Lung re-expansion and urinary lipid peroxidation in neonatal pneumothorax

AIM

Experiential studies suggest that re-expansion of a collapsed lung may result in pulmonary ischaemia-reperfusion injury. We aimed to evaluate the effect of lung re-expansion on urinary lipid peroxidation products in neonates with pneumothorax.

METHODS

This study included 20 mechanically ventilated neonates with pneumothorax, and 18 healthy neonates (controls). A chest tube was inserted immediately following the diagnosis of pneumothorax. Urine samples were obtained just before tube thoracostomy (first period), after one hour (second period), every 12 hours by complete reexpansion (third period). Vital signs and ventilatory parameters were recorded. Urinary lipid peroxidation was evaluated by measurement of thiobarbituric acid-reacting substances (TBARS).

RESULTS

No significant difference was found between urinary TBARS concentrations in the first, second and third periods (4.08 +/- 2.4 nmol/L, 2.8 +/- 2.3 nmol/L and 3.3 +/- 2.1 nmol/L, respectively). Control TBARS levels (4.1 +/- 2.1 nmol/L) did not significantly differ from those of the neonates with pneumothorax (p > 0.05). The neonates with pneumothorax had higher heart rates compared to the controls (p < 0.01). When compared with controls, the systolic pressure was lower in all periods (p < 0.01), and diastolic blood pressure was lower only in the first and second period (p < 0.05). Oxygen saturation significantly decreased in the first period compared to saturation of the second period and of controls (p < 0.01). Ventilatory parameters did not show any significant difference between the periods.

CONCLUSIONS

This prospective study showed that re-expansion of the lung did not significantly affect urinary TBARS concentration in neonatal pneumothorax. Indirectly, short-term lung collapse followed by re-expansion might not cause a clinically significant reperfusion injury in newborns.

Urinary arginine vasopressin: pattern of excretion in the neonatal period

The pattern of arginine vasopressin (AVP) secretion in the immediate neonatal period is unclear. Plasma concentrations of AVP are reflected by its urinary excretion, thus providing a noninvasive method for studying the pattern of AVP release in the neonate. In these studies, we determined the pattern of urinary AVP excretion (microU/mg creatinine) during the first 2-4 days after birth in 78 neonates, 53 of whom had various prenatal and/or neonatal complications. In well term (n = 12) and preterm (n = 13) infants mean urinary AVP excretion decreased gradually during the first 24-36 h after birth. Although term and preterm infants with perinatal asphyxia had highest initial levels of urinary AVP (greater than 200 microU/mg creatinine) and a significant negative correlation with the 1-min Apgar score was obtained, their pattern of excretion was similar to respective controls. After delivery, elevated values for urinary AVP excretion were found among infants with neonatal courses complicated by intracranial hemorrhage, hypoxic encephalopathy, and pneumothorax. Urine osmolality did not correlate linearly with urinary AVP levels, but rather attained a maximum value of approximately 400 mosmol/kg at urinary AVP levels less than 200 microU/mg creatinine and then plateaued. It is concluded that the decrease in urinary AVP excretion observed soon after birth generally reflects diminution of the hypersecretion of AVP during parturition; neonates with evidence of intrapartum asphyxia initially have increased urinary AVP excretion; however, the pattern of excretion is similar to normal infants. During the neonatal period insults such as pneumothorax and intracranial hemorrhage may cause hypersecretion of this hormone.

Diuresis and natriuresis following acute pneumothorax in very low birthweight infants

Seven tension pneumothoraces developed in six very low birthweight infants receiving assisted ventilation for hyaline membrane disease. Mean values for blood pressure and creatinine clearance (Ccr) tended to increase following pneumothorax decompression, although neither increase was statistically significant. Urine volume, osmolar clearance and urine sodium excretion all increased significantly in the 8 h following diagnosis and decompression of pneumothoraces. However, when expressed as a percentage of Ccr, none of these variables changed significantly. Mean sodium balance changed from positive to negative despite a significant increase in urine aldosterone excretion. It is suggested that the increases in osmolar clearance and sodium excretion were consequences of the increase in Ccr following pneumothorax decompression. Developmental immaturity in the renal tubular response to aldosterone might also have contributed to development of negative sodium balance.

Hyponatraemia in the first week of life in preterm infants. Part I. Arginine vasopressin secretion

Continuous sequential urinary arginine vasopressin measurements in 14 preterm, ventilated infants suggest that both osmoreceptor and volume receptor systems are able to stimulate the prolonged secretion of arginine vasopressin from 26 weeks' gestation. The kidney is able to respond to arginine vasopressin stimulation from the first day of life and from 26 weeks' gestation. A maximum urine osmolality not exceeding 550 mOsm/kg was reached which varied with hydration of the infant. Excretion of arginine vasopressin and urine osmolality increased during deterioration of respiratory illness, mask ventilation, bilateral pneumothoraces, and severe intraventricular haemorrhage. The data show that inappropriate arginine vasopressin secretion is common during illness in the first week of life in preterm infants and that strict attention must be paid to water balance during this time.

Vasopressin and pneumothorax in the neonate

The release of vasopressin (AVP) was assessed by measuring urinary excretion of the hormone in ten neonates who had an acute and symptomatic pneumothorax in the first three days after birth. AVP excretion rose significantly (paired t analysis) after the pneumothorax occurred. When apparent re-expansion of the lungs occurred after treatment, excretion of AVP returned to prepneumothorax levels within eight to 16 hours. If the pneumothorax persisted or worsened. AVP excretion remained elevated. Urine osmolality rose significantly (paired t analysis) after pneumothorax, presumably in response to the increased AVP levels. Two of the ten infants had hyponatremia in the period studied, while in a state of sodium balance. It was concluded that AVP release is increased after a pneumothorax occurs. This increase is apparently not due to osmoregulatory requirements. Fluid intake in these infants may need adjustment to prevent an inappropriate positive water balance.