Perioperative hypothermia: use and therapeutic implications

Management of Intraoperative Rupture of Intracranial Aneurysms: Agony and Ecstasy

Intraoperative rupture (IOR) of an intracranial aneurysm is a serious complication, often with catastrophic consequences that are difficult to manage even by the best hands. Like most surgical complications, this one is better to avoid than to treat, but any vascular neurosurgeon should know how to deal with IOR of an aneurysm, because it is bound to occur. The aims of this study were to evaluate the incidence and factors associated with IOR during clipping of intracranial aneurysms, to analyze strategies for controlling hemorrhage in such cases, and to assess outcomes. Overall, 911 cases of intracranial aneurysms, which were treated surgically by the author during 26 years of his professional career, were reviewed. IOR was never noted during clipping of an unruptured intracranial aneurysm (65 cases) but was encountered in 49 of 846 cases (5.8%) presenting with subarachnoid hemorrhage. This complication occurred most often in cases of internal carotid artery aneurysms (22 cases; 45%), followed by anterior communicating artery aneurysms (12 cases; 24%), distal anterior cerebral artery aneurysms (6 cases; 12%), middle cerebral artery aneurysms (6 cases; 12%), and posterior circulation aneurysms (3 cases; 6%). IOR was mostly encountered during early surgery (within 3 days) after the ictus (26 cases; 53%) and most frequently occurred during dissection of the aneurysm (26 cases; 53%). Overall, 22 patients (45%) had good outcome, 18 (37%) had variable morbidity, and 9 (18%) died. Fatal consequences of IOR were noted only in cases of big or multilobulated internal carotid artery aneurysms. Detailed planning of the surgical procedure, application of meticulous microdissection techniques, and anticipation of possible intraoperative incidents during intervention aimed at clipping of an intracranial aneurysm can reduce the risk of IOR, as well as the associated morbidity and mortality.

Intraoperative Cerebral Monitoring During Carotid Surgery: A Narrative Review

BACKGROUND

Intra-operative neurological monitoring (IONM) during carotid endarterectomy (CEA) aims to reduce neurological morbidity of surgery.

OBJECTIVE

This narrative review analyses the role and results of different methods of IONM.

METHODS

review articles on PUBMED and Cochrane Library, by searching key words related to IONM and CEA, from 2000 up to date.

RESULTS

regional anesthesia in some centers represents the "gold standard". The most often used alternative techniques are: stump pressure, electroencephalogram, somatosensory evoked potentials, transcranical doppler ultrasound, near infrared spectroscopy and routine shunting. Every technique shows limitations. Regional anesthesia can make difficult prompt intubation when needed. Stump pressure shows a wide operative range. Electroencephalogram is unable to detect ischemia in sub-cortical regions of the brain. Somatosensory evoked potentials certainly demonstrate the presence of cerebral ischemia, but are no more specific or sensitive than the electroencephalogram. Transcranical doppler monitoring is undoubtedly operator-dependent and suffers from the limitations that the probe has to be placed relatively near to the surgical site and may impede the operator, especially if it needs constant adjustments; moreover, an acoustic window may not be found in 10% -20% of the subjects. Near infrared spectroscopy appears to have a high negative predictive value for cerebral ischemia, but has a poor positive predictive value and low specificity, because predominantly estimates venous oxygenation as this makes up about 80% of cerebral blood volume. The data on the use of Routine Shunting (RS) from RCTs are limited.

CONCLUSIONS

currently, with no clear consensus on monitoring technique, choice should be guided by local expertise and complication rates. With reflection, best practice may dictate that a standard technique is selected as suggested above and this remains the default position for individual practice. Nevertheless, current techniques for monitoring cerebral perfusion during CEA are associated with false negative and false positive resulting in inappropriate shunt insertion.

Cold-induced chromatin compaction and nuclear retention of clock mRNAs resets the circadian rhythm

Cooling patients to sub‐physiological temperatures is an integral part of modern medicine. We show that cold exposure induces temperature‐specific changes to the higher‐order chromatin and gene expression profiles of human cells. These changes are particularly dramatic at 18°C, a temperature synonymous with that experienced by patients undergoing controlled deep hypothermia during surgery. Cells exposed to 18°C exhibit largely nuclear‐restricted transcriptome changes. These include the nuclear accumulation of mRNAs encoding components of the negative limbs of the core circadian clock, most notably REV‐ERBα. This response is accompanied by compaction of higher‐order chromatin and hindrance of mRNPs from engaging nuclear pores. Rewarming reverses chromatin compaction and releases the transcripts into the cytoplasm, triggering a pulse of negative limb gene proteins that reset the circadian clock. We show that cold‐induced upregulation of REV‐ERBα is sufficient to trigger this reset. Our findings uncover principles of the cellular cold response that must be considered for current and future applications involving therapeutic deep hypothermia.

