RESUMO
PURPOSE: To assess the frequency and pathogenesis of hyperkalemia in the very low birth weight infant. METHODS: Infants who weighed less than 1000 gm at birth were prospectively entered into the study within 12 hours of birth. Potential risk factors for hyperkalemia were assessed. Body weight, fluid and electrolyte balance, serum levels of sodium and potassium, creatinine clearance, fractional sodium excretion, and urine sodium/potassium ratio were measured every 8 hours for 72 hours. Measurements of plasma renin, serum aldosterone, and plasma atrial natriuretic factor were made at study entry and repeated when hyperkalemia (serum potassium greater than 6.5 mmol/L) occurred or at 72 hours. Infants in whom hyperkalemia developed were compared with those in whom it did not. RESULTS: Thirty-one infants completed the study; hyperkalemia developed in 16 (51.6%). The only difference in the occurrence of perinatal complications was the more frequent occurrence of pH less than 7.20 in infants with subsequent development of hyperkalemia. Creatinine clearance, urine output, and potassium excretion were significantly lower in the hyperkalemia group during the first 24 hours. Serum potassium concentration at 24 hours was inversely related to urine output in the prior 24 hours. Fractional sodium excretion, urine sodium/potassium ratio, and levels of renin, aldosterone, and atrial natriuretic factor did not differ between groups. CONCLUSIONS: Hyperkalemia is a frequent complication in very low birth weight infants. Infants with low urinary flow rates during the first few hours after birth are at greatest risk for the development of hyperkalemia.
Assuntos
Hiperpotassemia/etiologia , Recém-Nascido de Baixo Peso/metabolismo , Potássio/sangue , Aldosterona/sangue , Humanos , Hiperpotassemia/epidemiologia , Hiperpotassemia/metabolismo , Incidência , Recém-Nascido , Estudos Prospectivos , Fatores de TempoRESUMO
We assessed sodium balance and extracellular volume regulation in very low birth weight infants by examining the effect of differences in sodium intake on postnatal sodium homeostasis and body water composition. Twenty infants (mean birth weight 1103 +/- 216 gm, mean gestation 28.5 +/- 1.7 weeks) were randomly assigned to receive sodium in doses of either 1 or 3 mmol.kg-1.day-1 for the first 10 postnatal days. Extracellular volume (estimated by the bromide dilution method), sodium excretion, creatinine clearance, fractional sodium excretion, plasma atrial natriuretic factor level, urine aldosterone concentration, and vasopressin excretion were measured on postnatal days 1, 5, 10, 20, and 30. The corrected bromide space was large at birth and decreased in both groups during the first 5 days of observation, concomitant with a negative sodium balance. After 5 days of age, sodium excretion decreased in both groups so that sodium balance became positive and the corrected bromide space increased in proportion to increasing body weight. Differences in sodium intake were associated with differences in tubular sodium reabsorption; corrected bromide space and net sodium balance were similar in the two groups. Serum sodium concentration was significantly lower in the low-sodium intake group. Creatinine clearance, plasma atrial natriuretic factor level, and excretion of aldosterone and vasopressin were not significantly different between the two groups. We conclude that very low birth weight infants are able to regulate sodium balance by altering renal sodium excretion. However, the renal response to sodium intake may be insufficient to prevent changes in serum sodium concentration. The roles of specific renal and hormonal mechanisms regulating sodium excretion in very low birth weight infants remain incompletely defined.
Assuntos
Espaço Extracelular/metabolismo , Recém-Nascido de Baixo Peso/metabolismo , Sódio/metabolismo , Aldosterona/urina , Fator Natriurético Atrial/urina , Creatinina/metabolismo , Diurese , Humanos , Recém-Nascido , Valores de Referência , Vasopressinas/urinaRESUMO
Serial extracellular volume (ECV) changes were measured in 18 infants of less than 32 weeks gestation. Results were compared with changes in body weight, fluid and sodium intake, urine output, and serum sodium concentration. Mean +/- SD ECV decreased from 550 +/- 116 mL/kg on day 1 to 359 +/- 66 mL/kg on day 14. Thereafter, mean ECV/kg remained between 336 +/- 42 and 349 +/- 54 mL/kg. Clinical hydration and serum sodium concentration usually remained normal during this reduction of stabilization of ECV/kg. Six episodes of hyponatremia occurred at 11 to 31 days of age. Mean ECV/kg was significantly lower in infants with hyponatremia compared with infants of similar age with normal serum sodium concentration (303 +/- 36 mL/kg vs 368 +/- 56 mL/kg, P less than 0.01). Sodium intake in the two groups was similar. We conclude that ECV in the VLBW infant decreases postnatally and is regulated within a range similar to that in older infants, and that postnatal natriuresis in the first 2 weeks of life represents physiologic reduction of the expanded ECV of the fetus. Late hyponatremia may indicate excessive sodium loss and ECV depletion.
