Isoproterenol Improves Hemodynamics And Right Ventricle-Pulmonary Artery Coupling After Heart Transplantation

BACKGROUND

Right ventricular failure (RVF) is a major cause of early mortality after heart transplantation (HT). Isoproterenol has chronotropic, inotropic, and vasodilatory properties which might improve right ventricle function in this setting. We aimed to investigate the hemodynamic effects of isoproterenol on patients with post-HT RVF.

METHODS

We conducted a one-year retrospective observational study including patients receiving isoproterenol and dobutamine for early RVF after HT. A comprehensive multiparametric hemodynamic evaluation was performed successively at three times: no isoproterenol, low doses: 0.025 µg/kg/min and high doses: 0.05 µg/kg/min (henceforth respectively called no-iso, low-iso and high-iso).

RESULTS

From June 2022 to June 2023, 25 patients, median [IQR25-75] age 54 [38-61] years, were included. Before isoproterenol introduction, all patients received dobutamine and 15 (60%) were on veno-arterial extracorporeal membrane oxygenation. Isoproterenol significantly increased heart rate from 84 [77-99] (no-iso) to 91 [88-106] (low-iso) and 102 [90-122] bpm (high-iso, p<0.001). Similarly, cardiac index raised from 2.3 [1.4-3.1] to 2.7 [1.8-3.4] and 3 [1.9-3.7] l/min/m2 (p<0.001) with concomitant increase of indexed stroke volume (28 [17-34] to 31 [20-34] and 33 [23-35] mL/m2, p<0.05). Effective pulmonary arterial elastance and pressures were not modified by isoproterenol. Pulmonary vascular resistance tended to decrease from 2.9 (1.4-3.6) WU to 2.3 (1.3-3.5) WU, p=0.06. Right ventricular ejection fraction/systolic PAP evaluating RV-PA coupling increased after isoproterenol from 0.8 to 0.9 and 1 %.mmHg-1 (p=0.001).

CONCLUSIONS

In post-HT RVF, isoproterenol exhibits chronotropic and inotropic effects, thereby improving RV-PA coupling and resulting in a clinically relevant increase in the cardiac index.

Effects on Lung Gas Volume, Respiratory Mechanics and Gas Exchange of a Closed-Circuit Suctioning System during Volume- and Pressure-Controlled Ventilation in ARDS Patients

Mechanically ventilated patients periodically require endotracheal suctioning. There are conflicting data regarding the loss of lung gas volume caused by the application of a negative pressure by closed-circuit suctioning. The aim of this study was to evaluate the effects of suctioning performed by a closed-circuit system in ARDS patients during volume- or pressure-controlled ventilation. In this prospective crossover-design study, 18 ARDS patients were ventilated under volume and pressure control applied in random order. Gas exchange, respiratory mechanics and EIT-derived end-expiratory lung volume (EELV) before the suctioning manoeuvre and after 5, 15 and 30 min were recorded. The tidal volume and respiratory rate were similar in both ventilation modes; in volume control, the EELV decreased by 31 ± 23 mL, 5 min after the suctioning, but it remained similar after 15 and 30 min; the oxygenation, PaCO₂ and respiratory system elastance did not change. In the pressure control, 5 min after suctioning, EELV decreased by 35 (26–46) mL, the PaO₂/FiO₂ did not change, while PaCO₂ increased by 5 and 30 min after suctioning (45 (40–51) vs. 48 (43–52) and 47 (42–54) mmHg, respectively). Our results suggest minimal clinical advantages when a closed system is used in volume-controlled compared to pressure-controlled ventilation.

Different Inspiratory Flow Waveform during Volume-Controlled Ventilation in ARDS Patients

The most used types of mechanical ventilation are volume- and pressure-controlled ventilation, respectively characterized by a square and a decelerating flow waveform. Nowadays, the clinical utility of different inspiratory flow waveforms remains unclear. The aim of this study was to assess the effects of four different inspiratory flow waveforms in ARDS patients. Twenty-eight ARDS patients (PaO₂/FiO₂ 182 ± 40 and PEEP 11.3 ± 2.5 cmH₂O) were ventilated in volume-controlled ventilation with four inspiratory flow waveforms: square (SQ), decelerating (DE), sinusoidal (SIN), and trunk descending (TDE). After 30 min in each condition, partitioned respiratory mechanics and gas exchange were collected. The inspiratory peak flow was higher in the DE waveform compared to the other three waveforms, and in SIN compared to the SQ and TDE waveforms, respectively. The mean inspiratory flow was higher in the DE and SIN waveforms compared with TDE and SQ. The inspiratory peak pressure was higher in the SIN and SQ compared to the TDE waveform. Partitioned elastance was similar in the four groups; mechanical power was lower in the TDE waveform, while PaCO₂ in DE. No major effect on oxygenation was found. The explored flow waveforms did not provide relevant changes in oxygenation and respiratory mechanics.

A validation study of a continuous automatic measurement of the mechanical power in ARDS patients

The mechanical power (MP) is the energy delivered into the respiratory system over time. It can be computed as a direct measurement of the inspiratory area of the airway pressure and volume loop during the respiratory cycle or calculated by "power equations". The absence of a bedside computation limited its widespread use. Recently, it has been developed an automatic monitoring system inside of a mechanical ventilator.

PURPOSE

Our aim was to investigate the repeatability and the accuracy of the measured MP at different PEEP values and tidal volume compared with the calculated MP.

MATERIAL AND METHODS

MP was measured and calculated in sedated and paralyzed ARDS patients at low and high tidal volume, at 5-10-15 cmH₂O of PEEP both in volume and pressure-controlled ventilation. The same measurements were performed twice.

RESULTS

Fifty ARDS patients were enrolled. MP was measured and calculated for a total of 300 measurements. The bias and limits of agreement were 0.38 from -1.31 to 2.0 J/min. The measured and calculated MP were similar in each ventilatory condition.

CONCLUSIONS

The mechanical power measured by a new automatic real time system implemented in a mechanical ventilator was repeatable and accurate compared with the computed one.