Hemdynamic Wavefrm Interpretatin Hemdynamic wavefrms are maps f the pressure changes that take place within a given vessel r chamber. T understand the shape r mrphlgy f a nrmal wavefrm, a clear understanding f the events f the cardiac cycle is required. Fcus n the chamber r vessel that is being measured, and visualize the pressure changes that ccur during ne cmplete perid f systle and diastle. All f the wavefrms btained frm arterial lines, pulmnary artery catheters, r during cardiac catheterizatin can be recgnized by recalling 3 basic wavefrm mrphlgies. These 3 wavefrm shapes include: 1) atrial, 2) arterial, and 3) ventricular wavefrms. Because bth atria fill, empty and cntract in the same sequence during systle and diastle, the right atrial and left atrial wavefrms have similar patterns. Similar changes ccur between the pulmnary artery and arta, and the right and left ventricles. Nrmal wavefrms will be reviewed by examining wavefrms that demnstrate each f these 3 patterns. WAVEFORM DESCRIPTIONS 1. ATRIAL WAVEFORMS (right and left atrium) Wavefrms btained frm the right and left atria have similar mrphlgies. Thus, CVP (right atrial) and left atrial pressure tracings have similar shapes. Direct left atrial pressure mnitring is uncmmn, but can be dne by inserting a small catheter int the pulmnary vein during pen-heart surgery. Mre cmmnly, left atrial pressure wavefrms are btained thrugh indirect measurement. Pulmnary artery wedge pressure wavefrms (PAWP, PWP) are indirect measurements f the left atrial pressure. Thus, CVP and PWP wavefrms have similar shapes. We will begin by examining a right atrial pressure wavefrm. These principles will then be cmpared t the left atrial pressure wavefrm btained frm a pulmnary artery wedge pressure tracing (Table 1). RIGHT ATRIAL PRESSURE TRACING RIGHT ATRIAL CATHETER Subclavian Line Table 1 Brenda Lynn Mrgan, Critical Care Cncepts 1
The right and left atrial wavefrms will take n the same appearance, but the right-sided pressures are slightly lwer than the left. The right atrial wavefrm can be identified thrugh any catheter lcated in the right atrium r great veins, including: The CVP (blue: prximal injectin) prt f the pulmnary artery catheter The VIP (white: prximal infusin) prt f a VIP mdel pulmnary artery catheter An intrducer (crdis) that is lcated in a large central vein Any single r multi-lumen prt f a central venus catheter The tip f a right atrial catheter shuld nt be lcated in the right atrium due t the risk f atrial wall injury. The tip shuld be lcated prir t the entry t the right atrium in the SVC (jugular r subclavian access) r IVC (femral access). Because there are n valves between the IVC r SVC and the right atrium, pressures mnitred in the great veins will prvide an pen pathway t the right atrium and reveal a right atrial wavefrm. CVP measurements btained via duble r triple lumen catheters r frm intrducers that are inserted via the femral vein, may be influenced by intra-abdminal pressures and subject t inaccuracies. We are nt really interested in measuring atrial pressures. Our true gal is t measure the pressure in the ventricles at the end f diastle, t identify a filling pressure. This prvides directin fr intravascular fluid management. It wuld be unsafe t leave a catheter with the tip lcated in the ventricle, therefre, the catheter is safely psitined abve the ventricle in the atrium. T identify ventricular pressure, we measure the atrial pressure at a time when the AV valve (tricuspid and mitral) is pen, prviding an pen pathway t the ventricle. The AV valves are pen during diastle. The atrial pressure remains higher than the ventricular pressure during the entire diastlic perid; this is why the valve remains pen and bld cntinues t flw frm the atrium t the ventricle. T capture the true ventricular pressure, the atrial pressure shuld be measured as clse t the end f diastle as pssible. At end-diastle, the atrial and ventricular pressures equilibrate. Beynd this pint, the ventricular pressure rises abve the atrial pressure, clsing the AV valve (preventing further access t the ventricle frm the atrium). The gal fr any atrial pressure measurement is t btain the measurement at the very end f diastle, when the atrial pressure is clsest t the ventricular pressure. This shuld represent the ventricular pressure at the end f filling. CVP and PAWP are filling PRESSURES. Althugh a lw pressure generally indicates lw prelad r vlume, a high pressure des nt necessarily crrelate t a high end-diastlic vlume. Fr example, a nn-cmpliant ventricle (ne that cannt stretch easily) can generate high pressures during filling, even when the actual vlume in the ventricle is lw. Ischemia can prduce this type f prblem, because xygen is needed t facilitate muscle relaxatin (referred t as diastlic dysfunctin). In additin, pathlgy that elevates pressures between the PA catheter tip and the left ventricle can prduce high PAWP readings that are nt a reflectin f the left ventricular pressure. Fr example, high PEEP, r pulmnary vascnstrictin can prduce this type f errr. The greatest value in mnitring these pressures is btained by ensuring that each pressure is measured the same way, enabling the trend in pressures t be fllwed. Each pressure shuld be cmpared t the Brenda Lynn Mrgan, Critical Care Cncepts 2
