Blood-Brain
Barrier
|
Blood-Brain Barrier
|
|
The blood-brain barrier (BBB) is a selectively permeable boundary that protects the brain from drugs and other toxins. The BBB limits access to the brain for most medications; access to the brain depends on the characteristics of a particular drug, such as the drug's molecular weight and protein binding ability. Following a traumatic brain injury (TBI), the BBB is often disrupted. This disruption may potentially allow increased drug access to the brain. Several therapy options are available to compensate for the change in permeability in the BBB. These treatments include: dietary considerations, hypothermia, and hyperosmolar therapy.
Dietary
Considerations
The majority of patients
who have sustained a traumatic brain injury become hypermetabolic and metabolize
drugs too quickly. Nutritional intervention is used to counterbalance
the effects of hypermetabolism. Dietary modifications can change the rate
a drug is metabolized. Increasing protein intake to 15-20% of total caloric
intake trhough the use of protein supplements is recommended. Raising
dietary protein intake has been associated with correcting the BBB's drug metabolizing
capacity.
Hypothermia
Patients with a head
injury that have been treated with mild to moderate hypothermia have shown an
increased chance of recovery. Exposure to decreased temperatures causes
a decrease in the permeability of the blood - brain barrier which produces a
decrease in the absorption of medications. This decease in absorbtion
counteracts the increased permeability of the BBB, which is common after a TBI.
During the period of hypothermia, standard dosage guidelines need to be followed
to avoid the effects of drug accumulation.
Hyperosmolar
Therapy
Hyperosmolar therapy
(e.g., mannitol or hypertonic saline) is used to manage increased intracranial
pressure in patients who have experienced a TBI . This therapy technique results
in increased permeability of substances across the BBB. The duration and
magnitude of the BBB permeability is determined by the molecular size of the
drug.
|
|
|
|
|
