Atrial natriuretic peptide and patent ductus arteriosus in preterm infants

Cardiovascular biomarkers in the evaluation of patent ductus arteriosus in very preterm neonates: A cohort study

BACKGROUND

The evaluation of the patent ductus arteriosus (PDA) in the very premature neonate is a challenge. Echocardiography provides an interpretation of the hemodynamic condition. It is however, only a snapshot. Biomarkers may represent a physiological response to the hemodynamic alterations brought on by the PDA and may add to the identification of the clinical significant PDA.

AIM

To investigate the association between mid regional proadrenomodulin (MR-proADM), N-terminal pro b-type natriuretic peptide (NT-proBNP), mid regional pro-atrial natriuretic peptide (MR-proANP), C-terminal pro endothelin-1 (CT-proET1) and copeptin and echocardiographic measures of PDA.

STUDY DESIGN

Cohort study with echocardiography performed on day 3 and 6. Blood samples from day 3.

SUBJECT

139 consecutive neonates born at a gestational age <32 weeks.

OUTCOME MEASURES

The main outcomes were presence of a PDA day 3 and 6, PDA diameter, left atrium to aorta ratio (LA:Ao-ratio), and descending aorta diastolic flow (DADF).

RESULTS

Adjusted plasma levels of all investigated biomarkers, except CT-proET1, were found to be associated with both PDA diameter and LA:Ao-ratio, and also the presence of a large PDA. CT-proET1 and copeptin was found to be associated with abnormal DADF. Using pre-specified cut-off values NT-proBNP and MR-proANP day 3 seemed to be of value in identifying a large PDA day 3 and 6 in very preterm neonates.

CONCLUSION

Among the investigated biomarkers NT-proBNP and MR-proANP performed best in relation to echocardiographic markers of PDA severity in very preterm neonates.

The Atrial Natriuretic Peptide and Its Relation to Hemodynamic and Laboratory Values in Mitral Valve and Coronary Surgery

In 22 patients who underwent mitral valve replacement (13) or coronary bypass surgery (9), preoperative and postoperative plasma atrial natriuretic peptide (p-ANP) concentration, hemodynamic changes, plasma aldosterone, and twenty-four-hour urine sodium-potassium concentrations were studied.

Preoperative ANP levels were 261±172 pg/mL in mitral valve replacement (MVR) and 68±22 in coronary artery bypass grafting (CABG); control levels were 15±4.7 (p < 0.001).

After the induction of anesthesia, ANP levels decreased to 154.5±96.7 pg/mL in MVR and 51±17.5 in CABG (p < 0.01) patients. In the early postop erative period ANP increased to 332±217 pg/mL in MVR and to 94.3 ± 29.7 in CABG (p < 0.001).

In the late postoperative period, the p-ANP of both groups returned to nor mal levels (16 ± 8.05, 11.2 ± 2.82 pg/mL, respectively).

Negative correlations were detected in both MVR and CABG groups be tween p-ANP, p-aldosterone (p < 0.001), p—ANP—cardiac output (p < 0.001), and p—ANP—cardiac index (p < 0.001).

In vivo dilatation of the postnatal ductus arteriosus by atrial natriuretic peptide in the rat

BACKGROUND

Alpha-human atrial natriuretic peptide (hANP) reportedly increases in premature infants with patent ductus arteriosus (PDA).

OBJECTIVES

To clarify a possible hANP effect to reopen the postnatal ductus, we studied in vivo reopening of the postnatal DA by a recombinant hANP, carperitide, in rats.

METHODS

Near-term rat pups were incubated at 33 degrees C following caesarean section. The inner diameter of the ductus was measured with a microscope and a micrometer following rapid whole-body freezing. The DA constricted quickly after birth, and the inner diameter was 0.80 and 0.08 mm at 0 min (fetal state) and 60 min after birth. hANP concentration in the pup blood and the ductus-dilating effect of hANP were studied by subcutaneous injection of hANP at 60 min after birth, and by measurement 7, 15, 30 and 60 min later.

RESULTS

The peak hANP concentration was 790 pg/ml at 7 min with 1 mg/kg, which is similar to the level seen in preterm infants with symptomatic PDA. hANP dilated the postnatal ductus dose dependently and maximally at 7 min after injection. hANP dilated the postnatal constricted ductus completely to 0.79 mm in diameter with a large dose (10 mg/kg) and to 0.55 mm with 1 mg/kg.

CONCLUSIONS

hANP reopens the constricted postnatal DA dose dependently in rats. The increased hANP, accompanying premature PDA, may delay closure of the DA.

Prostacyclin concentrations and transitional circulation in preterm infants requiring mechanical ventilation

AIM

To describe the association between early postnatal prostacyclin concentrations in preterm infants; echocardiographic measurements of ductal diameter and ventricular output and clinical outcomes of intraventricular haemorrhage (IVH) and patent ductus arteriosus (PDA).

METHODS

Forty nine preterm infants born before 30 weeks of gestational age (median birthweight 980 g, median gestational age 27 weeks) underwent echocardiographic studies at 5, 12, 24 and 48 hours of postnatal age. Measurements included ventricular outputs and the ductal shunt diameter as a measure of the shunt size. Simultaneous measurements of blood pressures, mean airway pressure and inspired fraction of oxygen (FIO2) were recorded. A blood sample for the prostacyclin metabolite 6-ketoprostaglandin F1-alpha (6KPGF1 alpha) was taken at the 5 and 24 hour echocardiogram.

