Continuous Noninvasive Hemoglobin Monitoring Reflects the Development of Acute Hemodilution After Consecutive Fluid Challenges.

BACKGROUND: Consecutive fluid challenges (FCs) are frequently administered to maximize the stroke volume (SV) as part of a goal-directed therapy (GDT) strategy. However, fluid administration may also cause acute hemodilution that might lead to an actual paradoxical decrease in oxygen delivery (DO2). The aim of this study was to examine whether continuous noninvasive hemoglobin (SpHb) monitoring can be used to detect the development of acute hemodilution after graded fluid administration. METHODS: In 40 patients who underwent major vascular or gastrointestinal surgery, an FC, consisting of 250 mL colloid solution, was administered. When the SV increased by ≥10%, the FC was repeated up to a maximum of 3 times. Laboratory-measured hemoglobin concentrations (BHb), SpHb, SV, cardiac output (CO), and DO2 values were recorded after each FC. RESULTS: All 40 patients received the first FC, 32 patients received the second FC, and 20 patients received the third FC (total of 750 mL). Out of the 92 administered FCs, only 55 (60%) caused an increase in SV ≥10% ("responders"). The first and the second FCs were associated with a significant increase in the mean CO and DO2, while the mean SpHb and BHb decreased significantly. However, the third and last FC was associated with no statistical difference in CO and SV, a further significant decrease in mean SpHb and BHb, and a significant decrease in DO2 in these patients. Compared to their baseline values (T0), BHb and SpHb decreased by a mean of 5.3% ± 4.9% and 4.4% ± 5.2%, respectively, after the first FC (T1; n = 40), by 9.7% ± 8.4% and 7.9% ± 6.9% after the second FC (T2; n = 32), and by 14.5% ± 6.2% and 14.6% ± 5.7% after the third FC (T3; n = 20). Concordance rates between the changes in SpHb and in BHb after the administration of 250, 500, and 750 mL colloids were 83%, 90%, and 100%, respectively. CONCLUSIONS: Fluid loading aimed at increasing the SV and the DO2 as part of GDT strategy is associated with acute significant decreases in both BHb and SpHb concentrations. When the administration of an FC is not followed by a significant increase (≥10%) in the SV, the DO2 decreases significantly due to the development of acute hemodilution. Continuous noninvasive monitoring of SpHb does not reflect accurately absolute BHb values, but may be reliably used to detect the development of acute hemodilution especially after the administration of at least 500 mL of colloids.

Alternatives to the Swan-Ganz catheter.

While the pulmonary artery catheter (PAC) is still interesting in specific situations, there are many alternatives. A group of experts from different backgrounds discusses their respective interests and limitations of the various techniques and related measured variables. The goal of this review is to highlight the conditions in which the alternative devices will suffice and when they will not or when these alternative techniques can provide information not available with PAC. The panel concluded that it is useful to combine different techniques instead of relying on a single one and to adapt the "package" of interventions to the condition of the patient. As a first step, the clinical and biologic signs should be used to identify patients with impaired tissue perfusion. Whenever available, echocardiography should be performed as it provides a rapid and comprehensive hemodynamic evaluation. If the patient responds rapidly to therapy, either no additional monitoring or pulse wave analysis (allowing continuous monitoring in case potential degradation is anticipated) can be applied. If the patient does not rapidly respond to therapy or complex hemodynamic alterations are observed, pulse wave analysis coupled with TPTD is suggested.

The value of dynamic preload variables during spontaneous ventilation.

PURPOSE OF REVIEW: To discuss the physiological significance and clinical value of dynamic preload variables in spontaneously breathing patients. RECENT FINDINGS: Dynamic preload variables reflect the response of the cardiac output to a modification of preload and can therefore be used to assess fluid responsiveness. Continuous dynamic parameters that are calculated from the variations in the arterial and plethysmographic waveforms following a mechanical breath have been shown to predict fluid responsiveness much better than static preload parameters. These parameters are displayed on many patient monitors though their use is limited to mechanically ventilated patients. However, spontaneous breathing may also induce significant hemodynamic changes because of the repetitive negative swings in the pleural pressure. By better understanding the physiological basis of these changes, the same 'dynamic parameters' can be used to gain unique physiological insights during spontaneous breathing. These include the ability to identify and/or monitor respiratory rate, respiratory effort (e.g., patient-ventilator asynchrony), fluid responsiveness (to some degree), pulsus paradoxus (e.g. asthma, cardiac tamponade), and, importantly, upper airway obstruction. SUMMARY: Although originally intended to be used only during mechanical ventilation, 'dynamic parameters' may offer valuable clinical information in spontaneously breathing patients.

