Correlation of carotid stump pressure and back flow during carotid surgery

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Correlation of carotid stump pressure and back
flow during carotid surgery

• Jenny Yun Jiang
• MSc. Candidate
• Medical Biophysics, University of Western Ontario

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Objectives

• 1. Review the role of endarterectomy, the anatomy
  of the Circle of Willis collateral blood flow
• 2. To provide preliminary results of our study of
  carotid stump pressure vs. carotid back flow

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Blood flow in diseased arteries

• Blood vessels thicken in atherosclerosis
• Carotid artery primary location for
  atherosclerotic plaque to develop in arteries
  supplying brain
• Vessel stenosis gt70 diameter (i.e. gt90 area)
  experience significant pressure losses limited
  blood flow and significant risk of stroke

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Carotid endarterectomyreduces stroke risk

• Internal, external and common carotid arteries
  clamped
• Lumen of the internal carotid artery opened,
  atheromatous plaque removed.

internal
external
common
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But lots of blood flows in the internal carotid
artery!

• Soustiel et al. (2002)
• Mean ICA flow volume 277/-25mL/min
• range 239-338mL/min
• Schebesch et al. (2004)
• Mean ICA flow 202-205 mL/min

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How does the brain get blood while the artery is
clamped?

• Circle of Willis THE primary provider of
  collateral blood flow during carotid
  endarterectomy
• Anatomy varies by individual

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Importance of collateral flow

• Poor collateral flow is a cause of intraoperative
  stroke (1 to 2 of persons operated)
• Surgeons try to predict collateral flow during
  surgery using two main techniques
• Carotid stump pressure
• Carotid back flow

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Measuring stump pressure

• 19-gauge needle connected to nylon pressure
  tubing by transducer and recorder

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Measuring carotid backflow

• Carotid artery clamped during endarterectomy
• Rate of back flow measured by syringe
• Internal carotid artery
• clamp removed
• Blood washes back
• Measure volume/time

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Our hypothesis

• There is a positive correlation between carotid
  stump pressure and carotid back flow during
  carotid endarterectomy

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Methods

• Prospective database of surgical carotid
  endarterectomies
• Cases with both CSP and BF selected
• Mean CSP versus BF plotted using linear
  regression model.
• y mxb (yBF, mslope, xCSP, bintercept)

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Results

• Positive correlation between CSP and BF
• Stump pressure useful in predicting volume of
  back flow
• Higher stump pressure yielded more back flow

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Discussion (1)

• Delaurentis et al. (1993)
• Significant correlation between stump pressure
  retrograde flow (plt0.001)
• y9.503 0.8301x, R20.67
• Stump pressure measured highest systolic
  pressure after stabilization
• Blood drawn after flowing through narrow tube

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Discussion (2)

• Our equation y19.195 3.0749x, R20.48
• DeLaurentiss equation y9.503 0.8301x,
  R20.67
• Much different than DeLaurentis!!
• Stump pressure measured mean between systolic
  diastolic
• Mean (systolic 2 diastolic) /3
• Blood drawn from syringe after drainage

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Discussion (3)

• Hunter et al. (1982)
• Stump pressure gt25mmHg indicate good collateral
  circulation
• Kurata et al. (1996)
• Stump pressure of over 50mmHg? safe to operate
  without shunt
• Good collateral blood flow

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Further research

• Additional data to be obtained from prospective
  surgical database
• Major hypothesis Radiographic anatomy of the
  circle of Willis predicts the effectiveness of
  the cerebral collateral circulation

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Acknowledgement

• Supervisor
• Dr. Stephen Lownie, M.D.
• Advisory Committee
• Dr. Andrew Leung, M.D.
• Dr. David Holdsworth, Ph.D.

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• The End

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Stress

• Force/AreaStress
• Force acting over an area
• Units Pa

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Strain

• Ratio of change in objects dimensions to
  original dimension, caused by stress applied
• Shear strain
• Distance of shear /original length
• Tensile or compressive strain
• change in length /original length

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Features of Newtonian Non-Newtonian flow

• Newtonian flow
• Viscosity depends on temperature pressure, NOT
  forces acting on it (doesnt change shape)
• Non-Newtonian flow
• Viscosity subject to change even at given
  temperature pressure
• More prominent at resting flow conditions
  (Relt100) less prominent at high Re (Regt400)

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Non-Newtonian flow in blood

• Low shear rates orientation of RBC random
  relative to flow
• Increasing shear rate RBC orient with minimal
  cross-section to flow
• Absence of aggregation, velocity profile
  approximates Poiseuille flow (parabolic). With
  aggregates, profile blunted (higher viscosity in
  center stream)

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Flow in capillaries is non-Newtonian

• Viscosity decreases in smaller vessels? Fahreus
  Effect
• Poiseuilles Law is inaccurate in capillary tubes
  lt0.3mm diameter
• Reduction in blood viscosity ceases when vessel
  diameter 5-7µ further reductions, viscosity
  increases? INVERSION phenomenon.
• Erythrocyte deforms if vessel diameter is further
  reduced.

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Measuring Newtonian fluid flow

• Q flow rate
• ? fluid viscosity
• L tube length
• Ppressure difference between the ends

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Reynolds

• Dimensionless number measure of ratio of
  inertial forces to viscous forces
• Quantifies the relative importance of the two
  forces

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• Spencer et al. (1992).
• Good collateral circulation
• disproportional drop in stump pressure for small
  decrease in flow velocity in MCA
• Poor collateral circulation
• disproportional drop in velocity for small
  decrease in stump pressure