The dominance and growth of shallow groundwater resources in continuous permafrost environments.

Water is a limited resource in Arctic watersheds with continuous permafrost because freezing conditions in winter and the impermeability of permafrost limit storage and connectivity between surface water and deep groundwater. However, groundwater can still be an important source of surface water in such settings, feeding springs and large aufeis fields that are abundant in cold regions and generating runoff when precipitation is rare. Whether groundwater is sourced from suprapermafrost taliks or deeper regional aquifers will impact water availability as the Arctic continues to warm and thaw. Previous research is ambiguous about the role of deep groundwater, leading to uncertainty regarding Arctic water availability and changing water resources. We analyzed chemistry and residence times of spring, stream, and river waters in the continuous permafrost zone of Alaska, spanning the mountains to the coastal plain. Water chemistry and age tracers show that surface waters are predominately sourced from recent precipitation and have short (<50 y) subsurface residence times. Remote sensing indicates trends in the areal extent of aufeis over the last 37 y, and correlations between aufeis extent and previous year summer temperature. Together, these data indicate that surface waters in continuous permafrost regions may be impacted by short flow paths and shallow suprapermafrost aquifers that are highly sensitive to climatic and hydrologic change over annual timescales. Despite the lack of connection to regional aquifers, continued warming and permafrost thaw may promote deepening of the shallow subsurface aquifers and creation of shallow taliks, providing some resilience to Arctic freshwater ecosystems.

Diuretic response after neonatal cardiac surgery: a report from the NEPHRON collaborative.

BACKGROUND: Multicenter early diuretic response (DR) analysis of single furosemide dosing following neonatal cardiac surgery is lacking to inform whether early DR predicts adverse clinical outcomes. METHODS: We performed a retrospective cohort study utilizing data from the NEPHRON registry. Random forest machine learning generated receiver operating characteristic-area under the curve (ROC-AUC) and odds ratios for mechanical ventilation (MV) and respiratory support (RS). Prolonged MV and RS were defined using ≥ 90th percentile of observed/expected ratios. Secondary outcomes were prolonged CICU and hospital length of stay (LOS) and kidney failure (stage III acute kidney injury (AKI), peritoneal dialysis, and/or continuous kidney replacement therapy on postoperative day three) assessed using covariate-adjusted ROC-AUC curves. RESULTS: A total of 782 children were included. Cumulative urine output (UOP) metrics were lower in prolonged MV and RS patients, but DR poorly predicted prolonged MV (highest AUC 0.611, OR 0.98, sensitivity 0.67, specificity 0.53, p = 0.006, 95% OR CI 0.96-0.99 for cumulative 6-h UOP) and RS (highest AUC 0.674, OR 0.94, sensitivity 0.75, specificity 0.54, p < 0.001, 95% CI 0.91-0.97 UOP between 3 and 6 h). Secondary outcome results were similar. DR had fair discrimination for kidney failure (AUC 0.703, OR 0.94, sensitivity 0.63, specificity 0.71, 95% OR CI 0.91-0.98, p < 0.001, cumulative 6-h UOP). CONCLUSIONS: Early DR poorly discriminated patients with prolonged MV, RS, and LOS in this cohort, though it may identify severe postoperative AKI phenotype. Future work is warranted to determine if early DR or late postoperative DR later, in combination with other AKI metrics, may identify a higher-risk phenotype.

Peritoneal catheters in neonates undergoing complex cardiac surgery: a multi-centre descriptive study.

