Curs 2012 Monitoring in Anesthesia

CLINICAL MEASUREMENT

Prof. Serban Bubenek MD

ESA - EDA Basic Sciences Course PARIS 2012

Dr. Med. Khaled Radaideh, Facharzt

Monitoring in Anaesthesia and Intensive Care

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Monitoring: A Definition... interpret available clinical data to help recognize present or future mishaps or unfavorable system conditions ... not restricted to anesthesia (change clinical data above to system data to apply to aircraft and nuclear power plants)


What is monitoring?Physiologic parameter & Patient safety parameter

Clinical skills & Monitoring equipment

Data collection, interpretation, evaluation, decision

Problem seeking, Severity assessment, Therapeutic assessment, Evaluation of Anesthetic interventions


Patient Monitoring and Management Involves Things you measure (physiological measurement, such as BP or HR)Things you observe (e.g. observation of pupils)Planning to avoid trouble (e.g. planning induction of anesthesia or planning extubation)Inferring diagnoses (e.g. unilateral air entry may mean endobronchial intubation)Planning to get out of trouble (e.g. differential diagnosis and response algorithm formulation)


Level of monitoringRoutine / Specialize / Extensive

Non-equipment / Non-invasive / Minimally invasive / Penetrating / Invasive / Highly invasive

SystematicRespiratory / Cardiovascular / Temperature/FetalNeurological / Neuro-muscular / Volume status & Renal

Standards for basic intraoperative monitoring ( ASA)


Standards for basic intraoperative monitoring ( ASA : American Society of Anesthesiologists)

Standard I Qualified anesthesia personnel shall be present in the room throughout the conduct of all GA, RA, MAC

Standard II During all anesthetics, the patients respiratory (ventilation, oxygenation), circulation and temperature shall be continually evaluated


Monitoring in AnesthesiaOBJECTIVES:Guidelines to the practice of anesthesia and patient monitoring

2. Elements to monitor (Anesthesia depth, Oxygenation, Ventilation, Circulation, Temperature)2.1. ECG2.2. Pulse Oximetry ( Function, Values, Limitations)2.3. Blood Pressure (methods, indications, limitations, Insertion sites, values)2.4. central venous line and pressure (methods, indications, limitations, Insertion sites and it's advantages, Complications, values)

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Monitoring in AnesthesiaOBJECTIVES:2.5. Capnography and EtCO2 (Uses, Measurement, values, factors affecting EtCO2)2.6. Cyanosis2.7. The oxyhemoglobin dissociation curve (interpretation, causes of Left and right shifting , key values, O2-Content of Blood)2.8. Temperature ( Methods, Values, sites)

3. Normal values for a healthy adult undergoing anesthesia

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Guidelines to the practice of anesthesia and patient monitoring: Monitoring in the PastVisual monitoring of respiration and overall clinical appearance

Finger on pulse

3. Blood pressure*

Monitoring in the PastFinger on the pulse


Harvey Cushing Not just a famous neurosurgeon but the father of anesthesia monitoringInvented and popularized the anesthetic chart

Recorded both BP and HR

Emphasized the relationship between vital signs and neurosurgical events ( increased intracranial pressure leads to hypertension and bradycardia )


Guidelines to the practice of anesthesia and patient monitoring:

1. Qualified anesthesia personnel shall be present in the room throughout the conduct of : all general anesthetics regional anesthetics monitored anesthesia care

2. A completed pre-anesthetic checklist. (history, physical exam, lab investigations, NPO policy)

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Guidelines to the practice of anesthesia and patient monitoring:

3. An anesthetic record. in general anaesthesia, regional anesthesia, or monitored IV conscious sedation HR and BP should be measured every 5 min. also time, dose and route of drugs and fluids should be charted

4. During all anesthetics, the patients oxygenation ventilation circulation shall be continously evaluated ! temperature*

MONITORINGBPMAPTempRRO2 satHR*

Elements to Monitor : Patients with local or regional anesthesia provide verbal feedback regarding well being.Onset of general anesthesia signaled by lack of response to verbal commands, in addition to loss of blink reflex to light touch.Inadequate anesthesia can be signaled by : Facial grimacing or movement of arm or leg. But with muscle relaxants ( fully paralysis), it can be signaled by : Hypertension, tachycardia, tearing or sweating.Excessive anesthesia can be signaled by : Cardiac depression, bradycardia, and Hypotension. And also may result in hypoventilation, hypercapnia and hypoxemia when muscle relaxants is not given.

I. Anesthetic Depth:*

Elements to Monitor : Clinically, monitored by patient color ( with adequate illumination ) and pulse oximetry. Quantitavely monitored by using oxygen analyzer, equipped with an audible low oxygen concentration alarm.

III. TemperatureContinuous temperature measurements monitoring is mandatory if changes in temperature are anticipated or suspected.

II. Oxygenation:*

Elements to Monitor : Clinically, monitored by pulse palpation, heart auscultation and monitoring intra-arterial pressure or oximetry.Quantitavely using ECG signals and arterial blood pressure measurements every 5 min.V. VentilationClinically, monitored through a correctly positioned endotracheal tube, also observing chest excursions, reservoir bag displacement, and breath sounds over both lungs.Quantitavely by ETCO2 analysis, equipped with an audible disconnection alarm.Arterial blood gas analysis for assessing both oxygen and ventilation.

