Transcript vs vs - Deranged Physiology

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A comparison of accuracy and efficiency
among different techniques
for measuring cardiac output
Alex Yartsev, 10-05-2011
Cardiac Output
• Volume of blood pumped by the left ventricle over 1 minute
• Measured in litres per minute
• Expresed as
Q
Q = stroke volume x heart rate
Measurement of Cardiac Output
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Holy grail of physiology
Numerous methods tried
Each has strengths
Each has weaknesses
The Gold Standard
There is no gold standard.
The “practical gold standard”
is the PA catheter,
which uses
The Fick Principle
Pugsley et al. Cardiac output monitoring: is there a gold standard and how do the newer technologies compare? Seminars
in Cardiothoracic & Vascular Anesthesia. 14(4):274-82, 2010 Dec.
The Fick Principle
–
First described by Adolf Eugen Fick in 1870
BASIC PREMISE:
Blood flow out of the heart can be calculated using oxygen as
a marker, provided you know how much oxygen is being
consumed by the whole body.
Requires several technically complex measurements to be taken
Guyton and Hall Textbook of Medical Physiology - 10th ed.
The ICU Book by Paul L Marino, 3rd ed.
The Fick Principle
Concentration of
oxygen in
arterial blood
(CA)
Human Body
Concentration of
oxygen in
venous blood
(CV)
Oxygen consumption in ml/min
(VO2)
VO2 = (Q x CA) – (Q x CV)
Guyton and Hall Textbook of Medical Physiology - 10th ed.
The ICU Book by Paul L Marino, 3rd ed.
The Fick Principle
Concentration of
oxygen in
arterial blood
(CA)
Human Body
Concentration of
oxygen in
venous blood
(CV)
Oxygen consumption in ml/min
(VO2)
Or…
Q=
Guyton and Hall Textbook of Medical Physiology - 10th ed.
The ICU Book by Paul L Marino, 3rd ed.
VO2
CA - C V
The Fick Principle
Concentration of
oxygen in
arterial blood
(CA)
Human Body
Concentration of
oxygen in
venous blood
(CV)
Oxygen consumption in ml/min
(VO2)
Or…
Q=
Guyton and Hall Textbook of Medical Physiology - 10th ed.
The ICU Book by Paul L Marino, 3rd ed.
VO2
CA - C V
Assumed:
125ml O2
per minute
per m2
of body surface area
Comparing Indirect Measurement of
Cardiac Output
• Pulmonary Artery Thermodilution (PAC)
• Pulse Contour measurement (PiCCO)
• Observation of signs of adequate / inadequate
cardiac output
The Swan-Ganz
Pulmonary Artery Catheter
William Ganz 1919-2009
Jeremy Swan 1922-2005
Swan-Ganz catheter, 1970 -
• Measurement of Q with trans-right-heart thermodilution
• Modification of the Fick principle
Guyton and Hall Textbook of Medical Physiology - 10th ed.
The ICU Book by Paul L Marino, 3rd ed.
Swan HJ, Ganz W, Forrester J, Marcus H, Diamond G, Chonette D (August 1970). "Catheterization of the heart in man with use of a flow-directed
balloon-tipped catheter". N. Engl. J. Med. 283 (9):
Cardiac Output Measurement with PAC
• Modification of Fick principle
• Injection of 10ml of cold
glucose into the RA
• Measurement of
temperature 10cm
downstream
• The degree and rate of
change in temperature is
inversely proportional to the
cardiac output
•
i.e. higher cardiac output = less change in
temperature, and faster; the cold glucose is rapidly
mixed with a large amount of blood, and quickly
pumped past the thermister.
Limitations of PAC
• Despite using correction factors, heat transfer to catheter wall and right heart
tissues leads to overestimation of cardiac output
• Other sources of error:
–
–
–
–
Rate of cold fluid infusion
Hematocrit
Intracardiac shunts
Fluctuation in pulmonary artery temperature in a humidified
heated circuit
– Variation in cardiac output due to positive pressure ventilation
…Also, it kills people
Gomez CM, Palazzo MG. Pulmonary artery catheterization in anaesthesia and intensive care. Br J Anaesth 1998; 81: 945–5
PiCCO: pulse contour cardiac output monitoring
• Area under aortic flow curve
• Continuous monitoring
• Requires frequent calibration:
properties of the vessels are
constantly changing
• Calibrated with transpulmonary
thermodilution
Wesseling KH, Jansen JR, Settels JJ, Schreuder JJ (May 1993). "Computation of aortic flow from pressure in humans using a nonlinear, three-element model". J. Appl.