patient s clinical respnse, t identify the ptimal filling pressure fr a given patient. The PAWP is an indirect measurement f the left atrial pressure, therefre, it has the same mrphlgy as a right atrial wavefrm (Table 2). LEFT ATRIAL PRESSURE TRACING (FROM PAWP) PAWP Table 2 During wedging f the PA catheter, frward flw frm the right ventricle is bstructed, and the frward, static pressure is mnitred. The absence f valves creates an uninterrupted pathway between the catheter tip and left atrium. Thus, the PAWP tracing is a measure f the left atrial pressure. The wavefrm shape will be similar t the right atrial tracing, hwever, the time it takes fr the left atrial pressure wavefrm t be transmitted backward tward the tip f the catheter is prlnged. Cnsequently, the PAWP will be delayed r slightly later in relatinship t the ECG than the right atrial wavefrm. The PAWP tracing is ften less crisp and clear, and is subject t significant mvement and respiratry artifact. PAWP wavefrms will ften have additinal artifact waves. 2. VENTRICULAR WAVEFORMS Wavefrms btained frm the right and left ventricle have similar mrphlgies. Right ventricular wavefrms are btained during insertin f a pulmnary artery catheter, if the pulmnary artery catheter slips backward int the right ventricle and frm any lumen f the pulmnary artery catheter that terminates in the right ventricle (e.g., Paceprt lumen f the Swan Ganz ). Left ventricular wavefrms are nt nrmally bserved, with the exceptin f during a left heart catheterizatin (e.g., in the cardiac catheterizatin rm) r during pen surgery. Left ventricular wavefrms have a similar shape, but much higher pressures than right ventricular wavefrms. Brenda Lynn Mrgan, Critical Care Cncepts 3
RIGHT VENTRICULAR WAVEFORM (measured frm within the right ventricle) RIGHT VENTRICULAR WAVEFORM (measured frm a pulmnary artery catheter) Nte the timing delay between the QRS and the rise in the right ventricular pressure when btained frm the tip f the 110 cm lng PA catheter (wavefrm n right) versus direct measurement (wavefrm abve). Table 3 3. ARTERIAL PRESSURE WAVEFORMS (Pulmnary artery, arterial lines) The pressure changes in the pulmnary artery and the arta during systle and diastle prduce similar mrphlgy (Table 4). PULMONARY ARTERY WAVEFORM AORTIC WAVEFORM Table 4 Brenda Lynn Mrgan, Critical Care Cncepts 4
Arterial lines r pulmnary artery lines demnstrate the same mrphlgy r shape. Arterial lines have much higher pressures than pulmnary artery lines Pulmnary artery tracings are subject t cnsiderable mvement artifact nt seen in arterial tracings. 4. WAVEFORM RECOGNITION ATRIAL PRESSURE WAVEFORMS (right atrial, PAWP) In a nrmal sinus rhythm, the atrial wavefrm can be recgnized by tw r three lw amplitude waves fr every cardiac cycle (r tw-three small bumps between ne R R interval. The a is the rise in atrial pressure as a result f atrial cntractin, the c (nt always visible) is the rise in atrial pressure when the clsed AV valve bulges upward int the right atrium fllwing valve clsure, and the v is the rise in the atrial pressure as it refills during ventricular cntractin (Figure 1). Figure 1 The atrial pressures initially increase during systle as the cntracting ventricles return bld t the atria, refilling the upper chambers. This rise in the atrial pressure is identified as the v wave. The upstrke f the v wave is the rise in atrial pressure as a result f atrial filling (Figure 2). Because it is prduced as a result f ventricular cntractin, its lcatin is relative t the QRS n the ECG. The QRS is the deplarizatin f the ventricle (r the getting ready t cntract phase). The ventricle must deplarize first, then cntract and eject bld int the great vessels. Ejectin eventually leads t the return f bld t the atria (left ventricular cntractin refills the right atrium and prduces the right atrial v wave; right ventricular cntractin refills the left atrium and prduces the left atrial v wave). Thus, the QRS causes the v wave, hwever, the QRS always appears befre the v wave is prduced. In a CVP tracing, the v is generally lcated immediately after the peak f the T wave n the ECG. On the left atrial r PWP tracing, the v wave appears a little bit later (due t the timing delay). Figure 2 Brenda Lynn Mrgan, Critical Care Cncepts 5
