Neuroanesthesia small animal

Question 1

Objectives (4)

Answer 1

1. Discuss pathophysiology of cerebral blood flow and intracranial pressure
2. Present effect of anesthetic and preanesthetic agents on intracranial pressure
3. Discuss different ways to decrease intracranial pressure
4. Discuss anesthetic considerations for intervertebral disc dz and spinal injuries

Question 2

Elastance

Answer 2

The change in pressure per change in volume

-elastence increases significantly when increase in volume reaches a critical point

Question 3

Flow-metabolism coupling

Answer 3

As the metabolic rate (CMR) of the brain increases, cerebral blood (CBF) flow also increases
-Exact mechanism unknown

Question 4

Cushing reflex

Answer 4

The combination of arterial hypertension and bradycardia due to an increase in ICP

Question 5

Intrinsic regulation of Cerebral Blood Flow

Answer 5

Autoregulation between CPP of 50-150

-above and below, the CBF passively follows flow changes

Question 6

Factors inhibiting Auto-regulation (6)

Answer 6

1. brain tumor
2. inhalant agents
3. head trauma
4. intracranial hemorrhage
5. hypoxia
6. lactic acidosis

Question 7

Extrinsic factors in Cerebral Blood flow (3)

Arterial Carbon Dioxide Tension (PaCO2)

Answer 7

1. most potent regulator
2. PaCO2 < 20 may ischemic the brain
3. Prolonged hypocapnia decreases response of CBF to CO2

Question 8

Extrinsic factors in Cerebral Blood flow (3)

Arterial oxygen tension (PaO2)

Answer 8

1. PaO2 less than 50 mmHg will inc CBF
2. Prolonged hypoxia indirectly affects CBF due to vasodilation caused by lactic acidosis
3. PaO2 > 300 mmHg causes cerebral vasoconstriction from oxygen toxicity

Question 9

Extrinsic factors in Cerebral Blood flow (3)

Body Temperature

Answer 9

1. Hyperthermia increases CBF and cerebral metabolic requirement (CMR)
2. 7.0 % increase in CBF and CMR per degree C increase in body temp
3. Body temp > 42C causes CMR to decrease (brain death)

Question 10

Extrinsic factors in Cerebral Blood flow (2)

Blood viscosity

Answer 10

1. Polycythemia can dec CBF to one-half of normal values

2. Anemia inc CBF

Question 11

Extrinsic factors in Cerebral Blood flow (4)

Drainage of venous blood from head

Answer 11

1. Interference to drainage of venous blood from head can inc blood volume in head
2. Positioning of head to allow drainage of venous blood helps
3. Avoid leashes
4. Avoid jug sticks

Question 12

Premeds

Answer 12

1. Ace
   - can control and prevent seizures
   - don’t use in BAR patient
2. Benzos
   - anticonvulsant, use for a seizure patient pre or during
   - dec CBF by dec brain O2 consumption
   - Have readily available during recovery in case seiz during extubation
3. Opiods
   - be careful of vomiting (butorphanol, buprenorphine, fentanyl bester)
   - be careful of respiratory depression->inc PaCO2->inc ICP
4. Alpha-2 agonists (Dexmedetomidine)
   - dec CBF with iso
   - Causes bradycardia and hypertension (mimics cushings response)

Question 13

Induction agent should

Answer 13

1. Decrease ICP
2. Decrease CBF
3. Decrease CMR

Question 14

Induction drugs that dec, ICP, CBF, and CMRO2

Answer 14

Propofol, alfaxalone, etomidate

Question 15

Anesthetic maintenance

Answer 15

Inhalents minimally affect CBF when used at conc < 1 MAC

Question 16

The effect of inhalants on CBF and ICP can be minimized by

Answer 16

hyperventilating to mild hypocapnea

Question 17

Fluid therapy goals

Answer 17

1. Maintain euvolemia
2. avoid hypervolemia
3. correct blood loss

Question 18

Methods to decrease/prevent inc in ICP (5)

Answer 18

1. Tracheal intubation-good plane anesth and lidocaine
2. positioning-head up w/o occluding jug
3. ventilate patient to eucapnia, hyperventilate paCO2 30-35 because hyocapnia can worsen cerebral ischemia
4. Mannitol
5. Corticosteroids-tumor, not trauma

Question 19

Specific case IVDD/spinal injuries

Answer 19

1. maropitant to avoid post op asp peumon

2. adjuct analgesia-ketamine/lidocaine CRI