Immediate Hypothermia Is Not Neuroprotective After Severe Hypoxia-Ischemia and Is Deleterious When Delayed by 12 Hours in Neonatal Rats

Abstract

T herapeutic hypothermia (HT) has become standard treatment for term newborns experiencing perinatal asphyxia.1 Randomized controlled trials have shown that HT significantly improves outcome after hypoxia-ischemia (HI). [2][3][4][5][6] Meta-analysis of these suggests that HT improves outcome more in the group with moderate rather than severe HI encephalopathy.7 HI encephalopathy develops during different phases. 8 Initial reperfusion restores cellular energy metabolism in ≈30 to 60 minutes. A latent phase of 6 to 12 hours follows, in which cellular energy metabolism is fully or partially restored 9 before a secondary decline in energy failure may occur. This secondary phase is characterized by excessive entry of Ca 2+ into cells, free radical production, excitotoxic amino acid release, inflammation, and activation of apoptotic pathways, [10][11][12] commencing within 24 hours and lasting days or weeks. These phases of injury and recovery are not strictly sequential, might overlap, and are likely to be changed by severity of injury or other conditions. 13 As previously shown in different animal models, HT during reperfusion and the latent phase is neuroprotective. [14][15][16] Clinical guidelines recommend that HT should be started within the first 6 hours after birth based on findings in a term-equivalent fetal sheep HI model 16,17 showing significant neuroprotection when HT was initiated before 5.5 hours after cerebral injury.8 There are few studies published about the effect of HT initiated late after HI of different severity, 8,18,19 and no study asks whether HT might increase injury if started very late. There might be species, age, and injury differences. In newborn pigs, delaying HT by 3 hours was ineffective. 20 In adult rat stroke models, delayed treatment up to 3 hours is neuroprotective. [21][22][23] Our aim was to investigate in moderate and severe unilateral brain injury in neonatal rats the effect of HT, the optimal duration of HT, and the effective time window of HT.Background and Purpose-Hypothermia (HT) for neonatal hypoxic-ischemic encephalopathy is advised to start within the first 6 hours after birth. There is some clinical evidence that HT is more effective against moderate than against severe hypoxic-ischemic encephalopathy, but it is unknown whether delayed HT beyond 6 hours is effective or even injurious. Methods-One-hundred seven 7-day-old rat pups underwent unilateral hypoxia-ischemia of moderate severity. Pups were randomized to receive 5 hours of normothermia (NT) or HT starting immediately, 3 hours, 6 hours, or 12 hours after the 90-minute hypoxic period. One-hundred five 7-day-old rat pups underwent severe hypoxia-ischemia lasting 150 minutes, followed by the same group design as mentioned. Relative area loss of the left/right hemisphere was measured after 1 week of survival. Results-In the moderate NT group, the mean area loss of the left hemisphere was 40.5%. Materials and Methods ProceduresAll procedures were performed under Home Office license in accordance with United Kingdom r...

Adding 5 h delayed xenon to delayed hypothermia treatment improves long-term function in neonatal rats surviving to adulthood

“…The hippocampal area loss ratio on the ipsilateral side was calculated as: Hippocampal area loss % = (1−(remaining hippocampal area on the ipsilateral side)/(hippocampal area on the contralateral side)) × 100 A larger brain area loss ratio represents more severe brain injury (7). By using this method, we were able to reliably measure gross morphology change such as cavitations or atrophy.…”

“…The recommended clinical HT protocols state that cooling should start within 6 h after birth (3)(4)(5). The effective time window of HT is 5-6 h in both fetal lamb (6) and postnatal day 7 (P7) rats (7) and <3 h in injured newborn pigs (8). In NE infants, better motor outcome has been found at 18 mo if cooling was started within 3 h as compared to those were cooled between 3-6 h of age (9).…”

Limitations of Mild, Moderate, and Profound Hypothermia in Protecting Developing Hippocampal Neurons After Simulated Ischemia

“…These conflicting results may not be oppositional considering the possibility that delayed hypothermia may be protective only with milder insults. We consider that the OGD used in this study involves a moderate to severe insult and it is possible that a less severe insult would be compatible with a protective effect of delayed hypothermia as recently demonstrated in a neonatal rat model of hypoxia ischemia (Sabir et al, 2012). As in the Sabir study, delayed hypothermia, or profound hypothermia, increased rather than prevented postischemic injury, which is a clinical concern.…”

“…We used an organotypic culture model of the developing rat hippocampus that is sensitive to hypothermia protection and damage Warren et al, 2012) A recent study in intact rats showed that when hypothermia postcerebral ischemia was delayed by 3 hours or more, it was not protective or added to injury (Sabir et al, 2012), so we also examined the effects of delaying hypothermia on outcome after OGD. We examined temperatures of 32°C, 23°C, 17°C, and 4°C to span both the therapeutic and potentially injurious range of temperatures, applying hypothermia either immediately after or after a delay from simulated ischemia.…”

Terápiás hypothermia alkalmazása az asphyxiás újszülöttek kezelésében – egy hazai neonatológiai centrum eredményei

“…A sikeres kezelés-hez mindenképpen szükség van a szülészeti intézmény, a neonatalis transzportért felelős mentőszolgálat és az asphyxiacentrumok közötti jó együttműködésre, hogy a hypothermiás kezelés elérhető legyen akár már a neonatalis transzport során is. Állatkísérletes eredmények és újszülötteken végzett klinikai vizsgálatok alapján ugyanis igazolódott, hogy a terápiás hűtés hatékonysága növel-hető a hypothermia mihamarabbi megkezdésével [28][29][30][31]. A harmadik életórán belül elkezdett terápia tovább fokozza a neuroprotekciót és javítja a hosszú távú kimenetelt a 3-6. életórában megkezdett hűtéshez képest [30].…”