The atrial pressures peaks at the end f atrial filling r end systle (Figure 3). End systle is the peak f the v wave. Figure 3 As the v wave peaks, the pressure in the newly filled atria will exceed the pressure in the relaxing, empty ventricles belw. This pressure change (atrium higher than ventricle) causes the pening f the mitral and tricuspid valves (nset f diastle). Once the valves pen, the favurable pressure gradient causes atrial bld t rush tward the ventricle. This prduces a rapid decline in atrial pressure (Figure 4), and reflects the initial third f diastle (perid f rapid inflw ). This decline in the atrial pressure is referred t as the Y descent ( Y fr atrial emptying). Y Descent Figure 4 At the bttm f the dwnslpe f the v wave, the pressure drps int a valley between the v wave and the next pressure rise (Figure 5). This drp in atrial pressure crrelates t the decline in atrial pressure fllwing rapid emptying. This decline in atrial pressure reduces the pressure gradient between the atrial and ventricular pressures and temprarily reduces the rate f ventricular filling. This perid f reduced bld flw is called diastasis and represents the middle third f diastle. Figure 5 In rder t ptimize ventricular filling, the atrial pressure needs t rise in late diastle t augment the pressure gradient. Thus, in the final third f diastle, the atria deplarize, causing the atrial pressures t increase. This secnd rise in pressure is displayed n the atrial wavefrm as the a wave (Figure 6). The a wave begins t frm as deplarizatin begins, therefre, it is lcated in the PR interval n a right Brenda Lynn Mrgan, Critical Care Cncepts 6
atrial pressure wavefrm (slightly later fr a left atrial r PWP wavefrm). The a wave is the rise in atrial pressure as a result f atrial deplarizatin and subsequent cntractin. Figure 6 Fllwing cntractin, the atria begin t relax, and the atrial pressures nce again fall (Figure 7). This fall in atrial pressures is identified by the dwnslpe f the a waves. This is referred t as the X descent ( X fr atrial relaxatin). X Descent Figure 7 As the atrial pressures cntinue t fall, the ventricles belw begin t deplarize. This causes the ventricular pressures t begin t rise. The rising pressure causes the ventricle pressures t exceed the atrial pressures. This causes the mitral and tricuspid valves t clse. The ventricle pressures cntinue t rise as a result f deplarizatin, even thugh the pulmnary and artic valves have nt yet pened. This perid fllwing diastle when all 4 heart valves are clsed is called isvlumetric cntractin. This perid is called isvlumetic cntractin (cntractin withut flw) because the ventricle pressure is rising due t ismetric cntractin (due t deplarizatin), but the clsed valves prevent bld flw. As the pressure builds in the ventricle, the clsed AV valves begin t bulge upward int the atria, prducing a small rise in the pressure. This pressure rise in the atria is called the c wave (Figure 8). The c wave is nt always visible, but can appear as a bump n the dwnslpe f the a wave, r as a separate wave in between the a and the v. In a right atrial wavefrm, it generally cincides with the mid t late QRS. It will appear slightly later in a left atrial r PAWP tracing. Figure 8 Brenda Lynn Mrgan, Critical Care Cncepts 7
The pressures in the atria cntinue t decline fllwing the C wave as the atria cntinue t relax (Figure 9). The atrial pressures will remain lw until they begin t receive enugh bld frm the cntracting ventricles t generate a rise in pressure. Figure 9 Obtaining PAWP and CVP Measurements The trend in data prvides the mst meaningful infrmatin frm PAWP r CVP measurements. If each pressure is measured using the same technique, then changes in the pressure will truly reflect a change in the patient. CVP and PAWP shuld be measured using the same techniques. If different techniques are used, the relatinship between CVP and PAWP cannt be cmpared. CVP shuld be lwer than the PAWP Elevated PAWP r left atrial pressures back up t prduce cardiac pulmnary edema. Elevated CVP r right atrial pressures back up t prduce jugular venus distensin and peripheral edema. Left heart failure prduces elevated left heart pressures that can be transmitted all the way back t the right heart. Pulmnary edema is prduced as a result f the elevated left heart pressure, and jugular venus distentin and peripheral edema is prduced as a result f the secndary right heart pressure elevatin. Althugh bth PAWP and CVP readings will be elevated, if the right heart pressure elevatin is due t left heart pressure elevatin, the PAWP will be higher than the CVP. CVP pressures equal t r higher than PAWP readings indicate right sided disease. Pulmnary edema will nt be present, unless due t a secndary prblem (e.g., simultaneus left heart pressure r nn-cardiac edema). T accurately interpret a CVP r PAWP, a paper tracing f the PAWP r CVP with a simultaneus ECG is required. This allws careful