Intravenous Fluid Therapy in Neurologic Injury

[Hypernatremia in neurointensive care]

Hypernatremia invariably denotes hyperosmolarity and, at least transiently, causes cellular dehydration. Because of blood brain barrier properties, cerebral tissue volume is modified by acute changes in osmolarity. An acute hyperosmolarity (by intravenous sodium or mannitol) temporally decreases intracranial pressure. This treatment is thus useful in critical situations, allowing time for diagnosis and, if possible, other treatment. But in cases of sustained hypernatremia, cellular dehydration is rapidly counterbalanced by an increase in cellular osmolarity. For the brain, it has been shown that cerebral volume is restored in a few hours during prolonged hypernatremia. Moreover, the plasmatic osmotic load induces an increase in diuresis and natriuresis. A tight control is then necessary to prevent hypovolemia and electrolytes disorders. Teams using this treatment should undertake controlled randomized studies to ascertain any beneficial effect that cannot be explained by physiology.

[Osmotic cerebral oedema: the role of plasma osmolarity and blood brain barrier]

There are five types of oedema: vasogenic, cytotoxic, interstitial, hyperemic and osmotic. The differences lie on the type and localization of the oedema, the state of the blood-brain barrier (BBB) and the pathological context. Under physiological conditions, the osmolarity of extra cellular fluids (ECFs) is equal on both sides of the BBB. However, the pathophysiological variations of circulating osmolarity (including acute hyponatremia and hypernatremia) do not affect, at the same time, the osmolarity of cerebral ECFs. This situation generates an osmotic gradient on either side of the BBB. The latter, if intact, behaves like a semi-permeable membrane allowing water transport according to the osmotic laws. Depending on its direction, water movement could induce cerebral liquid inflation (i.e. osmotic oedema) or cerebral dehydration. In case of osmotic insult, cerebral cell modify their active osmotic molecular contents in order to limit volume variation. There are two types of osmoactive molecules, organic (i.e. ideogenic osmoles: amino acids, polyols and trimethylamines) and non organic (i.e. electrolytes). In the event of plasma hypotonicity, cerebral cells expel active osmotic molecules to reduce the osmotic gradient and water movement thereby reducing edema. The opposite reaction is observed in the case of hypertonic insult. This cerebral osmoregulation becomes more effective, the slower the osmotic disorder. It explains, for example, why patients with chronic and severe hyponatremia could be asymptomatic. Severe osmotic oedema is observed mainly in water intoxication, acute hyponatremia or too rapid reduction of hyperosmolarity. However, osmotic oedema is not limited to extreme clinical circumstances. Hyponatremia, even modest, could modify cerebral blood volume and impair osmoregulation. Generally these minor modifications do not affect normal brain tissue. In the presence of cerebral lesion, osmoregulation operates only in areas of preserved BBB. The pathological zones are therefore exposed to osmotic oedema (even in cases of moderate hyponatremia) with deterioration of both clinical status and intracranial pressure. This authentic phenomenon could be insidious and difficult to differentiate from osmotic central oedema. Hyponatremia constitutes an authentic secondary cerebral insult of systemic origin, an entity clearly identified by experimental studies to justify the choice between crystalloids and colloids in neuroanaesthesia and neurointensive care. These studies have revealed an increase in water content in normal brain tissues after administration of hypotonic solutions. The increase in plasma osmolarity as a treatment modality using mannitol or hypertonic saline is based on the same concepts. The most remote indication is the occurrence of a reactive mydriasis in the context of trauma for example. More recently, therapeutic hypernatremia has been proposed to control intracranial hypertension.

Acute care management of severe traumatic brain injuries

Preservation or restoration of optimal neurologic function following traumatic brain injury (TBI) requires timely and aggressive therapeutic interventions. Effective diagnostic tools, together with an armamentarium of treatment modalities, have augmented the treatment strategies utilized today. In addition, the Guidelinesfor the Management of Severe Head Injury have established a standardized approach for the TBI patient. This article will provide current information regarding the resuscitation priorities, appropriate interventions, and pharmacological agents used in the treatment required by the complex nature of TBI. Also, a review of the occurrences associated with TBI will be discussed.

