Cerebral hypothermia is not neuroprotective when started after postischemic seizures in fetal sheep.

Prolonged cerebral hypothermia is neuroprotective if started within a few hours of hypoxia-ischemia. However, delayed seizure activity is one of the major clinical indicators of an adverse prognosis after perinatal asphyxia. The aim of this study was to determine whether head cooling delayed until after the onset of postasphyxial seizures may still be neuroprotective. Unanesthetized near-term fetal sheep in utero received 30 min of cerebral ischemia induced by bilateral carotid artery occlusion. Eight and one-half hours later, they received either cooling (n = 5) or sham cooling (n = 13) until 72 h after the insult. Intrauterine cooling, induced by circulating cold water through a coil around the fetal head, was titrated to reduce fetal extradural temperature from 39.4+/-0.1 degrees C to between 30 and 33 degrees C. Cerebral ischemia led to the delayed development of intense epileptiform activity from 6 to 8 h postinsult, followed by a marked secondary rise in cortical impedance (a measure of cytotoxic edema) and in carotid blood flow. Cerebral cooling markedly attenuated the secondary rise in impedance and reduced carotid blood flow (p < 0.001). After 5 d recovery, there was no significant difference in loss of parietal EEG activity relative to baseline in the hypothermia compared with the control group (-12.5+/-1.4 versus -15.2+/-1.2 dB, mean +/- SEM, NS) or in parasagittal cortical neuronal loss (82+/-9 versus 90+/-5%, NS). In conclusion, delayed prolonged head cooling begun after the onset of postischemic seizures was not neuroprotective. These data highlight the importance of intervention in the latent phase, after reperfusion but before the onset of secondary injury.     

Effect of cerebral hypothermia on cortisol and adrenocorticotropic hormone responses after umbilical cord occlusion in preterm fetal sheep

The hypothalamic-pituitary-adrenal (HPA) axis is essential for adaptation to stress. In the present study, we examined the hypothesis that head cooling with mild systemic hypothermia would adversely affect fetal adrenocorticotropic hormone (ACTH) and cortisol responses to an asphyxial insult. Chronically instrumented preterm fetal sheep (104 d of gestation, term is 147 d) were allocated to sham occlusion (n = 7), 25 min of complete umbilical cord occlusion (n = 7), or occlusion and head cooling with mild systemic hypothermia (n = 7, mean +/- SEM esophageal temperature 37.6 +/- 0.3 degrees C vs 39.0 +/- 0.2 degrees C; p < 0.05) from 90 min to 70 h after occlusion, followed by spontaneous rewarming. During umbilical cord occlusion, there was a rapid rise in ACTH and cortisol levels, with further increases after release of cord occlusion. ACTH levels returned to sham control values after 10 h in both occlusion groups. In contrast, plasma cortisol levels remained elevated after 48 h in both occlusion groups and were still significantly elevated in the hypothermia-occlusion group 2 h after rewarming, at 72 h, compared with the normothermia-occlusion and sham groups. In conclusion, hypothermia does not affect the overall HPA responses to severe asphyxia in the preterm fetus but does prolong the cortisol response.     

Hypothermia for 24 hours after asphyxic cardiac arrest in piglets provides striatal neuroprotection that is sustained 10 days after rewarming