analysis f the tracing t identify the a, c and v waves, and t find the mst suitable pint fr pressure measurement. It als prvides a reference t evaluate the significance f a change later n (analysis f the wavefrm n the mnitr screen des nt prvide this pprtunity) A previus tracing can be reviewed t identify whether a change in the pressure reading represents a change in the patient, r a change in the measurement technique r wavefrm Crrelatin t the ECG The easiest wave t evaluate an atrial tracing is t first lcate the v wave. It will appear immediately after the T wave n a CVP wavefrm, hwever, it will be.08-.12 secnds after the T wave n a PAWP tracing. Yu can generally identify the v wave by ruling ut ther waves. It must be after the peak f the T wave. Once the v wave is identified, the a and c can be determined. Brenda Lynn Mrgan, Critical Care Cncepts 8
Observe the ECG rhythm. If the patient has a sinus rhythm, an a wave shuld be present. The a shuld be in the PR interval fr a CVP. It is later in the PAWP, appearing within r even after the QRS. If present, the c wave is generally within the QRS fr a CVP. It will be after the QRS fr a PAWP. CVP PWP Table 5 Figure 10 If the patient des nt have a P wave, the a wave will be absent. If the P is nt synchrnized t the QRS (i.e., retrgrade P waves that ccur simultaneus with r after the QRS), very large a waves may be present. These large a waves may appear as ne very large wave during a cardiac cycle. The large a waves are called cannn a waves. They are actually exaggerated atrial pressures that ccur when the atria cntract against a clsed AV valve, adding t the pressure that is already being generated due t the c r v wave (Figure 10). In atrial fibrillatin, a waves are absent. The c and the v ften merge tgether, prducing ne wider r full figured pressure wavefrm fr each cardiac cycle (Figure 11). Brenda Lynn Mrgan, Critical Care Cncepts 9
Figure 11 Where t Measure CVP and Wedge We measure atrial pressures as a means f viewing the pressures in the ventricles when they are full f bld. Thus, we must measure the atrial pressures during diastle when the mitral and tricuspid valves are pen. During diastle, the atrial pressure is higher than the ventricular pressure (this is the gradient that keeps the valves pen and bld mving tward the ventricle). At the very end f diastle, the atrial pressure equilibrates with the ventricular pressure, at the very end f ventricular filling. Measurement f the atrial pressure at the end f diastle prvides the best pprtunity t capture ventricular filling pressure. Bth CVP and PAWP shuld be measured the same way. The lcatin n the atrial pressure wave that best reflects end-diastlic pressure is the pint just prir t the C wave (Figure 12). Althugh the C wave is the ideal lcatin, there are sme realistic limitatins t using the C wave as a landmark. The C is ften absent r difficult t find. This is particularly true in the PAWP wavefrm, which is subject t cnsiderable mvement artifact frm right ventricular systle and breathing. Right Atrial Pressure (CVP) Pre C Figure 12 If the Pre C wave pint is nt available, a secnd methd fr identificatin f the enddiastlic pressure is t take the mean f the highest and lwest a wave pressure (Figure 13). Brenda Lynn Mrgan, Critical Care Cncepts 10
Right Atrial Pressure (CVP) 35 25 15 5 Figure 13 A third methd can be used if the a is hard t interpret r absent. A number f arrhythmias can alter r eliminate the a wave. If it is unavailable, the end-diastlic pressure can be estimated by identifying the Z pint. Draw a line frm the end f the QRS t the atrial tracing. The pint where the line intersects with the wavefrm is the Z line. Nte: the Z pint is delayed.08-.12 secnds frm the QRS n the PAWP (Figure 14). Right Atrial Pressure (CVP) Z pint Figure 14 Fr a PAWP wavefrm, the same technique is used, hwever, the Z line shuld be estimated as.08-.12 secnds (tw-three small bxes n the ECG paper) t the left f the end f the QRS. At Lndn Health Sciences Centre, we cnsidered the challenges assciated with selecting a measurement technique that wuld prduce inter-rater reliability. Because variable interpretatin skills exist amng staff, we felt that varying the measurement technique accrding t the wavefrm wuld make reprducibility f results prblematic. Cnsequently, we decided t use an apprach that wuld select a pressure similar t the end-diastlic pressure and wuld facilitate easier detectin. The nly prtin f the atrial tracing that will always be present is the v wave. The tp r peak f the v wave is end-systle, therefre, the tp f the v wave wuld nt be a suitable lcatin (the atrial pressure wuld be significantly higher than the ventricle and the AV valves wuld still be clsed). The bttm r base f the v, n the right side f the dwnslpe, is mid-diastle (diastasis). This is the perid when atrial and ventricular pressures are very similar, just prir t atrial deplarizatin. At this pint, the atrial pressure is still slightly higher than the ventricular pressure, but is reasnably clse t the pre C wave pint. Because the bttm f the v (n the right hand side f the slpe) is easy t lcate and is clse t the pre c wave pressure, we chse t make this ur standard fr measurement (Figure 15). Brenda Lynn Mrgan, Critical Care Cncepts 11
