Med Intensiva. 2012;36(3):220---232

www.elsevier.es/medintensiva

UPDATE IN INTENSIVE CARE MEDICINE: HEMODYNAMIC MONITORIZATION IN THE CRITICALPATIENT

Role of echocardiography in the hemodynamic monitorization of

critical patients�

J.M. Ayuela Azcarate a,∗, F. Clau Terréb, A. Ochagavia c, R. Vicho Pereirad

a Servicio de Medicina Intensiva, Hospital General Yagüe, Burgos, Spainb Servicio de Medicina Intensiva, Hospital de Vall d’Hebrón, Barcelona, Spainc Servicio de Medicina Intensiva, Corporación Sanitaria y Universitaria Parc Taulí, Sabadell, Barcelona, Spaind Servicio de Medicina Intensiva Clínica USP-Palmaplanas, Palma de Mallorca, Spain

KEYWORDSEchocardiography;Hemodynamic;Left ventricularfunction;Monitoring;Critical care patients

Abstract The use of echocardiography in intensive care units in shock patients allows us to

measure various hemodynamic variables in an accurate and non-invasive manner.

By using echocardiography not only as a diagnostic technique but also as a tool for continuous

hemodynamic monitorization, the intensivist can evaluate various aspects of shock states, such

as cardiac output and fluid responsiveness, myocardial contractility, intracavitary pressures,

heart---lung interaction and biventricular interdependence.

However, to date there has been little guidance orienting echocardiographic hemodynamic

parameters in the intensive care unit, and intensivists are usually not familiar with this tool.

In this review, we describe some of the most important hemodynamic parameters that can be

obtained at the patient bedside with transthoracic echocardiography in critically ill patients.

© 2011 Elsevier España, S.L. and SEMICYUC. All rights reserved.

PALABRAS CLAVEEcocardiografía;Hemodinámica;Función delventrículo izquierdo;Monitorización;Pacientes críticos

Papel de la ecocardiografía en la monitorización hemodinámica de los pacientes

críticos

Resumen El uso de la ecocardiografía en las unidades de cuidados intensivos para los pacientes

en estado de shock permite la medición precisa de varias variables hemodinámicas de una forma

no invasiva.

Mediante el uso de la ecocardiografía, no como un instrumento diagnostico sino como

herramienta de monitorización hemodinámica continua, el intensivista puede evaluar varios

aspectos de los estados de shock, como el gasto cardíaco y la respuesta de fluidos, contractilidad

miocárdica, las presiones intracavitarias, la interacción corazón-pulmón y las interdependencia

biventricular.

� Please cite this article as: Ayuela Azcarate JM, et al. Papel de la ecocardiografía en la monitorización hemodinámica de los pacientescríticos. Med Intensiva. 2012;36:220---32.

∗ Corresponding author.E-mail address: josemariaayuela8@gmail.com (J.M. Ayuela Azcarate).

2173-5727/$ – see front matter © 2011 Elsevier España, S.L. and SEMICYUC. All rights reserved.

Role of echocardiography in the hemodynamic monitorization of critical patients 221

Sin embargo, hasta la fecha, ha habido pocas guías que orienten respecto a los parámetros

hemodinámicos ecocardiográficos en la unidad de cuidados intensivos, y la mayoría de los

intensivistas por lo general no están familiarizados con esta herramienta.

En esta revisión, se describen algunos de los parámetros hemodinámicos más importantes

que pueden obtenerse con la ecocardiografía transtorácica en los pacientes críticos.

© 2011 Elsevier España, S.L. y SEMICYUC. Todos los derechos reservados.

Introduction

Hemodynamic instability is common in critical patients,and the usefulness of monitorization systems in situationsof shock is based on the capacity to obtain quantifiableand reliable hemodynamic variables able to assess preload(central venous pressure or pulmonary capillary pressure),afterload (vascular resistances), and contractility (ventri-cle function and cardiac output, CO).1 Once these variableshave been obtained, they can be grouped to establish hemo-dynamic profiles in specific clinical situations producingshock, such as hypovolemia, left or right ventricle dys-function or diminished peripheral resistances, and to assessdifferent anatomical structures (pericardium, major vesselsand heart valves).

The need to obtain continuous hemodynamic informa-tion in these patients, and the ongoing controversy over useof the Swan-Ganz catheter, have focused attention on theusefulness of ultrasound in determining systolic and dias-tolic function indexes that can be used for monitoring thecardiovascular system.2

The role of echocardiography as a useful tool for theevaluation and monitorization of cardiovascular function inthese patients has been clearly established, with class Aindication as recently defined by the recommendations forthe appropriate use of echocardiography.3 This is because inaddition to its applicability at the patient bedside, its non-invasiveness in the case of transthoracic echocardiography(TTE) or semi-invasive nature in the case of transesophagealechocardiography (TEE), the technique offers further advan-tages of great importance in evaluating patients withhemodynamic instability, such as immediate (real-time)image analysis and the obtainment of reliable etiologicalas well as functional parameters.4---6

Usefulness of echocardiography in situationsof hemodynamic instability in the criticalpatient

The current technological advances applied to echocardio-graphy make it possible to study most patients via thetransthoracic route, using the standard windows and planes(Fig. 1) from which clinically applicable conclusions can bedrawn.

