Treatment of term infants with head cooling and mild systemic hypothermia (35.0 degrees C and 34.5 degrees C) after perinatal asphyxia

Intracardiac temperature monitoring in infants after cardiac surgery

BACKGROUND

Hyperthermia after cerebral ischemia is associated with worse neurologic outcome. Our goals were 3-fold: (1) to describe the postoperative temperature course in infants after cardiac surgery, (2) to compare intracardiac temperature monitoring with traditional monitoring in infants, and (3) to determine variables that influence the patients' temperatures.

METHODS

Longitudinal temperature data were collected for 100 infants undergoing cardiac surgery. Intra-atrial, nasopharyngeal, esophageal, rectal, and axillary temperatures were recorded in all patients.

RESULTS

The mean age at the time of operation was 128 +/- 166 days, and the mean weight was 5.1 +/- 2.4 kg. Circulatory arrest was used for 54 patients. In the operating room, the maximum intra-atrial temperature (37.5 degrees C +/- 0.6 degrees C) was significantly greater than both the simultaneous esophageal temperature (36.9 degrees C +/- 1.9 degrees C, P = .03) and nasopharyngeal temperature (36.3 degrees C +/- 2.5 degrees C, P < .001). In the cardiac intensive care unit, intra-atrial temperature was significantly greater than both axillary and rectal temperatures. During the first 24 postoperative hours, intra-atrial temperature was greater than 38 degrees C in 48 (48%) patients, rectal temperature was greater than 38 degrees C in 36 (36%) patients, and axillary temperature was greater than 38 degrees C in 7 (7%) patients.

CONCLUSIONS

In patients less than 2 years of age undergoing cardiac surgery requiring cardiopulmonary bypass, intra-atrial temperature peaked 4 to 6 hours after leaving the operating room. Traditional methods of temperature monitoring significantly underestimate core temperature after cardiac surgery in infants. Use of intracardiac temperature monitoring might result in avoidance of cerebral hyperthermia.

Effect of Therapeutic Moderate Hypothermia on Multi-drug Resistance Protein 1-Mediated Transepithelial Transport of Drugs

To clarify the effect of therapeutic moderate hypothermia on drug distribution, transepithelial transport via multi-drug resistance protein 1 (MDR1) (also called P-glycoprotein or ABCB1) was evaluated at various temperatures in vitro using LLC-GA5-COL150 cells, which were established by transfecting human MDR1 complementary deoxyribonucleic acid into kidney epithelial LLC-PK(1) cells and express MDR1 on the apical membrane. MDR1 is expressed in the blood-brain barrier to limit drug distribution to the brain by exporting exogenous substances including calcium blockers and antiarrhythmic drugs. Digoxin was used as a typical substrate, as well as the non-substrate tetracycline and paracellular marker inulin. MDR1-mediated transport of digoxin decreased at lower temperatures. Transport of tetracycline also decreased at lower temperatures, probably due to changes in membrane fluidity. However, no change was found at over 32 degrees C, suggesting that passive diffusion does not change during moderate hypothermia. The distribution of MDR1 substrates should be considered during hypothermic conditions, as the clinical outcome could be affected.

Induced hypothermia: A novel neuroprotective treatment of neonatal encephalopathy after intrapartum hypoxia-ischemia

The current treatment approach to an infant at risk for progression to neonatal encephalopathy after intrapartum hypoxia-ischemia is threefold: 1) early identification of the infant at highest risk for evolving brain injury based on the criteria of a sentinel event during labor, prolonged depression at birth with the need for resuscitation, and evidence of severe fetal acidemia based on a cord umbilical arterial pH less than 7 and/or a base deficit more than -16 meq per L, with early clinical and/or electroencephalogram assessment of moderate to severe encephalopathy; 2) supportive therapy instituted to maintain adequate ventilation and in particular pCO2 levels in a normal range, mean arterial blood pressure within a normal range so as to avoid perturbations in cerebral perfusion, glucose in a normal range to avoid hypoglycemia, and the judicious treatment of seizures; and 3) neuroprotection--induced hypothermia is currently the only strategy that has been rigorously evaluated in two large, multicenter randomized studies. The first study used selective cooling with a cool cap to a rectal temperature at 34.5 degrees C, and the second study used total body cooling to an esophageal temperature of 33.5 degrees C, with the temperature in both studies maintained for 72 hours. No significant side effects were noted with this degree of cooling. The combined data indicate that hypothermia is associated with a reduction in the incidence of death and/or severe disability at 18 months follow-up, with the most significant effect observed in infants who at the initiation of therapy present with modest encephalopathy and/or do not exhibit electrographic seizures.

