To the Editor
We read with great interest the retrospective study titled “Incidence of Concurrent Cerebral Desaturation and Electroencephalographic Burst Suppression in Cardiac Surgery Patients” by Ramachandran et al.1 The authors found that cerebral desaturation during cardiac surgery, particularly during cardiopulmonary bypass (CPB), is closely linked to intraoperative burst suppression. They suggest that targeted interventions to address cerebral desaturation may help mitigate burst suppression and enhance postoperative cognitive function. This research broadens our understanding of perioperative neuroprotection, though several aspects remain to be discussed.
First, intraoperative hypothermia, a significant confounding factor, was not considered in their analysis. In the study by Pedemonte et al,2 the lowest CPB temperature and physical function, both unadjusted in the current study, were identified as predictors of burst suppression. Additionally, hypothermia reduces anesthetic requirements, necessitating dose adjustments to prevent burst suppression, as persistent burst suppression during surgery is linked to postoperative delirium (POD).3 Including patient physical function status and intraoperative temperature data would therefore enhance our understanding of the relationship between cerebral desaturation, burst suppression, and neurological outcomes.
Furthermore, Joshi et al4 have shown that cerebral blood flow (CBF) autoregulation may be disrupted during CPB, with patients experiencing impaired CBF autoregulation being at greater risk for stroke. Since perioperative stroke often follows cerebral desaturation, dysfunction in CBF autoregulation is strongly correlated with cerebral desaturation during rewarming. Incorporating these factors into future studies could provide more comprehensive insights and guide the development of more effective neuroprotective strategies during cardiac surgery.
Lastly, the assumed association between burst suppression and POD is debatable. In the previous ENGAGES randomized clinical trial,5 it was demonstrated that among older adults undergoing major surgery, EEG-guided anesthetic administration, compared with usual care, did not reduce the incidence of postoperative delirium. This finding underscores the complexity of the pathophysiology of POD.
Once again, we would like to express our gratitude to Ramachandran et al for their significant contribution to this field. We look forward to future studies that build on their work and further advance neuroprotective strategies during cardiac surgery.
Cheng-Ying Chang, MD
Department of Anesthesiology
Far Eastern Memorial Hospital
New Taipei City, Taiwan
Li-Chung Chen, MD
Department of Anesthesiology
Far Eastern Memorial Hospital
New Taipei City, Taiwan
Cheng-Wei Lu, MD, PhD
Department of Anesthesiology
Far Eastern Memorial Hospital
New Taipei City, Taiwan
Department of Mechanical Engineering
Yuan Ze University
Taoyuan, Taiwan
drluchengwei@gmail.com