Spontaneous variability of cardiac output in ventilated critically ill patients

Precision and consistency of the passive leg raising maneuver for determining fluid responsiveness with bioreactance non-invasive cardiac output monitoring in critically ill patients and healthy volunteers

Objective

The passive leg raising (PLR) maneuver has become standard practice in fluid resuscitation. We aim to investigate the precision and consistency of the PLR for determining fluid responsiveness in critically ill patients and healthy volunteers using bioreactance non-invasive cardiac output monitoring (NiCOM™, Cheetah Medical, Inc., Newton Center, Massachusetts, USA).

Methods

This study is prospective, single-center, observational cohort with repeated measures in critically ill patients admitted to the medical intensive care unit and healthy volunteers at a tertiary academic medical center. Three cycles of PLR were performed, each at 20–30 minutes apart. Fluid responsiveness was defined as a change in stroke volume index (ΔSVI) > 10% with each PLR as determined by NiCOM™. Precision was the variability in ΔSVI after the 3 PLR’s, and determined by range, average deviation and standard deviation. Consistency was the same fluid responsiveness determination of “Yes” (ΔSVI > 10%) or “No” (ΔSVI ≤ 10%) for all 3 PLR’s.

Results

Seventy-five patients and 25 volunteers were enrolled. In patients, the precision was range of 17.2±13.3%, average deviation 6.5±4.0% and standard deviation 9.0±5.2%; and for volunteers, 17.4±10.3%, 6.6±3.8% and 9.0±6.7%, respectively. There was no statistical difference in the precision measurements between patients and volunteers. Forty-nine (65.3%) patients vs. twenty-four (96.0%) volunteers had consistent results, p < 0.01. Among those with consistent results, twenty-four (49.0%) patients and 24 (100%) volunteers were fluid responsive.

Conclusions

The precision and consistency of determining ΔSVI with NiCOM™ after PLR may have clinical implication if ΔSVI > 10% is the absolute cutoff to determine fluid responsiveness.

Normal Fluctuations in Pulmonary Artery Pressures and Cardiac Output in Patients with Severe Left Ventricular Dysfunction

Background: One barrier to accurate interpretation of changes in hemodynamic pressures and cardiac output is lack of data about what constitutes a normal fluctuation. Few investigators have examined normal fluctuations in these parameters and none have done so in patients with left ventricular dysfunction. Aims: To describe normal fluctuations in pulmonary artery pressures and cardiac output in patients with left ventricular dysfunction. Methods: Hemodynamically stable advanced heart failure patients ( N=39; 55±6 years old; 62% male) with left ventricular dysfunction (mean ejection fraction 22±5%) were studied. Cardiac output and pulmonary artery pressures were measured every 15 min for 2 h. Results: Mean±standard deviation fluctuations were as follows: pulmonary artery systolic pressure=7±4 mmHg; pulmonary artery diastolic pressure=6±3 mmHg; pulmonary capillary wedge pressure=5±3 mmHg; cardiac output=0.7±0.3 l/min. The coefficient of variation for fluctuations in pulmonary artery systolic pressure was 6.7%, in pulmonary artery diastolic pressure was 9.3%, in pulmonary capillary wedge pressure was 9.2%, and in cardiac output was 7.2%. Conclusions: Values that vary <8% for pulmonary artery systolic pressure, <11% for pulmonary artery diastolic pressure, <12% for pulmonary capillary wedge pressure, and <9% for cardiac output from baseline represent normal fluctuations in these parameters in patients with left ventricular dysfunction.

Biological variation of the cardiac index in patients with stable chronic heart failure: inert gas rebreathing compared with impedance cardiography

AIMS

In chronic heart failure (CHF), changes in cardiac function define the course of the disease. The cardiac index (CI) is the most adequate indicator of cardiac function. Interpretation of serial CI measurements, however, requires knowledge of the biological variation of CI. Because measurements of CI can be confounded by the clinical situation or the method applied, biological variation might be subject to the same confounders.

METHODS AND RESULTS

We prospectively included 50 CHF patients who met rigid criteria for clinical stability. CI was measured by both inert gas rebreathing (IGR) and impedance cardiography (ICG) in weekly intervals over 3 weeks-each measurement performed at rest (IGR_rest/ICG_rest) and during low-exercise 10 Watt pedalling (IGR_10W/ICG_10W). Intra-class correlation coefficients (ICCs), reference change values, and minimal important differences of CI were determined for IGR_rest, ICG_rest, IGR_10W, and ICG_10W. Impedance cardiography and IGR showed moderate agreement at rest (20% (6-36)) and good agreement at 10 Watt (-4% (-23-16)). Depending on time interval, measurement modality for CI, and mode, ICC ranged between 0.42 and 0.78, ICC values for IGR were lower than those for ICG. Reference change value ranged between 3 and 15%, and minimal important difference ranged between 0.2 and 0.5 L/min/m². Values for IGR were lower at rest and higher at 10 Watt than those for ICG.

CONCLUSION

Non-invasive measurements of CI are stable over time. Measurement modalities for CI, however, are not interchangeable. Biological variation is less pronounced when obtained by ICG. The influence of low-level exercise on stability of CI depends on the measurement modality.

Quantifying the volume of documented clinical information in critical illness

OBJECTIVES

The purpose of this study is to describe the volume of clinical information documented in critical illness, its relationship to the use of intensive care unit (ICU) technology, and changes over time.

METHODS

We performed a 6-year retrospective cohort study. Eligible patients were admitted to a university-affiliated pediatric ICU for at least 24 hours during the years 2000 to 2005. For each complete 24-hour period (midnight-midnight) that each patient was admitted to the ICU, we extracted the total number of items of documented clinical information and the use of 5 ICU technologies. For each day of the study, we calculated the total volume of documented information available to inform the daily ward round. A 2-level hierarchical linear model was used to analyze the primary outcome variable.

