Acute Brain injury

Question 1

What is the difference between 1º and 2º brain injury?

Answer 1

1º = immediate effect of injury on brain substance
2º = changes that evolve over time to cause further damage to the brain

Question 2

Why is cerebral blood flow important?

Answer 2

High energy demand
- 15% of Q; 20% of O2 consumption

No metabolic reserves!
- all energy derived from AEROBIC oxidation of glucose

Question 3

What are the 3 major factors affecting cerebral BF?

Answer 3

1. MAP
2. Vascocontriction and dialation of arterioles
3. ICP

Question 4

How does ICP affect cerebral BF?

Answer 4

CPP = MAP - ICP
*MAP = DBP + (SBP-DBP)/3

CPP = cerebral perfusion pressure
- normally kept in 70-90 mmHg range (50-70 for TBI pts)
if CPP < 40 - brain ischemia
if CPP too high = damage to blood vessels - edema - brain injury

up until 25mmHg - changes in volume result in negligible changes in ICP; but above 25mmHg, small changes in volume result in LARGE changes in ICP

large ICP = small CPP = less blood getting to brain = ischemia

Question 5

How is CPP calculated?

Answer 5

CPP = MAP - ICP

*MAP = DBP + 1/3(SBP-DBP)

Question 6

Describe autoregulation

Answer 6

• an ongoing process in the normal healthy brain
• affected by head injury

Autoregulation:

• HIGH MAP = vasoconstriction to reduce blood going into brain
• LOW MAP = vasodialation to increase blood going into brain

*this only works for pressures 60-160mmHg; past these pressures (lower or higher) - vasodialation and constriction have reached their max and can no longer control blood flow

Question 7

How does PaCO2 and PaO2 affect cerebral blood flow?

Answer 7

LOW PaO2 (< 60 mmHg)= vasodialation to get more blood into the brain (ie. more oxygen)

HIGH PaCO2 (40-80mmHg) = vasodialation to get more CO2 OUT of the brain

High PaO2 = vasoconstriction (but not nearly to the same extent as vasodialation with low PaO2)

Question 8

What does the evidence say re:effects of multimodal physio on ICP and CPP?

Answer 8

Multimodal physio:

• increases ICP
• but CPP remains unchanged due to increases in MAP

Question 9

How does MHI increase ICP?

Answer 9

Increase in introthoracic pressure - reduces cerebral venous outflow - increase cerebral venous volume - increased ICP

Question 10

What can be done to reduce the ICP hike from suctioning?

Answer 10

Sedation prior to suctioning lessens but doesn’t remove the effect on ICP; without suctioning there is a rise in ICP

Question 11

What is the clinical implication of the findings by Paratz and Burns (1993) that percs, vibes, shakes cause a drop in ICP

Answer 11

Take a break between different techniques to give ICP a chance to recover

Question 12

How does positioning affect ICP?

Answer 12

• Cx flexion/extension increases ICP
• supine to side lying increases ICP
• HDT increases ICP (cephalad fluid shift, reduced cerebral venous return, raised ICP)

Question 13

How does exercise affect ICP?

Answer 13

• AROM/PROM no effect on CPP/ICP

- valsalva maneuvre - raises ICP

Question 14

What are the general principles of intervention for acute TBI pt?

Answer 14

1. Treat when CPP/ICP is stable (not too low/not too high)
2. Avoid interventions in quick succession bc this can raise ICP
3. Keep treatments short/frequent
4. Modify/stop as necessary
5. MONITOR! - ICP/CPP/EtCO2/SpO2/BP/MAP/ECG