Assuntos
Espaço Extracelular/fisiologia , Recém-Nascido de Baixo Peso/fisiologia , Brometos/sangue , Nutrição Enteral , Humanos , Hiponatremia/etiologia , Lactente , Recém-Nascido , Respiração Artificial , Síndrome do Desconforto Respiratório do Recém-Nascido/complicações , Síndrome do Desconforto Respiratório do Recém-Nascido/terapia , Sódio/sangue , Fatores de TempoRESUMO
Using a rat model, we assessed the efficacy of varying doses of superoxide dismutase of (SOD) to affect plasma and tissue SOD concentrations and to attenuate dysplastic changes of lung and pulmonary vascular growth, which are chronic sequelae of neonatal oxygen exposure. One hundred forty-three 1-day-old Sprague-Dawley rats were divided into two groups and exposed to hyperoxia (0.96 to 1.0 Fio2) or room air for 8 postnatal days. Each group was subdivided into five treatment groups, which received 6, 20, 100, or 200 mg/kg/d SOD or a placebo, intramuscularly every 12 hours. All rats were then placed in room air; 52 were killed, and lung tissue and blood samples were obtained for measurement of bovine SOD concentration. The remaining rats received routine care until 58 to 60 days of age, when functional and morphologic cardiopulmonary changes were assessed. Bovine SOD concentration of pooled plasma samples increased 26-fold, from 2 to 50 micrograms/mL, between the 6 and 200 mg/kg/d SOD groups, but mean tissue concentration increased only six-fold, from 0.34 to 2.1 micrograms/lung. Cardiovascular and pulmonary changes found in each oxygen group, regardless of SOD dosage, included elevated right ventricular pressure, increased right ventricular weight, decreased number of small pulmonary arteries/mm2, decreased number of alveoli/mm2, and increased volume proportion of lung parenchyma. Thus, high plasma concentrations of bovine SOD failed to prevent the chronic cardiovascular and pulmonary sequelae of neonatal oxygen exposure in the rat, possibly because SOD did not reach the intracellular sites of action.
Assuntos
Pulmão/efeitos dos fármacos , Oxigênio/toxicidade , Superóxido Dismutase/administração & dosagem , Animais , Animais Recém-Nascidos , Displasia Broncopulmonar/prevenção & controle , Bovinos , Modelos Animais de Doenças , Relação Dose-Resposta a Droga , Avaliação Pré-Clínica de Medicamentos , Recém-Nascido , Pulmão/irrigação sanguínea , Pulmão/crescimento & desenvolvimento , Ratos , Ratos Endogâmicos , Superóxido Dismutase/metabolismo , Fatores de TempoRESUMO
Atrial natriuretic factor (ANF) plasma concentrations were measured in 16 healthy term newborn infants and in 18 preterm infants with respiratory distress syndrome during the first 4 postnatal days. Changes in the plasma concentration of ANF were then correlated with postnatal age, severity of respiratory distress, and water and sodium balance. The plasma ANF concentration in healthy term infants increased during the first 2 days of life. Similar values were observed among preterm infants requiring hood oxygen. The plasma ANF concentrations were substantially higher in preterm infants receiving positive pressure ventilation. All infants had negative water and sodium balance during the period of study. No correlation was found, however, between absolute plasma ANF concentrations and urinary flow rate, sodium excretion, or fractional sodium excretion, suggesting that ANF did not exert a dominant role in the excretion of sodium in these infants.
Assuntos
Fator Natriurético Atrial/sangue , Síndrome do Desconforto Respiratório do Recém-Nascido/sangue , Adulto , Animais , Água Corporal/metabolismo , Humanos , Recém-Nascido de Baixo Peso/sangue , Recém-Nascido/sangue , Recém-Nascido Prematuro/sangue , Ventilação com Pressão Positiva Intermitente , Ratos , Sódio/urinaRESUMO
Body water compartment changes were assessed during postnatal weight loss in 14 infants with respiratory distress syndrome. Total body water and extracellular volume were measured by dilution methods on the first day of life and again between the third and sixth days of life. Extracellular volume changes were calculated between the first and second determinations by measurement of chloride balance. Fluid therapy was prescribed to allow negative net water balance and a 1% to 3% reduction in body weight per day. All infants had concurrent reductions in body weight, total body water, and extracellular volume. Progressive daily extracellular volume reduction concurrent with weight loss was also apparent from chloride balance data. The correlation of changes in body weight with extracellular volume in individual subjects was poor (r = 0.05). We speculate that variations between sodium and free water balance in the sick preterm infant may be responsible for variability in the distribution of postnatal body water losses. Assessment of hydration in the newborn infant should include consideration of sodium balance and alterations of serum osmolality, and changes in body weight.