Haemodynamic Monitoring Theory and Practice

Haemodynamic Monitoring Physiological Background Monitoring Optimising the Cardiac Output Measuring Preload Introduction to PiCCO Technology Practical Approach Fields of Application Limitations

Volume Responsiveness Measuring Preload Volumetric Preload Parameters, Volume Responsiveness and Filling Pressures Preload Volumetric Preload parameters GEDV / ITBV Volume Responsiveness SVV / PPV Filling Pressures CVP / PCWP What parameters are available for measuring the preload? - classical parameters: cardiac filling pressures CVP (via CVC) and PCWP (via pulmonary arterial catheter) - static volumetric preload parameters: GEDV (global end-diastolic volume and ITBV (intrathoracic blood volume) - dynamic parameters SVV (stroke volume variation) and PPV (pulse pressure variation). In the narrower sense, these are not preload parameters but parameters of the heart‘s preload responsiveness (reaction of cardiac stroke volume to volume administration) 3

Correlation between Central Venous Pressure CVP and Stroke Volume Measuring Preload Role of the filling pressures CVP / PCWP Correlation between Central Venous Pressure CVP and Stroke Volume The relevance of the filling pressures for assessing cardiac preload has long been disputed and has been refuted in numerous publications. Neither the absolute level of the CVP (shown on left) nor the changes in CVP (shown on right) correlate with stroke volume. CVP therefore not suitable for assessing volume status. Kumar et al., Crit Care Med 2004;32: 691-699 4

Measuring Preload Role of the filling pressures CVP / PCWP Correlation between Pulmonary Capillary Wedge Pressure PCWP and Stroke Volume The pulmonary capillary wedge pressure (PCWP) and alterations of this do not show any correlation with cardiac ejection either. Thus measurement of cardiac preload is not possible by means of the traditionally employed PCWP either. Kumar et al., Crit Care Med 2004;32: 691-699 5

Measuring Preload Role of the filling pressures CVP / PCWP The filling pressures CVP and PCWP do not give an adequate assessment of cardiac preload. The PCWP is, in this regard, not superior to CVP (ARDS Network, N Engl J Med 2006;354:2564-75). Pressure is not volume! FACCT study by the ARDS Networks, published in the New England Journal of Medicine: no difference in the outcome of ARDS patients with CVP-guided fluid management and those with volume therapy guided by the PCWP. Better: measure volumes directly instead of estimating them from the pressure measurement. The level of the filling pressures is subject to many influencing factors so a valid statement about volume status is not possible. Only exception: low filling pressures indicate hypovolaemia Influencing Factors: Ventricular compliance Position of catheter (PAC) Mechanical ventilation Intra-abdominal hypertension 6

Volume Responsiveness Volumetric Preload parameters Measuring Preload Role of the volumetric preload parameters GEDV / ITBV Preload Volume Responsiveness SVV / PPV Filling Pressures CVP / PCWP Volumetric Preload parameters GEDV / ITBV Introduction to the volumetric preload parameters. These allow direct measurement of the cardiac filling volume so that this does not have to be estimated through a pressure measurement. 7

GEDV = Global Enddiastolic Volume Measuring Preload Role of the volumetric preload parameters GEDV / ITBV GEDV = Global Enddiastolic Volume Lungs Pulmonary Circulation The global end-diastolic volume consists of the end-diastolic volumes of all four cardiac chambers. Even if this volume does not exist physiologically (diastole of all four cardiac chambers is not simultaneous), it does reflect the filling status of the heart and is a valid parameter of cardiac preload compared to the filling pressures. Left heart Right Heart Body Circulation Total volume of blood in all 4 heart chambers 8

GEDV shows good correlation with the stroke volume Measuring Preload Role of the volumetric preload parameters GEDV / ITBV GEDV shows good correlation with the stroke volume The correlation of the global end-diastolic volume with the cardiac stroke volume is considerably better than with CVP or PCWP. GEDV is thus much better suited for measuring the cardiac preload. Michard et al., Chest 2003;124(5):1900-1908 9

