Mild intraoperative hypothermia during surgery for intracranial aneurysm

Controversies in the management of aneurysmal subarachnoid hemorrhage*

BACKGROUND

The care of patients with aneurysmal subarachnoid hemorrhage has evolved significantly with the advent of new diagnostic and therapeutic modalities. Although it is believed that these advances have contributed to improved outcomes, considerable uncertainty persists regarding key areas of management.

OBJECTIVE

To review selected controversies in the management of aneurysmal subarachnoid hemorrhage, with a special emphasis on endovascular vs. surgical techniques for securing aneurysms, the diagnosis and therapy of cerebral vasospasm, neuroprotection, antithrombotic and anticonvulsant agents, cerebral salt wasting, and myocardial dysfunction, and to suggest venues for further clinical investigation.

DATA SOURCE

Search of MEDLINE and Cochrane databases and manual review of article bibliographies.

DATA SYNTHESIS AND CONCLUSIONS

Many aspects of care in patients with aneurysmal subarachnoid hemorrhage remain highly controversial and warrant further resolution with hypothesis-driven clinical or translational research. It is anticipated that the rigorous evaluation and implementation of such data will provide a basis for improvements in short- and long-term outcomes.

New cerebral protection strategies

PURPOSE OF REVIEW

This article presents an overview of the most recent and important strategies to reduce secondary brain damage.

RECENT FINDING

There is currently no magic bullet available to protect the brain after neuronal injury. This is related to the complex pathophysiology of cerebral ischemia, which makes it unlikely that a single pharmacological intervention results in sustained neuroprotection. Analyses of clinical studies reveal that acute physiologic derangements (e.g. fever, hypertension and hypotension, hypoxemia, hypercapnia, hyperglycemia) are the most important predictors of unfavorable outcome after brain injury and have to be treated. The effectiveness of anesthetic agents to extend the ischemic tolerance of neurons has been demonstrated in experimental settings, but such benefits have not been demonstrated in humans. The effectiveness of osmodiuretics to decrease elevated intracranial pressure, a factor with relevance to outcome, has been demonstrated. Infusion of magnesium in patients with subarachnoidal hemorrhage can reduce the occurrence of delayed ischemia caused by cerebrovascular spasm. The prophylactic administration of glucocorticoids should be avoided. While the positive effects of chronic administration of statins to reduce the incidence of stroke has been demonstrated in several clinical studies, the protective effect of acute administration of statins after a cerebral insult has do be defined.

SUMMARY

Control of physiological variables, avoidance of hyperthermia, intensive control of plasma glucose concentrations, use of anesthetic agents and osmodiuretics to control intracranial hypertension and the possible prophylactic administration of magnesium in patients at risk of vasospasm and of statins in patients with cerebrovascular risk factors are currently the most important strategies to reduce neuronal injury.

Management of brain arteriovenous malformations

PURPOSE OF REVIEW

This review highlights recent data regarding factors associated with brain arteriovenous malformation hemorrhage and different treatment options.

RECENT FINDINGS

More risk factors were identified in association with intracranial hemorrhage, including age at initial diagnosis of arteriovenous malformation, co-existing extranidal aneurysms and genetic factors. Patients with unruptured arteriovenous malformations were found to be more susceptible to worsening in neurological function after microsurgery compared with those presenting with hemorrhagic arteriovenous malformation. Radiosurgery has achieved satisfactory obliteration of deep arteriovenous malformations, but with increased actuarial hemorrhage rates from the first to the fifth year. Although the Intraoperative Hypothermia for Aneurysm Surgery Trial failed to show a significant neurological improvement, the superior efficiency of endovascular cooling has offered optimism in cerebral protection during neurovascular surgeries by shortening the time to achieve hypothermia and rewarming. A multi-center trial (ARUBA) has been proposed to test the hypothesis that, for unruptured brain arteriovenous malformations, there is no difference between interventional and conservative management. Recent studies have also shown the promise of using tetracyclines to decrease the rate of spontaneous arteriovenous malformation rupture.

SUMMARY

The recent identification of clinical and genetic factors associated with brain arteriovenous malformation hemorrhage, as well as studies on treatment outcomes, will help risk stratification in management choices. Future studies are needed to identify arteriovenous malformation patients at the greatest risk of spontaneous hemorrhage and to develop specific medical therapies.