Two-dimensional (2D) echocardiography7 allows us tovisualize most of the heart structures, with an assessmentof the morphology and size of the right and left cavities,cardiac walls and of the presence of masses within theheart chambers. This information is basically qualitative,and Doppler ultrasound8 in its different modes (pulsed, con-tinuous and color) is required to obtain information on the

direction and velocity of blood flow in the different cham-bers and major vessels. Knowing the flow velocity, andsimplifying the Bernoulli equation, we can calculate thepressure gradient between the cavities, establish the valveareas and determine the intracavitary pressures of the dif-ferent heart chambers.

TEE is reserved for situations where the existing win-dow is inadequate or suboptimal for TTE; when we needto evaluate structures that are difficult to examine withTTE (e.g., the appendages, thoracic aorta or valve pros-theses); or where a diagnosis must be established in whichhigh imaging quality is crucial----as in acute aortic syndrome,endocarditis and its complications, and the detection ofthrombi or masses, or prosthesis dysfunction.9,10

As with all imaging techniques, its main limitation isdependency on operator experience and on the apparatusbeing used. Adequate training and capacitation are there-fore needed. Recent articles11---14 show the usefulness ofdifferent echocardiographic methods in obtaining hemody-namic measurements that can be used for both diagnosticpurposes and for analyzing the variability and changesinduced by applied treatments.

Likewise, focused ultrasound and echocardiography(FUSE)15,16 has been shown to be useful in critical, emer-gency and out-hospital patient care.17,18 In this context,a basic two-dimensional echocardiographic study allows usto establish or discard clinical situations based on binary(yes/no) responses to ensure the provision of urgent treat-ment.

A series of basic questions must be considered on per-forming echocardiography in the critical patient underconditions of shock.

How is patient left ventricle function (LVF)?

The analysis of LVF is one of the basic elements and thefirst to be considered before carrying out volume replace-ment and/or providing inotropic support. There are multiplecauses of reversible left ventricle myocardial dysfunction innon-cardiac critical disease in the Intensive Care Unit (ICU):pancreatitis, sepsis, neurogenic causes, intoxications, braindeath and anaphylaxis. A left ventricle dysfunction rate ofup to 40% has also been described in septic shock.

The quantitative methods used for estimating left ven-tricle systolic function with echocardiography include lineardeterminations in M-mode, two-dimensional measurementsin 2D-mode, and calculations derived from intracardiacflows using Doppler echocardiography (Table 1).

At basic level, and following the criteria of the FocusedEchocardiography Entry Level (FEEL) protocol,19,20 the eval-uation of LVF should be made visually with the purpose

222 J.M. Ayuela Azcarate et al.

Table 1 Echocardiographic parameters in evaluating left

ventricle function.

Evaluation of left ventricle function

Echocardiography, two-dimensional and M-mode:

Size and configuration of cavities.

Global systolic function and ejective phase indexes:

Ejection fraction (EF)

Shortening fraction (SF)

Global and regional systolic function of LV and RV.

Detection and assessment of pericardial effusion.

Assessment of valve anatomy.

Echo-Doppler:

Calculation of cardiac output.

Evaluation of regurgitations and valve stenoses.

Evaluation of diastolic function.

Estimation of pulmonary capillary pressure (PCP).

of establishing whether the left ventricle (LV) is dilated,and whether function is normal or moderately/severelydepressed, in order to integrate the response in the clini-cal context, with a view to defining a correct managementstrategy.

Subjective visual estimation of the ejection fraction (EF)is widely used in daily clinical practice, though experience isrequired on the part of the explorer in order to establish thedifferent degrees of dysfunction (<30% severely depressed,>30% to <40% moderately depressed, >40% to <55% slightlydepressed and >55% normal) with acceptable correlation tothe quantitative determinations.21

The extreme values are easily identified. In this context,a group of intensivists with 2 h of theoretical training andonly 4 h of practice, using a portable echocardiograph, wereable to correctly identify normal LVF in 92% of the cases anddepressed LVF in 80% of the cases----the most common errorbeing the overestimation of ventricle function.22

Other forms of quantitative evaluation require greaterexperience. With the transducer in the parasternal lon-gitudinal plane and combining two-dimensional imaging

Figure 1 Schematic representation of windows and images obtained by transthoracic echocardiography. Parasternal longitudinal

plane of the LV (1A) showing the left atrium (LA), left ventricle (LV), aorta (Ao) and right ventricle (RV). Parasternal transverse plane

at major vessel level (1B), with the right ventricle outlet tract (RVOT), pulmonary artery (PA) and right atrium. Apical four-chambers

plane (1C), and subcostal plane (1D) showing the right and left cavities.

Role of echocardiography in the hemodynamic monitorization of critical patients 223

with the M-mode, the ultrasound beam should be madeto section the LV as perpendicular as possible (nevertangentially), in order to register the smallest diame-ters, the end-diastolic diameter (DEd coincides with thepeak of the R-wave of the ECG tracing) and the end-systolic diameter (DEs with the maximum excursion pointof the endocardial margin). From these values we calcu-late the shortening fraction (SF = (DEd − DEs)/DEd × 100),which expresses the percentage relationship between thediastolic and systolic diameters standardized with respectto the diastolic diameter (normal value > 30%), and theejection fraction, which relates the end-diastolic ventric-ular volume (VEd) and the end-systolic ventricular volume(VEs), standardized with respect to the end-diastolic volume(EF = (VEd − VEs)/VEd × 100).