While this may slightly ver r underestimate the pressure in sme patients, it is easy t lcate during repeated pressure measurements. As lng as the lcatin fr determining the pressure remains unchanged, a trend f data can be btained. While this strategy may nt be acceptable t ther institutins, it is imprtant that every critical care unit adpt a methd that will be used cnsistently by all individuals measuring CVP and PAWP at their facility. Figure 15 Hemdynamic Changes Assciated with Breathing. Cardiac pressures will rise and fall with breathing. This is identified by excursins in the wavefrm that cincide with ventilatin. Psitive pressure ventilatin will cause cardiac pressure t rise upn inspiratin. Spntaneus ventilatin usually prduces the largest respiratry artifact (mask, CPAP r lw PS ventilatin). It causes a drp in vascular pressures immediately befre inspiratin, with a gradual rise until end-expiratin. Exhalatin usually represents the lngest perid f the respiratry cycle and is generally the mst stable interval (inverse I:E rati ventilatin can prlng exhalatin). Because hemdynamic pressures rise and fall with breathing, clinically significant pressure measurement differences can be btained just by altering when in the breathing cycle the measurement was taken. T eliminate variatins in pressure measurements as a result f breathing, we attempt t measure pressures at the same phase f the respiratry cycle each time. Recrd pressure measurements at end exhalatin. Fr psitive pressure ventilatin, this is usually at the lw pint (valley) in the respiratry fluctuatins. Fr spntaneus breathing, this is just prir t the dip in respiratry fluctuatins. End-tidal CO2 r flw recrdings can be used t lcate end-expiratin. Putting the Breathing and Cardiac Cycle Tgether 1. Obtain an atrial tracing (CVP r PAWP) with a simultaneus ECG. 2. Observe the ventilatry excursin. Identify the end f expiratin accrding t the mde f ventilatin. If in dubt, place yur hand n the patient s chest and bserve the real time excursins n the PAP tracing as the patient s chest rises. This will help t identify whether the excursin are increasing with inspiratin (typical mechanical ventilatin pattern) r are falling with inspiratin (typical spntaneus pattern). PS ventilatin is the mst typical mde that can cause variatin in the pattern f excursin. Lw PS levels may prduce spntaneus variatins, whereas, higher levels f PS ften prduce mechanical type variatins. Patients may have a mixture f spntaneus and mechanical breaths (e.g., SIMV) r a mixture f triggered versus ventilatr initiated breaths (e.g., AC). 3. Lcate the a, c and v waves fr a cycle within the end-expiratin perid. Identify the landmark t be used t identify end-diastle. 4. In the example belw, the patient is n psitive pressure ventilatin. The valley in the respiratry excursin was identified as end expiratin. The Pre C wave pint frm ne f the cardiac cycles within this end expiratin perid was used (Figure 16). Brenda Lynn Mrgan, Critical Care Cncepts 12
I 5. Identify the pressure by referring t the scale n the paper tracing. Place the strip in the chart fr future reference. E End-diastle: Pre C wave End-expiratin Figure 16 5. WAVEFORM RECOGNITION VENTRICULAR PRESSURE WAVEFORMS (right ventricle, PAWP) Nte that a direct right ventricle wavefrm has been used t describe the pressure changes during the cardiac cycle. Right ventricle wavefrms btained frm a pulmnary artery catheter will display cnsiderably delay t the right f the QRS. During diastle, the ventricles relax and stretch in respnse t incming bld (ventricular filling). Because the ventricles get larger as vlume increases, the pressure in the ventricles remain very lw and change little during diastle (Figure 17). Figure 17 In late diastle, atrial cntractin frces a blus f bld int the ventricles, which can causes a small rise in the ventricular pressure. This may be seen as a small pressure wave immediately prir t the main rise in ventricular pressure, if the patient is in a sinus Brenda Lynn Mrgan, Critical Care Cncepts 13
