10.1136/adc.60.7.614.
Renal control of water and electrolyte homeostasis was studied in 10 healthy babies (gestation 29 to 34 weeks; birthweight 1.19 to 2.19 kg) while water intake was varied. Glomerular filtration rate and urine flow were estimated daily from spot plasma and urine samples for six days using a constant inulin infusion, and simultaneous sodium, potassium, osmolar, and free water clearances were calculated. The infusion was started at an average age of 14 hours. Each baby received a total fluid intake of 96 ml/kg daily on study days 1, 2, and 5, and about 200 ml/kg on study days 3, 4, and 6. Daily sodium intake was kept constant at 3 mmol/kg. At the end of the first study day the babies were undergoing a diuresis, but thereafter their estimated daily water balances remained stable regardless of intake. Glomerular filtration remained stable; alterations in urine flow reflected a change in the percentage of filtrate excreted. Plasma electrolytes and osmolality were stable throughout, and on study days 2 to 6 the urinary excretion rates of sodium, potassium, and other osmoles remained the same regardless of urine flow. The delivery of sodium to the distal tubule was estimated to be between 17 and 20% of the filtered load. Well preterm babies can cope with daily water intakes between 96 and 200 ml/kg from the third day of life.
在10名健康婴儿（胎龄29至34周；出生体重1.19至2.19千克）中，研究了水分摄入变化时肾脏对水和电解质稳态的控制。使用恒定的菊粉输注，连续六天每天从即时血浆和尿液样本中估算肾小球滤过率和尿流，并计算同时期的钠、钾、渗透压和自由水清除率。输注在平均年龄14小时时开始。在研究的第1、2和5天，每个婴儿每天的总液体摄入量为96毫升/千克，在研究的第3、4和6天约为200毫升/千克。每日钠摄入量保持恒定，为3毫摩尔/千克。在第一个研究日结束时，婴儿处于利尿状态，但此后，无论摄入量如何，他们估计的每日水平衡保持稳定。肾小球滤过保持稳定；尿流的变化反映了排泄滤液百分比的变化。整个过程中血浆电解质和渗透压保持稳定，在研究的第2至6天，钠、钾和其他渗透溶质的尿排泄率与尿流无关，保持不变。钠向远端小管的输送估计为滤过负荷的17%至20%。健康的早产儿从出生第三天起就能应对每天96至200毫升/千克的水分摄入。
