Pre-operative, non-invasive cardiac output measurement

H.G. WAKELING Department of AnaesthesiaWestern Sussex Hospitals NHS Trust

ChairCancer Enhanced Survival Clinical Advisory GroupSE Coast Strategic Network and Clinical SenateNHS Englandhoward.wakeling@nhs.net

Conflict of Interest

HonorariaFinancial help with travel to attend scientific meetings

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

One ‘novice’ vs expert compared in 24 patients

First 10 measurements Median(IQR)

PrePLR PostPLRExperienced 71(59 – 85) 87(76 – 93)Novice 66(53 – 76) 77(67 – 86)

Measurements 20 – 25

Experienced 64(57 – 75) 79(74 – 87)Novice 65(56 – 71) 78(73 – 86)

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

Poor exercise toleranceOrthopnoea, swollen ankles, PND+No Angina

Medications and PMH

Atenolol 50mg odFrusemide 40mg odISMN 60mg pdIronGTN

Ca BladderTURPIschaemic heart diseasePleural effusions 2012‘normal’ echo

PH

CI 1.1 l/min/m2

FT 303ms

SVRI 6384 ds.cm-5m2

DO2 300 ml/min

INO 0.68 W/m2

PKR 132

PHSymptoms and Signs of LVFLow CIVery high SVR and PKRLow Inotropy

PlanStop Atenolol and ISMNAdditional diuretic (Co-Amilofruse)

PH 4 weeks later

PHBefore and AfterCI 1.1

FT 303

SVRI 6384

DO2 300

INO 0.68

PKR 132

2.1 l/min/m2

268 ms

3679 ds.cm-5m2

572 ml/min

0.93 W/m2

107

PH

Successful surgeryStroke Volume optimisation ODMNo crystalloidLow dose dobutamine 24 hours

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