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INTRA-ARTERIAL BLOOD PRESSURE MONITORING
- 1. INVASIVE ARTERIAL PRESSURE MONITORING Dr. T. Vikram Kumar Naidu MD(Anaesthesia), (DM) (Cardiac anaesthesia) (UNMICRC)
- 2. 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 26-07-2016 2Dr. Vikram Naidu
- 3. 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 26-07-2016 3Dr. Vikram Naidu
- 4. Indications for Arterial Cannulation Continuous, 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 26-07-2016 4Dr. Vikram Naidu
- 5. 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. 26-07-2016 5Dr. Vikram Naidu
- 6. 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 26-07-2016 6Dr. Vikram Naidu
- 7. 26-07-2016 7Dr. Vikram Naidu
- 8. • “Transfixation” technique 26-07-2016 8Dr. Vikram Naidu
- 9. ULTRASOUND IMAGING 26-07-2016 9Dr. Vikram Naidu
- 10. Alternative Arterial Pressure Monitoring Sites • Ulnar • Brachial • Axillary • Femoral – seldinger technique • Dorsalis pedis 26-07-2016 10Dr. Vikram Naidu
- 11. Complications of Direct Arterial Pressure Monitoring • Hemorrhage • Misinterpretation of data • Distal ischemia • Pseudoaneurysm • Arteriovenous fistula • Arterial embolization • Infection • Peripheral neuropathy 26-07-2016 11Dr. Vikram Naidu
- 12. 26-07-2016 12Dr. Vikram Naidu
- 13. 26-07-2016 13Dr. Vikram Naidu
- 14. 26-07-2016 14Dr. Vikram Naidu
- 15. 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 26-07-2016 15Dr. Vikram Naidu
- 16. • 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. 26-07-2016 16Dr. Vikram Naidu
- 17. Properties • Natural frequency • Damping coefficient 26-07-2016 17Dr. Vikram Naidu
- 18. • 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 26-07-2016 18Dr. Vikram Naidu
- 19. 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. 26-07-2016 19Dr. Vikram Naidu
- 20. 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 26-07-2016 20Dr. Vikram Naidu
- 21. 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. 26-07-2016 21Dr. Vikram Naidu
- 22. Underdamped arterial pressure waveform Overdamped arterial pressure waveform 26-07-2016 22Dr. Vikram Naidu
- 23. 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 26-07-2016 23Dr. Vikram Naidu
- 24. 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 26-07-2016 24Dr. Vikram Naidu
- 25. 26-07-2016 25Dr. Vikram Naidu
- 26. COMPONENTS OF AN IBP MEASURING SYSTEM 26-07-2016 26Dr. Vikram Naidu
- 27. COMPONENTS OF AN IABP MEASURING SYSTEM • Intra-arterial cannula 26-07-2016 27Dr. Vikram Naidu
- 28. COMPONENTS OF AN IABP MEASURING SYSTEM • Intra-arterial cannula • Fluid filled tubing 26-07-2016 28Dr. Vikram Naidu
- 29. COMPONENTS OF AN IABP MEASURING SYSTEM • Intra-arterial cannula • Fluid filled tubing • Transducer 26-07-2016 29Dr. Vikram Naidu
- 30. COMPONENTS OF AN IBP MEASURING SYSTEM • Intra-arterial cannula • Fluid filled tubing • Transducer • Infusion/flushing system 26-07-2016 30Dr. Vikram Naidu
- 31. COMPONENTS OF AN IBP MEASURING SYSTEM • Intra-arterial cannula • Fluid filled tubing • Transducer • Infusion/flushing system • Signal processor, amplifier and display 26-07-2016 31Dr. Vikram Naidu
- 32. Levelling and zeroing Zeroing : • 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. 26-07-2016 32Dr. Vikram Naidu
- 33. 26-07-2016 33Dr. Vikram Naidu
- 34. • 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. 26-07-2016 34Dr. Vikram Naidu
- 35. 26-07-2016 35Dr. Vikram Naidu
- 36. 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 26-07-2016 36Dr. Vikram Naidu
- 37. 26-07-2016 37Dr. Vikram Naidu
- 38. • 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. 26-07-2016 38Dr. Vikram Naidu
- 39. 26-07-2016 39Dr. Vikram Naidu
- 40. 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 26-07-2016 40Dr. Vikram Naidu
- 41. 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. 26-07-2016 41Dr. Vikram Naidu
- 42. 26-07-2016 42Dr. Vikram Naidu
- 43. Abnormal Arterial Pressure Waveforms • Morphologic features of individual arterial pressure waveforms can provide important diagnostic information 26-07-2016 43Dr. Vikram Naidu
