How and where should I measure arterial pressure in a shocked patient, and what does it mean? Richard Beale Guy’s and St Thomas’ Hospital Trust London, UK
Dec 27, 2015
How and where should I measure arterial pressure in a shocked
patient, and what does it mean?
How and where should I measure arterial pressure in a shocked
patient, and what does it mean?
Richard Beale
Guy’s and St Thomas’ Hospital Trust
London, UK
DisclosuresDisclosures
Dr Beale and the Adult Critical care Dr Beale and the Adult Critical care Service at Guy’s and St Thomas’ NHS Service at Guy’s and St Thomas’ NHS Foundation Trust have research Foundation Trust have research collaborations with:collaborations with:
LiDCO LtdLiDCO Ltd Philips Medical SystemsPhilips Medical Systems Edwards LifesciencesEdwards Lifesciences Pulsion Medical SystemsPulsion Medical Systems
Why is measuring arterial blood pressure important?Why is measuring arterial blood pressure important?
Although there are other, more sophisticated Although there are other, more sophisticated definitions of shock – hypoperfusion and definitions of shock – hypoperfusion and hypotension are key aspects of the syndromehypotension are key aspects of the syndrome
Measurement and monitoring of arterial blood Measurement and monitoring of arterial blood pressure are therefore intrinsic to the pressure are therefore intrinsic to the diagnosis and treatment of shockdiagnosis and treatment of shock
In modern critical care practice, virtually all In modern critical care practice, virtually all shocked patients have invasive arterial blood shocked patients have invasive arterial blood pressure monitoringpressure monitoring
Current practice (1)Current practice (1)
Continuous invasive ABP measurement is Continuous invasive ABP measurement is now absolutely standardnow absolutely standard
High quality, disposable measuring kits are High quality, disposable measuring kits are routinely usedroutinely used
Blood pressure values are key components Blood pressure values are key components of definitions of shock and organ of definitions of shock and organ dysfunction, and of treatment guidelinesdysfunction, and of treatment guidelines
Current practice (2)Current practice (2)
Modern haemodynamic monitoring now Modern haemodynamic monitoring now frequently includes:frequently includes: continuous cardiac output monitoring
based upon arterial pulse wave analysis measurement of variation in ABP with
controlled ventilation as a marker of volume responsiveness
Purpose of this reviewPurpose of this review
To concentrate upon ABP measurement as To concentrate upon ABP measurement as currently performed in modern ICU practicecurrently performed in modern ICU practice
To consider the strengths and weaknesses To consider the strengths and weaknesses of current practiceof current practice
To make recommendations for practice To make recommendations for practice based upon literature, experience and based upon literature, experience and common sense!common sense!
Historical perspectiveHistorical perspective
Attempts to interpret the pulse are as old as Attempts to interpret the pulse are as old as the practice of medicinethe practice of medicine
The “modern” era of invasive blood The “modern” era of invasive blood pressure measurement is generally held to pressure measurement is generally held to have started with the Reverend Stephen have started with the Reverend Stephen HalesHales
Rapid developments in non-invasive and Rapid developments in non-invasive and invasive blood pressure measurement in invasive blood pressure measurement in the last hundred yearsthe last hundred years
Approaches to measuring ABPApproaches to measuring ABP
Indirect (non-invasive) methodsIndirect (non-invasive) methods Sphygmomanometry
– Palpatory method– Auscultatory method
Oscillometric technique Finger plethysmography External tonometry
Approaches to measuring ABPApproaches to measuring ABP
Direct (invasive) methodsDirect (invasive) methods Intra-arterial catheter
– Widely used in modern intensive care– Radial artery the most common site– Femoral artery increasingly used– Brachial and axillary vessels sometimes used– Used with modern high-fidelity disposable
transducer sets
Regarded as “Gold Standard” Catheter tip transducers also available
DampingDamping
Four damping conditionsFour damping conditions Critically damped
– Mass does not oscillate and returns exponentially to equilibrium position
Overdamped– Rate of return is also non-oscillatory, but slower
Underdamped– Mass will oscillate, but will decay exponentially
Undamped– Mass will oscillate sinusoidally indefinitely
Different damping conditionsDifferent damping conditions
McDonald’s Blood FlowIn Arteries 5th EdHodder Arnold, London
Artifacts in pressure recording (1)Artifacts in pressure recording (1)
End-pressure artifactEnd-pressure artifact If a catheter tip faces the direction of
flow, it will measure the sum of the lateral pressure and the kinetic energy pressure resulting from flow
Effect is usually small
Artifacts in pressure recording (2)Artifacts in pressure recording (2)
Catheter impact artifactCatheter impact artifact Transient pressures are created when a
catheter is hit e.g. when in the heart Any component that coincides with the
resonant frequency of the system will cause a superimposed oscillation
May cause LV dp/dt to be as much as 100% too high, but will decay exponentially
Pressure patterns within the circulationPressure patterns within the circulation
Arterial pressure waves vary considerably:Arterial pressure waves vary considerably: With site With age With drugs With disease
Is this clinically relevant?Is this clinically relevant?
