CHAPTER 37 | Neuroanesthesia Flashcards
Intracranial hypertension is defined as a sustained increase in intracranial pressure (ICP) above
A. 5 to 10 mm Hg
B. 15 to 20 mm Hg
C. 25 to 30 mm Hg
D. 30 + mm Hg
A. 5 to 10 mm Hg
The normal ICP is 5 to 15 mm Hg (or 7-20 cm H2O)
- In patients with elevated ICP, premedication must be carefully titrated, or AVOIDED completely.
What is the normal CPP?
80-100 mm Hg
CPP progressively decreases as ICP or CVP increases. Likewise, CPP decreases as MAP decreases.
CPP less than 50 mm Hg shows slowing on EEG, CPP of 25-40 mm Hg shows flat EEG, and CPP sustained at less than 25 mm Hg results in irreversible brain damage.
The normal CMRO2 is:
A. 3 - 3.8 mL/100g/min
B. 5 mL/100g/min
C. 2 mL/100g/min
The cerebral metabolic rate of oxygen consumption (CMRO2) is normally **3 to 3.8 mL/100 g/min. **
The brain glucose consumption is approximately 5 mg/100 g/min.
Normal cerebral blood flow is:
A. 50 mL/100 g/min
B. 450 mL/min
C. 35 mL/100g/min
A. 50 mL/100 g/min or 750 mL/min
What is the effect of sitting position during neuroanesthesia?
Increase risk of VAE
Calculate cerebral perfusion pressure (CPP) from the following data:
Blood pressure (BP) 100/70
Heart rate (HR) 65 beats/min
Cardiac output 5 L/min,
CVP of 5 cm/H2 O
ICP 15 mm Hg
A. 60 mm Hg
B. 65 mm Hg
C. 70 mm Hg
D. 75 mm Hg
B. 65 mm Hg
CPP is equal to mean arterial pressure (MAP) minus the ICP or CVP, whichever is greater.
In some institutions, CVP and/or ICP is measured in cm H2 O; to convert from cm H2 O to mm Hg, multiply the amount of cm of H2 O by 0.74 (i.e., 10 cm H2 O pressure = 7.4 mm Hg).
CPP = MAP − (ICP or CVP, whichever is greater)
MAP equals the diastolic blood pressure + 1/3 of the pulse pressure. Pulse pressure equals the systolic blood pressure minus the diastolic blood pressure.
In this case the Pulse pressure is (100 mm Hg -70 mm Hg) / 3 = 10 mm Hg. Thus the MAP = 70 mm Hg = 10 mm Hg = 80 mm Hg.
Since the ICP is greater than the CVP the CPP = 80 mm Hg (MAP) − 15 mm Hg (ICP) = 65
Which of the following intravenous (IV) anesthetic induction agents is relatively contraindicated in patients with intracranial hypertension?
A. Propofol
B. Etomidate
C. Ketamine
D. Thiopental
C. Ketamine
Barbiturates (such as thiopental or methohexital), propofol, and etomidate all decrease CMR, CBF,
CBV, and ICP and can be used for IV anesthesia in patients with elevated ICP.
A 62-year-old patient is scheduled to undergo resection of a large frontal lobe intracranial tumor under general anesthesia. Preoperatively, the patient is alert and oriented, and has no focal neurologic deficits. Within what range should Paco 2 be maintained during surgery?
A. 15 and 20 mm Hg
B. 30 and 35 mm Hg
C. 40 and 45 mm Hg
D. 45 and 50 mm Hg
C. 40 and 45 mm Hg
To help prevent an increase in ICP, mild hypocarbia is often induced. With severe hypocarbia (i.e., Paco 2 reduced below 20 mm Hg), cerebral ischemia
has been reported in both normal humans and laboratory animals.
When the Paco 2 is < 20 mm Hg, it is likely that cerebral ischemia is caused by a leftward shift of the oxyhemoglobin dissociation curve (produced by the severe respiratory alkalosis) and possibly by intense cerebral vasoconstriction.
