During major surgical procedures performed under general anesthesia, changes in blood flow and oxygen delivery to tissues may occur due to blood loss, hemodynamic fluctuations, and anesthesia-related physiological effects. These changes can lead to impaired tissue perfusion, which is commonly reflected by increased arterial lactate levels. However, lactate measurements are intermittent and may not detect early perfusion abnormalities.
This prospective observational study aims to investigate the relationship between submental tissue oxygenation measured by near-infrared spectroscopy (NIRS), microvascular reactivity assessed by the vascular occlusion test, and arterial lactate levels during major surgery. Adult patients undergoing major abdominal, neurosurgical, or orthopedic procedures will be monitored intraoperatively using non-invasive NIRS techniques, while arterial blood gas analyses will be performed as part of routine clinical care.
The study does not involve any changes to standard anesthesia or surgical management. All treatments and clinical decisions will be made by the responsible care team according to routine practice. By evaluating non-invasive indicators of tissue oxygenation and microvascular function, this study aims to improve the understanding of early intraoperative tissue perfusion changes and their association with metabolic markers.
Adults aged 18 years and older
Scheduled for major surgical procedures under general anesthesia
Major surgery defined as procedures associated with a risk of significant blood loss and/or impaired tissue perfusion, requiring invasive arterial blood pressure monitoring and hourly arterial blood gas analysis
Planned intraoperative arterial catheter placement as part of routine clinical care
Age younger than 18 years
Refusal or inability to provide informed consent
Absence of invasive arterial blood pressure monitoring
Known pregnancy
The study population consists of adult patients aged 18 years and older undergoing major surgical procedures under general anesthesia at a single tertiary care center. Major surgery includes abdominal, neurosurgical, and major orthopedic procedures associated with a risk of significant blood loss and/or impaired tissue perfusion, requiring invasive arterial blood pressure monitoring and hourly arterial blood gas analysis as part of routine clinical care. All participants are enrolled prospectively and monitored intraoperatively without any alteration to standard anesthetic or surgical management.
Cohort
Prospective
No intervention. This is a prospective observational study. Near-infrared spectroscopy measurements are performed for monitoring purposes only and do not influence clinical management.
Other interventionThis study does not include any therapeutic, diagnostic, or experimental intervention. It is a prospective observational study in which non-invasive near-infrared spectroscopy is used solely for intraoperative monitoring of submental tissue oxygenation and microvascular reactivity. Study measurements are collected for research purposes only and do not guide or alter anesthetic, surgical, or transfusion-related clinical decisions. All perioperative management is conducted according to standard institutional practice by the responsible clinical team.
Correlation between submental tissue oxygenation and arterial lactate levels
The strength and direction of the association between intraoperative submental tissue oxygenation measured by near-infrared spectroscopy and arterial lactate levels during major surgery.
Correlation between microvascular reactivity and arterial lactate levels
The association between microvascular reactivity assessed by the vascular occlusion test (reoxygenation slope) and arterial lactate levels measured intraoperatively during major surgery.
Intraoperative submental NIRS desaturation events
Occurrence of submental tissue oxygenation desaturation events, defined as a decrease of 10% or more from baseline lasting at least three minutes during the intraoperative period.
Relationship between submental tissue oxygenation and microvascular reactivity
The association between intraoperative submental tissue oxygenation measured by near-infrared spectroscopy and microvascular reactivity assessed by the vascular occlusion test during major surgery.
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