Division of Perioperative and Emergency Medicine, University Medical Center Utrecht, the Netherlands

Transcription

1 04RC1 Advances in cardiovascular monitoring Wolfgang Buhre Division of Perioperative and Emergency Medicine, University Medical Center Utrecht, the Netherlands Saturday, 11 June :00-13:45 Room: G Peri-operative cardiovascular complications contribute signifi cantly to the morbidity and mortality associated with surgical procedures where altered cardiopulmonary reserve has been demonstrated to be a major factor. Inadequate oxygen delivery to organs resulting in oxygen debt has been shown to be a leading cause of peri-operative complications. Advanced monitoring of the cardiovascular system to assist timely treatment of underlying abnormalities would appear to be an essential aspect of improving peri-operative outcome. There is widespread agreement on minimal monitoring standards for patients undergoing anaesthesia or intensive care therapy. This includes ECG, non-invasive blood pressure measurement, pulse oximetry and capnography in ventilated patients. In contrast, it has not been fully established whether, and if so which, patients benefi t from advanced cardiovascular monitoring providing measurement of cardiac output, venous oximetry, transthoracic and transoesophgeal echocardiography and the estimation of cardiac preload and afterload. The main goal of the global circulation is to support end-organ function by optimum delivery of substrates including oxygen. Advanced haemodynamic monitoring should be capable of monitoring this aspect of the circulation. Ideally, such monitoring should be non-invasive, easy to use, continuous, cheap and operator independent. The monitoring parameters should be sensitive and specifi c. Evidence for advanced cardiovascular monitoring Currently there are relatively few evidence-based guidelines on advanced cardiovascular monitoring. Recently, the German Society of Cardiothoracic and Vascular Surgery and the German Society of Anaesthesia and Intensive Care Medicine published guidelines on advanced cardiovascular monitoring for the postoperative care of cardiac surgical patients [1]. Additionally, a number of meta analyses have been published [2-5]. Here the literature can be subdivided into two groups. In the fi rst group, the reliability and validity of different monitoring techniques such as pulmonary artery catheters, oesophageal ultrasound, and transpulmonary thermodilution, have been studied to compare the relative accuracy of these measurement techniques. Secondly, a number of studies have assessed patient outcome associated with the use of these monitoring technologies in different populations. However, the majority of these studies have a number of methodological shortcomings making the interpretation of their results diffi cult. Physiological basics and measurement technology The basic parameters of cardiovascular monitoring are cardiac output, preload and afterload. In clinical practice, cardiac output is frequently measured using a variety of techniques employing indicator dilution or Doppler technology. The ideal preload parameter is yet to be established. From a physiological point of view, the Frank-Starling curve describes the curvilinear relationship between cardiac preload and left ventricular cardiac output. Under normal physiological conditions, both ventricles operate on the ascending part of the Frank-Starling curve, resulting in a concomitant increase in stroke volume (SV) as preload increases. However, a further increase in preload does not necessarily result in a proportional increase in SV if the left ventricle is already functioning on the fl at part of the Frank- Starling curve. In particular, in patients with pre-existing heart failure, an increase in preload can result in a signifi cant decrease in cardiac output due to overfi lling (Figure 1)

