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Targeted fluid administration for major surgery
Current Anaesthesia & Critical Care 21 (2010) 108–113
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Current Anaesthesia & Critical Care journal homepage: www.elsevier.com/locate/cacc
FOCUS ON: ENHANCED RECOVERY
Targeted fluid administration for major surgery Daniel Conway a, *, Stuart Gold b,1 a b
Department of Anaesthesia, Manchester Royal Infirmary, Oxford Road, Manchester M13 9WL, UK Department of Anaesthesia, Derby Royal Hospital, Uttoxeter Road, Derby DE22 3NE, UK
s u m m a r y Keywords: Cardiac output monitoring Intravenous fluid administration Oesophageal Doppler monitoring Major surgery
Targeted Fluid Adminstration (TFA) is a technique using less invasive cardiac output monitors to guide individualised intra-operative fluid therapy. Typically, the anaesthetist administers boluses of approximately 200–250 ml of colloid solution whilst measuring changes in stroke volume or another measure of fluid responsiveness, such as stroke volume variation. When the stroke volume measurements indicate that the cardiovascular system is no longer fluid responsive, the patient is assumed to be close to the upper flat phase of the Frank–Starling Curve. Research using TFA suggests that post-operative complications such as ileus and length of hospital stay are reduced when fluid therapy is managed in this way. Most of the positive evidence for TFA has been achieved using the oesophageal Doppler (CardioQ, Deltex Medical, Chichester UK), although other cardiac output monitors are available, there are few clinical outcome studies that justify their use in routine practice. Widespread adoption of TFA for patients undergoing major surgery will help achieve the goals of enhanced recovery. Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction Adequate tissue perfusion during the peri-operative period is a key determinant of post-operative outcomes, complications, length of stay and even survival. Standard cardiovascular monitors available to the anaesthetist include pulse, non-invasive blood pressure and urine output in addition to clinical observation. These physiological observations are not rapid or sensitive indicators of hypovolaemia: it is possible to have a 15% reduction in circulating volume without any effect on heart rate or blood pressure. Similarly urine output is assessed over at least 1 h before any effect of fluid resuscitation can be interpreted. Unfortunately standard monitoring does not detect occult hypovolaemia or respond to large fluid shifts rapidly. This prevents the anaesthetist from giving fluids to treat hypovolaemia and provide optimal perfusion conditions. More invasive estimates of cardiac pre-load such as central venous pressure and pulmonary artery pressure have been advocated as peri-operative monitors. Extensive investigation of invasive pressure monitoring has consistently demonstrated that these devices poorly predict the response of the cardiovascular system to changes such as fluid challenge, fluid loss, changes in PEEP or changes in
* Corresponding author. Tel.: þ44 1612764551; fax: þ44 1612768027. E-mail addresses: [email protected], [email protected] (D. Conway), [email protected] (S. Gold). 1 Tel.: þ44 1332 783430. 0953-7112/$ – see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.cacc.2010.01.001
patient position.1–3 Furthermore pressure-based monitoring is invasive, time consuming, expensive and associated with significant clinical complications. Studies in very high risk surgical patients have demonstrated that targeting oxygen delivery using the pulmonary artery catheter to guide fluid and vasoactive drugs could improve post-operative patient outcomes.4,5 However the benefits suggested by these promising early studies failed to materialise when repeated in larger multi-centric randomised controlled trials.6,7 The use of the pulmonary artery catheter during major surgery has diminished as a result of the published evidence and the emergence of less invasive monitoring systems. Less invasive cardiac output monitors have been developed in response to the desire of anaesthetists to offer optimal tissue perfusion using blood flow based monitors to guide fluid and drug therapy. In order to gain widespread acceptability, these monitors have demonstrated reliability and validity in estimating cardiac output and other cardiovascular parameters. They also need to be user friendly, suitable for the theatre environment, minimally invasive and cost effective. These monitors can then be integrated into a technique of ‘Targeted Fluid Administration’ (TFA): a proactive, individualised approach to intravenous fluid therapy. Crucially, peri-operative techniques such as TFA should optimise tissue perfusion and improve the post-operative experience for patients undergoing major surgery. In this article, we will review the various monitors, fluids and drugs which can be used to apply TFA for major surgical patients.
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2. Fluid therapy during major surgery: achieving a balance in unknown quantities Major surgery presents a number of significant challenges to the anaesthetist such as producing adequate ventilation, oxygenation, hypnosis, muscle relaxation and pain relief (nociception) both during and after surgery. All these require a careful balance of the beneficial and unwanted effects of drugs and mechanical interventions during surgery which itself involves significant tissue damage over a prolonged period of time. Perhaps the most controversial area of anaesthetic management is intravenous fluid therapy where advocates of liberal or restrictive administration techniques; different fluid formulations and various vasoactive drugs can all claim to have supporting evidence. Below we will outline the challenge and propose a rational fluid replacement technique, which is practical and associated with improved patient outcomes. We believe that this technique should be fully integrated into Enhanced Recovery Services. 2.1. Measuring tissue perfusion One of the greatest challenges during and after major surgery is maintaining adequate tissue perfusion to allow optimal delivery of oxygen and nutrients whilst helping eliminate metabolic waste products. Optimal tissue perfusion has been shown to reduce excessive pro-inflammatory states and hence complications following surgery. Adequate perfusion is very difficult to measure at the tissue beds in routine clinical practice, and so the anaesthetist must rely on surrogate cardiovascular markers such as blood pressure, stroke volume and cardiac output. 2.2. Measuring fluid status Although fluid losses during surgery are to be anticipated, the state of hydration before and during surgery is unknown and measuring blood volume directly, whilst possible in principle, is invasive and sufficiently complex to prohibit use in day-to-day practice. Measuring fluid loss relies on careful measurement of surgical swabs and crude estimation of evaporative and other insensible losses of perhaps up to 1 mL/kg/h. Fluid overload is equally difficult to assess yet is associated with complications related to excessive tissue oedema such as ileus and respiratory distress. Again the anaesthetist has to rely on surrogate markers to assess volume status yet commonly adopted pressure-based surrogates: pulmonary capillary wedge pressure and central venous pressure, consistently fail to predict fluid responsiveness.1–3,8 Dynamic surrogate measures of fluid responsiveness such as stroke volume variation, pulse pressure variation and to a lesser extent corrected flow time have all been shown to be superior to pressure-based surrogates.9,10
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Measure Stroke Volume
200ml fluid over 5 minutes
Yes
Stroke Volume up > 10%?
Yes
No
Stroke Volume down > 10%?
No Monitor Stroke Volume Fig. 1. Targeted Fluid Administration. Clinical Algorithm.
