Curr Heart Fail Rep DOI 10.1007/s11897-015-0256-6 NONPHARMACOLOGIC THERAPY: SURGERY, VENTRICULAR ASSIST DEVICES, BIVENTRICULAR PACING, AND EXERCISE (AK HASAN, SECTION EDITOR)

Is There a Role for Invasive Hemodynamic Monitoring in Acute Heart Failure Management? Daniel De Backer

# Springer Science+Business Media New York 2015

Abstract The place of invasive hemodynamic monitoring in patients with acute heart failure is still debated, even though frequently used. Invasive techniques, which include the pulmonary artery catheter and transpulmonary thermodilution, provide important information on cardiac output and intravascular pressures or volume. These techniques should be used in combination with echocardiography and allow nurse-driven semicontinuous hemodynamic monitoring. These techniques are useful not only in the diagnosis of circulatory or respiratory failure but also for the evaluation of the effects of therapies. Admittedly, large-scale randomized trials failed to demonstrate a survival benefit with the pulmonary artery catheter (and were even not yet performed with transpulmonary thermodilution). However, these trials may be subjected to selection bias, as patients from recruiting centers not included in the trial but receiving the pulmonary artery catheter were more severe and had higher mortality rates than patient included in the trial. Hence, invasive techniques may still have a place in selected patients with acute circulatory failure and especially in the most severe cases.

Keywords Pulmonary artery catheter . Transpulmonary thermodilution . Cardiac output . Cardiac function . Tissue perfusion . Respiratory failure . Circulatory failure

This article is part of the Topical Collection on Nonpharmacologic Therapy: Surgery, Ventricular Assist Devices, Biventricular Pacing, and Exercise D. De Backer (*) Department of Intensive Care, CHIREC Hospitals, Université Libre de Bruxelles, Rue Wayez 35, B-1420 Braine L’Alleud, Brussels, Belgium e-mail: [email protected]

Introduction The place of hemodynamic monitoring is still debated, even though frequently used. Invasive techniques still have a place [1], but noninvasive hemodynamic monitoring is more and more used. In this context, echocardiography is the most useful tool, allowing full hemodynamic evaluation in addition to accurate determination of the cause of the cardiac problem [2•]. However, it has the disadvantage to be discontinuous and requires skills that go beyond the basic level [3••]. Several hemodynamic techniques can be used, and these can be classified according to their invasiveness. Invasive techniques comprise the pulmonary artery catheter and transpulmonary thermodilution. Minimally invasive techniques comprise noncalibrated pulse wave analysis and esophageal Doppler. Noninvasive techniques comprise bioreactance and bioimpedance techniques, and noninvasive pulse contour methods, in addition to echocardiography. The reliability of the various techniques in severely ill patients is quite variable and often inversely proportional to its invasiveness. In addition, more invasive techniques also provide more information such as intravascular pressures and cardiac volumes. Accordingly, the choice of the hemodynamic tool should not be guided only on invasiveness but should also take into account the potential interest of additional measured variables and accuracy of the technique in the condition presented by the patient. The choice of the hemodynamic monitoring device should thus be individualized, and there is clearly still a place for invasive techniques. The pulmonary artery catheter, even though invasive, has the advantage to provide continuous information on the cardiovascular status. Admittedly, the pulmonary artery catheter is less frequently used than before [4•], but one of its main indications remains cardiogenic shock. Interestingly, hemodynamic variables obtained at baseline as well after follow-up are associated with long-term outcome [5].

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The main indications for hemodynamic monitoring are the identification of the type of shock [6••] and guidance of therapeutic interventions. Another important indication is the cardiopulmonary evaluation of the patient with respiratory failure. In this review, we will discuss the different techniques used for hemodynamic monitoring and the interpretation of the most useful measured variables.

CVP to evaluate preload responsiveness and even cardiac function. However, it remains an important variable to measure, as it reflects the backpressure of the venous system and hence the driving force for tissue edema. Measurement of central venous oxygen saturation (ScvO2) provides information on the adequacy of oxygen transport, and hence cardiac output. A low ScvO2 suggests a low or inadequate cardiac output, anemia, hypoxemia, agitation, or a combination of all factors.

