Pre-operative, non-invasive cardiac output measurement H.G. WAKELING Department of Anaesthesia Western Sussex Hospitals NHS Trust Chair Cancer Enhanced Survival Clinical Advisory Group SE Coast Strategic Network and Clinical Senate NHS England [email protected]
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Pre operative, non-invasive cardiac output measurement
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From Deltex Medical Intavent Astratech
The USCOM Device
Describe the USCOM DeviceWhat it doesHow to use itLearning curve identificationCorrelation with Oesophageal DopplerCase HistoriesBedside Inotropy and CPET
The USCOM Device
Continuous wave USAortic and pulmonary valvesTrans-cutaneousCompletely non-invasiveNeonates to Geriatrics
How does it work?
Fd= 2Ft x V x cosθ C
Fd Doppler frequencyFt Transmitted frequencyV Velocity of bloodθ Angle between beam and blood flowC Velocity of sound in soft tissue (constant)
USCOM looks at flow through valvesDifferent waveform from desc. aorta
Velocity-time integral VTi
Aortic valve outflowFibrous AnnulusRigid
Little systolic change
Constant size in adulthood
Linear relationship with height
Outflow Tract Diameter:Linearly related to height in adultsLinearly related to height in childrenNeonates <50cm
weight is used
1 Start of systole2 Valve opening3 Peak velocity4 End of blood flow
valve closes
5 VTi6 Diastolic flow Early diastolic filling Atrial contraction
Pulmonary Valve
Learning Curve?
4 novice operators1 experienced operatorSV measurementsBefore Passive leg raise (PLR)After PLR In 25 healthy volunteers
Inter-rater correlation between assessorsA: during training, pre leg raise (R2 = 0.71) B: during training, post leg raise (R2= 0.59)
C: post-training, pre leg raise (R2= 0.94) D: post training, post leg raise (R2= 0.95)
Comparison with ODM
135 paired observations in theatre
Bland–Altman plot All 135 paired readings
Mean Bias 5.9ml, 95%CI -20-+32, % error 30%
Testing for Concordance
77 paired readings pre/post fluid
45% of challenges SVODM ↑≥10%
94% SVUSCOM also ↑
5 cases SVUSCOM ≥10% when no ΔSVODM
Sensitivity was 94%, Specificity 88%Positive predictive value (PPV) 87% Negative predictive value (NPV) of 95%.
Testing for Concordance
Bedside InotropyAcknowledgement Prof. B.Smith and Veronica Madigan, Bathurst Base Hospital and
Charles Sturt University.
USCOM allows for Inotropy assessment
Inotropy – heart power
External cardiac workKinetic energy – flow of the bloodPotential energy – generation of BP
Power is work per unit time
Kinetic energy½.mass.velocity2
Mass = SV x DensityDensity is dependant on Hb
Mean velocityVelocity sampled every 10 milliseconds If flow time 360ms – 36 readings to
average
Potential EnergyΔ Pressure x Δ Volume
Δ PressurePressure leaving the heart (MAP) minus
pressure of blood entering heart (CVP)
Δ VolumeStroke Volume
Work = KE + PEPower is work per unit time
Time for heart to work is the flow timeMeasured in Watts
Power = Kinetic energy + Potential energy Flow time Flow time
Indexed by dividing by BSASmith-Madigan Inotropy Index (SMII) W.m-2
Application of Inotropy Index
Normal heart SMII 1.6 – 2.2 W.m-2
LVF patients SMII 0.4 – 1.0 W.m-2
Failing heart 33% normal inotropy
Ratio of Potential to Kinetic energyPKR
Normally 30:1Sepsis much lower – possibly only 3:1Flow but little Pressure
Arterial hypertension - vasoconstriction May be over 150:1Very little flowVery high SVR
Comparison with CPET data
USCOM measurements pre and immediately post CPET23 patients so farPreliminary data shows good correlation between SMII and Anaerobic ThresholdBoth pre and post CPET
SMII Pre CPET vs AT
SMII Post CPET vs AT
Correlation Coefficient 0.56
SMII vs AT
In addition 3 patients with low SMII
failed to reach AT!
So preliminary data suggests SMII may
be useful as correlates well with AT
Important - independent of exercise
Case historySpecialist Pre-assessment Anaesthesia and Medicine Clinic (SPAM)
Mr PH 88 years 80.6Kg 173.5cmExtended right hemicolectomy
2 days level HDUTroponin riseEcho confirmed diastolic heart failureAspirin, ramipril clopidogrel started
2 days level 1
PH
3 days level 1 bedHome day 11
Echo 8 weeks laterDilated and severely impaired LVEF 35%
6/12Remains well
USCOM Summary
Effective, non-invasive cardiac output4 hour or 50 uses learning curveGood comparison with ODMGood concordance with ODMIn Pre-op setting:Allows advanced cardiac assessment Inotropy appears to correlate with ATEnables effective use of CVS medication