Neuro Anesthesia Part 1 (VanPelt) Flashcards

Question

Answer 1

80% Brain 12% Blood 8% CSF

Answer 2

**Increase** in the volume of **ONE** requires a corresponding **decrease** in the volume of the other **TWO** components.

Answer 3

Largely responsible for the development of the anesthesia record (1905) Out of concern for the safety of his patients, he emphasized the need to record the surgical patient’s pulse, RR, temp, & B/P

Answer 4

1. Hypertension 2. Bradycardia 3. Respiratory disturbances *Late & unreliable sign that usually precedes brain herniation

Answer 5

1. Hypertension 2. Bradycardia 3. Respiratory disturbances *Late & unreliable sign that usually precedes brain herniation

Answer 6

1. Decrease **CSF Volume**: with lumbar drain, shunt, or loop diuretics 2. Decrease **Intracranial blood volume**: hyperventilation, IV agents (mannitol) burst suppression, hypothermia 3. Decrease **brain cell volume:** osmotic duretics, and dehydration/avoid free water

Answer 7

Lateral Ventricle Foramina of Monro Third Ventricle Cerebral aqueduct of Sylvius Fourth Ventricle --> Foramen of Magendie (medial) Foramen of Luschka (lateral) Cisterna Magna SA Circulation Absorbed in the arachnoid granulations over the cerebral hemispheres ***memorize*** The mnemonic is Lady Monroe's Three Siblings Fought, for Magical Lights Seeing Arrogant Seniors

Answer 8

**100-160cc in the body 500cc produced q 24 hours** **Production**: Choroid plexus **Elimination/Reabsorbed:** Arachnoid villi Effects of drugs: Enflurane/Lasix: decreases reabsorption, therefore, is avoided

Answer 9

ensure its at proper level, open vs. closed, and NOT on a pressure bag

Answer 10

Complete inhibition of carbonic anhydrase maximally reduces CSF flow 40-60% Acetazolamide 30 mg/kg IV (Diamox) They have found only ~ 20% reduction from control after furosemide at 50 mg/kg - partial inhibition of carbonic anhydrase of choroid plexus (and perhaps other sites of CSF secretion) based on the affinity of furosemide for carbonic anhydrase

Answer 11

Reversible inhibition of the enzyme carbonic anhydrase resulting in reduction of hydrogen ion secretion at renal tubule and an increased renal excretion of sodium, potassium, bicarbonate, and water to decrease production of aqueous humor Also inhibits carbonic anhydrase in central nervous system to retard abnormal and excessive discharge from CNS neurons

Answer 12

Neurosurgical patients may be on Acetazolamide preoperatively… Side effect: Metabolic Acidosis Duration of the drug: 4-5 hours Typically corrects itself…

Answer 13

Arterial blood pressure - ABP Cerebral blood flow - CBF Cerebral perfusion pressure - CPP Cerebral vascular resistance – CVR Arterial carbon dioxide levels - PaC02 Arterial oxygen Tension – PaO2 Cerebral metabolic rate – CMR Hyperventilation CMO2 rate in relation to CBF –how we effect the “coupling” of the two How does temperature effect blood volume?...

Answer 14

It has long been known that hyperventilation will decrease intracranial pressure (ICP) At the beginning of the 1990s, it was widely held that this provided universal therapeutic value The advent of the oximetric pulmonary artery catheter: - Allowed investigators to retrogradely cannulate the jugular vein in head trauma patients - examine venous hemoglobin oxygen saturation in response to therapeutic intervention.

Answer 15

In some patients, hyperventilation actually increased brain oxygen deficit. Presumably was a result of vasoconstriction, which augmented ischemic states Jugular venous hemoglobin oxygen saturation monitoring has become widely applied in the intensive care unit ***Remains impractical in most operative settings

Answer 16

Without such monitoring, it is impossible to predict in which patients hyperventilation may be detrimental or beneficial Owing to the observations made in head trauma patients, the use of hyperventilation in the OR has been largely abandoned unless surgical conditions directly dictate additional brain relaxation

Answer 17

We do hyperventilate (“*mild*”) **Goal: Between 30-35** Reasons: Surgical Exposure (Inverse Steal) Use of VA AND Robin Hood effect