The neuroprotective effect of hypothermia instituted after resuscitation from asphyxic cardiac arrest has not been studied in immature brain, particularly in a large animal model with recovery periods greater than 4 d. Moreover, protection from severe hypoxia seen with 3 h of hypothermia was reported to be lost when hypothermic duration was extended to 24 h in unsedated piglets, in contrast to the neuroprotection reported by 72 h of intrauterine head cooling in fetal sheep. Piglets (5-7 postnatal days) were subjected to asphyxic cardiac arrest followed by 24 h of either hypothermia (34 degrees C) or normothermia (38.5-39 degrees C). Comparisons were made with normothermic and hypothermic surgical sham animals without asphyxia. All of these groups were sedated, paralyzed, and mechanically ventilated for the first 24 h to prevent shivering and possible depletion of glucose stores. Hypothermia per se did not cause remarkable structural abnormalities. Ischemic damage was evaluated in putamen at 1 d of recovery without rewarming and at 11 d (10 d +/- SD after rewarming). Ischemic cytopathology affected 60 +/- 12% of neurons in putamen of normothermic animals compared with 9 +/- 6% in hypothermic animals at 1 d of recovery without rewarming. At 11 d of recovery from hypoxia-ischemia, the density of viable neurons (neuron profiles/mm2) in putamen was markedly reduced in normothermic animals (81 +/- 40) compared with hypothermic animals (287 +/- 22), which was the same as in sham normothermic (271 +/- 21), sham hypothermic (288 +/- 46) and na?ve animals (307 +/- 51). These data demonstrate that 24 h of hypothermia at 34 degrees C with sedation and muscle relaxation after asphyxic cardiac arrest prevents necrotic striatal neuronal cell death in immature brain before rewarming, and that the effect is sustained at 11 d after injury without deleterious side effects.     

Recooling for rebound seizures after rewarming in neonatal encephalopathy

Infants undergoing therapeutic hypothermia for hypoxic ischemic encephalopathy are at risk for rebound seizures during and after the rewarming phase. We report a term male infant who was cooled for hypoxic ischemic encephalopathy. He developed electrographic seizures for the first time during the warming phase, which continued in the hours after rewarming. The seizures stopped within 30 minutes of recooling to 33.5°C without anticonvulsant medication. He was uneventfully cooled for an additional 24 hours and then rewarmed with no recurrence of seizures. Hypothermia appeared to have an antiepileptic effect in this case and may be worthy of additional investigation as an adjunct to antiepileptic drug therapy in newborns.     

Twenty-four hours of mild hypothermia in unsedated newborn pigs starting after a severe global hypoxic-ischemic insult is not neuroprotective

Three to 12 h of mild hypothermia (HT) starting after hypoxia-ischemia is neuroprotective in piglets that are anesthetized during HT. Newborn infants suffering from neonatal encephalopathy often ventilate spontaneously and are not necessarily sedated. We aimed to test whether mild posthypoxic HT lasting 24 h was neuroprotective if the animals were not sedated. Thirty-nine piglets (median weight 1.6 kg, range 0.8-2.2 kg; median age 24 h, range 7-48 h) were anesthetized and ventilated and subjected to a 45-min hypoxic (FiO(2) approximately 6%) global insult (n = 36) or sham hypoxia (n = 3). On reoxygenation, 18 were maintained normothermic (NT, 39.0 degrees C) for 72 h, and 21 were cooled from 39 (NT) to 35 degrees C (HT) for the first 24 h before NT was resumed (18 experimental, three sham hypoxia). Cardiovascular parameters and intermittent EEG were documented throughout. The brain was perfusion fixed for neuropathology and five main areas examined using light microscopy. The insult severity (duration in minutes of EEG amplitude < 7 microV) was similar in the NT and HT groups, mean +/- SD (28 +/- 7.2 versus 27 +/- 8.6 min), as was the mean FiO(2) (5.9 +/- 0.7 versus 5.8 +/- 0.8%) during the insult. Six NT and seven HT piglets developed posthypoxic seizures that lasted 29 and 30% of the time, respectively. The distribution and degree of injury (0.0-4.0, normal-maximal damage) within the brain (hippocampus, cortex/white matter, cerebellum, basal ganglia, thalamus) were similar in the NT and HT groups (overall score, mean +/- SD, 2.3 +/- 1.5 versus 2.4 +/- 1.3) as was the EEG background amplitude at 3 h (13 +/- 3.5 versus 10 +/- 3.3 microV). The HT animals shivered and were more active. The sham control group (n = 3) shivered but had normal physiology and neuropathology. Plasma cortisol was significantly higher in the HT group during the HT period, 766 +/- 277 versus 244 +/- 144 microM at 24 h. Mild postinsult HT for 24 h was not neuroprotective in unsedated piglets and did not reduce the number of animals that developed posthypoxic seizures. Cortisol reached 3 times the NT value at the end of HT. We speculate that the stress of shivering and feeling cold interfered with the previously shown neuroprotective effect of HT. Research on the appropriateness of sedation during clinical HT is urgent.     