MAIN MEASUREMENTS AND RESULTS

There were 5623 admissions and 41202 complete patient-days studied. The median number of items of documented clinical data for each complete 24-hour period was 1348 (interquartile range, 1018-1664; mean, 1341). Significantly, more clinical information was documented about children who were ventilated with conventional ventilation (1483), children on inotropes or vasoactive medications (1685) and high-frequency oscillation (1726), and children receiving extracorporeal membrane oxygenation therapy (2354) or hemodialysis (1889) than children not in these categories (all P < .0001). The number of items documented per patient-day increased by 26% from 1165 in 2000 to 1471 items in 2005 (P < .0001). This finding was independent of ICU technology use.

CONCLUSIONS

A large and increasing volume of information was documented during the course of critical illness. More information was documented in patients receiving ICU technologies, suggesting that the volume of documented information is a marker of therapeutic intensity. It is also a source of workload and provides opportunity for error. Our findings underscore the importance of effective information management and communication strategies. Additional work is needed to evaluate the implications of current documentation practices for workload and quality of care.

Modelling in the study of interaction of Hemopump device and artificial ventilation

The aim of this work is to evaluate in different ventricular conditions the influence of joint mechanical ventilation (MV) and Hemopump assistance. To perform this study, we used a computer simulator of human cardiovascular system where the influence of MV was introduced changing thoracic pressure to positive values. The simulation confirmed that haemodynamic variables are highly sensitive to thoracic pressure changes. On the other hand, Hemopump assistance raises, among the others, mean aortic pressure, total cardiac output (left ventricular output flow plus Hemopump flow) and coronary flow. The simulation showed that the joint action of Hemopump and positive thoracic pressure diminishes these effects.

Report of a case series of ultra low-frequency oscillations in cardiac output in critically ill adults with sepsis, systemic inflammatory response syndrome, and multiple organ dysfunction syndrome

Healthy physiological systems exhibit irregular variability whereas diseased systems display decreased signal variability or greater regularity. The objective of this article is to report a case series of critically ill adults who displayed ultra low-frequency periodic sinusoidal oscillations in cardiac output (ULF-CO) that were discovered during a clinical study testing software for continuous physiological monitoring. Data were collected from 13 critically ill surgical and trauma patients who required continuous cardiac output monitoring. Physiologic data were collected from clinical monitors. The computerized time series of cases displaying CO oscillations were manually reviewed. Ten patients with sepsis or the systemic inflammatory response syndrome exhibited 18 episodes of ultra low-frequency periodic oscillations (ULF-CO) with frequencies ranging from 0.0028 to 0.000053 Hz (periods, 6 to 316 min). Intensive care unit mortality rate was 50%. The amplitude and coefficient of variation of cardiac output during ULF-CO ranged from 0.1-4.6 L and 3.9-14.3%, respectively. Duration of ULF-CO ranged from 4-108.1 h. ULF-CO could not be explained as a result of patterned artifact from measurement error or therapeutic intervention. ULF-CO may be a pathophysiologic marker that might serve the diagnosis, prognosis, and treatment of critical illness.

Enoximone in contrast to dobutamine improves hepatosplanchnic function in fluid-optimized septic shock patients

OBJECTIVE

To investigate the impact of dobutamine and enoximone on hepatosplanchnic perfusion and function in fluid-optimized septic patients.

DESIGN

Prospective, randomized, double-blinded interventional study.

SETTING

Intensive care unit of a university hospital.

PATIENTS

Forty-eight septic shock patients were examined within 12 hrs after onset of septic shock. Patients were conventionally resuscitated, achieving an optimal pulmonary artery occlusion pressure at which the left ventricular stroke work was on the maximal plateau. Liver blood flow was estimated by venous suprahepatic catheterization using the continuous indocyanine green infusion technique. Microsomal liver function was assessed by the plasma appearance of monoethylglycinexylidide, and release of hepatic tumor necrosis factor-alpha (TNF-alpha) was measured to estimate the severity of hepatic ischemia-reperfusion syndrome.

INTERVENTIONS

Patients were randomly treated with dobutamine or enoximone. Within the first 10 hrs after baseline measurements, the dosage was increased until no further increase in the left ventricular stroke work index occurred. Then, positive inotropes were kept constant throughout the study.

MEASUREMENTS AND MAIN RESULTS

Measurements were performed at baseline and after 12 and 48 hrs after baseline measurements. Cardiac index, systemic oxygen delivery, systemic oxygen consumption, and liver blood flow increased significantly in both groups during treatment (p <.01) without a significant difference between groups. Fractional liver blood flow (liver blood flow/cardiac index) did not change in the enoximone group and showed a significant but only minor (median, 10%) decrease in the dobutamine group (p <.05 after 12 hrs and p <.01 after 48 hrs vs. baseline). After 12 hrs of enoximone treatment, monoethylglycinexylidide kinetics and hepatosplanchnic oxygen consumption demonstrated a significant increase (p <.05). The release of hepatic TNF-alpha after 12 hrs of dobutamine treatment was twice as high (p <.05) as during enoximone.

CONCLUSION

The increase in hepatosplanchnic oxygen consumption, together with an increased lignocaine metabolism and decreased release of hepatic TNF-alpha, indicates improved hepatosplanchnic function and antiinflammatory properties after 12 hrs of enoximone treatment. Therefore, if the inflammatory response should be attenuated in high-risk patients, administration of enoximone in fluid-optimized septic shock patients may be favorable compared with dobutamine.