Therapeutic hypothermia: from lab to NICU

The possibility of a therapeutic role for cerebral hypothermia during or after resuscitation from perinatal asphyxia has been a long-standing focus of research. However, early studies had limited and contradictory results. It is now known that severe hypoxia-ischemia may not cause immediate cell death, but may precipitate a complex biochemical cascade leading to the delayed development of neuronal loss. These phases include a latent phase after reperfusion, with initial recovery of cerebral energy metabolism but EEG suppression, followed by a secondary phase characterized by accumulation of cytotoxins, seizures, cytotoxic edema, and failure of cerebral oxidative metabolism from 6 to 15 h post insult. Although many of the secondary processes can be injurious, they appear to be primarily epiphenomena of the 'execution' phase of cell death. This conceptual framework allows a better understanding of the experimental parameters that determine effective hypothermic neuroprotection, including the timing of initiation of cooling, its duration and the depth of cooling attained. Moderate cerebral hypothermia initiated in the latent phase, between one and as late as 6 h after reperfusion, and continued for a sufficient duration in relation to the severity of the cerebral injury, has been consistently associated with potent, long-lasting neuroprotection in both adult and perinatal species. The results of the first large multicentre randomized trial of head cooling for neonatal encephalopathy and previous phase I and II studies now strongly suggest that prolonged cerebral hypothermia is both generally safe - at least in an intensive care setting - and can improve intact survival up to 18 months of age. Both long-term followup studies and further large studies of whole body cooling are in progress.

The evolution of neonatology

In 1960, the terms "neonatology" and "neonatologist" were introduced. Thereafter, an increasing number of pediatricians devoted themselves to full-time neonatology. In 1975, the first examination of the Sub-Board of Neonatal-Perinatal Medicine of the American Board of Pediatrics and the first meeting of the Perinatal Section of the American Academy of Pediatrics were held. One of the most important factors that improved the care of the neonate was the miniaturization of blood samples needed to determine blood gases, serum electrolytes, glucose, calcium, bilirubin, and other biochemical measurements. Another factor was the ability to provide nutrition intravenously, and the third was the maintenance of normal body temperature. The management of respiratory distress syndrome improved with i.v. glucose and correction of metabolic acidosis, followed by assisted ventilation, continuous positive airway pressure, antenatal corticosteroid administration, and the introduction of exogenous surfactant. Pharmacologic manipulation of the ductus arteriosus, support of blood pressure, echocardiography, and changes in the management of persistent pulmonary hypertension, including the use of nitric oxide and extracorporeal membrane oxygenation, all have influenced the cardiopulmonary management of the neonate. Regionalization of neonatal care; changes in parent-infant interaction; and technological changes such as phototherapy, oxygen saturation monitors, and brain imaging techniques are among the important advances reviewed in this report. Most remarkable, a 1-kg infant who was born in 1960 had a mortality risk of 95% but had a 95% probability of survival by 2000. However, errors in neonatology are acknowledged, and potential directions for the future are explored.

Prolonged hypothermia protects neonatal rat brain against hypoxic-ischemia by reducing both apoptosis and necrosis

Although hypothermia is an effective treatment for perinatal cerebral hypoxic-ischemic (HI) injury, it remains unclear how long and how deep we need to maintain hypothermia to obtain maximum neuroprotection. We examined effects of prolonged hypothermia on HI immature rat brain and its protective mechanisms using the Rice-Vannucci model. Immediately after the end of hypoxic exposure, the pups divided into a hypothermia group (30 degrees C) and a normothermia one (37 degrees C). Rectal temperature was maintained until they were sacrificed at each time point before 72h post HI. Prolonged hypothermia significantly reduced macroscopic brain injury compared with normothermia group. Quantitative analysis of cell death using H&E-stained sections revealed the number of both apoptotic and necrotic cells was significantly reduced by hypothermia after 24h post HI. Hypothermia seemed to decrease the number of TUNEL-positive cells. Immunohistochemistry and Western blot showed that prolonged hypothermia suppressed cytochrome c release from mitochondria to cytosol and activation of both caspase-3 and calpain in cortex, hippocampus, thalamus and striatum throughout the experiment. These results showed that prolonged hypothermia significantly reduced neonatal brain injury even when it was started after HI insult. Our results suggest that prolonged hypothermia protects neonatal brain after HI by reducing both apoptosis and necrosis.

