Ann Thorac Surg 2008;86:27-28. doi:10.1016/j.athoracsur.2008.04.111
© 2008 The Society of Thoracic Surgeons
Original Articles: Adult Cardiac
Invited Commentary
Song Wan, MD, FRCS
Division of Cardiothoracic Surgery, The Chinese University of Hong Kong, Prince of Wales Hospital, Hong Kong, China
(Email: swan{at}cuhk.edu.hk).
Although it is well recognized that hypoglycemic and hyperglycemic conditions during cardiopulmonary bypass (CPB) can lead to untoward clinical outcomes, normoglycemia in this particular setting may still need to be better defined. In the current randomized study involving 52 patients undergoing coronary artery bypass grafting (CABG), Albacker and colleagues [1] demonstrated that maintaining a high blood insulin level perioperatively while maintaining the lower limit of normoglycemia could result in a reduced production of pro-inflammatory cytokines after CPB. Echoing with their previous observation [2], such treatment is associated with better myocardial protection as reflected by the lower postoperative release of cardiac troponin I.
Compared with the widely used glucose-insulin-potassium solution, which sometimes leads to hyperglycemia during CPB, the "insulin clamp" technique advocated by Albacker and colleagues [1] seems unique in that high-dose insulin can be safely delivered while maintaining normoglycemia. In addition, the authors are to be commended for demonstrating that high-dose insulin therapy may provide additional anti-inflammatory benefits independent of (or in combination with) tightly controlling blood glucose levels before, during, and after CPB. These observations are of interest and importance, but they do not eliminate the need for further investigation.
A potentially important concern of the current study, as acknowledged by the authors, is the lack of a proper measurement of insulin resistance, which is known to be positively linked with the release of pro-inflammatory cytokines. Without thorough intergroup analysis of this particular issue, it is difficult to reach a solid conclusion. The heterogeneity among the patients recruited (ie, the presence or absence of diabetes mellitus and the mixed diabetic types of patients) can lead to different insulin resistance statues. For instance, unlike the chronic insulin resistance typically seen in diabetic patients, acute insulin resistance in nondiabetic subjects, which occurs only during CPB, may not be predictive of poor outcomes after cardiac operations. Moreover, it has been revealed that diabetic myocardial metabolism carries some special characteristics. Hence, the clinical significance of high-dose insulin therapy for different patient subgroups can only be proven when the underlying mechanisms are completely understood.
Regarding myocardial injury after cardiac surgery, it has been proposed that pro-inflammatory cytokines such as interleukin (IL)-6 and IL-8 do not exert equally important effects. The current study would have provided more meaningful insights into the mechanisms involved if the authors had been able to simultaneously investigate some anti-inflammatory mediators, such as IL-10. In fact, careful evaluation of the anti-inflammatory profiles can always supply much food for thought. We and other investigators have noted that the release of IL-10 during CABG is often proportional to the levels of IL-8. Therefore, to focus all of one's attention on Yin and ignore Yang, or vice versa, may well turn out not to be the best approach to take [3]. At the end of the day, maintaining a balance between the pro-inflammatory and anti-inflammatory responses, rather than blocking each individual mediator, is more likely to be our ideal therapeutic target.
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References
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- Albacker TB, Carvalho G, Schricker T, Lachapelle K. High-dose insulin therapy attenuates systemic inflammatory response in coronary artery bypass grafting patients Ann Thorac Surg 2008;86:20-28.[Abstract/Free Full Text]
- Albacker TB, Carvalho G, Schricker T, Lachapelle K. Myocardial protection during elective coronary artery bypass grafting using high-dose insulin therapy Ann Thorac Surg 2007;84:1920-1927.[Abstract/Free Full Text]
- Wan S, Yim APC. Tai Ji: the law of inflammatory response J Thorac Cardiovasc Surg 2002;124:1071-1073.[Free Full Text]
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High-Dose Insulin Therapy Attenuates Systemic Inflammatory Response in Coronary Artery Bypass Grafting Patients
- Turki Albacker, George Carvalho, Thomas Schricker, and Kevin Lachapelle
Ann. Thorac. Surg. 2008 86: 20-27.
[Abstract]
[Full Text]
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