Risk factors associated with umbilical vascular catheter-associated thrombosis in newborn infants

OBJECTIVE: To determine the risk factors associated with umbilical vascular catheter-associated thrombosis. METHODS: All consecutive inborn infants with umbilical arterial (UAC) and/or umbilical venous catheters (UVC) inserted for more than 6 h duration were included in the study. Each infant was screened for thrombosis in the abdominal aorta and inferior vena cava by 2-D abdominal ultrasonography within 48-72 h of insertion of umbilical vascular catheters. Subsequent serial scanning was performed at intervals of every 5-7 days, and within 48 h after removal of catheters. RESULTS: Upon removal of umbilical catheters, abdominal aortic thrombi were detected in 32/99 (32.3%) infants with UAC. Small thrombi were detected in the inferior vena cava of 2/49 (4.1%) infants with UVC (one of whom had both UAC and UVC). When compared with those who received only UVC (n = 18), infants who received either UAC alone (n = 68) or both UAC and UVC (n = 31) had significantly higher risk of developing thrombosis (odds ratio (OR): 7.6, 95% confidence interval (CI): 1.1, 325.5)). Logistic regression analysis of various potential risk factors showed that the only significant risk factor associated with the development of abdominal aortic thrombosis following insertion of UAC was longer duration of UAC in situ (for every additional day of UAC in situ, adjusted OR of developing thrombosis was: 1.2, 95% CI: 1.1, 1.3; P = 0.002). CONCLUSION: Umbilical arterial catheter-associated thrombosis was common. Umbilical arterial catheter should be removed as soon as possible when not needed. Upon removal of UAC, all infants should be screened for abdominal aortic thrombus by 2-D ultrasonography.     

Blood withdrawal and infusion via umbilical catheters: effect on cerebral perfusion and influence of ibuprofen

Withdrawal and infusion of blood via umbilical catheters can affect cerebral blood flow in preterm infants. We compared the effects on cerebral perfusion of 3 ml/kg blood withdrawal and infusion via umbilical arterial (UAC) and venous (UVC) catheters in 16 infants < or =32 weeks gestation, age <24 h, on mechanical ventilation. Near infrared spectroscopy was used to monitor changes in cerebral oxy- and deoxyhemoglobin, total cerebral hemoglobin (an index of cerebral blood volume; CBV) and HbD (an index of cerebral intravascular oxygenation). In 10 infants the study was repeated 1 h after intravenous administration of 10 mg/kg ibuprofen as prophylaxis against PDA. Withdrawal and infusion via the UVC caused significant MABP and concordant HbD and CBV changes. Smaller modifications were seen following blood withdrawal and infusion via the UAC. Ibuprofen attenuated cerebral hemodynamic changes associated with withdrawal, but not infusion, from UAC and UVC.     

Complications of diazoxide treatment in persistent neonatal hyperinsulinism.

Seven infants with persistent neonatal hyperinsulinism were treated in Dhahran Health Centre from 1983 to 1986. The insulin:glucose ratio (serum insulin concentration pmol/l) divided by the blood glucose concentration (mmol/l) ranged from 12 to 636, mean (SD) 177 (201). To control hypoglycaemia, diazoxide (12-24 mg/kg/day) was given in a continuous intravenous glucose infusion (12-22 mg/kg/min) on 11 separate occasions, four infants twice each and three infants once each. An increase of more than one standard deviation in the heart and respiratory rates, together with other symptoms of heart failure, was considered to be evidence of diazoxide toxicity. Cardiorespiratory failure (toxicity) occurred on eight of the 11 occasions (73%) in seven infants. The average daily fluid intake, weight change, respiratory rate and heart rate before treatment were similar whether or not the infant developed toxicity. A diazoxide toxicity index was obtained by multiplying the dose of diazoxide by the insulin:glucose ratio to relate the diazoxide dose to the severity of the disease. In all instances when the toxicity index was more than 1533 (mean (SD) 3732 (2741) cardiac toxicity developed. In contrast, infants with a toxicity index of less than 675 (mean (SD) 364 (270), had no symptoms of toxicity. Symptoms were significantly related to the severity of the disease and the diazoxide dose. It is possible to use the toxicity index to predict the risk of toxicity and to calculate a safe dose of diazoxide in infants with persistent neonatal hyperinsulinism.     