The technique has important limitations in the case ofnon-global structural and functional alterations (ischemicheart disease) or when the section plane does not meet therequired perpendicularity between the cardiac walls. It istherefore very dependent upon the operator. The method-ology is also dependent upon preload and contractility, andonly assesses the function of the segments sectioned by theultrasound beam. Accordingly, function of the left ventricleis estimated assuming contraction to be symmetrical. Nev-ertheless, the parameters are easy to obtain, reproducibleand reliable for evaluating function, since no mathematicalmodel needs to be assumed.

In relation to the different methods available formeasuring the ejection fraction with two-dimensionalechocardiography,23---25 the so-called modified Simpsonmethod has been established by consensus as the optionof choice. This method assumes the volume of the leftventricle to conform a series of ellipses stacked over thelength of the cavity, using measurements in orthogonalplanes to determine the systolic and diastolic volumes. Thestandard planes are the apical four-chamber (4C) and two-chambers (2C) planes, taking special care not to includethe papillary muscles in the planimetric tracing of thecavities, using a complex formula included in the mea-suring software of the system. In this way, calculationis made of the end-systolic volume (ESV) and the end-diastolic volume (EDV), with the ejection fraction beingderived from the formula: EF = (EDV − ESV)/EDV. The mainlimitations of the method are the difficulty in many casesof delimiting the endocardial margin, and the establish-ment of an apical sagittal plane at true apical level (oflesser thickness than the surrounding level), where it isvery common to obtain a two-chambers apical acquisitiontangential and not orthogonal to the four-chamber apicalacquisition.

These methods analyze LVF globally, but can also be usedto assess segmental systolic function. In this context, in thepresence of myocardial ischemia we observe a decrease incontractility of the affected ventricular segments that canbe evidenced by echocardiography as a decrease in seg-ment motility and systolic thickening (hypokinesia). In turn,if ischemia is prolonged, motility and systolic thickening areabolished (akinesis).

The left ventricle model currently accepted for theanalysis of segmental contractility26 includes 17 segmentsobtained from apical four-, two- and five-chamber planes,and parasternal transverse planes in the three sections.

Table 2 Echocardiographic parameters in evaluating right

ventricle function and central venous pressure.

Evaluation of right ventricle function

Basic level. Discard acute cor pulmonale:

RV dilatation and LV relationship.

Paradoxical septal motion

TAPSE

Dilatation of inferior vena cava, non-collapsible

Advanced level. Evaluate RV function:

Dimensions of RV and RA

Systolic function and BSA

Pulmonary artery flow: type and acceleration time

Systolic pulmonary artery pressure due to TI

Doppler tissue imaging (DTI)

Inferior vena cava and right atrial pressure

How is patient right ventricle function? Is thereacute cor pulmonale?

Until recently, right ventricle function (RVF) has beenignored, partly due to a lack of awareness of its importance,and partly because of technical difficulties in assessing func-tion in a reliable and reproducible manner. Under normalconditions, the right ventricle (RV) functions as a low-pressure chamber, with great capacity to adapt to volumeoverload, but with a poor response to pressure incrementsin the pulmonary territory. However, knowledge of RVF isof great diagnostic interest in pulmonary embolism, acuterespiratory distress syndrome or cardiac tamponade, andfor assessing the interactions with function in patients sub-jected to mechanical ventilation.

With the use of different planes and despite the anatomi-cal and technical difficulties involved (complex geometry ofthe RV, with an irregular, half-moon shape and thin walls, anirregular endocardial surface with the presence of a moder-ator band and trabeculae that make it difficult to recognizethe endocardial margins), echocardiography27,28 allows usto study the global right-side cavities, particularly with thetwo-dimensional mode, which serves as a guide for measure-ments in M-mode and orientation of the ultrasound beam inthe Doppler technique (Table 2).

According to the echocardiographic protocol, theparasternal longitudinal plane (LP) is generally the firstplane obtained, and reveals the size of the RV and its rela-tionship with the LV. It therefore offers a first impressionof the presence or absence of dilatation: an end-diastolicdiameter of the RV in LP is >30 mm is considered pathological(normal = 9---26 mm in left lateral decubitus).

The apical four-chambers plane is the projection offeringthe best information and with which it is easier to obtainmeasurements of both the right atrium and right ventri-cle. In general, different studies have demonstrated thepossibility of measuring29 the diameters, establishing theareas via planimetry, and of calculating the ejection frac-tion, though the procedure is difficult due to the geometry ofthe RV. In this context, different methods have been devel-oped, involving the measurements of different diameters,that are scantly reproducible in routine emergency practice.

224 J.M. Ayuela Azcarate et al.

Figure 2 Tricuspid annular plane systolic excursion (TAPSE) represented between the two asterisks (1) and registry of systolic wave

velocity using Doppler tissue imaging (DTI) (2), showing a systolic wave (S) and two retrograde E- and A-waves. Normal registries.

For these reasons, analysis is made of the relative size rela-tionship between RV and LV at the end of diastole (normalratio < 0.6 with RV < LV; moderate dilatation RV = LV; severedilatation RV > LV, with ratio > 1).

The interventricular septum (IVS) is a muscle wall sepa-rating the right ventricle (RV) from the left ventricle (LV),though it is anatomically and functionally part of the latter.The diameter in diastole is 7---11 mm, which is three-foldgreater than the RV free wall, with a systolic thickening of35%.

