Effect of aminophylline on brain blood flow in the newborn piglet

Aminophylline for renal protection in neonatal hypoxic-ischemic encephalopathy in the era of therapeutic hypothermia

BACKGROUND

Neonates with hypoxic-ischemic encephalopathy (HIE) frequently develop acute kidney injury (AKI). Aminophylline has been shown to reduce severe renal dysfunction in neonates after perinatal asphyxia. However, the effect of aminophylline on renal function in neonates undergoing hypothermia has not been studied.

METHODS

A single-center, retrospective chart review of neonates cooled for moderate/severe HIE who received aminophylline for AKI was conducted to assess changes in urine output (UOP) and serum creatinine (SCr). Comparisons were also made to control neonates matched for hours of life who were cooled but unexposed to aminophylline.

RESULTS

Sixteen neonates cooled for HIE received aminophylline starting at 25 ± 14 h of life. Within 12 h of starting aminophylline, UOP increased by 2.6 ± 1.9 mL/kg/h. SCr declined by 0.4 ± 0.2 mg/dL in survivors over the first 4 days. When compared to control neonates, UOP increase was greater in the aminophylline group (p < 0.001). SCr declined in survivors in both groups, although baseline SCr was higher in the aminophylline group.

CONCLUSIONS

Aminophylline use in neonates with HIE undergoing hypothermia was associated with an increase in UOP and a decline in SCr. A randomized trial will be needed to establish a potential renal protective role of aminophylline.

IMPACT

The renal protective effect of aminophylline in neonates with HIE has not yet been studied in the context of therapeutic hypothermia. Aminophylline exposure in neonates cooled for HIE was associated with increased UOP and a similar decline in SCr when compared to control infants unexposed to aminophylline. Improved renal function after receiving aminophylline in this observational cohort study suggests the need for future randomized trials to establish the potential benefit of aminophylline in the HIE population undergoing hypothermia.

Reductions in cardiac output in hypoxic young pigs: systemic and regional perfusion and oxygen metabolism

We tested the hypotheses that, in hypoxic young pigs, reductions in cardiac output restrict systemic oxygen transport to a greater extent than does hypoxia alone and that compensatory responses to this restriction are more effective in higher than in lower priority vasculatures. To study this, 10- to 14-day-old instrumented awake hypoxic (arterial oxygen tension = 39 Torr) pigs were exposed to reduced venous return by inflation of a right atrial balloon-tipped catheter. Blood flow was measured with radionuclide-labeled microspheres, and oxygen metabolism was determined with arterial and venous oxygen contents from appropriate vessels. Hypoxia resulted in a reduction in oxygen tension; increases in cardiac output and perfusion to brain (72% over baseline), heart, adrenal glands, and liver without reductions to other organs except for the spleen; reductions in systemic and intestinal oxygen delivery; and increases in systemic and intestinal oxygen extraction without changes in systemic, cerebral, or intestinal oxygen uptake. During hypoxia, decreasing venous return was associated with increases in arterial lactic acid concentration and central venous pressure; attenuation of the hypoxia-related increase in cardiac output; sustained increases in brain (72% over baseline) and heart perfusion; reductions in lung (bronchial artery), pancreatic, renal, splenic, and intestinal (-50% below baseline) perfusion; decreases in systemic and gastrointestinal oxygen delivery; sustained increases in systemic and intestinal oxygen extraction; and decreases in intestinal oxygen uptake, without changes in cerebral oxygen metabolism. We conclude that when venous return to the heart is reduced in hypoxic young pigs, the hypoxia-related increase in cardiac output was attenuated and the relative reduction in cardiac output was associated with preserved cerebral oxygen uptake and compromised intestinal oxygen uptake. Regional responses to hypoxia combined with relative reductions in cardiac output differ from that of hypoxia alone, with the greatest effects on lower priority organs such as the gastrointestinal tract.

Aminophylline and Doppler time-averaged mean velocity in the middle cerebral artery in preterm neonates

OBJECTIVE

The purpose of this study was to assess the effect of an intravenous loading dose of aminophylline (6 mg/kg) on Doppler time-averaged mean velocity in the middle cerebral artery in ventilated preterm neonates.

METHODOLOGY

Twenty infants were studied by colour/duplex Doppler technique prior to and at 5, 10, 30 and 60 min after the administration of aminophylline.

RESULTS

Aminophylline treatment was associated with a statistically significant reduction in time-averaged mean velocity from baseline (P < 0.001) and an increase in heart rate (P < 0.001) at all timepoints. The largest reduction in time-averaged mean velocity of 19% (95% confidence interval -10 to -28%) occurred at 10 min post-dose. There were no statistically significant changes in transcutaneous PCO2 or mean arterial blood pressure.