Basic Hemodynamic Monitoring Arterial Pressure Monitoring

Advanced Hemodynamic Monitoring

Arterial pressure is a key determinant of organ perfusion. High arterial pressures are also reflecting an increased afterload. Hence, arterial pressure is routinely measured in critically ill patients, either noninvasively or invasively. Noninvasive measurements can be used in less severe patients but are unfortunately less reliable in patients with shock, when accuracy of measurements is more important. Mean arterial pressure is often used to target vasopressor or vasodilator therapy even though the exact pressure goal is often difficult to determine. Diastolic pressure should not be neglected as it is indicative of vascular tone and is also the key determinant of left ventricular coronary perfusion. Pulse pressure, the difference between systolic and diastolic pressure, is also of interest. A narrow pulse pressure suggests a low stroke volume, especially in elderly patients. Respiratory variations in pulse pressure in patients under mechanical ventilation and without arrhythmias and tamponade are highly suggestive of fluid responsiveness, even when left ejection fraction is compromised [7]. Of note, this test is misleading in the case of right ventricular dysfunction [8]. Of note, tidal volume should be higher than 8 ml/kg [9], and patients should not have spontaneous respiratory movements [10].

The Pulmonary Artery Catheter

Central Venous Pressure and Central Venous Oxygen Saturation Central venous access is often required for the care of critically ill patients, especially when in shock. Measurements of central venous pressure and oxygen saturation can provide important information on the hemodynamic state of the patient. Central venous pressure (CVP) measurements reflect right ventricular preload and function. A high CVP reflects an impaired cardiac function (biventricular or right heart), hypervolemia, or tamponade. A low or normal CVP value is less informative in patients with isolated left heart dysfunction as it does not reflect their left ventricular preload. Importantly, the measured CVP is also affected by intrathoracic pressures and may thus overestimate the true CVP (transmural CVP) in patients under mechanical ventilation, limiting the capacity of

The pulmonary artery catheter measures three types of variables: intravascular pressures, cardiac output, and mixedvenous blood gases. Pulmonary artery catheter data are more accurate than the clinical evaluation for the assessment of hemodynamic alterations, and its use is associated with significant changes in therapy [11]. However, its use has been questioned. Observational trials demonstrate that the use of pulmonary artery catheter is associated with significant changes in therapy and that these may be associated with improved outcome [11]. On the other hand, several randomized studies have not been able to detect any improvement in outcome associated with the use of the pulmonary artery catheter in ICU patients with various conditions [12–15]. Several factors may explain these findings. One factor may be the inability of many physicians to adequately interpret the data obtained with this device [16, 17], resulting in inadequate decisions. Interestingly, the addition of echocardiographic data does not necessarily improve the interpretation of the respondents [18], suggesting that the physicians are more in fault than the technique [19]. Another factor is that the patients included in these trials were highly selected. In one trial, the number of patients not included because already equipped by a pulmonary artery catheter was twice the number of patient randomized, suggesting that the most severe patients (in whom information was deemed more valuable) were not included. These physicians’ preferences may bias the results of these trials [20••]. Patients not included in one trial and who received the pulmonary artery catheter were sicker and had significantly higher mortality rates than patients included in the trial [21]. As a result of these negative trials and due to the wide availability of alternative techniques, the use of the pulmonary artery catheter has decreased over time [4•]. Nevertheless, the pulmonary artery catheter has still some indications, and physicians should be aware on how to best use it. Pressures The pulmonary artery (PA) pressures (systolic, diastolic, mean) are measured from the distal end of the catheter.

