How Transcranial Doppler can assess the effect of hyperosmolar therapy and the degree of circulatory compromise in acute brain herniation

Mannitol is a widely accepted in therapy for the treatment of intracranial hypertension (ICHT), as it has positive effect on cerebral perfusion pressure (CPP) and cerebral blood flow (CBF) more so in those patients with focal injury (vs. diffuse), those with lesions on the brain imaging, and those in whom the CPP is at or below the auto regulation threshold (Brown et al. 1979;Mendelow et al. 1985;Rosner & Coley 1987;Bratton et al. 2007;Wakai et al. 2007). The mannitol doses reported in these studies ranged from 0.25 to 0.5 gm/kg bolus of 20% mannitol given intravenously over 10 to 15 minutes. In acute herniation, high doses (1.5 g/kg) have been shown to improve patient outcome (Cruz et al. 2001;Cruz et al. 2002;Cruz et al. 2004).

Transcranial Doppler (TCD) has been widely used for the assessment of cerebral blood flow in several clinical conditions (Topcuoglu 2012) including intracranial hypertension. TCD is gaining acceptance as a rapid, portable and reliable method for assessing intracranial hypertension and cerebral blood flow compromise. In their recent study, Tazarourte et al., reported that 50% of TCD’s performed prior to the arrival to the trauma center were abnormal, resulting in administration of hyperosmolar therapy in the ambulance (Tazarourte et al. 2011). Moreover, only patients with abnormal TCD examination required emergency surgery and interestingly those patients in whom the TCD parameter where not improved after the administration of such therapy died within 48 hours (Tazarourte et al. 2011). The case presented in this article illustrates the usefulness of TCD in the monitoring of ICHT leading to herniation and its ability to assess response to therapy.

This case shows the potential utility of TCD examination in acute neurological deterioration to assess the extent of cerebral circulation compromise, the potential for reversal of circulatory arrest and the efficacy of the chosen dose of hyperosmolar therapy. In this case, the patient had no signs of brain stem function. This would have placed him on a conservative palliative approach given the poor neurological prognosis associated with such condition. The TCD on the other hand showed severely compromised yet persistent cerebral flow in a patient who was otherwise considered unsalvageable. This finding promted the use of an additional large dose of mannitol to objectively assess any changes in the cerebral blood flow dynamics. The TCD done after the mannitol dose demonstrated a tangible effect of hyperosmolar therapy on the cerebral circulation that was later responsible for a reversal of the herniation and the return of brain function. The patient care shifted from a consideration of a palliative approach to aggressive surgical and medical therapy with good outcome of the acute care of this patient, not achievable otherwise, had the TCD examination not been performed. This technique may also be useful in gauging whether the chosen dose of hyperosmotic agent is actually the appropriate one. In a pilot study by Tazarourte et al., TCD examination was carried out in a pre-hospital setting, or upon arrival, and patients were treated according to the TCD results of improved blood flow (Tazarourte et al. 2011). TCD was used to assess the efficacy of the maneuvers, and those patients for whom the cerebral perfusion could be corrected according to the pulsatility index fared better (Bellner et al. 2004).

Both TCD and optic nerve ultrasonography can be done with portable machines in the emergency department, intensive care unit and even in the operating room if necessary (Soldatos et al. 2009;Raboel et al. 2012). Performance of TCD examination by a trained technician or a physician is not time consuming. Most TCD units are easily transported to the point of care where the patient is (e.g. The emergency department or the operating room) and newer models even offer portable hand held forms of the device. The learning curve is not discouragingly steep. The major limitation is the logistic constrains of having a trained TCD performer available to capture such patients at these extreme conditions. In conclusion, the use of TCD and optic nerve ultrasonography at the point of care on patients with acute neurological deterioration could be a useful and objective adjunct to help gauge ICP and guide therapy outside of the Intensive Care environment and without the potential delays associated with the installation of invasive monitoring techniques.

The use of transcranial Doppler in patients presenting with acute neurological deterioration could be a valuable tool to objectively and non-invasively assesses the intracranial pressure dynamics and guide effective course of treatment.

Written informed consent was obtained from the patient for the publication of this report and any accompanying images.