BACKGROUND: The use of peritoneal catheters for prophylactic dialysis or drainage to prevent fluid overload after neonatal cardiac surgery is common in some centres; however, the multi-centre variability and details of peritoneal catheter use are not well described. METHODS: Twenty-two-centre NEonatal and Pediatric Heart Renal Outcomes Network (NEPHRON) study to describe multi-centre peritoneal catheter use after STAT category 3-5 neonatal cardiac surgery using cardiopulmonary bypass. Patient characteristics and acute kidney injury/fluid outcomes for six post-operative days are described among three cohorts: peritoneal catheter with dialysis, peritoneal catheter with passive drainage, and no peritoneal catheter. RESULTS: Of 1490 neonates, 471 (32%) had an intraoperative peritoneal catheter placed; 177 (12%) received prophylactic dialysis and 294 (20%) received passive drainage. Sixteen (73%) centres used peritoneal catheter at some frequency, including six centres in >50% of neonates. Four centres utilised prophylactic peritoneal dialysis. Time to post-operative dialysis initiation was 3 hours [1, 5] with the duration of 56 hours [37, 90]; passive drainage cohort drained for 92 hours [64, 163]. Peritoneal catheter were more common among patients receiving pre-operative mechanical ventilation, single ventricle physiology, and higher complexity surgery. There was no association with adverse events. Serum creatinine and daily fluid balance were not clinically different on any post-operative day. Mortality was similar. CONCLUSIONS: In neonates undergoing complex cardiac surgery, peritoneal catheter use is not rare, with substantial variability among centres. Peritoneal catheters are used more commonly with higher surgical complexity. Adverse event rates, including mortality, are not different with peritoneal catheter use. Fluid overload and creatinine-based acute kidney injury rates are not different in peritoneal catheter cohorts.

Therapeutic Hypothermia after In-Hospital Cardiac Arrest in Children.

BACKGROUND: Targeted temperature management is recommended for comatose adults and children after out-of-hospital cardiac arrest; however, data on temperature management after in-hospital cardiac arrest are limited. METHODS: In a trial conducted at 37 children's hospitals, we compared two temperature interventions in children who had had in-hospital cardiac arrest. Within 6 hours after the return of circulation, comatose children older than 48 hours and younger than 18 years of age were randomly assigned to therapeutic hypothermia (target temperature, 33.0°C) or therapeutic normothermia (target temperature, 36.8°C). The primary efficacy outcome, survival at 12 months after cardiac arrest with a score of 70 or higher on the Vineland Adaptive Behavior Scales, second edition (VABS-II, on which scores range from 20 to 160, with higher scores indicating better function), was evaluated among patients who had had a VABS-II score of at least 70 before the cardiac arrest. RESULTS: The trial was terminated because of futility after 329 patients had undergone randomization. Among the 257 patients who had a VABS-II score of at least 70 before cardiac arrest and who could be evaluated, the rate of the primary efficacy outcome did not differ significantly between the hypothermia group and the normothermia group (36% [48 of 133 patients] and 39% [48 of 124 patients], respectively; relative risk, 0.92; 95% confidence interval [CI], 0.67 to 1.27; P=0.63). Among 317 patients who could be evaluated for change in neurobehavioral function, the change in VABS-II score from baseline to 12 months did not differ significantly between the groups (P=0.70). Among 327 patients who could be evaluated for 1-year survival, the rate of 1-year survival did not differ significantly between the hypothermia group and the normothermia group (49% [81 of 166 patients] and 46% [74 of 161 patients], respectively; relative risk, 1.07; 95% CI, 0.85 to 1.34; P=0.56). The incidences of blood-product use, infection, and serious adverse events, as well as 28-day mortality, did not differ significantly between groups. CONCLUSIONS: Among comatose children who survived in-hospital cardiac arrest, therapeutic hypothermia, as compared with therapeutic normothermia, did not confer a significant benefit in survival with a favorable functional outcome at 1 year. (Funded by the National Heart, Lung, and Blood Institute; THAPCA-IH ClinicalTrials.gov number, NCT00880087 .).

Therapeutic hypothermia after out-of-hospital cardiac arrest in children.