CONCLUSIONS

The observed reduction of 19% from baseline in time-averaged mean velocity following treatment with aminophylline alone is unlikely to be of clinical importance. Whether aminophylline in combination with other drugs that decrease central blood flow velocity such as indomethacin and/or dexamethasone could result in a clinically significant reduction deserves further study.

Cerebral blood flow and left ventricular output in spontaneously breathing, newborn preterm infants treated with caffeine or aminophylline

Aminophylline and caffeine are commonly used for prophylaxis of apnea in premature infants. Previous studies have indicated different effects of the drugs on cerebral circulation. Therefore, we have compared the acute effects of bolus administration of caffeine citrate or aminophylline on left ventricular output, heart rate, blood pressure and global cerebral blood flow. The study group consisted of 33 newborn, spontaneously breathing, preterm infants randomly assigned to receive either aminophylline 5 mg/kg (n = 19) or caffeine citrate 20 mg/kg (n = 14). Two hours after iv drug administration, global cerebral blood flow measured by the Xe-clearance technique was significantly lower after aminophylline than after caffeine (mean (SD)): 13.2 (+2.9/-2.3) versus 17.2 (+7.1/-5.1) ml/100 g/min) (p = 0.01). There were no other statistically significant differences in circulatory or ventilatory parameters between the groups. Further studies are needed to clarify the clinical relevance of these results.

Aminophylline therapy and cerebral blood flow velocity in preterm infants

Pulsed Doppler ultrasound was used to evaluate the cerebral blood flow velocity (CBFV), in the middle and anterior cerebral arteries in 10 infants before and after the administration of aminophylline (7.5 mg/kg). Mean CBFV, heart rate, blood pressure, oxygen and carbon dioxide tensions were recorded before the loading dose, and then at 1, 2, 6 and 24 h after completion of the infusion. Mean CBFV in the middle and anterior cerebral arteries were 16.8 cm/s and 10.8 cm/s respectively prior to the infusion. There was a significant decrease (P < 0.05) in velocities in both arteries at 1 and 2h post drug therapy, which returned to base values by 6 h, and remained as such at 24 h. The heart rate increased (P < 0.05) after the infusion, while no consistent changes were observed in blood pressure or oxygen tension. Carbon dioxide levels were significantly reduced (P < 0.05) at 2 h. The reduction in CBFV, however, was more than would be expected on the basis of the change in carbon dioxide levels alone, suggesting that other factors may be exerting an influence. While no adverse effects were noted in the infants studied, it is suggested that aminophylline should be used judiciously in sick preterm infants at highest risk from ischaemic brain injury.

Methylxanthines: toxicity to humans. 3. Theobromine, paraxanthine and the combined effects of methylxanthines

This review provides a brief overview of known information on the human toxicity of theobromine and paraxanthine. Theobromine has some pharmacological effects, although these activities are considerably weaker than those of theophylline and/or caffeine, described in parts 1 and 2 of this series (Stavric, Fd Chem. Toxic. 1988, 26, 541 & 645). Paraxanthine, which is not found in plants or foods, is the major metabolite of caffeine in humans, in whom its toxicological potency appears to be very low. This paper gives a brief retrospective view of possible toxicological effects when methylxanthines are taken simultaneously or are present in combination as a result of metabolic transformation. Critical review of toxic manifestations due to exposure to relatively large doses of caffeine and theophylline indicates that such combined exposure may potentiate the toxic effects of either drug.

Maturation of circulatory system in three mammalian models of human development

The review surveys the literature on maturation of vasoconstrictor and vasodilator functions in cerebral, renal and intestinal circulations of three non-primate models of human development. An ovine model has been refined for use at both fetal and neonatal stages of development. Important variables controlling regional circulations in the lamb fetus at term include arterial O2 content and pCO2 (brain), angiotensin-II (kidney) and norepinephrine (small intestine). Blood flow autoregulation to decreasing perfusion pressure has been inferred for the renal circulation of the neonate. A canine model has been employed in the postnatal period, usually later than the first week after birth. Important variables controlling regional circulations in the young puppy include arterial pO2 and pCO2 (brain) and epinephrine and angiotensin-II (kidney). Blood flow autoregulation to decreasing pressure has been demonstrated in the cerebral circulation at birth and in the renal circulation at one week thereafter. The intestinal circulation has not been studied with respect to blood flow control. A porcine model has been examined from birth through at least two months of postnatal life. Important variables controlling regional circulations in swine at birth include adrenergic nerve stimulation, arterial pCO2 (brain), angiotensin-II (kidney) and norepinephrine (kidney and small intestine). Blood flow autoregulation to decreasing perfusion pressure has been demonstrated in the brain by the fourth day, in the kidney by the end of the second week and in the small intestine by the end of the first month after birth. The advantage of each model for further investigation of functional maturation of regional circulatory control is summarized.