‘Where there’s smoke, there’s fire’: near-infrared spectroscopy as a safeguard perioperative perfusion tool in cardiac surgery

We read with great interest the systematic review by Semrau et al. [1] regarding the value of cerebral oximetry monitoring using near-infrared spectroscopy (NIRS) in preventing neurologic damage after cardiac surgery. The authors conclude that no clear answer remains as to whether or not we should be monitoring or intervening on cerebral desaturations.

We agree with the authors that there are a number of significant limitations among different studies that evaluate NIRS in cardiac surgery, as related to definition of outcomes, the assessment methods, the algorithms of intervention to reverse the desaturation and the time-frame of the studies. However, we strongly oppose to the clinical implication of potentially disregard cerebral desaturation during cardiac surgery.

Certainly, NIRS is ‘blind’ to cerebral embolic events or hypoperfusion affecting the brain stem or the middle and posterior cerebral circulation since this technology actually provides mixed arterial and venous saturation monitoring in the areas of frontal lobes. Cerebral blood flow is preserved physiologically at the expense of relative systemic hypoperfusion; thus, the presence of cerebral desaturation reflects significant systemic circulatory compromise, correspondingly. By all means, cerebral NIRS represents a delicate easy-to-use tool for monitoring adequacy of tissue perfusion by using the brain as an index and not the target organ [2]. This concept is allied to the intriguing findings by Heringlake et al. [3] that baseline cerebral oxygen saturation is an independent and more accurate predictor of 30-day and 1-year mortality than the EuroSCORE.

Continuous monitoring of the adequacy of global tissue perfusion during cardiac surgery poses a significant challenge to the cardiac team (cardiac surgeon, anaesthesiologist, perfusionist). While contemporary technology enables real-time in-line monitoring of critical metabolic variables during cardiopulmonary bypass, NIRS represents a perfusion tool that may safeguard malperfusion during the whole perioperative period [4]. This integrated concept has not been addressed by any randomized study.

Perturbations in cerebral oximetry, although highly sensitive, are conversely substantially non-specific. On the other hand, neurologic outcome combines stroke, that is primarily embolic, with neurocognitive decline and delirium that are multifactorial and related mainly to systemic or regional cerebral hypoperfusion. By using NIRS exclusively for neuro-monitoring, we just see the tip of the iceberg, which is actually tissue microcirculation.

We believe that ‘where there’s smoke, there’s fire’. Therefore, we advocate NIRS as a safeguard perioperative monitoring tool in cardiac surgery. Any desaturation observed should be clinically evaluated and translated by the multidisciplinary operating team followed by action, aiming to correct the underlying derangement and prevent ultimately remote end-organ damage [5].

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