Post cardiac arrest hyperoxic resuscitation enhances neuronal vulnerability of the respiratory rhythm generator and some brainstem and spinal cord neuronal pools in the dog

Normoxic post-ROSC ventilation delays hippocampal CA1 neurodegeneration in a rat cardiac arrest model, but does not prevent it

The European Resuscitation Guidelines recommend that survivors of cardiac arrest (CA) be resuscitated with 100% O₂ and undergo subsequent-post-return of spontaneous circulation (ROSC)-reduction of O₂ supply to prevent hyperoxia. Hyperoxia produces a "second neurotoxic hit," which, together with the initial ischemic insult, causes ischemia-reperfusion injury. However, heterogeneous results from animal studies suggest that normoxia can also be detrimental. One clear reason for these inconsistent results is the considerable heterogeneity of the models used. In this study, the histological outcome of the hippocampal CA1 region following resuscitation with 100% O₂ combined with different post-ROSC ventilation regimes (21%, 50%, and 100% O₂) was investigated in a rat CA/resuscitation model with survival times of 7 and 21 days. Immunohistochemical stainings of NeuN, MAP2, GFAP, and IBA1 revealed a neuroprotective potency of post-ROSC ventilation with 21% O₂, although it was only temporary. This limitation should be because of the post-ROSC intervention targeting only processes of ischemia-induced secondary injury. There were no ventilation-dependent effects on either microglial activation, reduction of which is accepted as being neuroprotective, or astroglial activation, which is accepted as being able to enhance neurons' resistance to ischemia/reperfusion injury. Furthermore, our findings verify the limited comparability of animal studies because of the individual heterogeneity of the animals, experimental regimes, and evaluation procedures used.

The effect of hyperoxia following cardiac arrest - A systematic review and meta-analysis of animal trials

AIM

There are conflicting findings from observational studies regarding the nature of the association between hyperoxia and risk of mortality in patients admitted to intensive care following cardiac arrest. This systematic review and meta-analysis evaluates animal data investigating the effect of administration of high concentrations of oxygen following cardiac arrest on neurological outcome and the clinical applicability of this data.

METHODS

A systematic search of Medline and Embase identified controlled animal studies modelling cardiac arrest with subsequent cardiopulmonary resuscitation that compared ventilation with 100% oxygen to lower concentrations following return of spontaneous circulation. Eligible studies were included in a meta-analysis in which the inverse variance weighted differences were calculated for the standardised mean difference of the primary outcome measure, the neurological deficit score.

RESULTS

Ten studies met the criteria for inclusion in the systematic review. In a meta-analysis of six studies, with 95 animals, treatment with 100% oxygen resulted in a significantly worse neurological deficit score than oxygen administered at lower concentrations, with a standardised mean difference of -0.64 (95% CI -1.06 to -0.22). In four of five studies, histological evidence of increased neuronal damage was present in animals that received 100% oxygen therapy.

CONCLUSIONS

The administration of 100% oxygen therapy is associated with worse neurological outcome than lower oxygen concentrations in animal models of cardiac arrest. However, due to limitations in study design and poor generalisability of the animal models to the situation of post cardiac arrest resuscitation in humans, the clinical applicability of this data is uncertain.

Airway management in cardiac arrest

Airway management has been emphasized as crucial to effective resuscitation of patients in cardiac arrest. However, recent research has shown that coronary and cerebral perfusion should be prioritized rather than airway management. Endotracheal intubation has been deemphasized. This article reviews the current state of the literature regarding airway management of the patient in cardiac arrest. Ventilatory management strategies are also discussed.

Part 10: Pediatric basic and advanced life support: 2010 International Consensus on Cardiopulmonary Resuscitation and Emergency Cardiovascular Care Science With Treatment Recommendations

Note From the Writing Group: Throughout this article, the reader will notice combinations of superscripted letters and numbers (eg, “Family Presence During ResuscitationPeds-003”). These callouts are hyperlinked to evidence-based worksheets, which were used in the development of this article. An appendix of worksheets, applicable to this article, is located at the end of the text. The worksheets are available in PDF format and are open access.