Age-dependent cardiovascular effects of verapamil in newborn swine

Since there are limited studies concerning the hemodynamic effects of verapamil in pediatric patients, cardiovascular effects of clinical doses (100 or 300 micrograms/kg) of verapamil, given as a 2-min intravenous infusion, were examined in sodium pentobarbital anesthetized swine, aged 1 day (n = 15) and 2 wk (n = 18). Aortic and left ventricular pressures, index of left ventricular contractility, heart rate, and phasic superior mesenteric, renal, and femoral arterial flows were recorded; mean aortic pressure and vascular resistances were calculated. Maximum changes in cardiovascular function (mean % delta +/- SEM) occurred at the end of the infusion. Mean aortic pressure and index of left ventricular contractility decreased in all animals; responses were larger in magnitude with the higher dose. By 30 min after infusion of 300 micrograms/kg verapamil had ended, mean aortic pressure in both 1 day and 2 wk olds and index of left ventricular contractility and femoral flow in 1 day olds were still decreased. During infusion of verapamil, heart rate decreased (-11.6 +/- 2.9) to the high dose in 1 day olds but increased (+6.4 +/- 2.7) to 100 and 300 micrograms/kg verapamil in 2 wk olds. After infusion of 300 micrograms/kg verapamil ended, heart rate decreased and reached the nadir (-10.0 +/- 2.9) by 10 min in 2 wk olds. Decreases in renal resistance (-7.6 +/- 1.7) were not dose dependent while superior mesenteric resistance decreased (-12.9 +/- 2.7) only to low dose verapamil in 2 wk olds. In 1 day olds decreases in renal and superior mesenteric resistance were not sustained throughout the infusion.(ABSTRACT TRUNCATED AT 250 WORDS)     

Hypothalamic-pituitary-adrenal axis function in very low birth weight infants treated with dexamethasone

The effect of dexamethasone therapy on hypothalamic-pituitary-adrenal axis function was prospectively investigated in very low birth weight infants with bronchopulmonary dysplasia. Ten infants (mean +/- SD birth weight 825 +/- 265 g, gestation 25.8 +/- 1.9 weeks, postnatal age 33.1 +/- 17.7 days) initially received intravenous dexamethasone, 0.5 mg/kg per day for 3 days, and then were weaned over a period of 45 +/- 19.0 days to a replacement dose, followed by a metyrapone test. Morning plasma cortisol and 11-deoxycortisol levels were measured before and after an oral metyrapone dose given at midnight. Five infants (group A: birth weight 876 +/- 313 g, gestation 26.2 +/- 1.3 weeks, age of entry 31.8 +/- 22.8 days) had normal metyrapone test results, and five infants (group B: 778 +/- 234 g, 25.4 +/- 2.5 weeks, 34.4 +/- 13.4 days) had suppressed test results. Group A infants, in comparison with group B infants, had higher basal cortisol plasma levels (14.52 +/- 12.53 and 3.00 +/- 1.38 micrograms/dL, P = .047), higher postmetyrapone 11-deoxycortisol plasma levels (3.11 +/- 3.93 and 0.55 +/- 0.51 micrograms/dL, P = .028), larger differences between basal and postmetyrapone cortisol levels (7.10 +/- 4.67 and 2.12 +/- 1.31 micrograms/dL, P = .047), and larger differences between basal and postmetyrapone 11-deoxycortisol levels (2.99 +/- 3.93 and 0.29 +/- 0.25 micrograms/dL, P = .009). The hypothalamic-pituitary-adrenal axis function in group B infants eventually returned to normal when they continued to receive low-dose dexamethasone therapy after a period of 36.8 +/- 16.6 days.(ABSTRACT TRUNCATED AT 250 WORDS)     

Efficacy and safety of intravenous amiodarone for incessant tachycardias in infants

Amiodarone is an effective anti-arrhythmic agent for the treatment of supraventricular and ventricular tachycardias. The safety and efficacy of intravenous amiodarone has been described in adults and children but only to a limited extent in infants. The purpose of this study was to evaluate the safety and efficacy of intravenous amiodarone in infants. Between February 1994 and June 2001, 23 infants with a median age of 8 days (range 1–300 days) with life-threatening incessant tachycardias (17 supraventricular, 6 ventricular) were treated with intravenous amiodarone as single anti-arrhythmic agent. At presentation, 22 infants were haemodynamically unstable. Amiodarone was given as an intravenous loading dose of 5 mg/kg over 1 h followed by an intravenous maintenance dose of 5 µg/kg per min with stepwise increase up to 25 µg/kg per min until arrhythmia control or side-effects occurred. Amiodarone was effective in 19 infants, partially effective in three and ineffective in one infant. The median time until arrhythmia control was 24 h (range 1–96 h) and the median maintenance dosage 15 µg/kg per min (range 5–26 µg/kg per min). Electrophysiological side-effects necessitating dose reduction comprised of sinus bradycardia in two patients. Hypotension in one patient resolved after dose diminution. Neurological side-effects consisted of choreatic movements in one infant, which resolved over time. Amiodarone administration was stopped in one patient with elevated liver enzymes. Conclusion:intravenous amiodarone is a safe and effective therapy for life-threatening incessant tachycardias in infants.     

