Neurocritical Care Interventions

Invasive monitoring

Invasive monitoring involves the placement of a device, inside the body, in order to monitor parameters essential for making critical decisions in saving the neurologically injured patient. Invasive monitoring is used to monitor blood pressure, monitor how the heart is working, monitor brain pressure, temperature and oxygen levels.

While a blood pressure cuff can intermittently measure blood pressure, continuous, second by second monitoring requires an arterial catheter. An arterial catheter is a small tube that is inserted in either a groin or wrist artery. The catheter is then hooked to a small tube, in turn connected to a monitor. Doctors and nurses can then continuously monitor blood pressure by looking at the monitor.

Sometimes, in order to maintain the best degree of blood flow to the brain possible, it is necessary to make sure that the heart is functioning optimally. Invasive monitoring allows us to monitor, and manipulate, certain heart functions to maintain blood flow to the brain. A central venous catheter is a tube inserted into the neck or shoulder, which travels from a neck or shoulder vein to a major vein near the heart. This measures central venous pressure (CVP). CVP is a measure of how full the heart is before it pumps. Having the heart full of blood prior to pumping insures an optimal amount of blood will be pumped. To optimize CVP, intravenous fluids are given. Cardiac output measures how much blood is being pumped from the heart with each beat. The heart usually does not pump out all of the blood that fills it. By measuring cardiac output, we can give drugs and administer intravenous fluids that maintain an ideal amount of output with each beat of the heart. Cardiac output is measured by a special catheter inserted in the veins of the shoulder or neck, which to the heart and into the arteries of the lung, or by a combination of a central venous catheter and an arterial catheter.

While brain pressure can be monitored by a ventriculostomy, (see above), an intracranial pressure monitor (ICP monitor) is invasive, but less so. Rather than being placed through the brain and into the ventricle, an ICP monitor requires a smaller hole in the skull and is a small bolt that is placed just under the surface of the brain. The main disadvantage to a ventriculostomy is that the ICP monitor cannot be used to drain brain fluid. The main advantage is that in cases where there is a large hemorrhage or brain swelling an ICP monitor may be easier to place than a ventriculostomy.

Along with an ICP monitor, several other small tubes may be placed through a small hole in the skull. These tubes can measure brain oxygen levels and temperature. Since the goal of Neurocritical care is to maintain brain oxygenation, it makes sense that measuring oxygen levels from the brain itself would be helpful. This has been shown to improve outcomes in brain trauma patients. Temperature monitoring in the brain can be very useful. We know that elevated brain temperatures are associated with worsened neurological outcomes. Since fever is very common in the brain injured patient, this is a common concern in the critical care unit. Typically we measure temperature in the body, but the actual brain temperature may be higher. Therefore, there is an obvious advantage to direct brain temperature monitoring. Interventions to lower body and brain temperature will be based on more accurate and timelier information.