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.     

Effective selective head cooling during posthypoxic hypothermia in newborn piglets

Selective head cooling has been proposed as a neuroprotective intervention after hypoxia-ischemia in which the brain is cooled without subjecting the rest of the body to significant hypothermia, thus minimizing adverse systemic effects. There are little data showing it is possible to cool the brain more than the body. We have therefore applied selective head cooling to our hypoxia-ischemia piglet model to establish whether it is possible. Nine piglets were anesthetized, and brain temperature was measured at the surface and in the superficial (0.2 cm) and deep (1.7-2.0 cm) gray matter. Rectal (6-cm depth), skin, and scalp temperatures (T) were recorded continuously. Lowering T-rectal from normothermia (39 degrees C) to hypothermia (33.5-33.8 degrees C) using a head cap perfused with cold (6-24 degrees C) water was undertaken for up to 6 h. To assess the impact of the 45-min hypoxia-ischemia insult on the effectiveness of selective head cooling, four piglets were cooled both before and after the insult, and four, only afterward. During selective head cooling, it was possible to achieve a lower T-deep brain than T-rectal in all animals both before and after hypoxia. However, this was only possible when overhead body heating was used. The T-rectal to T-deep brain gradient was significantly smaller after the insult (median, 5.3 degrees C; range, 4.2-8.5 degrees C versus 3.0 degrees C; 1.7-7.4 degrees C; p = 0.008). During rewarming to normothermia, the gradient was maintained at 4.5 degrees C. We report for the first time a study, which by direct measurement of deep intracerebral temperatures, validates the cooling cap as an effective method of selective brain cooling in a newborn animal hypoxia-ischemia model.     

选择性头部亚低温治疗新生儿缺氧缺血性脑病安全性临床多中心研究

目的：尽管小规模的临床研究表明亚低温治疗新生儿缺氧缺血性脑病（hypoxic-ischemic，HIE）是安全的，但仍需大规模的临床多中心的研究进一步证明。本研究目的通过临床多中心研究观察选择性头部亚低温治疗新生儿HIE的安全性。方法：入选标准：生后6 h以内；胎龄 ≥36周，体重≥2 500 g；脐动脉血气分析 pH < 7.0或BE ≤-16 mmol·L-1或生后1 min Apgar评分 ≤ 3并持续到5 min仍然 ≤ 5；生后6 h内出现脑病的临床表现或EEG明显异常。排除标准：严重先天性疾病、合并感染、其他原因导致颅内损伤、严重贫血（Hb < 120 g·L-1）。从2002年5月- 2006年2月共收集246例不同严重程度的新生儿HIE，随机分为治疗组（低温治疗）134例和对照组112例。低温组和常温组各失访17例和12例，故有效病例共217例（低温组117例，对照组100例）。低温组生后6 h内开始选择性头部亚低温治疗，维持鼻咽部温度（34±0.2）℃℃，肛温维持在35℃以上,持续72 h，然后自然复温。常温组维持肛温在36～37.5oC。两组均进行心电、血压、经皮氧饱和度、鼻咽部温度和肛温监测。发现心率失常者进行EEG检测。观察主要不良反应包括：死亡率、严重心律失常、静脉血栓或出血、难以纠正的低血压。低温组72 h时检测肝、肾功能和血常规、血电解质、血糖及血气分析。观察可能出现的其他不良反应。结果：低温组和常温组的死亡率分别为17.9％和25％(P＝0.20)，死亡原因中两组均以重度脑病(低温组和对照组分别为：6.8%和7%，P＝0.96)和呼吸衰竭(低温组和对照组分别为：6.8%和6%，P＝0.8)为主；对照组有1例患者出现室性心律失常和DIC；低温组发生DIC和消化道出血患者各1例；两组均未出现难以纠正的严重低血压和大静脉血栓。低温组和常温组发生严重不良反应的概率分别为 1.7％和2％（P＝1.0）。低温治疗期间心率降低，但仅有4例(3.4%)患儿心率低于80次/分钟；两组之间血压、肝及肾功能、电介质、血生化、血气分析及血常规的变化均无显著性差异。结论：选择性头部亚低温结合全身轻度低温72 h治疗足月新生儿HIE是可行的和安全的。     