Effects of cisapride on ventricular depolarization-repolarization and arrhythmia markers in infants

To study prospectively the effects of cisapride on ventricular repolarization, depolarization, and arrhythmia markers in neonates, we determined before and three days after starting cisapride (1 mg/kg/day): corrected QT interval (QTc) and QT dispersion (QTd) on standard ECGs, and duration of filtered QRS (fQRS) and of low amplitude (<40 microV) terminal signals (LAS40, ms) and root mean square of the last 40 ms (RMS40, microV) using high-gain signal-averaged ECG (SAECG). Twenty-four term and 11 preterm infants (gestational age 23-35 weeks) were studied at a median chronological age of 32 days. QTc and QTd were not different between term and preterm infants. Cisapride lengthened QTc (mean +/- SD; ms: 396.6 +/- 24.8 before vs. 417.0 +/- 35.2 after, p < 0.001). Three term and two preterm infants (5/35 = 14%; 95% CI: 5-30%) had a QTc >450 ms after cisapride. QTd after cisapride increased significantly in all infants with prolonged QTc. Filtered QRS, LAS40, and RMS40 before and after cisapride were within our normal values. We conclude that cisapride prolongs ventricular repolarization in neonates and infants without altering depolarization. Although no clinical arrhythmias were observed the dose of 0.8 mg/kg/day should not be exceeded.     

Pulmonary vascular resistance during lipid infusion in neonates.

Using two-dimensional echocardiography, pulmonary vascular resistance was estimated from right ventricular pre-ejection period to ejection time (RVPEP/ET) in 11 preterm infants with respiratory distress, to test the effect of different doses of continuous lipid infusion. Echocardiography was performed at baseline with no lipid infusing 2 and 24 hours after 1.5 and 3 g/kg/day of intravenous lipid, 24 hours after discontinuing intravenous lipid emulsion, and 2 hours after restarting intravenous lipid. After 24 hours of intravenous lipid at 1.5 g/kg/day the RVPEP/ET rose to mean (SD) 0.287 (0.03) from a baseline value of 0.225 (0.02) and to 0.326 (0.05) after 24 hours of intravenous lipid at 3 g/kg/day. Pulmonary arterial pressure returned to baseline 24 hours after the intravenous lipid had been discontinued. Continuous 24 hour infusion of lipid caused significant dose and time-dependent increases in pulmonary vascular resistance. Intravenous lipid may aggravate pulmonary hypertension.     

Effect of heparinization of fluids infused through an umbilical artery catheter on catheter patency and frequency of complications.

Heparinization of fluids (1 unit/ml) infused through an umbilical artery catheter (UAC) was efficacious in prolonging catheter patency in a double-blind, randomized, controlled clinical study. On the basis of life-table analysis, the half-life of catheter function was seven days in the heparinized group as compared with just over two days in the nonheparinized group (P less than .01). UAC occlusion occurred in 4 of 32 patients in the heparinized and 19 of 30 in the nonheparinized group (chi 2 = 17.6, P less than .01). Blood transfusions, number of arterial blood gases drawn through the UACs, and fluid infusion rates were not related to catheter occlusion. Heparinization of the UAC infusion did not alter the partial thromboplastin time or the incidence of catheter-related thromboembolic phenomena in the extremities. Heparinization of fluids infused through a UAC appears to be useful in the care of critically ill neonates.     