IV. Circulation:*

Monitoring: Electrocardiogram ECG:

A 3 or 5 lead electrode system is used for ECG monitoring in the OR.

The 3 lead system has electrodes positioned on the right arm, left arm and chest position. ( placed in the left anterior axillary line at the 5th interspace, referred to as V5 ). Lead II is usually monitored by this system.

The 5 lead system adds a right leg and left leg electrodes, which allows monitoring v1, v2, v3, AVR, AVL, AVF and V5.

II and V5 very important !

ST segment *

Monitoring: Electrocardiogram ECG:

Identification of P waves in lead II and its association with the QRS complex is useful in distinguishing a sinus rhythm from other rhythms.

Analysis of ST segment is used as an indicator of MI. ( Dep.-ischemia / elev.-infarction )

Over 85% of ischemic events can be detected by monitoring ST seg. of leads II and V5.*

Monitoring: Pulse Oximetry:

Allows beat to beat analysis of oxygenation.

Depends on differences in light absorption between oxyHb and deoxyHb.

Red and Infra-red light frequencies transmitted through a translucent portion. (finger-tip or earlobe)

Microprocessors then analyze amount of light absorbed by the 2 wavelengths, comparing measured values, then determining concentrations of oxygenated and deoxygenated forms. (oxy- and deoxy-)*

PULSEOXIMETRY is for OXYGENATION

Principle : Spectrophotometry & Plethysmography

relies on the differing absorption of light, at different wavelengths by the various states of oxyhaemoglobin - HbO2 has a higher absorption at 940 nm (blue light) - Hb has a higher absorption at 660 nm (red light)

the light signal following transmission through the tissues has a pulsatile component

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two LEDs : one emitting red light (660 nm) and the other a blue light (940nm) on the finger nail

on the other side of the finger : photo sensor (photocell) detects the transmitted light

the LEDs are switched on and off at 30 Hz to detect the cyclical changes in the signal due to pulsatile arterial blood flow

by calculating the absorption at the two wavelengths the processor can compute the proportion of haemoglobin which is oxygenated


Pulse oximeters measure:The oxygen saturation of haemoglobin in arterial blood- which is a measure of the average amount of oxygen bound to each haemoglobin molecule

- Haemoglobin is a compound of iron (haem) and globin chains. Each globin chain is linked to one atom of iron, each of which can carry 4 molecules of oxygen, and as each molecule of oxygen contains two atoms of oxygen (O2), each haemoglobin molecule can carry 8 atoms of oxygen.

This makes haemoglobin a very efficient means of oxygen transport: each gram of haemoglobin can carry 1.34ml of oxygen.

2. The pulse rate - in beats per minute, averaged over 5 to 20 seconds.


A pulse oximeter is affected by :

ambient light shivering abnormal haemoglobins ( carboxyhaemoglobin, methaemoglobin, dyes as methylene blue and bilirubin )

pulse rate and rhythm vasoconstriction poor tissue perfusion ( shock, low CO, cold extremities )

NOT affected by : dark skin or anaemia.


A pulse oximeter gives no information about :

The oxygen content of the blood The amount of oxygen dissolved in the blood The respiratory rate or tidal volume i.e. ventilation The cardiac output or blood pressure ?


Monitoring: Blood Pressure BP:

Methods of BP measurement:1. Simplest method of BP measurement, estimating the SBP, is by palpating the return of arterial pulse as cuff is deflated (Riva-Rocci).2. auscultation of the Kortokoff sounds on deflation (providing both SBP and DBP)Mean Arterial Pressure MAP = DBP + 1/3(SBP DBP)MAP = ( SBP + 2 DBP ) / 3

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MEASUREMENT OF ARTERIAL PRESSURE

INDIRECT measurement (non-invasive) - signals generated by the occlusion of a major artery using a cuff - gives not continous but intermittent measurements

- palpation method ( Riva Rocci) - auscultation of the Korotkoff sounds - osccilometry method

DIRECT measurement (invasive and continous)


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 (1905) on deflation created by the turbulent blood flow in the artery (providing both SBP and DBP)Mean Arterial Pressure (MAP) = DBP + 1/3(SBP DBP)


Indirect Methods of BP measurement (2)

3. OSCCILOMETRY - a microprocessor controlled oscillometer. DINAMAP- a pressure transducer that digitalizes signals ( microprocesor). - rapid, accurate ( 9 mmHg) measurements of SBP, DBP, MAP and HR

- SAP corresponds to the onset of rapidly increasing oscillations - MAP corresponds to 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 BP fluctuations- compressive peripheral nerve injuries (repeated measurements )


Cuff Size

Too small cuff will result in false high blood pressure reading

Too large cuff will result in false low blood pressure reading

from Barbara Bates: A Guide to Physical Examination


DIRECT Measurement of the BPinvasive : catheter into the artery

METHODS

1. open Liquid column method (obsolete) , measures only MAP 13.4 cm. H2O = 10 mm.Hg.