Mild hypothermia and the distribution of cerebral lesions in neonates with hypoxic-ischemic encephalopathy

Hypothermia induced by whole-body cooling (WBC) and selective head cooling (SHC) both reduce brain injury after hypoxia-ischemia in newborn animals, but it is not known how these treatments affect the incidence or pattern of brain injury in human newborns. To assess this, 14 term infants with hypoxic-ischemic encephalopathy (HIE) treated with SHC, 20 infants with HIE treated with WBC, and 52 noncooled infants with HIE of similar severity were studied with magnetic resonance imaging in the neonatal period. Infants fulfilling strict criteria for HIE were recruited into the study after assessment of an amplitude-integrated electroencephalography (aEEG). Cooling was commenced within 6 hours of birth and continued for 48 to 72 hours. Hypothermia was not associated with unexpected or unusual lesions, and the prevalence of intracranial hemorrhage was similar in all 3 groups. Both modes of hypothermia were associated with a decrease in basal ganglia and thalamic lesions, which are predictive of abnormal outcome. This decrease was significant in infants with a moderate aEEG finding but not in those with a severe aEEG finding. A decrease in the incidence of severe cortical lesions was seen in the infants treated with SHC.

Depth of delayed cooling alters neuroprotection pattern after hypoxia-ischemia

Hypothermia after perinatal hypoxia-ischemia (HI) is neuroprotective; the precise brain temperature that provides optimal protection is unknown. To assess the pattern of brain injury with 3 different rectal temperatures, we randomized 42 newborn piglets: (Group i) sham-normothermia (38.5-39 degrees C); (Group ii) sham-33 degrees C; (Group iii) HI-normothermia; (Group iv) HI-35 degrees C; and (Group v) HI-33 degrees C. Groups iii through v were subjected to transient HI insult. Groups ii, iv, and v were cooled to their target rectal temperatures between 2 and 26 hours after resuscitation. Experiments were terminated at 48 hours. Compared with normothermia, hypothermia at 35 degrees C led to 25 and 39% increases in neuronal viability in cortical gray matter (GM) and deep GM, respectively (both p < 0.05); hypothermia at 33 degrees C resulted in a 55% increase in neuronal viability in cortical GM (p < 0.01) but no significant increase in neuronal viability in deep GM. Comparing hypothermia at 35 and 33 degrees C, 35 degrees C resulted in more viable neurons in deep GM, whereas 33 degrees C resulted in more viable neurons in cortical GM (both p < 0.05). These results suggest that optimal neuroprotection by delayed hypothermia may occur at different temperatures in the cortical and deep GM. To obtain maximum benefit, you may need to design patient-specific hypothermia protocols by combining systemic and selective cooling.

A pH-dependent increase in neuronal glutamate efflux in vitro: Possible involvement of ASCT1

Efflux of glutamate from intracellular pools during hypoxia-ischemia has been postulated to be mediated by amino acid transporters and can lead to excitotoxicity. In addition, a decrease in pH seen during global hypoxia-ischemia may influence which transporter is responsible for this glutamate efflux. For example, the neutral amino acid transporter ASCT1 is an effective transporter of glutamate at low pH. We have examined the effects of pH, pH and temperature, and hypoxia on glutamate efflux in a rat primary neuronal cell culture model. We observed a marked increase of glutamate efflux as pH was decreased from 7.4 to 5.5. This pH-dependent efflux is likely due to a transporter-mediated process because it was seen in the presence of tetrodotoxin and was blunted by decreasing the temperature to either 35 degrees C or 33 degrees C. In addition, no increase in LDH was seen at pH 5.5 suggesting that increased glutamate levels were not due to cellular death. No change in glutamate levels was seen when the oxygen tension of the medium was lowered from 150 mm Hg to either 30 or 15 mm Hg. Given that EAAT transporters are inhibited by low pH, other transporters, such as ASCT1, may be responsible for this pH-dependent efflux of glutamate.