4. Using cardiac output monitoring to guide intravenous fluid Targeted Fluid Administration has been demonstrated most reliably with less invasive cardiac output monitors. Of these, the oesophageal Doppler is the most popular device, used in 7 randomised controlled trials; quality improvement projects and routine clinical practice around the world. For the purpose of this review article, we will concentrate on the use of the oesophageal Doppler. 5. Oesophageal Doppler monitoring (ODM) ODM measures the velocity of blood flowing down the descending aorta with each heartbeat. This is achieved by careful placement of a soft, flexible probe in the mid-oesophagus via the nose or mouth. The probe tip is gently manoeuvred until the ultrasound beam is directed at the descending aorta. The Doppler shift principle then allows measurement of blood velocity in the aorta. This is can be represented by a typical triangular waveform (Fig. 2) and characteristic sound. By integrating the velocity waveform to derive the average velocity and making assumptions about aortic cross- sectional area (based on weight, height and age)
3. Targeted fluid administration ‘Targeted Fluid Administration’ is a technique that utilises less invasive cardiac output monitors such as oesophageal Doppler to guide fluid boluses with the intention of maximising stroke volume (Fig. 1). These devices also display flow based surrogates of volume status. Whilst there is no proof that maximised stroke volume is equivalent to either optimal tissue perfusion or euvolaemia, it is clear that this technique particularly when instituted in a timely manner at the start of anaesthesia is associated with a reduction in the production of pro-inflammatory cytokines.11 Whilst these are merely surrogate markers, using this technique has reduced postoperative complications leading to enhanced recovery and a reduction in length of hospital stay for patients undergoing major surgery in a number of randomised controlled trials.12,13
Fig. 2. The characteristic waveform of oesophageal Doppler representing the velocity change over time of blood pulsating in the descending aorta.
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and the proportion of cardiac output that flows to the head and upper body, the ODM will estimate stroke volume and cardiac output. ODM will also provide continuous measures of other variables such as corrected flow time. ODM has been shown to have reasonable validity, with no bias and high clinical agreement when compared to cardiac output monitoring with the invasive pulmonary artery catheter. This agreement is maintained during periods of significant haemodynamic change which occur in patients on intensive care or in theatre when techniques such as Targeted Fluid Administration are employed.14 These changes can be quantified in terms of change in flow time, peak velocity as well as stroke volume (Fig. 3). Some experienced anaesthetists will use the changes in the characteristic sound to judge subtle haemodynamic change during surgery. ODM has been shown to have a short learning curve with most users competent with a programme of classroom and theatre training. Whilst some commentators claim that this device is easy to use compared with invasive devices, we would advocate that an experienced anaesthetist will be able to achieve Targeted Fluid Administration during major surgery most effectively. This is because intra-operative haemodynamic changes should be interpreted in the context of the effects of anaesthesia, analgesia, surgery and the signal from the ODM probe which frequently requires re-adjustment. Post-operatively ODM can facilitate nurseled fluid therapy on the Intensive Care Unit.15 The ODM has a number of significant drawbacks which prevent it from being the ideal monitor for Targeted Fluid Administration in all patients who could benefit. ODM cannot be used in patients with oesophageal pathology. ODM use in head and neck, oesophageal and gastric surgery is limited due to the proximity of the probe to the surgical field. Despite attempts to design and promote nasal probes for use in patients who are awake, these have failed to gain popularity. Thus the ODM is rarely used in patients having procedures under regional anaesthesia or retained for post-operative use in the High Dependency or Post-Anaesthesia Care Units. Despite these limitations, a recent report from the Centre for Evidence Based Purchasing concluded that the ODM had significant potential to improve care for patients undergoing high risk surgery.16 This report reviewed all the relevant research into patient outcome following ODM guided management and stated
Fig. 3. Predictable changes in the shape of the oesophageal Doppler waveform occur during changes in the haemodynamic state of an individual. The most common abnormality seen during Targeted Fluid Administration is hypovolaemia, usually at the start of surgery which is represented by the narrow triangular waveform ‘Pre-load reduction’.
that the addition of ODM should result in fewer post-operative complications with the cost of ODM being compensated for by a reduction in length of stay. A 2007 report from the US Federal Agency for Healthcare Research and Quality came to similar conclusions.17 The National Institute for Health Research Health Technology Assessment Programme have performed an economic evaluation of ODM compared with standard care with or without CVP monitoring. The HTA modelled the impact of ODM on Quality Adjusted Life Year (QALY) calculations. This assessment revealed ODM guided Targeted Fluid Administration during major surgery to be cost effective under almost all potential circumstances. The HTA estimated that between £581 and £11 600 extra would have to be spent on each survivor of surgery receiving ODM guided fluid before ODM would no longer be regarded as cost effective.18
5.1. Targeted fluid administration with oesophageal Doppler – a practical guide Where possible the ODM probe should be inserted as soon as practicable following induction of anaesthesia. Some prefer to do this in the anaesthetic room before moving into the operating theatre. To avoid connecting and disconnecting the probe and moving the monitor, it is feasible to move into the operating room and insert the probe while the surgical team are preparing the patient for surgery, for example by inserting the urinary catheter. The probe can be inserted orally or nasally, there are markings to guide average depth of insertion for either of these sites. Many anaesthetists find the nasal route provides the easiest route into the oesophagus and seems to hold the probe in a more stable position intra-operatively. The initial signal can be very difficult to pick up – this is likely to be the lowest stroke volume the patient has during the whole case, making the signal difficult to find. If unable to find an adequate aortic signal we would advocate giving a small fluid bolus which often increases the stroke volume enough for the signal to be sufficient for continuous monitoring. Fluid boluses are given and stroke volume is assessed prior to, and following each bolus, The ODM signal should be optimised each time a fluid boluses are given. Newer ODM monitors have the facility to graph, save and analyse changes in stroke volume which makes this process much easier to follow and record during the operation. Essentially the process of fluid boluses is continued as long as fluid boluses increase stroke volume by at least 10%. This process makes physiological sense as we are attempting to construct a Frank–Starling curve for each individual patient by administering fluid challenge until the peak of the individual’s particular Frank– Starling curve is reached (Fig. 1). Clinicians who have extensive experience of using this monitor tend to give more fluid at the beginning of the case than they would have without ODM monitoring. Sudden changes in SV are often the result of probe displacement and an attempt should be made to refocus the probe, however if the probe cannot be refocused to a better signal, alternative causes should sought; bleeding and myocardial dysfunction being the two commonest causes. As the operation comes to an end, the need for ODM guided fluid boluses has usually ceased for most uncomplicated elective surgery. Some ODM users attempt to leave the probe in while anaesthesia is reversed and the patient is woken up. There are significant advantages to being able to use ODM in the recovery room to further guide fluid therapy in the conscious patient. In our experience the signal is often too unstable to interpret in a recovering patient. However a study in post-operative cardiac surgical patients
D. Conway, S. Gold / Current Anaesthesia & Critical Care 21 (2010) 108–113