BACKGROUND: Therapeutic hypothermia is recommended for comatose adults after witnessed out-of-hospital cardiac arrest, but data about this intervention in children are limited. METHODS: We conducted this trial of two targeted temperature interventions at 38 children's hospitals involving children who remained unconscious after out-of-hospital cardiac arrest. Within 6 hours after the return of circulation, comatose patients who were older than 2 days and younger than 18 years of age were randomly assigned to therapeutic hypothermia (target temperature, 33.0°C) or therapeutic normothermia (target temperature, 36.8°C). The primary efficacy outcome, survival at 12 months after cardiac arrest with a Vineland Adaptive Behavior Scales, second edition (VABS-II), score of 70 or higher (on a scale from 20 to 160, with higher scores indicating better function), was evaluated among patients with a VABS-II score of at least 70 before cardiac arrest. RESULTS: A total of 295 patients underwent randomization. Among the 260 patients with data that could be evaluated and who had a VABS-II score of at least 70 before cardiac arrest, there was no significant difference in the primary outcome between the hypothermia group and the normothermia group (20% vs. 12%; relative likelihood, 1.54; 95% confidence interval [CI], 0.86 to 2.76; P=0.14). Among all the patients with data that could be evaluated, the change in the VABS-II score from baseline to 12 months was not significantly different (P=0.13) and 1-year survival was similar (38% in the hypothermia group vs. 29% in the normothermia group; relative likelihood, 1.29; 95% CI, 0.93 to 1.79; P=0.13). The groups had similar incidences of infection and serious arrhythmias, as well as similar use of blood products and 28-day mortality. CONCLUSIONS: In comatose children who survived out-of-hospital cardiac arrest, therapeutic hypothermia, as compared with therapeutic normothermia, did not confer a significant benefit in survival with a good functional outcome at 1 year. (Funded by the National Heart, Lung, and Blood Institute and others; THAPCA-OH ClinicalTrials.gov number, NCT00878644.).

Use of nesiritide in critically ill children with biventricular dysfunction suffering from oliguria despite standard heart-failure management.

Although nesiritide has been used in adults with left heart failure, the experience in the paediatric population is limited. We reviewed and analysed our experience with continuous nesiritide infusion as adjunct therapy in children with biventricular dysfunction due to diverse aetiologies and suffering from oliguria despite intravenous diuretics and inotropic therapies for heart-failure management.

Pronounced chemical response of Subarctic lakes to climate-driven losses in surface area.

Losses in lake area have been observed for several Arctic and Subarctic regions in recent decades, with unknown consequences for lake ecosystems. These reductions are primarily attributed to two climate-sensitive mechanisms, both of which may also cause changes in water chemistry: (i) increased imbalance of evaporation relative to inflow, whereby increased evaporation and decreased inflow act to concentrate solutes into smaller volumes; and (ii) accelerated permafrost degradation, which enhances sublacustrine drainage while simultaneously leaching previously frozen solutes into lakes. We documented changes in nutrients [total nitrogen (TN), total phosphorus (TP)] and ions (calcium, chloride, magnesium, sodium) over a 25 year interval in shrinking, stable, and expanding Subarctic lakes of the Yukon Flats, Alaska. Concentrations of all six solutes increased in shrinking lakes from 1985-1989 to 2010-2012, while simultaneously undergoing little change in stable or expanding lakes. This created a present-day pattern, much weaker or absent in the 1980s, in which shrinking lakes had higher solute concentrations than their stable or expanding counterparts. An imbalanced evaporation-to-inflow ratio (E/I) was the most likely mechanism behind such changes; all four ions, which behave semiconservatively and are prone to evapoconcentration, increased in shrinking lakes and, along with TN and TP, were positively related to isotopically derived E/I estimates. Moreover, the most conservative ion, chloride, increased >500% in shrinking lakes. Conversely, only TP concentration was related to probability of permafrost presence, being highest at intermediate probabilities. Overall, the substantial increases of nutrients (TN >200%, TP >100%) and ions (>100%) may shift shrinking lakes towards overly eutrophic or saline states, with potentially severe consequences for ecosystems of northern lakes.

