[Recent advances in regional cerebral monitoring in the neurocritical patient: brain tissue oxygen pressure monitoring, cerebral microdialysis and near-infrared spectroscopy]

The long term outcome of head-injured patients depends not only on the primary brain lesions but also to a large extent on the secondary lesions. The diagnosis of many secondary lesions, and specially that of brain ischemia, is based on simultaneous monitoring of several intracranial and systemic variables. Continuous intracranial pressure (ICP) monitoring is currently considered indispensable in the management of all patients with a severe head injury and intracranial lesions. However, the information provided by this technique is insufficient to diagnose some of the complex physiopathological processes that characterize traumatic brain lesions. Consequently, the use of methods to estimate cerebral blood flow such as transcranial Doppler and jugular oximetry to complement ICP monitoring is becoming increasingly widespread. Nevertheless, determining the effect of tissue lesions and therapeutic measures on cerebral metabolism currently requires direct access to the brain parenchyma at the bedside. In this review we focus on three methods of regional cerebral monitoring: oxygen tissue pressure (PtiO(2)) monitoring, microdialysis and near-infrared spectroscopy. The bases of each method and reference values for the variables analyzed will be discussed. We also make a series of recommendations on how results should be interpreted in light of current knowledge.

[Variability in the surgical indications for posttraumatic intradural lesions]

INTRODUCTION

The surgical treatment of focal intradural lesions is still a matter of considerable debate. This is especially important in the decision to evacuate brain contusions. We present the results of a prospective observational study in which the main goal was to analyze intracenter variability in the indication for surgery in focal posttraumatic intradural lesions in a department of Neurosurgery of a University Hospital with a specialized neurotrauma unit.

CLINICAL MATERIAL AND METHODS

Between May 1 and December 31, 2001, 32 patients with a closed traumatic brain injury and an intradural posttraumatic focal lesion were included. The patients studied were a subgroup included in the European multicenter observational study of the management of intradural lesions conducted under the aegis of the European Brain Injury Consortium (EBIC).

RESULTS

Intradural lesions > 25 cc were immediately evacuated. Nine out of thirteen patients with lesions < 25 cc also underwent surgery due to intracranial hypertension or neuroworsening. In all patients in whom lesions were surgically evacuated, the postoperative CT-scan showed neuroradiological improvement of the signs of mass effect or midline shift.

CONCLUSIONS

In our center, we found no evidence of significant variability in the indications for surgery in intradural lesions of more than 25 cc. However, significant differences were detected among neurosurgeons in the surgical indications for lesions below 25 cc. The small sample analyzed precludes generalization of these conclusions. The definitive results of the EBIC study will provide the neurosurgical community with a better understanding of variability in the management of these lesions.

Moderate Hypothermia in the Management of Severe Traumatic Brain Injury: A Good Idea Proved Ineffective?

Many drugs with proven efficacy in the preclinical stage have failed to show any benefit in improving the outcome of severe traumatic brain injury (TBI) when tested in controlled clinical trials. Hypothermia is still the most powerful neuroprotective method in experimental models of TBI. Its ability to influence the multiple biochemical cascades that are set in motion after TBI is quite unique. In experimental models hypothermia protects against mechanical neuronal and axonal injury and improves behavioral outcome. Encouraging results from phase II and III clinical trials of hypothermia in TBI reported in the 1990s generated great enthusiasm. However, enthusiasm faded in 2001 after the final report of the multicenter phase III trial in which the neuroprotective effects of moderate hypothermia in TBI were formally tested. This study found no significant effect on outcome in the hypothermia group, leading many clinicians to lose interest in this therapy. The present article reviews the historical background of the use of hypothermia, presents the rationale for using both immediate and deferred hypothermia, and summarizes both experimental and clinical evidence supporting its potential benefits in the management of severe TBI. New technologies using intravascular methods to induce fast hypothermia have recently become available. Cooling either through the intravenous or intra-arterial route is an exciting alternative with great potential. We argue that moderate hypothermia is still the most powerful neuroprotective candidate for severe TBI and that it merits further research and discussion. We also defend the need for further clinical trials to prove or refute its potential for treating high intracranial pressure refractory to first level therapeutic measures. The premature abandonment of hypothermia could close new avenues for improving the devastating effects of TBI.

[Intraoperative detection of ischemic brain hypoxia using oxygen tissue pressure microprobes]

OBJECTIVE AND IMPORTANCE

Detection of intraoperative ischemic events could lead to the resolution of their cause and to the prevention of the definitive establishment of a postoperative infarct. We want to illustrate the possibilities that intraoperative monitoring of oxygen tissue pressure (PtiO2) in critical areas during a neurosurgical vascular procedure offers, enhancing its reliability and immediacy in obtaining information about tissue oxygenation status as a marker of ischemia in the vascular territory at risk.

CLINICAL PRESENTATION

We report the case of a 32 year-old male with a deep arteriovenous malformation (AVM) localised in the insular region. The patient had been previously treated with radiosurgery without achieving a satisfactory result.

INTERVENTION

AVM removal was performed through a transylvian transinsular approach. PtiO2 was monitorised at the temporal pole (reference area) and at the posterior temporal region (risk area). Both probes maintained close tissue oxygenation levels until the last stage of the AVM resection when, during the coagulation of a supposed afferent vessel, a brisk fall of the oxygen tissue pressure in the posterior temporal region was detected. An ischemic infarct in this area was observed postoperatively.

CONCLUSIONS

PtiO2 monitoring has a high reliability in the detection of intraoperative tissue hypoxia. Data obtained could lead to early identification of these events and, whatever possible, to resolve this situation preventing the definitive establishment of an ischemic infarct.

