Clinical Usefulness of Transcranial Doppler as a Screening Tool for Early Cerebral Hypoxic Episodes in Patients with Moderate and Severe Traumatic Brain Injury.

BACKGROUND

Brain tissue oxygenation (PbtO) in traumatic brain injury (TBI) is known to be dependent on cerebral blood flow (CBF) which remains difficult to assess during the very early phase of TBI management. This study evaluates if blood flow velocity measurement with 2D color-coded transcranial Doppler (TCD) can predict cerebral hypoxic episodes in moderate-to-severe TBI measured with a PbtO probe.

METHODS

This is a prospective observational study of serial TCD measurements to assess blood flow velocity and its association with PbtO. Measurements were done bilaterally on the middle cerebral artery (MCA) early after the insertion of PbtO monitoring, daily for 5 days and during dynamic challenge tests. Physiological parameters affecting PbtO and Doppler velocities were collected simultaneously (PaO, PaCO, hemoglobin [Hb] level, intracranial pressure, and cerebral perfusion pressure [CPP]).

RESULTS

We enrolled 17 consecutive patients with a total of 85 TCD studies. Using 2D color-coded TCD, signal acquisition was successful in 96% of the cases. Twenty-nine (34%) TCD measures were performed during an episode of cerebral hypoxia (PbtO ≤ 20 mmHg). For early episodes of cerebral hypoxia (occurring ≤ 24 h from trauma), all Vmean < 40 cm/s were associated with an ipsilateral PbtO ≤ 20 mmHg (positive predictive value 100%). However, when considering all readings over the course of the study, however, we found no correlation between PbtO and MCA's mean blood flow velocity (Vmean). Vmean is also positively correlated with PaCO, whereas PbtO2 is also correlated with PaO, CPP, and Hb level.

CONCLUSIONS

Early TCD measurements compatible with low CBF (mean velocity < 40 cm/s) detect brain tissue hypoxia early after TBI (≤ 24 h) and could potentially be used as a screening tool before invasive monitoring insertion to help minimize time-sensitive secondary injury. Various factors influence the relationship between Vmean and PbtO, affecting interpretation of their interaction after 24 h.