2. Liquid manometers (obsolete)

3. Electromechanical transducers : - conversion of mechanic signal into an electric signal - and then electronically converted and displayed as : SAP,DAP and MAP.


Electromechanical - TRANSDUCERS

The diaphragm : - is moved by arterial pulsations which push the saline column- should be thin, small and rigid !

Transducers :

- based upon strain gauge principle : stretching (by PRESSURE ) a wire or silicone crystal changes its electrical resistance

- connected to a wheatstone bridge circuit : so that the voltage output is proportionate to the pressure applied it


The 3 major problems may occur :

1. Improper zeroing and zero drift2. Improper transducer / monitor calibration

3. Inadequate dynamic response of system : RF and damping Resonant (natural) Frequency (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.


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

MONITORING SYSTEMThe RF 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 FR >20 Hz to avoid ringing and systolic overshoot


The ARTERIAL PRESSURE WaveformThe damping coefficient (DC) is a measure of how quickly an oscillating system comes to rest method to test the DC: the fast-flush test ( square wave test) optimal damping

- underdamping = overestimates SAP and underestimates DAP - overdamping = underestimates SAP and overestimates DAP

- both cases however MAP is relatively accurate


REDUCING ARTIFACTS IN A-LINES

Lines free of kinks and clots

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

Short and rigid : catheter and lines



Methods of BP measurement:3. Automated non-invasive BP measurements. METHODOLOGY: a microprocessor controlled oscillometer (Dinamap) which is used routinely intraoperatively. It allows automatic inflation of the BP cuff at preset time intervals, sending readings into a pressure transducer that digitalizes them. This technique gives rapid, accurate ( 9 mmHg) measurements of SBP, DBP, MAP and HR several times a minute. LIMITATIONS: Errors occur due to movements, arrhythmias or BP fluctuations due to respiration. 3 5 minutes intervals is recommended to prevent compressive peripheral nerve injury due to repeated rapid measurements.*


Methods of BP measurement:4. Invasive BP measurements. (Arterial BP):Indications: Rapid moment to moment BP changes Frequent blood samplingMajor surgeries (cardiac, thoracic, vascular)Circulatory therapies: vasoactive drugs, deliberate hypotensionFailure of indirect BP: burns, morbid obesitySever metabolic abnormalities Major traumaThe radial artery at the wrist is the most common site for an arterial catheter. Alternatives are femoral, brachial and dorsalis pedis.

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Central Venous line and Pressure (CVP)Catheter inserted into the SVC providing an estimate of the right atrial and ventricular pressures.

Serial CVP measurements are more useful than a single value in order to assess blood volume, venous tone and right ventricular performance. HR, BP and CVP response to a volume infusion (100 500 ml) is also a useful test of right ventricular performance.

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Central Venous line and Pressure (CVP)Indications:CVP monitoring provides Right Atrial and Right Ventricle pressures

Advanced Cardiopulmonary disease + major operation

Secure vascular access for drugs

Secure access for fluids + traumatic pts

Aspiration of entrained air: sitting craniotomies

Inadequate peripheral IV access*

Central Venous Line: PERFORMANCE of Right Internal Jugular VeinInternal jugular (Int. Jug.) vein lies in groove between sternal and clavicular heads of sternocleidomastoid muscle

It is lateral and slightly anterior to carotid artery

Aseptic technique, head down

Insert needle towards ipsilateral nipple

Seldinger method: 22 G finder; 18 G needle, guide-wire, scalpel blade, dilator and catheter

Observe ECG and maintain control of guide-wire

Ultrasound guidance; Chest-Xray post insertion.*

Advantages of Right Int. Jug. veinConsistent, predictable anatomic locationReadily identifiable landmarksShort straight course to Superior Vena CavaEasy access for anesthesiologist at patients headHigh success rate, 90-99%

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Complications of Central lines (jugular): BleedingInjury to surrounding structures as carotid arteryPneumothoraxArrhythmia *

Central Venous line Alternative Sites Subclavian vein: Easier to insert versus Int. Jug. veinBetter patient comfort v. Int. Jug.Higher Risk of pneumothorax- 2%

External jugular: Easy to cannulate if visible.no risk of pneumothoroax, high risk or bleeding20%: cannot access central circulation

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Central Venous Pressure (CVP ) MonitoringReflects pressure at junction of vena cava + RA CVP is driving force for filling RA + RVCVP provides estimate of:Intravascular blood volumeRV preloadTrends in CVP are very usefulMeasure at end-expirationCentral Venous Pressure (CVP): 1-10 mmHg

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SWAN GANZ = PA CATHETER


SWAN-GANZ catheterWaveform during Insertion


PA CATHETER


PA CATHETERZone III allows for uninterrupted blood flow and a continuous communication with distal intracardiac pressures. (PAand PV exceed Palv)


PAC-Thermodilution

The change of the bloods temperature in is measured in the pulmonary artery using the PAC thermistor

The thermistor records the temperature change and 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 intracardiac shunt )


Capnography and EtCO2 Capnometry: is the numerical measurement of CO2 concentration during inspiration and expiration.

Capnogram: refers to the continuous display of the CO2 concentration waveform sampled from the patients airway during ventilation.

