Reduced heart rate variability across the first 24 h of intensive care unit in non-survivable traumatic brain injuries

Abstract

Despite major improvements in the resuscitation and management of a Traumatic Brain Injury (TBI), predicting patient trajectories remains difficult to establish, particularly within the first 24 h of ICU admission. The natural variation of the hearts beat-to-beat intervals (heart rate variability – HRV) has demonstrated promise in the literature as a marker of physiological and pathological conditions, including autonomic nervous system function.

Within the TBI population subgroup, enhanced outcome prediction may enable better resource allocation and potentially assist with end-of-life decisions. This study investigated and explored differences in HRV between ICU survivors and non-survivors of TBI across the first 24 h of ICU admission.

A prospective, observational and non-interventional study, of TBI patients >18 years admitted to the ICU at Gold Coast University Hospital, a total of seventeen patients were enrolled in the study. Patients ECG data was acquired at 300 Hz separately from the patient monitor utilising GE iCollect software from admission continuously across the first 72 h of ICU stay. HRV was manually screened for ectopic beats before RR interval was assessed in both time and frequency domains utilising Kubios 2.2. HRV measures were compared between TBI survivors and non-survivors.

Survivable TBI was associated with increased global HRV complexity (p < 0.01) and low-frequency powers (LF) dominance (p < 0.05); non-survivable brain injuries were associated with a dramatic reduction in overall variability and demonstrated a shift from LF to high-frequency powers (HF) across the first 24 h of ICU. Patients who progressed to brain death in first 24 h showed significantly reduced LF (p < 0.027).

Survivable TBI correlated with increased overall HRV as measured by LF variations. Thus, HRV demonstrates promise as a eBiomarker to assist in determining first 24 h ICU survivability of TBI, as well as a marker of patient clinical trajectory utilising pre-existing, non-invasive standards of patient care. Further exploration with a larger patient group is warranted.