suggested that ODM guided fluid therapy in the intensive care unit may be beneficial.15 5.2. Disadvantages of applying targeted fluid administration with ODM Using TFA can be distracting for a single anaesthetist providing anaesthesia to the patient and interacting with the rest of the theatre team. The noise of ODM can be distracting to surgeons while it is being focused. Surgical diathermy and harmonic scalpels cause electrical interference which impairs the signal. If a nasogastric tube is placed, the air inside the tube can interfere with the ODM signal. This can sometimes be rectified by filling the tube with fluid. The ODM can be quite user dependent and requires regular readjustment to achieve an optimal signal. Ideally the probe should be re-focussed prior to any clinical decision such as administering a fluid challenge. This is particularly important when multiple anaesthetists are involved in a case. The ODM is less reliable when the heart rate is high, or when the rhythm is irregular. The readings in patients with atrial fibrillation can be difficult to interpret and we suggest that the ODM is programmed to average the stroke volume measurement over a longer period of time in these circumstances. 6. Alternative cardiac output devices Other less invasive cardiac output monitors have been advocated for Enhanced Recovery Programmes and there is some data to support their use. It is even possible that by using measures of fluid responsiveness, such as pulse pressure variation during mechanical ventilation, occult hypovolaemia can be detected and eliminated. 6.1. Pulse contour analysis less invasive cardiac output monitors The potential for the arterial waveform to estimate the cardiac output has been recognised for some time. Devices using pulse contour analysis techniques (PCA) are commercially available. Unfortunately, these devices have not been investigated in clinical trials of Targeted Fluid Administration to the same extent as ODM. However they may still have an important role to play, particularly in situations where ODM use is precluded. Continuous monitoring of stroke volume with PCA was described by Wesseling, Langewouters and colleagues. Their calculations identified three key factors which will affect the interpretation of PCA based on the Windkessel (German for ‘Air Chamber’) phenomena, namely aortic impedance, peripheral vascular resistance and aortic compliance.19 Interpretation of PCA when rapid changes in haemodynamic changes occur can lead to inaccuracy. The devices become less reliable at extremes of cardiac output. As a result, most PCA devices utilise a second cardiac output measurement technique in order to calibrate continuous PCA. Examples of calibration include transpulmonary thermodilution (PiCCO) and Lithium dye dilution (LiDCO). Auto calibrating PCA such as Flotrac Vigileo have been developed using mathematical techniques which avoid the need for time consuming calibration during surgery. 6.2. LiDCO LiDCOÔ plus system employs two technologies. Initial cardiac output calibration is performed by lithium indicator dilution where lithium chloride is injected iv and then detected by a lithium-sensitive electrode attached to an arterial cannula. The technique requires arterial and venous cannulation; a central venous catheter is preferable. Although some patients receiving Targeted Fluid Administration require invasive arterial and central venous monitoring, many do not
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and so LiDCO would require additional invasive cannulation. LiDCO calculates change in stroke volume by power analysis of the first harmonic of the arterial pressure waveform looking for changes in stroke volume rather than absolute values. This means that calibration may be necessary during TFA. Only one clinical trial has reported the use of LiDCO in surgical patients. This study used a combination of TFA and the vasoactive drug dopexamine after the end of surgery to achieve a target oxygen delivery of 600 mL/min/m2. This study demonstrated less post-operative complications and a 3 day length of stay reduction.20 6.3. PiCCO PiCCOÔ differs from other PCA devices in that it utilizes only the area under the systolic portion of the curve. It is calibrated by the transpulmonary thermodilution technique, which requires the placement of a 5-French (Fr) thermistor-tipped arterial catheter. It is necessary that the catheter is inserted into the femoral artery, making the PiCCO relatively invasive and therefore at increased risk of bleeding complications. Usually a central venous catheter is required as the injection point for thermodilution. As with LiDCO, these requirements are more invasive than would often be required for patients undergoing elective colorectal surgery for example. The authors are unaware of any clinical studies or randomised controlled trials which evaluate the use of the PiCCO device for Targeted Fluid Administration. 6.4. Autocalibrating PCA (Edwards VigileoÔ) One drawback of PCA with PiCCO and LiDCO, is that it relies on a relatively simple, three-parameter model and needs recalibration during haemodynamic change, such as occurs during Targeted Fluid Administration. The Edwards Flotrac Vigileo system incorporates a more complex model to account for other phenomena, such as the pattern of pressure wave reflections due to impedance mis-matches. Vigileo attempts to improve PCA by estimating SV as a function of the ratio between the area under the entire pressure curve and a linear combination of various components of impedance. In attempting to account for pressure reflections, the Vigileo system relies not only on accurate estimates of pressure function, but also on mathematical adjustments of the mean pressure value. Although initially disappointing validation studies of the FloTrac/Vigileo device were reported, more encouraging results after software updates have been published which demonstrate improvements in a variety of patient groups including those with obesity.21 However, even with these software upgrades, many studies investigating Vigileo continue to report cardiac output measurement outside of the acceptable clinical range when compared to other less invasive devices.22 The authors are unaware of any clinical studies or randomised controlled trials which evaluate the use of the Vigileo device for Targeted Fluid Administration. 6.5. Bioimpedance cardiac output monitoring Bioimpedance describes the passive electrical properties of biological materials. When a current is passed between electrodes attached to the body, the ability to oppose current flow is termed impedance (Z) which is measured in Ohms. Bioimpedance can act as an indirect transducing mechanism for monitoring physiological phenomena. For example, the rapid changes in bioimpedance that occur following the opening of the aortic valve probably relate to volumetric changes in the aorta. Tetrapolar systems have been developed which estimate the velocity of blood in the aorta. These newer techniques use either four electrodes – two electrodes around the neck, one electrode around the apex of the heart, and the fourth
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further in caudal direction (ICON, Osypka Medical, Berlin) or eight spot electrodes arranged as four double electrodes which are placed on the upper and lower chest wall on each side (NICOM, Cheetah Medical, Tel Aviv) (Fig. 4). These systems allow the amplitude of the impedance change (dZ) to be measured as well as the frequency. The dZ waveform is similar to the characteristic aortic velocity curve displayed by the ODM. The first time derivative dZ/dt is called the impedance cardiographic curve. The Cheetah system claims to reduce the signal to noise ratio further by analysing phase shift between the injected current and the measured voltage. By adding information about patient age, sex, and weight, it is possible to estimate the heart stroke volume and cardiac output.22 Bioimpedance devices are yet to be fully evaluated in terms of being used to guide Targeted Fluid Administration techniques. 6.6. Pulse pressure variation monitoring The superiority of dynamic measures of fluid responsiveness over static measures such as central venous pressure are well established in the literature.1–3,8–10 Unfortunately most patient monitoring systems do not display modalities such as pulse pressure variation (PPV) and the anaesthetist has hitherto relied on a visual inspection of the arterial pulse pressure trace colloquially referred to as the ‘swing’. A pilot study which used a calculated PPV from the arterial pressure wave to guide fluid therapy found significant improvement in clinical outcomes.23 It is likely that the manufacturers of patient monitoring systems will incorporate the relatively simple software to calculate and display PPV in the future. However, larger randomised controlled trials are needed to establish the place of PPV guided Targeted Fluid Administration. 7. Peri-operative fluid administration. Ongoing controversy and the place of targeted fluid administration Most anaesthetists and surgeons with an interest in improving the care for the high risk surgical patient will be very aware of the intense controversy that surrounds the use of peri-operative fluid.
