CLINICAL MEASUREMENT topics

Transcription

1 CLINICAL MEASUREMENT topics Prof. Şerban Bubenek MD 1-st. Cardiovascular Anesthesia & Intensive Care Dept «C.C.Iliescu» Institute for Cardiovascular Diseases Bucharest - ROMANIA

2 TODAY we speak about : Arterial Pressure Measurement Cardiac Output Measurement

3 Essential requiremets for CLINICAL MEASUREMENT ACCURACY - is the difference between the measurements and the real biological signal - in practice: Δ between a certain technique and a superior 'gold standard technique PRECISION = reproducibility of repeated measurements of the same biological signal. - calibration is important ( against predetermined signals or for absolute measurements to zero)

4 . MEASUREMENT of ARTERIAL PRESSURE a wide range of instruments are used to measure pressure : liquid column manometers : height, zero point, fluid density mechanical pressure gauges : aneroid manometer diafragm gauges (coupled to transducers)

5 MEASUREMENT OF ARTERIAL PRESSURE INDIRECT measurement (non-invasive & not-continous ) - signals generated by the occlusion of a major artery using a cuff - gives not continous but intermittent measurements a. palpation method ( Riva Rocci) b. auscultation of the Korotkoff sounds c. oscilometry method DIRECT measurement (invasive and continuous)

6 Indirect Methods of BP measurement (1) 1. Riva Rocci: simplest method of BP measurement, estimating only the SBP, is by palpating the return of arterial pulse as cuff is deflated. 2. Auscultation of the Korotkoff sounds : both SBP and DBP on deflation created by the turbulent blood flow in the artery Mean Arterial Pressure (MAP) = (SBP + 2 DBP) / 3

7 Indirect Methods of BP measurement (2) 3. OSCCILOMETRY - a microprocessor controlled oscillometer: DINAMAP - a pressure transducer that digitalizes signals ( microprocesor). - rapid, accurate, measurements of SBP, DBP, MAP and HR - SAP = the onset of rapidly increasing oscillations - MAP = the maximal oscillation at the lowest cuff pressure - DAP corresponds to the onset of rapidly decreasing oscillations LIMITATIONS: - tendency to: overestimate at low pressures and underestimate at high pressures - errors : movements, arrhythmias or rapid BP fluctuations - compressive peripheral nerve injuries (repeated measurements )

8 Cuff Size! Too small cuff will result in false high blood pressure reading Too large cuff will result in false low blood pressure reading

9 DIRECT Measurement of the BP invasive : a catheter into the artery METHODS 1. open Liquid column method : it is obsolete and measures only MAP 2. Liquid manometers (obsolete) 13.4 cm. H2O = 10 mm.hg.! 3. Electromechanical transducers : - conversion of mechanic signal into an electric signal - and then electronically converted and displayed as : SAP, DAP, MAP

10 Electromechanical transducers The diaphragm : - is moved by arterial pulsations which push the saline column - should be thin, small and rigid! Transducer : - based upon strain gauge principle : stretching (by PRESSURE ) a wire or silicone crystal changes its electrical resistance - connected to a wheatstone bridge circuit the voltage output is proportionate to the pressure applied it!

11 The 3 major problems may occur: 1. Improper zeroing and zero drift 2. Improper transducer / monitor calibration 3. Inadequate dynamic response of system : a. RF ( resonant or natural frequency) b. damping RF = frequency at which a system oscillates when stimulated - if the frequency of an input signal (i.e., pressure waveform) approaches the RF of a system : progressive amplification of the output signal occurs, a phenomenon known as ringing.

12 The ARTERIAL PRESSURE Waveform ARTERIAL WAVEFORM is a complex sine-wave The fundamental frequency (FF) or the 1-st harmonic is equal to the HR ( ex: for HR 60 b/min = 1 beat / sec = 1 cycle/sec = 1Hz.) physiologic peripheral arterial waveforms have a FF = 3 to 5 Hz ( beats / min) The MONITORING SYSTEM ( catheter + transducer + lines) - RF of the monitoring system should be at least at least 5 times higher than the highest frequency in the input signal or better : approx.10 times the FF at least RF > Hz to avoid ringing and systolic overshoot

13 The ARTERIAL PRESSURE Waveform, Damping Coefficient (DC): is a measure of how quickly an oscillating system comes to rest Testing DC: the fast-flush test ( square wave test) optimal damping overdamping = underestimates SAP and overestimates DAP - underdamping = overestimates SAP and underestimates DAP - in both cases however, MAP is relatively accurate!!!