Why do we AVOID premedication on a patient with elevated ICP?
Benzodiazepines and opioids, even in small doses, can depress respiration, leading to elevated PaCO2 and subsequent exacerbation of intracranial hypertension.
Depressed ventilation > Elevation of PCO2 > Elevation of ICP!
Also, in patients with preexisting or resolved motor deficits, even sedative doses of common anesthetic drugs, especially those with significant GABA-ergic activity, have been shown to exacerbate or “unmask” these deficits.
Hemodynamic GOAL when inducting a patient with elevated ICP EXCEPT:
A. Avoid hypertension
B. short-acting opioid and lidocaine (1.5 mg/kg) intravenously to blunt the sympathetic response to laryngoscopy is recommended
C. Succinylcholine is an absolute contraindication
D. Avoid hypoventilation
E. Avoid hypercapnia
C. Succinylcholine is an absolute contraindication - NOT AN ABSOLUTE contraindication
Succinylcholine should be used with caution in patients with preexisting motor deficits as upregulation of nicotinic receptors at the neuromuscular junction can lead to increased risk of hyperkalemia. Also, succinylcholine can increase ICP but this effect is of short duration.
Dose of mannitol for ICP control?
A. 0.5 - 1.5 g/kg
B. 500 mcg/kg
C. 2.5mg/kg
D. 10mg/kg
A. 0.5 - 1.5 g/kg
For intracranial surgeries, ICP control is
paramount until the dura mater is opened.
To this end, once Mayfield fixation of the head and positioning are safely completed, mannitol (0.5 to 1.5 g/kg) may be administered if ICP control is needed, as are steroids (e.g., dexamethasone 10 mg) and, in some cases, a prophylactic anticonvulsant.
MAC of __ may interfere with neuromonitoring:
A. 2.0 MAC
B. 1.0 MAC
C. more than 0.5 MAC
> 0.5 MAC
For patients with elevated ICP, volatile anesthetics are often limited to 0.5 MAC, if used at all, to minimize the degree of cerebral vasodilation and inhibition of autoregulation that can result.
more than 0.5 MAC of volatile agent may interfere with SSEP and MEP monitoring.
A 1°C decrease in core temperature will decrease the CBF to ___
A. 5 - 10%
B. 10 - 15%
C. 6 - 7%
D. 2 -3 %
C. 6 - 7%
Temperature is also an important determinant of CBF, with a 6% to 7% decrease in CBF per 1°C
decrease in core temperature.
CBF changes by approximately __ of baseline for each 1 mmHg change in PaCO2:
A. 2%
B. 3%
C. 7%
D. 5%
B. 3%
Maximum peak pressure in the setting of SAH or increased ICP:
A. 40 mmHg
B. 20 mmHg
C. 10 mmHg
D. 8 mmHg
A. 40 mmHg
For patients undergoing an intracranial procedure, tidal volume should be maintained at 6 to 8 mL/kg to minimize potential inflammatory injury to the lungs, with peak pressures kept at less than 40
cmH2O.
Which of the following is INACCURATE in terms of the fluid management in intracranial surgeries?
A. The goal of fluid management should be to keep the patient euvolemic
B. Hypotonic solutions can be used on patients with TBI
C. Glucose containing solutions are generally avoided
D. Hypertonic saline (3%) supplementation is indicated in moderate to severe hyponatremic states
E. Rapid rises in serum sodium (more than 3 to 4 mEq/L/h) must be avoided as this poses a risk for central pontine myelinolysis
B. Hypotonic solutions can be used on patients with TBI
Neurosurgical patients having nonurgent surgery should have a platelet count over:
A. 145,000
B. 80,000
C. 100,000
C. 100,000/mm
Serum glucose during neurosurgical procedures should be maintained between:
A. 90 to 180 mg/dL
B. 140 - 180 mg/dL
C. 80 - 120 mg/dL
A. 90 to 180 mg/dL
Intraoperative hyperglycemia >180 mg/dL has also been associated with an increase in postoperative infections after craniotomy.
