Tissue oximetry during cardiac surgery and in the cardiac intensive care unit: A prospective observational trial

Background: Cerebral oximetry using near-infrared spectroscopy (NIRS) has well-documented benefits during cardiac surgery. The authors tested the hypothesis that NIRS technology can be used at other sites as a tissue oximeter during cardiac surgery and in the Intensive Care Unit (ICU). Aims: To establish feasibility of monitoring tissue oximetry during and after cardiac surgery, to examine the correlations between tissue oximetry values and cerebral oximetry values, and to examine correlations between oximetry values and mean arterial pressure (MAP) in order to test whether cerebral oximetry can be used as an index organ. Settings and Designs: A large, single-center tertiary care university hospital prospective observational trial of 31 patients undergoing cardiac surgery with cardiopulmonary bypass was conducted. Materials and Methods: Oximetry stickers were applied to both sides of the forehead, the nonarterial line forearm, and the skin above one paraspinal muscle. Data were collected from before anesthesia induction until extubation or for at least 24 h in patients who remained intubated. Statistical Analysis: Categorical variables were evaluated with Chi-square or Fisher's exact tests, while Wilcoxon rank-sum tests or student's t-tests were used for continuous variables. Results: The correlation between cerebral oximetry values and back oximetry values ranged from r = 0.37 to 0.40. The correlation between cerebral oximetry values and forearm oximetry values ranged from r = 0.11 to 0.13. None of the sites correlated with MAP. Conclusions: Tissue oximetry at the paraspinal muscle correlates with cerebral oximetry values while at the arm does not. Further research is needed to evaluate the role of tissue oximetry on outcomes such as acute renal failure, prolonged need for mechanical ventilation, stroke, vascular ischemic complications, prolonged ICU and hospital length of stay, and mortality in cardiac surgery.

Duration of deep hypothermia during aortic surgery and the risk of perioperative blood transfusion.

Deep hypothermia, which is used during thoracic aortic surgery for neuroprotection, is associated with coagulation abnormalities in animal and in vitro models. However, there is a paucity of data regarding the impact of deep hypothermia duration on perioperative bleeding. The objective of the current study was to examine the relationship between the duration of deep hypothermia and perioperative bleeding. A retrospective review of 507 consecutive thoracic aortic surgery patients who had surgery with deep hypothermic circulatory arrest was performed. The degree of bleeding and coagulopathy was estimated using perioperative transfusion. Log linear modeling with Poisson regression was used to analyze the relationship between deep hypothermia duration and perioperative bleeding, while controlling for other preselected variables. There was a significant association between deep hypothermia duration and RBC transfusion (P = 0.001). There was no significant association between deep hypothermia duration and FFP and platelet transfusion (P = 0.18 and P = 0.06). The association between deep hypothermia duration and the amount of bleeding (RBC transfusion) was dependent on total CPB time. In general, for shorter CPB times (approximately 120 to 180 minutes) there was an upward sloping line or positive relationship between deep hypothermia duration and bleeding. However, for cases with longer CPB times (300 to 360 minutes), there was no such relationship. The relationship between deep hypothermia duration and perioperative bleeding is dependent on CPB time. For surgeries with short CPB times (120 to 180 minutes), prolonged deep hypothermia is associated with increased post-operative bleeding, as estimated by RBC transfusion. For cases with longer CPB times (300 to 360 minutes), there appears to be no relationship.