Effect of environmental hypothermia on vitelline artery blood pressure and vascular resistance in the stage 18, 21, and 24 chick embryo

We studied the effect of environmental hypothermia on arterial blood pressure, dorsal aortic blood flow, and vascular resistance in stage 18, 21, and 24 chick embryos. The arterial pressure was measured with a servonull micropressure system. Mean dorsal aortic blood flow was calculated from pulsed-Doppler measurement of mean dorsal aortic blood velocity and dorsal aortic diameter. Vascular resistance was calculated by dividing mean vitelline arterial blood pressure by dorsal aortic blood flow. Sequential data were obtained at temperatures of 34.7, 31.1, and 34.1 degrees C. At stage 21, the vitelline arterial blood pressure decreased from 0.82 +/- 0.03 (means +/- SEM) to 0.72 +/- 0.03 mm Hg on cooling and increased from 0.66 +/- 0.05 to 0.87 +/- 0.06 mm Hg on rewarming (p less than 0.05). At stage 21, mean dorsal aortic blood flow decreased from 0.49 +/- 0.02 to 0.33 +/- 0.02 mm3/s with cooling and increased from 0.34 +/- 0.02 to 0.47 +/- 0.02 mm3/s with rewarming. The vascular resistance in stage 21 embryos increased after cooling from 1.68 +/- 0.19 to 2.23 +/- 0.39 mm Hg/mm3/s (means +/- 95% confidence interval). The changes were similar in stage 18 and 24 embryos. We conclude that the reduction of vitelline artery blood pressure resulted from a decrease in cardiac output. In addition, we noted that the vitelline arterial vascular bed can constrict in response to hypothermia prior to autonomic innervation. These changes in hemodynamics may be a teratogenic mechanism for hypothermia-induced cardiac defects in the chick embryo.     

The effect of temperature on the QTc interval in the newborn infant receiving extracorporeal membrane oxygenation (ECMO)

OBJECTIVE: To explore the changes in the QTc interval during mild hypothermia in neonates receiving extracorporeal membrane oxygenation (ECMO). DESIGN: Twenty seven neonates (median gestation 40 weeks; range 33-41 weeks) enrolled in a pilot study of mild hypothermia were studied during the first five days of ECMO. The first group (N=7) were maintained at 37 degrees C throughout the study period. Subsequent groups (N=5) were cooled to 36 degrees C, 35 degrees C and 34 degrees C respectively for twenty four hours and the final group to 34 degrees C for forty eight hours before being rewarmed to 37 degrees C. Using a 24 h digital monitor, the QT and QTc intervals were recorded continuously during the cooling and rewarming period and validated using standard 12 lead electrocardiograms. Patients were carefully assessed clinically and routine biochemistry (including magnesium and calcium) laboratory tests measured pre ECMO and at timed intervals during cooling and rewarming. RESULTS: The mean difference between the continuous digital and 12 lead ECG values for QTc was -13.3 ms. During the first 24 h of cooling, the mean (95th centile) values for the digitally measured QTc interval at 37 degrees C=431(506) milliseconds (ms); 36 degrees C=459(521) ms; 35 degrees C=445(516) ms; 34 degrees C=465(531) ms; 34 degrees C for 48 h=466(521) ms. During this period overall QTc increased by 3.12 ms (95% confidence intervals 6.17 to 0.84; p=0.04) for each degree fall in body temperature. During rewarming, there was no significant relationship between QTc and temperature change. No serious arrhythmias were during cooling. Using univariate analysis, no relationship was found between QTc and electrolytes, heart rate and blood pressure. CONCLUSIONS: QTc shows significant variability in individuals, and only a small proportion of this can be explained by rectal temperature. Mild hypothermia was not associated with serious cardiac arrhythmias.     

