Noninvasive Assessment of Cardiac Output: Accuracy and Precision of the Closed-Circuit Acetylene Rebreathing Technique for Cardiac Output Measurement.

Background Accurate assessment of cardiac output is critical to the diagnosis and management of various cardiac disease states; however, clinical standards of direct Fick and thermodilution are invasive. Noninvasive alternatives, such as closed-circuit acetylene (C2H2) rebreathing, warrant validation. Methods and Results We analyzed 10 clinical studies and all available cardiopulmonary stress tests performed in our laboratory that included a rebreathing method and direct Fick or thermodilution. Studies included healthy individuals and patients with clinical disease. Simultaneous cardiac output measurements were obtained under normovolemic, hypovolemic, and hypervolemic conditions, along with submaximal and maximal exercise. A total of 3198 measurements in 519 patients were analyzed (mean age, 59 years; 48% women). The C2H2 method was more precise than thermodilution in healthy individuals with half the typical error (TE; 0.34 L/min [r=0.92] and coefficient of variation, 7.2%) versus thermodilution (TE=0.67 [r=0.70] and coefficient of variation, 13.2%). In healthy individuals during supine rest and upright exercise, C2H2 correlated well with thermodilution (supine: r=0.84, TE=1.02; exercise: r=0.82, TE=2.36). In patients with clinical disease during supine rest, C2H2 correlated with thermodilution (r=0.85, TE=1.43). C2H2 was similar to thermodilution and nitrous oxide (N2O) rebreathing technique compared with Fick in healthy adults (C2H2 rest: r=0.85, TE=0.84; C2H2 exercise: r=0.87, TE=2.39; thermodilution rest: r=0.72, TE=1.11; thermodilution exercise: r=0.73, TE=2.87; N2O rest: r=0.82, TE=0.94; N2O exercise: r=0.84, TE=2.18). The accuracy of the C2H2 and N2O methods was excellent (r=0.99, TE=0.58). Conclusions The C2H2 rebreathing method is more precise than, and as accurate as, the thermodilution method in a variety of patients, with accuracy similar to an N2O rebreathing method approved by the US Food and Drug Administration.

Back to Basics: Key Physical Examinations and Theories in Patients with Heart Failure.

Heart failure (HF) is a leading cause of hospitalization. Suitable pharmacologic management is critical. Distinct physical findings such as congestion and peripheral hypoperfusion need to be considered in selecting pharmacologic therapy. By applying the pretest probability and likelihood ratios of unique physical findings of HF to a Markov model, a definite posttest probability can be obtained. This article focuses on the findings of S3, jugular venous pressure, proportional pulse pressure, bendopnea, trepopnea, and various heart murmurs. Incorporating statistical precision in physical assessments, diagnoses of HF can be further refined, providing a sophisticated approach to evaluate patients hemodynamics status noninvasively.

Management of Common Cardiovascular Emergencies in Critically Ill Patients.

This article reviews treatment and management of common cardiovascular emergencies in critically ill patients, focusing on acute decompensated heart failure, cardiogenic shock, pulmonary embolism, and hypertensive crisis management with inotropes, vasopressors, diuretics, and antiarrhythmic drugs. Clinicians frequently come across challenging clinical scenarios, and there is a gap between evidence-based medicine and clinical practice. Inotropic and vasopressor agents are useful in the acute setting but must be weaned off or used as a bridge for mechanical circulation support devices. Clinicians should aim to lower complications by choosing medications with respect to comorbidities and close the gap between evidence-based medicine and clinical practice.