TRUE or FALSE
Dexamethasone should also be avoided following pituitary surgery.
Why?
TRUE!
No dexamethasone in post-pituitary surgery!
Dexamethasone should also be avoided following pituitary surgery as it can suppress the
hypothalamic–pituitary–adrenal axis and significantly increase the false positive rate for diagnosis of postoperative hypopituitarism.
Which of the following statements concerning air embolism during intracranial operations is true?
(A) It does not occur in supine patients
(B) It is prevented by positive end-expiratory pressure
(C) It is confined to the right side of the heart and the pulmonary vasculature
(D) It is detectable by measurement of end-tidal nitrogen
(E) It is most efficiently treated by aspiration from a pulmonary artery catheter
(D) It is detectable by measurement of end-tidal nitrogen
An infarct involving the hypothalamus would most likely result from occlusion of which artery?
A. Anterior spinal artery
B. Vertebral artery
C. Anterior cerebral artery
D. Middle cerebral artery
E. Posterior cerebral artery
C. Anterior cerebral artery
The anterior portion of the hypothalamus, which consists largely of the preoptic region, obtains its blood supply from branches of the anterior cerebral arteries, where they lie above the optic nerves. There may be an element of blood supply
from the anterior communicating artery as well.
Cerebral perfusion pressure (CPP), in the absence of intracranial pathology, is MOST closely correlated with which parameter?
A. Intracranial pressure (ICP)
B. Central venous pressure (CVP)
C. Cerebral blood volume (CBV)
D. Mean arterial blood pressure (MAP)
D. Mean arterial blood pressure (MAP)
CPP = MAP—ICP or CVP, whichever is greatest.
Because the ICP (and CVP) is usually less than 10 mm Hg, CPP is primarily determined by MAP. Normal CPP is approximately 80-100 mm Hg.
CPP progressively decreases as ICP or CVP
increases. Likewise, CPP decreases as MAP decreases. CPP less than 50 mm Hg
shows slowing on EEG, CPP of 25-40 mm Hg shows flat EEG, and CPP sustained
at less than 25 mm Hg results in irreversible brain damage. CBV refers to cerebral
blood volume.
Which of the following situations has the least significant effect on cerebral blood flow (CBF)?
A. PaCO2 of 80
B. Temperature of 34°C
C. Increased blood viscosity
D. Acute metabolic acidosis
D. Acute metabolic acidosis
Acute metabolic acidosis has little effect on CBF because hydrogen ions cannot readily cross the blood-brain barrier.
Paco2 affects CBF. CBF increases approximately 1-2 mL/100 g/min per mm Hg increase in Paco2. This effect is thought to be due to CO2 diffusing across the blood-brain barrier and inducing changes in the pH of the CSF and the cerebral tissue. CBF changes 5%-7% per 1°C change in temperature.
Hypothermia decreases both CMR and CBF, whereas hyperthermia has the reverse effect. The most important determinant of blood viscosity is hematocrit.
A decrease in hematocrit decreases viscosity and can improve CBF though probably not to an appreciable extent. Conversely, elevated
hematocrit increases blood viscosity and can reduce CBF to an appreciable extent.
All of the following medications can be used to decrease elevated ICP EXCEPT which one?
A. Hypertonic saline
B. Furosemide
C. Propofol
D. Ketamine
E. Acetazolamide
D. Ketamine
IV induction agents generally decrease CBF. Ketamine is the only exception in that it increases CBF.
A 54 year old male ASA II for smoking came in the ER with the following symptoms: severely obtunded, hemiparesis, early decerebrate posturing. BP 160/90 HR 90 O2 sat 92%
Based on the Hunt and Hess grading scale, the patient should have a score of:
A. 2
B. 3
C. 4
D. 5
C. 4
Which of the following assessment tool utilizes GCS and motor deficit in evaluating aneurysm?
A. Fisher grading system
B. Hunter and Hess grading system
C. World Federation of Neurological Surgeons Grading Scale
C. World Federation of Neurological Surgeons Grading Scale