rhythm (Figure 18). Figure 18 At the end f diastle, the deplarizatin wave (that nrmally riginates in the right atrium) reaches the ventricles. The ventricles subsequently begin t deplarize, causing the ventricular pressures t rise (as wall tensin in the ventricle increases). As sn as the pressure in the ventricle exceeds that f the atrium abve, the tricuspid and mitral valves clse. This prduces a rapid and tall pressure elevatin in the ventricular wavefrm. The pressures in the right and left ventricles will cntinue t rise after the AV valves clse, but befre the semilunar valve pen. The perid when all 4 valves are clsed is called isvlumetric cntractin (Figure 19). When the right ventricle pressure is measured directly, this rise cincides with the QRS. The timing delay seen in right ventricular tracings measured frm the pulmnary artery catheter is displayed in Figure 22. Figure 19 As the ventricular pressures peak, the right ventricular pressure will exceed the pressure in the pulmnary artery and the left ventricular pressure will exceed the artic pressure. This causes the pulmnic and artic valves t pen. An imprtant timing pint: the right ventricle pressure must rise until it is higher than the pulmnary artery in rder t pen the pulmnic valve. The pulmnary artery pressure rises after the pulmnary valve pens, and the ventricle begins t cntract. The rise in the right ventricular pressure wavefrm is clser t the QRS than the rise in the pulmnary artery tracing. The ventricular pressures peak with ventricular cntractin (Figure 20). Figure 20 Brenda Lynn Mrgan, Critical Care Cncepts 14
As sn as the ventricles cntract, bld leaves the ventricles, causing the ventricular pressures t begin t fall (Figure 21). The ventricular pressure waves will cntinue t fall as bld leaves the ventricle. At end systle, the ventricles begin t stretch and relax, and the ventricular pressures fall t the their lwest pint. This lw pressure is maintained during early diastle, because the ventricles stretch as they fill. Mrphlgy nte: the right ventricular pressure wavefrm has a steep slpe up and steep slpe dwnward. This gives the wavefrm a symmetrical shape. The pulmnary artery wavefrm has a mre prlnged dwnslpe, prviding helpful clues when differentiating the tw wavefrms. Figure 21 Right Ventricle Wavefrm frm the tip f a Pulmnary Artery Catheter In direct measurement f the right ventricular tracing, the rise in the right ventricular pressure ccurs simultaneusly with the QRS. The detectin f the rise in the right ventricular pressure wave is delayed when the RV pressure is measured thrugh a pulmnary artery catheter, because f the transit time thrugh the catheter (110 cm in length). This will cause the rise in pressure t appear after the QRS in an RV tracing measured frm a PA catheter (Figure 21). Figure 22 6. WAVEFORM RECOGNITION ARTERIAL PRESSURE WAVEFORMS (pulmnary artery, arterial wavefrm) Pulmnary artery and arterial pressure wavefrms have similar mrphlgy. The pulmnary artery, like the PAWP, is subject t cnsiderable respiratry and mvement artifact. A pulmnary artery wavefrm will be used t display the pressure changes. Arterial lines take n a similar shape. Systle begins with the pening f the artic and pulmnic valves. Prir t pening f the pulmnary valve, the pulmnary artery pressure is very lw (Figure 23). Brenda Lynn Mrgan, Critical Care Cncepts 15
Figure 23 As the ventricles cntract, they eject bld int the pulmnary artery and arta. This causes an immediate rise in the arterial pressure. As bld enters the great vessels, the pressure rises quickly and steadily, prducing a steep vertical rise (Figure 24). Figure 24 Late in systle, the rate f ejectin slws as the pressure gradient between the left ventricle and arta, and right ventricle and pulmnary artery, narrws. Althugh bld is still mving frm the ventricles t the great vessels, the rate f mvement is slwed t the pint where the pressure begins t decline. This causes the early dwnslpe in the arterial tracing that represents this perid f reduced ejectin (Figure 25). This is late systle. Figure 25 The ventricles begin t relax, causing the ventricular pressures t drp belw the pressures in the great vessels. This causes the pulmnic and artic valves t clse, prducing a small rise in the arterial pressures. This is seen as a bump n the dwnslpe f the arterial pressure tracing, knwn as the dicrtic ntch (Figure 25). Figure 26 Brenda Lynn Mrgan, Critical Care Cncepts 16
Fllwing clsure f the semi-lunar valves, the pulmnary artery and artic pressures cntinue t fall as bld leaves the great vessels t perfuse the tissues and lungs. Nte that the dwnslpe is mre gradual than the upstrke (cmpared t the symmetrical shape f the RV) [Figure 27). Figure 27 The pressure nce again begins t rise at the nset f the next systle (Figure 28). Figure 28 DIFFERENTIATION OF RIGHT VENTRICULAR WAVEFORM FROM PULMONARY ARTERY WAVEFORM Nurses caring fr patients with pulmnary artery catheters must cntinually display the pressure frm the tip f the catheter. In gd psitin, this shuld display a pulmnary artery pressure wavefrm. Tw imprtant risks exist. First, the catheter can migrate int a smaller branch f the circulatin, prducing a spntaneus wedge placement