14 REDUCING ARTIFACTS IN A-LINES Lines free of kinks and clots avoid Air Bubbles : small amount may augment systolic pressure reading, while large amount cause an over-damped system One stopcock per line Heparinized saline flushed maintaining patency Transducer should be electronically balanced or re-zeroed because the zero point may drift if the room temperature changes to have an adequate damping = flushing TEST! The catheter and lines: short and rigid

15 MEASUREMENT OF BLOOD FLOW: CARDIAC OUTPUT

16 Potential Methods able to measure the Cardiac Output Fick method Indicator dilution Pulse waveform ( pulse contour) methods Ultrasounds ( 2D-Echo and Doppler techique) Bioimpedance ANGIOGRAPHY MRI

17 Ideal Cardiac Output Monitoring Technique Precise and No bias Non-invasive Continous and instantaneous Automatic Operator independent Cheap Easy available in OR the ICU Leads to treatment changes / improvement in outcome IT DOES NOT EXIST! Use the Best Compromise : feasibility precision patient!

18 The FICK principle defines flow by: the ratio of the uptake or clearance of a tracer within an organ to the arterio-venous difference in concentration CO = VO2 / ( CaO2 CvO2) VO2 is measured by: a spirometer + Douglas bag CvO2 is taken from the pulmonary artery CaO2 is taken from a catheter in a peripheral artery

19 The FICK method considered to be the most accurate method for CO but : - invasive, time consuming - accurate VO2 samples are difficult to acquire discontinous CO : Deltatrac (Datex) continous CO : possible, but no integrated system available modified Fick equation : continous CO by NICO2 apparatus!

20 INDICATOR DILUTION CO measurement by indicator dilution has 3 phases : (a) an indicator is brought into the circulation (injection) (b) the indicator mixes with the bloodstream (mixing and dilution) (c) the concentration of the indicator is measured downstream (detection)

21 INDICATOR DILUTION Chemical indicator dilution (dye) Thermal indicator dilution ( Thermodilution ) the widest used : PAC = Swan-Ganz

22 Chemical indicator dilution The Stewart-Hamilton formula (time-concentration curve) using indocyanine green was the conventional indicator dilution method used to measure CO in ICU until the 1970 s. Indocyanine green : - nontoxic, inert, safe - short half-life - not affected by arterial saturation

23 The Thermodilution (TD) method Thermodilution = the indicator is the change in blood temperature a known volume of injectate at low temperature is injected into the right atrium and the cooled blood traverses a thermistor in a major vessel branch downstream over a duration of time. TD Methods : 1. PULMONARY Thermodilution (P-TD) : PAC 2. TRANSPULMONARY Thermodiution (TP-TD)

24 The CLINICAL STANDARD is the PAC! Pulmonary -TD

25 PAC-Thermodilution The change of the blood s temperature in is measured in the pulmonary artery using the PAC thermistor and then,the monitor electronically displays a temperature/time curve. The CO is inversely proportional to - the temperature change - the area under the curve PAC measures the Pulm.CO = Global CO if no intra-cardiac shunt!

26 Sources of error for P-TD Loss of indicator Variation of injectate temperature and volume Recirculation - IC shunts : false high CO values Tricuspid regurgitation : false low CO values Fluctuations in baseline temperature

27 ml. cold saline (4-6 C) optimal < 4 sec. > 4-5 sec. false low CO during the same respiratory phase -at least 3 measurements with less than < 10 % between them!

28 Advantages of P-TD the standard method for clinical CO measurement simple and repeated measurements possible The modified PAC may provide CCO - thermal indicator : intermitent heating of a resistance - 44 C for 1-4 sec, each sec - Not really continuous : mean of 3-4 min! - expensive The PAC provides not only CO, SV,.. but also PA pressures, PCWP, SvO2, and optionally RVEF and RVEDV.

29 TRANSPULMONARY Thermodiution (TPTD) - TD - TD The TPTD femoral artery curve appears later and has a lower peak temperature than the pulmonary artery TD curve. The TPTD was shown to be as accurate and precise as P-TD is! TP-TD is less invasive than P-TD, but does not offer: SvO2, PCWP and PAP values

30 The Clinical USE of TP-TD Mainly : as a calibration method for other systems : PiCCO, EV-1000 PiCCO and EV-1000 are able after the initial calibration by TPTD, to measure in a continuous manner ( beat by beat ) the C.C.O, using the Pulse Contour method!

