RE CH28 Part 2 Flashcards
Which inhalation Anesthetics cause the greatest increase in cerebral blood flow?
Isoflurane, followed by sevoflurane and des.
CBF is unaltered with isoflurane MAC _____ to ____
0.6 to 1.1
With inhalation anesthetics at what MAC does the EEG become isoelectric?
2.5 MAC
What does N2O do to CBF, CMRO2, and ICP
Increases
Through which mechanisms do inhalation agents decrease cerebral perfusion pressure?
Decreasing map and increasing ICP
What are the effects of propofol on CBF and CMRO2?
Dose dependent decreases of 40-50%
What is the effect of etomidate on CMRO2 and CBF?
Reduces both. Decreases ICP without reducing CPP.
What are the effects of dexmetomidine on CMRO2 and CBF?
No change in CMRO2. Decreases CBF.
What is the effect of synthetic opioids on CBF and CMRO2?
CBF: Dose dependent decreases (to 25 mL/100g/min)
CMRO2: Dose dependent decreases (40 to 50%)
Which synthetic opioid produces the greatest decrease in MAP and ICP?
Alfentanil
Why should meperidine be avoided in the neurosurgical patient?
It’s metabolite normeperidine is a well-known convulsant
What is the effect of benzodiazepines on CBF, CMRO2 and ICP?
CBF: dose dependent decrease
CMRO2: dose dependent decrease
ICP: no change
What is the effect of Ketamine on CBF, CMRO2, and ICP?
CBF: Increase (60-80%)
ICP: Increase
CMRO2: Unchanged
List the intracranial contents.
Brain (12%)
Intracellular water (78%)
CSF (75 mL)
Blood (50 mL)
What is the total volume of intracranial contents?
1200 to 1500 mL
What is the equation for CPP?
CPP = MAP-ICP
What is the normal adult ICP?
5-15 mmHg
How does the intracranial compartment compensate for increases in mass (blood or tumors)
Decrease the CSF compartment (Increase in CSF absorption)
What is the gold standard for monitoring ICP?
Intraventricular catheter.
What ICP level is considered to be intracranial hypertension?
20 - 25 mmHg
What are the signs/symptoms of intracranial hypertension?
Headache, N/V, papilledema, focal neurological deficits, altered ventilators function, decreasing LOC, seizures, and coma.
What occurs when ICP exceeds 30 mmHg?
CBF progressively decreases and a vicious cycle is established:
-ischemia produces brain edema, which increases ICP, which further precipitates ischemia.
CBF decreases ______% for every 1 mmHg decrease in Paco2
4%
What is the last resort treatment for intracranial hypertension?
Bilateral decompression craniectomy
How does lowering Paco2 decrease ICP?
Respiratory alkalosis causes vasoconstriction which decreases CBF and ICP
CMRO2 decreases ______% for every 1 degree centigrade decrease in body temperature.
7%
Paco2 is approximately ______ mmHg higher than ETco2
2-5
What pathologic changes cause a slowing of EEG activity?
When oxygen delivery is compromised.
What effect do inhaled Anesthetics have on latency and amplitude of SSEPs?
Increased latency, decreased amplitude.
What effect does fentanyl have on SSEP latency and amplitude?
Slight increase latency, slight decreased amplitude.
What effect does propofol have on SSEP latency and amplitude?
Increase latency, no change in amplitude.
What effect does ketamine and ethmoid ate have on SSEP latency and amplitude?
Increase both.
What effect does dexmetomidine have on SSEP latency and amplitude?
No change
What is the capillary pore size of the BBB?
0.7-0.9 nm
What are fluid goals for supratentorial surgery?
Patients should be kept isovolemic, isotonic, and isooncotic.
What is the fluid of choice for neurosurgery?
0.9 NaCl, LR should be avoided due to glucose content.
What is a paradoxical air embolism?
Entry of air into the systemic circulation
A PFO exists in what percent of the population?
30-35%
What are the signs/symptoms of a venous air embolism (VAE)
Pulmonary HTN Hypoxemia CO2 retention Increased dead space ventilation Decreased ETco2
What is the most sensitive monitor for VAE?
TEE
What is the treatment for VAE?
- Tell surgeon to flood the field
- Stop N20 and 100% O2
- Aspirated right atrial catheter
- Valsalva maneuver or compress jugular veins for 5-10 sec
- Position left lateral trendelenberg
A 50% N2O concentration does what to air bubble volume? What about 70% concentration?
50% concentration doubles air volume
70% concentration quadruples the air bubble volume.
What is a common surgical approach to pituitary tumors?
Transsphenoidal
Should you hyperventilate for pituitary tumor surgery?
No. It will cause retraction of the pituitary into the sella causing difficult access
What is the max dose of 1:100,000 epi for submucosal administration?
10 mL for 70 kg patient.
What is the max dose for cocaine?
200 mg
What dose of lidocaine should be administered to avoid coughing on emergence?
1.5 mg/kg
What are the signs/symptoms of Subarachnoid hemorrhage?
Intense headache in 85% of patients Transient loss of consciousness in 45% of patients N/V Photophobia Fever Meningismus Focal Neuro deficits
What is transmural pressure?
Differential pressure between MAP and ICP and represents the stress applied to an aneurysm wall.
Increases in blood pressure directly increase transmural pressure.
Why should caution be taken when reducing transmural pressure?
Cerebral autoregulation may be impaired after SAH and reduction in BP may aggravate cerebral ischemia.
What are the most common ECG changes seen with SAH?
T and ST segment changes.
What is the incidence of rebleeding in the first days following SAH? This is associated with what mortality rate?
50% incidence of rebleeding
80% mortality rate.
What is the leading cause of morbidity and mortality in patients with SAH after aneurysm rupture?
Cerebral vasospasm
What is triple H therapy?
The most effective regimen to prevent neuro deficits secondary to cerebral vasospasm:
Hypertension, hypervolemia, and hemodilution (Hct 27-30%).
What is the goal MAP in the face of aneurysm rupture?
40 to 50 mmHg
What is the first and most rapidly effective therapy for increased ICP?
Hyperventilation.