The role of hypothermia in neurosurgical patients

PURPOSE OF REVIEW

Interest in the therapeutic use of mild hypothermia was rekindled in the 1980s by the publication of promising animal studies. The results of several large clinical trials have become known in the last few years. This paper examines the recent evidence supporting the use of intraoperative hypothermia for neurosurgical patients.

RECENT FINDINGS

This article will cover advances made in three key areas: evidence for a clinical benefit from intraoperative hypothermia, advances in cerebral temperature monitoring, and new techniques for cooling the brain.

SUMMARY

There is currently insufficient evidence to support the use of mild intraoperative hypothermia for protection against focal cerebral ischaemia. Future investigations should focus on specific patient subgroups, and make use of recent advances in selective brain hypothermia and intracranial temperature monitoring.

International subarachnoid aneurysm trial (ISAT) of neurosurgical clipping versus endovascular coiling in 2143 patients with ruptured intracranial aneurysms: a randomised comparison of effects on survival, dependency, seizures, rebleeding, subgroups, and aneurysm occlusion

BACKGROUND

Two types of treatment are being used for patients with ruptured intracranial aneurysms: endovascular detachable-coil treatment or craniotomy and clipping. We undertook a randomised, multicentre trial to compare these treatments in patients who were suitable for either treatment because the relative safety and efficacy of these approaches had not been established. Here we present clinical outcomes 1 year after treatment.

METHODS

2143 patients with ruptured intracranial aneurysms, who were admitted to 42 neurosurgical centres, mainly in the UK and Europe, took part in the trial. They were randomly assigned to neurosurgical clipping (n=1070) or endovascular coiling (n=1073). The primary outcome was death or dependence at 1 year (defined by a modified Rankin scale of 3-6). Secondary outcomes included rebleeding from the treated aneurysm and risk of seizures. Long-term follow up continues. Analysis was in accordance with the randomised treatment.

FINDINGS

We report the 1-year outcomes for 1063 of 1073 patients allocated to endovascular treatment, and 1055 of 1070 patients allocated to neurosurgical treatment. 250 (23.5%) of 1063 patients allocated to endovascular treatment were dead or dependent at 1 year, compared with 326 (30.9%) of 1055 patients allocated to neurosurgery, an absolute risk reduction of 7.4% (95% CI 3.6-11.2, p=0.0001). The early survival advantage was maintained for up to 7 years and was significant (log rank p=0.03). The risk of epilepsy was substantially lower in patients allocated to endovascular treatment, but the risk of late rebleeding was higher.

INTERPRETATION

In patients with ruptured intracranial aneurysms suitable for both treatments, endovascular coiling is more likely to result in independent survival at 1 year than neurosurgical clipping; the survival benefit continues for at least 7 years. The risk of late rebleeding is low, but is more common after endovascular coiling than after neurosurgical clipping.

Induced hypothermia as a new approach to lung rest for the acutely injured lung*

OBJECTIVE

To investigate whether low-frequency ventilation during hypothermia could attenuate lung injury associated with endotoxin and mechanical ventilation.

DESIGN

: Experimental animal study.

SETTING

University-affiliated animal laboratory.

SUBJECTS

Forty-eight Sprague-Dawley rats.

INTERVENTIONS

: Lipopolysaccharide was administered to rats intratracheally to induce acute lung injury. After 1 hr of this treatment, animals were assigned to normothermia-only (NO, rectal temperature 37 degrees C, ventilatory frequency 90/min), normothermia-lung rest (NR, 37 degrees C, 45/min), hypothermia-only (HO, 27 degrees C, 90/min), or hypothermia-lung rest (HR, 27 degrees C, 45/min). After 1 hr of injurious ventilation, the lungs of the rats were removed for bronchoalveolar lavage and histologic examination.

