Contribution of edema and cerebral blood volume to traumatic brain swelling in head-injured patients

Changes in intracranial pressure and cerebral autoregulation in patients with severe traumatic brain injury

BACKGROUND

Impaired cerebral autoregulation is frequent after severe traumatic head injury. This could result in intracranial pressure fluctuating passively with the mean arterial pressure.

OBJECTIVE

This study examines the influence of autoregulation on the amplitude and direction of changes in intracranial pressure in patients with severe head injuries during the management of cerebral perfusion pressure.

DESIGN

Prospective study.

SETTING

Neurosurgical intensive care unit

PATIENTS

A total of 42 patients with severe head injuries.

INTERVENTIONS

Continuous recording of cerebral blood flow velocity, intracranial pressure, and mean arterial pressure during the start or change of continuous norepinephrine infusion.

MEASUREMENTS AND MAIN RESULTS

Cerebrovascular resistance was calculated from the cerebral perfusion pressure and middle cerebral artery blood flow velocity. The strength of autoregulation index was calculated as the ratio of the percentage of change in cerebrovascular resistance by the percentage of change in cerebral perfusion pressure before and after 121 changes in mean arterial pressure at constant ventilation between day 1 and day 18 after trauma. The strength of autoregulation index varied widely, indicating either preserved or severely perturbed autoregulation during hypotensive or hypertensive challenge in patients with or without intracranial hypertension at the basal state (strength of autoregulation index, 0.51 +/- 0.32 to 0.71 +/- 0.25). The change in intracranial pressure varied linearly with the strength of autoregulation index. There was a clinically significant change in intracranial pressure (> or =5 mm Hg) in the same direction as the change in mean arterial pressure in five tracings of three patients. This was caused by the mean arterial pressure dropping below the identified lower limit of autoregulation in three tracings for two patients. It seemed to be caused by a loss of cerebral autoregulation in the remaining two tracings for one patient.

CONCLUSION

Cerebral perfusion pressure-oriented therapy can be a safe way to reduce intracranial pressure, whatever the status of autoregulation, in almost all patients with severe head injuries.

Pediatric neurologic emergencies

Neuroemergencies are life-threatening situations in which, whatever the cause, common pathologic phenomena result in secondary brain lesions. The goal of critical care management is to stop these self-aggravating processes as soon as possible. Initial resuscitation is devoted to control of the airway and hemodynamic and hydroelectrolytic stabilization. With mass lesions, minimal computed tomographic exploration immediately precedes surgical decompression. Further critical care adapted to the child's needs requires multimodal monitoring. Normoventilation, deep sedation, osmotherapy with mannitol or hypertonic saline solutions, and optimization of mean arterial pressure are the basis of management. A purely pressure-driven approach aimed at controlling cerebral perfusion pressure could be potentially harmful, and associated measurement of blood flow velocity with transcranial Doppler and jugular bulb oxygen saturation monitoring allows an approach to cerebral blood flow and metabolism. Outcome can be improved in dangerous situations such as severe brain injuries, cerebral arteriovenous malformation rupture, status epilepticus, and acute hydrocephalus, provided that emergency management could be applied efficiently.

Cerebral resuscitation after traumatic brain injury and cardiopulmonary arrest in infants and children in the new millennium

As outlined in Figure 1, it is likely that a series of interventions beginning in the field and continuing through the emergency department, ICU, rehabilitation center, and possibly beyond, will be needed to optimize clinical outcome after severe TBI or asphyxial CA in infants and children. Despite the many differences between these two important pediatric insults, it is likely that many of the therapies targeting neuronal death, in either condition, will need to be administered early after the insult, possibly at the injury scene. Even cerebral swelling, a pathophysiologic derangement routinely treated in the PICU, almost certainly is better prevented rather than treated. Finally, this review includes, for one of the first times, a brief discussion of additional horizons in the management of patients with severe brain injury, namely, manipulation of the injured circuitry and stimulation of regeneration. Further research is needed to define better the pathobiology of these two important conditions at the bedside, to understand the optimal application of contemporary therapies, and to develop and apply novel therapies. The tools necessary to carry out these studies are materializing, although the obstacles are great. This difficult but important challenge awaits further investigation by clinician-scientists in pediatric neurointensive care.

Monitoring neurologic patients in intensive care

The brain is sensitive to changes in substrate delivery. In neurologically critically ill patients (e.g., those with head injury, subarachnoid hemorrhage, or stroke), interruption of this supply causes ischemic brain damage and thus impairs the outcome. To prevent, detect, and treat these ischemic events as soon as possible, the cerebral blood flow is continuously monitored, its coupling or not with the consumption of oxygen and so forth, and the detected derangements of normal physiology. Intracranial pressure and cerebral perfusion pressure are two parameters that often reflect ischemic events, and thus it is mandatory to continuously measure them. To better assess cerebral hemodynamics, jugular bulb oxymetry and brain pressure tissue oxygen monitoring are two neuromonitoring techniques that allow for a better understanding of the balance between oxygen supply and consumption, and therefore are useful in directing therapy. Transcranial Doppler ultrasonography is a noninvasive technique with the same purpose but with less clinical relevance. The new neuromonitoring technique, microdialysis, is useful for understanding the mechanisms involved in brain ischemia. However, it is clear that the physician who interprets the measurements given by devices and the clinical data (e.g., temperature, glycemia) is still the cornerstone in the management of neurologically critically ill patients.