Hemodynamic monitoring in the era of evidence-based medicine.

Hemodynamic instability frequently occurs in critically ill patients. Pathophysiological rationale suggests that hemodynamic monitoring (HM) may identify the presence and causes of hemodynamic instability and therefore may allow targeting therapeutic approaches. However, there is a discrepancy between this pathophysiological rationale to use HM and a paucity of formal evidence (as defined by the strict criteria of evidence-based medicine (EBM)) for its use. In this editorial, we discuss that this paucity of formal evidence that HM can improve patient outcome may be explained by both the shortcomings of the EBM methodology in the field of intensive care medicine and the shortcomings of HM itself.

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.

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; 95 % 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/m(2) 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 95 %, respectively. In 54 % of cases physicians underestimated the actual CO by more than 20 %. The information provided by the additional advanced monitoring led 33, 22, 22, and 13 % 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.

Non-invasive monitoring of oxygen delivery in acutely ill patients: new frontiers.

Hypovolemia, anemia and hypoxemia may cause critical deterioration in the oxygen delivery (DO2). Their early detection followed by a prompt and appropriate intervention is a cornerstone in the care of critically ill patients. And yet, the remedies for these life-threatening conditions, namely fluids, blood and oxygen, have to be carefully titrated as they are all associated with severe side-effects when administered in excess. New technological developments enable us to monitor the components of DO2 in a continuous non-invasive manner via the sensor of the traditional pulse oximeter. The ability to better assess oxygenation, hemoglobin levels and fluid responsiveness continuously and simultaneously may be of great help in managing the DO2. The non-invasive nature of this technology may also extend the benefits of advanced monitoring to wider patient populations.

Perioperative cardiovascular monitoring of high-risk patients: a consensus of 12.

A significant number of surgical patients are at risk of intra- or post-operative complications or both, which are associated with increased lengths of stay, costs, and mortality. Reducing these risks is important for the individual patient but also for health-care planners and managers. Insufficient tissue perfusion and cellular oxygenation due to hypovolemia, heart dysfunction or both is one of the leading causes of perioperative complications. Adequate perioperative management guided by effective and timely hemodynamic monitoring can help reduce the risk of complications and thus potentially improve outcomes. In this review, we describe the various available hemodynamic monitoring systems and how they can best be used to guide cardiovascular and fluid management in the perioperative period in high-risk surgical patients.

Perioperative fluid therapy: a statement from the international Fluid Optimization Group.

BACKGROUND: Perioperative fluid therapy remains a highly debated topic. Its purpose is to maintain or restore effective circulating blood volume during the immediate perioperative period. Maintaining effective circulating blood volume and pressure are key components of assuring adequate organ perfusion while avoiding the risks associated with either organ hypo- or hyperperfusion. Relative to perioperative fluid therapy, three inescapable conclusions exist: overhydration is bad, underhydration is bad, and what we assume about the fluid status of our patients may be incorrect. There is wide variability of practice, both between individuals and institutions. The aims of this paper are to clearly define the risks and benefits of fluid choices within the perioperative space, to describe current evidence-based methodologies for their administration, and ultimately to reduce the variability with which perioperative fluids are administered. METHODS: Based on the abovementioned acknowledgements, a group of 72 researchers, well known within the field of fluid resuscitation, were invited, via email, to attend a meeting that was held in Chicago in 2011 to discuss perioperative fluid therapy. From the 72 invitees, 14 researchers representing 7 countries attended, and thus, the international Fluid Optimization Group (FOG) came into existence. These researches, working collaboratively, have reviewed the data from 162 different fluid resuscitation papers including both operative and intensive care unit populations. This manuscript is the result of 3 years of evidence-based, discussions, analysis, and synthesis of the currently known risks and benefits of individual fluids and the best methods for administering them. RESULTS: The results of this review paper provide an overview of the components of an effective perioperative fluid administration plan and address both the physiologic principles and outcomes of fluid administration. CONCLUSIONS: We recommend that both perioperative fluid choice and therapy be individualized. Patients should receive fluid therapy guided by predefined physiologic targets. Specifically, fluids should be administered when patients require augmentation of their perfusion and are also volume responsive. This paper provides a general approach to fluid therapy and practical recommendations.

