Cardiac output changes secondary to theophylline therapy in preterm infants

Precision caffeine therapy for apnea of prematurity and circadian rhythms: New possibilities open up

Caffeine is the globally consumed psychoactive substance and the drug of choice for the treatment of apnea of prematurity (AOP), but its therapeutic effects are highly variable among preterm infants. Many of the molecular underpinnings of the marked individual response have remained elusive yet. Interestingly, the significant association between Clock gene polymorphisms and the response to caffeine therapy offers an opportunity to advance our understanding of potential mechanistic pathways. In this review, we delineate the functions and mechanisms of human circadian rhythms. An up-to-date advance of the formation and ontogeny of human circadian rhythms during the perinatal period are concisely discussed. Specially, we summarize and discuss the characteristics of circadian rhythms in preterm infants. Second, we discuss the role of caffeine consumption on the circadian rhythms in animal models and human, especially in neonates and preterm infants. Finally, we postulate how circadian-based therapeutic initiatives could open new possibilities to promote precision caffeine therapy for the AOP management in preterm infants.

Acute hemodynamic effects of methylxanthine therapy in preterm neonates: Effect of variations in subgroups

BACKGROUND

Methylxanthines have cardiac stimulant effects. The current study aimed to compare acute hemodynamic changes between caffeine and aminophylline in ≤34 weeks' preterm neonates.

METHODS

The study was performed using information on echocardiography measurements from preterm neonates recruited for apnea of prematurity (75 of 240) and preventing extubation failure (113 of 156) studies. The neonates were randomized either to the caffeine or aminophylline groups. Neonates with no maintenance followed by loading doses with both the methylxanthines (caffeine and aminophylline) and incomplete echocardiography examination were excluded.

RESULTS

Cardiac parameters were found to be similar between groups. The heart rate was higher among the aminophylline-treated neonates (p < 0.001) than among the caffeine-treated ones. End-systolic volume was higher among both caffeine- (p < 0.001) and aminophylline-treated neonates (p = 0.001) when compared with pretreatment values. End-diastolic volume was statistically higher in both groups' neonates (p = 0.01). The odds of increase in cardiac output was higher; however, increase in ejection fraction was less in caffeine-treated small-for-gestation-age neonates.

CONCLUSION

Caffeine has similar effects on cardiac parameters as aminophylline; however, caffeine-treated small-for-gestation stratification gave rise to significant cardiac variations.

Acute hemodynamic effects of caffeine administration in premature infants

OBJECTIVE

Administration of caffeine citrate (caffeine) has been a central component of the treatment of apnea of prematurity. However, given its multiple pharmacologic effects, caffeine might be expected to produce hemodynamic changes in heart rate, stroke volume, cardiac output and vascular resistance.

STUDY DESIGN

In this prospective observational study, we report the hemodynamic effects of intravenous caffeine administration in a population of premature infants who received caffeine to correct or prevent apnea of prematurity.

METHODS

Hemodynamic effects of caffeine were determined in 31 infants. Stroke volume was measured via echocardiogram, using velocity time integral at the aortic root diameter. Statistically univariate analyses were performed parametrically using paired t-test and nonparametrically (sign test). Multivariate linear regression models were used to identify subgroup covariate effects.

RESULTS

After intravenous caffeine, cardiac index increased in 31 of 31 trials, by an average of 14.6+/-16.3% (s.d.); stroke volume increased in 24 of 31 trials, by 7.8+/-12.2%; heart rate increased in 28 of 31 trials by 7.7+/-7.2 beats per min; and blood pressure increased in 25 of 31 trials, by 4.1+/-5.8 mm Hg (all P<0.001). Multivariate linear regression revealed no significant effect of dose, birth weight, gestational age or postnatal age.

CONCLUSIONS

Intravenous caffeine consistently increases cardiac output and blood pressure in relatively stable premature infants, when given to treat or prevent apnea of prematurity. We speculate that there may be a role for caffeine in the hemodynamic treatment of hypotensive/hypoperfused infants.