Brief induced hypothermia improves outcome after asphyxial cardiopulmonary arrest in juvenile rats

The American Heart Association has endorsed the use of mild hypothermia for adults after cardiopulmonary arrest. However, there are no contemporary trials testing hypothermia in children after cardiopulmonary arrest and extrapolation from adult studies is problematic given differences in brain development and primary etiology (asphyxia in children vs. ventricular arrhythmia in adults). Accordingly, we tested the effects of mild postresuscitative hypothermia on functional and histopathological outcome after asphyxial cardiac arrest in juvenile rats. Postnatal day 17 rats were subjected to 8 min of asphyxia-induced cardiac arrest followed by resuscitation. Rats were randomized to normothermic (37 degrees C), hypothermic (32 degrees C), or unregulated temperature groups (n = 7-8/group) to begin after return of spontaneous circulation for a duration of 1 h. Brain temperature in the unregulated group dropped to 34.0 +/- 0.4 degrees C at 1 h. The hypothermic group had improved motor function assessed using beam balance and inclined plane tests vs. the normothermic group. The depth of hypothermia was associated with increased CA1 hippocampal neuron survival at 5 weeks. Neurodegeneration in the CA1 hippocampus assessed using Fluoro-Jade B labeling at 5 weeks was not detected in the 32 degrees C group, whereas 2/7 and 4/7 rats in the 34 and 37 degrees C groups, respectively, showed neurodegeneration. Brief treatment with moderate induced hypothermia improved functional outcome and prevented long-term neurodegeneration in a model that mimics the clinical and histopathological scenario of pediatric cardiac arrest. Similar to adults, infants and children may benefit from induced hypothermia after cardiopulmonary arrest, warranting further study.

Demographic characteristics and clinical course in infants with moderate or severe neonatal encephalopathy

A chart review of 64 infants with moderate or severe neonatal encephalopathy showed that resuscitation was required for 61 (95%), respiratory support for 53 (83%) and anticonvulsants for 58 (91%). Death occurred in 2 (4%) infants with moderate encephalopathy and 12 (86%) with severe encephalopathy. In addition, subsequent neurodevelopment was abnormal in approximately a quarter of infants who survived after a moderate to severe encephalopathy.

Post-ischemic modest hypothermia (35 degrees C) combined with intravenous magnesium is more effective at reducing CA1 neuronal death than either treatment used alone following global cerebral ischemia in rats

In this study, we investigated the efficacy of pre- and 2 h post-ischemic magnesium treatment with different durations of modest hypothermia (35 degrees C) induced immediately or 2 h following global cerebral ischemia in rats. In experimental group 1, rats received an intravenous loading dose (LD) of 360 micromol/kg MgSO4 immediately before ischemia followed by a 48 h intravenous infusion (IVI) at 120 micromol/kg/h. Immediately post-ischemia, body temperature was lowered to 35 degrees C for 6 h or maintained at 37 degrees C. In experimental group 2, 2 h after ischemia, rats received the MgSO4 LD/IVI and/or had their body temperature lowered to 35 degrees C for 6, 12 or 24 h. In experimental group 1, ischemic rats receiving 6 h of modest hypothermia demonstrated 9.4% CA1 neuronal survival, whereas rats treated with magnesium alone or magnesium and 6 h of modest hypothermia demonstrated 5.1% and 37.9% neuronal survival, respectively. In experimental group 2, ischemic rats receiving 6, 12 or 24 h of modest hypothermia demonstrated 6.1, 5 and 43% CA1 neuronal survival, respectively. Rats treated with magnesium and 6, 12 or 24 h of modest hypothermia demonstrated 8.1, 9 and 76% neuronal survival, respectively. Our findings demonstrate that post-ischemic treatment with a 24 h duration of modest hypothermia and magnesium is more effective than either treatment used alone.

Potential for protection and repair following injury to the developing brain: a role for erythropoietin?

Perinatal brain injury is a major contributor to perinatal morbidity and mortality, and a considerable number of these children will develop long term neurodevelopmental disabilities. Despite the severe clinical and socio-economic significance and the advances in neonatal care over the past twenty years, no therapy yet exists that effectively prevents or ameliorates detrimental neurodevelopmental effects in cases of perinatal/neonatal brain injury. Our objective is to review recent evidence in relation to the pervading hypothesis for targeting time-dependent molecular and cellular repair mechanisms in the developing brain. In addition we review several potential neuroprotective strategies specific to the developing nervous system, with a focus on erythropoietin (Epo) because of its potential role in protection as well as repair.

