Journal of veterinary internal medicine2015; 29(2); 663-672; doi: 10.1111/jvim.12570

Cerebral and brainstem electrophysiologic activity during euthanasia with pentobarbital sodium in horses.

Abstract: An overdose of pentobarbital sodium administered i.v. is the most commonly used method of euthanasia in veterinary medicine. Determining death after the infusion relies on the observation of physical variables. However, it is unknown when cortical electrical activity and brainstem function are lost in a sequence of events before death. Objective: To examine changes in the electrical activity of the cerebral cortex and brainstem during an overdose of pentobarbital sodium solution for euthanasia. Our testing hypothesis is that isoelectric pattern of the brain in support of brain death occurs before absence of electrocardiogram (ECG) activity. Methods: Fifteen horses requiring euthanasia. Methods: Prospective observational study. Horses with neurologic, orthopedic, and cardiac illnesses were selected and instrumented for recording of electroencephalogram, electrooculogram, brainstem auditory evoked response (BAER), and ECG. Physical and neurologic (brainstem reflexes) variables were monitored. Results: Loss of cortical electrical activity occurred during or within 52 seconds after the infusion of euthanasia solution. Cessation of brainstem function as evidenced by a lack of brainstem reflexes and disappearance of the BAER happened subsequently. Despite undetectable heart sounds, palpable arterial pulse, and mean arterial pressure, recordable ECG was the last variable to be lost after the infusion (5.5-16 minutes after end of the infusion). Conclusions: Overdose of pentobarbital sodium solution administered i.v. is an effective, fast, and humane method of euthanasia. Brain death occurs within 73-261 seconds of the infusion. Although absence of ECG activity takes longer to occur, brain death has already occurred.
Publication Date: 2015-03-19 PubMed ID: 25800436PubMed Central: PMC4895516DOI: 10.1111/jvim.12570Google Scholar: Lookup
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  • Journal Article
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The research paper studies the sequence of the loss of electrical activity in the brain and the heart during euthanasia of horses performed using pentobarbital sodium solution. It demonstrates that brain death occurs first, followed by the cessation of electrocardiogram (ECG) activity.

Objective and Hypothesis

The objective of this exploratory study was to understand the sequence of organ shutdown when an overdose of pentobarbital sodium solution is given intravenously for euthanasia. The researchers hypothesized that brain death, marked by an isoelectric pattern in the brain, may occur before the cessation of ECG activity.


  • The observational study involved the euthanasia of 15 horses suffering from neurological, orthopedic, and cardiac conditions.
  • Using various medical instruments, the scientists recorded electroencephalogram, electrooculogram, brainstem auditory evoked response (BAER), and ECG data during the administration of euthanasia solution.
  • Along with these electronic variables, they observed and noted physical variables like brainstem reflexes.


  • The results showed that the loss of cortical electrical activity happened during or within 52 seconds of the infusion of the euthanasia solution.
  • The cessation of brainstem function followed this, marked by the lack of brainstem reflexes, and the disappearance of BAER.
  • Despite the heart sounds becoming undetectable, the arterial pulse disappearing, and the mean arterial pressure dropping, ECG remained the last electronic variable to be lost, between 5.5 to 16 minutes after the end of the infusion.


In conclusion, administering an overdose of pentobarbital sodium solution was found to be a quick, effective, and humane method of euthanasia. The research concluded that brain death, an important marker of overall death, happened within 73 to 261 seconds of the infusion. The absence of ECG activity, although delayed, confirmed the occurrence of brain death.

Cite This Article

Aleman M, Williams DC, Guedes A, Madigan JE. (2015). Cerebral and brainstem electrophysiologic activity during euthanasia with pentobarbital sodium in horses. J Vet Intern Med, 29(2), 663-672.


ISSN: 1939-1676
NlmUniqueID: 8708660
Country: United States
Language: English
Volume: 29
Issue: 2
Pages: 663-672

Researcher Affiliations

Aleman, M
  • Department of Medicine and Epidemiology, School of Veterinary Medicine, University of California, Davis, CA, 95616.
Williams, D C
    Guedes, A
      Madigan, J E

        MeSH Terms

        • Animals
        • Blood Pressure
        • Brain Stem / drug effects
        • Brain Stem / physiology
        • Cerebrum / drug effects
        • Cerebrum / physiology
        • Electroencephalography / veterinary
        • Euthanasia, Animal / methods
        • Female
        • Horses / physiology
        • Hypnotics and Sedatives / administration & dosage
        • Hypnotics and Sedatives / pharmacology
        • Male
        • Pentobarbital / administration & dosage
        • Pentobarbital / pharmacology


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