The effect of theophylline on apnoea and hypoxaemic episodes in the premature neonate during the 1st 3 days after birth

Although the effect of theophylline on apnoea is well documented, its influence on hypoxaemic episodes in premature neonates is less well known. To investigate the influence of the drug on both parameters, 37 apnoeic neonates were monitored before and after theophylline treatment. Incidents and densities of pathological apnoea (cessation of nasal airflow > or = 20 seconds) were recorded. A fall of > or = 10% for > 10 seconds in peripheral oxygen saturation was classified as a hypoxaemic episode. Ethical constraints precluded the inclusion of a control group. Each infant served as its own control. Theophylline serum concentrations were 5.6 (3.4), 8 (7.1) and 8 (5.3) mg/l on days 1, 2 and 3, respectively. The apnoea incidents and densities decreased significantly (p = 0.0001) from baseline on all 3 days. The total number of hypoxaemic episodes, as well as those not associated with pathological apnoea, decreased, though not significantly. However, those hypoxaemic episodes associated with pathological apnoea and a fall in pulse rate of > or = 20% decreased significantly from baseline on day 2 only. Throughout the study period, over 80% of hypoxaemic episodes were not associated with apnoea. It is concluded that in the doses used, theophylline was more effective in reducing apnoea than hypoxaemic episodes in premature neonates.

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.

Intravenous aminophylline and cerebral blood flow in preterm infants

The effect of aminophylline on cerebral blood flow (CBF) was studied in 10 preterm infants who were receiving 6.2 mg/kg intravenously over 20 minutes followed by a maintenance infusion. CBF was measured intermittently using near infrared spectroscopy. Heart rate, blood pressure, oxygen saturation, and transcutaneously measured carbon dioxide tension (TcPCO2) were recorded continuously. Aminophylline administration was associated with a fall in CBF from a median of 15.9 ml/100 g/min to 11.2 ml/100 g/min. Median fall in CBF was 4.1 ml/100 g/min (95% confidence interval 1.7 to 6.5). Heart rate rose and TcPCO2 fell in all infants, median fall being 0.66 kPa. The reduction in CBF was greater than would be expected on the basis of the modest fall in TcPCO2.

Cerebral blood flow velocity in term infants treated with phototherapy

The relationship between phototherapy and changes in the cerebral circulation was studied in 50 jaundiced newborn infants. The aim of the study was to determine whether important alterations in cerebral hemodynamic occur under blue light therapy. Blood flow velocity, i.e., the pulsatility index (PI) and the area under the velocity curve (AUVC), was measured in the anterior cerebral arteries (ACA) using a Duplex scan technique. No prominent changes compromise flow in the ACA. PI and AUVC values were similar during and after phototherapy (p greater than 0.5) suggesting effective cerebral autoregulation in term infants undergoing light treatment for hyperbilirubinemia.

A comparison of thermodilution and pulsed Doppler cardiac output measurement in critically ill children

To evaluate the pulsed Doppler cardiac output method as a noninvasive means for determining cardiac output in critically ill children, we performed paired pulsed Doppler and thermodilution cardiac output determinations in 17 critically ill children. Commercially available equipment, specifically designed for this purpose, was employed. Forty paired thermodilution and pulsed Doppler determinations were made. There was a significant correlation between the two measurements (pulsed Doppler = 0.84 thermodilution + 0.39; r = 0.79, p less than 0.01). The ranges of thermodilution measurements (1.02 to 6.26 L/min; median 2.77 L/min) and pulsed Doppler measurements (1.13 to 6.35 L/min; median 2.57 L/min) were not different (p = 0.25). However, differences between individual paired thermodilution and pulsed Doppler measurements were large (-3.13 to 2.03 L/min; median 0.12 L/min), and the percentage difference between individual paired thermodilution and pulsed Doppler measurements ranged from 0.41% to 102.5% (median 12.7%). A discrepancy of 15% or more between thermodilution and pulsed Doppler was encountered in 18 (45%) of 40 of paired measurements (95% confidence interval: 29% to 61%), and one fourth of the paired measurements differed by more than 25%. We conclude that, as employed in this study, pulsed Doppler cardiac output determination is not sufficiently representative of the thermodilution output to be employed for hemodynamic monitoring in critically ill children.