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

A damped oscillatorA damped oscillator

McDonald’s Blood FlowIn Arteries 5th EdHodder Arnold, London

A Wheatstone BridgeA Wheatstone Bridge

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

Kanazara et al, Anesthesiology 2003;99:48-53Kanazara et al, Anesthesiology 2003;99:48-53

Kanazara et al, Anesthesiology 2003;99:48-53

Kanazara et al, Anesthesiology 2003;99:48-53

Arnal et al, Anaesthesia 2005;60:766-771Arnal et al, Anaesthesia 2005;60:766-771

Arnal et al, Anaesthesia 2005;60:766-771Arnal et al, Anaesthesia 2005;60:766-771

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

Dorman et al, CCM 1998; 26: 1646-1649Dorman et al, CCM 1998; 26: 1646-1649

Dorman et al, CCM 1998; 26: 1646-1649Dorman et al, CCM 1998; 26: 1646-1649

Mignini et al, Crit Care 2006Mignini et al, Crit Care 2006

Mignini et al, Crit Care 2006Mignini et al, Crit Care 2006

Mignini et al, Crit Care 2006Mignini et al, Crit Care 2006

Authors conclude that two approaches are interchangeable

Brachial vs FemoralBrachial vs Femoral

Femoral Brachial One BeatFemoral Brachial One Beat

Radial vs Femoral Radial vs Femoral

Radial vs Femoral (One Wave)Radial vs Femoral (One Wave)

In Extremis- epinephrine bolusIn Extremis- epinephrine bolus

Post EpinephrinePost Epinephrine

Pre Dobutamine and BicarbonatePre Dobutamine and Bicarbonate

Post Bicarbonate (Dobutamine still running)Post Bicarbonate (Dobutamine still running)

Pre Second EpinephrinePre Second Epinephrine

2nd Epinephrine Bolus2nd Epinephrine Bolus

Post 2nd Adrenaline InjectionPost 2nd Adrenaline Injection

Post 2nd Epinephrine BolusPost 2nd Epinephrine Bolus

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