All protagonists agree that inappropriate fluid management is likely to lead to clinical complications and adverse patient outcomes. The evidence from research papers and review articles as to what constitutes inappropriate fluid management can often appear conflicting, as management regimes using different types of fluids, with or without cardiac output monitoring, at different points of the surgical patients pathway have all been reported. 7.1. Targeted fluid administration: liberal, restrictive or neither? The complexity of peri-operative fluid management is compounded by the fact that both over-administration and underadministration of fluid is likely to result in sub-optimal care. However based on the evidence outlined above, a consensus is emerging that at least in the intra-operative period, Targeted Fluid Administration is a reasonable method to minimise the harm caused by over-administration or under-administration of fluid. The key features of Targeted Fluid Administration that enable safe care are:i. Fluid therapy is started early, before tissue injury or major fluid losses occur. ii. Early fluid challenge and continuous review of stroke volume minimise the occult hypovolaemia which has resulted from starvation and anaesthetic techniques. iii. Fluid administration is individualised and curtailed as soon as the patient is no longer fluid responsive. iv. By achieving adequate perfusion at the start of surgery, there appears to be an attenuation of the burst of pro-inflammatory cytokines. This may lead to a reduction in capillary leak postoperatively and the development of tissue oedema which is often exacerbated by inappropriately excessive fluid therapy following surgery. v. Continuous monitoring of cardiac output intra-operatively allows the anaesthetist to rapidly detect when sudden haemodynamic changes occur during surgery when compared to standard monitoring modalities.
7.2. Targeted fluid administration and the choice of fluid Another great source of controversy and debate is the choice of intra-operative fluid. It is essential to acknowledge that intravenous fluids are drugs with indications, contraindications, and side effects. With this in mind the anaesthetist must carefully choose the type of fluid used intra-operatively. This choice is based on a large number of factors. The evidence for Targeted Fluid Administration suggests that early administration of colloid provides benefit. However no head-to-head trials of crystalloid versus colloid or colloid versus colloid during Targeted Fluid Administration have been performed. Likewise all the clinical trials of Targeted Fluid Administration used saline-based fluids. The development and widespread availability of ‘balanced’ colloid solutions have led many to advocate their use during Targeted Fluid Administration, based on evidence supporting ‘balanced’ intra-operative fluids such as Hartmanns solution.24,25 In our clinical practice, the authors have used colloids (hydroxylethyl starch) suspended in both balanced and saline-based solutions, to perform fluid challenges as part of Targeted Fluid Administration. 8. Targeted fluid administration – a practical guide to technology adoption
Fig. 4. A tetrapolar Bioimpedance device which is entirely non-invasive, relying on four double electrodes placed on the chest wall. Change in electrical impedance to a current passed between the electrodes, represent the movement of blood during the aortic pulse wave.
Introducing TFA into practice requires adequate resources, comprehensive training, local protocols, robust data collection and quality assurance of the whole process.
D. Conway, S. Gold / Current Anaesthesia & Critical Care 21 (2010) 108–113
The fiscal constraints affecting healthcare mandates that a business case is made to justify the purchase of monitors and ongoing consumable costs. Training in the use of the monitors is usually provided by the manufacturer upon agreement of a service level agreement for the product. This will usually take the form of classroom theoretical explanation of the principals involved in using the monitors followed by in theatre, practical training in the use of ODM to maximise stroke volume. In this way, users can be demonstrated to be competent in the use of the monitor and able to follow the locally agreed protocol to maximise stroke volume. When introducing a change in practice such as this, it is necessary to collect data regarding use of equipment and consumables, case selection, intra-operative use, fluids administered and patient outcomes. Outcome data are necessary to ensure safe use of the monitor and TFA protocol, as well as demonstrate improvement in patient outcomes. Practical difficulties encountered introducing TFA include; Organisational difficulties: most hospitals have a complex committee structure making authorisation of the project laborious e.g. Trust and directorate management board, equipment committee, audit committee, clinical practice committee. Short term management aims: demonstrating improved outcomes and efficiency gains will probable take 2 years from capital outlay. This is a long time for a medical manager to wait to justify investment, bear in mind their performance will be assessed each financial year. Silo budgeting: in many hospitals, monitors and consumables will be purchased using theatre budgets, however it is the surgical ward that will benefit from the efficiency saving of reduced complications and length of stay. The practical solution to these administrative difficulties is to engage with a senior manager who has responsibility for theatres and wards. They will be able to take a high level view and support the project. 9. Conclusion Targeted Fluid administration using less invasive cardiac output monitors such as oesophageal Doppler is an effective strategy that can be employed by the anaesthetist during major surgery to improve tissue perfusion, reduce post-operative complications and enhance the patient’s recovery from surgery which will lead to reduced length of hospital stay. The oesophageal Doppler is a minimally invasive device that can be widely and rapidly implemented by committed clinicians, with the support of healthcare managers. The ODM is not suitable for all cases and therefore alternative devices will also need to be available. The benefits of widespread implementation of TFA should be integral to any enhanced recovery programme for major surgical patients. Conflict of interest None. Acknowledgements Images in Figs. 2 and 3 were provided by Deltex Medical Ltd. Image in Fig. 4 was provided by PROACT Medical Ltd. References 1. Kumar A, Anel R, Bunnell E, Habet K, Zanotti S, Marshall S, et al. Pulmonary artery occlusion pressure and central venous pressure fail to predict ventricular filling volume, cardiac performance, or the response to volume infusion in normal subjects. Crit Care Med 2004;32:691–9.
