Alterations in intracranial volume following cross-clamping of the descending thoracic aorta in pigs--an experimental study using MRI

Guidelines for the early management of patients with acute ischemic stroke: a guideline for healthcare professionals from the American Heart Association/American Stroke Association

BACKGROUND AND PURPOSE

The authors present an overview of the current evidence and management recommendations for evaluation and treatment of adults with acute ischemic stroke. The intended audiences are prehospital care providers, physicians, allied health professionals, and hospital administrators responsible for the care of acute ischemic stroke patients within the first 48 hours from stroke onset. These guidelines supersede the prior 2007 guidelines and 2009 updates.

METHODS

Members of the writing committee were appointed by the American Stroke Association Stroke Council's Scientific Statement Oversight Committee, representing various areas of medical expertise. Strict adherence to the American Heart Association conflict of interest policy was maintained throughout the consensus process. Panel members were assigned topics relevant to their areas of expertise, reviewed the stroke literature with emphasis on publications since the prior guidelines, and drafted recommendations in accordance with the American Heart Association Stroke Council's Level of Evidence grading algorithm.

RESULTS

The goal of these guidelines is to limit the morbidity and mortality associated with stroke. The guidelines support the overarching concept of stroke systems of care and detail aspects of stroke care from patient recognition; emergency medical services activation, transport, and triage; through the initial hours in the emergency department and stroke unit. The guideline discusses early stroke evaluation and general medical care, as well as ischemic stroke, specific interventions such as reperfusion strategies, and general physiological optimization for cerebral resuscitation.

CONCLUSIONS

Because many of the recommendations are based on limited data, additional research on treatment of acute ischemic stroke remains urgently needed.

Partial aortic occlusion and cerebral venous steal: venous effects of arterial manipulation in acute stroke

Acute ischemic stroke therapy emphasizes early arterial clot lysis or removal. Partial aortic occlusion has recently emerged as an alternative hemodynamic approach to augment cerebral perfusion in acute ischemic stroke. The exact mechanism of cerebral flow augmentation with partial aortic occlusion remains unclear and may involve more than simple diversion of arterial blood flow from the lower body to cerebral collateral circulation. The cerebral venous steal hypothesis suggests that even a small increase in tissue pressure in the ischemic area will divert blood flow to surrounding regions with lesser tissue pressures. This may cause no-reflow (absence of flow after restoration of arterial patency) in the ischemic core and "luxury perfusion" in the surrounding regions. Such maldistribution may be reversed with increased venous pressure titrated to avoid changes in intracranial pressure. We propose that partial aortic occlusion enhances perfusion in the brain by offsetting cerebral venous steal. Partial aortic occlusion redistributes blood volume into the upper part of the body, manifested by an increase in central venous pressure. Increased venous pressure recruits the collapsed vascular network and, by eliminating cerebral venous steal, corrects perifocal perfusion maldistribution analogous to positive end-expiratory pressure recruitment of collapsed airways to decrease ventilation/perfusion mismatch in the lungs.

Cerebral haemodynamics during thoracic- and thoracoabdominal aortic aneurysm repair

OBJECTIVE

To investigate cerebral haemodynamics during operations for thoracic and thoracoabdominal aortic aneurysms.

DESIGN

Prospective clinical study.

MATERIAL

10 patients operated on consecutively with resection for thoracic (5) or thoracoabdominal aortic (5) aneurysms.

METHODS

Blood flow velocity of the middle cerebral artery was measured through a temporal approach using a TC Doppler with a 2 MHz probe. Recordings were made during induction of anaesthesia and performed continuously before, during and after cross-clamping of the aorta.

RESULTS

Following 10 min. of aortic cross-clamping blood flow velocity of the middle cerebral artery increased from 44 to 55 cm/s (p < 0.01). A further increase to 69 cm/s (p < 0.01) was observed 5 min after declamping. The pulsatility index averaged 0.74 increasing to 1.21 (p < 0.05) at clamping and 0.87 (p < 0.05) after declamping.

CONCLUSION

There was an increased blood flow velocity of the middle cerebral artery during cross-clamping of the descending thoracic aorta in patients operated on for thoracic and thoracoabdominal aortic aneurysms. This increase in cerebral blood flow and blood volume could explain the acute increase in cerebrospinal fluid pressure observed during cross-clamping of the thoracic aorta.