The Effect of Mild Hypothermia on Plasma Fentanyl Concentration and Biotransformation in Juvenile Pigs

Therapeutic hypothermia may alter the required dosage of analgesics and sedatives, but no data are available on the effects of mild hypothermia on plasma fentanyl concentration during continuous, long-term administration. We therefore assessed in a porcine model the effect of prolonged hypothermia on plasma fentanyl concentration during 33 h of continuous fentanyl administration. Seven female piglets (weight: 11.8 +/- 1.1 kg) were anesthetized by IV fentanyl (15 microg . kg(-1) . h(-1)) and midazolam (1.0 mg . kg(-1) . h(-1)). After preparation and stabilization (12 h), the animals were cooled to a core temperature of 31.6 degrees +/- 0.2 degrees C for 6 h and were then rewarmed and kept normothermic at 37.7 degrees +/- 0.3 degrees C for 6 more hours. Plasma fentanyl concentrations were measured by radioimmunoassay, cardiac index by thermodilution, and blood flows of the kidney, spleen, pancreas, stomach, gut, and hepatic artery by a colored microspheres technique. Furthermore, in an additional 4 pigs, temperature dependency of hepatic microsomal cytochrome P450 3A4 (CYP3A4) was determined in vitro by ethylmorphine N-demethylation. Plasma fentanyl concentration increased by 25% +/- 11% (P < 0.05) during hypothermia and remained increased for at least 6 h after rewarming. Hypothermia reduced the cardiac index (41% +/- 15%, P < 0.05), as well as all organ blood flows except the hepatic artery. A strong temperature dependency of CYP3A4 was found (P < 0.01). Mild hypothermia induced a distribution and/or elimination-dependent increase in plasma fentanyl concentration which remained increased for several hours after rewarming. Consequently, a prolonged increase of the plasma fentanyl concentration should be anticipated for appropriate control of the analgesia/sedatives during and early after therapeutic hypothermia.

Epileptiform activity during rewarming from moderate cerebral hypothermia in the near-term fetal sheep

Moderate hypothermia is consistently neuroprotective after hypoxic-ischemic insults and is the subject of ongoing clinical trials. In pilot studies, we observed rebound seizure activity in one infant during rewarming from a 72-h period of hypothermia. We therefore quantified the development of EEG-defined seizures during rewarming in an experimental paradigm of delayed cooling for cerebral ischemia. Moderate cerebral hypothermia (n=9) or sham cooling (n=13) was initiated 5.5 h after reperfusion from a 30-min period of bilateral carotid occlusion in near-term fetal sheep and continued for 72 h after the insult. During spontaneous rewarming, fetal extradural temperature rose from 32.5 +/- 0.6 degrees C to control levels (39.4 +/- 0.1 degrees C) in 47 +/- 6 min. Carotid blood flow and mean arterial blood pressure increased transiently during rewarming. The cooling group showed a significant increase in electrical seizure events 2, 3, and 5 h after rewarming, maximal at 2 h (2.9 +/- 1.2 versus 0.5 +/- 0.5 events/h; p <0.05). From 6 h after rewarming, there was no significant difference between the groups. Individual seizures were typically short (28.8 +/- 5.8 s versus 29.0 +/- 6.8 s in sham cooled; NS), and of modest amplitude (35.9 +/- 2.8 versus 38.8 +/- 3.4 microV; NS). Neuronal loss in the parasagittal cortex was significantly reduced in the cooled group (51 +/- 9% versus 91 +/- 5%; p <0.002) and was not correlated with rebound epileptiform activity. In conclusion, rapid rewarming after a prolonged interval of therapeutic hypothermia can be associated with a transient increase in epileptiform events but does not seem to have significant adverse implications for neural outcome.

Selective head cooling with mild systemic hypothermia after neonatal encephalopathy: multicentre randomised trial

BACKGROUND

Cerebral hypothermia can improve outcome of experimental perinatal hypoxia-ischaemia. We did a multicentre randomised controlled trial to find out if delayed head cooling can improve neurodevelopmental outcome in babies with neonatal encephalopathy.

METHODS

234 term infants with moderate to severe neonatal encephalopathy and abnormal amplitude integrated electroencephalography (aEEG) were randomly assigned to either head cooling for 72 h, within 6 h of birth, with rectal temperature maintained at 34-35 degrees C (n=116), or conventional care (n=118). Primary outcome was death or severe disability at 18 months. Analysis was by intention to treat. We examined in two predefined subgroup analyses the effect of hypothermia in babies with the most severe aEEG changes before randomisation--ie, severe loss of background amplitude, and seizures--and those with less severe changes.

