Ultrasound in the Neurointensive Care Unit

Abstract

Bedside ultrasound plays an important role in the neurointensive care unit. Patients with aneurysmal subarachnoid hemorrhage (aSAH) are at risk for cerebral vasospasm and delayed cerebral ischemia (DCI). The use of transcranial Doppler to detect and monitor vasospasm is well established. Transcranial color-coded sonography (TCCS) permits B-mode imaging of cerebral parenchyma and duplex imaging of intracranial vessels. The use of TCCS permits angle correction for more accurate determination of mean cerebral blood flow velocities (mCBFV). Measured mCBFV greater than 200 cm/s is highly suggestive of severe vasospasm with the consequent risk for cerebral infarction. Other recognized applications for TCCS include confirmation of brain death and assessment of recanalization following thrombolysis for ischemic stroke. Distension of the optic nerve sheath (ONS) identified on ocular ultrasound may be useful for the detection of raised intracranial pressure (ICP), with an ONS diameter ≥0.50 cm predicting ICP > 20 mmHg in the ventilated patient. The use of B-mode imaging of cerebral parenchyma to detect intracerebral hematomas, measure midline shift, and monitor lateral ventricle size in hydrocephalus is under investigation. The use of bedside echocardiography in aSAH patients may be useful for the identification of a Takotsubo pattern of cardiomyopathy as well as for titration of hemodynamic augmentation therapy for DCI. The use of thoracic ultrasound in aSAH may be useful for the detection and monitoring of neurogenic as well as cardiogenic pulmonary edema through the presence of B-lines. Other applications of ultrasound in the neuroICU include assessment of shock, the BLUE protocol for acute respiratory failure, eFAST in trauma, detection of deep venous thrombosis, and performance of bedside procedures.