An evaluation of the outcomes associated with peritoneal catheter use in neonates undergoing cardiac surgery: A multicenter study.

Objective: The study objective was to determine if intraoperative peritoneal catheter placement is associated with improved outcomes in neonates undergoing high-risk cardiac surgery with cardiopulmonary bypass. Methods: This propensity score-matched retrospective study used data from 22 academic pediatric cardiac intensive care units. Consecutive neonates undergoing Society of Thoracic Surgeons-European Association for Cardio-Thoracic Surgery category 3 to 5 cardiac surgery with cardiopulmonary bypass at centers participating in the NEonatal and Pediatric Heart Renal Outcomes Network collaborative were studied to determine the association of the use of an intraoperative placed peritoneal catheter for dialysis or passive drainage with clinical outcomes, including the duration of mechanical ventilation. Results: Among 1490 eligible neonates in the NEonatal and Pediatric Heart Renal Outcomes Network dataset, a propensity-matched analysis was used to compare 395 patients with peritoneal catheter placement with 628 patients without peritoneal catheter placement. Time to extubation and most clinical outcomes were similar. Postoperative length of stay was 5 days longer in the peritoneal catheter placement cohort (17 vs 22 days, P = .001). There was a 50% higher incidence of moderate to severe acute kidney injury in the no-peritoneal catheter cohort (12% vs 18%, P = .02). Subgroup analyses between specific treatments and in highest risk patients yielded similar associations. Conclusions: This study does not demonstrate improved outcomes among neonates with placement of a peritoneal catheter during cardiac surgery. Outcomes were similar apart from longer hospital stay in the peritoneal catheter cohort. The no-peritoneal catheter cohort had a 50% higher incidence of moderate to severe acute kidney injury (12% vs 18%). This analysis does not support indiscriminate peritoneal catheter use, although it may support the utility for postoperative fluid removal among neonates at risk for acute kidney injury. A multicenter controlled trial may better elucidate peritoneal catheter effects.

Tolvaptan increases serum sodium in pediatric patients with heart failure.

This study aimed to evaluate the use of tolvaptan in a consecutive series of pediatric patients with heart failure. Patients 18 years of age or younger with heart failure prescribed tolvaptan between January 2009 and October 2011 were retrospectively identified at Children's Medical Center Dallas. Laboratory parameters, urine output, fluid balance, and concurrent medications were recorded at baseline and at specified intervals after a single dose of tolvaptan. The 28 patients in the study had a median age of 2 years (range 1 month-18 years). The median tolvaptan dose administered was 0.3 mg/kg (range 0.1-1.3 mg/kg). The study patients had a median baseline serum sodium concentration of 127 mmol/L, and the increases in sodium were 2.5 mmol/L at 12 h, 5 mmol/L at 24 h, 4 mmol/L at 48 h, and 5 mmol/L at 72 h (all p < 0.001). Urine output was increased at 24 h (p < 0.001) and 48 h (p = 0.03), and fluid balance changes were significantly different at 24 h (p = 0.004). The changes in potassium, blood urea nitrogen, and serum creatinine were not significant at any interval. When controlling for traditional diuretic therapy, increases in serum sodium concentration and urine output remained statistically significant. A single dose of tolvaptan increased serum sodium concentrations for the majority in this small series of pediatric patients with heart failure. These results suggest that tolvaptan can be safely and effectively administered to pediatric patients. Prospective, randomized controlled trials are needed to evaluate the safety and efficacy of its use further.

Protecting the future: neuroprotective strategies in the pediatric intensive care unit.

