Assessment of Cerebral Microvascular Circulation

One of the fundamental goals of anesthesia care is to optimize tissue perfusion and oxygenation, especially in critically ill patients. The standard monitors such as blood pressure, heart rate and pulse oximetry do not directly reflect tissue information and can be misleading sometimes. Coherent hemodynamics spectroscopy (CHS) based on cerebral oximetry is proposed as a continuous and non-invasive tool assessing cerebral microvascular hemodynamics. The investigators propose this study to explore the validity of CHS via comparison with transcranial Doppler measurement in anesthetized surgical patients. The hypotheses are: 1) CHS can effectively measure cerebral microvascular hemodynamic changes associated with mechanical ventilation adjustment during anesthesia. 2) CHS can assess functional status of cerebral autoregulation that is altered by hypercapnia and inhalational anesthetic agent.

One of the essential goals in taking care of anesthetized surgical patients is to maintain adequate tissue perfusion and oxygenation. This is especially true for vital organs like the brain. Unfortunately, neither cerebral oxygen consumption nor cerebral oxygen delivery are directly monitored in the clinical setting while this type of information is of particular importance when taking care of patients inflicted with critical neurologic conditions. In addition, cerebral autoregulation - the mechanism of maintaining a constant cerebral blood flow in the face of arterial blood pressure fluctuation, is also not routinely monitored. The recent establishment of Coherent Hemodynamics Spectroscopy (CHS) is promising in offering what is needed in this context. The uniqueness of CHS is that it does not add any additional monitoring modality other than the cerebral oximeter based on near-infrared spectroscopy (NIRS) that is currently used in clinical care. However, CHS is based on its own innovative algorithm that quantifies microvascular cerebral blood flow and oxygen consumption, separates arterial and venous blood, and assesses functional status of cerebral autoregulation while the conventional cerebral oximeters do not. The investigators have established collaborations with Dr. Fantini from Tufts University and Dr. Tromberg from Beckman Laser Institute who are both leading scientists in Biophotonics research and development. Based on the clinical strength at UCSF, it is the investigators collaborative plan to explore the clinical application of CHS in patients with and without intracranial pathophysiologies. The study protocol has been submitted for review at UCSF.

Eligibility Criteria:
Inclusion Criteria:

* Patients are 18 years of age or older
* Relative healthy (ASA I-II)
* Scheduled for elective intra-abdominal surgeries including colorectal, urological and gynecological procedures under general anesthesia with placements of endotracheal tube and radial arterial catheter.
* Paralysis is required for surgery
* A total of 30 patients will be recruited. These 30 patients are randomly divided into 2 groups based on the technique of anesthesia maintenance during surgery. The anesthesia in one group (n=15) is maintained using inhalational agent. The anesthesia in the other group (n=15) is maintained using intravenous agents.

Exclusion Criteria:

* Patients \<18 years of age
* ASA physical status ≥III
* Emergent or urgent surgery
* Laparoscopic surgery
* History of pulmonary diseases including COPD
* Asthma
* Restrictive lung disease, etc.
* History of cardiac diseases including symptomatic coronary artery disease, heart failure, arrhythmia, moderate to severe valvular abnormalities, and cardiomyopathies
* History of neurological diseases including carotid artery disease, stroke or TIA, etc.