Monitoring and intraoperative management of elevated intracranial pressure and decompressive craniectomy

There are numerous clinical scenarios wherein a critically ill patient may present with neurologic dysfunction. In a general sense these scenarios often involve ischemia, trauma, or neuroexcitation. Each of these may include a period of decreased cerebral perfusion pressure, usually due to elevated intracranial pressure (ICP), eventually compromising cerebral blood flow sufficiently to produce permanent neuronal loss, infarction, and possibly brain death. Elevated ICP is thus a common pathway for neural demise and it may arise from a variety of causes, many of which may result in a neurosurgical procedure intended to ameliorate the impact or etiology of elevated ICP.

Neuronal nitric oxide synthase immunopositivity in motoneurons of the rabbit's spinal cord after transient ischemia/reperfusion injury

1. Motoneurons in the spinal cord are especially vulnerable to ischemic injury and selectively destroyed after transient ischemia. To evaluate the role of nitric oxide (NO) in the pathophysiology of the spinal cord ischemia, the expression of neuronal nitric oxide synthase (nNOS) in the motoneurons of the lumbosacral spinal cord was examined in the rabbit model of transient abdominal aorta occlusion. 2. The aim of the present study was to find if there is any consensus between the duration of transient abdominal aorta occlusion, nNOS positivity of the motoneurons and neurological hind limb impairment. 3. According to the degree of neurological damage (i.e., from the group with almost no sign of damage to a group with fully developed paraplegia), the experimental animals were divided into three groups. The respective spinal cord segments of each experimental group were compared to the control group. 4. Spinal cord ischemia (15 min) was induced by Fogarty arterial embolectomy catheter occlusion of abdominal aorta with a reperfusion period of 7 days. On seventh day, the sections of lumbosacral segments were immunohistochemically treated and L1-L7, and S1-S2 segment sections were monitored using light microscopy.

Regional changes of membrane phospholipid concentrations in rabbit spinal cord following brief repeated ischemic insults

Changes in the concentration of membrane-bound phospholipids following single (25-min) spinal cord ischemia and 3 h of reperfusion were determined. These were compared with the changes following brief repeated (8-, 8-, and 9-min) ischemia followed each time by reperfusion for 1 h, or the same periods of ischemia followed by 8 h, 8 h, and 24 h of reperfusion, respectively. Phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylserine (PS), phosphatidylinositol (PI), and sphingomyelin (SM) were assayed in regions of the spinal cord of the rabbit, including gray matter, white matter, dorsal horns, intermediate zone, and ventral horns. The brief repeated ischemia with 1-h reperfusions produced more extensive degradation of phospholipids in almost all regions compared with the equivalent time of ischemia (25 min) in a single period. After a lengthy reperfusion after repeated ischemia, the phospholipids were resynthesized with the exception of the phosphatidylinositol in the gray matter. The resynthesis was most pronounced in the dorsal horns and in the white matter.

Neuroprotective effect of graded postischemic reoxygenation in spinal cord ischemia in the rabbit

Early ischemia/reperfusion-induced changes of four phospholipid compounds bound to the inner cell membrane leaflet, i.e., phosphatidic acid, inositol phospholipids, serine phospholipids, and ethanolamine plasmalogens, were studied in a model of spinal cord ischemia in the rabbit during normoxic and graded postischemic reoxygenation. Light and electron microscopic analysis after normoxic reoxygenation disclosed neuronal membrane argyrophilia of the interneuronal pool located in lamina VII of L4-L6 segments. The number of small neurons (10-25 microm in diameter) affected by somatodendritic argyrophilia was greatly reduced, and concomitantly the ultrastructure of the endoplasmic reticulum, mitochondria, and Golgi complexes remained almost undamaged when graded postischemic reoxygenation had been applied. A statistically significant increase of phosphatidylserine and ethanolamine plasmalogen levels, and a decrease of phosphatidic acid, were detected after a short-lasting graded postischemic reoxygenation. The formation of thiobarbituric acid-reactive substances was significantly reduced during 60 min of graded postischemic reoxygenation and remained close to control or ischemic levels. The present data indicate that graded postischemic reoxygenation, which is considered to be neuroprotective, can prevent neuronal argyrophilia and the development of reperfusion-induced alterations of organelles. Moreover, reoxygenation can positively modify ischemia-induced changes of some membrane-bound phospholipids.