ITBV = Intrathoracic Blood Volume Measuring Preload Role of the volumetric preload parameters GEDV / ITBV ITBV = Intrathoracic Blood Volume Lungs Pulmonary Circulation Left heart The intrathoracic blood volume corresponds to the global end-diastolic blood volume plus the blood in the pulmonary circulation. Right heart Body Circulation ITBV =GEDV + PBV Total volume of blood in all 4 heart chambers plus the pulmonary blood volume 10

ITBV is normally 1.25 times the GEDV Measuring Preload Role of the volumetric preload parameters GEDV / ITBV ITBV is normally 1.25 times the GEDV ITBVTD (ml) 1000 2000 3000 The intrathoracic blood volume is usually 25% higher than the global end-diastolic blood volume. A linear association has been demonstrated for the two parameters. The ITBV can therefore be calculated from the GEDV. ITBV = 1.25 * GEDV – 28.4 [ml] GEDV (ml) GEDV vs. ITBV in 57 Intensive Care Patients Sakka et al, Intensive Care Med 2000; 26: 180-187 11

The static volumetric preload parameters GEDV and ITBV Measuring Preload Role of the volumetric preload parameters GEDV / ITBV The static volumetric preload parameters GEDV and ITBV Are superior to filling pressures for assessing cardiac preload (German Sepsis Guidelines) Are, in contrast to cardiac filling pressures, not falsified by other pressure influences (ventilation, intra-abdominal pressure) The German Sepsis Society confirms in its official guidelines that volumetric parameters are superior to the classical filling pressures for assessing cardiac preload. GEDV and ITBV are not falsified by extravascular pressure influences, in contrast to CVP and PCWP. 12

Volumetric Preload parameters Volume Responsiveness Measuring Preload Role of the dynamic volume responsiveness parameters SVV / PPV Preload Filling Pressures CVP / PCWP Volumetric Preload parameters GEDV / ITBV Volume Responsiveness SVV / PPV The parameters stroke volume variation (SVV) and pulse pressure variation (PPV) are not preload parameters in the narrower sense but parameters of the heart‘s preload responsiveness. They thus provide information on whether the heart will respond to volume administration with an increase in cardiac stroke volume. They can help to determine whether volume administration is useful to increase cardiac output. 13

Fluctuations in blood pressure during the respiration cycle Measuring Preload Physiology of the dynamic parameters of volume responsiveness Fluctuations in blood pressure during the respiration cycle Early Inspiration Late Inspiration Intrathoracic pressure „Squeezing “ of the pulmonary blood Left ventricular preload Left ventricular stoke volume Systolic arterial blood pressure Intrathoracic pressure Venous return to left and right ventricle Left ventricular preload Left ventricular stroke volume Systolic arterial blood pressure Inspiration Expiration Inspiration Expiration Everyone knows the “fluctuation“ of the arterial pressure curve in hypovolaemic patients, that is, the fluctuation in pulse pressure amplitude with the respiratory cycle. This is due to ventilation-induced preload changes, which are more marked, the more hypovolaemic the patient is. PPmax PPmin PPmax PPmin 14 Reuter et al., Anästhesist 2003;52: 1005-1013

Fluctuations in stroke volume throughout the respiratory cycle Measuring Preload Physiology of the dynamic parameters of volume responsiveness Fluctuations in stroke volume throughout the respiratory cycle SV SV SV Preload An identical preload change (x-axis) leads to different changes in the stroke volume (y-axis) depending on the area of the Frank-Starling curve in which the heart is working. The more hypovolaemic the patient, the greater the stroke volume variation and pulse pressure variation. The SVV and PPV can be measured correctly only if the induced preload changes are always the same and no other fluctuations in the stroke volume occur. For correct measurement of SVV and PPV the patient‘s ventilation must be completely controlled (no spontaneous breathing) and there has to be a regular sinus rhythm. V V Mechanical Ventilation Intrathoracic pressure fluctuations Changes in intrathoracic blood volume Preload changes Fluctuations in stroke volume 15

