Measuring and Treating Brain Oxygen Levels in Open Heart Surgery

Background

There is a high incidence of cognitive dysfunction, neurological dysfunction, and multi-system organ dysfunction syndrome following cardiac surgery. There is preliminary evidence that optimization of cerebral oxygenation is associated with improved neurological and clinical outcomes.

Cerebral oximetry using near infrared spectroscopy (NIRS) is based on the ability of near-infrared light to penetrate scalp and skull, and its differential intracranial absorbance by oxyhemoglobin (HbO2) and deoxyhemoglobin (Hb). Cerebral oximetry measures regional cerebral tissue oxygen saturation (SctO2) at the microvascular level (arterioles, venules, and capillaries) and provides information on the availability of oxygen in brain tissue. Unlike digital pulse oximetry, SctO2 reflects regional cerebral metabolism and the regional balance of cerebral oxygen supply and demand. NIRS SctO2 is the most promising monitoring technology for the purpose of guiding interventions targeted to improve brain and other organ preservation. The reasons for this include: (1) SctO2 is continuous, non-invasive, and available at the point of care; and (2) SctO2 is a sensitive index of cerebral hypoxia and/or cerebral ischemia, which are the main causes of brain injury in clinical settings. The preliminary work of Murkin strongly suggests that optimizing tissue perfusion using protocol-based treatments that optimize SctO2 decrease end-organ dysfunction in cardiothoracic surgical patients.

Recruitment Methods

Potential subjects are patients who are planned to undergo elective cardiac surgery at Mount Sinai Hospital. Potential subjects will be identified by checking the pre-admission schedule f or cardiothoracic surgery on a daily basis. Patients will be recruited at the surgical pre-admission screening; written informed consent will be obtained.

Risks to Subjects

Cerebral oximetry and computerized neurocognitive testing pose no known risk of harm to subjects.

Cerebral oximetry is an evolving technology that is not currently or imminently becoming a standard of care in monitoring for cardiothoracic surgical patients. The expense and the lack of outcome data make this a discretionary monitoring technology that is advocated by some, but that is not incorporated into any evidence-based guidelines or practice parameters. Therefore, compared with the existing standards of care, patients are not exposed to additional risk by withholding cerebral oximetry information from the practitioners.

Interventions to maintain cerebral oximetry above threshold values could be potentially injurious (e.g., initiating a red blood cell transfusion when it would not otherwise be given), however, any potential risk that is imparted by the interventions to maintain cerebral oximetry values are justified by the benefits of averting low or very low period of cerebral oximetry within the context of this research protocol.

Inclusion criteria

• Adult patients scheduled to undergo elective cardiac or thoracic aortic surgery requiring cardiopulmonary bypass

Exclusion criteria

• Severe preoperative cognitive impairment (i.e., dementia or developmental intellectual disability)
• Sensory or motor impairment that would preclude reliable operation of a computer and keyboard
• Lack of access to use computer-based cognitive evaluation
• Non-English speaking patients
• Renal failure requiring dialysis
• Respiratory failure requiring home oxygen use
• Child's B or C hepatic failure