PURPOSE OF REVIEW: Brain injury is the leading cause of death in pediatric intensive care units, and improvements in therapy and in understanding the pathogenesis are urgently needed. This review presents recent advances in the understanding of neuroprotective therapy and brain-specific monitoring for critically ill pediatric patients. RECENT FINDINGS: Two neuroprotective strategies are becoming increasingly accepted as they are applied to different mechanisms of brain injury. The rapid application of hypothermia and avoidance of hyperoxia after cardiac arrest and other brain injuries are each being more commonly used as both human and animal data advocating for these approaches accumulate. In addition, more advanced and noninvasive technologies are emerging that are designed to serve as surrogates for brain function and may be used to help predict outcome. Near-infrared spectroscopy is one such commonly used technique that has prompted many studies to understand how to incorporate it into practice. SUMMARY: Protection of the pediatric brain from both a primary insult and the common subsequent secondary injury is essential for improving long-term neurologic outcomes. Whereas monitoring technology is being constantly modified, it must be proven efficacious in order to understand the utility of new and presumed neuroprotective therapies like hypothermia and avoidance of hyperoxia.

Nitrogen biogeochemistry in a boreal headwater stream network in interior Alaska.

High latitude, boreal watersheds are nitrogen (N)-limited ecosystems that export large amounts of organic carbon (C). Key controls on C cycling in these environments are the biogeochemical processes affecting the N cycle. A study was conducted in Nome Creek, an upland tributary of the Yukon River, and two headwater tributaries to Nome Creek, to examine the relation between seasonal and transport-associated changes in C and N pools and N-cycling processes using laboratory bioassays of water and sediment samples and in-stream tracer tests. Dissolved organic nitrogen (DON) exceeded dissolved inorganic nitrogen (DIN) in Nome Creek except late in the summer season, with little variation in organic C:N ratios with time or transport distance. DIN was dominant in the headwater tributaries. Rates of organic N mineralization and denitrification in laboratory incubations were positively correlated with sediment organic C content, while nitrification rates differed greatly between two headwater tributaries with similar drainages. Additions of DIN or urea did not stimulate microbial activity. In-stream tracer tests with nitrate and urea indicated that uptake rates were slow relative to transport rates; simulated rates of uptake in stream storage zones were higher than rates assessed in the laboratory bioassays. In general, N-cycle processes were more active and had a greater overall impact in the headwater tributaries and were minimized in Nome Creek, the larger, higher velocity, transport-dominated stream. Given expectations of permafrost thaw and increased hydrologic cycling that will flush more inorganic N from headwater streams, our results suggest higher N loads from these systems in the future.

Field-based method for assessing duration of infectivity for influenza A viruses in the environment.

Understanding influenza A virus (IAV) persistence in wetlands is limited by a paucity of field studies relating to the maintenance of infectivity over time. The duration of IAV infectivity in water has been assessed under variable laboratory conditions, but results are difficult to translate to more complex field conditions. We tested a field-based method to assess the viability of IAVs in an Alaska wetland during fall and winter which incorporated physical and chemical properties of the waterbody in which samples were held. Filtered pond water was inoculated with avian fecal samples collected from the environment, aliquoted into a series of duplicate sealed vials and submerged back in the wetland for up to 132 days (October 2018-March 2019). Sample aliquots were sequentially recovered and tested for IAVs by rRT-PCR and virus isolation. One sample remained rRT-PCR positive for the duration of the study and virus isolation positive for 118 days. The surrounding water temperature was 1°-6 °C with near neutral pH (6.6-7.3) for the duration of the study. This proof of concept study demonstrates a protocol for testing the persistence of infectious IAV naturally shed from waterfowl under ambient environmental conditions.

Adrenal insufficiency in neonates undergoing cardiopulmonary bypass and postoperative hypothalamic-pituitary-adrenal function after prophylactic glucocorticoids.

