Lorenz J M, Kleinman L I, Markarian K
Department of Pediatrics and Human Development, Michigan State University, East Lansing, USA.
J Pediatr. 1997 Jul;131(1 Pt 1):81-6. doi: 10.1016/s0022-3476(97)70128-8.
Nonoliguric hyperkalemia has been reported to occur in the first week of life in as many as 50% of extremely low birth weight (ELBW) infants. We studied potassium balance and renal function in the first 5 days of life to characterize potassium metabolism during the three phases of fluid and electrolyte homeostasis that we have described in ELBW infants and to elucidate the factors that contribute to the development of nonoliguric hyperkalemia.
Plasma potassium concentration (PK), potassium intake and output, and renal clearances were obtained for the first 6 days of life in 31 infants with a birth weight of 1000 gm or less. Collection periods in which urine flow rate was greater than or equal to 3 ml/kg per hour and weight loss was greater than or equal to 0.8 gm/kg per hour were denoted to be diuretic. Prediuresis includes all collection periods before the first diuretic period; diuresis includes all collection periods between the first and last diuretic periods; postdiuresis includes all collection periods after the last diuretic period. Infants with a PK greater than 6.7 mmol/L on at least one measurement were denoted to have hyperkalemia.
PK increased initially after birth--despite the absence of potassium intake- and then decreased and stabilized by the fourth day of life. Diuresis occurred in 27 of 31 infants. The age at which PK peaked was closely related to the onset of diuresis. PK decreased significantly during diuresis as the result of a more negative potassium balance, despite a significant increase in potassium intake. In fact, PK fell to less than 4 mmol/L in 13 of 27 infants during diuresis. After the cessation of diuresis, potassium excretion decreased even though there was a significant increase in potassium intake, potassium balance was zero, and PK stabilized. Hyperkalemia developed in 11 of 31 infants. The pattern of change in PK with age was similar in infants with normokalemia and hyperkalemia: PK initially increased (essentially in the absence of potassium intake) and then decreased and stabilized by the fourth day of life. However, the rise in PK after birth was greater in infants with hyperkalemia than in those with normokalemia: 0.7 +/- 0.2 versus 1.8 +/- 0.2 mmol/L (p < 0.001). No differences in fluid and electrolyte homeostasis or renal function were identified as associated with hyperkalemia.
PK increases in most ELBW infants in the first few days after birth as a result of a shift of potassium from the intracellular to the extracellular compartment. The increase in the glomerular filtration rate and in the fractional excretion of sodium, with the onset of diuresis, facilitates potassium excretion, and PK almost invariably decreases. Hyperkalemia seems to be principally the result of a greater intracellular to extracellular potassium shift immediately after birth in some ELBW infants.
据报道，多达50%的极低出生体重（ELBW）婴儿在出生后第一周会出现非少尿性高钾血症。我们研究了出生后前5天的钾平衡和肾功能，以描述ELBW婴儿在我们所描述的液体和电解质稳态三个阶段的钾代谢情况，并阐明导致非少尿性高钾血症发生的因素。
对31例出生体重1000克或更低的婴儿在出生后前6天测定血浆钾浓度（PK）、钾的摄入量和排出量以及肾脏清除率。尿流率大于或等于每小时3毫升/千克且体重减轻大于或等于每小时0.8克/千克的收集期被定义为利尿期。利尿前期包括第一个利尿期之前的所有收集期；利尿期包括第一个和最后一个利尿期之间的所有收集期；利尿后期包括最后一个利尿期之后的所有收集期。至少有一次测量PK大于6.7毫摩尔/升的婴儿被定义为患有高钾血症。
出生后PK最初升高——尽管没有钾摄入——然后在出生后第4天下降并稳定。31例婴儿中有27例出现利尿。PK达到峰值的年龄与利尿的开始密切相关。由于钾平衡更负，尽管钾摄入量显著增加，但利尿期间PK显著下降。事实上，27例婴儿中有13例在利尿期间PK降至低于4毫摩尔/升。利尿停止后，尽管钾摄入量显著增加，但钾排泄减少，钾平衡为零，PK稳定。31例婴儿中有11例发生高钾血症。正常血钾和高钾血症婴儿PK随年龄变化的模式相似：PK最初升高（基本上在没有钾摄入的情况下），然后在出生后第4天下降并稳定。然而，高钾血症婴儿出生后PK的升高幅度大于正常血钾婴儿：分别为0.7±0.2和1.8±0.2毫摩尔/升（p<0.001）。未发现与高钾血症相关的液体和电解质稳态或肾功能差异。
大多数ELBW婴儿出生后最初几天PK升高是由于钾从细胞内转移到细胞外间隙。随着利尿的开始，肾小球滤过率和钠分数排泄增加，促进了钾的排泄，PK几乎总是下降。高钾血症似乎主要是一些ELBW婴儿出生后立即细胞内到细胞外钾转移增加的结果。