Capnography: is the continuous monitoring of a patients capnogram.

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Capnography and EtCO2 End-tidal CO2 monitoring is standard for all patients undergoing GA with mechanical ventilation.

It is an important safety monitor and a valuable monitor of the patients physiologic status, and it has been an important factor in reducing anesthesia-related mortality and morbidity.

CO2 monitoring is considered the best method for verifying successful intubation and extubation procedures.

It helps in assessment of the adequacy of ventilation and an indirect estimate of PaCO2.

Also it aids in diagnosis of PE, recognition of a partial airway obstruction, and indirect measurement of airway reactivity (bronchospasm).

ETCO2 levels have also been used to predict outcome of resuscitation.

Capnography and EtCO2 Measurement of ETCO2Sampling the patients respiratory gases near the airway.Using infra-red gas analysis or mass spectrometry on the values and concentrations obtained.

Provided that when sampling, inspired CO2 value should be near zero. (i.e. ETCO2 value is a function of CO2 production, alveolar ventilation and pulmonary circulation; excluding inspired CO2).During general anesthesia, with absence of ventilation perfusion abnormalities, difference between PaCO2 and ETCO2 is about 5 mm Hg (PaCO2 = 40 mmHg, ETCO2 = 35 mmHg)

Increases or decreases in ETCO2 values maybe the result of increases or decreases in production and elimination.

Capnography and EtCO2 Factors affecting ETCO2:

Increased ETCO2Decreased ETCO2Changes in CO2 ProductionHyperthermiaSepsisThyroid stormMalignant HyperthermiaMuscular ActivityHypothermiaHypometabolismChanges in CO2 EliminationHypoventilationRebreathingPartial airway obstructionExogenous CO2 absorption (laparoscopy)HyperventilationHypoperfusionEmbolismTransient increases in ETCO2 may be noted after: IV bicarbonate administration, release of extremity tourniquets, or removal of vascular cross-clamps.

Capnography and EtCO2Normal

Esophageal 0 ! > 4 curves !

Cardiac arrest bronhospasm

Curare cleft spontaneous


exhausted CO2 absorberIMV

Expiratory Valve

Inspiratory valve

Hyper and hypo VENTILATION


Cyanosis:Defined as the presence of 5 g./dL of deoxygenated hemoglobin (deoxy Hb). i.e. Hb level = 15 g/dL, 5 g/dL release O2 which leaves 10 g/dL of oxyhemoglobin

SaO2 = OxyHb / (OxyHb + DeoxyHb) = 10 / (10 + 5) = 66%

SaO2 of 66% corresponds to PaO2 of 35mmHg.

In anemic patients the oxygen tension at which cyanosis is detectable will be even lower.i.e. Hb level = 10 gm/dL, 5 gm/dL release O2SaO2 = OxyHb / (oxyHb + DeoxyHb) = 5 / (5 + 5) = 50%

SaO2 of 50% corresponds to PaO2 of only 27 mmHg.

The oxyhemoglobin dissociation curveIt is a sigmoid curve that describes the relationship between oxygen tension (PaO2) and binding (SpO2).When PaO2 is low, the hemoglobin affinity to oxygen falls rapidly , explaining the sharp sloping .(PaO2< 60 mmHg)

The oxyhemoglobin dissociation curve A decrease in PaO2 of less than 60 mmHg (corresponding to SpO2 90 %) results in a rapid fall in the oxygenation saturation.The lowest acceptable O2 saturation level is 90%.

Left And Right Shifts of the Oxyhemoglobin Dissociation CurveRightLeftDecreased affinity of Hb for O2.Increased affinity of Hb for O2.Causes:Inc. PCO2HyperthermiaAcidosisIncreased altitudeIncreased 2,3-DPGSickle Cell AnemiaInhalational anestheticsCauses:Dec. PCO2HypothermiaAlkalosisFetal hemoglobinDecreased 2,3-DPGCarboxyhemoglobinMethemoglobin

The oxyhemoglobin dissociation curveKey Values:At PO2 100 mmHg, Hb 100% saturation.At PO2 40 mmHg, Hb 75% saturation.At PO2 27 mmHg, Hb 50% saturation. Oxygen content of blood:is the total amount of O2 carried in blood, including bound and dissolved O2.O2 content = (O2-binding capacity * % saturation) + O2 dissolved O2-binding capacity = maximal amount of O2 bound to Hb at 100 % sat.

The dissolved O2 isnt measured by oximetry but by blood gas analysis.

