Bernd Saugel

Less invasive hemodynamic monitoring in critically ill patients

Over the last decade, the way to monitor hemodynamics at the bedside has evolved considerably in the intensive care unit as well as in the operating room. The most important evolution has been the declining use of the pulmonary artery catheter along with the growing use of echocardiography and of continuous, real-time, minimally or totally non-invasive hemodynamic monitoring techniques. This article, which is the result of an agreement between authors belonging to the Cardiovascular Dynamics Section of the European Society of Intensive Care Medicine, discusses the advantages and limits of using such techniques with an emphasis on their respective place in the hemodynamic management of critically ill patients with hemodynamic instability.

Noninvasive continuous cardiac output monitoring in perioperative and intensive care medicine

The determination of blood flow, i.e. cardiac output, is an integral part of haemodynamic monitoring. This is a review on noninvasive continuous cardiac output monitoring in perioperative and intensive care medicine. We present the underlying principles and validation data of the following technologies: thoracic electrical bioimpedance, thoracic bioreactance, vascular unloading technique, pulse wave transit time, and radial artery applanation tonometry. According to clinical studies, these technologies are capable of providing cardiac output readings noninvasively and continuously. They, therefore, might prove to be innovative tools for the assessment of advanced haemodynamic variables at the bedside. However, for most technologies there are conflicting data regarding the measurement performance in comparison with reference methods for cardiac output assessment. In addition, each of the reviewed technology has its own limitations regarding applicability in the clinical setting. In validation studies comparing cardiac output measurements using these noninvasive technologies in comparison with a criterion standard method, it is crucial to correctly apply statistical methods for the assessment of a technologys accuracy, precision, and trending capability. Uniform definitions for clinically acceptable agreement between innovative noninvasive cardiac output monitoring systems and criterion standard methods are currently missing. Further research must aim to further develop the different technologies for noninvasive continuous cardiac output determination with regard to signal recording, signal processing, and clinical applicability.

Measurement of blood pressure

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. A basic technical understanding of these methods is crucial in order to avoid unreliable blood pressure measurements and consequential treatment errors. 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.

Severe hyperlactatemia, lactate clearance and mortality in unselected critically ill patients

PurposeHyperlactatemia may occur for a variety of reasons and is a predictor of poor clinical outcome. However, only limited data are available on the underlying causes of hyperlactatemia and the mortality rates associated with severe hyperlactatemia in critically ill patients. We therefore aimed to evaluate the etiology of severe hyperlactatemia (defined as a lactate level >10xa0mmol/L) in a large cohort of unselected ICU patients. We also aimed to evaluate the association between severe hyperlactatemia and lactate clearance with ICU mortality.MethodsIn this retrospective, observational study at an University hospital department with 11 ICUs during the study period between 1 April 2011 and 28 February 2013, we screened 14,040 ICU patients for severe hyperlactatemia (lactate >10xa0mmol/L).ResultsOverall mortality in the 14,040 ICU patients was 9.8xa0%. Of these, 400 patients had severe hyperlactatemia and ICU mortality in this group was 78.2xa0%. Hyperlactatemia was associated with death in the ICU [odds ratio 1.35 (95xa0% CI 1.23; 1.49; pxa0<xa00.001)]. The main etiology for severe hyperlactatemia was sepsis (34.0xa0%), followed by cardiogenic shock (19.3xa0%), and cardiopulmonary resuscitation (13.8xa0%). Patients developing severe hyperlactatemia >24xa0h of ICU treatment had a significantly higher ICU mortality (89.1xa0%, 155 of 174 patients) than patients developing severe hyperlactatemia ≤24xa0h of ICU treatment (69.9xa0%, 158 of 226 patients; pxa0<xa00.0001). Lactate clearance after 12xa0h showed a receiver-operating-characteristics area under the curve (ROC-AUC) value of 0.91 to predict ICU mortality (cut-off showing highest sensitivity and specifity was a 12xa0h lactate clearance of 32.8xa0%, Youden Index 0.72). In 268 patients having a 12-h lactate clearance <32.8xa0% ICU mortality was 96.6xa0%.ConclusionsSevere hyperlactatemia (>10xa0mmol/L) is associated with extremely high ICU mortality especially when there is no marked lactate clearance within 12xa0h. In such situations, the benefit of continued ICU therapy should be evaluated.

