Monitoring Cerebral Blood Flow in Neurosurgical Intensive Care
Monitoring Cerebral Blood Flow in Neurosurgical Intensive Care
Therapeutic concepts in neurosurgical intensive care require sophisticated and refined neuromonitoring applications, because the individualised approach to the treatment of head-injured patients relies on the assessment and interpretation of the key parameters of brain tissue viability and function. Monitoring of regional cerebral blood flow (rCBF) in particular has been a long-term problem due to a lack of devices available for continuous bedside online monitoring. A novel thermal diffusion (TD) microprobe was introduced recently for continuous bedside monitoring of rCBF (TD-rCBF). The following article provides a description of the technique and describes the clinical application and the potential of this novel microprobe to assess CBF in patients suffering from subarachnoid haemorrhage (SAH) or traumatic brain injury (TBI).
In neurosurgical practice, monitoring of CBF plays an important role, as the brain depends on continuous blood supply due to its inability to store glucose or oxygen. During pathological conditions such as SAH or TBI, the patient – and consequently the functions of the brain – cannot be supervised clinically. Furthermore, secondary insults in SAH or TBI represent dangerous and often lethal complications, making continuous neuromonitoring essential for neurosurgical intensive care. Under these conditions, rCBF is considered an important upstream monitoring parameter that is indicative of tissue viability. In order to be able to establish new therapeutic approaches that focus on the pathophysiological basis of the secondary insult, neuromonitoring strategies need further refinement, as continuous monitoring of intracranial pressure (ICP) and cerebral perfusion pressure (CPP) has failed to adequately identify malperfusion in the brain-injured patient.1 In this scenario, continuous monitoring of rCBF could provide the opportunity to diagnose and to correct insufficient rCBF before deficits in tissue oxygenation and metabolism are recognised.2 There are a variety of CBF measurement techniques available, such as stable xenon-enhanced computed tomography (sXe-CT), single-photon-emission computed tomography (SPECT), magnetic resonance imaging (MRI) and positron emission tomography (PET); however, these methods are hampered by several clinical and practical drawbacks.
Monitoring of rCBF in neurosurgical intensive care should ideally be performed in a continuous way at the bedside, providing quantitative rCBF values with high temporal and spatial resolution. Although laser- Doppler flowmetry (LDF)- and thermal diffusion flowmetry (TDF)-based measurement techniques provide continuous bedside monitoring of CBF, their clinical acceptance has been very low due to enduring technical drawbacks. Since LDF detects and measures erythrocyte flux, definite conclusions about nutritive perfusion and quantitative CBF cannot be drawn by means of this method.3 Furthermore, TDF-based measurement techniques, such as cortically placed probes, were hampered by difficulties regarding the reliability and validity of the readings obtained.3 Recently, however, the TD-rCBF microprobe, which is implanted intra-parenchymally and therefore circumvents the major drawbacks of the old systems that have been in use so far, has been introduced in clinical practice. It enables the quantitative, continuous bedside assessment of rCBF, which guarantees high reliability due to advanced mathematical modelling systems.4 This article illustrates the technique of the TD-rCBF microprobe and introduces its clinical application in patients with SAH and TBI.
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