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48 Cards in this Set
- Front
- Back
Normal CBF
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is 40 to 50 ml 100 g/min and represents about 15% of cardiac output.
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Changes in CBF are directly coupled with
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CMR02.
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Hypothermia, which reduces CMR02, also decreases CBF
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about 7% for every 10C decrease in body temperature below 37°
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all volatile anesthetics
r/t CMRO and CBF |
All volatile anesthetics also reduce CMR02; however, because they are cerebral vasodilators, they increase CBF.
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Changes in Paco2 produce corresponding directional changes between
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a PaC02 of 20 to 80 mm Hg
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Paco2 induced changes in CBF are transient became of an increase in cerebrospinal fluid (CSF) HC03 concentrations. CBF returns to normal in
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6 to 8 hours, even if the altered PaC02 levels are maintained.
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Autoregulation refers to
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the mechanism that maintains CBF constant in the presence of a changing cpp and reflects the ability of cerebral arterioles to COJ.strict or relax in response to changes in perfusion (distending) pressure.
this response normally requires 1 to 3 mnutes to develop |
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"With respect to inhaled anesthetics, autoregulation is maintained at anesthetic concentrations
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less than 1 minimum alveolar concentration (MAC).
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It higher concentrations, inhaled anesthetics abolish autoregulation, and CBF becomes proportional to
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MAP.
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Intravenous anesthetics do not disrupt
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autoregulation.
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The autoregulation curve in patients with chronic hypertension is shifted to the right such
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that a lower MAP is less well tolerated.
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Decreases in Pao2 result in an exponential increase in CBF below a threshold value of about
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50 mm Hg
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Volatile anesthetics administered during normocapnia at concentrations higher than 0.5 MAC rapidly produce .
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cerebral vasodilation and result in dose-dependent increases . in CBF. CBF remains increased relative to CMR02 during administration of halothane, isoflurane, or sevoflurane .
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The largest increase in CBF occurs with __________
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halothane, with less of an effect seen with isoflurane, desflurane, and sevoflurane. Nitrous oxide also increases CBF.
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Thiopental, propofol, and etomidate are cerebral
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vasoconstrictors that decrease CMR02> CBF, and ICP. These n< drugs may 1:le administered to patients with intracranial : hypertension to decrease ICP.
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Normal CBF % CO
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15
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5 Determinants of CBF include
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(1)CMR02,
(2) PaCO2 (3) cerebral perfusion pressure (CPP) and autoregulation, (4) Pao2 (5) anesthetic drugs |
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Changes in Pacoz produce corresponding directional changes in CBF between a Paco2
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20 to 80 mmHg
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for every 1-mm Hg increase or decrease in Paco2 from 40 mmHg, CBF changes
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As a guide, CBF increases or decreases 1 mL/100 g/min
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Autoregulation refers to the mechanism that maintains CBF constant in the presence of a changing cpp and reflects the ability of cerebral arterioles to constrict or relax in response to changes in perfusion (distending) pressure.
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the mechanism that maintains CBF constant in the presence of a changing cpp and reflects the ability of cerebral arterioles to constrict or relax in response to changes in perfusion (distending) pressure.
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Autoregulation response time
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This response normally requires 1 to 3 minutes to develop, so a rapid increase in MAP is associated with a brief period of cerebral hyperperfusion.
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Autoregulation maintains CBF relatively constant between a CPP of
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50 and 150 mm HG
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With normal autoregularion and an intact blood-brain barrier, vasopressors affect' CBF only when
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MAP is below 50 to 60 mm Hg or above 150 to 160 mm Hg.
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With respect to inhaled anesthetics, autoregulation is maintained at anesthetic concentrations less than
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1 minimum alveolar concentration (MAC). At higher concentrations, inhaled anesthetics abolish autoregulation, and CBF becomes proportional to MAP.
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intravenous anesthetics and autoregulation
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In contrast, intravenous anesthetics do not disrupt autoregulation.
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The autoregularion curve in patients with chronic hypertension is shifted to
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the right such that a lower MAP is less well tolerated.
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The anesthetic state shifts the autoregulatory response to
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the left, which provides for some safety from the decreases in MAP that can occur intraoperatively.
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Decreases in Pa02 result in an exponential increase in CBF below a
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threshold value of about 50 mm Hg
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Volatile anesthetics administered during normocapnia concentrations higher than 0.5 MAC rapidly produce
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cerebral vasodilation and result in dose-dependent increases in CBF
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All intravenous drugs except __________ reduce CMRO2 and CBF in a dose dependent fashion
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All intravenous drugs except ketamine reduce CMROz
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3 IV drugs may be administered to patients with intracranial hypertension to decrease ICP.
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Thiopental, propofol, and etomidate are cerebral vasoconstrictors that decrease CMR02, CBF, and ICP.
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T F Autoregulation of CBF is not altered by propofol or thiopental.
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True
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a Agonists (clonidine and dexmedetomidine) with respect to neuro anesthesia
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a Agonists (clonidine and dexmedetomidine) have sedative, sympatholytic, and analgesic properties. They are unique sedatives in that they do not cause significant respiratory depression. They have no effects on ICP. Because they reduce arterial blood pressure without · having an effect on ICP, they reduce CPP. a Agonists cerebrovascular response to changes in PaC02. Clinically, ar brovascular response to changes in PaC02. Clinically, ar of other anesthetics and analgesics or postoperatively as of other anesthetics and analgesics or postoperatively as and tachycardia. and tachycardia.
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Neuromuscular blocking drugs do not usually affect ICP unless they
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induce release of histamine or hypotension.
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Histamine can cause cerebral
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vasodilation leading to an increase in ICP.
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Succinylcholine may increase ICP through
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stimulation of muscle spindles, which in turn either directly or indirectly results in increased CMRO2
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ICP is normally less than
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10 mm Hg.
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sustained increase in rep above _____ is defined as intracranial hypertension.
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15 mm Hg
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As the intracranial volume increases, CSF is initially translocated into the
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spinal canal.
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The duration of the efficacy of hyperventilation and the duration of decreased Iep are unclear. In patients, however, the effect of hyperventilation wanes with time and CBF returns to normal after about
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6 hours.
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Hyperventilation to decrease Pac02 to _____ attenuates the tendency for volatile anesthetics to increase ICP
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< 35 mm Hg
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Mannitol dose
onset max effects duration |
Mannitol (0.25 to 1 glkg IV) acts as an osmotic diuretic and reduces cerebral water content. The onset of action is 5 to 10 minutes, maximum effects are seen in 20 to 30 minutes, and its effects last for about 2 to 4 hours.
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why NS in neuro cases
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Dextrose solutions are not recommended because they are rapidly distributed throughout body water and, if blood glucose concentrations decrease more rapidly than brain glucose concentrations, water crosses the blood-brain barrier and cerebral edema results.
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VENOUS AIR EMBOLISM Detection
most sensitive |
Transesophageal echocardiography
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most common cause of intracranial hemorrhage.
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Intracranial aneurysms
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Vasospasm of the cerebral arteries is generally manifested
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clinically 3 to 5 days after subarachnoid hemorrhage and is the foremost cause of morbidity and mortality.
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treatment of vasospasm includes "triple H"
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hypervolemia,
hypertension, hemodilution |
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autonomic hyperreflexia,
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manifested as abrupt systemic hypertension with an associated baroreflex-mediated compensatory bradycardia spinal cord transection above T6 is frequently associated with autonomic hyperreflexia, with as many as 85 % of patients manifesting this response.
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