Multiple protracted cauda equina constrictions cause deep derangement in the lumbosacral spinal cord circuitry in the dog

Neuropathological changes of the neuronal pools and spinal cord circuitry in the lumbosacral segments were studied in a canine model of multiple protracted cauda equina constrictions. Anterograde degeneration of all sacrococcygeal and L7 dorsal root fibers was detected in S1-S3 and lower lumbar segments. A narrow degenerated gracile fascicle was found in all thoracic and cervical segments terminating in the gracile nucleus. Transneuronal degeneration of middle-sized and large neurons, located in S1-S3 and sporadically in L7 segments, was noted. Identical transneuronal degeneration was seen in a group of small neurons located in the ventralmost part of lamina VII in S1-S3 segments. Simultaneously, a terminal degeneration was detected in the lateral cervical nucleus and in the ventral posterior lateral nucleus of the ventrobasal thalamic complex. Concomitantly, a fully developed retrograde degeneration affecting motoneurons in the ventrolateral portion of the anterior horn in S1-S3 segments appeared.

Postischemic reperfusion causes a massive calcium overload in the myelinated spinal cord fibers

The visualization of Ca binding in the myelinated axons of lumbosacral segments of rabbit was done at the electron microscopic level using the spinal cord ischemia model. To assess the calcium accumulation, the binding agent pyroantimonate was used. Nonsignificant Ca2+ binding was found in the myelinated axons after 40 min of ischemia followed immediately by perfusion fixation. A high concentration of calcium pyroantimonate deposits, seen as electron dense particles, was detected in the myelin interlamellar clefts and axoplasm. The paranodal region was the most affected site.

Ischemia-induced delayed-onset paraplegia is accompanied by an unusual form of synaptic degeneration in the lumbosacral segments: an experimental light and electron microscopic study in dogs

We studied the effect of high thoracic aorta cross-clamping, complete transverse section of the spinal cord at Th6 level, and combined hemisection at Th6 level followed later by high thoracic aorta cross-clamping upon the morphology and number of identified presynaptic knobs in lumbosacral segments in dogs. In animals surviving 48-72 hours after high thoracic aorta cross-clamping the occurrence of an unusual form of boutons accompanied by periboutonal halo in L3-S1 segments was found. According to the bouton size and light as well as electron microscopic appearance, four types, i.e., light giant (T1), dark enlarged (T2), light giant with periboutonal halo (T3), and giant disintegrating (T4) boutons were detected after 48 and 72 hour reperfusion. The appearance of four boutonal types in the lumbosacral segments is caused by spinal cord ischemia secondary to high thoracic aorta cross-clamping followed by 48 or 72 hour reperfusion. At the end of the sixth reperfusion day no signs of enlarged and giant boutons were detected in L3-S1 segments. A statistically significant increase of enlarged and giant boutons was noted at the end of the third reperfusion day in comparison with 48 hour survival. After spinal cord transection at midthoracic (Th6) level, followed by 72 hour survival, no such unusual synaptic knobs could be found in L3-S1 segments. The laminar distribution pattern of T1-T4 types based on light microscopic analysis and confirmed electron microscopically is characteristic and strictly bound to those spinal cord gray matter layers which serve as main termination sites of the descending cortical, brain stem, as well as long propriospinal projections in the lumbosacral segments (laminae V-VII). A statistically significant increase of enlarged and giant boutons was found in the intermediate zone (lamina VII). Hemisection at midthoracic level (Th6) followed later by 30 minute high thoracic aorta cross-clamping and 48 hour reperfusion caused a marked decrease of enlarged and giant boutons in L3-S1 segments on the hemisectioned side in comparison with the contralateral one. Large amounts of irregularly arranged round vesicles and tubular profiles were disclosed in the boutonal matrix of T1, T3, and T4 types in L3-S1 segments of animals subjected to 30 minute high thoracic aorta cross-clamping followed by 72 hour reperfusion. Accumulation of tubular and membranous materials was invariably seen in the bulbous enlargement of the terminal axonal branch.(ABSTRACT TRUNCATED AT 400 WORDS)