Cerebral and tissue oximetry

Abstract

The use of near-infrared spectroscopy (NIRS) has been increasingly adopted in cardiac surgery to measure regional cerebral oxygen saturation. This method takes advantage of the fact that light in the near-infrared spectrum penetrates tissue, including bone and muscle. Sensors are placed at fixed distances from a light emitter, and algorithms subtract superficial light absorption from deep absorption to provide an index of tissue oxygenation. Although the popularity of NIRS monitoring is growing, definitive data that prove outcome benefits with its use remain sparse. Therefore, widespread, routine use of NIRS as a standard-of-care monitor cannot be recommended at present. Recent investigations have focused on the use of NIRS in subgroups that may benefit from NIRS monitoring, such as pediatric patients. Furthermore, a novel application of processed NIRS information for monitoring cerebral autoregulation and tissue oxygenation (e.g., kidneys and the gut) is promising.

Trial registration: ClinicalTrials.gov NCT01765504.

Keywords: NIRS; anesthesia; cardiac surgery; cerebral autoregulation; monitor; near-infrared spectroscopy.

Fig. 1

Cerebral oximetry. A: Schematic illustration of cerebral oximetry. Used with permission from Anesth Analg. 2013 Mar;116(3):663-76 B: Absorption spectrum of hemoglobin and oxyhemoglobin with the peak absorption wavelength of oxyhemoglobin (B: 920 nm) and total hemoglobin (A: 760 nm). Hb, deoxyhemoglobin; HbO₂, oxyhemoglobin. Used with permission from Lima et al., Rev Bras Ter Intensiva. 2011 August 23(3):341–351.

Fig. 1

Cerebral oximetry. A: Schematic illustration of cerebral oximetry. Used with permission from Anesth Analg. 2013 Mar;116(3):663-76 B: Absorption spectrum of hemoglobin and oxyhemoglobin with the peak absorption wavelength of oxyhemoglobin (B: 920 nm) and total hemoglobin (A: 760 nm). Hb, deoxyhemoglobin; HbO₂, oxyhemoglobin. Used with permission from Lima et al., Rev Bras Ter Intensiva. 2011 August 23(3):341–351.

Fig. 2

Cerebral oximetry index (COx) recording from a patient undergoing cardiopulmonary bypass. The top graph is the time series for mean arterial pressure (ABP) and the raw left and right regional cerebral oxygen saturation (rSO₂). The bottom graph is the percent of time the patient spent with a blood pressure at each 5 mmHg bin. The right and left COx data in the middle two graphs represent the correlation between regional cerebral oxygen saturation and mean arterial pressure. When mean blood pressure is in the autoregulation range, there is no correlation between regional cerebral oxygen saturation and blood pressure, represented by COx near zero. When blood pressure is outside the limits of autoregulation, regional cerebral oxygen saturation and blood pressure are correlated or cerebral blood flow is pressure passive. In this example, a mean blood pressure > 60 mmHg would ensure that blood pressure is above the lower limit of autoregulation. An upper limit of autoregulation is also demonstrated at a mean blood pressure of approximately 90 mmHg.