Effect of the mechanical ventilatory cycle on thermodilution right ventricular volumes and cardiac output

Abstract

The purpose of this study was to evaluate right ventricular (RV) loading and cardiac output changes, by using the thermodilution technique, during the mechanical ventilatory cycle. Fifteen critically ill patients on mechanical ventilation, with 5 cmH(2)O of positive end-expiratory pressure, mean respiratory frequency of 18 breaths/min, and mean tidal volume of 708 ml, were studied with help of a rapid-response thermistor RV ejection fraction pulmonary artery catheter, allowing 5-ml room-temperature 5% isotonic dextrose thermodilution measurements of cardiac index (CI), stroke volume (SV) index, RV ejection fraction (RVEF), RV end-diastolic volume (RVEDV), and RV end-systolic volume (RVESV) indexes at 10% intervals of the mechanical ventilatory cycle. The ventilatory modulation of CI and RV volumes varied from patient to patient, and the interindividual variability was greater for the latter variables. Within patients also, RV volumes were modulated more by the ventilatory cycle than CI and SV index. Around a mean value of 3.95 +/- 1.18 l. min(-1). m(-2) (= 100%), CI varied from 87.3 +/- 5.2 (minimum) to 114.3 +/- 5.1% (maximum), and RVESV index varied between 61.5 +/- 17.8 and 149.3 +/- 34.1% of mean 55.1 +/- 17.9 ml/m(2) during the ventilatory cycle. The variations in the cycle exceeded the measurement error even though the latter was greater for RVEF and volumes than for CI and SV index. For mean values, there was an inspiratory decrease in RVEF and increase in RVESV, whereas a rise in RVEDV largely prevented a fall in SV index. We conclude that cyclic RV afterloading necessitates multiple thermodilution measurements equally spaced in the ventilatory cycle for reliable assessment of RV performance during mechanical ventilation of patients.

Continuously assessed right ventricular end-diastolic volume as a marker of cardiac preload and fluid responsiveness in mechanically ventilated cardiac surgical patients

“…Over recent years numerous studies have been performed to evaluate the usefulness of thermodilution-derived estimates of RVEDV index in a variety of clinical situations [17-20,25-28]. Several investigators emphasized the good correlation between RVEDV index and CI [17-20], suggesting that a volumetric assessment of cardiac preload may provide a more useful evaluation of ventricular filling than that offered by the assessment of cardiac filling pressures.…”

Pulmonary Hemodynamics and Right Heart Catheterization

“…While concern has been raised regarding safety and influence of sedatives used during catheterization on medical status and physiologic indices including loading conditions and inotropy, this is probably of minor concern unless liver and kidney functions are significantly impaired [57][58][59]. Nonetheless, it is becoming more common practice to avoid standard use of systemic sedation prior to or during RHC.…”

Rechtsherzfunktion bei ARDS und maschineller Beatmung

“…Mechanische Beatmung mit Tidalvolumina zwischen 5 und 10 ml/kgKG ohne PEEP, Rechtsherzinsuffizienz und pulmonale Hyperinflation steigert den pulmonalarteriellen Widerstand um 12% [1], was in der Regel ohne Konsequenz für den suffizienten rechten Ventrikel bleibt. [8]. Inspiration erhöht die rechtsventrikuläre Nachlast, den endsystolischen Druck und das Volumen, während die Ejektionsfraktion fällt [9].…”

“…Inspiration erhöht die rechtsventrikuläre Nachlast, den endsystolischen Druck und das Volumen, während die Ejektionsfraktion fällt [9]. Diastolisch sinkt das Volumen bei unverändertem oder steigendem Druck [8,9], um einen massiven Abfall des Schlagvolumens zu verhindern. Vor diesem Hintergrund erscheint Hochfrequenzventilation ein sinnvolles Prinzip in der Behandlung des Rechtsherzversagens [16].…”