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When the balloon is inflated, the inflated balloon wedges in a branch of the PA, occluding blood flow distal to this point. The PA occluded pressure (PAOP) is the pressure measured from the distal end of the catheter but with the balloon briefly inflated. PAOP is obtained occluding relatively large segments of the pulmonary vascular tree. This pressure mostly represents the pressure in the large pulmonary veins, reflecting the pressure in the left atrium which, in the absence of any abnormality of the mitral valve, is equal to the end-diastolic left ventricular pressure. PA wedge is the pressure obtained when the catheter is wedged, balloon deflated, and occludes a smaller portion of the pulmonary bed and hence is closer, but not equivalent, to the capillary pressure. The capillary pressure is calculated from the decay of the PA curve during balloon inflation [22]. The three pressures may not be equivalent, especially in the cases of lung disease in which capillary pressure is higher than the wedge pressure, itself higher than PAOP. Right atrial pressure measured from the proximal end of the catheter and is equivalent to CVP. The intrathoracic pressures fluctuate during the respiratory cycle, and intravascular pressures should be measured at the end of expiration, when the intrathoracic pressure is closest to atmospheric pressure. These pressures are not necessarily equal to atmospheric pressure in the case of (auto-)PEEP. Several methods have been used to estimate transmural PAOP in patients ventilated with high PEEP levels [23–25]. Admittedly, these are unfrequently used. Of note, these cannot be applied to the right atrial pressure. What is the interest of measuring pressures? Measurements of pulmonary artery pressure are particularly indicated in the cases of right ventricular dysfunction where evaluation of the right ventricular afterload is crucial for diagnosis as well as for guiding therapy [26]. Except with echocardiography, there is no other means to determine pulmonary artery pressure at bedside. In addition, reliability of pulmonary artery pressure with echocardiography has been challenged [27••, 28] so that the use of pulmonary artery catheter is still recommended for this practice. When normal or with minimal impact on right ventricular function, the measurements of pulmonary artery pressure are less relevant. Measurements of PAOP are also important to identify left ventricular dysfunction and to help fluid management. Admittedly, noninvasive and less invasive techniques can also provide similar measurements. Cardiac Output Cardiac output is measured intermittently by bolus injection or semicontinuously with catheters equipped with intraventricular therm istors. Even with the semicontinuous method, several cardiac output measurements are averaged, and rapid changes cannot be detected. The precision of semicontinuous cardiac output measurements is lower than that of classical thermodilution [29], but this mostly

occurs at high cardiac output values and is thus usually less relevant in acute heart failure. Measurement of the thermodilution cardiac output may be biased in severe tricuspid regurgitation and intracardiac shunt, and these should always be looked at time of echocardiographic assessment. Thermodilution also tends to overestimate cardiac output values less than 2.5 l/min. Measurement of the Central Venous and Mixed Venous Oxygen Saturation (SvO2) in the Pulmonary Artery Venous blood from all parts of the body is collected and mixed in the right heart chambers before passing through the pulmonary capillaries. SvO2 can therefore be accurately measured using the PA catheter by repeated blood withdrawal. Continuous SvO2 measurements can be obtained if the PA catheter is equipped with fiber optic fibers. Each hemodynamic evaluation should be accompanied by measurement of SvO2, as the determination of the oxygen saturation in mixed venous blood (SvO2) enables the interpretation of the cardiac output by considering oxygen transport in relation with oxygen consumption. When noninvasive techniques are used, ScvO2 is often used as a surrogate of SvO2. Even though there may be some differences in some situations, ScvO2 often provides relevant information, especially in low flow states. Transpulmonary Thermodilution and Pulse Wave Analysis The most commonly used alternative to the pulmonary artery catheter is the transpulmonary thermodilution technique (Fig. 1) and pulse wave analysis. These are minimally invasive techniques that still require placement of an arterial line and, in addition for transpulmonary thermodilution, a central venous line. Stroke volume can be computed from an arterial pressure waveform. However, the arterial pressure waveform depends not only on stroke volume but also on arterial compliance, vascular tone, and reflection waves [30, 31], and several ways are used to take these factors into account. Calibration with transpulmonary thermodilution is used to capture differences in arterial compliance and vascular tone from one patient to another and from one time to another in a given patient [30, 31]. As these factors are considered fixed from the time of calibration to the next one, the accuracy of these techniques is highly dependent on the delay between two manual calibrations. Any change in vascular tone can significantly alter the precision of these devices and require recalibration [32]. Calibration is usually performed every 6–8 h or in the case of changes in vascular tone (suggested by changes in blood pressure or in vasoactive agents). An alternative way is used in the Flo Trac/Vigileo based on an autocalibration factor derived from a proprietary equation including biometric variables (e.g., age and sex which are known to affect arterial compliance [33, 34]) and Bshape variables.^ Refinements of the

