Antithrombin replacement in neonates: is there any indication?

The Endothelial Glycocalyx and Neonatal Sepsis

Sepsis carries a substantial risk of morbidity and mortality in newborns, especially preterm-born neonates. Endothelial glycocalyx (eGC) is a carbohydrate-rich layer lining the vascular endothelium, with important vascular barrier function and cell adhesion properties, serving also as a mechano-sensor for blood flow. eGC shedding is recognized as a fundamental pathophysiological process generating microvascular dysfunction, which in turn contributes to multiple organ failure and death in sepsis. Although the disruption of eGC and its consequences have been investigated intensively in the adult population, its composition, development, and potential mechanisms of action are still poorly studied during the neonatal period, and more specifically, in neonatal sepsis. Further knowledge on this topic may provide a better understanding of the molecular mechanisms that guide the sepsis pathology during the neonatal period, and would increase the usefulness of endothelial glycocalyx dysfunction as a diagnostic and prognostic biomarker. We reviewed several components of the eGC that help to deeply understand the mechanisms involved in the eGC disruption during the neonatal period. In addition, we evaluated the potential of eGC components as biomarkers and future targets to develop therapeutic strategies for neonatal sepsis.

Population pharmacokinetics of human antithrombin concentrate in paediatric patients

AIMS

Antithrombin is increasingly used in paediatric patients, yet there are few age-specific pharmacokinetic data to guide dosing. We aimed to describe the pharmacokinetic profile of human (plasma-derived) antithrombin concentrate in paediatric patients.

METHODS

A 5-year retrospective review was performed of patients <19 years of age admitted to our institution who received antithrombin concentrate, were not on mechanical circulatory support and had baseline (predose) and postdose plasma antithrombin activity levels available for analysis. Demographic and laboratory variables, antithrombin dosing information and data on the use of continuous infusion unfractionated heparin were collected. Population pharmacokinetic analysis was performed with bootstrap analysis. The model developed was tested against a validation dataset from a cohort of similar patients, and a predictive value was calculated.

RESULTS

A total 184 patients met the study criteria {46.7% male, median age [years] 0.35 [interquartile range (IQR) 0.07-3.9]}. A median of two antithrombin doses (IQR 1-4) were given to patients (at a dose of 46.3 ± 13.6 units kg^-1 ), with median of three (IQR 2-7) postdose levels per patient. Continuous infusion unfractionated heparin was administered in 87.5% of patients, at a mean dose of 34.1 ± 22.7 units kg^-1 h^-1 . A one-compartment exponential error model best fit the data, and significant covariates included allometrically scaled weight on clearance and volume of distribution, unfractionated heparin dose on clearance, and baseline antithrombin activity level on volume of distribution. The model resulted in a median -1.75% prediction error (IQR -11.75% to 6.5%) when applied to the validation dataset (n = 30).

CONCLUSIONS

Antithrombin pharmacokinetics are significantly influenced by the concurrent use of unfractionated heparin and baseline antithrombin activity.

Long-term ongoing coagulopathy in premature infants with respiratory distress syndrome

The previously reported activated intravascular coagulation system in the acute phase of respiratory distress syndrome (RDS) has not been evaluated in the long term. We assessed the activities of coagulation system of a cohort of premature infants with RDS in comparison with healthy premature infants (HPIs), healthy mature infants (HMIs), and pediatric laboratory controls over a 6-month period. Cord and venous blood samples were taken at birth, at the first month and sixth month. Protein C (PC), free protein S (f-PS), and antithrombin (AT) activities, thrombin-antithrombin (TAT) complex, prothrombin fragment 1 + 2 (PF1 + 2), and fibrinogen levels were measured. Mean PC, f-PS, d-dimer, and fibrinogen values were similar at all periods for HPI and RDS groups. Low neonatal anticoagulant proteins increased within 6 months in HMI and HPI groups. However, in RDS group, the AT activity remained significantly lower together with significantly higher TAT and PF1 + 2 levels both at the first month and at sixth month, suggesting a long-term consumption coagulopathy.