OBJECTIVES: Determine incidence of preoperative adrenal insufficiency in neonates >35 weeks gestation with congenital heart disease undergoing cardiothoracic surgery with bypass and effects of prophylactic methylprednisolone on postoperative hypothalamic-pituitary-adrenal function and hemodynamic stability. DESIGN: Prospective observational study in 36 neonates with preoperative adrenocorticotrophic hormone stimulation tests and serial total cortisol and adrenocorticotrophic hormone measurements before and after surgery. Data analyses: analysis of variance and regression. RESULTS: Baseline circulating adrenocorticotrophic hormone and cortisol were unchanged 4-20 days postnatal (P > 0.1); however, cortisol levels rose with increasing adrenocorticotrophic hormone, P = 0.02. Ten neonates (29%) demonstrated preoperative adrenal insufficiency (∆cortisol ≤9 µg/dl); one had postoperative hemodynamic instability. Growth-restricted neonates had lower baseline cortisol, but normal stimulation tests and responded well to surgical stresses. Seventy-five percent of neonates receiving perioperative methylprednisolone demonstrated postoperative hypothalamic-pituitary-adrenal inhibition. CONCLUSION: Adrenal insufficiency appears common in neonates >35 weeks gestation with congenital heart disease, but did not contribute to postoperative hemodynamic instability despite hypothalamic-pituitary-adrenal inhibition.

Elevated cranial ultrasound resistive indices are associated with improved neurodevelopmental outcomes one year after pediatric cardiac surgery: A single center pilot study.

OBJECTIVE: To determine if a non-invasive, repeatable test can be used to predict neurodevelopmental outcomes in patients with congenital heart disease. METHODS: This was a prospective study of pediatric patients less than two months of age undergoing congenital heart surgery at the Children's Health Children's Medical Center at Dallas. Multichannel near-infrared spectroscopy (NIRS) was utilized during the surgery, and ultrasound (US) resistive indices (RI) of the major cranial vessels were obtained prior to surgery, immediately post-operatively, and prior to discharge. Pearson's correlation, Fischer exact t test, and Fischer r to z transformation were used where appropriate. RESULTS: A total of 16 patients were enrolled. All had US data. Of the sixteen patients, two died prior to the neurodevelopmental testing, six did not return for the neurodevelopmental testing, and eight patients completed the neurodevelopmental testing. There were no significant correlations between the prior to surgery and prior to discharge US RI and neurodevelopmental outcomes. The immediate post-operative US RI demonstrated a strong positive correlation with standardized neurodevelopmental outcome measures. We were able to demonstrate qualitative differences using multichannel NIRS during surgery, but experienced significant technical difficulties implementing consistent monitoring. CONCLUSIONS: A higher resistive index in the major cerebral blood vessels following cardiac surgery in the neonatal period is associated with improved neurological outcomes one year after surgery. Obtaining an ultrasound with resistive indices of the major cerebral vessels prior to and after surgery may yield information that is predictive of neurodevelopmental outcomes.

Pediatric cardiac arrest due to drowning and other respiratory etiologies: Neurobehavioral outcomes in initially comatose children.

AIM: To describe the 1-year neurobehavioral outcome of survivors of cardiac arrest secondary to drowning, compared with other respiratory etiologies, in children enrolled in the Therapeutic Hypothermia after Pediatric Cardiac Arrest Out-of-Hospital (THAPCA-OH) trial. METHODS: Exploratory analysis of survivors (ages 1-18 years) who received chest compressions for ≥2min, were comatose, and required mechanical ventilation after return of circulation (ROC). Participants recruited from 27 pediatric intensive care units in North America received targeted temperature management [therapeutic hypothermia (33°C) or therapeutic normothermia (36.8°C)] within 6h of ROC. Neurobehavioral outcomes included 1-year Vineland Adaptive Behavior Scales, Second Edition (VABS-II) total and domain scores and age-appropriate cognitive performance measures (Mullen Scales of Early Learning or Wechsler Abbreviated Scale of Intelligence). RESULTS: Sixty-six children with a respiratory etiology of cardiac arrest survived for 1-year; 60/66 had broadly normal premorbid functioning (VABS-II≥70). Follow up was obtained on 59/60 (30 with drowning etiology). VABS-II composite and domain scores declined significantly from premorbid scores in drowning and non-drowning groups (p<0.001), although declines were less pronounced for the drowning group. Seventy-two percent of children had well below average cognitive functioning at 1-year. Younger age, fewer doses of epinephrine, and drowning etiology were associated with better VABS-II composite scores. Demographic variables and treatment with hypothermia did not influence neurobehavioral outcomes. CONCLUSIONS: Risks for poor neurobehavioral outcomes were high for children who were comatose after out-of-hospital cardiac arrest due to respiratory etiologies; survivors of drowning had better outcomes than those with other respiratory etiologies.