Phentolamine administration increases blood S100B protein levels in pediatric open-heart surgery patients

AIM: Phentolamine administration during open-heart surgery shortens the cooling and rewarming phases of cardiopulmonary bypass (CPB) and hastens weaning from mechanical ventilation and extubation. Data on the effects of phentolamine on cerebral circulation and function in this setting are lacking. This study reports the cerebral effects of phentolamine using blood S100B protein levels and the middle cerebral artery pulsatility index (MCA PI). METHODS: Sixty pediatric patients undergoing congenital heart disease repair were randomly assigned to receive either phentolamine 0.2 mg kg(-1) i.v. (n = 30) or placebo (n = 30) before the cooling and rewarming phases of CPB. Samples for S100B measurement were collected at seven predetermined time-points before, during and after surgery. MCA PI values were recorded at the same times as sampling. RESULTS: S100B blood levels were higher in the phentolamine-treated group than in controls after rewarming (3.53 +/- 1.88 vs 1.58 +/- 0.53 microg l(-1); p < 0.001), remained persistently higher at the end of surgery (2.95 +/- 0.91 vs 0.79 +/- 0.21 microg l(-1); p < 0.001) and returned to normal ranges 12 h later than in the placebo group (p > 0.05). MCA PI values were also significantly higher at the end of surgery in the phentolamine-treated group (1.83 +/- 0.50 vs 1.22 +/- 0.34; p < 0.01). Cooling and rewarming times were shorter in the phentolamine-treated group (p < 0.01, for all). CONCLUSION: Despite improved peripheral vasodilatation and perfusion, phentolamine administration in pediatric open-heart surgery is correlated with increased cerebrovascular resistance and brain damage.     

选择性头部降温治疗对窒息新生儿心脏功能影响的研究

目的　研究亚低温治疗对窒息新生儿心脏功能的影响。方法　将 50例重度窒息足月新生儿分为治疗组 (2 3例 )和对照组 (2 7例 )。治疗组采用选择性头部降温方法 ,维持鼻咽温度在34 0℃± 0 .5℃ ,持续 72h ;对照组不进行亚低温治疗。超声心动图评估心脏收缩及舒张功能 ,并测定肌钙蛋白T(cardiactroponinT ,cTnT)的含量 ,以判断心肌细胞的损伤程度。 结果　 (1 )亚低温治疗组患儿心率与对照组比较 [分别为 (1 0 3± 1 5)次 /min、(1 2 6± 1 4 )次 /min ,P <0 .0 5]明显降低 ,但无心律失常和低血压。 (2 )亚低温治疗组左室射血分数 (EF)、每搏量 (SV)、每分输出量 (CO)与对照组相比 ,差异无显著意义 (P均 >0 .0 5) ;两组左、右室舒张功能不全例数和肺动脉高压例数 ,差异也无显著意义 (P均 >0 .0 5)。 (3)亚低温治疗组和对照组cTnT水平分别为 (0 .47± 0 .1 5)ng/ml和 (0 .35±0 2 1 )ng/ml,差异无显著意义 (P >0 .0 5)。结论　选择性头部降温 (鼻咽温度 34℃ ,持续 72h)治疗新生儿窒息 ,未加重患儿心脏功能的损伤     

营养不良对幼鼠癫癎持续状态后海马神经发生影响的研究

目的　探讨发育期营养不良伴发癫持续状态对海马神经发生的影响。方法　采用5 溴脱氧尿苷 (BrdU)标记新生细胞 ,β微管蛋白Ⅲ ( βⅢtubulin ,TuJ1)和胶质原纤维酸性蛋白(glialfibrillaryacidicprotein ,GFAP)分别标记早期神经元和胶质细胞的单、双标免疫组织化学染色 ,观察幼鼠海马的神经发生。结果　营养良好 (N)组和营养不良 (M)组幼鼠癫发作的潜伏时间差异无显著性 [( 12 4± 2 6)min与 ( 11 9± 2 9)min ,P >0 0 5 ]。组织学染色示各组幼鼠海马部位均无明显的神经元丢失。各组幼鼠齿状回BrdU阳性细胞数 ,营养不良 +惊厥组 (MS组 ,3 74± 18)和营养良好 +惊厥组 (NS组 ,3 12± 2 4)分别明显高于营养不良组 (M组 ,3 0 3± 2 0 )和营养良好组 (N组 ,2 69± 18) (P均 <0 0 1) ,而M组和MS组分别明显高于N组和NS组 (P均 <0 0 1)。BrdU阳性细胞中 ,约有 60 %的BrdU阳性细胞同时表达神经元特异性标记物TuJ1,5 %～ 10 %的BrdU阳性细胞同时表达神经胶质特异性标记物GFAP。结论　早期营养不良没有改变幼鼠在海藻酸致过程中惊厥的易感性和行为表现。营养不良和癫持续状态均可促进幼鼠海马齿状回新生细胞的增殖 ,营养不良伴发癫持续状态时这种增殖将进一步加强 ,而且大多数新生细胞分化为早期     