Monitoring TemperatureObjectiveaid in maintaining appropriate body temperatureApplicationreadily available method to continuously monitor temperature if changes are intended, anticipated or suspectedMethodsthermostattemperature sensitive chemical reactions

Monitoring TemperaturePotential heat loss or risk of hyperthermia necessitates continuous temperature monitoring Normal heat loss during anesthesia averages 0.5 - 1 C per hour, but usually not more that 2 - 3 C Temperature below 34C may lead to significant morbidity

Monitoring TemperatureHypothermia develops when thermoregulation fails to control balance of metabolic heat production and environment heat loss Normal response to heat loss is impaired during anesthesia Those at high risk are elderly, burn patients neonates, spinal cord injuries

Monitoring TemperatureHyperthermia Causes Malignant hyperthermia Endogenous pyroxenes (IL1) Excessive environmental warming Increases in metabolic rate secondary to:ThyrotoxicosisPheochromocytoma

Monitoring TemperatureMonitoring Sites Tympanic Esophagus Rectum Nasopharynx

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Normal values for a healthy adult undergoing anesthesia Systolic Blood Pressure Diastolic Blood Pressure Heart Rate Respiratory Rate Oxygen sat. by oximetry End Tidal Carbon Dioxide tension Skin appearance Color Temperature Urine ProductionSBPDBPHRRRSpO2ETCO285 160 50 9550 1008 2095 10033 45warm, drypink36 37.5>= 0.5mmHgmmHgbpmrpm%mmHg

O Cml.kg-1.min-1 Central Venous Pressure Pulmonary Artery Pressure Pulmonary Capillary Wedge Pressure Mixed venous oxygen saturation Cardiac OutputMean Arterial Pressure *MAP = DBP + 1/3 ( SBP DBP )CVPPAP (mean)PCWPSvO2COMAP1 1010 205 15754.5 680 120mmHgmmHgmmHg%1.Min-1mmHg

THANK YOU

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Clinical measurement is limited by 4 major constraints:Feasibility

Reliability

3. Interpretation

4. Value


4 mandatory steps in clinical measurement:

Detection : sensing device ( biological signal : mechanical, electrical, electromagnetic, chemical or thermal energy)

Transduction : the output is converted into another form, usually to a continuous electrical signal

Amplification and signal processing : - extract and magnify the relevant features of the signal and reduce unwanted noise

Display and Storage : the output of the instrument is presented to the operator


Mechanical versus Digital instrumentsMechanical instruments ;

- use the natural signal energy to drive a display,with minimal intermediate processing

Digital instruments - non-electrical signals are converted by a transducer to an electrical signal suitable for electronic processing by digital computers.

- higher accuracy and precision


Essential requiremets for CLINICAL MEASUREMENTAccuracy is the difference between the measurements and the real biological signal, or in practice, between a certain techique and a superior 'gold standard technique.

Precision describes the reproducibility of repeated measurements of the same biological signal.

calibration is important ( against predetermined signals or for absolute measurements to zero)


MECHANICAL SIGNALS: 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)


MEASUREMENT OF BLOOD FLOW:CARDIAC OUTPUTThe Nexfin HDA truly non-invasive CCO monitor


Potential Methods To Measure Cardiac Output Fick metdodIndicator dilutionPulse waveform ( pulse contour) methods ULTRASOUNDS ( 2D-Echo and Doppler techique)Bioimpedance

ANGIOGRAPHYMRI


Ideal Cardiac Output Monitoring TechniquePrecise and No biasNon-invasiveContinous and instantaneousAutomaticOperator independentCheapEasy available in the ICULeads to treatment changes / improvement in outcome

IT DOES NOT EXIST !

Use the Best Compromise : feasibility precision patient !


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])*100

VO2 per minute using a spirometer + Douglas bagCvO2 is taken from the pulmonary artery CaO2 a cannula in a peripheral artery


The FICK methodconsidered 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


INDICATOR DILUTION Chemical indicator dilution (dye)

Thermal indicator dilution ( Thermodilution )

the widest used : PAC = Swan Ganz


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).


Chemical indicator dilution The Stewart-Hamilton formula (time-concentration curve)

using indocyanine green as indicator was the conventional indicator dilution method used to measure CO in ICU until the 1970s.

Indocyanine green : - nontoxic, inert, safe - short half-life, - not affected by arterial saturation


The Thermodilution (TD) methodThermodilution = indicator is the change in blood temperature

An injectate of known volume and 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 :

PULMONARY Thermodilution (P-TD)

TRANSPULMONARY Thermodiution (TP-TD)


The CLINICAL STANDARD is the PAC !Pulmonary -TD


PAC-Thermodilution

The change of the bloods temperature in is measured in the pulmonary artery using the PAC thermistor

The thermistor records the temperature change and 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 intracardiac shunt )


Sources of measurement error for P-TDLoss of indicator Variation of injectate temperature and volumeRecirculation - IC shunts : false high CO valuesTricuspid regurgitation : false low CO valuesFluctuations in baseline temperature


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10 ml. cold optimal < 4 sec.> 4-5 sec. false low CO ! at least 3 measurements and less than < 10 % between them


Advantages of P-TDThe standard method for clinical CO measurement

Simple and Repeated measurements possible.

The modified PAC may provide CCOthermal indicator : intermitent heating of a resistace44C for 1-4 sec each 30-60 secNot really continous : mean of 3-4 min ! expensive

The PAC provides, in addition, PA pressures, PAOP, SvO2, and optionally, RVEF and RVEDV.


PULMONARY Thermodilution TRANSPULMONARY Thermodiution

The pulmonary artery TD curve appears earlier and has a higher peak temperature than the femoral artery TD curve.

TP-TD is less invasive than P-TD, but does NOT give : SvO2 an PAP values !