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2. Hofer CK, Mu¨ller SM, Furrer L, Klaghofer R, Genoni M, Zollinger A. Stroke volume and pulse pressure variation for prediction of fluid responsiveness in patients undergoing off-pump coronary artery bypass grafting. Chest 2005;128(2):848–54. 3. Marik PE, Baram M, Vahid B. Does central venous pressure predict fluid responsiveness? A systematic review of the literature and the tale of seven mares. Chest 2008 Jul;134(1):172–8. 4. Shoemaker WC, Appel PL, Kram HB, Waxman K, Lee TS. Prospective trial of supranormal values of survivors as therapeutic goals in high-risk surgical patients. Chest 1988;94(6):1176–86. 5. Boyd O, Grounds RM, Bennett ED. A randomized clinical trial of the effect of deliberate perioperative increase of oxygen delivery on mortality in high-risk surgical patients. JAMA 1993;270(22):2699–707. 6. Takala J, Meier-Hellmann A, Eddleston J, Hulstaert P, Sramek V. 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Current Anaesthesia & Critical Care journal homepage: www.elsevier.com/locate/cacc
FOCUS ON: ENHANCED RECOVERY
Targeted fluid administration for major surgery Daniel Conway a, *, Stuart Gold b,1 a b
Department of Anaesthesia, Manchester Royal Infirmary, Oxford Road, Manchester M13 9WL, UK Department of Anaesthesia, Derby Royal Hospital, Uttoxeter Road, Derby DE22 3NE, UK
s u m m a r y Keywords: Cardiac output monitoring Intravenous fluid administration Oesophageal Doppler monitoring Major surgery
Targeted Fluid Adminstration (TFA) is a technique using less invasive cardiac output monitors to guide individualised intra-operative fluid therapy. Typically, the anaesthetist administers boluses of approximately 200–250 ml of colloid solution whilst measuring changes in stroke volume or another measure of fluid responsiveness, such as stroke volume variation. When the stroke volume measurements indicate that the cardiovascular system is no longer fluid responsive, the patient is assumed to be close to the upper flat phase of the Frank–Starling Curve. Research using TFA suggests that post-operative complications such as ileus and length of hospital stay are reduced when fluid therapy is managed in this way. Most of the positive evidence for TFA has been achieved using the oesophageal Doppler (CardioQ, Deltex Medical, Chichester UK), although other cardiac output monitors are available, there are few clinical outcome studies that justify their use in routine practice. Widespread adoption of TFA for patients undergoing major surgery will help achieve the goals of enhanced recovery. Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction Adequate tissue perfusion during the peri-operative period is a key determinant of post-operative outcomes, complications, length of stay and even survival. Standard cardiovascular monitors available to the anaesthetist include pulse, non-invasive blood pressure and urine output in addition to clinical observation. These physiological observations are not rapid or sensitive indicators of hypovolaemia: it is possible to have a 15% reduction in circulating volume without any effect on heart rate or blood pressure. Similarly urine output is assessed over at least 1 h before any effect of fluid resuscitation can be interpreted. Unfortunately standard monitoring does not detect occult hypovolaemia or respond to large fluid shifts rapidly. This prevents the anaesthetist from giving fluids to treat hypovolaemia and provide optimal perfusion conditions. More invasive estimates of cardiac pre-load such as central venous pressure and pulmonary artery pressure have been advocated as peri-operative monitors. Extensive investigation of invasive pressure monitoring has consistently demonstrated that these devices poorly predict the response of the cardiovascular system to changes such as fluid challenge, fluid loss, changes in PEEP or changes in
* Corresponding author. Tel.: þ44 1612764551; fax: þ44 1612768027. E-mail addresses: [email protected], [email protected] (D. Conway), [email protected] (S. Gold). 1 Tel.: þ44 1332 783430. 0953-7112/$ – see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.cacc.2010.01.001
patient position.1–3 Furthermore pressure-based monitoring is invasive, time consuming, expensive and associated with significant clinical complications. Studies in very high risk surgical patients have demonstrated that targeting oxygen delivery using the pulmonary artery catheter to guide fluid and vasoactive drugs could improve post-operative patient outcomes.4,5 However the benefits suggested by these promising early studies failed to materialise when repeated in larger multi-centric randomised controlled trials.6,7 The use of the pulmonary artery catheter during major surgery has diminished as a result of the published evidence and the emergence of less invasive monitoring systems. Less invasive cardiac output monitors have been developed in response to the desire of anaesthetists to offer optimal tissue perfusion using blood flow based monitors to guide fluid and drug therapy. In order to gain widespread acceptability, these monitors have demonstrated reliability and validity in estimating cardiac output and other cardiovascular parameters. They also need to be user friendly, suitable for the theatre environment, minimally invasive and cost effective. These monitors can then be integrated into a technique of ‘Targeted Fluid Administration’ (TFA): a proactive, individualised approach to intravenous fluid therapy. Crucially, peri-operative techniques such as TFA should optimise tissue perfusion and improve the post-operative experience for patients undergoing major surgery. In this article, we will review the various monitors, fluids and drugs which can be used to apply TFA for major surgical patients.
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2. Fluid therapy during major surgery: achieving a balance in unknown quantities Major surgery presents a number of significant challenges to the anaesthetist such as producing adequate ventilation, oxygenation, hypnosis, muscle relaxation and pain relief (nociception) both during and after surgery. All these require a careful balance of the beneficial and unwanted effects of drugs and mechanical interventions during surgery which itself involves significant tissue damage over a prolonged period of time. Perhaps the most controversial area of anaesthetic management is intravenous fluid therapy where advocates of liberal or restrictive administration techniques; different fluid formulations and various vasoactive drugs can all claim to have supporting evidence. Below we will outline the challenge and propose a rational fluid replacement technique, which is practical and associated with improved patient outcomes. We believe that this technique should be fully integrated into Enhanced Recovery Services. 2.1. Measuring tissue perfusion One of the greatest challenges during and after major surgery is maintaining adequate tissue perfusion to allow optimal delivery of oxygen and nutrients whilst helping eliminate metabolic waste products. Optimal tissue perfusion has been shown to reduce excessive pro-inflammatory states and hence complications following surgery. Adequate perfusion is very difficult to measure at the tissue beds in routine clinical practice, and so the anaesthetist must rely on surrogate cardiovascular markers such as blood pressure, stroke volume and cardiac output. 2.2. Measuring fluid status Although fluid losses during surgery are to be anticipated, the state of hydration before and during surgery is unknown and measuring blood volume directly, whilst possible in principle, is invasive and sufficiently complex to prohibit use in day-to-day practice. Measuring fluid loss relies on careful measurement of surgical swabs and crude estimation of evaporative and other insensible losses of perhaps up to 1 mL/kg/h. Fluid overload is equally difficult to assess yet is associated with complications related to excessive tissue oedema such as ileus and respiratory distress. Again the anaesthetist has to rely on surrogate markers to assess volume status yet commonly adopted pressure-based surrogates: pulmonary capillary wedge pressure and central venous pressure, consistently fail to predict fluid responsiveness.1–3,8 Dynamic surrogate measures of fluid responsiveness such as stroke volume variation, pulse pressure variation and to a lesser extent corrected flow time have all been shown to be superior to pressure-based surrogates.9,10
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Measure Stroke Volume
200ml fluid over 5 minutes
Yes
Stroke Volume up > 10%?