The myocardial function during and after whole-body therapeutic hypothermia for hypoxic–ischemic encephalopathy,a cohort study

Background

Therapeutic hypothermia has become standard treatment for moderate and severe neonatal hypoxic–ischemic encephalopathy (HIE) to reduce cerebral morbidity and mortality. The effect on the heart is incompletely explored.

Aim

To assess the myocardial function during and after whole-body therapeutic hypothermia for HIE.

Study design

Observational cohort study.

Subjects

Forty-four infants with HIE cooled for 72 hours were compared with 48 healthy term infants and 20 normothermic infants with HIE.

Outcome measures

Tissue Doppler deformation indices of myocardial function (peak systolic strain, peak systolic strain-rate, early diastole strain-rate and strain-rate in atrial systole) during (days 1 and 3) and after (day 4) therapeutic hypothermia.

Results

On days one and three all indices in both HIE groups were lower than the corresponding indices in the healthy infants. The two HIE groups had similar indices, except peak systolic strain-rate on days 1 and 3 and strain-rate in atrial systole on day 1. All strain-rate indices improved from day 3 to 4 (after rewarming) in the cooled group and achieved similar values to those in healthy infants on day 3. All indices were higher in the cooling-group after rewarming than in the normothermic infants with HIE on day 3, except early diastolic strain-rate.

Conclusions

Infants with HIE had similarly impaired myocardial function during days 1–3 whether normothermic or hypothermic. The myocardial function improved significantly at day 4 (after rewarming), approaching the day 3 levels in the healthy neonates.     

Effect of mild hypothermia and hypoxia on blood flow and oxygen consumption of the fetal sheep brain

This study was undertaken to measure the effects of mild hypothermia on cerebral blood flow and metabolism and cardiovascular responses to hypoxia in the fetal sheep. Near-term fetal sheep were chronically instrumented with laser Doppler flowmetry in the parietal cortex for measurement of relative changes in cerebral blood flow, as well as with arterial and sagittal sinus catheters for measurement of oxygen extraction by the brain and a cooling coil around the fetal thorax. Fetuses were studied during cooling alone, cooling with superimposed maternal hypoxia to achieve a fetal arterial Po2 of 1.33 to 1.60 kPa, or hypoxia alone. In response to cooling alone [1.6 degrees +/- 0.1 degrees C (mean +/- SEM) decrease in brain temperature], fetal blood pressure and heart rate both increased significantly whereas cerebral blood flow decreased 14 +/- 4%, commensurate with a 24 +/- 8% decline in cerebral metabolic rate. Administration of moderate hypoxia during cooling resulted in a significant increase in cerebral blood flow, decreased heart rate, and no further increase in blood pressure. In response to hypoxia alone, fetal blood pressure was significantly increased, heart rate was decreased, and cerebral blood flow increased by 24 +/- 8%, whereas cerebral metabolic rate decreased by 38 +/- 13%. Arteriovenous oxygen extraction was unchanged by cooling alone but increased significantly in response to hypoxia administered during cooling. We therefore conclude that oxygen delivery to the fetal sheep brain remains coupled to metabolic rate during hypothermia and that hypothermia does not impair the compensatory cardiovascular responses of the fetus to acute moderate hypoxia.     