SVV = Stroke Volume Variation Measuring Preload Role of the dynamic volume responsiveness parameters SVV / PPV SVV = Stroke Volume Variation SVmax SVmin SVmean mean The variation in stroke volume over the respiratory cycle Correlates directly with the response of the cardiac ejection to preload increase (volume responsiveness) 16

SVV is more accurate for predicting volume responsiveness than CVP Measuring Preload Role of the dynamic volume responsiveness parameters SVV / PPV SVV is more accurate for predicting volume responsiveness than CVP Sensitivity 1 0,8 0,6 0,4 The illustration shows that the SVV has considerably greater sensitivity and specificity for assessing volume responsiveness than CVP. According to the graph, the probability of predicting volume responsiveness correctly with the CVP is 50%, thus equivalent to tossing a coin. - - - CVP ___ SVV 0,2 0,5 Specificity 1 Berkenstadt et al, Anesth Analg 92: 984-989, 2001 17

PPV = Pulse Pressure Variation Measuring Preload Role of the dynamic volume responsiveness parameters SVV / PPV PPV = Pulse Pressure Variation PPmean PPmax PPmin The variation in pulse pressure amplitude over the respiration cycle Correlates equally well as SVV for volume responsiveness 18

Measuring Preload Role of the dynamic volume responsiveness parameters SVV / PPV A PPV threshold of 13% differentiates between responders and non-responders to volume administration respiratory changes in arterial pulse pressure (%) Non – Responders n = 24 This study showed how the PPV can distinguish the reaction of cardiac ejection to volume administration (preload increase). A value of 13% differentiates between responders (PPV>13%) and non-responders (PPV<13%) to volume administration. Responders n = 16 Michard et al, Am J Respir Crit Care Med 162, 2000 19

The dynamic volume responsiveness parameters SVV and PPV Measuring Preload Role of the dynamic volume responsiveness parameters SVV / PPV The dynamic volume responsiveness parameters SVV and PPV are good predictors of a potential increase in CO due to volume administration are only valid with patients who are fully ventilated and who have no cardiac arrhythmias Despite the limitations, PPV and SVV are valuable parameters for optimising the patient‘s volume status. 20

EVLW = Extravascular Lung Water Role of extravascular lung water EVLW EVLW = Extravascular Lung Water Lungs Pulmonary circulation Left Heart Brief presentation of another parameter that is not a preload parameter but is nevertheless highly important for guiding volume management: Extravascular lung water signifies the water content of the lungs outside the blood vessels. The EVLW therefore consists of the interstitial, intracellular and intraalveolar water of lung tissue. Right Heart Body circulation Extravascular water content of the lung 21

The Extravascular Lung Water EVLW Role of extravascular lung water EVLW The Extravascular Lung Water EVLW is useful for differentiating and quantifying lung oedema is, for this purpose, the only parameter available at the bedside functions as a warning parameter for fluid overload Pulmonary oedema can be diagnosed with certainty and its severity determined with the extravascular lung water. The parameter can be measured at the bedside using thermodilution, in contrast to conventional methods such as chest X-ray. The level of lung water and changes in this can provide important information for guiding volume therapy, as the point of time from which volume therapy leads to the development of pulmonary oedema can be identified. 22

Measuring Preload Summary and Key Points The volumetric parameters GEDV / ITBV are superior to the filling pressures CVP / PCWP for measuring cardiac preload. The dynamic parameters of volume responsiveness (SVV and PPV) can predict whether CO will respond to volume administration. GEDV and ITBV show what the actual volume status is, whilst SVV and PPV reflect the volume responsiveness of the heart. For optimal control of volume therapy simultaneous monitoring of both the static preload parameters and the dynamic parameters of volume responsiveness is sensible (F. Michard, Intensive Care Med 2003;29: 1396). 23