and risk fr pulmnary infarctin. Secnd, the tip f the catheter can slip back int the right ventricle, placing the patient at risk fr lethal ventricular arrhythmias. Right ventricular placement can ccur as a result f accidental withdrawal f the catheter, r in the setting f a dilated right ventricle (the catheter can lp in the right ventricle leaving less catheter available fr the pulmnary artery). The right ventricle must generate a pressure during systle that exceeds the pulmnary artery pressure (t pen the semilunar valves). In diastle, the right ventricle stretches and relaxes during filling, prducing very lw right ventricular diastlic pressures. The Systlic (S) - Diastlic (D) pressure gradient in the right ventricle [(S:20-25) (D:0-5) = 20-25] is higher than in the right atrium [(S:~6-10) (D:0-5) = 5-10] r the pulmnary artery [(S:20-25) (D:10-12) = 10-15)], giving the right ventricle pressure a taller wavefrm. The right ventricle pressure is the same as the right atrial pressure during diastle, when the tricuspid valve pens and the tw chambers equilibrate. The right ventricle pressure is the same as the pulmnary artery pressure during systle, when the pulmnary valve pens and the right ventricle and pulmnary artery pressures equilibrate. The right ventricle pressure must increase in rder t pen the pulmnary valve, the pulmnary pressure rises after the valve pens and the ventricle ejects. Thus, the rise in Brenda Lynn Mrgan, Critical Care Cncepts 17
the right ventricle pressure is clser t the QRS than the rise in the pulmnary artery pressure. In a sinus rhythm, a small rise in right ventricle pressure may be detected, in respnse t atrial cntractin and subsequent ventricular filling. The pulmnary artery wavefrm has a dicrtic ntch. Examine the differences between the right ventricle pressure and the pulmnary artery pressure belw. Nte that the systlic pressures are equal, but the right ventricle diastlic pressure is much lwer. Nte the symmetrical appearance t the right ventricle tracing, versus the crisp upstrke and prlnged dwnstrke f the pulmnary artery tracing. The right ventricle pressure rise is clser t the QRS. RV PAP Table 6 Differentiating the Right Ventricle and Pulmnary Artery Wavefrms I think that the tip f my pulmnary artery catheter is displaying a Right Ventricular wavefrm. What clues wuld help t validate that this is a right ventricular tracing? The wave lks taller. The systlic pressure equals the previusly recrded pulmnary artery systlic pressure. The diastlic pressure matches the right atrial diastlic pressure. Inflatin f the balln fails t prduce a PAWP wavefrm. The wavefrm is symmetrical in shape. There is n dicrtic ntch. A small preliminary rise in late diastle is present prir t the main rise in the pressure wavefrm. The new pressure is clser t the QRS than the previus pulmnary artery tracing. New ventricular ectpe is present. Brenda Lynn Mrgan, Critical Care Cncepts 18
RV PAP Ensuring Mnitring Accuracy Small changes in hemdynamic pressure readings are ften clinically significant. This is especially true in lw pressure systems such as CVP and PAWP. Table 7 Fr this reasn, it is crucial that individuals respnsible fr cllecting hemdynamic data, make every effrt t ensure accurate data cllectin. The fllwing steps are imprtant in the cllectin f data: 1. Obtain baseline pressure tracings f all wavefrms with simultaneus ECG at the start f each shift. This can prvide a valuable reference t assist in interpretatin later changes t a wavefrm. 2. Always check the transducer level prir t each bld pressure, PAP, CVP r PWP reading. 3. Always evaluate the quality f the wavefrm befre recrding numbers. All pressure numbers are derived frm the wavefrm, therefre, a pr quality wavefrm will prduce inaccurate readings. If the wavefrm is t small t discriminate the wavefrm characteristics, decrease the scale size t make the wavefrm larger. If the wavefrm is f a pr quality, trublesht the equipment. A runded, sluggish arterial upstrke suggests dampening f an arterial wavefrm. 4. Artifact is cmmn, especially in PAP and PAWP tracings. 5. Obtain the pressures when the patient is settled; d nt recrd data while the patient is restless, cughing r has just been suctined. 6. Obtain wedge and CVP recrdings in the supine psitin. Pressure recrdings can be made with elevatins in the head f the bed, prvided that the transducer is apprpriately placed. Measurement inaccuracies have been shwn in studies that evaluated lateral rtatin psitins. Crdinate pressure measurements arund patient turning versus the hurly clck dn t write a number dwn that has been measured inaccurately. 7. Measure hemdynamic values prir t cardiac utput measurements. Transient elevatins in CVP and PWP can ccur in sme patients during cardiac utput injectin. 8. Lk at hemdynamic values as a grup; they shuld tell a stry. If ne value seems ut f synch with ther values, it shuld be repeated. 9. Always remember t lk at the patient; des yur clinical assessment match the hemdynamic findings? 10. Mean BP is a mre meaningful pressure t mnitr and t use fr drug titratin. 11. If the mnitr identifies hyptensin, lk at the patient. Is there evidence f shck r lw cardiac utput? Check the cuff pressure t validate the prblem. DO NOT WASTE UNNECESSARY TIME LOOKING FOR A BETTER BLOOD PRESSURE IF THE PATIENT S CLINICAL APPEARANCE MATCHES A LOW BP! Brenda Lynn Mrgan, Critical Care Cncepts 19