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The Clinical USE of TP-TD

Mainly : as a calibration method for other systems : PiCCO, LiDCO-Pulse CO

PiCCO and LiDCO-Pulse CO are able after the initial calibration, to measure in a continous manner ( beat by beat ) the C.O, using : the Pulse Contour method


The Pulse Contour method

CALIBRATED techniques PiCCO LiDCO Pulse CO

NON-CALIBRATED techniques Flow-Track VIGILEO Nexfin


CCO by the pulse contour methodThe area under the systolic part of the AP waveform correlates : - directly with Left Ventricular STROKE VOLUME - inversely with aortic impedance

For calibrated techiques : the Aortic impedance is estimated from AP and CO pre-measured values ( calibration : CO is ussualy measured by TP-TD)

SV


PiCCO Continous pulse contour analysis with intermittent TP-TD calibration.

Enables continuous hemodynamic monitoring using: - femoral or axillary artery catheter - central venous catheter


LiDCO Pulse COthe independent 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 derivation.

Continuous, real-time cardiovascular monitoring


Pulse Contour NON-CALIBRATED techniques Flow-Track VIGILEO - only arterial line

NEXFIN - totally non-invasive


BIOIMPEDANCEbio tissues (bone, muscle,blood, etc) have different electric proprietiesblood is the most conductive tissue ( Na+ and Cl-)pulsatile modification of ITBV TB TB ~ stroke volume

SV = K x (dZ / dt) / Zo x TEV

TB is measured by : producing and transmiting electricity ( high = 70 kHz low A = 2,5 mA ) betwwen 2 pairs of electrodes


Echocardiography for measuring the CO 2 D method

Doppler - method


Ultrasounds (1.)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 (delta pressure : ambient to peak) 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.


Ultrasounds (2.)Transducers : - generate and sense US - are made from ceramic materials able to transform mechanical energy (pressure) to electrical energy and vice versa ( the piezoelectric effect )

Transducers : generates ultrasound of the same frequency as the applied voltage

Shorter wavelengths and higher frequencies improve the resolution of distance, but tissue penetration is simultaneously reduced.

Amplitude determines the intensity of the ultrasound beam and therefore the sensitivity of the instrument.


2-D MethodPrinciple

Stroke volume= End diastolic volume End systolic volume

LV volumes estimated by Simpsons method, which is the summation of the volume of stacked cylinders within the LV at end-diastole and end-systole 150 ml - 52 ml= 98 ml


Doppler Effect (1)frequency of US waves reflected from a stationary object is the same as that transmited

frequency of transmitted US is altered as it is reflected from a moving object

there is an increase in the observed frequency of a signal when the signal source approaches the observer

e.g. ambulance siren


Doppler Effect - 3Doppler effect represented by:

V = _F . c _2 F0 cos

Where V = velocity of objectF = frequency shiftc = speed of sound in medium (body tissue here)F0 = frequency of emitted soundcos = angle between sound wave and flow (RBC)

cos 90 = 0 so the US beam should be parallel to RBC Maximum angle = 20


Doppler MethodPrinciple Flow (stroke volume)=Area x Velocity

CO=Stroke volume * Heart rate

Area of left ventricular outflow tractObtain LVOT dimension in parasternal long axis viewSimplified formula= (2.1cm)2 * 0.785

D=2.1 cm3.46cm2 Flow Velocity at LVOTPulsed wave Doppler at LVOT in apical 5 chamber viewVelocity time integral 25 cm25cm = 87 cm3X


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

CO (cardiac output) SV (stroke volume) FTc (corrected f low time) PV (peak velocity) MD (minute distance) HR (heart rate)


THANKS for your attention !


*******Traditionally, cyanosis has been relied on for detecting hypoxia, for example during post-operative recovery or from severe respiratory disease.But severe hypoxia usually precedes cyanosis.Severe respiratory failure generally occurs when arterial saturation of haemoglobin falls to 85-90 % , whereas cyanosis does not usually appear until saturation falls to 75 per % - the normal saturation of venous blood. Without invasive monitoring, detecting hypoxia in the critical 75-90 per cent range was, therefore, largely guesswork, leaving medical and nursing staff without clear evidence to guide their practice. Pulse oximetry replaces guesswork with evidence.

The technology involved is complicated but there are two basic physical principles.First, the absorption of light at two different wavelengths by haemoglobin differs depending on the degree of oxygenation of haemoglobin. Second, the light signal following transmission through the tissues has a pulsatile component, resulting from the changing volume of arterial blood with each pulse beat. This can be distinguished by the microprocessor from the non-pulsatile component resulting from venous, capillary and tissue light absorption.

