Active Expiration and the Measurement of Central Venous Pressure

Diagnostic value of an increase in central venous pressure during SBT for prediction of weaning failure in mechanically ventilated patients: A cross-sectional study

Background

Timely and successful extubation is an essential step forward in clinical practice to minimize complications of mechanical ventilation and unsuccessful weaning processes. Thus, research into predictive factors of weaning outcome to optimize spontaneous breathing trial (SBT) precision before extubation is critical in intensive care practices. In this study, we aimed to investigate the predictive factors of the weaning outcome before and during SBT in mechanically ventilated patients.

Methods

In this cross-sectional study, 159 mechanically ventilated patients who were eligible for SBT were enrolled. Of these patients, 140 had successful extubation, whereas the remainder failed. Each patient's PaCO2 and PaO2 levels, respiratory rate (RR), SpO2, mean arterial pressure (MAP), heart rate (HR), and central venous pressure (CVP) values at the start of SBT, 3 min later, and at the end of SBT were measured. These values, along with the patients' clinical characteristics, were then investigated to determine if there was any correlation between these variables and the weaning outcome.

Results

Our analysis revealed that increase in CVP, independent of hemoglobin (Hb) concentration, PaO2, SpO2, duration of mechanical ventilation (MV), length of intensive care unit (ICU) stay, and SBT process, as well as underlying disease, was positively correlated with extubation/weaning failure. While age, gender, vital signs (MAP, RR, and HR), sequential organ failure assessment (SOFA), and acute physiology and chronic health evaluation (APACHE) scores had no significant correlation with patients' extubation outcomes.

Conclusion

According to our findings, integrating CVP assessment into SBT besides routine indices measurement and monitoring can be considered for the prediction of weaning outcome in critically ill mechanically ventilated patients.

Effect of variability of central venous pressure values to prevent atrial fibrillation after coronary bypass grafting

BACKGROUND

Atrial fibrillation is an arrhythmia that results from abnormal depolarization of the atrium. Atrial fibrillation occurs in 5-40% of patients with cardiovascular bypass surgery, usually occurs on 2 to 4 days postoperatively. The aim of this study was Effect of variability of central venous pressure values to prevent atrial fibrillation after coronary bypass grafting.

METHODS

The present clinical trial study was performed on 150 patients undergoing cardiac surgery referred to Ayatollah Rohani Hospital of Babol. Patients were divided into 3 groups, with normal range pressure (8 to 12 mmHg), low pressure (less than 8), high pressure (greater than 12) based on central venous pressure measurements. Patients were evaluated every 4 hours to 72 hours for central venous pressure, AF incidence and urine output. Finally, the data are analyzed by spss statistical software.

RESULTS

In this study 79 (52.7%) patients were male and 71 (47.3%) were female. In examining changes in central venous pressure, the time effect also significantly increased central venous pressure. The results of independent t-test showed that the mean of central venous pressure changes in subjects with at day 16, second day at 16, 20, 24, third day at 4, 8, 12, 16, 20 and 24 hours Atrial fibrillation. Significantly more than those without atrialfibrillation (P<0.05).

CONCLUSION

In the study, central venous pressure changes the effect of time significantly increases the central venous pressure. Individuals with atrial fibrillation also had significantly greater central venous pressure changes than those without atrial fibrillation.

Early rise in central venous pressure during a spontaneous breathing trial: A promising test to identify patients at high risk of weaning failure?

Background

The spontaneous breathing trial (SBT) assesses the risk of weaning failure by evaluating some physiological responses to the massive venous return increase imposed by discontinuing positive pressure ventilation. This trial can be very demanding for some critically ill patients, inducing excessive physical and cardiovascular stress, including muscle fatigue, heart ischemia and eventually cardiac dysfunction. Extubation failure with emergency reintubation is a serious adverse consequence of a failed weaning process. Some data suggest that as many as 50% of patients that fail weaning do so because of cardiac dysfunction. Unfortunately, monitoring cardiovascular function at the time of the SBT is complex. The aim of our study was to explore if central venous pressure (CVP) changes were related to weaning failure after starting an SBT. We hypothesized that an early rise on CVP could signal a cardiac failure when handling a massive increase on venous return following a discontinuation of positive pressure ventilation. This CVP rise could identify a subset of patients at high risk for extubation failure.

Methods

Two-hundred and four mechanically ventilated patients in whom an SBT was decided were subjected to a monitoring protocol that included blinded assessment of CVP at baseline, and at 2 minutes after starting the trial (CVP-test). Weaning failure was defined as reintubation within 48-hours following extubation. Comparisons between two parametric or non-parametric variables were performed with student T test or Mann Whitney U test, respectively. A logistic multivariate regression was performed to determine the predictive value on extubation failure of usual clinical variables and CVP at 2-min after starting the SBT.

Results

One-hundred and sixty-five patients were extubated after the SBT, 11 of whom were reintubated within 48h. Absolute CVP values at 2-minutes, and the change from baseline (dCVP) were significantly higher in patients with extubation failure as compared to those successfully weaned. dCVP was an early predictor for reintubation (OR: 1.70 [1.31,2.19], p<0.001).

Conclusions

An early rise in CVP after starting an SBT was associated with an increased risk of extubation failure. This might represent a warning signal not captured by usual SBT monitoring and could have relevant clinical implications.

Heart-Lung interaction in spontaneous breathing subjects: the basics

Heart-lung interactions occur primarily because of two components of lung inflation, changes in pleural pressure and changes in transpulmonary pressure. Of these, changes in pleural pressure dominate during spontaneous breathing. Because the heart is surrounded by pleural pressure, during inspiration the environment of the heart falls relative to the rest of the body. This alters inflow into the right heart and outflow from the left heart. Alterations in transpulmonary pressure can alter the outflow from the right heart and the inflow to the left heart. These interactions are modified by the cardiac and respiratory frequency, ventricular function and magnitude of the respiratory efforts.