Excessive variations in the plethysmographic waveform during spontaneous ventilation: an important sign of upper airway obstruction.

The respiratory variations in the plethysmographic (PLET) waveform of the pulse oximeter during mechanical ventilation can be automatically quantified as the PLET variation index (PVI(®)). Like other dynamic variables, the PVI may provide useful information about fluid responsiveness but only when the patient is receiving fully controlled mechanical ventilation with no spontaneous breathing activity. However, a growing number of monitors that automatically measure and display the values of the PVI and other dynamic variables are being introduced into clinical practice. Using these monitors in spontaneously breathing patients may cause inadequately trained personnel to make erroneous decisions or may eventually lead to a total disregard of dynamic parameters altogether. The aim of this study is to call attention to the fact that excessive variations in the PVI during spontaneous ventilation, termed sPVI, should not be regarded as artifactual since they may be an early important sign of upper airway obstruction (UAO). Among the monitor screen shots that were stored for educational purposes, I have identified 4 screen shots of patients who were clinically diagnosed as having significant UAO. In all instances, UAO was associated with prominent variations in the PLET waveform. These variations were calculated as the difference between the maximal and minimal amplitudes of the PLET signal divided by either the maximal amplitude (sPVI) or by the mean of the 2 values (ΔPOP). The ranges of the measured ΔPOP and sPVI values during UAO were 28% to 42% and 25% to 39%, respectively. These values are 2 to 3 times higher than the range of 9.5% to 15% that was repeatedly found as the best threshold for the identification of fluid responsiveness in mechanically ventilated patients. In 2 of these cases, simultaneously measured values of the pulse pressure variation were high as well (19% and 34%), while the calculated pulsus paradoxus was 28 and 40 mm Hg. In 2 cases, the analog signals of impedance plethysmography and capnography persisted, despite the presence of clinically significant UAO. It is, therefore, suggested that monitoring the sPVI may be of great clinical importance in spontaneously breathing patients who are susceptible to develop UAO.

Respiratory variations in the arterial pressure during mechanical ventilation reflect volume status and fluid responsiveness.

Optimal fluid management is one of the main challenges in the care of the critically ill. However, the physiological parameters that are commonly monitored and used to guide fluid management are often inadequate and even misleading. From 1987 to 1989 we published four experimental studies which described a method for predicting the response of the cardiac output to fluid administration during mechanical ventilation. The method is based on the analysis of the variations in the arterial pressure in response to a mechanical breath, which serves as a repetitive hemodynamic challenge. Our studies showed that the systolic pressure variation and its components are able to reflect even small changes in the circulating blood volume. Moreover, these dynamic parameters provide information about the slope of the left ventricular function curve, and therefore predict the response to fluid administration better than static preload parameters. Many new dynamic parameters have been introduced since then, including the pulse pressure (PPV) and stroke volume (SVV) variations, and various echocardiographic and other parameters. Though seemingly different, all these parameters are based on measuring the response to a predefined preload-modifying maneuver. The clinical usefulness of these 'dynamic' parameters is limited by many confounding factors, the recognition of which is absolutely necessary for their proper use. With more than 20 years of hindsight we believe that our early studies helped pave the way for the recognition that fluid administration should ideally be preceded by the assessment of "fluid responsiveness". The introduction of dynamic parameters into clinical practice can therefore be viewed as a significant step towards a more rational approach to fluid management.