2 Figure 1 Frank-Starling curve There is some consensus that left ventricular end-diastolic volume is the best parameter to describe cardiac preload in patients. However, measurement of cardiac preload in clinical practice has been diffi cult to achieve as no continuous, user-independent, direct measurement technique of left ventricular end-diastolic volume (LVEDV) has been available. Therefore, surrogate preload parameters for LVEDV are commonly used. These can be divided into static and dynamic parameters [6-8]. Static parameters are either pressure based, for example central venous pressure (CVP) and pulmonary artery occlusion pressure (PAOP) or volume based, for example intrathoracic blood volume (ITBV), global end-diastolic volume (GEDV) and left ventricular end-diastolic area (LVEDA) [9-10]. In contrast to static preload parameters, dynamic preload parameters are usually based on beat-to-beat analysis of arterial pressure and fl ow (Table 1). Table 1 Clinically used cardiac preload parameters. (Adapted from de Waal EEC, Buhre W. Hemodynamic monitoring, UNI-MED 2009) Abbreviation Parameter Measurement Formula for calculation Static preload indicators CVP PAOP LVEDA FTc DT Central Venous Pressure Pulmonary Artery Occlusion Pressure Left Ventricular End- Diastolic Area Flow Time corrected for heart rate Deceleration Time of the early rapid fi lling phase Measured directly with PAC or CVP-line Measured directly with PAC (Off-line) by planimetry by means of echocardiography machine, indexed to BSA Measured directly with ODM TTE/TOE Measured directly Measured directly or off-line - 2 -

3 GEDVI/ITBV Global End-Diastolic Volume Index Transpulmonary thermodilution PiCCO Measured directly during transpulmonary thermodilution Volumetric preload indicators RVEDVI ITBVI SVI Right Ventricular End- Diastolic Volume Index Intrathoracic Blood Volume Index Stroke Volume Index variation (Off-line) by planimetry by means of echocardiography, indexed to body surface area, or measured directly with PAC Estimated by PiCCO Measured with Oesophageal Doppler Measured directly during transpulmonary thermodilution ΔSVI = SV Ipost FC - SV Ipre FC SOI Stroke Output Index variation Measured with Oesophageal Doppler FTc SVI FTc SVI SOI = ( ) postfc ( ) prefc down Difference between Systolic BP during short apnoea and its minimal value during one mechanical breath Measured (off-line) by analysis of arterial BP line SPV Systolic Pressure Variation Measured (off-line) by analysis of arterial BP line Difference between minimal and maximal values of systolic BP during mechanical breath PPV Pulse Pressure Variation Pulse contour analysis Difference between minimal and maximal values of pulse pressure during one mechanical breath related to the average between the values Dynamic preload indicators SVV Stroke Volume Variation Pulse contour analysis VPV Ventilation-induced Plethysmographic Variation Measured (off-line) by analysis of plethysmography curve Difference between minimal and maximal values of stroke volume during one mechanical breath related to the average between the values Difference between minimal and maximal values of pulse amplitude of the plethysmography waveform during mechanical breath RSVT Respiratory Systolic Variation Test Measured and calculated off-line from the recording of the response of arterial BP to respiratory manoeuvre Vpeak Variation in peak fl ow velocity at the aorta valve Measured with TTE/TOE and calculated off-line ABF Variation in Aortic Blood Flow in the descending aorta Measured with Oesophageal Doppler and calculated off-line by analysis of aortic blood fl ow at the aortic valve Difference between minimal and maximal values of ABF during mechanical breath - 3 -

4 Determination of normo-, hypo- or hypervolaemic status of the patient and the effect of administration of fl uid challenges on the cardiac output (fl uid responsiveness) is particularly relevant to clinical practice. Thus, monitors that measure parameters describing fl uid responsiveness are useful [11, 12]. The ideal cardiac preload monitor should respond rapidly and acquire data directly. Invasive monitoring technologies can cause complications and therefore minimally invasive or non-invasive monitoring techniques are preferable. Hence, indices of dynamic preload such as stroke volume variation (SVV) and pulse pressure variation (PPV) are increasingly being used. Recent studies suggest that these indices are reliable predictors of fl uid responsiveness in different patient populations. The pulmonary artery catheter Following the introduction of the pulmonary artery catheter (PAC) advanced cardiovascular monitoring in anaesthesia and intensive care medicine was based on this technology for more than two decades. However, pulmonary artery catheterisation is a particularly invasive technique, time consuming to set up and associated with