CVP and Arterial MonitoringCVP and Arterial Monitoring

OutlineOutline

• Direct Arterial MonitoringDirect Arterial Monitoring• Transducer TroublesTransducer Troubles• CVP Monitoring and its clinical CVP Monitoring and its clinical

significancesignificance

Direct Arterial MonitoringDirect Arterial Monitoring

• Arterial cannulation w/ continuous pressure waveform display Arterial cannulation w/ continuous pressure waveform display remains the accepted standard for BP monitoringremains the accepted standard for BP monitoring

• Indications and AdvantagesIndications and Advantages• Frequent ABG’sFrequent ABG’s• Continuous real-time monitoring when rapid, moment-to-moment BP Continuous real-time monitoring when rapid, moment-to-moment BP

changes are anticipated, i.e. CV instability, major fluid shifts or EBLchanges are anticipated, i.e. CV instability, major fluid shifts or EBL• Failure of indirect BP monitoring i.e. morbid obesity, burned extremityFailure of indirect BP monitoring i.e. morbid obesity, burned extremity• Intra-aortic balloon counterpulsationIntra-aortic balloon counterpulsation• Deliberate induced induced hypotensionDeliberate induced induced hypotension• Cardiac surgery for cardiopulmonary bypassCardiac surgery for cardiopulmonary bypass• Major vascular surgeryMajor vascular surgery• Administration of vasoactive drug infusionsAdministration of vasoactive drug infusions

Natural Frequency and DampingNatural Frequency and Damping

• Left ventricular ejection initiates a pressure wave that is Left ventricular ejection initiates a pressure wave that is propagated down the aorta toward the peripherypropagated down the aorta toward the periphery

• The arterial BP waveform is a periodic complex wave, The arterial BP waveform is a periodic complex wave, reproduced by Fourier analysis : a technique that recreates reproduced by Fourier analysis : a technique that recreates the original pressure wave by summing a series of simple the original pressure wave by summing a series of simple sine waves of various amplitudes and frequenciessine waves of various amplitudes and frequencies

• The original pressure wave has a characteristic periodicity The original pressure wave has a characteristic periodicity that is called the that is called the Fundamental FrequencyFundamental Frequency, which is equal , which is equal to the pulse rateto the pulse rate

• Each measuring system has a natural frequency about Each measuring system has a natural frequency about which it can oscillatewhich it can oscillate

Natural Frequency and DampingNatural Frequency and Damping

• If the frequency of the monitored pressure If the frequency of the monitored pressure waveform approaches the natural frequency of waveform approaches the natural frequency of the measuring system, the system will resonate the measuring system, the system will resonate and pressure waveforms recorded on the monitor and pressure waveforms recorded on the monitor will appear exaggerated (Resonance or Ringing)will appear exaggerated (Resonance or Ringing)

• Damping Damping prevents a system from overshooting prevents a system from overshooting after responding to a change, particularly at after responding to a change, particularly at frequencies close to the natural frequency of the frequencies close to the natural frequency of the system system

OverdampingOverdamping

• Overdamping Overdamping causes causes slurred upstroke, slurred upstroke, absent dicrotic notch, absent dicrotic notch, and loss of fine detailand loss of fine detail

• Causes include blood Causes include blood clots, air bubbles in clots, air bubbles in the tubing, and kinked the tubing, and kinked catheterscatheters

UnderdampingUnderdamping

• Underdamping Underdamping produces produces exaggerated peaks and exaggerated peaks and troughs in the waveformtroughs in the waveform

• It can cause falsely high It can cause falsely high systolic pressures and low systolic pressures and low diastolic pressuresdiastolic pressures

• Causes include long Causes include long connecting lines (>1.4 connecting lines (>1.4 mm), small tubing (<1.5 mm), small tubing (<1.5 mm internal diameter), or mm internal diameter), or when the catheter occlude when the catheter occlude the vesselthe vessel

Transducer Leveling and ZeroingTransducer Leveling and Zeroing

• The pressure transducer is exposed to atmospheric The pressure transducer is exposed to atmospheric pressure to establish the zero pressure reference value pressure to establish the zero pressure reference value against which all intravascular pressures are measuredagainst which all intravascular pressures are measured

• In the supine patient, pressure transducers are leveled In the supine patient, pressure transducers are leveled most often to the midchest position in the midaxillary linemost often to the midchest position in the midaxillary line

• In other than supine positions (head injuries, CHF etc.), the In other than supine positions (head injuries, CHF etc.), the transducer should be placed at the level of the aortic root transducer should be placed at the level of the aortic root (Chest 2001;120:1322-1326)(Chest 2001;120:1322-1326)