Physiol. 74 (5): 2566–73.
PiCCO: pulse contour cardiac output monitoring
• Bottom line: The area under the curve correlates with the stroke volume
• Cardiac output is calculated from stroke volume and heart rate.
Wesseling KH, Jansen JR, Settels JJ, Schreuder JJ (May 1993). "Computation of aortic flow from pressure in humans using a nonlinear, three-element model". J. Appl.
Physiol. 74 (5): 2566–73.
http://www.creaghbrown.co.uk/anae/hdmon.htm#PiCCO
Limitations of PiCCO
• If poorly calibrated, yields garbage data
• Copes poorly with sudden changes of vascular tone
• Relies on OPTIMAL arterial pressure signal
• Pulse contour cannot be interpreted in
– IABP
– Severe aortic regurgitation
– Sustained arrhythmias
• Essentially, you need a normal-looking arterial waveform,
and a hemodynamically stable patient. ? Defeats the purpose.
Wesseling KH, Jansen JR, Settels JJ, Schreuder JJ (May 1993). "Computation of aortic flow from pressure in humans using a nonlinear, three-element model". J. Appl.
Physiol. 74 (5): 2566–73.
Intensive Care Medicine: Annual Update 2008 By Jean-Louis Vincent
Clinical assessment of cardiac output
• Externally obvious or non-invasively
measurable markers of cardiac
performance and tissue perfusion
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–
–
–
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Capillary refill
Peripheral temperature
Palpated pulse pressure
Heart rate
Noninvasive blood pressure
Cardiac auscultation
History, rumour and intuition
.
Shephard JN et al Bedside assessment of myocardial performance in the critically ill. Intensive Care Med. 1994 Aug;20(7):513-21
Conway J. Clinical assessment of cardiac output. Eur Heart J. 1990 Dec;11 Suppl I:148-50.
“What is his cardiac output, doctor?
• Nobody will give you that at the bedside.
• “is this patient shocked” is a better
question
• Most of us wont reliably answer even that
• Disagreement between any two clinicians
Stevenson LW, Perloff JK. The limited reliability of physical signs for estimating hemodynamics in chronic heart failure.JAMA. 1989;261:884-888.
Joly HR, Weil MH. Temperature of the great toe as an indication of the severity of shock. Circulation. 1969;39:131-138.
Butman SM, Ewy GA, Standen JR, et al. Bedside cardiovascular examination in patients with severe chronic heart failure: importance of rest or
inducible jugular venous distension. J Am Coll Cardiol. 1993;22:968-974.
EMST course (ATLS handbook 2009), RACS
Limitations of
Bedside Cardiac Output Assessment
• Blood pressure and heart rate are of minimal use in shock
• Cap refill assessment has large variability between clinicians
– We only seem to agree when its normal or SIGNIFICANTLY delayed
• Proportional pulse pressure correlates well with cardiac index
….in at least one study…
– PPP = (systolic minus diastolic, divided by systolic)
– PPP ≤25% = 91% sensitive for a cardiac index ≤2.2 L/min/m2.
Stevenson LW, Perloff JK. The limited reliability of physical signs for estimating hemodynamics in chronic heart failure.JAMA. 1989;261:884-888
WO, CHARLES C. J et al Unreliability of blood pressure and heart rate to evaluate cardiac output in emergency resuscitation and critical illness Crit
Care Med 1993; 21:218-22
H Otieno et.al. Are bedside features of shock reproducible between different observers? Arch Dis Child. 2004 October; 89(10): 977–979
How do they compare?
What do you compare?
… Accuracy? versus which gold standard?
…Safety?
…influence on hard outcomes?
Which is “better”, in a non-specific sense?
Pugsley et al. Cardiac output monitoring: is there a gold standard and how do the newer technologies
compare? Seminars in Cardiothoracic & Vascular Anesthesia. 14(4):274-82, 2010 Dec.