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Fig. 1 Transpulmonary thermodilution and pulse waveform analysis. In transpulmonary thermodilution, a cold bolus of fluid is injected in a central vein. After passing through the right heart and pulmonary artery, as in standard thermodilution, the fluid bolus is transported to the left heart and up to peripheral arteries. A femoral arterial catheter equipped with a thermistor detects temperature changes, and a thermodilution curve

is constructed. This provides intermittent cardiac output measurements and is used for calibration of pulse waveform analysis, allowing continuous measurements of cardiac output. The transpulmonary thermodilution curve also allows computation of derived variables such as end-diastolic cardiac volumes and extravascular lung water

algorithm now allow reliable measurements even in patients with septic shock [29]. Of note, pulse wave analysis can be misleading during acute changes in vascular tone and requires either recalibration (with transpulmonary thermodilution) or several minutes to regain accuracy after stabilization of vascular tone (with autocalibration). Transpulmonary thermodilution requires the use of a modified arterial catheter equipped with a thermistor. This catheter is mostly inserted in the femoral artery. Injection of the fluid bolus has to be performed through a regular central line. It has not to be a dedicated one, but it is recommended not to have it in a femoral vessel close to arterial catheter. The thermodilution curve can be determined using a modified proprietary algorithm (EV1000 or PiCCO). Basically, cardiac output is determined by the area under the curve as in standard thermodilution. Transpulmonary thermodilution is slightly less sensitive to valvular regurgitation than right-sided thermodilution. Transpulmonary thermodilution curve characteristics also allow to determine extravascular lung water (EVLWI) and the volumes of cardiac chambers (GEDVI). GEDVI is an index of preload. It performs better than pressures in patients with raised intrathoracic or intraabdominal pressures or with decreased left ventricular compliance. EVLWI reflects the degree of pulmonary edema, whatever its cause, and is associated with outcome. Both indices are useful in establishing diagnosis and for fluid management. Given the additional value of volumetric measurements, transpulmonary thermodilution should be considered not only for calibration of pulse contour devices but as integral part of hemodynamic assessment. Hence, these should be obtained each time hemodynamic

assessment is performed (diagnostic purposes as well as evaluation of response to therapy). Cardiac function index (CFI) is a derived parameter calculated as cardiac index divided by GEDVI. In patients with cardiogenic shock, CFI reflects left ventricular ejection fraction [35, 36•], provided that right ventricular function is maintained [36•]. Complications related to hemodynamic monitoring with transpulmonary thermodilution are related to arterial and central venous catheterization and mostly consist in local bleeding and infections [37••].

Interpretation of Hemodynamic Measurements Although interesting in orienting the diagnosis, all the hemodynamic abnormalities that we will describe below usually lack specificity, and echocardiography should thus be used to further refine the diagnosis. However, pressure/volume measurements are usually useful to monitor patients with circulatory failure, as echocardiographic measurements cannot be easily repeated, especially in large-volume ICUs. The use of pulmonary artery catheter (Table 1) and transpulmonary thermodilution (Table 2) is described. Characterization of the Type of Shock The four types of shock (hypovolemic, cardiogenic, obstructive, and distributive) can easily be determined a simple evaluation of basic hemodynamics and confirmed by echocardiography [6••]. However, this exercise may become much

Curr Heart Fail Rep Table 1 Hemodynamic evaluation with pulmonary artery catheter in patients with clinical signs of acute heart failure Clinical condition

CO

RAP

PAP

PAOP

Hemodynamic pulmonary edema Hypovolemic shock Cardiogenic shock (left or global) Pulmonary embolism

↓ or ↔ ↓↓ ↓↓ ↓↓

↑ or ↔ ↓ ↑ or ↔ ↑↑↑

↑↑ ↓ ↑↑ ↑↑

↑↑↑ ↓ or ↔ ↑↑↑ ↔ or ↑

Primary pulmonary hypertension Right ventricular infarction Tamponade

↓↓ ↓↓ ↓↓

↑↑ ↑↑↑ ↑↑↑

↑↑↑↑↑ ↔ or ↑ ↔ ↔ ↑↑↑ ↑↑↑

CO cardiac output, RAP right atrial pressure, PAP pulmonary artery pressure, PAOP pulmonary artery occluded pressure, ↑ increased, ↔ unchanged or normal, ↓ decreased

