Measuring the Effect of External Pressure on the Regional Cerebral Oxygen Saturation Monitored by Near-infrared Spectroscopy(NIRS) Technology

Study Overview
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Brief Summary
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During general anaesthesia, to ensure sufficient oxygen supply to the brain, the NIRS technology can be used. It consist of two sensors placed on the forehead, and measures the oxygen saturation of the tissue underneath the sensor. For patients undergoing back surgery placed in the prone position, the NIRS measurement will be affected, because the weight of the head will produce a pressure on the sensors. We wish to investigate how much the measurement is affected. Furthermore we plan to lift the head to remove the pressure, and record the time needed for the measurements to return to baseline.

Detailed Description
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When placed in the prone position an external pressure is applied to the NIRS sensor. This pressure changes the amount of blood in the underlying tissue and thereby has an influence on the regional cerebral oxygen saturation measured. We wish to investigate to which extend this value is affected by the external pressure. Furthermore by lifting the head we want to investigate how long takes for the measurements to return to baseline (no pressure in the supine position). Patients will receive written and oral information about the study, when seen by an anaesthesiologist prior to surgery. Before the anaesthesia one NIRS sensors is placed on the right side of the forehead, avoiding til frontal sinus, and one NIRA sensor is placed on the left musculus deltoideus. The patient is placed in the prone position with the head in af prone-view face mask. Measurements will start after 30 minutes with no change in infusion rate of anaesthetic and no inotropics administered. Registration of NIRS measurements will be done every 15 seconds, first five minutes without intervention, then five minutes with headlift, and last five minutes without interventions. Blood pressure, pulse, saturation, end-tidal carbon dioxide and temperature, will be recorded. Registration wil be om case report forms.

Official Title
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Measuring the Cerebral Oxygen Saturation With NIRS Sensor Placed on the Forehead of Patients in the Prone Position. How Does the External Pressure Affect the Measurement.

Conditions
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Anaesthesia

Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: Surgery in the lumbar spine, in the prone position, with the head in a proneview facemask Free and painless movement of the neck Exclusion Criteria: Known cervical spine pathology.

Ages Eligible for Study
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Minimum Age: 18 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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No

Study Plan
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How is the study designed?
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Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Lumbar spine surgical patients<br>Patients undergoing lumbar spine surgery in the prone position | |

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Change in the regional cerebral oxygen saturation | Measured by Near Infrared Spectroscopy | 15 seconds | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| The duration before the steady state in the regional cerebral oxygen saturation is obtained after changing the head position. |  | 15 seconds | 

 Terms related to the study
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Keywords Provided by Centre Hospitalier Valida
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Near infrared Spectroscopy