招請講演(3)
Perioperative Stroke in Non-Neurosurgical and Non-Cardiac Surgery
演者：Adrian W Gelb (Department of Anesthesia and Perioperative Medicine
University of Western Ontario, Canada)
座長：並木昭義 (札幌医科大学麻酔学教室)
Perioperative stroke associated with non-cardiac and non-neurosurgical procedures is rarely reported and therefore assumed to be rare. The reported incidence varies from 0.08% to 4.8% and this again gives the impression that it is relatively infrequent. Unfortunately, almost all the studies have been retrospective reviews and therefore significantly underestimate the true incidence because neurologic deficits may be mild, transient or misdiagnosed as confusion or other behavioral problems. Most strokes in this population are detected by nursing staff. When one considers the huge number of patients who have non-cardiac non-neurosurgical procedures then even these relatively small percentages represent large numbers of patients. For example in the USA this represents approximately 30-40,000 strokes per year.
The importance of stroke in this surgical population was reemphasized by a recent study that found that 10-15% of all strokes seen by the neurology service were in hospitalized patients and 30% of these were in patients who had abdominal or thoracic surgical procedures. A further reason why this patient population merits our attention is the high mortality which is about 30% in patients who have had no previous stroke and as high as 60% in those who have had a previous stroke.
Risk factors include advanced age, atrial fibrillation (odds ratio 2), vascular disease (odds ratio 8), and a previous stroke (odds ratio 14). It has been suggested that perioperative strokes simply represent the (random) occurrence of stroke in the general population. However, a large and detailed review from the Mayo Clinic which included matched controls indicates that surgery (odds ratio 2.9), especially orthopaedic surgery (odds ratio 4), substantially increases the relative risk of having a stroke.
The timing of perioperative strokes is of interest. The vast majority occurs well into the postoperative period and are not hemorrhagic in nature. Therefore, intraoperative events are rarely the direct immediate cause of these neurologic events. Intraoperative hypotension has not been identified as an independent risk factor in these (small) studies although hypotension in the recovery period has been found to be a predictive event. There is however no doubt that if a stroke from an embolus or thrombus were to occur intraoperatively that hypotension would worsen the outcome. This however is different from the hypotension actually causing the stroke.
The majority of perioperative strokes are thought to be embolic in origin with about 30% being associated with arrhythmias especially atrial fibrillation. The exact roles and mechanism by which anesthesia and surgery increase the risk of stroke is unclear but it is perhaps related the hypercoagulable state that occurs perioperatively. Prevention of perioperative stroke should therefore include meticulous prevention and treatment of atrial fibrillation and perhaps more aggressive approaches at preventing the hypercoagulable state.
The prevention of stroke associated with atrial fibrillation has been extensively investigated. The consensus is that oral anticoagulation with warfarin results in a 60% relative risk reduction while aspirin results in only a 20% risk reduction. Patients with chronic atrial fibrillation should continue to receive perioperative anticoagulation. If the stroke has been within the past month, intravenous heparin is appropriate while in other patients subcutaneous heparin or low molecular weight preparations are appropriate. Aspirin may be suitable in addition and it is possible that its use would also result in a reduction in strokes not associated with atrial fibrillation in the perioperative period.
A common clinical management problem in patients who are awaiting surgery and have a stroke is whether surgery should proceed or be delayed. An example would be a patient who has a stroke 1-2 weeks prior to their planned hip arthroplasty. There are no good outcome studies to guide our decision. Clinical studies suggest that cerebral autoregulation returns to normal within 1-3 months after a stroke although there are reports of derangements lasting much longer. In a chronic study of baboons that had their middle cerebral artery occluded, Symon demonstrated that in the infarct region cerebral autoregulation was still impaired three years after the initial event.
The risk of a recurrent stroke/TIA is 0.5% per day in the first month and thereafter 12% per year if the cause is an embolus from atrial fibrillation. In such patients who presented to an emergency department with a transient ischemic attack, by three months 25% of the patients had suffered a recurrent TIA, stroke or death. Although it may be reasonable to proceed with elective surgery within a month of a stroke, I would recommend that elective surgery be deferred as long as possible and the closer one is to the time of the stroke the more careful the anesthesiologist needs to be with the management of blood pressure so as to ensure adequate cerebral perfusion but without producing hemorrhage.
In summary, I believe that perioperative stroke deserves more attention from anesthesiologists and surgeons. The first step is an acceptance that it occurs and is a problem with high mortality that merits our concern. The next step would be better prospective data collection together with a better understanding of the pathophysiology.
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