Early high-dose phenobarbital treatment for prevention of hypoxic-ischemic brain damage in very low birth weight infants

In a randomized prospective trial, we studied the effect of early high-dose phenobarbital treatment on the early (intraventricular hemorrhage) and late (neurodevelopmental abnormalities) manifestations of hypoxic-ischemic encephalopathy in preterm infants weighing 1500 g or less at birth. The first intravenous dose of 15 mg/kg was given at a mean age of 110 minutes, followed by 15 mg/kg after 4 hours and then by 5 mg/kg at 24-hour intervals for 5 days. The overall incidence of intraventricular hemorrhage was 32% in treated and 46% in control infants, a nonsignificant difference. An ultrasound brain scan at 9 months old revealed no significant difference in the incidence of ventricular dilatation between treated (19%) and control (29%) infants. At 27 months, a similar incidence of mild (10%) and severe (10%) neurodevelopmental handicaps was found in both treated and control groups. Since beneficial effects could not be documented by any of the criteria used, we conclude that routine administration of phenobarbital to low birth weight infants is not justified.     

Low-dose doxapram for treatment of apnoea following early weaning in very low birthweight infants: a randomized, double-blind study

The effects of low-dose doxapram (0.5 mg kg⁻¹ h⁻¹) in combination with caffeine were evaluated on apnoea frequency following weaning from mechanical ventilation, and on blood pressure, in very low birthweight (BW) premature infants. Twenty-nine infants with BW <1250 g, gestational age at birth (GA) <34 weeks and postnatal age <5 d, who required minimal respiratory support, were included. Following randomization, they received a loading dose of caffeine citrate and a continuous infusion of doxapram (doxapram, n = 14) or placebo ( n = 15) was started. They were extubated 8 h after starting the infusion, which was continued for 5 d. During this period, weaning was well tolerated in both groups, apnoeas occurred less frequently and there was a greater increase in systolic blood pressure in infants treated with doxapram than in controls. Plasma doxapram levels were also higher than expected. It is therefore suggested that doxapram, even at low doses, should not be used during the first few days of life. Careful monitoring of blood pressure is required if doxapram is used later.     

Efficacy of thromboresistant umbilical artery catheters in reducing aortic thrombosis and related complications

Previous in vitro and in vivo reports suggest that catheters constructed of polyurethane with heparin bonded to the surface (HB-PU) are less thrombogenic than catheters made of polyvinyl chloride (PVC). A randomized trial sufficiently large (power 80%) to detect a reduction in the incidence of umbilical artery (UA) catheter complications, including aortic thrombus formation, from 45% to 20% was conducted in 125 infants. The infants were monitored for complications possibly related to the use of a UA catheter, such as systemic hypertension and abnormalities of lower extremity perfusion. The presence of aortic thrombi was assessed by ultrasound study 3.5 +/- 1.2 (SD) days and 11.1 +/- 2.3 days after insertion of the catheter. The use of HB-PU umbilical catheters did not lead to a significant reduction in the incidence of complications and aortic thrombi compared with the use of PVC catheters. The lack of reduction may have been related to the prolonged duration of catheter use in both groups. A much larger study would have been required to detect a smaller, but perhaps clinically significant, reduction in catheter-associated complications.     

Response of neonatal hypocalcaemia to 1 alpha-hydroxyvitamin D3.

Administration of 1 alpha-OH-D3 to hypocalcaemic neonates (mean +/- SD, serum calcium 1.50 +/- 0.13 mmol/l) significantly increased serum calcium in all 24 infants within 48 hours after starting therapy (mean +/- SD 1.83 +/- 0.23 mmol/1). The time required to correct hypocalcaemia was significantly shorter (2.04 +/- 0.56 days) in infants treated with 1 alpha-OH-D3, than in 24 infants treated with calcium gluconate infusions (4.12 +/- 1.0 days). Treatment with 1 alpha-OH-D3 was effective, easy to maintain, and produced no side effects.     

A randomised, double blind, placebo controlled trial of the effect of theophylline in prevention of vasomotor nephropathy in very preterm neonates with respiratory distress syndrome

BACKGROUND: Vasomotor nephropathy is a common renal dysfunction in very preterm neonates. OBJECTIVE: To determine whether theophylline could prevent vasomotor nephropathy in very preterm infants with respiratory distress syndrome. METHODS: A randomised, double blind, placebo controlled trial of 50 preterm infants of gestational age < or = 32 weeks needing assisted ventilation. Infants received an intravenous dose of theophylline (1 mg/kg) or placebo for three days. The 24 hour urine volume was measured daily. On days 2, 5, and 11, blood samples and 12 hour urine collections were analysed for electrolytes, creatinine, and urea. RESULTS: On day 1, urine output was significantly higher in the theophylline (2.4 (0.9) ml/kg/h) than the placebo (1.6 (1.0) ml/kg/h; p = 0.023) group (values are mean (SD)). The incidence of oligoanuria was significantly lower in the theophylline treated (5%) than the placebo (33%) group. Twenty four hours after the first administration of theophylline/placebo, serum creatinine concentration was significantly lower in the theophylline (0.76 (0.23) mg/dl) than the placebo (1.0 (0.41) mg/dl; p = 0.025) group. On day 5 an increase in serum creatinine was observed in both groups. On day 11 a significant reduction in serum creatinine was observed, compared with day 5, with no difference between the two groups. CONCLUSION: The results suggest that, in very preterm infants with respiratory distress syndrome, early theophylline administration improves renal function during the first two days of life.     

