Author Date

2020-03-20

Degree Name

BS

Department

Biology

College

Life Sciences

Defense Date

2020-02-24

Publication Date

2020-03-20

First Faculty Advisor

Dr. Stephen Piccolo

First Faculty Reader

Dr. Jacob Crandall

Honors Coordinator

Dr. Steven Peck

Keywords

burst suppression, neurocritical care, causal inference

Abstract

This thesis examines the effects of brain inactivation (burst suppression) on mortality in mechanically ventilated ICU patients. Past research has associated burst suppression with increased mortality. However, the effects of burst suppression on ICU patients while taking into account the relative contributions of propofol (a sedative), and critical illness to mortality, and whether preventing burst suppression might reduce mortality, has not yet been quantified. This thesis explores this relationship, and the effect of critical illness and propofol infusion on burst suppression to understand what drives burst suppression.

To measure the relationship between burst suppression, critical illness, propofol infusion, and mortality, we use a “counterfactual” randomized controlled trial. This is a form of causal inference that allows one to estimate causal effects from retrospective data. We create a causal graph and train independent multivariate regression models using random forests, XGBoost, and logistic regression to estimate causal effects.

These results show that patients with mild vs. severe illness are expected to have a 39% difference in burst suppression burden, 95% CI [8-66%], and a 35% difference in mortality [29-41%]. Assigning patients to maximal (100%) burst suppression burden is expected to increase mortality by 12% [7-17%] compared to 0% burden.

Our analysis clarifies how important factors contribute to mortality in ICU patients. Burst suppression appears to contribute to mortality but is primarily an effect of critical illness rather than propofol infusion. Thus, limiting burst suppression through clinical intervention may be more difficult than previously thought.

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