These results support the use of warm CPB (34 degrees C) in patients undergoing coronary artery bypass surgery regardless of the type of blood gas strategy.

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Regional cerebral oxygen saturation (rSo 2 ) obtained from near-infrared spectroscopy (NIRS) provides valuable information during cardiac surgery. The rSo 2 is calculated from the proportion of oxygenated to total hemoglobin in the cerebral vasculature. Root O3 cerebral oximetry (Masimo) allows for individual identification of changes in total (ΔcHbi), oxygenated (Δo 2 Hbi), and deoxygenated (ΔHHbi) hemoglobin spectral absorptions. Variations in these parameters from baseline help identify the underlying mechanisms of cerebral desaturation. This case series represents the first preliminary description of Δo 2 Hbi, ΔHHbi, and ΔcHbi variations in 10 cardiac surgical settings. Hemoglobin spectral absorption changes can be classified according to 3 distinct variations of cerebral desaturation. Reduced cerebral oxygen content or increased cerebral metabolism without major blood flow changes is reflected by decreased Δo 2 Hbi, unchanged ΔcHbi, and increased ΔHHbi Reduced cerebral arterial blood flow is suggested by decreased Δo 2 Hbi and ΔcHbi, with variable ΔHHbi. Finally, acute cerebral congestion may be suspected with increased ΔHHbi and ΔcHbi with unchanged Δo 2 Hbi. Cerebral desaturation can also result from mixed mechanisms reflected by variable combination of those 3 patterns. Normal cerebral saturation can occur, where reduced cerebral oxygen content such as anemia is balanced by a reduction in cerebral oxygen consumption such as during hypothermia. A summative algorithm using rSo 2 , Δo 2 Hbi, ΔHHbi, and ΔcHbi is proposed. Further explorations involving more patients should be performed to establish the potential role and limitations of monitoring hemoglobin spectral absorption signals. (Anesth Analg 2022;135:1304-14) GLOSSARY ΔcHbi = index representing changes in the total (ΔHHbi + Δo 2 Hbi) hemoglobin component of the rSo 2 ; ΔHHbi = index representing changes in the deoxygenated hemoglobin component of the rSo 2 ; Δo 2 Hbi = index representing changes in the oxygenated hemoglobin component of the rSo 2 ; Cao 2 = arterial oxygen content; CBF = cerebral blood flow; CMRo 2 = cerebral metabolic rate of oxygen; COVID-19 = coronavirus disease 2019; CPB = cardiopulmonary bypass; dP/dT = change in the pressure over time ratio; HITS = high-intensity transient signal; IT = intratracheal; LE = lower extremity; LV = left ventricular; LVEF = left ventricular ejection fraction; NIRS = near-infrared spectroscopy; pEEG = processed electroencephalography; Pfa = femoral artery pressure; Ppa = pulmonary artery pressure; Pra = radial arterial pressure; Prv = right ventricular pressure; rSo 2 = regional oxygen saturation; RV = right ventricular; SVC = superior vena cava; TCD = transcranial Doppler; UE = upper extremity

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