To test whether the variations of tissue hemoglobin concentration (鈭?sub>THb) measured by the FORE-SIGHT
TM cerebral oximeter can accurately detect changes in arterial hemoglobin concentration (鈭?sub>AHb) 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 (THb) was recorded continuously via 2 sensors applied on the forehead and connected to the cerebral oximeter. Arterial hemoglobin concentration (AHb) 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 鈭?sub>THb and 鈭?sub>AHb was 0.4 (p<0.001). After exclusion of Hb variations<5%, the trending ability of THb to predict 鈭?sub>AHb was 87%. However, the Bland and Altman plot graph for THb and AHb showed major limits of agreement (2.4 times the standard deviation). Central venous pressure and carbon dioxide tension were linked independently and positively with THb (p = 0.03).
Conclusions
Continuous monitoring of THb cannot accurately track variations of AHb during the transition from pulsatile to continuous flow and vice versa in cardiac surgery. Local hemodynamic factors such as PaCO2 and vasodilation significantly impact THb. In this setting, THb monitoring should not be used to guide eventual blood transfusion management.
