Aspects on the Physiological and Biochemical Foundations of Neurocritical Care

Abstract

Neurocritical care (NCC) is a branch of intensive care medicine characterized by specific physiological and biochemical monitoring techniques necessary for identifying cerebral adverse events and for evaluating specific therapies. Information is primarily obtained from physiological variables related to intracranial pressure (ICP) and cerebral blood flow (CBF) and from physiological and biochemical variables related to cerebral energy metabolism. Non-surgical therapies developed for treating increased ICP are based on knowledge regarding transport of water across the intact and injured blood–brain barrier (BBB) and the regulation of CBF. Brain volume is strictly controlled as the BBB permeability to crystalloids is very low restricting net transport of water across the capillary wall. Cerebral pressure autoregulation prevents changes in intracranial blood volume and intracapillary hydrostatic pressure at variations in arterial blood pressure. Information regarding cerebral oxidative metabolism is obtained from measurements of brain tissue oxygen tension (PbtO2) and biochemical data obtained from intracerebral microdialysis. As interstitial lactate/pyruvate (LP) ratio instantaneously reflects shifts in intracellular cytoplasmatic redox state, it is an important indicator of compromised cerebral oxidative metabolism. The combined information obtained from PbtO2, LP ratio, and the pattern of biochemical variables reveals whether impaired oxidative metabolism is due to insufficient perfusion (ischemia) or mitochondrial dysfunction. Intracerebral microdialysis and PbtO2 give information from a very small volume of tissue. Accordingly, clinical interpretation of the data must be based on information of the probe location in relation to focal brain damage. Attempts to evaluate global cerebral energy state from microdialysis of intraventricular fluid and from the LP ratio of the draining venous blood have recently been presented. To be of clinical relevance, the information from all monitoring techniques should be presented bedside online. Accordingly, in the future, the chemical variables obtained from microdialysis will probably be analyzed by biochemical sensors.

Surgically Treated Intracerebral Haemorrhage : Pathophysiology and Clinical Aspects

“…In Paper I we report on the LPR, lactate and pyruvate levels, and the prevalence of type 1 and 2 LPR elevations in accordance with the various definitions available in the literature (8,10,16,168,194,195,197,232,261). Observations in PHZ were compared to those seen in seemingly normal, uninjured cortex.…”

“…CBF is regulated by various mechanisms including metabolic coupling, neural control, partial pressure of carbon dioxide in blood and pressure autoregulation (166,168). CBF regulation following ICH has been the subject of debate.…”

“…Both situations may render the same numerical LPR but by different mechanisms. There are an increasing number of reports of a type 2 LPR elevation, indicative of mitochondrial dysfunction rather than ischemia, in various acute brain injury conditions (8,10,168,(192)(193)(194)(195)(196).…”

Cerebral microdialysis in TBI—limitations and possibilities

“…The limitations and possibilities inherent in the technique of microdialysis have been described in detail in many publications [4]. In the present context, the fact that microdialysis gives information regarding chemical variables from a very narrow zone surrounding the catheter constitutes an important limitation.…”

“…1). These variables are analyzed bedside utilizing enzymatic techniques, and the analytical precision of these methods has been documented [4]. The precision is sufficient for clinical routine but is insufficient for the detection and interpretation of previously unknown biochemical principles or pathophysiological mechanisms.…”