When transitioning onto cardiopulmonary bypass (CPB) during cardiac surgery, blood flow to the brain is maintained by controlling the CPB flow rate and mean arterial pressure (MAP). CPB flow rates are based on patient body mass, and a MAP target of 60 mmHg is based on clinical experience and guidelines for CPB. However, studies have shown that up to 20% of the population has limited cerebral autoregulation and that conditions such as hypertension can exceed an individual’s autoregulatory limits, leaving room for potential adverse cerebral events. Therefore, maintenance of adequate cerebral blood flow (CBF), oxygen delivery, and metabolism during surgery plays a critical role in reducing the risk of neurological complications. Given its sensitivity to tissue oxygen saturation (StO2), near-infrared spectroscopy (NIRS) is frequently used for intraoperative neuromonitoring modalities; however, StO2 is not a direct marker of CBF, or the energy demands of brain tissue. CBF can be measured by diffuse correlation spectroscopy (DCS) and the unique absorption features of cytochrome c oxidase (oxCCO) offers a means of assessing oxygen metabolism. In this study, an in-house built hyperspectral NIRS/DCS system was used to continuously monitor changes in the redox state of oxCCO (ΔoxCCO), StO2, and CBF in fifteen patients when transitioning onto CPB, with the purpose of evaluating the relationship between MAP on pump and brain blood flow and metabolism. Results demonstrated a nonsignificant ΔoxCCO (-0.13 ± 0.12 μM) in those patients with MAP > 70 mmHg, while a significant decrease in ΔoxCCO (-0.69 ± 0.17 μM) was found for patients for whom their MAP dropped to < 50 mmHg when placed on CPB. These results indicate that ΔoxCCO monitoring has the capability of providing real-time assessment of the effect of MAP on brain health during cardiac surgery, which could help reduce the incidence of cerebral complications.
Cardiac surgery with cardiopulmonary bypass (CPB) is associated with postoperative neurological complications. Targeted mean arterial blood pressure (MAP) during cardiac surgery is used as one method of maintaining adequate cerebral blood flow (CBF) and perfusion pressure. However, an MAP target of 60 mmHg after transitioning on CPB, which is used in many centers, does not account for the reported broad range of lower autoregulatory limits (50-90 mmHg) [1]. In an effort to maintain cerebral perfusion, near-infrared spectroscopy (NIRS) is used to monitor tissue oxygen saturation (StO2); however, StO2 is not a direct marker of CBF or tissue oxygen demand. As an alternative, possible effects on cerebral energy metabolism could be monitored by using hyperspectral NIRS (hsNIRS) to measure changes in the redox state of cytochrome c oxidase (ΔoxCCO), which are linked to ATP production. In this study, an in-house built hsNIRS/diffuse correlation spectroscopy (DCS) was used to monitor ΔoxCCO, CBF and StO2 in patients during cardiac surgery with CPB. Fourteen patients were retrospectively grouped according to the level of their MAP when transitioning onto CPB: high (70-90 mmHg), target (57-69 mmHg), and low MAP (40-56 mmHg). The aim was to evaluate the potential effects of MAP on ΔoxCCO during the transition onto CPB. Results demonstrated that the smallest changes in oxCCO (-0.08 ± 0.24 μM) were observed in the high MAP group and significantly larger changes (-0.73 ± 0.25 μM) in the low MAP group. The results highlight the potential of ΔoxCCO monitoring for real-time assessment of MAP management during CPB with the ultimate aim of mitigating adverse cerebral events.
During surgery with cardiopulmonary bypass (CPB), maintaining adequate cerebral blood flow (CBF) is paramount to prevent adverse neurological outcome; tissue damage can occur if CBF reduction is sufficient to impair energy metabolism. Ten adult patients undergoing cardiothoracic surgery with CPB received perfusion and metabolic neuromonitoring using a novel optical system combining diffuse correlation spectroscopy and broadband near-infrared spectroscopy. CPB onset resulted in large increases in CBF and significant drops in mean arterial pressure and metabolism. No changes were observed transitioning off CPB. Real-time assessment of cerebral perfusion and metabolism could alert clinicians to relevant hemodynamic events before brain injury occurs.
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