Yes
No
Stroke Volume down > 10%?
No Monitor Stroke Volume Fig. 1. Targeted Fluid Administration. Clinical Algorithm.
4. Using cardiac output monitoring to guide intravenous fluid Targeted Fluid Administration has been demonstrated most reliably with less invasive cardiac output monitors. Of these, the oesophageal Doppler is the most popular device, used in 7 randomised controlled trials; quality improvement projects and routine clinical practice around the world. For the purpose of this review article, we will concentrate on the use of the oesophageal Doppler. 5. Oesophageal Doppler monitoring (ODM) ODM measures the velocity of blood flowing down the descending aorta with each heartbeat. This is achieved by careful placement of a soft, flexible probe in the mid-oesophagus via the nose or mouth. The probe tip is gently manoeuvred until the ultrasound beam is directed at the descending aorta. The Doppler shift principle then allows measurement of blood velocity in the aorta. This is can be represented by a typical triangular waveform (Fig. 2) and characteristic sound. By integrating the velocity waveform to derive the average velocity and making assumptions about aortic cross- sectional area (based on weight, height and age)
3. Targeted fluid administration ‘Targeted Fluid Administration’ is a technique that utilises less invasive cardiac output monitors such as oesophageal Doppler to guide fluid boluses with the intention of maximising stroke volume (Fig. 1). These devices also display flow based surrogates of volume status. Whilst there is no proof that maximised stroke volume is equivalent to either optimal tissue perfusion or euvolaemia, it is clear that this technique particularly when instituted in a timely manner at the start of anaesthesia is associated with a reduction in the production of pro-inflammatory cytokines.11 Whilst these are merely surrogate markers, using this technique has reduced postoperative complications leading to enhanced recovery and a reduction in length of hospital stay for patients undergoing major surgery in a number of randomised controlled trials.12,13
Fig. 2. The characteristic waveform of oesophageal Doppler representing the velocity change over time of blood pulsating in the descending aorta.
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and the proportion of cardiac output that flows to the head and upper body, the ODM will estimate stroke volume and cardiac output. ODM will also provide continuous measures of other variables such as corrected flow time. ODM has been shown to have reasonable validity, with no bias and high clinical agreement when compared to cardiac output monitoring with the invasive pulmonary artery catheter. This agreement is maintained during periods of significant haemodynamic change which occur in patients on intensive care or in theatre when techniques such as Targeted Fluid Administration are employed.14 These changes can be quantified in terms of change in flow time, peak velocity as well as stroke volume (Fig. 3). Some experienced anaesthetists will use the changes in the characteristic sound to judge subtle haemodynamic change during surgery. ODM has been shown to have a short learning curve with most users competent with a programme of classroom and theatre training. Whilst some commentators claim that this device is easy to use compared with invasive devices, we would advocate that an experienced anaesthetist will be able to achieve Targeted Fluid Administration during major surgery most effectively. This is because intra-operative haemodynamic changes should be interpreted in the context of the effects of anaesthesia, analgesia, surgery and the signal from the ODM probe which frequently requires re-adjustment. Post-operatively ODM can facilitate nurseled fluid therapy on the Intensive Care Unit.15 The ODM has a number of significant drawbacks which prevent it from being the ideal monitor for Targeted Fluid Administration in all patients who could benefit. ODM cannot be used in patients with oesophageal pathology. ODM use in head and neck, oesophageal and gastric surgery is limited due to the proximity of the probe to the surgical field. Despite attempts to design and promote nasal probes for use in patients who are awake, these have failed to gain popularity. Thus the ODM is rarely used in patients having procedures under regional anaesthesia or retained for post-operative use in the High Dependency or Post-Anaesthesia Care Units. Despite these limitations, a recent report from the Centre for Evidence Based Purchasing concluded that the ODM had significant potential to improve care for patients undergoing high risk surgery.16 This report reviewed all the relevant research into patient outcome following ODM guided management and stated
Fig. 3. Predictable changes in the shape of the oesophageal Doppler waveform occur during changes in the haemodynamic state of an individual. The most common abnormality seen during Targeted Fluid Administration is hypovolaemia, usually at the start of surgery which is represented by the narrow triangular waveform ‘Pre-load reduction’.
that the addition of ODM should result in fewer post-operative complications with the cost of ODM being compensated for by a reduction in length of stay. A 2007 report from the US Federal Agency for Healthcare Research and Quality came to similar conclusions.17 The National Institute for Health Research Health Technology Assessment Programme have performed an economic evaluation of ODM compared with standard care with or without CVP monitoring. The HTA modelled the impact of ODM on Quality Adjusted Life Year (QALY) calculations. This assessment revealed ODM guided Targeted Fluid Administration during major surgery to be cost effective under almost all potential circumstances. The HTA estimated that between £581 and £11 600 extra would have to be spent on each survivor of surgery receiving ODM guided fluid before ODM would no longer be regarded as cost effective.18
5.1. Targeted fluid administration with oesophageal Doppler – a practical guide Where possible the ODM probe should be inserted as soon as practicable following induction of anaesthesia. Some prefer to do this in the anaesthetic room before moving into the operating theatre. To avoid connecting and disconnecting the probe and moving the monitor, it is feasible to move into the operating room and insert the probe while the surgical team are preparing the patient for surgery, for example by inserting the urinary catheter. The probe can be inserted orally or nasally, there are markings to guide average depth of insertion for either of these sites. Many anaesthetists find the nasal route provides the easiest route into the oesophagus and seems to hold the probe in a more stable position intra-operatively. The initial signal can be very difficult to pick up – this is likely to be the lowest stroke volume the patient has during the whole case, making the signal difficult to find. If unable to find an adequate aortic signal we would advocate giving a small fluid bolus which often increases the stroke volume enough for the signal to be sufficient for continuous monitoring. Fluid boluses are given and stroke volume is assessed prior to, and following each bolus, The ODM signal should be optimised each time a fluid boluses are given. Newer ODM monitors have the facility to graph, save and analyse changes in stroke volume which makes this process much easier to follow and record during the operation. Essentially the process of fluid boluses is continued as long as fluid boluses increase stroke volume by at least 10%. This process makes physiological sense as we are attempting to construct a Frank–Starling curve for each individual patient by administering fluid challenge until the peak of the individual’s particular Frank– Starling curve is reached (Fig. 1). Clinicians who have extensive experience of using this monitor tend to give more fluid at the beginning of the case than they would have without ODM monitoring. Sudden changes in SV are often the result of probe displacement and an attempt should be made to refocus the probe, however if the probe cannot be refocused to a better signal, alternative causes should sought; bleeding and myocardial dysfunction being the two commonest causes. As the operation comes to an end, the need for ODM guided fluid boluses has usually ceased for most uncomplicated elective surgery. Some ODM users attempt to leave the probe in while anaesthesia is reversed and the patient is woken up. There are significant advantages to being able to use ODM in the recovery room to further guide fluid therapy in the conscious patient. In our experience the signal is often too unstable to interpret in a recovering patient. However a study in post-operative cardiac surgical patients