REMEMBER THAT DIRECT ARTERIAL BP MONITORING IS THE MOST ACCURATE. CUFF BP IS THE LEAST. NIBP IS BETTER THAN CUFF PRESSURE, HOWEVER, BOTH CUFF AND NIBP BECOME PROGRESSIVELY LESS ACCURATE AS HYPOTENSION WORSENS. Arterial line, cuff and NIBP pressure measurements all represent different technlgies. BP values d vary smewhat with each methd. A cuff that is t small will prduce inaccurate readings (e.g. when the Velcr pps during measurement). Fr example, peripheral arterial lines tend t amplify the systlic BP and lwer the DBP, hwever, the mean BP will generally be similar if all methds are accurate. A pr quality pulse ximetry tracing r may be anther imprtant indicatin f shck. Brenda Lynn Mrgan RN BScN MSc CNCC(C) Clinical Educatr, CCTC September 18, 2005 Brenda Lynn Mrgan, Critical Care Cncepts 20
Hme Challenge 1. Hw will an arterial pressure tracing change in atrial fibrillatin? 2. Hw will an arterial pressure tracing change with frequent PVCs? 3. Hw will a right ventriclular pressure tracing change in atrial fibrillatin? 4. Hw wuld a right atrial pressure tracing change in atrial fibrillatin? 5. Hw will a PAWP tracing change in a sinus rhythm with cmplete heart blck? 6. Hw wuld a PAWP tracing change with mitral insufficiency? 7. Hw wuld a CVP tracing change with tricuspid stensis? 8. What is pulsus paradxus? 9. What is pulsus alternans? 10. What is pulsus bisferians? Brenda Lynn Mrgan, Critical Care Cncepts 21
Hme Challenge 1. Hw will an arterial pressure tracing change in atrial fibrillatin? The rise in pressure will have the same pattern f irregularity as the R-R interval. The systlic pressure will vary, with the lwest pressure ccurring after the shrtest R-R interval indicating reduced strke vlume frm reduced filling vlume (shrtened diastlic time). If several very shrt R-R intervals appear in a rw, the strke vlume may be extremely reduced (r negligible), indicating the accumulative effect f several cycles f reduced filling time. 2. Hw will an arterial pressure tracing change with frequent PVCs? Every premature beat will result in a premature systlic rise. The rise assciated with the premature beat will usually have a decreased amplitude (lwer strke vlume), because f the shrtened preceding filling time. 3. Hw will a right ventricular pressure tracing change in atrial fibrillatin? It will have the same pattern f irregularity f the R-R intervals, and it will lse the small wave that is prduced as a result f atrial filling. 4. Hw wuld a right atrial pressure tracing change in atrial fibrillatin? The will be n a wave (fibrillatry waves might be evident), the V V interval will be irregular and display the same irregularity as the R-R interval, and sme V wave amplitudes might be reduced due t reduced filling time (n the V waves that fllw a shrt R-R interval). 5. Hw will a PAWP tracing change in a sinus rhythm with cmplete heart blck? Each P waves will prduce an a waves, even if ut f synch with the QRS. a waves will appear befre, during r after the V wave, cnsistent with the relatinship f the P t the QRS. If the a wave (atrial cntractin) ccurs at the same time time as the V wave (during ventricular systle), a super tall r cannn a wave is prduced. This is really a fused a and v, as a result f atrial cntractin that ccur simultaneus with atrial filling. 6. Hw wuld a PAWP tracing change with mitral insufficiency? The V will be very tall, and may bscure the a wave. 7. Hw wuld a CVP tracing change with tricuspid stensis? The a wuld be tall. 8. What is pulsus paradxus? When the systlic arterial bld pressure fluctuates with breathing. Nte that the variatin is due t breathing and ccurs in the presence f a regular ECG. Varying R-R interval des nt cause the changing systlic pressure. Pulsus paradxus ccurs when the difference between the systlic pressure during inspiratin versus expiratin is > 15 mmhg. 9. What is pulsus alternans? Every ther arterial wavefrm has a reduced systlic pressure, in the presence f a Brenda Lynn Mrgan, Critical Care Cncepts 22
regular ECG (arrhythmia is nt the cause fr the varying utput). 10. What is pulsus bisferians? A ntched r twice beating pulse during late systle (befre the dicrtic ntch appears, there is a secnd rise in the systlic pressure, making it lk ntched). Brenda Lynn Mrgan, Critical Care Cncepts 23