FINDINGS

In 16 babies, follow-up data were not available. Thus in 218 infants (93%), 73/110 (66%) allocated conventional care and 59/108 (55%) assigned head cooling died or had severe disability at 18 months (odds ratio 0.61; 95% CI 0.34-1.09, p=0.1). After adjustment for the severity of aEEG changes with a logistic regression model, the odds ratio for hypothermia treatment was 0.57 (0.32-1.01, p=0.05). No difference was noted in the frequency of clinically important complications. Predefined subgroup analysis suggested that head cooling had no effect in infants with the most severe aEEG changes (n=46, 1.8; 0.49-6.4, p=0.51), but was beneficial in infants with less severe aEEG changes (n=172, 0.42; 0.22-0.80, p=0.009).

INTERPRETATION

These data suggest that although induced head cooling is not protective in a mixed population of infants with neonatal encephalopathy, it could safely improve survival without severe neurodevelopmental disability in infants with less severe aEEG changes.

Effects of rapid rewarming on cerebral nitric oxide production and cerebral hemodynamics after hypothermia therapy for kainic acid-induced seizures in immature rabbits

BACKGROUND

The aim of the present study was to investigate whether rapid rewarming after hypothermia therapy during seizures alters the endogenous nitric oxide (NO) production in and around hippocampus, cortical cerebral blood flow (cCBF), and mean arterial blood pressure (MABP) in immature rabbits.

METHODS

The hypothermic rabbits (rectal temperatures, 33 degrees C) were given kainic acid (KA; 12 mg/kg, i.v; at 0 min), followed by cooling (33 degrees C) for 60 min (at 60 min), then either rewarming (RW; 33-37 degrees C) was started (KA[+]RW[+] group, n = 7) or cooling was continued (KA[+]RW[-] group, n = 7) for another 60 min (at the end 120 min). In the KA(-)RW(+) group (n = 5), 0.5 mL normal saline was given (at time 0 min), followed by cooling (33 degrees C) for 60 min (at 60 min), then rewarming to 37 degrees C was started with observation for another 60 min (at the end 120 min). NO production in and around hippocampus was continuously measured by an NO-selective electrode, cCBF by laser Doppler flowmetry, cortical electroencephalogram (EEG), rectal and cerebral temperatures, and MABP during the experiment. Comparisons were made of these parameters between the values at 60 min and 120 min after the KA administrations.

RESULTS

KA administration induced abnormal discharges in both KA(+)RW(+) and KA(+)RW(-) groups at the same degree. The KA(+)RW(+) group had a significant increase in %NO, and significant decreases in %cCBF and MABP after rapid rewarming, compared with before rewarming. In the KA(+)RW(-) group, there were no significant changes in %NO, %cCBF, and MABP between values at 60 and 120 min. These changes after rapid rewarming in the KA(+)RW(+) group were different from those with only elevation in brain temperature from 33 to 37 degrees C without seizures (KA[-]RW[+] group).

CONCLUSIONS

These results suggest that rapid rewarming after hypothermia therapy induces an increase in the NO production in and around hippocampus and the decreases in cCBF and MABP during seizures in immature rabbits.

Extracorporeal membrane oxygenation for cardiac disease: no longer a mistaken diagnosis

Extracorporeal membrane oxygenation (ECMO) has become a valuable adjunct in caring for infants and children with heart disease. Since the initial reports of ECMO support for cardiac failure in children, the number of centers providing cardiac support and the number of cases of cardiac ECMO have steadily increased. The International Registry for Extracorporeal Life Support Organization has reported survival statistics for cardiac cases in neonates, children, and adults ranging from 33% to 43%. These numbers are similar to the survival from recent reports by Morris (39%) and Chaturvedi (49%). Survival is influenced by ability to be weaned from bypass in the operating room and by residual structural disease and multi-organ system failure but not by cardiac arrest and single ventricle physiology. To improve results in the future, we need to focus on better predicting the need for support and avoiding multi-organ system failure before initiating ECMO. Rapid deployment of ECMO may further improve results for patients who deteriorate suddenly in the intensive care unit.

Randomized trial of systemic hypothermia selectively protects the cortex on MRI in term hypoxic-ischemic encephalopathy

Twenty-six infants with hypoxic-ischemic encephalopathy (HIE) were randomized to normothermia or to systemic hypothermia. The hypothermia group had less cortical gray matter signal abnormality on magnetic resonance imaging (MRI) (1/12 vs 7/14 infants in the normothermic group; P = .036), which may indicate differing regional benefit from systemic hypothermia.

Resuscitative mild hypothermia as a protective tool in brain damage: is there evidence?

Resuscitative mild hypothermia is and will increasingly be used in the emergency department as protection for the brain after an ischaemic insult. The clinical application of resuscitative mild hypothermia and its limitations will be summarized in this paper. The evidence for each application and its underlying mechanism will also be reviewed.