Feasibility Study Evaluating Therapeutic Hypothermia for Refractory Status Epilepticus in Children.

Pediatric refractory status epilepticus (RSE) is a neurological emergency with significant morbidity and mortality, which lacks consensus regarding diagnosis and treatment(s). Therapeutic hypothermia (TH) is an effective treatment for RSE in preclinical models and small series. In addition, TH is a standard care for adults after cardiac arrest and neonates with hypoxic-ischemic encephalopathy. The purpose of this study was to identify the feasibility of a study of pediatric RSE within a research group (Pediatric Neurocritical Care Research Group [PNCRG]). Pediatric intensive care unit (PICU) admissions at seven centers were prospectively screened from October 2012 to July 2013 for RSE. Experts within the PNCRG estimated that clinicians would be unwilling to enroll a child, unless the child required at least two different antiepileptic medications and a continuous infusion of another antiepileptic medication with ongoing electrographic seizure activity for ≥2 hours after continuous infusion initiation. Data for children meeting the above inclusion criteria were collected, including the etiology of RSE, history of epilepsy, and maximum dose of continuous antiepileptic infusions. There were 8113 PICU admissions over a cumulative 52 months (October 2012-July 2013) at seven centers. Of these, 69 (0.85%) children met inclusion criteria. Twenty children were excluded due to acute diagnoses affected by TH, contraindications to TH, or lack of commitment to aggressive therapies. Sixteen patients had seizure cessation within 2 hours, resulting in 33 patients who had inadequate seizure control after 2 hours and a continuous antiepileptic infusion. Midazolam (21/33, 64%) and pentobarbital (5/33, 15%) were the most common infusions with a wide maximum dose range. More than one infusion was required for seizure control in four patients. There are substantial numbers of subjects at clinical sites within the PNCRG with RSE that would meet the proposed inclusion criteria for a study of TH. The true feasibility of such a study depends on the sample size necessary to achieve therapeutic effects on justifiable clinical outcomes.

Brief exposure to hyperoxia depletes the glial progenitor pool and impairs functional recovery after hypoxic-ischemic brain injury.

Patterns of hypoxic-ischemic brain injury in infants and children suggest vulnerability in regions of white matter development, and injured patients develop defects in myelination resulting in cerebral palsy and motor deficits. Reperfusion exacerbates the oxidative stress that occurs after such injuries and may impair recovery. Resuscitation after hypoxic-ischemic injury is routinely performed using 100% oxygen, and this practice may increase the oxidative stress that occurs during reperfusion and further damage an already compromised brain. We show that brief exposure (30 mins) to 100% oxygen during reperfusion worsens the histologic injury in young mice after unilateral brain hypoxia-ischemia, causes an accumulation of the oxidative metabolite nitrotyrosine, and depletes preoligodendrocyte glial progenitors present in the cortex. This damage can be reversed with administration of the antioxidant ebselen, a glutathione peroxidase mimetic. Moreover, mice recovered in 100% oxygen have a more disrupted pattern of myelination and develop a static motor deficit that mimics cerebral palsy and manifests itself by significantly worse performance on wire hang and rotorod motor testing. We conclude that exposure to 100% oxygen during reperfusion after hypoxic-ischemic brain injury increases secondary neural injury, depletes developing glial progenitors, interferes with myelination, and ultimately impairs functional recovery.