MEASUREMENTS AND MAIN RESULTS

Compared with the normothermia groups (NO, NR), the neutrophil counts (per milliliter) (NO, 7708 +/- 5704; NR, 10,479 +/- 11,152; HO, 1638 +/- 955; HR, 805 +/- 591) and interleukin-1beta levels (pg/mL) (1180 +/- 439, 1081 +/- 652, 620 +/- 426, 420 +/- 182, respectively) in the bronchoalveolar lavage fluid, the wet-to-dry lung weight ratios (6.0 +/- 0.4, 5.7 +/- 0.4, 5.6 +/- 0.2, 5.2 +/- 0.2, respectively), and histologic acute lung injury scores (8.3 +/- 2.7, 10.4 +/- 3.1, 3.5 +/- 2.1, 3.1 +/- 2.2, respectively) of the hypothermia groups (HO, HR) were lower (all p < .001). Compared with the HO group, the neutrophil counts and protein content (HO, 1367 +/- 490 mug/mL vs. HR, 831 +/- 369 mug/mL) in the bronchoalveolar lavage fluid, the serum lactate dehydrogenase levels (units/mL) (9.1 +/- 3.6 vs. 5.3 +/- 1.5), and the wet-to-dry lung weight ratios of the HR group were lower (all p < .05).

CONCLUSIONS

Reduction of ventilatory frequency in conjunction with hypothermia attenuated many variables of acute lung injury in rats. Use of hypothermia could be exploited as a new approach to lung rest for the ventilatory management of the acutely injured lung.

Hypothermia enhances phosphorylation of I{kappa}B kinase and prolongs nuclear localization of NF-{kappa}B in lipopolysaccharide-activated macrophages

Hypothermia (HT) has been associated with both beneficial and detrimental consequences in various pathophysiological states. While HT is generally thought to have anti-inflammatory and cytoprotective effects, we have previously shown that moderate in vitro HT prolongs TNF-alpha production by LPS-stimulated mononuclear phagocytes, in part by prolonging TNF-alpha gene transcription and activation of the pleiotropic transcription factor NF-kappaB. In this study, we have further characterized the effect of moderate (32 degrees C) and marked (28 degrees C) HT in human monocytic THP-1 cells by showing that even short (2 h) exposure to HT followed by a return to normothermic conditions for 22 h resulted in augmented and prolonged production of TNF-alpha. Production of heat shock protein 72 and activation of heat shock factor 1 are not affected by HT in these studies, suggesting that the effect is not part of a generalized stress response. Using immunoblotting, we have shown that HT augments phosphorylation of IKK-beta and IKK-alpha (up to an 8-fold increase at 28 degrees C and a 3.6-fold increase at 32 degrees C vs. 37 degrees C). Furthermore, nuclear accumulation of NF-kappaB p65 was significantly prolonged in hypothermic cells (1.4- and 2.5-fold more nuclear p65 at 2 and 4 h at 28 vs. 37 degrees C). Reexpression of IkappaB-alpha, which contributes to the termination of NF-kappaB-dependent transcription, was delayed several hours in HT-exposed cells. Thus we have shown that clinically relevant HT alters both cytosolic and nuclear events responsible for NF-kappaB activation and deactivation. Enhanced NF-kappaB activation may contribute to the immunomodulatory effects of HT in various clinical settings.

Hypothermia – it's more than a toy

PURPOSE OF REVIEW

Perioperative hypothermia triples the incidence of adverse myocardial outcomes in high-risk patients; it significantly increases blood loss and augments allogeneic transfusion requirements. Even mild hypothermia increases the incidence of surgical wound infection following colon resection and therefore the duration of hospitalization. Hypothermia adversely affects antibody- and cell-mediated immune defenses, as well as the oxygen availability in the peripheral wound tissues. Mild perioperative hypothermia changes the kinetics and action of various anesthetic and paralyzing agents, increases thermal discomfort, and is associated with delayed postanesthetic recovery.

RECENT FINDINGS

On the other hand however, therapeutic hypothermia may be an interesting approach in various settings. Lowering core temperature to 32-34 degrees C may reduce cell injury by suppressing excitotoxins and oxygen radicals, stabilizing cell membranes, and reducing the number of abnormal electrical depolarizations. Evidence in animals indicates that even mild hypothermia provides substantial protection against cerebral ischemia and myocardial infarction. Mild hypothermia has been shown to improve outcome after cardiac arrest in humans. Randomized trials are in progress to evaluate the potential benefits of mild hypothermia during aneurysm clipping and after stroke or acute myocardial infarction.

SUMMARY

This article reviews recent publications in the field of accidental as well as therapeutic hypothermia, and tries to assess what evidence is available at the present time.