Neurocritical Care Interventions

Neuroprotection

An important part of neurocritical care is the management of other, non-neurological, related conditions in such a manner as to protect the injured brain from any untoward effects. This involves strict management of fever, blood electrolyte levels, blood pressure and oxygen levels.

A fever is defined as greater than 100.4 Fahrenheit (or 38 degrees Celsius). Fever is associated with worsened neurological injury in patients with brain injury. The reason for this is unknown. More than likely, injured brain cells are less likely to recover if brain temperature is high. Therefore, fevers are strictly managed in the intensive care unit. Patients are treated with an escalating regimen. First patients are given medications to relieve fever. If fever persists, a cooling blanket is used. Other measures which may be used include irrigating chilled fluids into the bladder, ice packs to the body and infusing chilled intravenous fluids. Because fever may be the first sign of infection, antibiotics are usually started and continued until laboratory tests confirm a lack of infection.

Electrolytes are substances found in blood. The most important neurologicaly are potassium, sodium and magnesium. An important part of neuroprotection is keeping these electrolyte levels “super normal.” Potassium is important for the conduction of electrical impulses in the heart and in nerves. Sodium is also important for nerve function, but also regulates fluid levels in brain cells and outside of brain cells. If sodium is too low the injured brain can begin to swell, even causing coma or seizures. Likewise, having sodium too low can effect brain cells as well. Magnesium may be associated with an improvement in neurological outcomes and is the subject of current studies. Electrolyte levels in the intensive care unit are regulated by intravenous administration of electrolyte containing fluids.

Management of blood pressure in the intensive care unit takes may serve multiple purposes, depending on the underlying condition. In cases where there is bleeding from within the brain, it’s felt that elevated blood pressure may cause further bleeding. In these cases strict monitoring and treatment insures that blood pressure remains normal. This is a difficult task because the body’s initial reaction to a brain hemorrhage is a type of reflex where blood pressure actually goes very high. We have to counter that reflex to prevent further bleeding. In cases where there is insufficient blood flow to the brain, it may be necessary to artificially elevate blood pressure to maintain blood flow and oxygen delivery. Conditions requiring this intervention include brain swelling and brain artery spasm, or vasospasm. In order to closely monitor blood pressure a small catheter may be inserted in a wrist or groin artery.

The goal of most intensive care unit interventions in the injured neurological patient is to maintain proper oxygen delivery for the brain. Oxygen is essential for recovery and survival of brain cells. Brain oxygenation is maintained in two ways. First, oxygen is delivered by blood, so it is essential to maintain brain blood flow. This is done by augmenting blood pressure and reducing pressure in the brain itself, which can counter blood flow to the brain. Secondly, we must insure that the blood that is being delivered to the brain is ideally saturated with oxygen to allow delivery of oxygen from the blood cells to the brain cells. When the percentage of blood cells that are bound to oxygen exceeds 90%, the amount of oxygen that can be carried is nearly saturated. Further oxygen must be administered in order to increase the amount that is dissolved in the blood fluid, or plasma. In other words, with supplemental oxygen, oxygen is not only being carried to the brain by the red blood cells but is also being carried to the brain by being dissolved in the plasma. The air that we normally breathe contains 21% oxygen. Patients in the intensive care unit are typically breathing 28% to 40%, or even higher, levels of oxygen. Lastly, in order to monitor oxygen levels a probe is applied to the patient’s finger. This probe measures the percentage that blood cells are saturated with oxygen. Sometimes, a blood sample has to be obtained directly from an artery in the wrist for a more comprehensive measure of oxygenation in the body.