Correspondence
Perioperative Stroke
N Engl J Med 2007; 356:2325-2327May 31, 2007
- Article
To the Editor:
In his review of perioperative stroke, Selim (Feb. 15 issue)1 states that regional anesthesia may pose less risk of perioperative complications than general anesthesia and that “isoflurane and thiopentone may provide neuroprotection.” However, the references that he cites2,3 do not provide support for these contentions. Breen and Park's2 review of the literature showed that no conclusions could be drawn about the risk of stroke associated with general as compared with regional anesthesia for carotid endarterectomy. In fact, the results of the randomized trials reviewed indicated that postoperative hypotension was more likely after regional anesthesia. The differences that have been identified may not have a great clinical impact and require further study.
Turner et al.3 reviewed the literature on agents for induction of general anesthesia and conclude that thiopental, propofol, and etomidate have similar effects on intracranial pressure, cerebral blood flow, and cerebral oxygen consumption, so the selection of an agent should be based on other considerations. They did not discuss isoflurane. The most one can conclude from the extant literature is that there are a number of hypotheses to test with robust methods before clinical recommendations can be made.
3 ReferencesRobert E. Kettler, M.D.
Medical College of Wisconsin, Milwaukee, WI 53226-3596
rkettler@mcw.edu 1
Selim M . Perioperative stroke. N Engl J Med 2007;356:706-713
Full Text | Web of Science | Medline2
Breen P ,Park KW . General anesthesia versus regional anesthesia. Int Anesthesiol Clin 2002;40:61-71
CrossRef | Medline3
Turner BK ,Wakim JH ,Secrest J ,Zachary R . Neuroprotective effects of thiopental, propofol, and etomidate. AANA J 2005;73:297-302
Medline
To the Editor:
Selim emphasizes that atrial fibrillation is an important cause of perioperative stroke, and he outlines its predictors. The current literature, however, does not provide support for including high magnesium levels among the risk factors for postoperative atrial fibrillation, as Selim does in Table 5 of his review. In fact, magnesium supplementation has been shown to have varying degrees of benefit in reducing the incidence of postoperative atrial fibrillation.1-4 Selim notes that beta-blockers and amiodarone are effective as prophylaxis against the development of postoperative atrial fibrillation. Magnesium supplementation may also have a role.
4 ReferencesAmitabh Parashar, M.D.
Carilion Clinic, Roanoke, VA 24018
aparashar@carilion.com 1
Burgess DC ,Kilborn MJ ,Keech AC . Interventions for prevention of post-operative atrial fibrillation and its complications after cardiac surgery: a meta-analysis. Eur Heart J 2006;27:2846-2857
CrossRef | Web of Science | Medline2
Mitchell LB . Prophylactic therapy to prevent atrial arrhythmia after cardiac surgery. Curr Opin Cardiol 2007;22:18-24
CrossRef | Web of Science | Medline3
Henyan NN ,Gillespie EL ,White CM ,Kluger J ,Coleman CI . Impact of intravenous magnesium on post-cardiothoracic surgery atrial fibrillation and length of hospital stay: a meta-analysis. Ann Thorac Surg 2005;80:2402-2406
CrossRef | Web of Science | Medline4
Naito Y ,Nakajima M ,Inoue H ,Hibino N ,Mizutami E ,Tsuchiya K . Prophylactic effect of magnesium infusion against postoperative atrial fibrillation. Kyobu Geka 2006;59:793-797
Medline
To the Editor:
With regard to the article by Selim, the unique anatomy of the vertebral arteries and their vulnerability to mechanical compression at the atlantoaxial and atlanto-occipital junction during neck angulation and hyperextension constitute an overlooked cause of perioperative stroke.1,2 We designed a study to simulate tracheal intubation in 160 consecutive high-risk patients (mean age, 66 years) who were scheduled for surgery with dynamic magnetic resonance angiography and flow analysis. Unsuspected hypoplastic vertebral-artery flow of less than 50 ml per second was present in 40 patients (25%). Reduced basilar-artery flow was noted with increased microinfarctions on magnetic resonance imaging (77% vs. 38% in patients with normal basilar-artery flow). Patients with unsuspected carotid occlusion (six patients) and those with vertebral-artery occlusion (two patients) also had reduced basilar-artery flow.
Carotid ultrasonography, although less costly, is also less accurate, with incomplete imaging of the vertebral arteries. Flow velocities and vessel diameters tend to be lower on the right side, with lower net flow volume, and they are significantly lower in women than in men.3 Ultrasonography is 80% as accurate as angiography in detecting vertebral-artery size and only 90% as accurate in determining the direction of flow.4
4 ReferencesMichael I. Weintraub, M.D.
New York Medical College, Valhalla, NY 10595
miwneuro@pol.net Andre Khoury, M.D.
