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Research Snapshot Theater: Neuroscience, Adult VIII

Carbogen-Augmented Apnea Testing in Brain Death

Tuesday, March 24, 2026
12:30 PM - 1:30 PM Central Time
Location: Connections Central - RST 06

  • Thomas Schmitzer, BS

    Medical College of Wisconsin, Wisconsin

    Disclosure(s): No relevant financial relationship(s) to disclose.

  • JL

    Jeremy Levin, MD

    Assistant Professor of Surgery
    MEDICAL COLLEGE OF WISCONSIN, Wisconsin

    Disclosure information not submitted.

  • Thomas W. Carver, MD (he/him/his)

    Medical College of Wisconsin Froedtert Hospital, Wisconsin

    Disclosure information not submitted.

Introduction: Carbogen-augmented apnea testing (ACO2) for the evaluation of death by neurologic criteria (DNC) may offer lower complication rates and faster time to test completion when compared to the standard apnea test (TAT), but there are few studies comparing the two. Our institution allows for both methods as part of a DNC protocol with the test selection left to physician discretion. We hypothesized that ACO2 results in shorter testing time, lower rate of test abortion, and comparable complication profile to TAT.


Methods: This study retrospectively reviewed adult ICU patients at a tertiary Level 1 academic medical center who underwent evaluation for brain death using the institutional DNC protocol between January 2012 and May 2025. Patients were included if they underwent TAT or ACO2 testing, were ≥18 years of age, and without neurologic injury that would preclude apnea testing. Collected data included demographics, diagnosis, admission service, clinical parameters related to the apnea test, and frequency of test complications. Comparative statistics were performed using Welch’s t-test, Chi-square test for independence, and Fisher’s exact test as applicable.


Results: An apnea test was performed on 372 patients and ACO2 was used in 242 (65.1%). There was no significant difference between the ACO2 and TAT groups in the occurrence of hypoxemia (5.0% vs. 10.0%, p = 0.06), hypotension (10.3% vs. 6.9% p=0.27), or aborted tests (2.1% vs. 6.2% p=0.07), respectively. There was a significant difference in the duration of apnea testing between the two groups, with the average ACO2 being nearly 2-times shorter than TAT (6.0 minutes vs. 11.8 minutes, p= < 0.001).


Conclusions: Carbogen-augmented apnea testing during the evaluation of DNC significantly reduced the total duration of testing without increasing complications. This study contributes to the body of literature supporting carbogen-augmented apnea testing as a faster and safe procedure for determining death by neurologic criteria.