a considerable morbidity and mortality. The PAC enables not only the measurement of cardiac output (CO) using thermodilution, but also the measurement of mixed venous oxygen saturation (SvO2), blood temperature, CVP and pulmonary artery occlusion pressure (PAOP). Assessment of cardiac preload was primarily based on the measurement of CVP and PAOP. There has been widespread debate as to whether the early use of the PAC in patients at risk of organ failure can help tailor treatment and decrease mortality. The majority of studies, however, have failed to demonstrate conclusive benefi ts associated with PAC use. Although CVP and PAOP measurements are advocated as a guide to fl uid therapy in critically ill patients, they fail to correlate with either ventricular end-diastolic volume (EDV) or changes in stroke volume after fl uid administration [1, 13]. Changes in fi lling pressures are not necessarily indicative of changes in cardiac preload [4, 12]. Some clinical studies have confi rmed that CVP measurement does not predict fl uid responsiveness adequately. Furthermore, the majority of clinical studies have indicated that PAOP measurement was unable to refl ect cardiac preload adequately and failed to predict an individual patient s response to a fl uid challenge. Consequently, the use of CVP and PAOP as a sole guide for fl uid therapy can no longer be recommended. Transpulmonary dilution In recent years a number of transpulmonary techniques have been developed to enable combined monitoring of cardiac output and static volumetric parameters [7, 9]. These parameters include central blood volume (CBV), global end-diastolic volume (GEDV) and intrathoracic blood volume (ITBV). Intrathoracic blood volume encompasses the volumes of all four cardiac chambers and the pulmonary circulation whereas GEDV only comprises the cardiac volumes in end-diastole. From a physiological point of view ITBV is a surrogate parameter for the central blood volume that serves as the fl uid reservoir for the left ventricle. This means severe hypovolaemia should be refl ected by a decrease in ITBV and GEDV. In clinical studies, it has been demonstrated that both ITBV and GEDV are more sensitive than CVP and PAOP and comparable with echocardiographically determined LVEDA. However, recently the value of both GEDV and ITBV to predict fl uid responsiveness has been questioned. Dynamic preload parameters The most commonly used parameters are pulse pressure variation (PPV) and stroke volume variation (SVV). These are derived from changes in the arterial pressure curve refl ecting respiratory variations of stroke volume [9, 11, 14-16]. In the presence of controlled mechanical ventilation, a positive airway pressure in the thorax causes intermittent alteration of biventricular preload. Thus, respiratory variations in arterial pressure refl ect, in large part, the corresponding variations in left ventricular stroke volume. Pulse pressure variation and SVV have been shown to predict fl uid responsiveness in different patient populations, including neurosurgical, cardiac surgery and critically ill patients. One of the main limitations of PPV and SVV estimation is that they can only be determined in mechanically ventilated patients with a stable heart rhythm. Both SVV and PPV are at least, in part, dependent on tidal volume. Tidal volumes of more than 8 ml/ kg increase the validity of the measurements. Pulse pressure variation describes the ventilation-induced variation of beat-to-beat pulse pressure (the difference between systolic and diastolic arterial pressure) from the mean value during the respiratory cycle. Accordingly, stroke volume variation represents the variation of pulse-contour derived beat-to-beat stroke volume from the mean value during the - 4 -

