CARDIOPULMONARY MONITORING: Edited by Anthony S. McLean
Although the need to properly assess and monitor the haemodynamic status of a critically ill patient appears self-evident, the plethora of information in the published literature over the past two decades has resulted in complexity rather than clarity. Factors contributing to the complexity include uncertainty as to which patient advanced monitoring should be used in, doubt about the underlying principles on which decisions are made, confusion over an ever-expanding array of available devices, and individual physician behaviour.
Why haemodynamic status should be measured is linked to the belief that it results in improved patient care. Measurement of blood pressure, heart rate, and SaO2 is routine whereas the benefit of more sophisticated techniques has yet to be demonstrated in large randomized controlled trials (RCT) . RCT, however, does not answer the questions about what additional parameters would bring the most treatment benefit. Relying on clinical examination and the basic parameters alone is common practice, although in many patients this relies more upon guesswork and in the deteriorating patient, more objective data should be considered necessary .
The first step in resuscitation is optimizing intravascular volume, and when looking at actual daily practice, the FENICE study demonstrates that we most often rely upon discreditable practices and shy away from objective evaluation . Monitoring fluid therapy is the first step in the haemodynamic monitoring journey, with Marik (pp. 246–251) encapsulating the current published opinions in a chapter on ‘Optimising Fluid Therapy in Shock’.
When to apply more advanced monitoring? It is recommended when the patient is not responding to fluid therapy and vasoactive agents. Few clinicians would now question the use of echocardiography as a first choice for patients not improving after initial resuscitation efforts, as it offers considerable diagnostic advantages, even with a basic study. However, advanced critical care echocardiography offers further benefit with measurement of intracardiac pressures. In particular, the left ventricular end-diastolic pressure is of considerable interest and are we at the stage where echo can provide this in an accurate and noninvasive way? This is explored by McLean (pp. 252–258) in ‘Echocardiographic Assessment of Left ventricular Diastolic Pressure’.
Which technique to use once the decision has been made to escalate the level of monitoring beyond the use of echo depends upon what devices are available in the clinician's ICU, the preference for noninvasive versus invasive, ease of application, ease of interpretability, and degree of accuracy. Messina et al. (pp. 259–265) explore useful specific clinical practices that can be helpful in the shocked patient and explores which advanced monitoring devices are available in ‘What should I use next if clinical evaluation and echocardiographic haemodynamic assessment is not enough?’. Importantly, the clinician needs to understand the advantages and disadvantages of whatever tool is chosen. The chapter by Huang (pp. 266–272) looks at the trade-off between accuracy and continuity when choosing what device to measure cardiac output in the chapter ‘Measuring cardiac output at the bedside’. This becomes particularly relevant with the current trend from invasive to noninvasive modalities when convenience and continuous measurements are linked to loss of accuracy.
Transpulmonary thermodilution techniques have gained a foothold in many ICUs and their role is explored by Monnet (pp. 273–279) in ‘Transpulmonary thermodilution techniques in the haemodynamically unstable patient’. At the other end of the circulatory tree from the heart, the tissues, is where all the clinician's efforts are ultimately directed in an effort to optimize cellular function. Hence, an emphasis on the microcirculation and how much better it would be if this could be reliably and accurately measured. De Backer (pp. 280–284), a pioneer in the field, leads us into the world of microcirculation monitoring in ‘Is microcirculatory assessment ready for regular use in clinical practice?’. Although patients receiving extracorporeal membrane oxygenation (ECMO) represent a very small fraction of ICU patients, they present real challenges, ironically in a group that desperately need it. In ‘Hemodynamic monitoring in the ECMO patient,’ Krishnan and Schmidt (pp. 285–291) discuss haemodynamic monitoring in this selected group, guiding us through what can be, and what cannot be used.
What the physician actually does with the information after obtaining data from the chosen device or technique is a field demanding further study. This is nowhere as simple as it first appears, as physician behavior is a key factor in determining whether monitoring is beneficial for the patient. Different clinicians, when presented with identical data can trigger completely different actions, and is in part an explanation for the lack of clarity from many studies. In this issue, Boerma and Bootsma (pp. 292–297) examine factors that influence the effective implementation of therapeutic strategies in the final chapter ‘Physician factors in utilizing haemodynamic data in patient care’.
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