more difficult in patients with chronic left or right heart dysfunction. In example, a patient with chronic heart failure may develop septic or hemorrhagic shock. In these patients, it is important to try to identify the factor contributing most to the hemodynamic instability. When cardiogenic shock is identified, it is important to discriminate between left and right ventricular dysfunctions. Advanced hemodynamic tools can easily detect acute heart failure, characterized by low cardiac output/indices of cardiac function and increased pressures/volumes. While the pulmonary artery catheter can relatively easily differentiate right from left heart failure, this is more complicated with transpulmonary thermodilution [36•]. The gradient between PAOP and RAP is usually close to 2 mmHg. When this gradient is elevated, it suggests predominant right side dysfunction, while an elevated gradient suggests left ventricular or valvular dysfunction. The cause of right side dysfunction can be further separated into primary and secondary. Primary right side dysfunction is usually due to right ventricular infraction or severe tricuspid regurgitation and is characterized by a normal pulmonary artery pressure. Secondary right ventricular dysfunction is due to an increase in right Table 2 Hemodynamic evaluation with transpulmonary thermodilution in patients with clinical signs of acute heart failure Clinical condition

CO

GEDV CFI

EVLW

Hemodynamic pulmonary edema Hypovolemic shock Cardiogenic shock (left or global) Pulmonary embolism Primary pulmonary hypertension Right ventricular infarction Tamponade

↓ or ↔ ↓↓ ↓↓ ↓↓ ↓↓ ↓↓ ↓↓

↑↑ ↓ ↑↑↑ ↑↑↑ ↑↑↑↑ ↑↑↑ ↑↑↑

↑↑↑ ↔ ↑ or ↔ ↔ ↔ or ↑ ↔ ↔

↓ or ↔ ↔ or ↑ ↓↓↓ ↓↓↓ ↓↓↓ ↓↓↓ ↓↓↓

CO cardiac output, GEDV global end diastolic volume, CFI cardiac function index, EVLW extravascular lung water, ↑ increased, ↔ unchanged or normal, ↓ decreased

ventricular afterload (and thus pulmonary artery pressure) which can be acute, such as in pulmonary embolism (in this case, the increase in PAP is usually moderate), or chronic, such as in primitive or secondary pulmonary hypertension (with usually very high PAP levels). Left-sided dysfunction can be due to systolic, diastolic, and/or valvular problems, but the PA catheter can usually not discriminate between these different possibilities. When transpulmonary thermodilution-derived volumetric measurements are used, differentiation of left and right ventricular dysfunction cannot be made [36•]. Echocardiography is thus needed to separate both possibilities. Is Cardiac Output Adequate? Measurements of cardiac output are important in critically ill patients and especially in severe heart failure. Cardiac output is one of the main determinants of tissue perfusion in low output states. Importantly, a low ejection fraction does not implicate that cardiac output is low (and vice versa). Cardiac output cannot be evaluated by clinical evaluation [38, 39] and should thus be measured. Another important question is whether cardiac output is adapted to metabolic requirements. During exercise, cardiac output is expected to be elevated, while it is expected to be low during anesthesia. To evaluate the adequacy of cardiac output, two factors need to be taken into account. First, SvO2, or ScvO2, reflects the balance between DO2 and VO2. A decrease in SvO2 suggests an inadequate cardiac output if hemoglobin and PaO2 are within the normal range. On the contrary, a normal SvO2 suggests that the low cardiac output is adapted to the low metabolic needs. This approach is unfortunately potentially biased when alterations in microvascular perfusion alter oxygen extraction capabilities such as in sepsis [40]. Microcirculatory alterations also occur in cardiogenic shock and severe heart failure [41, 42], but these have less impact on SvO2, as SvO2 is already low due to the low cardiac output. The second factor to take into account is lactate levels. Lactate reflects the balance between VO2 and oxygen requirements. When VO2 cannot meet oxygen requirements, anaerobic metabolism develops which is reflected by increased lactate levels. When cardiac output is inadequate, it seems justified to manipulate it with vasoactive agents [43]. Evaluation of Preload Responsiveness When cardiac output is inadequate, the first therapeutic intervention is often fluid administration. However, after initial resuscitation, many patients may fail to respond to fluids. Preload measurements, volumes or pressure, often fail to predict fluid responsiveness as each patient is characterized by