31 CCO by the Pulse contour method The area under the systolic part of the AP waveform correlates : - directly with Left Ventricular STROKE VOLUME - inversely with aortic impedance (Z) SV = Systolic Area / Z

32 The Pulse Contour method C.C.O. 1. CALIBRATED techniques PiCCO EV-1000 TP-TD LiDCO Pulse CO (TP- Lithium dilution) 2. NON-CALIBRATED techniques Flow-Track VIGILEO Pro-AQT Nexfin ( Clear-Sight)

33 PiCCO & EV-1000 C.C.O.( mean 5-15 sec.) with intermittent TP-TD calibration. Enables continuous hemodynamic monitoring using: - a femoral / axilary artery catheter + - a central venous catheter (CVC)

34 LiDCO Pulse CO the calibration technique is : Lithium indicator Dilution safe and minimally invasive : peripheral venous and arterial catheters the PulseCO algorithm used by LiDCO is based on pulse power analysis! Continuous, real-time cardiovascular monitoring

35 Pulse Contour NON-CALIBRATED techniques Flow-Track VIGILEO PulsioFlex- ProAQT LiDCO-rapid - demographics - only an arterial line + a proprietary sensor in line NEXFIN (Clear-Sight) - totally non-invasive!

36 BIOIMPEDANCE bio tissues (bone, muscle,blood, etc) have different electric proprieties blood is the most conductive tissue ( Na+ and Cl-) pulsatile modifications of ITBV Δ TB Δ TB ~ Δ stroke volume SV = K x (dz / dt) / Zo x TEV Δ TB is measured by : producing and transmiting electricity ( high υ = 70 khz low A = 2,5 ma ) between 2 pairs of electrodes

37 Echocardiography (ultrasounds) for measuring the CO 2 D method Doppler - method

38 Ultrasounds US techniques can detect : the shape, size and movement of tissue interfaces, especially soft tissues and blood (RBC) US are defined by : - amplitude of oscillation (db) - the wavelength (distance between successive peaks) - frequency (inversely proportional to wavelength) nr. of cycles / second human ear can detect frequencies : 20-20,000 Hz. US have frequencies > 20,000 cycles /sec ( 20 KHz) diagnostic US uses frequencies in the range of 1-10 MHz.!!!!!

39 2-D Method SV = EDV ESV LV volumes (Simpson s method): the summation of the volume of stacked cylinders within the LV at end-diastole and end-systole SV = 150 ml - 52 ml = 98 ml

40 Doppler Effect Doppler effect represented by: V = _ΔF. c _ 2 F 0 cos θ where V = velocity of object ΔF = frequency shift c = speed of sound in medium (body tissue here) F 0 = frequency of emitted sound cos θ = angle between sound wave and flow (RBC) cos 90 = 0 so the US beam should be parallel to RBC Maximum angle = 20!

41 Doppler Method for CO measurements Principle SV =Area x Velocity Area of left ventricular outflow tract Obtain LVOT dimension in parasternal long axis view Flow Velocity at LVOT PW Doppler at LVOT in apical 5 chamber view D=2.1 cm Simplified formula= (2.1cm) 2 * SV = 3.46cm 2 X Velocity time integral 25 cm 25 cm = 87 cm 3

42 OESOPHAGEAL DOPPLER Measurement of blood flow velocity in the descending aorta at the tip of the flexible probe 4 MHz continuous or 5 MHz pulsed wave DAF FTc (corrected flow time) PV (peak velocity) MD (minute distance) HR (heart rate)

43 n Methods: ESICM invited 12 experts to form a Task Force to update a previous consensus (Antonelli et al.: Intensive Care Med 33: , 2007) Conclusions This consensus provides 44 statements that can be used at the bedside to diagnose, treat and monitor patients with shock.

44 Monitoring - KEY MESSAGES (1) NOT routine for measuring CO 1 C In non-responders to initial therapy, CO or SV should be measured to evaluate response to fluid or inotropes 1 C Serial measurements of blood LACTATE 1 C Not only lactate, but ScvO2 and CO2-gap 2 B the commonly used preload measures (such as CVP, PAOP or LVEDAi or GEDV) alone should not be used to guide fluid resuscitation 1 B use: dynamic over static variables to predict fluid responsiveness 1B

45 Hemodynamic Monitoring We do NOT recommend the routine use of PAC for patients in shock. 1 A In complex pts. we suggest to use additionally to ECHO: PAC or TPTD to determine type of shock 2 C ECHO is first! We suggest PAC in patients with refractory shock + RV dysfunction. 2 C We suggest the use of PAC or TPTD with in pts. severe shock especially in the case of associated ARDS 2 C We recommend that less invasive devices are used, instead of more invasive devices, only when they have been validated in shock pts. UG-BP

46 THANKS for your attention! & GOOD LUCK!