ABP and flow from centre to peripheriesABP and flow from centre to peripheries
McDonald’s Blood FlowIn Arteries 5th EdHodder Arnold, London
IABP harmonics and distanceIABP harmonics and distance
McDonald’s Blood FlowIn Arteries 5th EdHodder Arnold, London
Contemporaneous central and peripheral ABPContemporaneous central and peripheral ABP
McDonald’s Blood FlowIn Arteries 5th EdHodder Arnold, London
Pressure and flow in the circulationPressure and flow in the circulation
McDonald’s Blood FlowIn Arteries 5th EdHodder Arnold, London
Changes in aortic and radial BP during exerciseChanges in aortic and radial BP during exercise
McDonald’s Blood Flow In Arteries 5th Ed, Hodder Arnold, London
Effect of nitroglycerinEffect of nitroglycerin
McDonald’s Blood Flow In Arteries 5th EdHodder Arnold, London
Clinical implications of these differencesClinical implications of these differences
Important to understandImportant to understand Not too problematic if peripheral SBP is Not too problematic if peripheral SBP is
higher than central SBP, DBP lower and higher than central SBP, DBP lower and MAP similarMAP similar
Does the obverse occur?Does the obverse occur? What happens in shock?What happens in shock? How might treatment be altered?How might treatment be altered? What are the clinical implications?What are the clinical implications?
Kanazara et al, Anesthesiology 2003;99:48-53Kanazara et al, Anesthesiology 2003;99:48-53
12 patients undergoing CPB12 patients undergoing CPB Wire tip transducer used to obtain pressure Wire tip transducer used to obtain pressure
recordings from aorta to radial arteryrecordings from aorta to radial artery 7 patients developed a reduction in ABP 7 patients developed a reduction in ABP
towards the peripheriestowards the peripheries This was explained by a reduction in This was explained by a reduction in
elasticityelasticity
Dorman et al, CCM 1998; 26: 1646-1649 Dorman et al, CCM 1998; 26: 1646-1649
14 patients with septic shock, requiring 14 patients with septic shock, requiring norepinephrine >5 mcg/minnorepinephrine >5 mcg/min
Simultaneous radial and femoral artery Simultaneous radial and femoral artery pressure measurementspressure measurements
Two patients also studied after resolution of Two patients also studied after resolution of shockshock
Mignini et al, Crit Care 2006Mignini et al, Crit Care 2006
Authors conclude that two approaches are interchangeable
Low output state and vasopressors: effect on PPV etcLow output state and vasopressors: effect on PPV etc
Our Clinical Observations Our Clinical Observations
Dramatic FA – RA ABP gradients do occur in severe shockDramatic FA – RA ABP gradients do occur in severe shock This is especially so with high dose vasopressor and This is especially so with high dose vasopressor and
hypovolaemiahypovolaemia Peripheral perfusion is usually poor clinicallyPeripheral perfusion is usually poor clinically Peripheral ABP may lead to false assumptions about need Peripheral ABP may lead to false assumptions about need
for more vasopressorfor more vasopressor Central ABP may allow vasopressor dose reduction and Central ABP may allow vasopressor dose reduction and
volume therapyvolume therapy Phenomenon reverses as patient improves – perhaps a Phenomenon reverses as patient improves – perhaps a
new therapeutic goal?new therapeutic goal?
Conclusions: measuring IABP in shockConclusions: measuring IABP in shock
Clinicians should be aware of technical Clinicians should be aware of technical issues when measuring ABPissues when measuring ABP
They should be aware of potential effect They should be aware of potential effect of site on amplitude and morphologyof site on amplitude and morphology
In shock, peripheral BP may In shock, peripheral BP may substantially underestimate central ABPsubstantially underestimate central ABP
If in doubt, measure central BPIf in doubt, measure central BP