White Plains Hospital, White Plains, NY 106011
Weintraub MI ,Khoury A . Cerebral hemodynamic changes induced by simulated tracheal intubation: a possible role in peri-operative stroke? Magnetic resonance angiography and flow analysis in 160 cases. Stroke 1998;29:1644-1649
CrossRef | Web of Science | Medline2
Weintraub MI ,Khoury A . Critical neck positioning as an independent risk factor for posterior circulation stroke: a magnetic resonance angiographic analysis. J Neuroimaging 1995;5:16-22
Medline3
Seidel E ,Eicke BM ,Tettenborn B ,Krummenauer F . Reference values for vertebral artery flow volume by duplex sonography in young and elderly adults. Stroke 1999;30:2692-2696
CrossRef | Web of Science | Medline4
Davis PC ,Nilsen B ,Braun IF ,Hoffman JC . A prospective comparison of duplex sonography vs. angiography of the vertebral arteries. AJNR Am J Neuroradiol 1986;7:1059-1064
Web of Science | Medline
Author/Editor Response
When I chose the references for this review, my intent was not to highlight the specific results of a particular study but rather to direct the reader to a balanced discussion of the topic, given the limited space for the article. With regard to local as compared with general anesthesia, various studies have had mixed results. A Cochrane meta-analysis of 41 nonrandomized and 7 small randomized studies showed that the use of local anesthesia was associated with significant reductions in the odds of death and stroke within 30 days after carotid surgery in the nonrandomized studies.1 In the randomized studies, the use of local anesthesia was associated with a significant reduction in hemorrhagic complications, but there was insufficient evidence of a reduction in perioperative stroke. Therefore, my statement that “regional anesthesia is less likely than general anesthesia to result in perioperative complications” is not inconsistent with the literature.
Kettler points to postoperative hypotension as a complication of regional anesthesia. I reiterate that most perioperative strokes are embolic. Hypoperfusion is responsible for only a small number of such strokes. Regional anesthesia facilitates neurologic assessments during surgery, thus permitting timely detection and treatment of stroke, and it is associated with less blood loss and shorter hospital stays,2 thereby decreasing postoperative thromboembolic complications. A quick literature search (www.pubmed.com) shows several reports that provide support for the neuroprotective properties of isoflurane,3 but I concur that the choice of the anesthetic agent should not be based solely on its putative neuroprotective properties.
Parashar questions whether a high level of magnesium is a risk factor for postoperative atrial fibrillation. Although several studies suggest that hypomagnesemia is associated with postoperative atrial fibrillation, there are conflicting data in the literature.4 Therefore, it would have been more appropriate to point to “disturbances of serum magnesium” instead of high magnesium levels. He also correctly suggests that magnesium supplementation may be beneficial in reducing the incidence of atrial fibrillation. The effects of magnesium seem to be independent of serum magnesium concentrations, and they are probably mediated through its direct effects on sinoatrial-node conduction. Most guidelines for the management of postoperative atrial fibrillation provide level A evidence of the efficacy of beta-blockers and amiodarone, in contrast to level B evidence for magnesium.5
Finally, I thank Weintraub and Khoury for sharing their findings on the pathophysiological basis of some perioperative strokes.
5 ReferencesMagdy Selim, M.D., Ph.D.
Beth Israel Deaconess Medical Center, Boston, MA 02215
mselim@bidmc.harvard. edu 1
Rerkasem K ,Bond R ,Rothwell PM . Local versus general anaesthesia for carotid endarterectomy. Cochrane Database Syst Rev 2004;2:CD000126-CD000126
Medline2
Mofidi R ,Nimmo AF ,Moores C ,Murie JA ,Chalmers RT . Regional versus general anaesthesia for carotid endarterectomy: impact of change in practice. Surgeon 2006;4:158-162
CrossRef | Web of Science | Medline3
Zheng S ,Zuo Z . Isoflurane preconditioning induces neuroprotection against ischemia via activation of P38 mitogen-activated protein kinases. Mol Pharmacol 2004;65:1172-1180
CrossRef | Web of Science | Medline4
Parikka H ,Toivonen L ,Pellinen T ,Verkkala K ,Jarvinen A ,Nieminen MS . The influence of intravenous magnesium sulphate on the occurrence of atrial fibrillation after coronary artery by-pass operation. Eur Heart J 1993;14:251-258
CrossRef | Web of Science | Medline5
Dunning J, Treasure T, Versteegh M, Nashef SA, EACTS Audit and Guidelines Committee
CrossRef | Web of Science | Medline