• The principle behind this is that the proper level for a The principle behind this is that the proper level for a transducer to negate the effects of hydrostatic pressure is transducer to negate the effects of hydrostatic pressure is always at the top of the fluid column in the system being always at the top of the fluid column in the system being analyzed (ie. Aortic root) analyzed (ie. Aortic root)

continuedcontinued

• The central MAP and particularly the aortic mean The central MAP and particularly the aortic mean is the key component in coronary and cerebral is the key component in coronary and cerebral perfusion as well as the pressure that is sensed perfusion as well as the pressure that is sensed by baroreceptor mechanismsby baroreceptor mechanisms

• This is the pressure that is indirectly measured This is the pressure that is indirectly measured using standard noninvasive BP techniquesusing standard noninvasive BP techniques

The Arterial Waveform in relation to The Arterial Waveform in relation to the EKGthe EKG

1.1. Systolic UpstrokeSystolic Upstroke2.2. Systolic Peak Systolic Peak

PressurePressure3.3. Systolic DeclineSystolic Decline4.4. Dicrotic NotchDicrotic Notch5.5. Diastolic RunoffDiastolic Runoff6.6. End-diastolic End-diastolic

PressurePressure

Comparative Analysis of Different SitesComparative Analysis of Different Sites

ComplicationsComplications

• IschemiaIschemia• HemorrhageHemorrhage• ThrombosisThrombosis• Embolism Embolism • Cerebral air embolism (retrograde flow assoc. w/ Cerebral air embolism (retrograde flow assoc. w/

flushing)flushing)• Aneurysm formationAneurysm formation• Arteriovenous Fistula formationArteriovenous Fistula formation• Skin necrosisSkin necrosis• Infection (Stopcocks are an important source)Infection (Stopcocks are an important source)

Indications for CVPIndications for CVP

• Central Venous Pressure MonitoringCentral Venous Pressure Monitoring• Pulmonary artery catheterization and monitoringPulmonary artery catheterization and monitoring• Transvenous cardiac pacing Transvenous cardiac pacing • Temporary hemodialysisTemporary hemodialysis• Drug administration: Drug administration: Concentrated vasoactive drugsConcentrated vasoactive drugs HyperalimentationHyperalimentation ChemotherapyChemotherapy Agents irritating to peripheral veinsAgents irritating to peripheral veins• Rapid infusion of large volumes : Trauma and Major surgeryRapid infusion of large volumes : Trauma and Major surgery• Aspiration of Air EmboliAspiration of Air Emboli• Inadequate peripheral IV accessInadequate peripheral IV access• Sampling site for repeated blood testingSampling site for repeated blood testing

Normal CVPNormal CVP

• ““Normal” CVPNormal” CVP• A normal value in a spontaneously A normal value in a spontaneously

breathing patient is approximately 5-breathing patient is approximately 5-10cm H10cm H22OO

• This rises about 3-5cm HThis rises about 3-5cm H22O during O during mechanical ventilationmechanical ventilation

What does this number mean?What does this number mean?

• CVP is a measure of the pressure in the CVP is a measure of the pressure in the right atrium, which reflects changes in right atrium, which reflects changes in right ventricular end-diastolic pressure right ventricular end-diastolic pressure

• Estimates cardiac function and blood Estimates cardiac function and blood volume. It does not measure either of volume. It does not measure either of these directly - it must be interpreted!these directly - it must be interpreted!

• Determined by the function of the right Determined by the function of the right heart and the pressure of venous blood heart and the pressure of venous blood in the vena cavain the vena cava

CVP and Left Heart PressuresCVP and Left Heart Pressures

• In a normal patient the CVP closely In a normal patient the CVP closely resembles the left atrial pressure and resembles the left atrial pressure and can be used to estimate itcan be used to estimate it

• This depends on the assumption that This depends on the assumption that there is no right ventricular disease there is no right ventricular disease and normal pulmonary vascular and normal pulmonary vascular resistanceresistance

CVP WaveformCVP Waveform

• Three Peaks (a, c, Three Peaks (a, c, v)v)

• Two Descents (x, y)Two Descents (x, y)

““a” wavea” wave

• Caused by atrial Caused by atrial contraction (follows contraction (follows the P-wave on the P-wave on EKG)EKG)

• End diastoleEnd diastole• Corresponds with Corresponds with

“atrial kick” which “atrial kick” which causes filling of the causes filling of the right ventricleright ventricle