Topiramate Extends the Therapeutic Window for Hypothermia-Mediated Neuroprotection After Stroke in Neonatal Rats

Background and Purpose— Critical factors influencing the neuroprotective efficacy of postischemic hypothermia include depth, duration, and time of onset of cooling. In clinical practice, there is an unavoidable lag between the hypoxic-ischemic (HI) insult and the opportunity to initiate cooling. We hypothesized that early administration of a neuroprotective agent in combination with later-onset cooling could represent an effective therapeutic intervention after neonatal HI. We evaluated whether treatment with topiramate, a clinically available anticonvulsant, increased the efficacy of delayed post-HI hypothermia in a neonatal rat stroke model.

Methods— Postnatal day 7 (P7) rats underwent right carotid artery ligation followed by 1.5 hours of exposure to 8% oxygen. Fifteen minutes post-HI, animals received injections of topiramate (30 mg/kg) or PBS. Cooling was initiated 3 hours later (“delayed hypothermia”) in all animals (3 hours, in 27°C incubator). Functional outcome (forepaw response to vibrissae stimulation) and pathology (morphometric lesion measurements) were evaluated at P15 and P35.

Results— Neither topiramate nor delayed hypothermia alone conferred protection in this protocol. Combined treatment with topiramate and delayed hypothermia improved both performance and pathological outcome in P15 and P35 rats compared with PBS-treated animals that underwent delayed hypothermia concurrently. At P15, functional measures were better in topiramate-treated animals (mean correct forepaw response 9.3/10 versus 4.8/10; P <0.001), and there was >50% reduction in tissue loss ( P <0.001); trends were similar at P35.

Conclusions— Our data provide the impetus for further evaluation of therapeutic approaches that combine drug therapy with delayed-onset cooling after neonatal HI brain injury.

Neonatal resuscitation: raising the bar

PURPOSE OF REVIEW

To provide an overview of neonatal resuscitation practices with an emphasis on interventions that are not currently accepted or adapted into existing resuscitation guidelines.

RECENT FINDINGS

Current resuscitation guidelines do not contain specific guidelines for the approach to the extremely low birth weight infant. The differences in environment and management between the neonatal ICU and delivery room are striking and are magnified in the resuscitation of extremely low birth weight infants for whom maintenance of a neutral thermal environment is essential. The use of a polyethylene wrap applied at delivery has been shown to reduce the occurrence of hypothermia and decrease mortality. There is substantial evidence that term and near-term newborn infants can be effectively resuscitated with room air, and recent follow-up studies have demonstrated that this approach is not associated with increased significant differences in neurologic handicap, somatic growth, or developmental milestones when compared with the use of 100% oxygen. The safety and potential benefits of this approach require prospective evaluation in the premature and especially extremely low birth weight infant. There is preexisting evidence that demonstrates that the use of prolonged inflations and t-piece resuscitators may be advantageous during resuscitation, but not all guidelines support these interventions. Although regulated continuous positive airway pressure, pulse oximeters, and blenders are routinely used once an infant is admitted to the neonatal ICU, none of these interventions is recommended in the delivery area. Although prospective studies have demonstrated that the use of colorimetric CO2 detectors significantly decreases the time to recognize misplaced endotracheal tubes placed during resuscitation, their use is not required by current guidelines. The duration of an intubation attempt during resuscitation had never been prospectively evaluated, and our recent findings suggest that a limit of 30 seconds is well tolerated and provides adequate time for a successful attempt.

SUMMARY

There is significant potential for improvement in current resuscitation environments and interventions that will only be realized through further prospective research.

Application of therapeutic hypothermia in the ICU: opportunities and pitfalls of a promising treatment modality. Part 1: Indications and evidence

OBJECTIVE

Hypothermia has been used for medicinal purposes since ancient times. This paper reviews the current potential clinical applications for mild hypothermia (32-35 degrees C).

DESIGN AND SETTING

Induced hypothermia is used mostly to prevent or attenuate neurological injury, and has been used to provide neuroprotection in traumatic brain injury, cardiopulmonary resuscitation, stroke, and various other disorders. The evidence for each of these applications is discussed, and the mechanisms underlying potential neuroprotective effects are reviewed. Some of this evidence comes from animal models, and a brief overview of these models and their limitations is included in this review.

RESULTS

The duration of cooling and speed of re-warming appear to be key factors in determining whether hypothermia will be effective in preventing or mitigating neurological injury. Some other potential usages of hypothermia, such as its use in the peri-operative setting and its application to mitigate cardiac injury following ischemia and reperfusion, are also discussed.