Coexistence of regional cerebral hypoxia with normal or hyperemic brain detected by global monitoring methods. Analysis of apparently contradictory findings based on the Siggaard-Andersen model of tissue hypoxia

The aim of our study was to perform and in-depth analysis of several episodes of regional brain hypoxia detected by monitoring brain partial pressure of oxygen (PtiO2) in which simultaneous measurements of cerebral oxygen extraction fraction (O2EF) suggested a normally perfused or even a hyperemic brain. To gain deeper insight into these episodes, we used the model of tissue hypoxia described by Siggaard-Andersen. In 244 simultaneous measurements, 31 episodes (12.7%) of brain hypoxia (PtiO2 < or = 15 mmHg) were detected simultaneously with an O2EF within the normal range or below the lowest normal percentile. Using Siggaard-Andersen methodology, we classified 6 episodes (19%) as high-affinity hypoxia and 25 (81%) as shunt hypoxia or dysperfusion hypoxia. Siggaard-Andersen's comprehensive classification of tissue hypoxia can be used as an integrative model to build coherent algorithms for diagnosing and managing neurocritical patients that are at risk of brain hypoxia due to either intracranial or extracranial conditions.

[First tier measures in the treatment of intracranial hypertension in the patient with severe craniocerebral trauma. Proposal and justification of a protocol]

The management of severe head injuries in general and that of high intracranial pressure (ICP) in particular are among the most challenging tasks in neurocritical care. One of the difficulties still faced by clinicians is that of reducing variability among centers when implementing management protocols. The purpose of this paper is to propose a standardized protocol for the management of high ICP after severe head injury, consistent with recently published clinical practice guidelines and other clinical evidence such as that provided by the systematic reviews of the Cochrane Collaboration. Despite significant advances in neuromonitoring, deeper insight into the physiopathology of severe brain trauma and the many therapeutic options available, standardized protocols are still lacking. Recently published guidelines provide sketchy recommendations without details on how and when to apply different therapies. Consequently, great variability exists in daily clinical practice even though different centers apply the same evidence-based recommendations. In this paper we suggest a structured protocol in which each step is justified and integrated into an overall strategy for the management of severe head injuries. The most recent data from both the preliminary and definitive results of randomized clinical trials as well as from other sources are discussed. The main goal of this article is to provide neurotraumatology intensive care units with a unified protocol that can be easily modified as new evidence becomes available. This will reduce variation among centers when applying the same therapeutic measures. This goal will facilitate comparisons in outcomes among different centers and will also enable the implementation of more consistent clinical practice in centers involved in multicenter clinical trials.

Water quality improvement of treated wastewater by intermittent soil percolation

Our research aimed to evaluate intermittent soil infiltration of treated sewage for reuse in the north of Chile. Aerated lagoon effluent was infiltrated in columns packed with native soils (sandy-lime, lime-gravel and limey-sand). Columns were operated for more than a year under different cycles of filling and drying, depths and load pressures depending on soil characteristics. The efficiency of the system was determined through influent-effluent microbiological indicators level (faecal coliforms, E. coli, Salmonella spp, MS2 phage, and protozoan cysts), physicochemical characterisation (TOC, COD, BOD, nitrogen), and hydraulic flow measurement. Results showed: (a) high reduction of enteric bacteria (5-7 log10), some inactivation of phage (2-4 log10) and complete removal of intestinal cyst; (b) stable removal of organic matter (80-90% reduction of TOC, COD, BOD); and (c) partial ammonia reduction through adsorption and nitrification with denitrification mainly occurring in sandy soil. Preliminary data from pilot plant working in the field showed better results that those obtained in the laboratory especially removal of microbiological indicators. Microbiological quality of effluent met Class A regulations for agricultural reuse (WHO, 1989) and the system looks like an attractive alternative to cope with water shortage in the region.

Epidermal growth factor secreted from submandibular salivary glands interferes with the lipolytic effect of adrenaline in mice

We had described that epidermal growth factor (EGF) interfered with the lipolytic effect of catecholamines in isolated adipocytes. Since catecholamines stimulate the release of EGF from submandibular salivary glands to blood plasma in male mice, we studied whether EGF affected also the lipolytic response to adrenaline in whole animals. We studied the effect of adrenaline in sialoadenectomized and sham-operated mice receiving or not a high dose of EGF following adrenaline injection. There was no difference in plasma EGF concentration between sham-operated and sialoadenectomized animals receiving saline. After adrenaline administration plasma EGF increased by 20-fold in sham-operated but did not increase in sialoadenectomized mice. Indeed, the increase was much higher (more than 100-fold) in mice receiving exogenous EGF. The effect of adrenaline on plasma concentration of both glycerol and nonesterified fatty acids was higher as lower was plasma EGF concentration. Isolated adipocytes obtained from sham-operated or sialoadenectomized mice had identical lipolytic response to adrenaline. The lipolytic response of adipocytes to isoproterenol was decreased by addition of EGF. To study whether the interference with the in vivo lipolytic effect of adrenaline had further metabolic consequences, we measured plasma beta-hydroxybutyrate concentration in plasma. There was no difference in the response to adrenaline between sham-operated and sialoadenectomized mice in spite of the difference in plasma nonsterified fatty acid concentration. Studies in isolated hepatocytes indicated that ketogenesis run at near maximal rate in this range of substrate concentration. These results suggest that EGF in the physiological range decreases the lipolytic effect of adrenaline but does not compromise further metabolic events like the enhancement of ketogenesis.