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suggested that ODM guided fluid therapy in the intensive care unit may be beneficial.15 5.2. Disadvantages of applying targeted fluid administration with ODM Using TFA can be distracting for a single anaesthetist providing anaesthesia to the patient and interacting with the rest of the theatre team. The noise of ODM can be distracting to surgeons while it is being focused. Surgical diathermy and harmonic scalpels cause electrical interference which impairs the signal. If a nasogastric tube is placed, the air inside the tube can interfere with the ODM signal. This can sometimes be rectified by filling the tube with fluid. The ODM can be quite user dependent and requires regular readjustment to achieve an optimal signal. Ideally the probe should be re-focussed prior to any clinical decision such as administering a fluid challenge. This is particularly important when multiple anaesthetists are involved in a case. The ODM is less reliable when the heart rate is high, or when the rhythm is irregular. The readings in patients with atrial fibrillation can be difficult to interpret and we suggest that the ODM is programmed to average the stroke volume measurement over a longer period of time in these circumstances. 6. Alternative cardiac output devices Other less invasive cardiac output monitors have been advocated for Enhanced Recovery Programmes and there is some data to support their use. It is even possible that by using measures of fluid responsiveness, such as pulse pressure variation during mechanical ventilation, occult hypovolaemia can be detected and eliminated. 6.1. Pulse contour analysis less invasive cardiac output monitors The potential for the arterial waveform to estimate the cardiac output has been recognised for some time. Devices using pulse contour analysis techniques (PCA) are commercially available. Unfortunately, these devices have not been investigated in clinical trials of Targeted Fluid Administration to the same extent as ODM. However they may still have an important role to play, particularly in situations where ODM use is precluded. Continuous monitoring of stroke volume with PCA was described by Wesseling, Langewouters and colleagues. Their calculations identified three key factors which will affect the interpretation of PCA based on the Windkessel (German for ‘Air Chamber’) phenomena, namely aortic impedance, peripheral vascular resistance and aortic compliance.19 Interpretation of PCA when rapid changes in haemodynamic changes occur can lead to inaccuracy. The devices become less reliable at extremes of cardiac output. As a result, most PCA devices utilise a second cardiac output measurement technique in order to calibrate continuous PCA. Examples of calibration include transpulmonary thermodilution (PiCCO) and Lithium dye dilution (LiDCO). Auto calibrating PCA such as Flotrac Vigileo have been developed using mathematical techniques which avoid the need for time consuming calibration during surgery. 6.2. LiDCO LiDCOÔ plus system employs two technologies. Initial cardiac output calibration is performed by lithium indicator dilution where lithium chloride is injected iv and then detected by a lithium-sensitive electrode attached to an arterial cannula. The technique requires arterial and venous cannulation; a central venous catheter is preferable. Although some patients receiving Targeted Fluid Administration require invasive arterial and central venous monitoring, many do not
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and so LiDCO would require additional invasive cannulation. LiDCO calculates change in stroke volume by power analysis of the first harmonic of the arterial pressure waveform looking for changes in stroke volume rather than absolute values. This means that calibration may be necessary during TFA. Only one clinical trial has reported the use of LiDCO in surgical patients. This study used a combination of TFA and the vasoactive drug dopexamine after the end of surgery to achieve a target oxygen delivery of 600 mL/min/m2. This study demonstrated less post-operative complications and a 3 day length of stay reduction.20 6.3. PiCCO PiCCOÔ differs from other PCA devices in that it utilizes only the area under the systolic portion of the curve. It is calibrated by the transpulmonary thermodilution technique, which requires the placement of a 5-French (Fr) thermistor-tipped arterial catheter. It is necessary that the catheter is inserted into the femoral artery, making the PiCCO relatively invasive and therefore at increased risk of bleeding complications. Usually a central venous catheter is required as the injection point for thermodilution. As with LiDCO, these requirements are more invasive than would often be required for patients undergoing elective colorectal surgery for example. The authors are unaware of any clinical studies or randomised controlled trials which evaluate the use of the PiCCO device for Targeted Fluid Administration. 6.4. Autocalibrating PCA (Edwards VigileoÔ) One drawback of PCA with PiCCO and LiDCO, is that it relies on a relatively simple, three-parameter model and needs recalibration during haemodynamic change, such as occurs during Targeted Fluid Administration. The Edwards Flotrac Vigileo system incorporates a more complex model to account for other phenomena, such as the pattern of pressure wave reflections due to impedance mis-matches. Vigileo attempts to improve PCA by estimating SV as a function of the ratio between the area under the entire pressure curve and a linear combination of various components of impedance. In attempting to account for pressure reflections, the Vigileo system relies not only on accurate estimates of pressure function, but also on mathematical adjustments of the mean pressure value. Although initially disappointing validation studies of the FloTrac/Vigileo device were reported, more encouraging results after software updates have been published which demonstrate improvements in a variety of patient groups including those with obesity.21 However, even with these software upgrades, many studies investigating Vigileo continue to report cardiac output measurement outside of the acceptable clinical range when compared to other less invasive devices.22 The authors are unaware of any clinical studies or randomised controlled trials which evaluate the use of the Vigileo device for Targeted Fluid Administration. 6.5. Bioimpedance cardiac output monitoring Bioimpedance describes the passive electrical properties of biological materials. When a current is passed between electrodes attached to the body, the ability to oppose current flow is termed impedance (Z) which is measured in Ohms. Bioimpedance can act as an indirect transducing mechanism for monitoring physiological phenomena. For example, the rapid changes in bioimpedance that occur following the opening of the aortic valve probably relate to volumetric changes in the aorta. Tetrapolar systems have been developed which estimate the velocity of blood in the aorta. These newer techniques use either four electrodes – two electrodes around the neck, one electrode around the apex of the heart, and the fourth
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further in caudal direction (ICON, Osypka Medical, Berlin) or eight spot electrodes arranged as four double electrodes which are placed on the upper and lower chest wall on each side (NICOM, Cheetah Medical, Tel Aviv) (Fig. 4). These systems allow the amplitude of the impedance change (dZ) to be measured as well as the frequency. The dZ waveform is similar to the characteristic aortic velocity curve displayed by the ODM. The first time derivative dZ/dt is called the impedance cardiographic curve. The Cheetah system claims to reduce the signal to noise ratio further by analysing phase shift between the injected current and the measured voltage. By adding information about patient age, sex, and weight, it is possible to estimate the heart stroke volume and cardiac output.22 Bioimpedance devices are yet to be fully evaluated in terms of being used to guide Targeted Fluid Administration techniques. 6.6. Pulse pressure variation monitoring The superiority of dynamic measures of fluid responsiveness over static measures such as central venous pressure are well established in the literature.1–3,8–10 Unfortunately most patient monitoring systems do not display modalities such as pulse pressure variation (PPV) and the anaesthetist has hitherto relied on a visual inspection of the arterial pulse pressure trace colloquially referred to as the ‘swing’. A pilot study which used a calculated PPV from the arterial pressure wave to guide fluid therapy found significant improvement in clinical outcomes.23 It is likely that the manufacturers of patient monitoring systems will incorporate the relatively simple software to calculate and display PPV in the future. However, larger randomised controlled trials are needed to establish the place of PPV guided Targeted Fluid Administration. 7. Peri-operative fluid administration. Ongoing controversy and the place of targeted fluid administration Most anaesthetists and surgeons with an interest in improving the care for the high risk surgical patient will be very aware of the intense controversy that surrounds the use of peri-operative fluid.