Ultrasound is the only technique allowing us to studyinterventricular dynamics and inter-dependency. Mobility ofthe IVS can be analyzed using two-dimensional ultrasound,particularly in the parasternal transverse plane, at mitralvalve level. The LV appears as a circle and the septum as anarc encompassing 2/5 of the circumference. Under normalconditions the IVS is convex towards the RV and concavetowards the LV, and maintains this morphology over theentire cardiac cycle. Movement alterations in the form ofsystolic fluttering, or the configuration of the RV in bothsystole and diastole, can be used to identify the existenceof diastolic or systolic overload. In situations of RV diastolicoverload, the IVS undergoes flattening during diastole, sincethe RV diastolic pressure equals or exceeds that of the LV.Systolic overload, in the presence of greater pressure in theRV than in the LF, is recognized by the presence of a flat-tened septum (septum in D) in both systole and diastole,with diminished dynamics.

The analysis of segmental contractility alterationsacquires greater importance in right ventricle infarction,which is typically characterized by akinesis or dyskinesiaof some of the explored surfaces in the different projec-tions. In pulmonary embolism, in the presence of pressureoverload, the McConnell sign has been described as contrac-tility alteration in the form of akinesis of the free wall butwithout affecting the apical zone----though its usefulness isquestionable.30

Tricuspid annular plane systolic excursion (TAPSE) is mea-sured in M-mode and represents the excursion or distancedisplaced by the tricuspid ring from the end of diastole tothe end of systole.31 To this effect, and in the apical four-chambers plane, the M-mode cursor is positioned at the freemargin of the tricuspid ring, with measurement of its sys-tolic displacement. It is not influenced by heart rate (HR)but is affected by pre- and afterload. This is an easy methodfor assessing right ventricular contractility. Values of under

15 mm are considered pathological and of prognostic value(Fig. 2).

Registry of the maximum velocity of the systolic waveusing Doppler tissue imaging (DTI)32 is carried out at RV lat-eral wall level in four-chambers apical acquisition. A positivewave is recorded after QRS, and is preceded by anotherwave of shorter duration, corresponding to isovolumetriccontraction. Normality is taken to be 15 ± 2 cm/s, whileRV dysfunction is considered to be present when <10 cm/s(Fig. 2).

By using ultrasound in its M and 2D modes, we can obtaindirect and indirect data relating to pulmonary hypertension,suspect its presence even though its evaluation is not quan-titative, and study its repercussions upon the heart valvesand chambers. However, Doppler echocardiography33 is thetechnique that informs of and quantifies pulmonary hyper-tension.

Analysis of the morphology of pulmonary flow is car-ried out in the parasternal transverse plane at major vessellevel, positioning the pulsed Doppler sample volume at pul-monary valve level. Under normal conditions a triangularpattern is observed, gradually accelerating with a peak inthe mid-portion of systole, followed by a slow decrease end-ing just before valve closure (Type I). The presence of amid-systolic notch is indicative of severe pulmonary hyper-tension (Type III), with a sensitivity of 56% and a specificity of100% for PAPs > 50 mmHg.34,35 Another very useful and acces-sible option from the same plane is the measurement ofthe acceleration time (AT) of pulmonary flow, which is mea-sured from the start of the wave to the maximum velocity(if >90 ms, pulmonary hypertension is discarded).36---38

The presence of tricuspid valve insufficiency (TI) isdetected as systolic flow in the right atrium, with a max-imum velocity that can be quantified by continuous Dopplerwith the help of color Doppler for correct assessment andpositioning of the sample, allowing us to calculate thetransvalvular pressure gradient between the right atrium(RA) and right ventricle (RV) from the modified Bernoulliequation: PRV − PRA = 4Vmax TI2.

Right ventricle systolic pressure equals the sum of thesystolic gradient between RA and RV plus the right atrialpressure (RAP), and in the absence of obstruction of theright atrium outlet tract, it equals the systolic pressure ofthe pulmonary artery, whereby: PAPs = 4Vmax IT2 + RAP.

Different alternatives are available for determining themean right atrial pressure to be summed to the gradient:

Role of echocardiography in the hemodynamic monitorization of critical patients 225

Figure 3 Obtainment of the diameter of the left ventricle outlet tract (LVOT) in the parasternal longitudinal plane (1) and

estimation of the area (0.785 × 2.22 = 3.79 cm2. We then (2) register the LVOT flow with pulsed Doppler, in the apical 5-chambers

plane, and obtain VTI (velocity time integral) (the figure registers three measurements with a mean of 24 cm). The stroke volume

(SV) = 3.79 × 24 = 91 ml.

• Use of a central venous catheter.• Use of the diameter of the inferior vena cava (IVC)

(normal diameter 16 ± 2 mm) and its inspiratory collapse(IC) index, due to the existence of good correlationbetween these parameters and right atrial pressure. AnIVC ≤ 21 mm with IC > 50% estimates a RA pressure ofbetween 0 and 5 mmHg, while IVC > 21 mm and a non-collapsible vein indicates a pressure of ≥15 mmHg.

The reliability of the estimation is well established inthe echocardiography laboratory; however, there are tech-nical limitations in patients admitted to the ICU. Mechanicalventilation in particular complicates the technique due tothe absence of an adequate echocardiographic window. Innon-ventilated patients, the presence of dyspnea and theimpossibility of tolerating left lateral decubitus are themain impediments. The presence of arrhythmias, particu-larly atrial fibrillation, makes it necessary to average themeasurements over 5---10 beats. Despite these limitations,the measurement of pulmonary artery systolic pressure usingDoppler ultrasound is reliable, with good correlation to theinvasive methods.

