INVASIVE ARTERIAL PRESSURE MONITORING

Dr. T. Vikram Kumar Naidu MD(Anaesthesia),

(DM) (Cardiac anaesthesia) (UNMICRC)

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SUBTITLES• Introduction

• Indications

• Basic priciples

• Percutaneous radial artery cannulation

• Complications

• Components

• Levelling and zeroing

• Normal arterial pressure waveforms

• Arterial blood pressure gradients

• Abnormal arterial pressure

waveforms

• Waveform analysis for prediction of

intravascular volume responsivenesss

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INTRODUCTION

• Intra-arterial blood pressure (IBP) measurement is often considered to

be the gold standard of blood pressure measurement.

• Despite its increased risk, cost, and need for technical expertise for

placement and management, its utility in providing crucial and timely

information outweighs its risks in many cases

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Indications for Arterial CannulationContinuous, real-time blood pressure monitoring

Planned pharmacologic or mechanical cardiovascular manipulation

Repeated blood sampling

Failure of indirect arterial blood pressure measurement, e.g. burns or

obesity

Supplementary diagnostic information from the arterial waveform

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BASIC PRICIPLES

• The pressure waveform of the arterial pulse is transmitted via the

column of fluid, to a pressure transducer where it is converted into an

electrical signal.

• This electrical signal is then processed, amplified and converted into a

visual display by a microprocessor.

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Percutaneous Radial Artery Cannulation

• The radial artery is the most common site for invasive blood pressure

monitoring because it is technically easy to cannulate and

complications are uncommon

• Modified Allen’s test

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• “Transfixation” technique

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ULTRASOUND IMAGING

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Alternative Arterial Pressure Monitoring Sites

• Ulnar

• Brachial

• Axillary

• Femoral – seldinger technique

• Dorsalis pedis

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Complications of Direct Arterial Pressure Monitoring• Hemorrhage• Misinterpretation of data• Distal ischemia• Pseudoaneurysm• Arteriovenous fistula• Arterial embolization• Infection• Peripheral neuropathy

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PHYSICAL PRINCIPLES

• A wave is a disturbance that travels through a medium, transferring

energy but not matter.

• One of the simplest waveforms is the sine wave

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• Fourier Analysis• The arterial waveform is clearly not a simple sine wave, but it can be

broken down into a series of many component sine waves• The process of analysing a complex waveform in terms of its

constituent sine waves is called Fourier Analysis.

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Properties

• Natural frequency

• Damping coefficient

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• The natural frequency of a system determines how rapidly the system

oscillates after a stimulus

• The damping coefficient reflects frictional forces acting on the system

and determines how rapidly it returns to rest after a stimulus

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Natural Frequency

• It is important that the IBP system has a very high natural frequency –

at least eight times the fundamental frequency of the arterial waveform

(the pulse rate).

• Therefore, for a system to remain accurate at heart rates of up to

180bpm, its natural frequency must be at least: (180bpm x 8) / 60secs

= 24Hz.

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Natural Frequency

• The natural frequency of a system may be increased by:

Reducing the length of the cannula or tubing

Reducing the compliance of the cannula or diaphragm

Reducing the density of the fluid used in the tubing

Increasing the diameter of the cannula or tubing

• Commercially available systems -200Hz

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Damping

• Anything that reduces energy in an oscillating system will reduce the

amplitude of the oscillations. This is termed damping.

• Some degree of damping is required in all systems (critical damping),

but if excessive (overdamping) or insufficient (underdamping) the

output will be adversely effected.

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Underdamped arterial pressure waveform Overdamped arterial pressure waveform

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Factors that cause overdamping include:

Friction in the fluid pathway

Three way taps

Bubbles and clots

Vasospasm

Narrow, long or compliant tubing

Kinks in the cannula or tubing

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FAST-FLUSH TEST

• Provides a convenient bedside method for determining dynamic

response of the system

• Natural frequency is inversely proportional to the time between

adjacent oscillation peaks

• The damping coefficient can be calculated mathematically, but it is

usually determined graphically from the amplitude ratio

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COMPONENTS OF AN IBP MEASURING SYSTEM

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COMPONENTS OF AN IABP MEASURING SYSTEM• Intra-arterial cannula

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COMPONENTS OF AN IABP MEASURING SYSTEM

• Intra-arterial cannula

• Fluid filled tubing

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COMPONENTS OF AN IABP MEASURING SYSTEM

• Intra-arterial cannula

• Fluid filled tubing

• Transducer

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COMPONENTS OF AN IBP MEASURING SYSTEM

• Intra-arterial cannula

• Fluid filled tubing

• Transducer

• Infusion/flushing system

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COMPONENTS OF AN IBP MEASURING SYSTEM

• Intra-arterial cannula

• Fluid filled tubing

• Transducer

• Infusion/flushing system

• Signal processor, amplifier and display

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Levelling and zeroingZeroing :• For a pressure transducer to read accurately, atmospheric pressure

must be discounted from the pressure measurement.

• This is done by exposing the transducer to atmospheric pressure and

calibrating the pressure reading to zero.

• The level of the transducer is not important.

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•Levelling :• The pressure transducer must be set at the appropriate level in relation

to the patient in order to measure blood pressure correctly.

• This is usually taken to be level with the patient’s heart, at the 4th

intercostal space, in the mid-axillary line.

• A transducer too low over reads, a transducer too high under reads.

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Normal Arterial Pressure Waveforms

• The systolic waveform components consist of a steep pressure

upstroke, peak, and ensuing decline, and immediately follow the ECG

R wave.

• The downslope of the arterial pressure waveform is interrupted by the

dicrotic notch, continues its decline during diastole after the ECG T

wave, and reaches its nadir at end-diastole

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• As the pressure wave travels from the central aorta to the periphery,

the arterial upstroke becomes steeper, the systolic peak increases, the

dicrotic notch appears later, the diastolic wave becomes more

prominent, and end-diastolic pressure decreases.

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Arterial Blood Pressure Gradients

• The nature of the operative procedure is important when choosing the

appropriate site

Ex:

• Coarctation of aorta

• Thoracic and abdominal aortic surgeries

• Cardiopulmonary bypass

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Cardiopulmonary bypass :• The mean radial artery pressure decreases on initiation of bypass and

remains less than mean femoral artery pressure throughout the bypass

period.

• Persists in the first few minutes following separation from bypass,

often by more than 20 mm Hg.

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Abnormal Arterial Pressure Waveforms• Morphologic features of individual arterial pressure waveforms can

provide important diagnostic information

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Condition CharacteristicsAortic stenosis Pulsus parvus (narrow pulse pressure)

Pulsus tardus (delayed upstroke)

Aortic regurgitation Bisferiens pulse (double peak)Wide pulse pressure

Hypertrophic cardiomyopathy Spike and dome (mid-systolic obstruction)

Systolic left ventricular failure Pulsus alternans (alternating pulse pressure amplitude)

Cardiac tamponade Pulsus paradoxus (exaggerated decrease in systolic blood pressure during spontaneous inspiration)

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Waveform analysis for prediction of intravascular volume responsiveness

• Variations in arterial blood pressure observed during positive pressure

ventilation, as well as a variety of derived indices, are the most widely

studied of these dynamic indicators.

• They result from changes in intrathoracic pressure and lung volume

that occur during the respiratory cycle.

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REFERENCESMiller's 8th edition

Physical principles of intra-arterial blood pressure measurement anaesthesia

Kaplan's cardiac anesthesia the echo era 6edition

Thank you