- 44. 26-07-2016 44 Condition Characteristics Aortic 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) Dr. Vikram Naidu
- 45. 26-07-2016 45Dr. Vikram Naidu
- 46. 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. 26-07-2016 46Dr. Vikram Naidu
- 47. 26-07-2016 47Dr. Vikram Naidu
- 48. REFERENCES Miller's 8th edition Physical principles of intra-arterial blood pressure measurement anaesthesia Kaplan's cardiac anesthesia the echo era 6edition 26-07-2016 48Dr. Vikram Naidu
- 49. Thank you
Editor's Notes
- Before attempting radial artery cannulation, many clinicians assess the adequacy of collateral flow to the hand by performing a modified Allen’s test
- In preparation for cannulation of the radial artery, STERILE*** the wrist and hand are immobilized and secured with the wrist resting across a soft pad. Dorsiflexion of the wrist should be mild at most to avoid attenuating the pulse by stretch or extrinsic tissue pressure. The course of the radial artery proximal to the wrist is identified by gentle palpation, the skin is prepared with an antiseptic, and a local anesthetic is injected intradermally and subcutaneously beside the artery. Arterial catheterization can be performed with a standard IV catheter or an integrated guidewire-catheter assembly designed for this purpose
- Some clinicians choose the “transfixion” technique for arterial cannulation, in which the front and back walls of the artery are punctured intentionally, the needle is removed from the catheter, the catheter is withdrawn until pulsatile blood flow appears, and then advanced into the vessel lumen either directly or over a wire using the Seldinger technique.
- Other aids to arterial cannulation include the use of ultrasound imaging to guide catheter insertion, especially as a rescue method following a failed attempt.
- Catheterization of the femoral artery is best achieved with a guidewire technique, and the point of vessel entry must be distal to the inguinal ligament to minimize the risk of arterial injury, hidden hematoma formation, or even uncontrolled haemorrhage into the pelvis or peritoneum
- Sine waves may be described in terms of their amplitude – their maximal displacement from zero, their frequency which is the number of cycles per second (expressed as Hertz or Hz), their wavelength, which is the distance between two points on the wave which have the same value (e.g. two crests or troughs) and their phase, which is the displacement of one wave as compared with another – expressed as degrees from 0 to 360 (see Fig. 2). Sine waves are of particular importance as any waveform may be produced by combining together sine waves of differing frequency, amplitude and phase. Another way of looking at this is that any complex wave can be broken down into a number of different sine waves.
- Every material has a frequency at which it oscillates freely called its natural frequency. If a force with a similar frequency to the natural frequency is applied to a system, it will begin to oscillate at its maximum amplitude. This phenomenon is known as resonance.
- If the natural frequency of an IABP measuring system lies close to the frequency of any of the sine wave components of the arterial waveform, then the system will resonate, causing excessive amplification, and distortion of the signal. In this case, an erroneously wide pulse pressure and elevated systolic blood pressure would result.
- The system is flushed with high-pressure saline via the flush system. This generates an undershoot and overshoot of waves, resonating at the natural frequency of the system. This frequency may be calculated by dividing the paper or screen speed by the wavelength. For example, in Fig. 5, the paper speed is 25mm/sec and the wavelength of the resonant waves is 1mm so the natural frequency is 25/1 = 25Hz – just acceptable. Most commercially available systems have a natural frequency of around 200Hz but this is reduced by the addition of three-way taps, bubbles, clots and additional lengths of tubing.