PAC vs. human
• Connors (1996): 5735 patients prospective cohort, 1989-1994
– PAC increases mortality in first 24 hrs
• Sandham (2003): RCT, 3800 pts,
– goal directed PAC-guided mx vs non-PAC care
– Surgical ICU for the over-60s
– No survival benefit, no mortality increase. PAC doesn’t seem to matter.
• Harvey (2006): Cochrane meta-analysis: PAC vs no PAC.
– PAC does not influence length of stay or mortality, but increases cost.
Uchino et.al Pulmonary Artery Catheter Versus Pulse Contour Analysis: A Prospective Epidemiological Study Crit Care. 2007;10(6)
Harvey S, Young D, Brampton W, Cooper A, Doig GS, Sibbald W, Rowan K. Pulmonary artery catheters for adult patients in intensive care. Cochrane Database of Systematic Reviews 2006, Issue 3
Sandham JD, Hull RD, Brant RF. A Randomized, Controlled Trial of the Use of Pulmonary-Artery Catheters in High-Risk Surgical Patients. Indian J Crit Care Med [serial online] 2003 [cited 2011 May 10
Connors AF Jr, Speroff T, Dawson NV, et al. The effectiveness of right heart catheterization in the initial care of critically ill patients. JAMA 1996; 276: 889–97
PiCCO vs Human
• De Waal (2007) – post cardiac surgery patients
– Acceptable assessment of CO in closed-chest conditions and in stable ICU patients
• Belda (2010) compared PiCCO to TTE:
– good correlation to systolic function
No studies comparing PiCCO vs no PiCCO?
Belda et. al. Clinical validation of minimally invasive evaluation of systolic function; Rev Esp Anestesiol Reanim. 2010 Nov;57(9):559-64.
de Waal EE Validation of a new arterial pulse contour-based cardiac output device. Crit Care Med. 2007 Aug;35(8):1904-9.
PiCCO vs PAC
• Cecconi (2010) : PiCCO accuracy, as compared to PAC gold standard
– CO measurements were in excellent agreement when PiCCO is well calibrated
• Uchino & Bellomo (2007) : 331 pts, prospective epidemiological study
– PiCCO fluid balance was more positive, ventilator free days were fewer
– “Choice of monitoring did not influence major outcomes”
All these studies have excluded patients with permanent arrhythmias.
All agree: in hemodynamically unstable patients, PiCCO becomes less reliable
than PAC
Uchino et.al Pulmonary Artery Catheter Versus Pulse Contour Analysis: A Prospective Epidemiological Study Crit Care. 2007;10(6)
Cecconi M. Dawson D. Casaretti R. Grounds RM. Rhodes A. A prospective study of the accuracy and precision of continuous cardiac outputmonitoring
devices as compared to intermittent thermodilution. Minerva Anestesiologica. 76(12):1010-7, 2010 Dec.
Mayer J, Boldt J, Schöllhorn T, et al. Semi-invasive monitoring of cardiac output by a new device using arterial pressure waveform analysis: a comparison with
intermittent pulmonary artery thermodilution in patients undergoing major cardiac surgery. Br J Anaesth 2007; 98:176–182.
A doctor’s intuition vs invasive measurements,
specifically for CO estimation.
• No RCTs or even large studies
• Eisenberg (1984) :
– 113 doctors asked to assessed CO before insertion of PAC
– Correctly guessed CO 50% of the time
– Changed their therapy based on PAC 58% of the time
– Added unanticipated therapy 30% of the time
Eisenberg PR, Jaffe AS, Schuster DP. Clinical evaluation com pared to pulmonary artery catheterization in the
hemody namic assessment of critically ill patients. Crit Care Med. 1984;12(7):549-553.
The bottom line:
• PAC remains the “gold standard”, in absence of an actual gold standard
• PAC and PiCCO in stable patients agree often enough to be interchangeable in
assessing cardiac output
• PAC reserved for abnormal aortas, balloon pumps arrhythmias and changing
vascular tone
• PiCCO is safer in every other situation
• Humans are 50% accurate in estimating cardiac output
No further questions, please.