Bench-to-bedside review: The importance of the precision of the reference technique in method comparison studies - with specific reference to the measurement of cardiac output

Bland-Altman analysis is used for assessing agreement between two measurements of the same clinical variable. In the field of cardiac output monitoring, its results, in terms of bias and limits of agreement, are often difficult to interpret, leading clinicians to use a cutoff of 30% in the percentage error in order to decide whether a new technique may be considered a good alternative. This percentage error of ± 30% arises from the assumption that the commonly used reference technique, intermittent thermodilution, has a precision of ± 20% or less. The combination of two precisions of ± 20% equates to a total error of ± 28.3%, which is commonly rounded up to ± 30%. Thus, finding a percentage error of less than ± 30% should equate to the new tested technique having an error similar to the reference, which therefore should be acceptable. In a worked example in this paper, we discuss the limitations of this approach, in particular in regard to the situation in which the reference technique may be either more or less precise than would normally be expected. This can lead to inappropriate conclusions being drawn from data acquired in validation studies of new monitoring technologies. We conclude that it is not acceptable to present comparison studies quoting percentage error as an acceptability criteria without reporting the precision of the reference technique

Clinical review: How to optimize management of high-risk surgical patients

For many patients optimal perioperative care may require little or no additional medical management beyond that given by the anaesthetist and surgeon. However, the continued existence of a group of surgical patients at high risk for morbidity and mortality indicates an ongoing need to identify such patients and deliver optimal care throughout the perioperative period. A group of patients exists in whom the risk for death and serious complications after major surgery is in excess of 20%. The risk is related mainly to the patient's preoperative physiological condition and, in particular, the cardiovascular and respiratory reserves. Cardiovascular management of the high-risk surgical patient is of particular importance. Once the medical management of underlying disease has been optimized, two principal areas remain: the use of haemodynamic goals to guide fluid and inotropic therapy, and perioperative β blockade. A number of studies have shown that the use of goal-directed haemodynamic therapy during the perioperative period can result in large reductions in morbidity and mortality. Some patients may also benefit from perioperative β blockade, which in selected patients has also been shown to result in significant mortality reductions. In this review a pragmatic approach to perioperative management is described, giving guidance on the identification of the high-risk patient and on the use of goal-directed haemodynamic therapy and β blockade

Cosmic Dust Collection Facility: Scientific objectives and programmatic relations

The science objectives are summarized for the Cosmic Dust Collection Facility (CDCF) on Space Station Freedom and these objectives are related to ongoing science programs and mission planning within NASA. The purpose is to illustrate the potential of the CDCF project within the broad context of early solar system sciences that emphasize the study of primitive objects in state-of-the-art analytical and experimental laboratories on Earth. Current knowledge about the sources of cosmic dust and their associated orbital dynamics is examined, and the results are reviewed of modern microanalytical investigations of extraterrestrial dust particles collected on Earth. Major areas of scientific inquiry and uncertainty are identified and it is shown how CDCF will contribute to their solution. General facility and instrument concepts that need to be pursued are introduced, and the major development tasks that are needed to attain the scientific objectives of the CDCF project are identified

Pharmacodynamic Analysis of a Fluid Challenge.

OBJECTIVE: This study aims to describe the pharmacodynamics of a fluid challenge over a 10-minute period in postoperative patients. DESIGN: Prospective observational study. SETTING: General and cardiothoracic ICU, tertiary hospital. PATIENTS: Twenty-six postoperative patients. INTERVENTION: Two hundred and fifty-milliliter fluid challenge performed over 5 minutes. Data were recorded over 10 minutes after the end of fluid infusion MEASUREMENTS AND MAIN RESULTS:: Cardiac output was measured with a calibrated LiDCOplus (LiDCO, Cambridge, United Kingdom) and Navigator (Applied Physiology, Sydney, Australia) to obtain the Pmsf analogue (Pmsa). Pharmacodynamics outcomes were modeled using a Bayesian inferential approach and Markov chain Monte Carlo estimation methods. Parameter estimates were summarized as the means of their posterior distributions, and their uncertainty was assessed by the 95% credible intervals. Bayesian probabilities for groups' effect were also derived. The predicted maximal effect on cardiac output was observed at 1.2 minutes (95% credible interval, -0.6 to 2.8 min) in responders. The probability that the estimated area under the curve of central venous pressure was smaller in nonresponders was 0.12. (estimated difference, -4.91 mm Hg·min [95% credible interval, -13.45 to 3.3 mm Hg min]). After 10 minutes, there is no evidence of a difference between groups for any hemodynamic variable. CONCLUSIONS: The maximal change in cardiac output should be assessed 1 minute after the end of the fluid infusion. The global effect of the fluid challenge on central venous pressure is greater in nonresponders, but not the change observed 10 minutes after the fluid infusion. The effect of a fluid challenge on hemodynamics is dissipated in 10 minutes similarly in both groups

Hemodynamic Effect of Different Doses of Fluids for a Fluid Challenge: A Quasi-Randomized Controlled Study.

OBJECTIVE: The objectives of this study are to determine what is the minimal volume required to perform an effective fluid challenge and to investigate how different doses of IV fluids in an fluid challenge affect the changes in cardiac output and the proportion of responders and nonresponders. DESIGN: Quasi-randomized controlled trial. SETTING: Cardiothoracic ICU, tertiary university hospital. PATIENTS: Eighty postcardiac surgery patients. INTERVENTION: IV infusion of 1, 2, 3, or 4 mL/Kg (body weight) of crystalloid over 5 minutes. MEASUREMENTS AND MAIN RESULTS: Mean systemic filling pressure measured using the transient stop-flow arm arterial-venous equilibrium pressure, arterial and central venous pressure, cardiac output (LiDCOplus; LiDCO, Cambridge, United Kingdom), and heart rate. The groups were well matched with respect to demographic and baseline physiologic variables. The proportion of responders increased from 20% in the group of 1 mL/kg to 65% in the group of 4 mL/kg (p = 0.04). The predicted minimal volume required for an fluid challenge was between 321 and 509 mL. Only 4 mL/Kg increases transient stop-flow arm arterial-venous equilibrium pressure beyond the limits of precision and was significantly associated with a positive response (odds ratio, 7.73; 95% CI, 1.78-31.04). CONCLUSION: The doses of fluids used for an fluid challenge modify the proportions of responders in postoperative patients. A dose of 4 mL/Kg increases transient stop-flow arm arterial-venous equilibrium pressure and reliably detects responders and nonresponders