RESULTS

The mean 6KPGF1 alpha concentrations were higher than adult concentrations at 5 (515 pg/ml) and 24 (255 pg/ml) hours. There was no association with gestational age. Raised 6KPGF1 alpha concentrations were related to increased need for mechanical ventilation and severity of respiratory disease. At 5 hours, increased 6KPGF1 alpha concentrations were associated with larger PDA and at 24 hours with larger PDA and higher left ventricular output. Infants with higher 6KPGF1 alpha concentrations were more likely to develop clinically significant PDA. There was no association between early measurements of 6KPGF1 alpha and IVH.

CONCLUSIONS

Early postnatal prostacyclin concentrations are markedly raised in preterm infants, particularly in those with more severe lung disease. Raised 6KPGF1 alpha concentrations were associated with an increased ductal diameter and subsequent PDA, but not IVH.

Regulation of extracellular fluid volume in neonates

This review summarises mechanisms of control of extracellular fluid volume in the neonatal period. 'Normal' body fluid distribution and methods of its measurement are discussed as well as regulatory mechanisms with particular emphasis on hormonal and renal aspects.

Atrial natriuretic peptide in the diagnosis of patent ductus arteriosus

The aim of this study was to measure plasma atrial natriuretic peptide in preterm infants with a patent ductus arteriosus before and after closure with indomethacin. Atrial natriuretic peptide was measured in 28 preterm infants with clinical and echocardiographic evidence of a patent ductus arteriosus and in eight preterm infants who did not develop clinical evidence of a patent ductus arteriosus. Plasma concentration of atrial natriuretic peptide was measured by radioimmunoassay. In 18 infants the patent ductus arteriosus closed after one course of indomethacin; atrial natriuretic peptide levels decreased from median 1240 pg/ml (range 201-5483 pg/ml) to 266 pg/ml (range 62-1108 pg/ml). In four infants the patent ductus arteriosus closed after two courses of indomethacin and two infants had surgical ligation after indomethacin treatment failed. The patent ductus arteriosus closed spontaneously in four infants (atrial natriuretic peptide median level 152 pg/ml, range 61-495 pg/ml). In the eight infants without patent ductus arteriosus, atrial natriuretic peptide level was median 224 pg/ml (range 38-876 pg/ml). Measurement of plasma atrial natriuretic peptide concentration has a role in predicting when indomethacin treatment is indicated.

Atrial natriuretic peptide and blood volume during red cell transfusion in preterm infants

Because raised plasma concentrations of atrial natriuretic peptide indicate volume expansion, we studied the effect of red cell transfusion on plasma atrial natriuretic peptide concentration, packed cell volume, and intravascular volume in eight preterm infants. Red cell transfusion increased red cell mass, packed cell volume and erythrocyte count, but decreased plasma volume. Total blood volume, plasma atrial natriuretic peptide concentration, urine flow rate, and urinary sodium excretion did not change. We conclude that a slow transfusion of less than 10 ml red cells/kg body weight does not cause volume expansion with subsequent atrial natriuretic peptide release thereby affecting the cardiovascular system.

Atrial natriuretic factor and postnatal diuresis in respiratory distress syndrome

To find out if atrial natriuretic factor plays a part in the control of urine output during the initiation alone or throughout postnatal diuresis in neonates with respiratory distress syndrome, atrial natriuretic factor concentrations and clinical and renal variables were measured prospectively three times during the first three days of life in 13 premature infants. Atrial natriuretic factor concentrations rose significantly between the first and second sample times as did the urine output and output:input ratio. By the time that the third sample was taken, atrial natriuretic factor concentration had decreased significantly since the second sample had been taken, while urine flow was maintained. All subjects initiated a spontaneous diuresis that was related to the second concentration of atrial natriuretic factor. With partial correlation analysis a significant relationship was shown between the concentration of atrial natriuretic factor and the maintenance of urine output throughout the study period. Individual hormone concentrations did not, however, correlate with simultaneous renal variables. Changes in the concentrations of atrial natriuretic factor coincided with initiation of spontaneous diuresis in babies with respiratory distress syndrome, and may have a role in the complex mechanisms that maintain this diuresis.

Endocrine control of electrolyte balance during development

The endocrine control of electrolyte balance during development is reviewed. It is suggested that the high urinary sodium excretion observed in premature infants may be secondary to the immaturity of the adrenal gland to adequately increase the secretion of aldosterone (Sulyok et al, 1979b), and to the inability of the distal tubule to respond appropriately to a rise in circulating aldosterone levels (Sulyok et al, 1979a). On the other hand, the elevated plasma aldosterone levels observed in term newborn infants may play an important role in the blunted response of the newborn kidney to saline loading (Sulyok et al, 1979a; Spitzer, 1982). The ability of ANP to induce a natriuresis and to contribute to fluid and electrolyte homeostasis during development has been investigated. It has been found that the immature kidney is less responsive to ANP than later in life (Chevalier et al, 1988; Robillard et al, 1988). On the other hand, it has been suggested that a rise in plasma ANP during the first five days of life may contribute to the physiological weight loss associated with the extracellular volume contraction occurring shortly after birth (Tulassay et al, 1987). The role of glucocorticoids, prostaglandins and the kallikrein-kinin system in regulating electrolyte balance during development is also reviewed.