Tissue hemoglobin monitoring is unable to follow variations of arterial hemoglobin during transitions from pulsatile to constant flow in cardiac surgery.

Objective To test whether the variations of tissue hemoglobin concentration (∆ T Hb) measured by the FORE-SIGHT TM cerebral oximeter can accurately detect changes in arterial hemoglobin concentration (∆ A Hb) before, during, and after cardiopulmonary bypass. Design A prospective clinical study. Setting Cardiac surgery operating room. Participants Thirty patients scheduled for cardiac surgery. Interventions Tissue hemoglobin concentration ( T Hb) was recorded continuously via 2 sensors applied on the forehead and connected to the cerebral oximeter. Arterial hemoglobin concentration ( A Hb) was measured in a hematology analyzer laboratory. Hemodynamic and respiratory parameters as well as epidemiologic data also were noted. Data were collected at 3 perioperative times: After induction of anesthesia, 10 minutes after cardioplegia, and at the end of the surgery. Measurements and Main Results Ninety pairs of data were collected. The coefficient of linear regression between ∆ T Hb and ∆ A Hb was 0.4 (p T Hb to predict ∆ A Hb was 87%. However, the Bland and Altman plot graph for T Hb and A Hb showed major limits of agreement (2.4 times the standard deviation). Central venous pressure and carbon dioxide tension were linked independently and positively with T Hb (p = 0.03). Conclusions Continuous monitoring of T Hb cannot accurately track variations of A Hb during the transition from pulsatile to continuous flow and vice versa in cardiac surgery. Local hemodynamic factors such as PaCO 2 and vasodilation significantly impact T Hb. In this setting, T Hb monitoring should not be used to guide eventual blood transfusion management.