Weekly intravenous administration of recombinant human erythropoietin in infants with the anaemia of prematurity

To study the safety and efficacy of administering human recombinant erythropoietin (rHuEPO) to infants with anaemia of prematurity, a combined phase I/II trial of weekly intravenous injections for 4 weeks was undertaken. We treated 16 infants with 10, 25, 50, 100 or 200 units/kg body weight in groups of two to four patients per dose level. They were all born prematurely (mean gestational age: 29 weeks; range 27–32), had a mean post-natal age of 42 days (range: 25–59) and haemoglobin concentration of 87 g/l (range: 72–94) when treatment was started. Four patients (25%) needed a transfusion during the trial, one at day 7 treated with 10 units/kg and 3 at days 15, 25, 29 with 100 units/kg. In the others, a progressive rise in mean haemoglobin values was seen in each group after 21 days of treatment, without a dosedependent effect. A positive change in absolute reticulocyte counts with a peak after 7–14 days of therapy was observed with low (25–50 units/kg) but not with higher doses, with a significant difference at day 14 between 25 and 100 units/kg (P<0.01). A dose-limiting severe neutropenia (absolute neutrophil count<0.5×10⁹/l) occurred transiently in five patients, with doses >25 units/kg. No infectious complication and no sign of iron deficiency were observed. Weekly low doses of rHuEPO appear safe, convenient to administer and able to induce a reticulocytic response in infants with anaemia of prematurity. A phase III placebo-controlled trial is needed to confirm these results. Neutropenia associated with rHuEPO administration in infants might be related to their stage of human ontogeny.     

Low-dose doxapram therapy in premature infants and its CSF and serum concentrations

The efficacy of low-dose doxapram therapy (0.2 mg/kg/h) in combination with methylxanthines was evaluated in 20 premature infants with idiopathic apnea unresponsive to methylxanthines alone, and in 13 premature infants with secondary apnea. The serum concentrations of doxapram and, in some infants, the simultaneous cerebrospinal fluid and serum concentrations were measured, and the correlation between cerebrospinal fluid and serum concentrations in the postnatal period was determined. The following results were obtained: 1) In idiopathic apnea of prematurity, low-dose doxapram therapy was as effective as a dose of 1.0-2.5 mg/kg/h and the side effects were few, mild, and reversible. 2) In premature infants over seven days of age, serum concentrations of doxapram were almost stable but were significantly lower than in infants within the first six days of life. 3) The ratio of the cerebrospinal fluid to serum doxapram concentration was 0.48 +/- 0.13 (mean +/- SD). There was a good correlation between cerebrospinal fluid and serum concentrations (r = 0.933, p less than 0.001). The initial doxapram dose can be set as low as 0.2 mg/kg/h in very young premature infants with idiopathic apnea of prematurity unresponsive to methylxanthines.     

Low-dose tissue plasminogen activator thrombolysis in children

PURPOSE: To compare results of low-dose tissue plasminogen activator (TPA) in children with arterial and venous thrombi relative to standard published dosing. METHODS: Subjects consisted of all consecutive children with objectively confirmed thrombi for whom TPA thrombolysis was clinically ordered by the authors. Initial dosing used published standard dose (0.1-0.5 mg/kg per hour). With experience, a low-dose regimen (0.01-0.06 mg/kg per hour) was given in an attempt to derive a minimal effective dose. RESULTS: Thirty-five children were treated with TPA. Either standard or low-dose infusions of TPA resulted in complete thrombolysis of 28 of 29 (97%) acute thrombi, while all 6 chronic thrombi had a partial response. In contrast to the recommended adult-derived dosages of 0.1 to 0.5 mg/kg per hour, the authors found that initial doses of less than 0.01 mg/kg per hour were effective in 12 of 17 patients with acute thrombosis. Neonates required 0.06 mg/kg per hour. Route of administration (local or systemic) did not affect efficacy. Major bleeding occurred in only one extremely preterm infant. Minor bleeding, primarily oozing at intravenous sites, occurred in 27% of children during TPA infusions. Prophylactic unfractionated or low-molecular-weight heparin was infused concomitant with TPA in 42% of the children and did not increase the risk of bleeding. CONCLUSIONS: TPA in very low doses appears to be safe and effective for thrombolysis of acute thromboses in most children, given appropriate patient selection.     

