cardiovascular monitoring in anaesthsia .pptx

Cardiovascular monitoring in anesthesiology

1. Cardiovascular Monitoring Part 1 Moderator: Dr. Arun Garg Presenter: Dr. Sachin

2. Introduction Anaesthesia has significant influences on the heart and blood pressure. The rationale for cardiovascular monitoring during anesthesia stems from the realization that it may blunt appropriate autonomic responses associated with procedural stresses. Furthermore, if anesthesia is inadequate, the patient may respond with potentially detrimental autonomic responses such as tachycardia and hypertension. Early detection of these cardiovascular changes may lead the practitioner to intervene earlier and thus reduce the risk of complications from these changes.

3. STANDARD MONITORING FOR CARDIAC SURGERY PATIENT Invasive BP ECG Pulse oximetry Capnography Temperature CVP Urine output Intermittent artificial blood gas analysis EXTENDED MONITORING FOR PATIENT BASED AS CASE SPECIFIC PAC TEE C.O. measurement Processed electroencephalography (e.g. Bispectral index) Cerebral oximetry Tissue oxygenation monitoring Spinal drain ( intrathecal pressure )

4. Heart Rate and Pulse Rate The distinction between heart rate and pulse rate is the difference between electrical depolarization with systolic contraction of the heart (heart rate) and a detectable peripheral arterial pulsation (pulse rate). Many monitors report heart rate and pulse rate separately, the former from the ECG trace and the latter from the pulse oximeter plethysmograph or arterial blood pressure monitor. In addition to indicating the pulse rate, this waveform may also provide supplementary diagnostic clues to cardiovascular function. .

5. INVESTIGATIONS Electrocardiography (ECG) is the recording of the electrical activity of the heart on an electrocardiogram and used to detect arrhythmias.

6. Pulse oximetry : A non invasive technology to monitor oxygen saturation of the haemoglobin . Capnography : A numerical value of the Etco2 and a waveform of the co2 conc present in airway. It is now the confirmation method of choice in anaesthesia for proper placement of an endotracheal tube Temperature monitoring: Sites: Pulmonary artery, Distal esophagus , Nasopharynx , Tympanic membrane, Mouth, Axilla, Bladder, Forehead skin

7. Arterial Blood Pressure Monitoring Force exerted by circulating blood against any unit area of the vessel wall. Mean arterial Pressure(MAP) is the time averaged pressure in the major arteries.(MAP=1/3SBP+2/3DBP) Depends on the Cardiac output and Peripheral resistance. Blood Pressure Monitoring: Indirect cuff devices Direct arterial cannulation and pressure transduction Noninvasive BP monitoring: Manual Intermittent techniques Automated Intermittent techniques Automated Continuous techniques

8. Direct Arterial Blood Pressure Monitoring Intra-arterial blood pressure (IABP) measurement is often considered to be the gold standard of blood pressure measurement. ◦ It allows continuous beat-to-beat pressure measurement, useful for the close monitoring of patients whose condition may change rapidly, or those who require careful blood pressure control. ◦ The waveforms produced may be analyzed, allowing further information about the patient’s cardiovascular status to be gained (pulse contour analysis) ◦ It allows frequent arterial blood sampling.

9. Allen’s Test The allen’s test must be performed prior to radial arterial line placement to assure adequate collateral arterial flow to the hand. Modified allens test is for placing pedal arterial lines. ( Dorsalis pedis ) Pallor indicates occlusion of the ulnar artery –(>15sec) Negative Allen’s test Erythematous blush indicates ulnar artery patency – Positive Allen’s test

10. BASIC PRICIPLES The commonly used IABP measuring systems consist of a column of fluid directly connecting the arterial system to a pressure transducer (hydraulic coupling). 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.

11. COMPONENTS OF AN IABP MEASURING SYSTEM Intra-arterial cannula The arterial system is accessed using a short, narrow, parallel sided cannula made of polyurethane 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. The radial artery is the most commonly used site of insertion as it usually has a good collateral circulation and is easily accessible.

12. Fluid Filled Tubing 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 color 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.

13. Transducer Fluid in the tubing is in direct contact with a flexible diaphragm, which in turn moves strain gauges in the pressure transducer, converting the pressure waveform into an electrical signal. Strain gauges are based on the principle that the electrical resistance of wire or silicone increases with increasing stretch. The flexible diagram is attached to wire or silicone strain gauges and then incorporated into a Wheatstone bridge circuit in such a way that with movement of the diaphragm the gauges are stretched or compressed, altering their resistance.

14. Infusion/flushing system A bag of either plain 0.9% saline or heparinized 0.9% saline is pressurized 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. A flush system will also allow a high-pressure flush of fluid through the system in order to check the damping and natural frequency of the system and to keep the tubing clear.

15. Signal processor, amplifier and display The pressure transducer relays its electrical signal via a cable to a microprocessor where it is filtered, amplified, analyzed 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.

16. PHYSICAL PRINCIPLES Sine Waves A wave is a disturbance that travels through a medium, transferring energy but not matter. One of the simplest waveforms is the sine wave . These may be thought of as the path of a point travelling round a circle at a constant speed and are defined by the function y = sin x.