The host response to sepsis and developmental impact

Invasion of the human by a pathogen necessitates an immune response to control and eradicate the microorganism. When this response is inadequately regulated, systemic manifestations can result in physiologic changes described as "sepsis." Recognition, diagnosis, and management of sepsis remain among the greatest challenges shared by the fields of neonatology and pediatric critical care medicine. Sepsis remains among the leading causes of death in both developed and underdeveloped countries and has an incidence that is predicted to increase each year. Despite these sobering statistics, promising therapies derived from preclinical models have universally failed to obviate the substantial mortality and morbidity associated with sepsis. Thus, there remains a need for well-designed epidemiologic and mechanistic studies of neonatal and pediatric sepsis to improve our understanding of the causes (both early and late) of deaths attributed to the syndrome. In reviewing the definitions and epidemiology, developmental influences, and regulation of the host response to sepsis, it is anticipated that an improved understanding of this host response will assist clinician-investigators in identifying improved therapeutic strategies.

Coagulopathy screening and early plasma treatment for the prevention of intraventricular hemorrhage in preterm infants

BACKGROUND

Despite the improvement in the assistance and treatment of preterm infants, intraventricular hemorrhage (IVH) remains a frequent complication in these patients. Our aim was to demonstrate the hypothesis that a coagulopathy screening and the early treatment with fresh-frozen plasma (FFP) of proven coagulopathy may contribute to decrease the occurrence of IVH in infants with gestational age of less than 29 weeks.

STUDY DESIGN AND METHODS

This study compared two cohorts of infants who received FFP (10 mL/kg) after the evidence of pathologic coagulation tests performed within 2 hours after birth (screening group, n = 127) or after the development of bleedings and evidence of pathologic coagulation tests (no-screening group, n = 91).

RESULTS

The screening strategy decreased the relative risk (RR) of developing IVH (RR = 0.65; 95% confidence interval, 0.44-0.98) compared to no-screening strategy, but the effect was limited to infants born at 23 to 26 weeks of gestation in whom screening strategy lowered IVH occurrence (34.5% vs. 61.1%, p = 0.008).

CONCLUSIONS

A coagulopathy screening strategy decreases the risk of developing IVH in preterm infants but this effect is limited to infants born at 23 to 26 weeks of gestation.

Enoxaparin Use in the Neonatal Intensive Care Unit: Experience Over 8 Years

STUDY OBJECTIVE

To evaluate the effectiveness and safety of enoxaparin therapy in a neonatal intensive care unit (NICU).

DESIGN

Retrospective chart review.

SETTING

Level III NICU in a Canadian academic center.

PATIENTS

All neonates treated with enoxaparin while in the NICU between January 1, 1998, and June 1, 2006.

MEASUREMENTS AND MAIN RESULTS

Data abstracted included patient demographics, diagnosis of thrombosis and its progression, enoxaparin dosages with corresponding antifactor Xa levels, and adverse events. Sixteen neonates (four term, 12 preterm) were treated with enoxaparin at a mean +/- SD initial subcutaneous dose of 1.41 +/- 0.15 mg/kg every 12 hours. The target therapeutic range (antifactor Xa level 0.5-1.0 U/ml) was achieved by 12 infants at a mean +/- SD dose of 1.92 +/- 0.43 mg/kg every 12 hours, after a mean of 5.6 days (range 1-15 days). Preterm infants required a higher dose (per kilogram) compared with term infants to maintain therapeutic antifactor Xa levels (mean +/- SD 1.94 +/- 0.39 vs 1.65 +/- 0.14 mg/kg every 12 hrs, p<0.001). Enoxaparin doses were more strongly correlated to antifactor Xa levels in term infants (r(2)=0.51, p<0.001) compared with preterm infants (r(2)=0.20, p<0.001). Ten (71%) of 14 thromboembolic events resolved, either partially or completely, at a mean of 39 days (range 8-61 days) of enoxaparin therapy. Nine infants (56%) experienced minor local adverse effects at the site of the indwelling subcutaneous catheter (induration, bruises, hematomas, or leakage). Systemic adverse events that were possibly related to enoxaparin therapy included osteopenia (one infant), scleral hemorrhage (one), and minor gastrointestinal tract bleeding (three) found in gastric feeding tubes. No adverse effects were associated with antifactor Xa levels greater than 1.0 U/ml.

CONCLUSION

Enoxaparin may be effective in the treatment of neonatal thrombosis. An initial dosage of 1.5 mg/kg every 12 hours is likely inadequate to obtain therapeutic antifactor Xa levels rapidly and differs for term and preterm neonates. Therapeutic levels in preterm infants may be more variable, and the pharmacokinetics of this drug in preterm infants requires further evaluation. Future studies in neonates should prospectively evaluate a higher starting dose of enoxaparin to document effectiveness, acceptance, compliance with treatment guidelines, and adverse effects.