Cardiac output method comparison studies: the relation of the precision of agreement and the precision of method

AbstractnCardiac output (CO) plays a crucial role in the hemodynamic management of critically ill patients treated in the intensive care unit and in surgical patients undergoing major surgery. In the field of cardiovascular dynamics, innovative techniques for CO determination are increasingly available. Therefore, the number of studies comparing these techniques with a reference, such as pulmonary artery thermodilution, is rapidly growing. There are mainly two outcomes of such method comparison studies: (1) the accuracy of agreement and (2) the precision of agreement. The precision of agreement depends on the precision of each method, i.e., the precision that the studied and the reference technique are able to achieve. We call this “precision of method”. A decomposition of variance shows that method agreement does not only depend on the precision of method but also on another important source of variability, i.e., the method’s general variability about the true values. Ignorance of that fact leads to falsified conclusions about the precision of method of the studied technique. In CO studies, serial measurements are frequently confused with repeated measurements. But as the actual CO of a subject changes from assessment to assessment, there is no real repetition of a measurement. This situation equals a scenario in which single measurements are given for multiple true values per subject. In such a case it is not possible to assess the precision of method.

When should we adopt continuous noninvasive hemodynamic monitoring technologies into clinical routine

The introduction of new technologies for noninvasive continuous hemodynamic monitoring requires the conduction of well-planned clinical studies in order to assess the technology’s measurement performance and to evaluate the potential benefit for the patient. But what is the right way to go with regard to clinical validation and evaluation studies from the technology’s first introduction to its medically useful application on a routine basis? From the article by Benes et al. [1] a general recommendation for a reasonable approach in order to answer this question can be derived. The existence of methodologically and statistically solid validation studies must be the prerequisite for any further scientific investigation of a potential clinical benefit of noninvasive continuous hemodynamic monitoring technologies. In order to assess a new technology’s accuracy and precision and thus its measurement performance in validation studies, we need the comparison with invasive arterial catheter-derived measurements as the clinical criterion standard method. However, invasive hemodynamic monitoring is usually reserved for critically ill and highrisk surgical patients. Therefore, the first step on the path towards establishing a new noninvasive technology must be the performance of validation studies in these patient groups equipped with invasive hemodynamic monitoring that can be used as a reference method [2, 3]. We should then carefully and critically check a new noninvasive technology’s validation data in order to avoid misinterpretation of the technology’s measurement performance. We must avoid performing premature outcome-oriented studies using devices and algorithms that have not been meticulously validated or that are simply not precise enough. Sometimes we might have to take a step back after the first validation data and try to improve the technology’s algorithms and technical shortcomings before proceeding to the next level of studies. Only when meticulously performed validation studies are available it will make sense—from a scientific and clinical point of view—to proceed to the second step. This next step is to precisely define the right target patient groups and clinical scenarios for the sensible application of the noninvasive continuous hemodynamic monitoring technology. At present, a recommendation to use a noninvasive continuous blood pressure measurement technology instead of an arterial catheter in critically ill patients treated in the intensive care unit or in high-risk surgical patients would not be appropriate. Instead, we should rather focus on patients who do not receive continuous hemodynamic monitoring but intermittent blood pressure measurements using oscillometry. Benes et al. [1] rightly decided to include low and intermediate-risk surgical patients during thyroid surgery in beach chair position. Thereby they offer us an excellent example for the possible use of noninvasive continuous blood pressure monitoring as a reasonable alternative to intermittent oscillometric blood pressure measurements in the perioperative setting. Other scenarios in which continuous noninvasive blood pressure measurement might contribute to the patient’s safety have been recently proposed [4, 5]. After having precisely defined patient groups and clinical scenarios for the new technology’s application, the third important step is conducting studies that are related to patient safety and outcome. Such studies might assess hospital mortality, hospital length of stay, or complication J. Y. Wagner (&) B. Saugel Department of Anesthesiology, Center of Anesthesiology and Intensive Care Medicine, University Medical Center HamburgEppendorf, Martinistrasse 52, 20246 Hamburg, Germany e-mail: jwagner.science@gmail.com

The effects of advanced monitoring on hemodynamic management in critically ill patients: a pre and post questionnaire study

In critically ill patients, many decisions depend on accurate assessment of the hemodynamic status. We evaluated the accuracy of physicians’ conventional hemodynamic assessment and the impact that additional advanced monitoring had on therapeutic decisions. Physicians from seven European countries filled in a questionnaire in patients in whom advanced hemodynamic monitoring using transpulmonary thermodilution (PiCCO system; Pulsion Medical Systems SE, Feldkirchen, Germany) was going to be initialized as part of routine care. The collected information included the currently proposed therapeutic intervention(s) and a prediction of the expected transpulmonary thermodilution-derived variables. After transpulmonary thermodilution measurements, physicians recorded any changes that were eventually made in the original therapeutic plan. A total of 315 questionnaires pertaining to 206 patients were completed. The mean difference (±standard deviation; 95xa0% limits of agreement) between estimated and measured hemodynamic variables was −1.54 (±2.16; −5.77 to 2.69) L/min for the cardiac output (CO), −74 (±235; −536 to 387) mL/m2 for the global end-diastolic volume index (GEDVI), and −0.5 (±5.2; −10.6 to 9.7) mL/kg for the extravascular lung water index (EVLWI). The percentage error for the CO, GEDVI, and EVLWI was 66, 64, and 95xa0%, respectively. In 54xa0% of cases physicians underestimated the actual CO by more than 20xa0%. The information provided by the additional advanced monitoring led 33, 22, 22, and 13xa0% of physicians to change their decisions about fluids, inotropes, vasoconstrictors, and diuretics, respectively. The limited clinical ability of physicians to correctly assess the hemodynamic status, and the significant impact that more physiological information has on major therapeutic decisions, support the use of advanced hemodynamic monitoring in critically ill patients.

Ultrasound-guided central venous catheter placement: a structured review and recommendations for clinical practice

The use of ultrasound (US) has been proposed to reduce the number of complications and to increase the safety and quality of central venous catheter (CVC) placement. In this review, we describe the rationale for the use of US during CVC placement, the basic principles of this technique, and the current evidence and existing guidelines for its use. In addition, we recommend a structured approach for US-guided central venous access for clinical practice. Static and real-time US can be used to visualize the anatomy and patency of the target vein in a short-axis and a long-axis view. US-guided needle advancement can be performed in an out-of-plane and an in-plane technique. There is clear evidence that US offers gains in safety and quality during CVC placement in the internal jugular vein. For the subclavian and femoral veins, US offers small gains in safety and quality. Based on the available evidence from clinical studies, several guidelines from medical societies strongly recommend the use of US for CVC placement in the internal jugular vein. Data from survey studies show that there is still a gap between the existing evidence and guidelines and the use of US in clinical practice. For clinical practice, we recommend a six-step systematic approach for US-guided central venous access that includes assessing the target vein (anatomy andxa0vessel localization, vessel patency), using real-time US guidance for puncture of the vein, and confirming the correct needle, wire, and catheter position in the vein. To achieve the best skill level for CVC placement the knowledge from anatomic landmark techniques and the knowledgexa0from US-guided CVC placement need to be combined and integrated.

Personalized hemodynamic management

Purpose of review To describe personalized hemodynamic management of critically ill patients in the operating room and the ICU. Recent findings Several recent clinical studies have investigated different strategies for optimizing blood pressure (BP) and flow in the operating room and in the ICU. In the past, (early) goal-directed hemodynamic treatment strategies often used predefined fixed population-based ‘normal’ values as hemodynamic targets. Most hemodynamic variables, however, have large interindividual variability and are dependent on several biometric factors. Personalized BP management aims to set specific BP targets for a given patient taking into account blood flow autoregulation and any history of chronic hypertension. To optimize cardiac output and oxygen delivery, individualized hemodynamic management based on functional assessment of fluid responsiveness is used. Innovative noninvasive technologies now enable preoperative assessment of a patients personal normal hemodynamic values, which can then be targeted in the perioperative phase. In critically ill patients admitted to the ICU, adaptive multiparametric hemodynamic monitoring can help to personalize hemodynamic management. Summary Personalized hemodynamic management targets personal normal values of hemodynamic variables, which are adjusted to biometric data and adapted to the clinical situation (i.e., adequate values). This approach optimizes cardiovascular dynamics based on the patients personal hemodynamic profile.

Journal of clinical monitoring and computing 2016 end of year summary: monitoring cerebral oxygenation and autoregulation.

In the perioperative and critical care setting, monitoring of cerebral oxygenation (ScO2) and cerebral autoregulation enjoy increasing popularity in recent years, particularly in patients undergoing cardiac surgery. Monitoring ScO2 is based on near infrared spectroscopy, and attempts to early detect cerebral hypoperfusion and thereby prevent cerebral dysfunction and postoperative neurologic complications. Autoregulation of cerebral blood flow provides a steady flow of blood towards the brain despite variations in mean arterial blood pressure (MAP) and cerebral perfusion pressure, and is effective in a MAP range between approximately 50–150 mmHg. This range of intact autoregulation may, however, vary considerably between individuals, and shifts to higher thresholds have been observed in elderly and hypertensive patients. As a consequence, intraoperative hypotension will be poorly tolerated, and might cause ischemic events and postoperative neurological complications. This article summarizes research investigating technologies for the assessment of ScO2 and cerebral autoregulation published in the Journal of Clinical Monitoring and Computing in 2016.