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.

Intracranial hypertension after surgery in patients with Chiari I malformation and normal or moderate increase in ventricular size

OBJECTIVE

To determine ICP changes in patients with Chiari type I malformation after posterior fossa reconstruction (PFR).

PATIENTS AND METHODS

We continuously monitored ICP before and after PFR in 12 patients with Chiari I malformation and with an Evans' Index below or equal to 0.33. Mean ICP (epidural sensor) and percentage of B waves were calculated 24 hours before surgery and during the first 7 days after surgery.

RESULTS

Mean ICP and percentage of B waves significantly increased after surgery despite a significant increase in the volume of the posterior fossa. The main finding revealed by control CT scans was compression of the quadrigeminal cistern with a reduction in size of the fourth ventricle. In six patients, a small transitory increase in supratentorial ventricular size was found.

CONCLUSIONS

A transitory increase in ICP is common after PFR. This increase could be explained by an initial reperfusion phenomena in the cerebellum that provokes a transitory deterioration in CSF dynamics. The effacement of the quadrigeminal cistern and the reduction in size of the fourth ventricle suggests this hypothesis.

[The use of moderate hypothermia in the treatment of patients with severe craniocerebral trauma]

Traumatic brain injury initiates several metabolic processes that can increase the primary injury. It is well established that in severe head injuries, posttraumatic secondary insults, such as brain hypoxia, hypotension or anemia, exacerbate neuronal injury and lead to a poorer outcome. Experimental and clinical evidence suggests that moderate hypothermia (32-34 degrees C), may limit some of these deleterious secondary metabolic responses. Recent laboratory studies and prospective controlled clinical trials of induced moderate hypothermia for relatively short periods (24-48 h) in patients with severe head injury, have demonstrated good intracranial pressure control and better outcome when compared with patients maintained in normothermia and given conventional treatment. Despite its proven clinical role in neuroprotection, hypothermia research has been inconstantly followed for various reasons. In this paper we review the mechanisms of neuroprotection in hypothermia, the different preclinical and clinical studies that favor its use as a neuroprotector in severe head injury or in patients in whom high intracranial pressure is refractory to first tier measures. The evidence that favors hypothermia is discussed. We also discuss the negative results of the still unpublished multicentre trial on prophylactic moderate hypothermia developed in the USA. The main problem with moderate hypothermia is the lack of a systematic methodology to induce and maintain it. Also, optimal duration of its use and the methodology and timing for rewarming have not been determined. Consequently, the results of different trials are difficult to analyze and compare. However, most evidence suggests that hypothermia provides remarkable protection against the adverse effects of neuronal damage that is exacerbated by secondary injury. Further prospective controlled trials with clearly defined methodology are needed before this method is implemented in daily clinical practice. The most important task for the years to come may be to focus on refining this procedure, defining the optimal time of cooling and rewarming and to optimize the methods of rapidly inducing and maintaining low temperature. It is also essential to define the most appropriate method and velocity of the rewarming phase, in which many successfully controlled patients deteriorate and die.

[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.