5 respiratory cycle. A number of commercial devices (PiCCO Pulsion, Munich, Germany, FloTrac /Vigileo Edwards Lifesciences, Irvine, CA, USA) enable monitoring of SVV. The algorithm used in the PiCCO system is based on a continuously sliding time window of 30 seconds duration that enables calculation of the mean stroke volume (SV mean ). The time window is divided into four 7.5-sec periods; within each period the highest stroke volume (SV max ) and the lowest stroke volume (SV min ) are determined and the average of the four 7.5 sec intervals are used to calculate SVV. Oesophageal Doppler The oesophageal Doppler monitor is a non-invasive monitor enabling the measurement of aortic blood fl ow (ABF) and the fl ow time corrected for heart rate (FTc). As SV is the primary target parameter of fl uid-optimization, a number of clinicians use oesophageal Doppler monitoring as a quick and easy method to assess cardiac output in patients at intermediate risk. A recent meta-analysis has shown that therapeutic interventions designed to optimise Doppler derived stroke volume result in a signifi cant decrease in morbidity in patients undergoing major abdominal surgery [3, 17-20]. Moreover, oesophageal Doppler monitoring is a relatively low risk modality. One major disadvantage of the technique is that it is not well tolerated by an awake patient. Echocardiography Echocardiography can be performed either via the transthoracic or the transoesophageal approach. Both transthoracic (TTE) and transoesophageal echocardiography (TOE) enable the assessment of cardiac morphology and pathology as well as the measurement of a number of static and dynamic preload parameters such as left ventricular end-diastolic area (LVEDA). Left ventricular end-diastolic area can be obtained by obtaining an outline of the endocardial border including the papillary muscles in the short axis cross-sectional view of the left ventricle. The value of LVEDA to predict volume status and fl uid responsiveness has been studied in different patient groups; however, the results from these studies are inconsistent. From a theoretical point of view, the measurement of LVEDA should refl ect preload dependency more accurately compared with other techniques. Seemingly confl icting results might be explained by the methodology governing measurement of LVEDA, which may not accurately refl ect actual left ventricle wall geometry. In particular, irregular geometry of the left ventricular cavity makes measurement of LVEDA diffi cult. Nevertheless where patients are scheduled for routine TOE monitoring, for example cardiac surgery patients, LVEDA measurement is commonly employed for the assessment of cardiac preload. In particular, echocardiography enables direct visualisation of the therapeutic effects in these patients. In addition to cardiac preload, echocardiography can be used to assess the morphology and pathology of the entire heart; therefore echocardiography is established as the method of choice for monitoring patients with acute haemodynamic decompensation where the cause is not clear either in the operating theatre or in the intensive care unit [21]. Summary Over the last few years, a number of studies have investigated the validity and reliability of a variety of cardiac output and preload monitors in different patient groups. Until now, thermodilution cardiac output has been the most widely used measurement in clinical practice. Data from studies obtained with oesophageal Doppler cardiac output based treatment protocols have demonstrated that these measurements enable early goal directed therapy with the potential to improve patient outcomes. In the event of haemodynamic instability, TTE and TOE are able to assist diagnosis of the underlying condition. However, these are not standard continuous monitoring techniques as they do not allow continuous quantitative measures. The presence of hypovolaemia is associated with increased morbidity, therefore cardiac preload measurement is important in the clinical setting. In mechanically ventilated patients, dynamic preload parameters are superior to static preload parameters (such as CVP, PAOP) in their assessment of fl uid responsiveness. However, the threshold value for both SVV and PPV is likely to vary between different groups Overall, the threshold value for SVV varies between 8 and 12.5 %, and for PPV between 9.4 and 13.5 %. In septic patients, a PPV of 13.5% will distinguish fl uid responders from non-responders, while in cardiac surgery patients PPV values between 8 and 12 % are predictive of hypovolaemia, responsive to fl uid therapy. Until now, no adequately powered study has demonstrated that the use of dynamic preload parameters improves outcome. Optimisation of cardiac output assisted by oesophageal Doppler monitoring has been shown to produce a positive outcome in a number of studies