- The arterial system is accessed using a short, narrow, parallel sided cannula made of polyurethane or Teflon™ to reduce the risk of arterial thrombus formation. The risk of arterial thrombus formation is directly proportional to the diameter of the cannula, hence small-diameter cannulas are used (20-22g), however, this may increase damping in the system 20G (pink) cannula - adult patients 22G (blue)- paediatrics 24G (yellow) - neonates and small babies
- This is attached to the arterial cannula, and provides a column of non-compressible, bubble free fluid between the arterial blood and the pressure transducer for hydraulic coupling. Ideally, the tubing should be short, wide and non-compliant (stiff) to reduce damping – extra 3-way taps and unnecessary lengths of tubing should be avoided where possible. This tubing should be colour coded or clearly labelled to assist easy recognition and reduce the risk of intra-arterial injection of drugs. A 3-way tap is incorporated to allow the system to be zeroed and blood samples to be taken.
- The transducer has to sit in a “transducer holder” – this is the white plastic plate that screws onto the rolling pole that holds the whole setup. The transducer has to be levelled correctly-to make sure that it’s at the fourth intercostal space, at the mid-axillary line (Phlebostatic axis)
- A bag of either plain 0.9% saline or heparinised 0.9% saline is pressurised to 300mmHg and attached to the fluid filled tubing via a flush system. This allows a slow infusion of fluid at a rate of about 2-4ml/hour to maintain the patency of the cannula.
- The pressure transducer relays its electrical signal via a cable to a microprocessor where it is filtered, amplified, analysed and displayed on a screen as a waveform of pressure vs. time. Beat to beat blood pressure can be seen and further analysis of the pressure waveform can be made, either clinically, looking at the characteristic shape of the waveform, or with more complex systems, using the shape of the waveform to calculate cardiac output and other cardiovascular parameters.
- A transducer should be zeroed several times per day to eliminate any baseline drift.
- This can be significant – every 10cm error in levelling will result in a 7.4mmHg error in the pressure measured;
- The dicrotic notch, known as the incisura when recorded at the central aorta (from the Latin, meaning “a cutting into”) is sharply defined and thought to result from aortic valve closure.82 In contrast, more peripheral arterial waveforms generally display a later, more blunted dicrotic notch that is more dependent on properties of the arterial wall. Note that the systolic upstroke starts 120 to 180 milliseconds after beginning of the R waveThis interval reflects total time required for depolarization of the ventricular myocardium, isovolumic left ventricular contraction, opening of the aortic valve, left ventricular ejection, propagation of the aortic pressure wave, and finally, transmission of the signal to the pressure transducer.
- This interval reflects total time required for depolarization of the ventricular myocardium, isovolumic left ventricular contraction, opening of the aortic valve, left ventricular ejection, propagation of the aortic pressure wave, and finally, transmission of the signal to the pressure transducer.
- An important feature of the arterial pressure waveform is distal pulse amplification As a result, compared with central aortic pressure, peripheral arterial waveforms have higher systolic, lower diastolic, and wider pulse pressures. Furthermore, as the signal is delayed in arriving at the peripheral site, the systolic pressure upstroke begins approximately 60 milliseconds later in the radial artery than in the aorta
- Distal pulse wave amplification of the arterial pressure waveform. Compared with pressure in the aortic arch, the more peripherally recorded femoral artery pressure waveform demonstrates a wider pulse pressure (compare 1 and 2), a delayed start to the systolic upstroke (3), a delayed, slurred dicrotic notch (compare arrows), and a more prominent diastolic wave.
- In most patients, this gradient resolves within the first hour, but occasionally it remains well into the postoperative period.
- Systolic pressure variation. Compared with systolic blood pressure recorded at end expiration (1) a small increase occurs during positive-pressure inspiration (2, Δ Up) followed by a decrease (3, Δ Down). Normally, systolic pressure variation does not exceed 10 mm Hg. In this instance, the large Δ Down indicates hypovolemia even though systolic arterial pressure and heart rate are relatively normal.