1,6-二磷酸果糖对大鼠热性惊厥性脑损伤保护作用的研究

目的　探讨 1,6 二磷酸果糖 (FDP)对大鼠热性惊厥性脑损伤是否具有保护作用。方法　 30只雄性SD大鼠随机均分为热性惊厥组 (FS) ,盐水对照组 (NS)及果糖干预组 (FD)。水浴法建立热性惊厥模型 ;FD组于惊厥前 30min腹腔注射FDP 2 5mg/ 10 0 g大鼠体重 ;而NS组腹腔注射相同体积的 0 9%氯化钠溶液。观察各组大鼠惊厥表现并制作电镜标本以了解海马CA1区神经元、线粒体及突触超微结构变化。结果　诱发热性惊厥前腹腔注射FDP可使大鼠惊厥潜伏期延长 [FD组为(5 16± 0 88)min ,FS组为 (4 2 5± 0 98)min ,NS组为 (4 2 3± 0 87)min]、惊厥持续时间缩短 [FD组为 (47± 34)s ,FS组为 (6 6± 32 )s,NS组为 (6 6± 32 )s]、惊厥级别下降。以上 3组数据中 ,FD组与其他两组相比差异均有显著性 (P <0 0 5 )。电镜标本观察发现FDP可使大鼠海马CA1区神经元变性坏死减轻 ,神经元变性坏死百分比在FD组、FS组及NS组分别为 13%、2 8%及 30 % ,FD组与其他两组相比差异有显著性 (P <0 0 5 )。FDP防止神经突触间隙异常增宽 ,平均神经突触间隙在FD组、FS组及NS组分别为 (6 4 7± 0 37) μm、(7 6 0± 0 36 ) μm及 (7 5 3± 0 4 0 ) μm ,FD组与其他两组相比差异有显著性 (P <0 0 1)。结论　FDP可使     

Phase Changing Material for Therapeutic Hypothermia in Neonates with Hypoxic Ischemic Encephalopathy — A Multi-centric Study

Objective

To assess the feasibility and safety of cooling asphyxiated neonates using phase changing material based device across different neonatal intensive care units in India.

Design

Multi-centric uncontrolled clinical trial.

Setting

11 level 3 neonatal units in India from November 2014 to December 2015.

Participants

103 newborn infants with perinatal asphyxia, satisfying pre-defined criteria for therapeutic hypothermia.

Intervention

Therapeutic hypothermia was provided using phase changing material based device to a target temperature of 33.5±0.5ºC, with a standard protocol. Core body temperature was monitored continuously using a rectal probe during the cooling and rewarming phase and for 12 hours after the rewarming was complete.

Outcome measures

Feasibility measure - Time taken to reach target temperature, fluctuation of the core body temperature during the cooling phase and proportion of temperature recordings outside the target range. Safety measure - adverse events during cooling

Results

The median (IQR) of time taken to reach target temperature was 90 (45, 120) minutes. The mean (SD) deviation of temperature during cooling phase was 33.5 (0.39) ºC. Temperature readings were outside the target range in 10.8% (5.1% of the readings were <33°C and 5.7% were >34°C). Mean (SD) of rate of rewarming was 0.28 (0.13)°C per hour. The common adverse events were shock/hypotension (18%), coagulopathy (21.4%), sepsis/probable sepsis (20.4%) and thrombocytopenia (10.7%). Cooling was discontinued before 72 hours in 18 (17.5%) babies due to reasons such as hemodynamic instability/refractory shock, persistent pulmonary hypertension or bleeding. 7 (6.8%) babies died during hospitalization.

Conclusion

Using phase changing material based cooling device and a standard protocol, it was feasible and safe to provide therapeutic hypothermia to asphyxiated neonates across different neonatal units in India. Maintenance of target temperature was comparable to standard servo-controlled equipment.

     

Reversible umbilical cord occlusion: effects on thermogenesis in utero.