6 Key learning points There is wide consensus governing use of basic monitoring including ECG, non-invasive blood pressure and oximetry The value of certain advanced haemodynamic monitoring techniques and deployment of such monitoring is still a matter of discussion The aim of advanced haemodynamic monitoring is to optimise use of therapeutic manoeuvres to prevent the onset of organ failure Dynamic preload parameters such as stroke volume variation and pulse pressure variation are superior in comparison to standard cardiac fi lling pressure monitoring. References 1. Carl M, Alms A, Braun J, et al. S3 guidelines for intensive care in cardiac surgery patients: hemodynamic monitoring and cardiocirculary system. German Medical Science 2010; 8: Peyton PJ, Chong SW. Minimally invasive measurement of cardiac output during surgery and critical care: a meta-analysis of accuracy and precision. Anesthesiology 2010; 113: Phan TD, Ismail H, Heriot AG, Ho KM. Improving perioperative outcomes: fl uid optimization with the esophageal Doppler monitor, a metaanalysis and review. Journal of the American College of Surgeons 2008; 207: Marik PE, Baram M, Vahid B. Does central venous pressure predict fl uid responsiveness? A systematic review of the literature and the tale of seven mares. Chest 2008; 134: Mayer J, Boldt J, Poland R, Peterson A, Manecke GR. Continuous arterial pressure waveform-based cardiac output using the FloTrac/Vigileo: a review and meta-analysis. Journal of Cardiothoracic and Vascular Anesthesia 2009; 23: Reuter DA, Felbinger TW, Schmidt C, et al. Stroke volume variations for assessment of cardiac responsiveness to volume loading in mechanically ventilated patients after cardiac surgery. Intensive Care Medicine 2002; 28: Reuter DA, Felbinger TW, Moerstedt K, et al. Intrathoracic blood volume index measured by thermodilution for preload monitoring after cardiac surgery. Journal of Cardiothoracic and Vascular Anesthesia 2002; 16: Kubitz JC, Kemming GI, Schultheib G, et al. The infl uence of cardiac preload and positive end-expiratory pressure on the preejection period. Physiological Measurement 2005; 26: Renner J, Meybohm P, Gruenewald M, et al. Global end-diastolic volume during different loading conditions in a pediatric animal model. Anesthesia and Analgesia 2007; 105: Renner J, Gruenewald M, Brand P, et al. Global end-diastolic volume as a variable of fl uid responsiveness during acute changing loading conditions. Journal of Cardiothoracic and Vascular Anesthesia 2007; 21: Renner J, Scholz J, Bein B. Monitoring fl uid therapy. Best Practice and Research. Clinical Anesthesiology 2009; 23: Marik PE. Techniques for assessment of intravascular volume in critically ill patients. Journal of Intensive Care Medicine 2009; 24: Kastrup M, Markewitz A, Spies C, et al. Current practice of hemodynamic monitoring and vasopressor and inotropic therapy in post-operative cardiac surgery patients in Germany: results from a postal survey. Acta Anaesthesiologica Scandinavica 2007; 51: Reuter DA, Goresch T, Goepfert MS, Wildhirt SM, Kilger E, Goetz AE. Effects of mid-line thoracotomy on the interaction between mechanical ventilation and cardiac fi lling during cardiac surgery. British Journal of Anaesthesia 2004; 92: Reuter DA, Goepfert MS, Goresch T, Schmoeckel M, Kilger E, Goetz AE. Assessing fl uid responsiveness during open chest conditions. British Journal of Anaesthesia 2005; 94: Renner J, Cavus E, Meybohm P, et al. Stroke volume variation during hemorrhage and after fl uid loading: impact of different tidal volumes. Acta Anaesthesiologica Scandinavica 2007; 51: McFall MR, Woods WG, Wakeling HG. The use of oesophageal Doppler cardiac output measurement to optimize fl uid management during colorectal surgery. European Journal of Anaesthesiology 2004; 21: Wakeling HG, McFall MR, Jenkins CS, et al. Intraoperative oesophageal Doppler guided fl uid management shortens postoperative hospital stay after major bowel surgery. British Journal of Anaesthesia 2005; 95: Goddard NG, Menadue LT, Wakeling HG. A case for routine oesophageal Doppler fl uid monitoring during major surgery becoming a standard of care. British Journal of Anaesthesia 2007; 99: Funk DJ, Moretti EW, Gan TJ. Minimally invasive cardiac output monitoring in the perioperative setting. Anesthesia and Analgesia 2009; 108: Kapoor PM, Chowdhury U, Mandal B, Kiran U, Karnatak R. Trans-esophageal echocardiography in off-pump coronary artery bypass grafting. Annals of Cardiac Anaesthesia 2009; 12: