Best practice & research. Clinical anaesthesiology
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Best Pract Res Clin Anaesthesiol · Dec 2014
Monitoring the microcirculation in critically ill patients.
Alterations in microvascular perfusion have been identified in critically ill patients, especially in sepsis but also in cardiogenic shock, after cardiac arrest, and in high-risk surgery patients. These alterations seem to be implicated in the development of organ dysfunction and are associated with outcome. Even though microvascular perfusion can sometimes be homogenously decreased as in acute hemorrhage or in non-resuscitated cardiogenic shock, heterogeneity of perfusion is observed in sepsis and in resuscitated hemorrhagic/cardiogenic shock. ⋯ Videomicroscopic techniques can nowadays be applied at bedside but are still restricted to some selected patients (quiet or sedated patients). Tissue PCO2 is an elegant alternative but is not yet broadly used. In this manuscript, we discuss the main advantages and limitations of the techniques available for bedside evaluation of the microcirculation in critically ill patients.
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Blood pressure is overwhelmingly the most commonly measured parameter for the assessment of haemodynamic stability. In clinical routine in the operating theatre and in the intensive care unit, blood pressure measurements are usually obtained intermittently and non-invasively using oscillometry (upper-arm cuff method) or continuously and invasively with an arterial catheter. However, both the oscillometric method and arterial catheter-derived blood pressure measurements have potential limitations. ⋯ In the recent years, technologies for continuous non-invasive blood pressure recording such as the volume clamp method or radial artery applanation tonometry have been developed and validated. The question in which patient groups and clinical settings these technologies should be applied to improve patient safety or outcome has not been definitively answered. In critically ill patients and high-risk surgery patients, further improvement of these technologies is needed before they can be recommended for routine clinical use.
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The photoplethysmographic (PPG) waveform, also known as the pulse oximeter waveform, is one of the most commonly displayed clinical waveforms. First described in the 1930s, the technology behind the waveform is simple. The waveform, as displayed on the modern pulse oximeter, is an amplified and highly filtered measurement of light absorption by the local tissue over time. ⋯ Research efforts are under way to analyze the PPG using improved digital signal processing methods to develop new physiologic parameters. It is hoped that when these new physiologic parameters are combined with a more modern understanding of cardiovascular physiology (functional hemodynamics) the potential utility of the PPG will be expanded. The clinical researcher's objective is the use of the PPG to guide early goal-directed therapeutic interventions (fluid, vasopressors, and inotropes), in effect to extract from the simple PPG the information and therapeutic guidance that was previously only obtainable from an arterial pressure line and the pulmonary artery catheter.
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Since its inception, the pulmonary artery catheter has enjoyed widespread use in both medical and surgical critically ill patients. It has also endured criticism and skepticism about its benefit in these patient populations. By providing information such as cardiac output, mixed venous oxygen saturation, and intracardiac pressures, the pulmonary artery catheter may improve care of the most complex critically ill patients in the intensive care unit and the operating room. ⋯ Major complications related to catheter placement are infrequent, but misinterpretation of monitored data is not uncommon and has led many to question the utility of the pulmonary artery catheter. The evidence to date suggests that the use of the catheter does not change mortality in many critically ill patients and may expose these patients to a higher rate of complications. However, additional clinical trials are needed, particularly in the most complex critically ill patients, who have generally been excluded from many of the research trials performed to date.