Cyclic changes in right ventricular output impedance during mechanical ventilation

Abstract

In a context such as acute respiratory distress syndrome, where optimum tidal volume and airway pressure levels are debated, the present study was designed to differentiate the right ventricular (RV) consequences of increasing lung volume from those secondary to increasing airway pressure during tidal ventilation. The study was conducted by combined two-dimensional echocardiographic and Doppler studies in 10 patients requiring mechanical ventilation in the controlled mode because of acute respiratory failure. Continuous monitoring of airway pressure on echocardiographic and Doppler recordings provided accurate timing of each cardiac event during the respiratory cycle, with particular attention being paid to end-expiratory and end-inspiratory atrial diameters, RV dimensions, and pulmonary artery and tricuspid flow estimated by the velocity-time integral (PA(VTI) and T(VTI), respectively). At baseline, lung inflation during the inspiratory phase of mechanical ventilation produced a drop in PA(VTI) from 14.3 +/- 2.6 cm at end expiration to 11.3 +/- 2.1 cm at end inspiration. This drop occurred without reduction in right atrial diameter or in RV diastolic dimensions. It was not preceded but was followed by a decrease in T(VTI), thus confirming an increase in RV outflow impedance. Manipulation of tidal volume without changing airway pressure and manipulation of airway pressure without changing tidal volume demonstrated that tidal volume, but not airway pressure, was the main determinant factor of RV afterloading during mechanical ventilation.

Executive summary on the use of ultrasound in the critically ill: consensus report from the 3rd Course on Acute Care Ultrasound (CACU)

“…It has also been proposed to use the mean acceleration of the RV ejection flow in mechanically ventilated patients for ARDS [42]. The mean acceleration is the ratio between the maximal velocity of the RV ejection flow and the acceleration time.…”

“…Consequently, a decrease in the mean acceleration time is suggestive of a decrease in RV systolic function and an increase in RV afterload, as observed during tidal volume in some patients. Although new ultrasound techniques (speckle tracking) may analyse much more accurately the systolic function of the RV, this technique is still under evaluation [42].…”

Can Passive Leg Raising Be Considered the Gold Standard in Predicting Fluid Responsiveness?

“…Nevertheless, additional limitations for using "dynamic" parameters such as high heart rate-to-respiratory rate ratio, low total respiratory system compliance, and decreased tricuspid annular peak systolic velocity have not been specifically assessed in our study (2). As anticipated by Lakhal and colleagues, a substantial proportion of our patients (pulse pressure variation: n = 257 [61%]; respiratory variation of the maximal Doppler velocity in left ventricular outflow tract: n = 232 [55%]; respiratory variation of superior vena cava diameter: n = 310 [58%]; respiratory variation of inferior vena cava diameter: n = 217 [51%]) exhibited individual values of "dynamic" parameters within a range of uncertainty; the so-called "gray zone" (3). In these patients, we proposed using distinct cutoff values to optimize either the sensitivity when the benefit of giving fluids exceeds the risk or the specificity when the risk for volume overload exceeds the potential hemodynamic benefit (2).…”

Doppler Echocardiographic Changes in Respiratory Diseases

“…On the other hand; a normal heart size and normal systolic and diastolic function in a patient with pulmonary oedema would suggest Adult Respiratory Distress Syndrome (ARDS). Estimation of PA pressure and evaluation of RV function are needed in chronic respiratory failure (Vieillard-Baron et al 1999) Mechanical ventilation may cause potentially detrimental consequences for systemic venous return produced by an increase in pleural pressure. It also decreases RV after-load due to increased positive end expiratory presurre (PEEP), incresed lung volume or both.…”

“…TTE appears as a sensitive noninvasive method which accurately detects changes in central haemodynamics induced by changes in breathing pattern. It is a powerful tool to assess RV function, especially if acute cor pulmonale is a concern, as well as to estimate LV function (Vieillard-Baron et al 1999).…”