Modeling the Effect of EtCO2 on Cerebral Oxygenation

Study Overview
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Brief Summary
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The aim of this study was to investigate the relationship between the end-tidal carbon dioxide (EtCO2) and cerebral oxygen saturation (rSO2) and to identify the covariates in the pharmacodynamic relationship between EtCO2 and rSO2.

Detailed Description
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Even though mild hypercapnia in the beach chair position (BCP) under general anesthesia was effective in reducing cerebral desaturation, there is no comprehensive data with regard to the dose-effect relationship of EtCO2 on rSO2 in the BCP under general anesthesia. Pharmacodynamic modeling can be useful in describing this relationship in which concurrent mean arterial pressure changes and disease state can be considered as covariates. Therefore, we investigated the relationship between the EtCO2 and rSO2 and identified the covariates in the pharmacodynamic relationship between EtCO2 and rSO2.

Official Title
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Pharmacodynamic Modeling of the Effect of End-tidal Carbon Dioxide on Cerebral Oxygen Saturation in Beach Chair Position Under General Anesthesia

Conditions
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Shoulder Surgery

Intervention / Treatment
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* Other: EtCO2


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: Age ≥19 years who were scheduled to elective arthroscopic shoulder surgery in BCP under general anesthesia Exclusion Criteria: Previous cerebrovascular disease, orthostatic hypotension, and the American Society of Anesthesiologists physical status IV or V

Ages Eligible for Study
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Minimum Age: 19 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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Design Details

Primary Purpose: Prevention
Intervention Model: Single Group Assignment
Masking: None (Open Label)


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Experimental: Change of EtCO2<br>Changes of rSO2 after adjustment of EtCO2 between 27-45 mmHg | Other: EtCO2<br>* Initial data collection during BCP was performed following three conditions were satisfied: after start of surgery; at least 15 min after BCP (for stabilization of MAP); after ventilation frequency was adjusted to produce EtCO2 of 27-29 mmHg with tidal volume of 8 ml/kg. Data was collected every 3 min after decreasing ventilation frequency by 1-2 breaths/min to increase EtCO2 until 42-45 mmHg. Once the value of EtCO2 42-45 mmHg was reached, ventilator frequency was increased in the same way to decrease EtCO2 until 27-29 mmHg. Fraction of inspired oxygen of 50% was maintained and end-tidal desflurane concentration was adjusted to achieve bispectral index values of 40-55 during data collection.<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| The parameters of indirect response model | fractional turnover rate (kout), baseline rSO2, baseline EtCO2, linear slope governing the relation between EtCO2 and rSO2 | 60 min | 
| The factors that influence the model parameters | mean blood pressure, end-tidal desflurane concentration, age, sex, hypertention, diabetes mellitus, weight | 60 min |