Answer 18

Back to hyperventilation: Decreased PCO2 constricts normal vessels but not the ischemic areas (d/t vasomotor paralysis). This is one reason we do hyperventilate patients with intracranial tumors and ICP

Answer 19

an increase in CMRO2 would be accompanied by an increase in CBF - CBF is COUPLED to CMRO2 - some drugs and processes cause an UNCOUPLING of CBF and CMRO2 -- such as hyperventilation - INCREASES in metabolism result in DECREASES in vascular resistance, increasing CBF

Answer 20

VA **alter** the normal coupling of CBF & CMR The combination of a DECREASE in neuronal metabolic demand with an increase in cerebral blood flow (metabolic supply) is termed** luxury perfusion** May only be desirable during induced hypotension & it supports the use of a VA, particularly Iso, during this technique

Answer 21

In contrast to this potentially beneficial effect during global ischemia: - a detrimental **circulatory steal** phenomenon is possible with VA in the setting of focal ischemia VA **INCREASES** CBF in normal areas of the brain but not in ischemic are, where arterioles are already maximally dilated AKA: **Vasomotor paralysis**

Answer 22

End result: redistribution of blood flow away from ischemic to normal areas

Answer 23

conflicting evidence ... Increases in CBF (from most to least) - Halothane - Enflurane - Isoflurane - Desflurane

Answer 24

decreases in CMRO2 - isoflurane - halothane - enflurane *enflurane at high concentrations cause SZ like activity

Answer 25

- VA dilate cerebral vasculature & impair autoregulation in a dose dependent manner - At equivalent MAC & MAC - Halo increases CBF up to 200%, ENFL up to 40%, Iso (& Des & Sevo) up to 20% - Dose-dependent impairment of autoregulation - Halo > 1 MAC - cerebral autoregulation abolished

Answer 26

Cerebrovascular response to **PCO2** is generally preserved Hyperventilation with use of VA counteracts the increase in CBF After 2-5 hours of administration of VA (NOT over MAC), CBF begins to normalize

Answer 27

- Reduction in CMR is maximal when EEG becomes isoelectric, unlike hypothermia - Barbiturates produce a dose dependent decrease in CMR & CBF until EEG becomes isoelectric - Iso & Enfl (& Des & Sevo?) reduce CMR by up to 50% - Halothane reduces CMR by less than 25%

Answer 28

Hypothermia - decreases CBF & CMR Decreases CMR by 6-7% per degree Celsius w/proportional decrease in CBF **CBF changes 5-7% per C** At 20 degrees C - EEG = isoelectric Hyperthermia - increases CBF & CMR At 42 degrees C - O2 activity begins to decrease & may reflect cell dam

Answer 29

A multinational consortium of investigators was formed to examine the risks and benefits of mild hypothermia in patients undergoing aneurysm surgery. The International Hypothermia Aneurysm Surgery Trial (IHAST2) was performed over five years

Answer 30

This was believed to be the first prospective, randomized, double-blinded outcome trial with sufficient statistical power to define whether an intervention made by neuroanesthesiologists benefits long-term postoperative outcome. Until this study is completed, the use of mild hypothermia remains of speculative benefit …

Answer 31

There were no significant differences between the group assigned to intraoperative hypothermia & the group assigned to normothermia in the duration of stay in the intensive care unit, the total length of hospitalization, the rates of death at follow-up or the destination at discharge. **Conclusions**: Intraoperative hypothermia did not improve the neurologic outcome after craniotomy among good-grade patients with aneurysmal subarachnoid hemorrhage.

Answer 32

Cerebral Edema: - Cytoxic: bad NA/K pump - Vasogenic: leaky capillaries - Osmotic Shrinking of brain cell: - mannitol - lasix avoid iatrogenic increase in brain volume d/t hypotonic crystalloids

Answer 33

Mechanisms: - intravascular compartment hypertonic relative to intracelebral fluid - requires intact cell membranes* - Osmotically active diuretic Major effect is to increase water excretion, in large doses, osmotically active diuretics also increase NA & K excretion 100ml of H2o is expected to be removed from the brain

Answer 34

Dose: - Initial: 0.25-1 gram/kg over 30 min - repeat: serum osmolality of 320 mOsm/L - 20% Mannitol: ***Know How To Calculate Dose!!!***