A two-sided probe transmits red and infrared light through body tissue, usually a fingertip. Most light will be absorbed by the tissue between the probe. The small amount of light that is not absorbed is detected by sensors on the other side of the probe, and this small amount is used to measure haemoglobin saturation. Absorption varies between oxygen-rich and oxygen-poor haemoglobin - measuring the difference of absorption between full capillaries (systole) and empty ones (diastole) produces a difference that enables microchip calculation of haemoglobin saturation.Saturation (S) is therefore measured in peripheral (p) capillaries; hence saturation of peripheral oxygen (SpO2). In health, this should accurately reflect the arterial saturation of oxygen (SaO2), so oximetry saturations are often called SaO2, although SpO2 remains the more accurate term.To calculate the difference between full and empty capillaries, oximetry measures light absorption over a number of pulses, usually five. This causes the short delay before readings are obtained. Pulse rate is also calculated over a few pulses. With irregular rhythms, such as atrial fibrillation, this can cause very inaccurate pulse measurements by oximeters, especially if there are significant apex/radial deficits. Oximeters only measure the pulse at the probe site, so may significantly underestimate actual heart rate. More accurate observation necessitates counting the radial or another pulse over one minute, and possibly, for example with atrial fibrillation, counting the heart beat through a stethoscope.

- which is a measure of the average amount of oxygen bound to each haemoglobin molecule. The percentage saturation is given as a digital readout together with an audible signal varying in pitch depending on the oxygen saturation. SO2 indica aportul procentual dintre continutul actual in O 2 al hemoglobinei si capacitatea maxima de transport a hemoglobinei. SO 2 este o masura a relatiei dintre O 2 si hemoglobina si nu indica continutul in O 2 al singelui arterial.

Haemoglobin is the active oxygen-carrying part of the erythrocyte (red blood cell).Haemoglobin is a compound of iron (haem) and four polypeptide (globin) chains. Each globin chain is linked to one atom of iron, each of which can carry four molecules of oxygen. As each molecule of oxygen contains two atoms of oxygen (O2), each haemoglobin molecule can carry eight atoms of oxygen. This makes haemoglobin a very efficient means of oxygen transport: each gram of haemoglobin can carry 1.34ml of oxygen.

The function of a pulse oximeter is affected by many variables, including: ambient light; shivering; abnormal haemoglobins; pulse rate and rhythm; vasoconstriction and cardiac function. A pulse oximeter gives no indication of a patient's ventilation, only of their oxygenation, and thus can give a false sense of security if supplemental oxygen is being given. In addition, there may be a delay between the occurrence of a potentially hypoxic event such as respiratory obstruction and a pulse oximeter detecting low oxygen saturation. However, oximetry is a useful non-invasive monitor of a patient's cardio-respiratory system, which has undoubtedly improved patient safety in many circumstances. A reduction in peripheral pulsatile blood flow produced by peripheral vasoconstriction (hypovolaemia, severe hypotension, cold, cardiac failure, some cardiac arrhythmias) or peripheral vascular disease. These result in an inadequate signal for analysis. Venous congestion, particularly when caused by tricuspid regurgitation, may produce venous pulsations which may produce low readings with ear probes. Venous congestion of the limb may affect readings as can a badly positioned probe. When readings are lower than expected it is worth repositioning the probe. In general, however, if the waveform on the flow trace is good, then the reading will be accurate. Bright overhead lights in theatre may cause the oximeter to be inaccurate, and the signal may be interrupted by surgical diathermy. Shivering may cause difficulties in picking up an adequate signal. Pulse oximetry cannot distinguish between different forms of haemoglobin. Carbo-xyhaemoglobin (haemoglobin combined with carbon monoxide) is registered as 90% oxygenated haemoglobin and 10% desaturated haemoglobin - therefore the oximeter will overestimate the saturation. The presence of methaemoglobin will prevent the oximeter working accurately and the readings will tend towards 85%, regardless of the true saturation. When methylene blue is used in surgery to the parathyroids or to treat methaemoglobinaemia a shortlived reduction in saturation estimations is registered. Nail varnish may cause falsely low readings. However the units are not affected by jaundice, dark skin or anaemia.

Human blood carries oxygen in two ways:Dissolved in plasmaAttached to haemoglobin. Ask group to list whatever they can remember about oxygen in the bloodstream - for example, what is different about oxygen dissolved in plasma and oxygen attached to haemoglobin?

The amount of oxygen dissolved in plasma at normal atmospheric pressure is only about 3 per cent of total oxygen carriage. Although this is measured in 'blood gases', it is insufficient to support life. *To calculate pressure in a U-tube manometer, the readings above and below zero are added. The manometer on the left is at equilibrium. The manometer on the right shows readings of 2 above zero and 2 below zero, indicating a pressure of 4.

Mercurial barometers are well-type manometers : they have one leg with a relatively small diameter, and the second leg is a reservoir. The cross-sectional area of the reservoir may be as much as 1500 times that of the vertical leg, so that the level of the reservoir does not change appreciably with a change of pressure.

*(automated non-invasive BP measurements- (DINAMAP) which is (Device for Indirect Non-invasive Automatic Mean Arterial Pressure) used routinely intraoperatively

*Explicatie figura :Fig. 31.1Simulation of the output of a catheter-transducer system withincreasing frequency of a constant amplitude input signal. Thelinearity of response is lost as the frequency approaches the resonantfrequency of the system.*Fig. 31.1 The first ten harmonics of the FF contribute to the waveformSimulation of the output of a catheter-transducer system withincreasing frequency of a constant amplitude input signal. Thelinearity of response is lost as the frequency approaches the resonantfrequency of the system.- high DC absorbs mechanical energy well (i.e., compliant tubing), causing a diminution (overdamping) in the transmitted waveform. - low DC results in underdamping and systolic overshoot Adequate damping -if underdamping continues to oscillate 3-4cycles, overestimates systolic and underestimates diastolic b/p. - if overdamping the system settles to baseline slowly without oscillating. It underestimates the systolic and overestimates the diastolic b/p.