Management of increased intracranial pressure: a review for clinicians

Emergency physicians are frequently confronted with head-injured patients, many of whom have intracranial hypertension. Since direct correlations have been reported between increased intracranial pressure (ICP) and adverse outcome, it is important to rapidly identify and treat these patients. Furthermore, since the actual brain damage that occurs at the time of injury cannot be modified, the maximization of neurological recovery depends upon minimizing secondary insults to the brain, most notably preventing hypotension and hypoxemia. Volume resuscitation to maintain an adequate mean arterial pressure, airway control, and sedation and analgesia to prevent surges in ICP remain the cornerstone of early management. These principles and the emergency department management of the head-injured patient are reviewed in this paper.

Current trends in the management of head injury

The importance of cerebral perfusion pressure (CPP) optimization has been recognized in the neurosurgical community in the United States as part of the recently published Guidelines for Management of Severe Head Injury. Although further basic and clinical research is needed before a CPP-directed head injury management standard of care is formulated, optimization of CPP is practical with present personnel and equipment resources in many emergency departments. Emergency Department physicians should be familiar with CPP management principles to facilitate interactions with neurosurgical colleagues and improve patient outcomes.

Traumatic brain injury

Traumatic brain injury (TBI) contributes significantly to the mortality and morbidity rates of traumatized patients. This article presents current concepts in the pathophysiology of TBI, including mechanisms of injury, biomolecular mediators of injury, and the occurrence of secondary injury. Emergency management, monitoring, and imaging of TBI also are reviewed.

[Subarachnoid hemorrhage: cerebral damage, fluid balance, intracranial pressure and pressure-volume relation]

Changes in osmolality and electrolyte concentrations are observed frequently in patients with subarachnoid haemorrhage (SAH). Intracranial pressure (ICP) plays a determinant role in the development of secondary brain damage following SAH and may be caused by haemorrhage itself, oedema formation and disturbance of cerebrospinal fluid (CSF) dynamics. The relationships among these factors are the aim of this investigation. In 17 comatose SAH patients, ICP was monitored through a ventricular catheter; serial of pressure-volume index (PVI) and CSF formation and reabsorption were performed. Arterio-jugular differences for oxygen and lactate were measured. The average ICP recorded for each 12 hour interval was 18.9 mmHg (SD = 5.9); mean cerebral perfusion pressure (CPP) was 75 mmHg (SD = 13); the lowest CPP value was 30 mmHg. Mean PVI was 22.7 mL (SD = 7.4), ranging from 5 to 36. Eleven patients however, showed a PVI less than 15 mL at some point during testing. Values of CSF dynamics indicated disturbances of CSF reabsorption in 11 cases. When the cause of ICP rise was identified in CSF disturbances, treatment was successful, even in case of reduced PVI. Mean C(a-v)O2, corrected for a PaCO2 of 40 mmHg, was 3.7 mL.dL-1 (SD = 1.1) ranging from the extremely low value of 0.2 to 6.8 mL.L-1. Three patients with extremely low C(a-v)O2 values showed a cerebral production of lactate and developed areas of ischaemia on the CT scan. Hyponatraemia, considered as a sodium plasma concentration of less than 135 mmol.L-1, was detected in seven patients. Hyponatraemia was treated by infusion of hypertonic sodium solutions. Mannitol (1 g.kg-1.d-1 in four doses) was infused if the sodium plasma concentration was not corrected by the former treatment or if ICP exceeded 20 mmHg. Treatment was aimed at preserving cerebral perfusion by providing adequate pre-load, low viscosity (Ht 30%) and sustained arterial pressure. Correction of hyponatraemia was therefore achieved more through hypertonic fluids infusion than by using diuretics.