Physiology Of Drowning: A Review

Drowning physiology relates to two different events: immersion (upper airway above water) and submersion (upper airway under water). Immersion involves integrated cardiorespiratory responses to skin and deep body temperature, including cold shock, physical incapacitation, and hypovolemia, as precursors of collapse and submersion. The physiology of submersion includes fear of drowning, diving response, autonomic conflict, upper airway reflexes, water aspiration and swallowing, emesis, and electrolyte disorders. Submersion outcome is determined by cardiac, pulmonary, and neurological injury. Knowledge of drowning physiology is scarce. Better understanding may identify methods to improve survival, particularly related to hot-water immersion, cold shock, cold-induced physical incapacitation, and fear of drowning.

Neuroprotective hypothermia - Why keep your head cool during ischemia and reperfusion

BACKGROUND

Targeted temperature management (TTM) is the induced cooling of the entire body or specific organs to help prevent ischemia and reperfusion (I/R) injury, as may occur during major surgery, cardiac resuscitation, traumatic brain injury and stroke. Ischemia and reperfusion induce neuronal damage by mitochondrial dysfunction and oxidative injury, ER stress, neuronal excitotoxicity, and a neuroinflammatory response, which may lead to activation of apoptosis pathways.

SCOPE OF REVIEW

The aim of the current review is to discuss TTM targets that convey neuroprotection and to identify potential novel pharmacological intervention strategies for the prevention of cerebral ischemia and reperfusion injury.

MAJOR CONCLUSIONS

TTM precludes I/R injury by reducing glutamate release and oxidative stress and inhibiting release of pro-inflammatory factors and thereby counteracts mitochondrial induced apoptosis, neuronal excitotoxicity, and neuroinflammation. Moreover, TTM promotes regulation of the unfolded protein response and induces SUMOylation and the production of cold shock proteins. These advantageous effects of TTM seem to depend on the clinical setting, as well as type and extent of the injury. Therefore, future aims should be to refine hypothermia management in order to optimize TTM utilization and to search for pharmacological agents mimicking the cellular effects of TTM.

GENERAL SIGNIFICANCE

Bundling knowledge about TTM in the experimental, translational and clinical setting may result in better approaches for diminishing I/R damage. While application of TTM in the clinical setting has some disadvantages, targeting its putative protective pathways may be useful to prevent I/R injury and reduce neurological complications.

Endovascular Cooling Method for Hypothermia in Injured Swine

We evaluated an endovascular cooling method to modulate core temperature in trauma swine models with and without fluid support. Anesthetized swine (N = 80) were uninjured (SHAM) or injured through a bone fracture plus soft tissue injury or an uncontrolled hemorrhage and then subdivided to target body temperatures of 38°C (normothermia) or 33°C (hypothermia) by using a Thermogard endovascular cooling device (Zoll Medical). Temperature regulation began simultaneously at onset of injury (T0). Body temperatures were recorded from a rectal probe (Rec Temp) and from a central pulmonary artery catheter (PA Temp). At T15, swine received 500 mL IV Hextend over 30 minutes or no treatment (NONE) with continued monitoring until 3 hours from injury. Hypothermia was attained in 105 ± 39 minutes, at a cooling rate of -0.061°C ± 0.007°C/min for NONE injury groups. Postinjury Hextend administration resulted in faster cooling (-0.080°C ± 0.006°C/min); target temperature was reached in 83 ± 11 minutes (p < 0.05). During active cooling, body temperature measured by the PA Temp was significantly cooler than the Rec Temp due to the probe's closer proximity to the blood-cooling catheter balloons (p < 0.05). This difference was smaller in SHAM and fluid-supported injury groups (1.1°C ± 0.4°C) versus injured NONE groups (2.1°C ± 0.3°C). Target temperatures were correctly maintained thereafter in all groups. In normothermia groups, there was a small initial transient overshoot to maintain 38°C. Despite the noticeable difference between PA Temp and Rec Temp until target temperature was attained, this endovascular method can safely induce moderate hypothermia in anesthetized swine. However, likely due to their compromised hemodynamic state, cooling in hypovolemic and/or injured patients will be different from those without injury or those that also received fluids.