The initiation of thermogenesis at birth is an important adaptation for survival. We examined the sequential effects of cooling, increased oxygenation, and repeated episodes of umbilical cord occlusion on nonshivering thermogenesis in six fetal sheep at 139 to 145 d of gestation. The fetal sheep were cooled by circulating cold water through a coil placed around the trunk for 4 h. The fetal core temperature fell 2.47 +/- 0.24 degrees C in the first 60 min of cooling with minimal changes in plasma FFA and glycerol levels. After fetal arterial O2 tension was increased above 6.65 kPa by ventilation, fetal temperature and thermogenic indices rose significantly in 60 min. After occlusion of the umbilical cord by a reversible occluder cuff, plasma FFA levels rapidly increased to 635 +/- 69 muEq/L (p less than 0.005) by 30 min, fetal temperature increased a further 0.96 +/- 0.20 degrees C (p less than 0.001) and fetal O2 consumption peaked at 25.3 +/- 4.9 mL.min-1.kg-1. Release of cord occlusion caused a rapid fall in FFA to 149 +/- 23 muEq/L (p less than 0.005) and a fall in fetal core temperature of 0.90 +/- 0.13 degrees C (p less than 0.001) in 30 min. After irreversibly snaring the umbilical cord, the plasma FFA rose to 611 +/- 83 muEq/L (p less than 0.005) and the fetal temperature rose 0.78 +/- 0.09 degrees C (p less than 0.02). The effects on thermogenesis of interrupting and reestablishing placental flow are rapid and reversible and suggest the presence of placental inhibitors of brown adipose tissue thermogenesis.     

The effect of chemical sympathectomy on catecholamine release at birth

The precise source of circulating catecholamine (CA) at birth and their role in circulatory adaptation is unclear. In order to determine the contribution of increased postganglionic sympathetic nerve activity to the CA surge at birth, we induced complete sympathectomy in near term fetal lambs prior to delivery by giving 6-hydroxydopamine. Chronically catheterized fetal sheep received either 6-hydroxydopamine (n = 5) or control infusion (n = 6). Chemical sympathectomy was verified by tyramine infusion. Lambs were delivered at 142 +/- 1 days of gestation and serial plasma CA, heart rate, blood pressure, cardiac output, blood gases, blood glucose, and free fatty acids, were measured before and for 4 h after delivery. Myocardial beta-adrenergic receptors and tissue CA concentration were determined following sacrifice. Baseline circulating norepinephrine (NE) values were lower in sympathectomized animals (183 +/- 45 versus 373 +/- 125 pg/ml, p less than 0.05) and epinephrine values were slightly higher (118 +/- 89 versus 48 +/- 1 pg/ml, NS). There was only a 2-fold increase in NE after cord cutting in sympathectomized animals while control animals had a 4-fold increase (peak NE values 354 +/- 121 versus 1305 +/- 363 pg/ml respectively, p less than 0.001). Epinephrine increased significantly in both groups and there were no significant differences between sympathectomized and control animals. Heart rate and blood pressure rose abruptly in both groups after cord cutting and there were no significant differences.(ABSTRACT TRUNCATED AT 250 WORDS)     

Cerebral oxygenation during cardiopulmonary bypass

Cerebral fractional oxygen extraction (FOE) was monitored in 30 children, using near infrared spectroscopy during cardiopulmonary bypass, to investigate the effect of hypothermia and circulatory arrest. One group of children (n = 15) underwent profound hypothermia with total circulatory arrest (n = 8) or continuous flow (n = 7). Another group (n = 15), of whom only one had circulatory arrest, underwent mild (n = 6) or moderate (n = 9) hypothermia. The mean FOE (SD) before bypass was 0.35 (0.12) and this correlated negatively with the preoperative arterial oxygen content (r = -0.58). Between the stage of cooling on bypass and cold bypass there was a reduction in FOE in all groups. Between cold bypass and rewarming there was an increase in FOE only in the groups with continuous flow. In the circulatory arrest group, the FOE remained low during rewarming and was significantly lower than that of the continuous flow group. No patients died and none had neurological abnormalities postoperatively. Apparent changes in oxidised cytochrome oxidase concentration were also monitored using near infrared spectroscopy. There was a fall in cytochrome aa3 on starting cardiopulmonary bypass, but there were no significant differences in the changes in cytochrome aa3 between any stage in any of the patient groups. Using this non-invasive technique, cooling was shown to reduce cerebral FOE. During rewarming on bypass there was an increase in cerebral FOE only in patients who had had continuous flow bypass. In contrast, the cerebral FOE in those with circulatory arrest remained constant after arrest and during the duration of the study. This may have implications for the timing of hypoxic brain injury.