Answer 35

admin with skin incision or dural opening, depending on hospital - theoretical risk of aneurysm rupture

Answer 36

1. Raises CVP 2. dehydration 3. brain swelling 4. rebound 5. aneurysm rupture

Answer 37

1. mannitol 2. lasix - avoid iatrogenic increase in cell size: - hypotonic crystalloids - large, sudden bolus' of fluids

Answer 38

0.9% NS: osmolarity 308 mOsmol/L LR: 273 mOsmol/L

Answer 39

Most of the formal logic for prohibiting the use of glucose-containing solutions still depends on studies performed in animals The near universal observation that hyperglycemia worsens outcome in models of ischemia and trauma has been supported by a large number of correlative human studies that indirectly provided similar conclusions In the Neurosurgery patient there may be a rise in blood glucose for various reasons... As in any illness or injury, a relative resistance to insulin effect with a decrease in glucose consumption in brain and muscle that can occur. **High glucose levels together with the failure of oxidative glucose metabolism combine to produce excess lactate, which may account for poor neurological outcome...**

Answer 40

Plasma glucose threshold values of **greater than 180 mg/dL** are consistent in both animal and human studies for predicting **worsened outcome** Remember, these patients may be on steroids preoperatively and have an elevated glucose to begin with Check glucose routinely

Answer 41

D5W = 253 = Hypo D5 1/4NS = 355 = Iso D51/2NS = 432 = Hyper D5NS = 586 = Hyper D5LR = 525 = Hyper

Answer 42

Tonicity = 273 = Iso Actually can be considered slightly *hypotonic* because it provides approximately 100ml of free water per liter The lactate in this solution is converted by the liver into bicarbonate In the event of ischemia, lactate is readily available for anaerobic metabolism & will worsen ischemic event *No more than 1L*

Answer 43

Dilutional hypercholemic acidosis High chloride content (154 meq/L) & HCO3 free Presentation: Metabolic acidosis

Answer 44

Need to determine the Anion gap **Anion gap = Major plasma cations - Major plasma anions** Anion Gap = NA - Cl + HCO3 Normal 140 - (104 + 24) =12 ( 9-15 meq/L)

Answer 45

Renal failure Ketoacidosis Lactic acidosis Ingestion of toxins Rhabdomyolysis

Answer 46

*Normal Anion Gap (Hyperchoremic)* Increased GI losses of HCO3 Increased renal losses of HCO3 TPN Increased intake of Cl containing solutions Dilutional Lg. Amounts of bicarb free fluids

Answer 47

Depends on the severity Change IVF Respiratory component corrected If pH remains below 7.20, alkali therapy, usually in the form of NaHCO3 (7.5% solution)

Answer 48

Dose = 1meq/kg or derived from the base excess - NaHCO3 = BE x 30% x body weight - NaHCO3 = -10meq/L x .30 x 70 = 210 meq - In practice, only 50% of the calculated dose (105) would be given , then perform ABG

Answer 49

In the 1980s, it remained standard practice to dehydrate patients with intracranial pathology under the assumption that brain volume would be decreased This was often performed at the expense of stable hemodynamics and cerebral perfusion pressure. A large body of laboratory evidence was accumulated that contradicted the logic for fluid restriction. Accordingly, many practitioners have substantially increased the volume of crystalloid administered during neurosurgical procedures. Recognition that plasma osmolality should be maintained.

Answer 50

Minimize post-op cerebral edema Minimal, 1-3 ml/kg/hr Limit crystalloid to <10 cc/kg + replacement of urine output Colloid of Choice = Albumin Hetastarch “OK” but be careful Blood

Answer 51

Innervated by: - Sympathetic (Vasoconstrictive) - Parasympathetic (Vasodilatory) - Noncholinergic nonadrenergic fibers: serotonin & vasoactive intestinal peptide The normal physiologic function of this innervation is uncertain but it may play a role in pathologic states…cerebral vasospasm/vasomotor paralysis

Answer 52

Maintenance of optimal CPP is critical ABP should be normal or slightly elevated & increases in ICP or CVP should be avoided O2 carrying capacity should be maintained…There is always exceptions to the rule “10/30” rule: UPENN research r/t this concept SAH undergoing an AVM resection

Neuro Anesthesia Part 1 (VanPelt) Flashcards

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