CONCLUSIONS

Although induced hypothermia appears to be a highly promising treatment, it should be emphasized that it is associated with a number of potentially serious side effects, which may negate some or all of its potential benefits. Prevention and/or early treatment of these complications are the key to successful use of hypothermia in clinical practice. These side effects, as well as various physiological changes induced by cooling, are discussed in a separate review.

Changes in FiO2 affect PaO2 with minor alterations in cerebral concentration of oxygenated hemoglobin during liquid ventilation in healthy piglets

OBJECTIVE

To measure the impact of changes in the fraction of inspired oxygen (FiO2) on systemic and cerebral oxygen supply in gas and liquid ventilated healthy animals.

DESIGN

Interventional prospective animal study.

SETTING

University research laboratory.

PARTICIPANTS

Ten healthy, new-born piglets.

INTERVENTIONS

Variations in FiO2 during conventional mechanical ventilation (CMV) followed by partial liquid ventilation (PLV) with two different filling volumes of PF 5080 (10 vs. 30 ml/kg).

MEASUREMENTS AND RESULTS

Arterial blood gases were obtained 15 min after changing FiO2 and concentrations of cerebral oxygenated and total hemoglobin were determined with near infrared spectroscopy. During CMV an increase in FiO2 1.0 was associated with a constant rise in PaO2 but only a small increase in the cerebral concentration of oxygenated Hb. Initiation of PLV (at FiO2 of 1.0) caused a rapid drop in PaO2 towards values that were similar to CMV at FiO2 of 0.5. At FiO2 of 0.5 a reduction in oxygenated Hb was found in the 30 ml/kg filling group. Complete filling of the lungs with PFC caused a significant drop in total cerebral Hb concentration. CONCLUSIONS. According to our data, PLV in healthy lungs should be performed with a FiO2 of 1.0 and a small filling volume to avoid deterioration in cerebral oxygen supply.

Cooling for newborns with hypoxic ischaemic encephalopathy

BACKGROUND

Newborn animal and human pilot studies suggest that mild hypothermia following peripartum hypoxia-ischaemia in newborn infants may reduce neurological sequelae, without adverse effects.

OBJECTIVES

To determine whether therapeutic hypothermia in encephalopathic asphyxiated newborn infants reduces mortality and long-term neurodevelopmental disability, without clinically important side effects.

SEARCH STRATEGY

The standard search strategy of the Neonatal Review Group as outlined in the Cochrane Library (Issue 2, 2003) was used. Randomised controlled trials evaluating therapeutic hypothermia in term newborns with hypoxic ischaemic encephalopathy were identified by searching the Oxford Database of Perinatal Trials, the Cochrane Central Register of Controlled Trials (CENTRAL, The Cochrane Library Issue Issue 2, 2003), MEDLINE (1966 to July 2003), previous reviews including cross-references, abstracts, conferences, symposia proceedings, expert informants and journal hand searching.

SELECTION CRITERIA

Randomised controlled trials comparing the use of therapeutic hypothermia with normothermia in encephalopathic newborn infants with evidence of peripartum asphyxia and without recognisable major congenital anomalies were included. The primary outcome measure was death or long-term major neurodevelopmental disability. Other outcomes included adverse effects of cooling and 'early' indicators of neurodevelopmental outcome.

DATA COLLECTION AND ANALYSIS

Three reviewers independently selected, assessed the quality of and extracted data from the included studies. Authors were contacted for further information. Meta-analyses were performed using relative risk and risk difference for dichotomous data, and weighted mean difference for continuous data with 95% confidence intervals.

MAIN RESULTS

Two randomised controlled trials were included in this review, comprising 50 term infants with moderate/ severe encephalopathy and evidence of intrapartum asphyxia. There was no significant effect of therapeutic hypothermia on the combined outcome of death or major neurodevelopmental disability in survivors followed. No adverse effects of hypothermia on short term medical outcomes or on some 'early' indicators of neurodevelopmental outcome were detected.

REVIEWER'S CONCLUSIONS

Although two small randomised controlled trials demonstrated neither evidence of benefit or harm, current evidence is inadequate to assess either safety or efficacy of therapeutic hypothermia in newborn infants with hypoxic ischaemic encephalopathy. Therapeutic hypothermia for encephalopathic asphyxiated newborn infants should be further evaluated in well designed randomised controlled trials.