Is cardiac output normal or reduced?

Cardiac output is an estimator of global cardiovascular sys-tem function, and is calculated as the product of heart rateand stroke volume (SV). According to classical hydrodynam-ics, the volume passing through a certain section can becalculated by multiplying the area of the section or zone(A, cm2) by the integral of velocity versus time of the flowpassing through it (IVT, cm)----this representing the systolicdistance traveled by the blood during the measured timeperiod: SV = A × IVT (Fig. 3).

The area most often used for this purpose in clinical prac-tice is the area of the aortic valve ring. The annular orring diameter (D) is measured at the level of insertion ofthe valve cusps or leaflets, which in most cases is correctlyvisualized in the parasternal longitudinal plane of the leftventricle in TTE and/or in the two-chambers mid-esophagealplane in TEE, assuming a circular geometry. To this effectzoom is applied to the zone at the start of systole, measur-ing from the insertion or junction of the anterior cusp on

the endocardium to the same point of the posterior cusp:area = Л × (D/2)2 = 0.785 × D2.

Stroke volume is determined by echocardiography usu-ally by calculating the volume of blood crossing the aorticvalve in each beat. Pulsed Doppler yields the flow velocityspectrum at that level, using the apical 5-chambers plane,which allows more parallel alignment between the directionof flow and the Doppler interrogation line. Measurement ofthe flow (IVT of the left ventricular outlet tract, LVOT) ismade placing the sample volume close to the valve area. Thenormal values are between 18 and 23 cm----a value of <12 cmindicating low output. At present, all echocardiography sys-tems provide IVT (in cm) when the Doppler signal curve isdelineated with the incorporated measurement software.

CO(cm3/min) = 0.785 × D2 (cm2) × IVT(cm/beat) ×

HR(beats/min)

This method,39 despite all the assumptions upon which itrests and the need for careful and good quality exploration,has revealed acceptable global correlations with the inva-sive techniques----though with great individual variability andthe need for a normal left ventricular outlet tract (LVOT) andthe absence of significant aortic insufficiency. The main lim-itation is represented by errors in measurement of the aorticring diameter, particularly when considering that such erroris moreover magnified by having to square the measure (i.e.,raise it to the second power) (Fig. 3).

Precisely with the idea of avoiding this error, Evangelistaet al.40 have shown that we can obviate measurement ofthe aortic ring, since there is a closer correlation betweenthe cardiac index (CI) estimated by thermodilution andthe mean velocity in the LVOT obtained by pulsed Doppler(r = 0.97) than between the cardiac index and the esti-mation made with the usual method described in thissection (r = 0.90). The resulting regression equation is: CI(ml/min/m2) = 172 × mean velocity − 172.

The standard deviation of the estimation is0.24 l/min/m2. The mean flow velocity in the LVOT isan extraordinarily useful parameter for estimation of thecardiac index, and especially for monitoring the changesoccurring in the face of new hemodynamic situations or asa result of treatment.

226 J.M. Ayuela Azcarate et al.

Table 3 Echocardiographic indexes in evaluation of left

ventricle filling pressures.

Indexes suggesting elevated PCP

E/A ratio ≥ 2

Mitral filling E-wave deceleration time < 150 ms

DT of the diastolic wave of PVF ≤ 160 ms

Relationship duration reverse PVF wave and mitral A-wave

(APdur > Adur)

E/VP > 2.5 → PCP: 15 mmHg

100/[(2 × IVRT) + Vp] > 5.5 → PCP: 15 mmHg

E/e′ > 15 → PCP: 15 mmHg

Can we estimate the filling pressures?

The filling pressure values classically have been the valuesprovided by the pulmonary artery catheter for hemodynamicassessment of a patient. Posteriorly, with the incorporationof the hemodilution techniques, it became possible to cal-culate SV, CO and peripheral vascular resistance (PVR). Theusefulness of the filling pressures has been greatly ques-tioned as a result of scientific confirmation that they arenot valid either for assessing heart function or for predictingresponse to volume.41,42

Nevertheless, in a patient with hemodynamic instability,the knowledge of pulmonary wedge pressure is basic whencomplemented by important data such as the anatomicalcharacteristics of the left ventricle (hypertrophic/dilated)and its global function. Wedge pressure is an indicator ofleft ventricle preload, and has diagnostic applications byallowing us to distinguish among the different etiologies oflung edema. Although theoretical preload is correlated toleft ventricle end-diastolic volume, in practical terms it isassimilated to wedge pressure. At present, pulmonary cap-illary pressure (PCP), as a reflection of left atrial pressure,can be reliably estimated from diastolic function parametersobtained by Doppler echocardiography43---46 (Table 3).

Mitral valve filling flow

During diastole, left ventricle filling is explored by pulsedDoppler (Pw), placing the sample volume at the free mar-gin of the mitral valve leaflets in the apical four-chambersplane. At each timepoint during diastolic filling, the velocityrepresented by the wave reflects the instantaneous pressuregradient between the left atrium and ventricle, in accor-dance with the Bernoulli equation.