Neurological complications of cardiac surgery

As increasing numbers of elderly people undergo cardiac surgery, neurologists are frequently called upon to assess patients with neurological complications from the procedure. Some complications mandate acute intervention, whereas others need longer term observation and management. A large amount of published literature exists about these complications and guidance on best practice is constantly changing. Similarly, despite technological advances in surgical intervention and modifications in surgical technique to make cardiac procedures safer, these advances often create new avenues for neurological injury. Accordingly, rapid and precise neurological assessment and therapeutic intervention rests on a solid understanding of the evidence base and procedural variables.

Controversies in the anesthetic management of intraoperative rupture of intracranial aneurysm

Despite great advancements in the management of aneurysmal subarachnoid hemorrhage (SAH), outcomes following SAH rupture have remained relatively unchanged. In addition, little data exists to guide the anesthetic management of intraoperative aneurysm rupture (IAR), though intraoperative management may have a significant effect on overall neurological outcomes. This review highlights the various controversies related to different anesthetic management related to aneurysm rupture. The first controversy relates to management of preexisting factors that affect risk of IAR. The second controversy relates to diagnostic techniques, particularly neurophysiological monitoring. The third controversy pertains to hemodynamic goals. The neuroprotective effects of various factors, including hypothermia, various anesthetic/pharmacologic agents, and burst suppression, remain poorly understood and have yet to be further elucidated. Different management strategies for IAR during aneurysmal clipping versus coiling also need further attention.

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

Mild hypothermia (33°C-34°C) after cerebral ischemia in intact animals or ischemia-like conditions in vitro reduces neuron death. However, it is now clear that more profound hypothermia or delayed hypothermia may not provide significant protection. To further define the limitations of hypothermia after cerebral ischemia, we used hippocampal slice cultures to examine the effects of various degrees, durations, and delays of hypothermia on neuron death after an ischemia-like insult. Organotypic cultures of the hippocampus from 7- to 8 day-old rat pups were cooled to 32°C, 23°C, 17°C, or 4°C immediately or after a 2-4 hour delay from an injurious insult of oxygen and glucose deprivation (OGD). Cell death in CA1, CA3 and dentate regions of the cultures was assessed 24 hours later with SYTOX® or propidium iodide, both of which are fluorescent markers labeling damaged cells. OGD caused extensive cell death in CA1, CA3, and dentate regions of the hippocampal cultures. Hypothermia (32°C, 23°C and 17°C) for 4-6 hours immediately after OGD was protective at 24 hours, but when hypothermia was applied for longer periods or delayed after OGD, no protection or increased death was seen. Ultra-profound hypothermia (4°C) increased cell death in all cell areas of the hippocampus even when after a milder insult of only hypoxia. In an in vitro model of recovery after an ischemia-like insult, mild to profound hypothermia is protective only when applied without delay and for limited periods of time (6-8 hours). Longer durations of hypothermia, or delayed application of the hypothermia can increase neuron death. These findings may have implications for clinical uses of therapeutic hypothermia after hypoxic or ischemic insults, and suggest that further work is needed to elucidate the limitations of hypothermia as a protective treatment after ischemic stress.

Protecting the brain during neurosurgical procedures: strategies that can work

PURPOSE OF REVIEW

The quest for neuroprotection strategies during periods of neuronal vulnerability persists despite decades of basic and clinical research. This review will focus on the latest developments in the area of clinical brain protection with the major emphasis on strategies that can be beneficial during neurosurgical procedures.

RECENT FINDINGS

Brain protection in neurosurgical patients may be achieved by nonpharmacological and pharmacological strategies. Pharmacological neuroprotection including anaesthetic administration have not been recently shown to be successful. Alternatively, nonpharmacological strategies including maintenance of cerebral perfusion by adequate control of mean arterial pressure (≥80 mmHg), liberal normoglycaemia (7.8-10 mmol/l), adequate haemoglobin levels (preoperative ≥120 g/l and intraoperative ≥90 g/l) and induction of hypertension (20-40% of preoperative values) in certain neurosurgical situations can be beneficial as neuroprotectants during neurosurgery. Mild hypothermia (32-35°C) failed to achieve neuroprotective effects in several situations of brain injury.

SUMMARY

The findings of this review suggest that the anaesthesiologist is compelled to use nonpharmacological strategies sometimes based on empiric evidence to protect the brain during neurosurgical procedures. These strategies are simple, have high benefit/risk ratios and are inexpensive. Rigorous controlled clinical studies are needed to investigate the neuroprotective efficacy of these commonly used nonpharmacological methods.