Intravenous metronidazole in the newborn

Twenty four neonates at high risk of anaerobic sepsis were treated with intravenous metronidazole, 7.5 mg/kg, 8 hourly, for a mean period of 5 days. The highest observed concentration after the first dose (mean +/- SD) 9.6 +/- 4.0 mg/l (56.1 +/- 23.4 mumol/l) was significantly lower (P less than 0.001) than the highest observed concentration after the final dose (mean +/- SD) 19.3 +/- 8.6 mg/l (112.7 +/- 50.2 mumol/l). The overall metronidazole half life was (mean +/- SD) 23.4 +/- 13.1 hours. The half life after the first dose (mean +/- SD) 21.9 +/- 10.1 hours was not appreciably different from the half life after the final dose (mean +/- SD) 21.6 +/- 12.4 hours. The concentrations of the major metabolite of metronidazole (20396RP) also rose appreciably during treatment. No side effects of metronidazole were noted and its extended half life in neonates suggests that less frequent dosage would be appropriate.     

Heparin lock intravenous line. Use in newborn infants. A controlled trial

The heparin lock technique has been available for parenteral access in older children and adults but has not yet been described for use in newborns. We randomized 39 newborns who needed parenteral medication in the intermediate care nursery to receive a heparin lock catheter (17) or an intravenous line kept patent by continuous low infusion rate (22). There were no differences between study groups with regard to birthweight, gestational age, or distribution of diagnoses. Infants in the heparin lock group were enrolled in the study on average 1 day longer than the continuous intravenous group (p less than 0.05). Subcutaneous infiltration occurred twice as frequently with the continuous intravenous line (p = 0.0015), and the life span was significantly less than heparin lock (1.0 +/- 0.5 days versus 2.1 +/- 1.0 days, p = 0.0003). Infants with continuous intravenous lines received approximately 20 ml/kg/day greater quantity of fluid (p less than 0.0001). There was no difference between groups with regard to mean heparin activity level. None of the infants developed hemorrhagic complications, thrombophlebitis, or documented nosocomial infection. Nurses significantly favored heparin locks over continuous intravenous lines for ease of use. The heparin lock technique is a safe and reasonable alternative to a continuous low infusion intravenous line for administering parenteral medications to intermediate care newborns.     

Fluctuations of anti-Xa concentrations during maintenance enoxaparin therapy for neonatal thrombosis

Aim: To evaluate fluctuations in anti‐Xa concentrations in infants treated with enoxaparin for thrombosis and describe clinical outcomes. Methods: A retrospective chart review was performed on infants treated with enoxaparin in the Neonatal Intensive Care Unit, and data on enoxaparin doses, anti‐Xa concentrations, clinical characteristics and outcomes were abstracted. Results: Our cohort (n = 26) had a median gestation of 36 (range, 23–41) weeks, birthweight of 2522 (510–3912) grams and 5‐min Apgar score of 8(4–9). Fifteen (57.7%) infants were males. Thromboses was diagnosed at a median age of 22 (range, 1–97) days; enoxaparin was initiated at 27.5 (range, 4–98) days at a mean (SD) dose of 1.4 (0.3) mg/kg every 12 h. Therapeutic anti‐Xa concentrations (0.5–1 U/mL) were achieved at a mean (SD) dose of 2.1 (0.6) mg/kg at 12.5 (12.2) days of treatment. Of the 143 anti‐Xa concentrations, 39 (27%) were within the therapeutic range. During maintenance therapy following initial therapeutic anti‐Xa concentration, 40% concentrations were therapeutic. Minor bleeding was noted in four infants and intracranial bleed in one infant; four infants died. During treatment, thrombocytopenia, renal and hepatic impairment during treatment were noted in 7, 2 and 4 infants, respectively. Clot resolution was observed in 21 (81%) infants. Conclusions: Anti‐Xa concentrations fluctuate during maintenance enoxaparin therapy, with therapeutic levels being achieved only sporadically in young infants. Despite this, enoxaparin appears efficacious in thrombosis resolution. Further studies on the impact of stringent control of concentrations on outcomes in this population are warranted.