17. Sine waves may be described in terms of their : ◦ amplitude – their maximal displacement from zero, ◦ 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) ◦ their phase, which is the displacement of one wave as compared with another – expressed as degrees from 0 to 360. 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.

18. The Wheatstone Bridge The Wheatstone bri dge is a circuit designed to measure unknown electrical resistance.

19. Newer Wheatstone bridge setups use strain gauges in all four positions.The diaphragm is attached in such a way that when pressure is applied to it, gauges on one side of the Wheatstone bridge become compressed, reducing their resistance, whilst the gauges on the other side are stretched, increasing their resistance. The bridge then becomes unbalanced and the potential difference generated is proportional to the pressure applied. This setup of four strain gauges has the advantage that it is four times more sensitive than a single gauge Wheatstone bridge. It also compensates for any temperature change as all of the strain gauges are affected equally.

20. Fourier Analysis The arterial pressure wave consists of a fundamental wave (the pulse rate) and a series of harmonic waves. These are smaller waves whose frequencies are multiples of the fundamental frequency (e.g. if the fundamental frequency is 1Hz, you would see harmonic waves with frequencies of 2Hz, 3Hz, 4Hz and so on.).The process of analysing a complex waveform in terms of its constituent sine waves is called Fourier Analysis. In the IABP system, the complex waveform is broken down by a microprocessor into its component sine waves, then reconstructed from the fundamental and eight or more harmonic waves of higher frequency to give an accurate representation of the original waveform.

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. In an IABP measuring system, most damping is from friction in the fluid pathway. Factors that will cause overdamping including: Three way taps Bubbles and clots Vasospasm Narrow, long or compliant tubing Kinks in the cannula or tubing

22. Damping also causes a reduction in the natural frequency of the system,allowing resonance and distortion of the signal. Whilst care must be taken to avoid overdamping , underdamping may also pose problems. In an underdamped system, one sees an overshoot of the pressure waves – with excessively high SBP and low DBP, as in a resonant signal. A compromise between over and under-damping must be therefore be found.

23. 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. At this point, the level of the transducer is not important. A transducer should be zeroed several times per day to eliminate any baseline drift.

24. 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. Failure to do this results in an error due to hydrostatic pressure (the pressure exerted by a column of fluid – in this case, blood) being measured in addition to blood pressure. This can be significant – every 10cm error in levelling will result in a 7.4mmHg error in the pressure measured; a transducer too low over reads, a transducer too high under reads.

25. Normal Arterial Pressure W Normal Arterial Pressure Waveforms aveforms

26. The bedside monitor displays values for the peak systolic and end-diastolic nadir pressures. MAP is dependent on the algorithm used by the monitor. In simplest terms, MAP is equal to the area beneath the arterial pressure curve divided by the beat period, averaged over multiple cardiac cycles. 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. As a result, compared with central aortic pressure, peripheral arterial waveforms have higher systolic, lower diastolic, and wider pulse pressures.

27. Indications: Continuous, real-time blood pressure monitoring Repeated blood sampling for arterial blood gases Failure of indirect arterial blood pressure measurement Supplementary diagnostic information from the arterial waveform Determination of volume responsiveness from systolic/pulse pressure variation Contraindications: Sites with known deficiencies in collateral circulation — such as those involved in Raynaud’s phenomenon and thromboangitis obliterans or end arteries such as the brachial artery Infection of the site. Traumatic injury proximal to the proposed insertion site.

28. Central Venous Pressure Monitoring CVP is the pressure measured at the junction of the superior venae cavae and the right atrium. It reflects the driving force for filling of the right atrium & ventricle. It reflects the relationship of blood volume to the capacity of the venous system. Normal CVP in an awake , spontaneously breathing patient - 1-7 mmHg or 5-10 cm H2O. Mechanical ventilation- 3-5 cm H2O higher.

29. The sites and techniques for placing central venous catheters are numerous. 1. Internal Jugular Vein 2. Subclavian vein 3. Femoral vein The reason for this popularity relates to its landmarks; it’s short, straight (right IJV), valveless course to the superior vena cava (SVC) and right atrium (RA); and its position at the patient’s head, which provides easy access by anesthetists in more intra operative settings.

30. CVP Recording CVP is usually recorded at the mid-axillary line where the manometer arm or transducer is level with the phlebostatic axis. This is where the fourth intercostal space and mid-axillary line cross each other allowing the measurement to be as close to the right atrium as possible.

31. a- atrial contraction c- isovolumetric ventricular contraction v- atrial filling x- atrial relaxation y- early ventricular filling The CVP waveform consists of five phasic events, three peaks (a, c, v) and two descents (x, y)

32. Conditions that Increase CVP RV infarct Severe tricuspid valve disease Cardiac tamponade Left/Right heart failure PEEP > 10 mmHg Pulmonary embolus Conditions that Decrease CVP Hypovolemia , Hypovolemic shock Deep inhalation

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