““c” wavec” wave

• Atrial pressure decreases Atrial pressure decreases after the “a” wave as a after the “a” wave as a result of atrial relaxationresult of atrial relaxation

• The “c” wave is due to The “c” wave is due to isovolemic right isovolemic right ventricular contraction; ventricular contraction; closes the tricuspid valve closes the tricuspid valve and causes it to bow and causes it to bow back into the right back into the right atriumatrium

• Occurs in early systole Occurs in early systole (after the QRS on EKG)(after the QRS on EKG)

““x” descentx” descent

• Atrial pressure Atrial pressure continues to decline continues to decline due to atrial due to atrial relaxation and relaxation and changes in geometry changes in geometry caused by ventricular caused by ventricular contractioncontraction

• Mid-systolic eventMid-systolic event• ““Systolic collapse in Systolic collapse in

atrial pressure”atrial pressure”

““v” wavev” wave

• The last atrial The last atrial pressure increase is pressure increase is caused by filling of caused by filling of the atrium with blood the atrium with blood from the vena cavafrom the vena cava

• Occurs in late systole Occurs in late systole with the tricuspid still with the tricuspid still closedclosed

• Occurs just after the Occurs just after the T-wave on EKGT-wave on EKG

““y” descenty” descent

• Decrease in atrial Decrease in atrial pressure as the pressure as the tricuspid opens and tricuspid opens and blood flows from blood flows from atrium to ventricleatrium to ventricle

• ““Diastolic collapse Diastolic collapse in atrial pressure”in atrial pressure”

Measuring CVPMeasuring CVP

• The peak of the “a” wave coincides with The peak of the “a” wave coincides with the point of maximal filling of the right the point of maximal filling of the right ventricleventricle

• Therefore, this is the value which should Therefore, this is the value which should be used for measurement of RVEDPbe used for measurement of RVEDP

• Machines just “average” the Machines just “average” the measurementmeasurement

• Should be measured at end-expirationShould be measured at end-expiration

Respiratory EffectsRespiratory Effects

• During spontaneous ventilation, a decrease During spontaneous ventilation, a decrease in pleural and pericardial pressures occurs in pleural and pericardial pressures occurs during inspiration - these are pressures during inspiration - these are pressures that are transmitted to the right atriumthat are transmitted to the right atrium

• This causes a decrease in the measured This causes a decrease in the measured CVP (but transmural pressure may actually CVP (but transmural pressure may actually INCREASE)INCREASE)

• Mechanical ventilation causes the opposite Mechanical ventilation causes the opposite effect during an forced inspiratory breatheffect during an forced inspiratory breath

Respiratory Effects (cont.)Respiratory Effects (cont.)

• Pleural and pericardial pressures are almost Pleural and pericardial pressures are almost equal to atmospheric pressure at end-equal to atmospheric pressure at end-expirationexpiration

• This is true with both spontaneous and This is true with both spontaneous and mechanical ventilationmechanical ventilation

• This point in time provides the best estimate This point in time provides the best estimate for transmural pressure and cardiac preloadfor transmural pressure and cardiac preload

Things to remember…Things to remember…

• There are three parts of the waveform There are three parts of the waveform that are systolic events (c, x, v)that are systolic events (c, x, v)

• There are two parts of the waveform There are two parts of the waveform that are diastolic events (a, y)that are diastolic events (a, y)

• The EKG is used as a reference to The EKG is used as a reference to properly identify the parts of the properly identify the parts of the waveformwaveform

• The terms systole and diastole refer to The terms systole and diastole refer to VENTRICULAR events onlyVENTRICULAR events only

Things to remember…Things to remember…

• The CVP wave represents changes in The CVP wave represents changes in pressure, not changes in volumepressure, not changes in volume

• Mnemonic for the CVP waveMnemonic for the CVP wave– ““aa” wave due to ” wave due to aatrial contractiontrial contraction– ““cc” wave due to tricuspid ” wave due to tricuspid cclosure and losure and

ventricular ventricular ccontractionontraction– ““vv” wave due to ” wave due to vvenous filling of atriumenous filling of atrium

Tachycardia and CVPTachycardia and CVP

• A short PR interval can cause the “a” A short PR interval can cause the “a” and “c” waves to fuseand “c” waves to fuse

• Tachycardia reduces the time spent Tachycardia reduces the time spent in diastole, causing a short “y” in diastole, causing a short “y” descentdescent

• This can make the “v” and “a” waves This can make the “v” and “a” waves appear to mergeappear to merge

Bradycardia and CVPBradycardia and CVP

• Causes each wave to Causes each wave to become more distinctbecome more distinct