The resonant frequency of a catheter-transducer measuring system is highest, and the frictional resistance to fluid flow which dampens the frequency response is lowest, when the velocity of movement of fluid in the catheter is minimized. This is achieved with a stiff, low-volume displacement diaphragm and a short, wide, rigid catheter.

*********** The introduction of the cold injectate causes a rapid upslope to a peak, a gradual downslope, and an exponential decay of the thermal signal.

The CO computer begins integration of the area under the TD curve until the exponential decay reaches a value of about 30%, and extrapolates the exponential decay to baseline in order to minimize artifacts due to recirculation of the indicator******1. Feasibility ( sensitivity and variability) depends on complex interactions and technical difficulties at the biological interface between the patient and the instrument

2. Reliability : depends on the properties of the measurement system. This is influenced by the calibration and correct use of the instrument in a demanding clinical environment. Simple examples include the correct placement of EGG electrodes, or the appropriate size of cuff for noninvasive measurement of arterial pressure. Delicate equipment, e.g. a blood gas analyser, requires regular maintenanceand calibration.3. Interpretation depends on the critical faculties of the anaesthetist who interprets the significance of measurements in the context of complex physiological systems. Arterial pressure may be within the normal range despite severe hypovolaemia or derangement of cardiovascular function within the limits of physiological compensation. Global measurements of end-tidal CO2 or pulse oximetry are influenced by many factors in a highly complex system; more information is required to deduce the cause of a change in the measurement.4. Value of clinical measurements in patient care is defined by the role of a measurement in improving the processes of patient care. This includes the ease, convenience, continuity and usefulness of a clinical measurement, and evidence ofimprovement in patient safety and clinical outcome.This chapter describes the feasibility and reliability of clinical measurements relevant to anaesthetic practice.

*There are four stages of clinical measurement: detection of the biological signal, by a sensing device whichresponds to a characteristic signal in the form of electrical,mechanical, electromagnetic, chemical or thermal energy transduction in which the output from the sensor is convertedinto another form, usually to a continuous electrical signal amplification and signal processing to extract and magnify therelevant features of the signal and reduce unwanted noise display and storage - the output from the instrument is presentedto the operator. Storage for future use may be achievedusing mechanical markers, printed copy or computer memory. - height of a fluid-column manometer provides pressure. - the expansion of mercury in a thin glass column measures temperature. - mechanical springs and gearing translate the rotation of a vane into the recording of expired volume on a dial Arcuri mecanice i angrenaje traduce rotaie de o paleta n nregistrarea de volumul expirat pe un forma The accuracy describes how close to the actual or real value the measurement is, whereas the precision describes how close the values of repeated measurements are. A good method should be both accurate and precise. A visual example may clarify this point (Figure 1).If we imagine a cardiac output monitor as a gun that is used to shoot a target (the cardiac output), we can classifyaccuracy as the characteristic of being able to shoot close tothe centre of the bulls-eye. Precision is related to how closerepeated shots are to each other.Several principles and a wide range of instruments are used to measure pressure.Direct mesurement commonly uses a pressure transducer connected to the lumen of the vessel by a fluid-filled catheter; the fluid and diaphragm of the transducer constitute a mechanical system which oscillates in simple harmonic motion at the natural resonant frequency - represents the usual standard - makes the average of a number of cycles more precisely reflecting mean pressures - modern instruments calculate mean arterial pressure automatically by integrating the area under the pressure waveformIndirect mesurement -signals generated by the occlusion of a major artery using a cuff - make intermittent measurements, with the systolic and diastolic readings reflecting the conditions in the artery at two instants at which the endpoints are detected - clinical methods of signal detection: palpation to estimate the systolic pressure at the return of a palpable distal pulse, and auscultation of the Korotkoff sounds for systolic and diastolic pressures. - The oscillometric measurement of arterial pressure estimates arterial pressure by analysis of the pressure oscillations that are produced in an occluding cuff by pulsatile blood flow in the underlying artery during deflation of the cuff ; tendency to overestimate at low pressures and underestimate at high pressures. -VO2 consumption per minute using a spirometer and a Douglas bag (with the subject re-breathing air) and a CO2 absorberthe oxygen content of blood taken from the pulmonary artery (representing mixed venous blood)the oxygen content of blood from a cannula in a peripheral artery (representing arterial bloodnot affected by arterial saturation because Indocyanine green has a peak spectral absorption at the wavelength at which absorption of oxygenated haemoglobin is identical to that of reduced haemoglobin.

The introduction of the cold injectate causes a rapid upslope to a peak, a gradual downslope, and an exponential decay of the thermal signal.

The CO computer begins integration of the area under the TD curve until the exponential decay reaches a value of about 30%, and extrapolates the exponential decay to baseline in order to minimize artifacts due to recirculation of the indicator

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Curs 2012 Monitoring in Anesthesia

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