Monitoring of autoregulation using laser Doppler flowmetry in patients with head injury

Abstract

The authors studied 31 comatose head-injured patients to assess the clinical usefulness of laser Doppler flowmetry (LDF) in continuous autoregulation monitoring. The LDF probes were placed on the surface of the cerebral cortex. Data on LDF, intracranial pressure (ICP), and arterial blood pressure (ABP) were recorded and continuously entered into a computer. The data were broken down into multiple segments of 15 minutes' duration (epochs). Epochs showing rapid change in cerebral perfusion pressure (CPP), change in CPP of less than 10 mm Hg, LDF values of less than five arbitrary units, and loss of ABP/ICP waveform were excluded from further analysis. A linear relationship between LDF and CPP in individual epochs was used as an indicator of loss of autoregulation. The relationship between LDF and CPP changed with time, indicating improvement or deterioration in autoregulation. Longitudinal analysis of all the epochs measured in a patient revealed three patterns of progress: 1) intact autoregulation; 2) transient loss; and 3) persistent loss of autoregulation. All five patients with intact autoregulation had a good outcome. Ten patients experienced transient loss of autoregulation; of these four had a good outcome, five were moderately disabled and one was severely disabled. Transient impairment of autoregulation did not always indicate poor outcome, provided the impaired autoregulation responded to treatment. In 11 patients who had persistent loss of autoregulation, nine died and two were severely disabled. In five cases the LDF probe lost contact with the cerebral cortex and no useful information was obtained. Real-time measurement of autoregulation using LDF and CPP monitors was achieved and the findings were related to outcome in these patients.

Influence of definition and location of hypotension on outcome following severe pediatric traumatic brain injury*

“…When cerebral autoregulation is impaired, cerebral ischemia may ensue if cerebral perfusion pressure (CPP) is low. This is important because adult TBI data suggest that persistently impaired autoregulation is associated with poor outcome (25).…”

Cerebral Blood Flow and Autoregulation After Pediatric Traumatic Brain Injury

“…Adult studies report poor outcomes with permanent but variable outcomes with transient loss of autoregulation [109]. Impaired cerebral autoregulation has been associated with poor outcome after pediatric TBI [104,110], but there is a paucity of information in children.…”

Neurointensive Care Monitoring for Severe Traumatic Brain Injury

“…In similar year, Czosnyka also noted that autoregulation is not only impaired when associated with a high ICP or low arterial blood pressure, but it can also be disturbed by an excessive CPP (Czosnyka et al, 2001). Studies have shown that impairment or failure of autoregulation can contribute to unfavorable outcome (Czosnyka et al, 2001;Lam et al, 1997;Smielewski et al, 1997). This could possibly be explained by a disturbance in the pressure-volume (elastance) curve that is steeper suggesting poor compliance of the brain (figure.…”