Despite the many advances made in cardiac surgery over the past decades, postoperative brain injury remains a dreaded complication that could result in excess mortality and medical resource utilization. Neurologic impairment following cardiac surgery could manifest as a spectrum, from a serious stroke (type I) to subtle cognitive impairment (type II). From the standpoint of prevention, embolization and perioperative cerebral hypoperfusion are the two commonest causes of neuropsychologic deterioration following coronary artery bypass grafting (CABG). In this issue of CHEST (see page 25), Bowles and colleagues suggest that avoiding the use of cardiopulmonary bypass (CPB) could lead to reduced cerebral microemboli during coronary revascularization, as measured by intraoperative transcranial Doppler ultrasonography. Considering that CABG represents more than half the workload in adult cardiac surgery worldwide, cerebral protection is an important issue that affects our decision-making process and impacts on our daily practice.
Should we all switch now to do CABG off pump to protect the brain? To answer this question, one needs first to realize that conventional CABG could affect the brain through a variety of mechanisms. The use of CPB is associated with a complex inflammatory cascade, which may contribute to the development of postoperative neurologic morbidity. In addition to the nonpulsatile flow and potentially inadequate perfusion pressure during CPB, inflammatory reactions may induce cerebral edema by changing permeability across the blood-brain barrier. Increased extracellular brain water has been demonstrated shortly after CPB using MRI. Moreover, microscopic air bubbles or particulates are almost unavoidable during the pump run. Cannulation and manipulation of the aorta could also precipitate embolization. Although aortic manipulation could be minimized by off-pump technique and arterial grafting, recent studies indicate that there are patient-related factors involved in post-CPB brain injury. For instance, advanced age and significant hypertension have been identified as independent risk factors in neurologic derangement after CABG. Other important predictors include proximal aortic atheromas, previous stroke or transient ischemic attack, diabetes, dysrhythmia such as atrial fibrillation, prior CABG, intracardiac thrombus, and peripheral vascular disease.[1,4-6] Thus, CPB is not the only factor involved in neuropsychologic deterioration following CABG.
The glial protein S-100 has recently been shown to be an early marker of brain injury after cardiac surgery. In one pilot study, the level of S-100 at the end of surgery was much higher in the group following conventional CABG than in the off-pump group. However, the Bristol group found that such an increase disappears a few hours after surgery. More importantly, the early release of S-100 may be unrelated to the postoperative neuropsychologic deterioration).[9,10] The Oxford group was unable to show any meaningful differences in cognitive outcomes in patients undergoing CABG with or without CPB using standardized neuropsychologic tests. In a larger study, the incidence of cerebrovascular accident or transient cerebral ischemia was identical (1.6%) in patients undergoing CABG off pump vs on pump.
In summary, the causes for neuropsychologic impairment following CABG are multifactorial, and the exact role of CPB in this remains controversial. While there are definite advantages in off-pump CABG, it would be premature to switch to this technique solely for better cerebral protection based on the currently available evidence. The interesting work by Bowles and colleagues will need to be validated in a prospective, randomized trial involving a much larger patient population using a standardized neurologic assessment protocol. As the interpretation of intraoperative transcranial Doppler ultrasonography could be very subjective, an independent sonographer blinded to the clinical data should review the color-encoded spectral display to avoid possible bias. Research along this direction is expected to have a major impact on our future practice.
Song Wan, MD, PhD Anthony P. C. Yim, DM, FCCP Shatin, Hong Kong, China
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 Wan S, LeClerc JL, Vincent JL. Inflammatory response to cardiopulmonary bypass: mechanisms involved and possible therapeutic strategies. Chest 1997; 112:676-692
 Anderson RE, Li TQ, Hindmarsh T, et al. Increased extracellular brain water after coronary artery bypass grafting is avoided by off-pump surgery. J Cardiothorac Vase Anesth 1999; 13:698-702
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 Hogue CW Jr, Murphy SF, Schechtman KB, et al. Risk factors for early or delayed stroke after cardiac surgery. Circulation 1999; 100:642-647
 Kilminster S, Treasure T, McMillan T, et al. Neuropsychological change and S-100 protein release in 130 unselected patients undergoing cardiac surgery. Stroke 1999; 30:1869-1874
 Anderson RE, Hansson LO, Vaage J. Release of S-100 during coronary artery bypass grafting is reduced by off-pump surgery. Ann Thorac Surg 1999; 67:1721-1725
 Lloyd CT, Ascione R, Underwood MJ, et al. Serum S-100 protein release and neuropsychologic outcome during coronary revascularization on the beating heart: a prospective randomized study. J Thorac Cardiovasc Surg 2000; 119:148-154
 Westaby S, Saatvedt K, White S, et al. Is there a relationship between serum S-100 protein and neuropsychologic dysfunction after cardiopulmonary bypass? J Thorac Cardiovasc Surg 2000; 119:132-137
 Taggart DP, Browne SM, Halligan PW, et al. Is cardiopulmonary bypass still the cause of cognitive dysfunction after cardiac operations? J Thorac Cardiovasc Surg 1999; 118:414-420
 Cartier R, Brann S, Dagenais F, et al. Systematic off-pump coronary artery revascularization in multivessel disease: experience of three hundred eases. J Thorac Cardiovasc Surg 2000; 119:221-229
Dr. Yim is Chief, Division of Cardiothoracic Surgery, The Chinese University of Hong Kong, Prince of Wales Hospital. Dr Wan is a cardiac surgeon at the Prince of Wales Hospital.
Correspondence to: Anthony P. C. Yim, DM, FCCP, Chief, Division of Cardiothoracic Surgery, The Chinese University of Hong Kong, Prince of Whales Hospital, Shatin, Hong Kong, China; e-mail: email@example.com
COPYRIGHT 2001 American College of Chest Physicians
COPYRIGHT 2001 Gale Group