Anesthesia for the Neurologic and Neurosurgical patient

Question 1

why is anesthesia for a pt with CNS pathology difficult?

Answer 1

the brain is encased within a complete bony structure (cranium/skull) and thus has minimal space for expansion

Question 2

what is intracranial pressure?

Answer 2

pressure exerted by the fluids and tissues inside on the fixed compartment of the cranium

these fluids and tissues are composed of 4 parts: blood, CSF, tissue or cells, and extracelular fluid

Question 3

what is cerebral metabolic rate?

Answer 3

rate of substrate utilization by the CNS tissue. substrates include oxygen, glucose, or any other molecules necessary for brain function

CMR depends on level of CNS activity, anesthetic depth, drugs, electrolytes, acid base balance, cellular needs etc

Question 4

what is cerebral blood flow?

Answer 4

amount of blood being delivered to the cells and tissues within the cranium. varies depending on CMR, blood gases (o2 and CO2),, blood viscosity, systemi cmean blood pressure and anestehtic drugs

Question 5

what is cerebral perfusion pressure?

Answer 5

intravascular pressure minus the pressure in the surrounding tissues, generally with the formula
CPP = MAP - ICP

body attempts to regulate the CPP to maintain appropriate delivery of oxygen and other metabolic substrates to the tissues within the cranium

Question 6

what is the equation for cerebral perfusion pressure?

Answer 6

CPP = MAP - ICP

Question 7

what should always be suspected in cases of head trauma or suspected intra cranial pathology?

Answer 7

increased ICP
other causes of increased ICP can be hydrocephalus,, invasion of masses into the calvarium, edema from seizures, hypercapnie

Question 8

increases in ICP decrease _____

Answer 8

CPP: cerebral perfusion pressure (CPP = MAP - ICP)
can cause focal or global ischemia and edema, which further exacerbates the increase in ICP. can cause herniation of the cerebellum through the foramen magnum and death

Question 9

what are signs of increased ICP?

Answer 9

• papilledema (swelling of optic disk)
• anisocoria or dilated/fixed pupils
• strabismus
• depressed mentation
• abnormal respiratory pattern
• opisthotonus
• brady cardia and hypertension: cushing’s reflex

Question 10

what is the Cushing’s reflex?

Answer 10

bradycardia and hypertension: often a late marker of ICP, where the MAP increases suddenly in the face of increased ICP to maintain CPP. the baroreceptors in the carotid and aortic bodies respond to the acute hypertension by significantly decreasing HR, manifested as bradycardia