Lorenz J M, Kleinman L I, Ahmed G, Markarian K
Department of Pediatrics and Human Development, Michigan State University, East Lansing, USA.
Pediatrics. 1995 Sep;96(3 Pt 1):484-9.
We had shown previously that preterm infants undergo three phases of fluid and electrolyte homeostasis; prediuretic, diuretic, and postdiuretic. The objectives of the present study were: (1) to determine whether infants even more immature and infants cared for under thermal environmental conditions different from those previously studied also undergo these three phases; and (2) to relate these phases to changes in renal function.
Consecutive, timed urine collections were made during the first 5 days of life in 32 infants with birth weights of 1000 g or less. Infants were cared for in radiant warmers for 24 hours and then transferred to nonhumidified incubators. Diuresis was defined as urine flow rate (V) of 3 mL or more/kg per hour and weight loss of 0.8 g or more/kg per hour. The physiologic relationships among water and sodium balance, insensible water loss, arterial blood pressure, and renal function were made during the three phases.
Twenty-eight (87%) of the 32 infants underwent the three homeostatic phases. The median ages of onset and cessation of diuresis were 25 and 96 hours, respectively. There was no correlation between onset of diuresis and change of thermal environment. During the prediuretic phase, V averaged 1.6 mL/kg per hour, and 17 of 28 infants had at least one collection period in which V was less than 1 mL/kg per hour; urinary sodium excretion was 0.1 mEq/kg per hour; the glomerular filtration rate (GFR) was 0.22 mL/kg per hour; fractional excretion of sodium (FENa) was 6.2%; and urine osmolality was dilute (221 mOsm/kg). During the diuretic phase, V and sodium excretion more than tripled; GFR and FENa doubled; and there was no change in urine osmolality. During postdiuresis, V and Na excretion decreased to values intermediate between the prediuretic and diuretic phases, and FENa fell to prediuretic levels, but there was no change in GFR or urine osmolality. There was poor correlation between blood pressure and GFR. Insensible water loss was high and variable during all phases, exceeding 190 mL/kg per day in the smallest infants.
Extremely low birth weight infants manifest three phases of fluid and electrolyte homeostasis, as do more mature infants, independent of thermal environment. Diuresis and natriuresis are the result of abrupt increases in GFR and FENa. We speculate that this may be the result of expansion of the neonatal extracellular space as fetal lung fluid is reabsorbed.
我们之前已经表明，早产儿会经历液体和电解质稳态的三个阶段：利尿前期、利尿期和利尿后期。本研究的目的是：（1）确定更不成熟的婴儿以及在与之前研究不同的热环境条件下护理的婴儿是否也会经历这三个阶段；（2）将这些阶段与肾功能变化相关联。
对32名出生体重1000克或更低的婴儿在出生后第1至5天进行连续定时尿液收集。婴儿在辐射保暖器中护理24小时，然后转移到非加湿培养箱中。利尿定义为尿流率（V）每小时3毫升或更多/千克且体重减轻每小时0.8克或更多/千克。在三个阶段中确定了水和钠平衡、不显性失水、动脉血压和肾功能之间的生理关系。
32名婴儿中有28名（87%）经历了三个稳态阶段。利尿开始和停止的中位年龄分别为25小时和96小时。利尿开始与热环境变化之间无相关性。在利尿前期，V平均为每小时1.6毫升/千克，28名婴儿中有17名至少有一个收集期V小于每小时1毫升/千克；尿钠排泄为每小时0.1毫当量/千克；肾小球滤过率（GFR）为每小时0.22毫升/千克；钠分数排泄（FENa）为6.2%；尿渗透压较低（221毫摩尔/千克）。在利尿期，V和钠排泄增加了两倍多；GFR和FENa增加了一倍；尿渗透压没有变化。在利尿后期，V和钠排泄降至利尿前期和利尿期之间的中间值，FENa降至利尿前期水平，但GFR或尿渗透压没有变化。血压与GFR之间相关性较差。在所有阶段不显性失水都很高且变化不定，最小的婴儿每天超过190毫升/千克。
极低出生体重婴儿表现出液体和电解质稳态的三个阶段，与更成熟的婴儿一样，与热环境无关。利尿和利钠是GFR和FENa突然增加的结果。我们推测这可能是由于胎儿肺液重吸收导致新生儿细胞外液扩张的结果。