• ““h” wave may h” wave may become evident - become evident - plateau wave in mid- plateau wave in mid- or late diastoleor late diastole

• The “h” wave has The “h” wave has very little clinical very little clinical significancesignificance

Clinical ExamplesClinical Examples

• Atrial FibrillationAtrial Fibrillation• Junctional RhythmJunctional Rhythm• Ventricular PacingVentricular Pacing• Tricuspid Regurgitation/StenosisTricuspid Regurgitation/Stenosis• Pericardial ConstrictionPericardial Constriction• Cardiac TamponadeCardiac Tamponade

Atrial FibrillationAtrial Fibrillation

• The “a” wave disappears (no atrial The “a” wave disappears (no atrial contraction or “kick”)contraction or “kick”)

• The “c” wave becomes more The “c” wave becomes more prominent (atrial volume is higher at prominent (atrial volume is higher at beginning of systole because the beginning of systole because the atrium did not empty)atrium did not empty)

Junctional RhythmJunctional Rhythm

• Atrial contraction occurs during systole Atrial contraction occurs during systole (when the tricuspid valve is closed)(when the tricuspid valve is closed)

• The blood has no place to go so the The blood has no place to go so the pressure goes up much more than pressure goes up much more than usual, resulting in a large “a” waveusual, resulting in a large “a” wave

• Cannon “a” waveCannon “a” wave• Also seen with A-V dissociation, Also seen with A-V dissociation,

ventricular pacing, etc.ventricular pacing, etc.

Tricuspid RegurgitationTricuspid Regurgitation

• The right atrium The right atrium gains volume during gains volume during systole - so the “c” systole - so the “c” and “v” wave is and “v” wave is much highermuch higher

• The right atrium The right atrium “sees” right “sees” right ventricular pressures ventricular pressures and the pressure and the pressure curve becomes curve becomes “ventricularized”“ventricularized”

Tricuspid StenosisTricuspid Stenosis

• Problem with atrial Problem with atrial emptying and a barrier emptying and a barrier to ventricular filling on to ventricular filling on the right side of the the right side of the heartheart

• Mean CVP is elevatedMean CVP is elevated• ““a” wave is usually a” wave is usually

prominent as it tries to prominent as it tries to overcome the barrier to overcome the barrier to emptyingemptying

• ““y” descent muted as a y” descent muted as a result of decreased result of decreased outflow from atrium to outflow from atrium to ventricleventricle

Pericardial ConstrictionPericardial Constriction

• Limited venous return Limited venous return to heart, elevated CVP, to heart, elevated CVP, end-diastolic pressure end-diastolic pressure equalization in all equalization in all cardiac chamberscardiac chambers

• Prominent “a” and “v” Prominent “a” and “v” waves, steep “x” and waves, steep “x” and “y” descents“y” descents

• Characteristic M or W Characteristic M or W pattern, dip and pattern, dip and plateau (square root plateau (square root sign)sign)

Cardiac TamponadeCardiac Tamponade• Changes in atrial and Changes in atrial and

ventricular volumes are ventricular volumes are coupled, so total coupled, so total cardiac volume does cardiac volume does not change when blood not change when blood goes from atrium to goes from atrium to ventricleventricle

• CVP becomes CVP becomes monophasic with a monophasic with a single, prominent “x” single, prominent “x” descent with a muted descent with a muted “y” descent“y” descent

• Similar to pericardial Similar to pericardial constriction but not constriction but not exactly the sameexactly the same

Central Line ComplicationsCentral Line ComplicationsComplications Total FatalitiesComplications Total Fatalities

• Cardiac Tamponade 11 10Cardiac Tamponade 11 10• Wire or catheter embolism 12 0Wire or catheter embolism 12 0• Vascular injuries (non-pulmonary artery) 13 5Vascular injuries (non-pulmonary artery) 13 5• Hemothorax 6 4Hemothorax 6 4• Hydrothorax 3 1Hydrothorax 3 1• Carotid artery injury 3 0Carotid artery injury 3 0• Subclavian a. aneurysm 1 0Subclavian a. aneurysm 1 0• Pulmonary artery rupture 2 2Pulmonary artery rupture 2 2• Pneumothorax 7 1Pneumothorax 7 1• Air embolism 1 0Air embolism 1 0• Fluid extravasation 1 0Fluid extravasation 1 0• Total 48 20Total 48 20• (Central Line complications from ASA Closed Claims Project. ASA (Central Line complications from ASA Closed Claims Project. ASA

Newsletter 1996;60:222-5Newsletter 1996;60:222-5