Conjunctival microcirculation in patients with traumatic brain injury

Introduction

Traumatic brain injury (TBI) is one of the most important causes of death in young adults. Treatment aims at controlling the intracranial pressure (ICP) in order to maintain an adequate cerebral blood flow, to reduce the risk of secondary ischemic damage. Abnormal blood flow in the middle cerebral artery in patients with TBI was previously associated with poor outcome. Because perfusion of the brain shares a common origin with blood flow in the conjunctiva, we hypothesized that conjunctival microcirculation is altered after TBI in comparison with healthy subjects.

Methods

We used sidestream dark-field (SDF) imaging for evaluation of the readily accessible microcirculation of the bulbar conjunctiva as a noninvasive research site. Conjunctival microcirculation was studied in eight patients with TBI requiring sedation and continuous ICP monitoring. In addition, we investigated eight age-matched healthy control individuals. Using MAS software we determined the functional vascular density (FVD) as the total length of perfused vessels per field of view as well as the microvascular flow index (MFI).

Results

Data are presented as the median (interquartile range). The TBI patients had an ICP of 20 (15–25) mmHg and a cerebral perfusion pressure of 61 (53–77) mmHg. The conjunctival MFI in TBI patients was 2.94 (2.88–3.00) in comparison with 2.93 (2.79–3.00) in healthy controls. The FVD was 7.78 (7.54–8.14) and 8.53 (7.60–9.97) in TBI patients and healthy controls, respectively. There was no significant difference in microcirculatory parameters found between the groups.

Conclusion

We found that the FVD and MFI did not differ between healthy subjects and patients with TBI. Based on these interim results, further research will focus on the effect of an elevated ICP on conjunctival microvascular blood flow.