All protagonists agree that inappropriate fluid management is likely to lead to clinical complications and adverse patient outcomes. The evidence from research papers and review articles as to what constitutes inappropriate fluid management can often appear conflicting, as management regimes using different types of fluids, with or without cardiac output monitoring, at different points of the surgical patients pathway have all been reported. 7.1. Targeted fluid administration: liberal, restrictive or neither? The complexity of peri-operative fluid management is compounded by the fact that both over-administration and underadministration of fluid is likely to result in sub-optimal care. However based on the evidence outlined above, a consensus is emerging that at least in the intra-operative period, Targeted Fluid Administration is a reasonable method to minimise the harm caused by over-administration or under-administration of fluid. The key features of Targeted Fluid Administration that enable safe care are:i. Fluid therapy is started early, before tissue injury or major fluid losses occur. ii. Early fluid challenge and continuous review of stroke volume minimise the occult hypovolaemia which has resulted from starvation and anaesthetic techniques. iii. Fluid administration is individualised and curtailed as soon as the patient is no longer fluid responsive. iv. By achieving adequate perfusion at the start of surgery, there appears to be an attenuation of the burst of pro-inflammatory cytokines. This may lead to a reduction in capillary leak postoperatively and the development of tissue oedema which is often exacerbated by inappropriately excessive fluid therapy following surgery. v. Continuous monitoring of cardiac output intra-operatively allows the anaesthetist to rapidly detect when sudden haemodynamic changes occur during surgery when compared to standard monitoring modalities.
7.2. Targeted fluid administration and the choice of fluid Another great source of controversy and debate is the choice of intra-operative fluid. It is essential to acknowledge that intravenous fluids are drugs with indications, contraindications, and side effects. With this in mind the anaesthetist must carefully choose the type of fluid used intra-operatively. This choice is based on a large number of factors. The evidence for Targeted Fluid Administration suggests that early administration of colloid provides benefit. However no head-to-head trials of crystalloid versus colloid or colloid versus colloid during Targeted Fluid Administration have been performed. Likewise all the clinical trials of Targeted Fluid Administration used saline-based fluids. The development and widespread availability of ‘balanced’ colloid solutions have led many to advocate their use during Targeted Fluid Administration, based on evidence supporting ‘balanced’ intra-operative fluids such as Hartmanns solution.24,25 In our clinical practice, the authors have used colloids (hydroxylethyl starch) suspended in both balanced and saline-based solutions, to perform fluid challenges as part of Targeted Fluid Administration. 8. Targeted fluid administration – a practical guide to technology adoption
Fig. 4. A tetrapolar Bioimpedance device which is entirely non-invasive, relying on four double electrodes placed on the chest wall. Change in electrical impedance to a current passed between the electrodes, represent the movement of blood during the aortic pulse wave.
Introducing TFA into practice requires adequate resources, comprehensive training, local protocols, robust data collection and quality assurance of the whole process.
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The fiscal constraints affecting healthcare mandates that a business case is made to justify the purchase of monitors and ongoing consumable costs. Training in the use of the monitors is usually provided by the manufacturer upon agreement of a service level agreement for the product. This will usually take the form of classroom theoretical explanation of the principals involved in using the monitors followed by in theatre, practical training in the use of ODM to maximise stroke volume. In this way, users can be demonstrated to be competent in the use of the monitor and able to follow the locally agreed protocol to maximise stroke volume. When introducing a change in practice such as this, it is necessary to collect data regarding use of equipment and consumables, case selection, intra-operative use, fluids administered and patient outcomes. Outcome data are necessary to ensure safe use of the monitor and TFA protocol, as well as demonstrate improvement in patient outcomes. Practical difficulties encountered introducing TFA include; Organisational difficulties: most hospitals have a complex committee structure making authorisation of the project laborious e.g. Trust and directorate management board, equipment committee, audit committee, clinical practice committee. Short term management aims: demonstrating improved outcomes and efficiency gains will probable take 2 years from capital outlay. This is a long time for a medical manager to wait to justify investment, bear in mind their performance will be assessed each financial year. Silo budgeting: in many hospitals, monitors and consumables will be purchased using theatre budgets, however it is the surgical ward that will benefit from the efficiency saving of reduced complications and length of stay. The practical solution to these administrative difficulties is to engage with a senior manager who has responsibility for theatres and wards. They will be able to take a high level view and support the project. 9. Conclusion Targeted Fluid administration using less invasive cardiac output monitors such as oesophageal Doppler is an effective strategy that can be employed by the anaesthetist during major surgery to improve tissue perfusion, reduce post-operative complications and enhance the patient’s recovery from surgery which will lead to reduced length of hospital stay. The oesophageal Doppler is a minimally invasive device that can be widely and rapidly implemented by committed clinicians, with the support of healthcare managers. The ODM is not suitable for all cases and therefore alternative devices will also need to be available. The benefits of widespread implementation of TFA should be integral to any enhanced recovery programme for major surgical patients. Conflict of interest None. Acknowledgements Images in Figs. 2 and 3 were provided by Deltex Medical Ltd. Image in Fig. 4 was provided by PROACT Medical Ltd. References 1. Kumar A, Anel R, Bunnell E, Habet K, Zanotti S, Marshall S, et al. Pulmonary artery occlusion pressure and central venous pressure fail to predict ventricular filling volume, cardiac performance, or the response to volume infusion in normal subjects. Crit Care Med 2004;32:691–9.
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