A recording composed of two waves is obtained in individ-uals under sinus node rhythm: the E-wave, corresponding torapid protodiastolic filling, and the A-wave, dependent uponatrial contraction. Likewise, on placing the sample volumeof the pulsed Doppler between the mitral valve and the leftventricle outlet tract, in the apical 5-chambers plane andusing color Doppler as a guide, we obtain the systolic flowcurve at that level and can thus measure the isovolumetricrelaxation time (IVRT). Its duration is measured between theaortic flow closing artifact and the start of the mitral flow(E-wave).

Typically, the normal mitral filling flow curve in a middle-aged individual presents an E-wave (velocity 80 ± 16 cm/s)that is slightly larger than the A-wave (56 ± 13 cm/s), with

an E/A ratio > 1, an E-wave deceleration time (DT) ofabout 180 ms (199 ± 32), and an IVRT in the order of 90 ms(69 ± 12 ms).

The diastolic ventricular filling patterns are the result ofthe interaction between filling flow and the diastolic proper-ties of the LV and the loading conditions.47,48 Thus, the mitralflow pattern affords global and nonspecific information ondiastolic function, resulting from interaction among the ven-tricular relaxation state, ventricular compliance and the leftatrial pressure value. Accordingly, the morphology of thecurve is modified by different factors, such as the existinghemodynamic conditions, heart rate and age. Its character-istics and the evolution of the filling patterns in relationto the degree of diastolic dysfunction are summarized inFigs. 4 and 5.

The mitral filling flow velocity curve is technically verysimple to obtain, reproducible and easy to perform at thepatient bedside. The Mayo Clinic49 investigated the rela-tionship between these parameters and filling pressure intwo groups of patients: 42 subjects with left ventricularsystolic dysfunction (EF < 40%) and 55 patients with hyper-trophic myocardiopathy. In this clinical context, left atrialpressure (LAP) was inversely correlated to the DT of theE-wave (r = 0.73, p < 0.001) and directly correlated to theE/A ratio (r = 0.49, p = 0.004). An E/A ratio of ≥2 had lowsensitivity (52%) but high specificity (100%) in detectingLAP ≥ 20 mmHg. In the case of DT < 180 ms there was anassociated PCP of ≥20 mmHg, with a sensitivity and speci-ficity of 100%. Due to their dependence upon the ventricularrelaxation state, these parameters were only useful in theadvanced systolic dysfunction group (EF < 40%) and underconditions of sinus rhythm.

This study coincides with earlier findings50---52 in patientswith normal systolic function, where none of these mea-sures showed sensitivity and specificity levels acceptable forclinical use, except in patients with depressed EF.

E-wave velocity by color Doppler in M-mode (Vp)

For recording in the apical four-chambers plane, we ana-lyze the color Doppler signal corresponding to mitral filling,adjusting the depth to include the entire left ventricle fromthe mitral valve to the apex (approximately 45 mm). Afterzooming in on the zone, we align the cursor of the M-modeat the center of the color signal. We thus obtain a wave cor-responding to propagation of the color Doppler in M-mode,which almost instantaneously reaches the apex of the LV inindividuals with normal relaxation. After freezing the image,we measure Vp as the gradient of the line separating firstaliasing of the early diastolic flow (blue/red transition) fromthe mitral valve ring to the apex (normal > 60 cm/s). Theo-retically, it could also be measured as the gradient of any ofthe isovelocity lines; to this effect it is useful to modify thecolor Doppler baseline.

It has been shown that Vp is independent of mean atrialpressure and is closely correlated to tau; as a result, it canbe used as an estimator of ventricular relaxation.

Two combined parameters have been found to be of prac-tical use:

• Usefulness of the ratio of the peak E-wave velocity topropagation velocity (E/Vp) in estimating PCP. An E/Vp

Role of echocardiography in the hemodynamic monitorization of critical patients 227

Figure 4 Pulsed Doppler recording showing the isovolumetric relaxation time (IVRT) and the ventricular filling patterns in normal

filling (1 and 2) and inadequate relaxation (3), the restrictive pattern (4) and its relation to the ECG tracing. An inadequate relaxation

pattern (2) is characterized by a decrease in E-wave velocity, an increase in A-wave velocity, E/A ratio < 1, and a prolongation of

the deceleration time (DT) of the E-wave and of IVRT. Diminished ventricular elasticity in turn produces an increase in left atrial

pressure that implies a filling pattern inverse to the previously described pattern, known as the restrictive pattern (4), with an

increase in E-wave velocity, a decrease in A-wave velocity, and shortening of DT and IVRT. In the progressive transition between the

inadequate or delayed relaxation pattern and the restrictive pattern, mitral flow may present a ‘‘pseudonormal’’ morphology, that

can shift to an inadequate relaxation pattern if the patient performs the Valsalva maneuver.

of >2.5 offers acceptable predictive value in predict-ing PCP > 15 mmHg (r = 0.80, p < 0.001)----its value beingestimated from PCP = 5.27 × [E/Vp] + 4.6.53 However, itsusefulness decreases in the presence of atrial fibrilla-tion, dilated myocardiopathy with an eccentric filling

jet, hypertrophic myocardiopathy, mitral valve stenosisor prosthesis, and in the presence of preserved LV systolicfunction.

• The combined parameter 1.000/([2 × IVRT] + Vp) is closelycorrelated to PCP, according to the regression equation

Figure 5 Restrictive mitral filling pattern (1) in a patient presenting Killip class III after anteroseptal infarction, with DT = 130 ms

and an E/A ratio of >2. E-wave velocity = 1.07 m/s. DTI (2) with e′-wave velocity = 0.80 cm/s, E/e′ ratio > 12, suggesting increased

filling pressures.

228 J.M. Ayuela Azcarate et al.

Depressed LV function (<40%) Normal global LV function (>40%)

E/A <1

E ≤ 50 cm/s

E/A ≥ 2

DT < 150 ms

Septal E/e’ ≥ 15

Lateral E/e’ ≥ 12

Mean E/e’ ≥ 13

E/e’ ≤ 8

Normal Elevated

Use mitral filling

E/A ratioUse DTI

Normal Elevated

Figure 6 Doppler evaluation of filling pressures. The extreme values have been represented, use being required of the E/Vp ratio,

pulmonary vein flow, IVRT/T E/e′ < 2, 100/([2 × IVRT] + PV) or combined parameters in the intermediate values.Source: Adapted from: Nagueh SF, Appleton CP, Gillebert TC, Marino PN, Oh JK, Smiseth OA et al. Recommendations for the

evaluation of left ventricular diastolic function by echocardiography. Eur J Echocardiogr 2009;10:165---93.

PCP = 4.5 × 1.000/[(2 × IVRT) + Vp] − 9, independently ofventricular systolic function.54 A value of >5.5 for thisparameter discriminates between PCP over or under15 mmHg in 96% of all cases. In practical terms,IVRT < 80 ms in the presence of a low EF is indicative ofdecompensation.

Doppler tissue imaging (DTI)

When the ultrasound beam is directed towards the heart,the waves are reflected from the cardiac structures. Inthe same way as with the red blood cells, mobile tis-sues such as the myocardium reflect low-velocity Dopplersignals. The longitudinal muscle fibers in the heart arelocated in the basal segments. Positioning of the pulsedDoppler sample, generally in the lateral portion of themitral valve ring or in the basal portion of the septum, inthe apical four-chambers plane, allows us to quantify themaximum velocities of this myocardial zone in the differ-ent phases of the cardiac cycle. By means of a series ofDoppler signal modifications, we can record a velocity/timecurve, obtaining a type of signal referred to as Dopplertissue imaging (DTI). In clinical practice, DTI measure-ments have been standardized in the mitral and tricuspidring to determine variables of systolic and diastolic func-tion. A normal registry comprises systolic and diastolicwaves:

• Sm, systolic wave, showing two components in somepatients, and representing isovolumetric contraction andthe ejective systolic phase. A peak systolic velocitySm > 5.4 cm/s predicts EF >50% with a sensitivity of 88%and a specificity of 97%.

• e′, early diastolic wave, representing the rapid fillingphase.

• a′, late diastolic wave, representing the late filling phaseand atrial contraction.

The peak velocity of the E-wave obtained by DTI (e′)is correlated to ventricular relaxation and is relativelyindependent of the preload. The ratio between the peakvelocity of the mitral E-wave and the E velocity of thelateral mitral ring (E/e′) shows close correlations to PCP(PCP = 1.24 [E/e′] + 1.9)----values above 15 being predictiveof PCP > 15 mmHg.55 Values of <8 in turn are associated withnormal PCP values). However, E/e′ ratios between 8 and 15have low predictive value. At present, septal E/e′ ≥ 15, lat-eral E/e′ ≥ 12 and mean E/e′ ≥ 13 is considered indicative ofincreased filling pressures.56

The method has been validated in the presence ofsinus node tachycardia, atrial fibrillation and hypertrophicmyocardiopathy. Its limitations are the presence of mitralvalve stenosis or prosthesis, moderate to severe mitralvalve insufficiency, severe mitral ring calcification andthe existence of posterolateral wall akinesis. Recently57

the recommendations for evaluating diastolic function viaechocardiography have been published. In this context,Fig. 6 shows the recommendations for estimating the fill-ing pressures in patients with normal and depressed systolicfunction.

The clinical usefulness of the described parametersdepends on two factors: (a) the experience and technicalknowledge of the explorer and the available technology;and (b) the physiological mechanisms that inter-relate theDoppler data with the diastolic properties of the LV, theloading conditions and their variations in different etio-logical situations, or the response to applied treatment.

Role of echocardiography in the hemodynamic monitorization of critical patients 229

SHOCK

Evaluation and context

Basic monitorization:

BP, HR, RF, CVP

Pulsioxymeter, arterial catheter and

venous catheter

Insufficient treatment response or need

to further explore the physiopathology

of the process

OBJECTIVE 1

Echocardiography (FUSE)*

OBJECTIVES 2 AND 3

Echocardiography and Doppler

Good clinical course

Need for continuous hemodynamic

monitorization with other systems

Good clinical course

Figure 7 Evaluation and monitorization algorithm based on echocardiography among patients in shock. FUSE: focused ultrasound

exam.

The main limitations of these studies are the number ofpatients involved, their very different characteristics, andthe by now classical controversy regarding the relationshipbetween pulmonary wedge pressure and left atrial pressure,and its usefulness as an indicator of left ventricular preload.Thus, no single parameter is correlated in a universal andstatistically significant manner to PCP, and we must use andintegrate all the information that can be obtained from thedifferent echocardiographic methods, either isolatedly or incombination.

Nevertheless, data such as the E/A ratio, IVRT, DT of theE-wave in patients with depressed EF, and the E/e′ ratiovia DTI (at present all systems are equipped with DTI) inpatients with normal EF not only can be easily obtained butmoreover form part of the routine protocol used in basicechocardiographic studies such as measurement of the sizeof the different heart chambers or the evaluation of systolicor valve function. Other data, including pulmonary vein flow(PVF), or combined parameters, can be used in those casesin which the mitral filling pattern presents some of the limi-tations commented above. It should be remembered that allof them are quickly obtainable by transthoracic echocardio-graphy at the patient bedside, and can be repeated as oftenas necessary.

Is the heart dependent upon preload?

Measurement of the size of the heart cavities (left ventri-cle end-diastolic surface and volume) has been proposed asreliable preload indexes. However, there are no sufficientlysensitive concrete values allowing us to predict the responseto volume expansion.

Recently, Doppler ultrasound and 2D imaging have ledto the development of new hypovolemia indicators andto the prediction of response to volume expansion. Theseparameters should serve to identify those patients who willbenefit from volume expansion, increasing their systolicvolume (responders) and at the same time avoiding use-less and potentially harmful therapy (non-responders). Thedynamic parameters, which analyze cardiovascular responseto the respiratory changes in pleural pressure produced by amechanical respiratory cycle, are the variables which havebeen most extensively studied to date.

Analysis of the diameter of the inferior vena cava (IVC)

The subcostal plane often allows us to evaluate the infe-rior vena cava and the suprahepatic veins and to indirectlyestimate right atrial pressure. Changes in intraabdominalpressure and breathing rapidly modify their volume. During

230 J.M. Ayuela Azcarate et al.

inspiration, venous return increases and the IVC decreasesin diameter. The size and decrease in diameter duringinspiration (collapse index: maximum diameter in expira-tion − minimum diameter in inspiration/maximum diameterin expiration) are related to mean right atrial pressure.

The respiratory variability index of the IVC (�IVC) hasbeen defined as Dmax − Dmin/(Dmax + Dmin)/2 × 100, whereDmax and Dmin are respectively the maximum and minimumvalues of the IVC in a mechanical respiratory cycle. Theobservation of �VCd ≥ 12% allows us to distinguish betweenvolume expansion responders and non-responders, with highsensitivity and specificity.58

Analysis of the variability of the diameter of the superior

vena cava (SVC)

In patients subjected to mechanical ventilation, trans-esophageal echocardiography can be used to explore theinspiratory increase in pleural pressure during lung insuf-flation, which produces a total or partial collapse of theSVC. The observation of collapse suggests that at this pointthe external pressure exerted by the chest cavity upon thesuperior vena cava is greater than the venous pressure. Inthis context, variability in the diameter of the SVC of over36% has been shown to predict a positive response to vol-ume expansion, with a sensitivity of 90% and a specificity of100%.59,60

Analysis of the variation in aortic peak flow velocity

(PFV)

This parameter is obtained by recording aortic flow in theleft ventricle outlet tract (see cardiac output). A value �PFV(PVmax − PVmin/PVmax + PVmin/2 × 100) of 12% can also be usedin the evaluation of volume expansion.61---64

Conclusions

Echocardiography, by generating a large body of infor-mation on the anatomy of the heart, ventricle functionand the hemodynamic condition of the critical patient, isbecoming increasingly common in the ICU as a diagnostictool and for evaluating cardiovascular function. Only ade-quate training can allow intensivists to perform reliableechocardiographic explorations of help in the diagnosticand therapeutic management of situations characterized byhemodynamic instability.

Hemodynamic monitorization using echocardiographyhas the following objectives:

• Objective 1: To exclude serious structural heart diseaseas the cause of hemodynamic instability, particularly car-diac tamponade, infectious endocarditis, structural valvedisease, acute aortic syndrome and acute myocardialinfarction and its mechanical complications, based ontwo-dimensional (2D) imaging.

• Objective 2: To monitor right and left ventricle function.• Objective 3: To monitor dynamic parameters of preload,

and contractility. Table 4 summarizes the basic echocar-diographic parameters in hemodynamic monitorization.

Fig. 7 offers a monitorization proposal based on theechocardiographic evaluation of patients in shock. We

Table 4 Echocardiographic parameters in hemodynamic

monitorization.

Preload Contractility

Diameter of inferior vena

cava and RA pressure

Visual estimation visual

of LV and RV function

Diameter, area and

end-diastolic volume

of LV and RV

Systolic collapse of LV cavity

Estimation of filling

pressures: E/A and E/e′

ratios

Ejection fraction

and shortening

Variation infusion of fluids Cardiac output and VTI

Pulmonary flow and TI

TAPSE

TDI-s of RV free wall

consider that the use of this protocol does not discardother monitorization methods; rather, the protocol can beused as a complement to other techniques depending onthe concrete parameters to be examined, the invasive-ness allowed by the patient condition, and the continuityconsidered opportune. In aspects such as the evaluationof extrapulmonary water in patients with respiratory dis-tress syndrome, close monitorization of right-side cardiacfunction in patients subjected to mechanical ventilation,pulmonary hypertension of any origin, etc., or the defini-tion of tissue perfusion and O2 transport and consumption(DO2/VO2), use must be made of the existing monitorizationsystems along with echocardiography.

Financial support

This study has not been funded by any institution or aid.

Conflict of interest

The authors declare no conflicts of interest.

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