Pharmacologic and toxicologic confounders in brain death determination: a multidisciplinary guide

The assessment of comatose ICU patients presents several challenges with respect to the etiology, depth and ultimate outcome. The acceptance in 1959 of the worst-outcome scenarios of coma, i.e. brain death, and the publication of the Harvard Brain Death Criteria in 1968, were key developments in the management of irreversible coma. Pharmacologic confounders often complicate coma assessments, including brain-death determination. Moreover, associated clinical factors during coma, such as organ failure, hypothermia, prolonged continuous infusions, intoxication, and extreme obesity often alter drug metabolism and clearance. Such circumstances may further complicate standard assessments, and guideline recommendations often do not account for altered pharmacokinetics and pharmacodynamics.

The assessment of comatose patients involves complex pharmacologic considerations that significantly impact diagnostic accuracy. Accurate differentiation between pharmacologic, metabolic, and structural causes of coma is essential, particularly since drug-related unconsciousness generally carries a more favorable prognosis than other etiologies. Nonetheless, for best outcomes, it is imperative that the etiology of any drug-induced coma be determined as early as possible. It is important to recognize, however, that routine toxicology screens are not comprehensive. Additionally, the interplay between hypothermia and drug metabolism poses unique challenges, as core temperature significantly affects pharmacokinetic parameters such as hepatic metabolism, leading to reduced drug clearance. Multiorgan dysfunction, common after severe neurological injury, further complicates these assessments. Overdose scenarios introduce additional complexity. While ancillary testing may aid in diagnosis of brain death, they have limitations, particularly in cases of profound intoxication. Additionally, premature use of ancillary testing could lead to misdiagnosis. This review is organized into two main sections: Part I examines general coma and its associated pharmacologic considerations, followed by Part II which focuses on brain death.

Accurate assessment of coma and brain death often requires a multidisciplinary approach, integrating expertise in neurology, pharmacy, critical care, and toxicology. Current brain death guidelines provide a framework but leave open critical gaps in pharmacologic and toxicologic confounders. This review article highlights the importance of multidisciplinary approach to the care of coma and brain death patients and further research to refine diagnostic accuracy and mitigate the risks of premature brain death declarations.