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his own Starling relationship. Only extreme values keep some predictive value. Dynamic variables such as pulse pressure and stroke volume variations reliably predict volume responsiveness provided that the prerequisite for their use are met (i.e., mechanical ventilation with enough tidal volume, absence of respiratory movements, and arrhythmias). These can be measured on arterial trace or by echocardiography. Alternatively, respiratory variations in vena cava diameter or passive leg raising test can be used. Of note, whenever fluids are indicated, it is important to administer these using the fluid challenge technique. The fluid challenge is not a way to predict the response to fluids but rather to evaluate whether these are tolerated and effectively increase cardiac output when administered. During fluid challenge, pressure measurements are particularly helpful. An increase in RAP and/or PAOP of more than 3 mmHg without change in stroke volume implies that fluid challenge failed, while an absence of change in both variables implies that the amount of fluid that was given was insufficient to affect preload. In addition, RAP and PAOP can be used as safety limits, indicating pending right ventricular failure or pulmonary edema. Of note, volumetric variables are less useful in this context. When the flat part of the Starling relationship is reached, the increase in volume is often minimal, while pressures markedly increase. EVLWI also increases quite lately, while pressures increase before lung flooding. Hemodynamic Optimization Based on the abovementioned principles of determination of adequacy of cardiac output, preload responsiveness, and cardiac function, several trials have evaluated the impact of hemodynamic optimization on outcome [44, 45•, 46•, 47, 48•]. Perioperative optimization using pulmonary artery catheter resulted in decreased perioperative complications [49] and improved survival rate [47]. Transpulmonary thermodilution can also be used for this purpose. In patients submitted to cardiac surgery, hemodynamic optimization decreased vasopressor load [44]. In patients with cardiogenic shock after cardiac arrest, hemodynamic monitoring with transpulmonary thermodilution was associated with higher fluid intake in the first 24 h and resulted in a lower incidence of acute kidney injury compared to CVP and arterial pressure monitoring [48•]. In patients with Tako Tsubo related to subarachnoid hemorrhage, the use of transpulmonary thermodilution variables was helpful for identifying patients with poor outcome [45•]. A CFI below 4.2/min was predictive not only of an impaired ejection fraction but also of an impaired 3-month neurologic outcome [45•]. Patients with poor neurologic outcome also had high values of EVLW. In a randomized trial, these authors further reported that hemodynamic resuscitation targeted on

transpulmonary thermodilution indices was associated with better long-term neurologic outcome [46•]. It is not easy to determine whether PAC or transpulmonary thermodilution should be preferred in patients with cardiac failure. In a small size randomized trial, pressure-guided resuscitation resulted in less time under mechanical ventilation in shock patients with impaired cardiac function, while survival rate was not affected [50••]. Evaluation of a Patient with Pulmonary Hypertension Pulmonary artery hypertension is either secondary to an increase in the PAOP or due to a pulmonary pathology (or a combination of both). In the first case, the gradient between PAP diastolic and PAOP is smaller than 3 mmHg, while it will be increased in the case of pulmonary or mixed pathologies. Evaluation of a Patient with Respiratory Failure Finally, PAOP can be used to differentiate a cardiogenic from a noncardiogenic cause of pulmonary edema. It can also be used to identify a cardiac origin when patients failed to be weaned from mechanical ventilation [51]. It is usually accepted that a PAOP higher than 18 mmHg characterizes hydrostatic pulmonary edema. It can be measured with PAC, taking into account alveolar and pleural pressures as illustrated above [23–25]. Alternatively, it can be measured by echocardiography. As the precision of echocardiographic measurements of PAOP are quite limited, these are often used in a semiquantitative way [52]. While transpulmonary thermodilution easily identifies pulmonary edema by the measurement of EVLW, the discrimination between hydrostatic and nonhydrostatic causes is more complex: Hydrostatic cause is suspected when associated with normal permeability index.

Conclusions Hemodynamic evaluation is often required in patients with acute heart failure. Basic hemodynamic monitoring may be sufficient in simple cases, but invasive hemodynamic monitoring is often needed in complex cases. Compliance with Ethics Guidelines Conflict of Interest Daniel De Backer has received nonfinancial support from Edwards Lifesciences, PULSION, Vytech, and ImaCor. Human and Animal Rights and Informed Consent This article does not contain any studies with human or animal subjects performed by any of the authors

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