Interactions between extracorporeal support and the cardiopulmonary system

Comparison of mechanical resuscitation by an LV Impella device to extracorporeal resuscitation using VAECMO in a large animal model

Extracorporeal cardiopulmonary resuscitation (ECPR) is an effective treatment for cardiac arrest (CA). Percutaneous left ventricular (LV) assist devices such as the Impella ECP (intravascular CPR [ICPR]) have been proposed as a less invasive alternative. The aim of this study was to explore the haemodynamic differences between ECPR and ICPR using a large animal model of electrically induced CA. Fourteen juvenile female German landrace pigs (72.4 ± 9.8 kg) were subjected to electrically induced CA for 5 mins followed by either ECPR (veno-arterial extracorporeal membrane oxygenation [VA-ECMO]) or ICPR (Impella ECP). Haemodynamic parameters and echocardiographic ventricular function indicators were monitored. Mechanical circulatory support (MCS) was continued until five hours after the return of spontaneous circulation (ROSC), when the devices were removed. Resuscitation outcomes and the haemodynamic effects of ECPR and ICPR were compared. The cannulation time for ECMO (469 ± 129 s) was significantly longer than the time for Impella device implantation (153 ± 64 s, p < 0.001). ECPR facilitated ROSC in 6/6 animals, whereas ICPR facilitated ROSC in 6/8 animals (p = 0.19). Echocardiography revealed no difference in LV or right ventricular (RV) dysfunction between the ECPR- and ICPR-treated animals after resuscitation (LV-global longitudinal strain [GLS] 3 h post-ROSC: ICPR: - 16.5 ± 5.6% vs. ECPR: - 13.7 ± 5.9%, p = 0.99; RV-GLS 3 h post-ROSC: ICPR: - 15.9 ± 3.3% vs. ECPR: - 17.3 ± 10.6%, p = 0.99). MCS using VA-ECMO and the Impella device both provided effective haemodynamic support during CA and post-ROSC in this large animal model. Despite LV unloading conferring a hypothetical advantage for ICPR, no significant differences in myocardial recovery were observed.

Optimising fluid therapy during venoarterial extracorporeal membrane oxygenation: current evidence and future directions

Venoarterial extracorporeal membrane oxygenation (VA-ECMO) offers an immediate and effective mechanical cardio-circulatory support for critically ill patients with refractory cardiogenic shock or selected refractory cardiac arrest. As fluid therapy is routinely performed as a component of initial hemodynamic resuscitation of ECMO supported patients, this narrative review intends to summarize the rationale and the evidence on the fluid resuscitation strategy in terms of fluid type and dosing, the impact of fluid balance on outcomes and fluid responsiveness assessment in VA-ECMO patients. Several observational studies have shown a deleterious impact of positive fluid balance on survival and renal outcomes. With regard to the type of crystalloids, further studies are needed to evaluate the safety and efficacy of saline versus balanced solutions in terms of hemodynamic stability, renal outcomes and survival in VA-ECMO setting. The place and the impact of albumin replacement, as a second-line option, should be investigated. During VA-ECMO run, the fluid management approach could be divided into four phases: rescue or salvage, optimization, stabilization, and evacuation or de-escalation. Echocardiographic assessment of stroke volume changes following a fluid challenge or provocative tests is the most used tool in clinical practice to predict fluid responsiveness. This review underscores the need for high-quality evidence regarding the optimal fluid strategy and the choice of fluid type in ECMO supported patients. Pending specific data, fluid therapy needs to be personalized and guided by dynamic hemodynamic approach coupled to close monitoring of daily weight and fluid balance in order to provide adequate ECMO flow and tissue perfusion while avoiding harmful effects of fluid overload.

Mechanisms maintaining right ventricular contractility-to-pulmonary arterial elastance ratio in VA ECMO: a retrospective animal data analysis of RV-PA coupling

BACKGROUND

To optimize right ventricular-pulmonary coupling during veno-arterial (VA) ECMO weaning, inotropes, vasopressors and/or vasodilators are used to change right ventricular (RV) function (contractility) and pulmonary artery (PA) elastance (afterload). RV-PA coupling is the ratio between right ventricular contractility and pulmonary vascular elastance and as such, is a measure of optimized crosstalk between ventricle and vasculature. Little is known about the physiology of RV-PA coupling during VA ECMO. This study describes adaptive mechanisms for maintaining RV-PA coupling resulting from changing pre- and afterload conditions in VA ECMO.

METHODS

In 13 pigs, extracorporeal flow was reduced from 4 to 1 L/min at baseline and increased afterload (pulmonary embolism and hypoxic vasoconstriction). Pressure and flow signals estimated right ventricular end-systolic elastance and pulmonary arterial elastance. Linear mixed-effect models estimated the association between conditions and elastance.

RESULTS

At no extracorporeal flow, end-systolic elastance increased from 0.83 [0.66 to 1.00] mmHg/mL at baseline by 0.44 [0.29 to 0.59] mmHg/mL with pulmonary embolism and by 1.36 [1.21 to 1.51] mmHg/mL with hypoxic pulmonary vasoconstriction (p < 0.001). Pulmonary arterial elastance increased from 0.39 [0.30 to 0.49] mmHg/mL at baseline by 0.36 [0.27 to 0.44] mmHg/mL with pulmonary embolism and by 0.75 [0.67 to 0.84] mmHg/mL with hypoxic pulmonary vasoconstriction (p < 0.001). Coupling remained unchanged (2.1 [1.8 to 2.3] mmHg/mL at baseline; - 0.1 [- 0.3 to 0.1] mmHg/mL increase with pulmonary embolism; - 0.2 [- 0.4 to 0.0] mmHg/mL with hypoxic pulmonary vasoconstriction, p > 0.05). Extracorporeal flow did not change coupling (0.0 [- 0.0 to 0.1] per change of 1 L/min, p > 0.05). End-diastolic volume increased with decreasing extracorporeal flow (7.2 [6.6 to 7.8] ml change per 1 L/min, p < 0.001).

CONCLUSIONS

The right ventricle dilates with increased preload and increases its contractility in response to afterload changes to maintain ventricular-arterial coupling during VA extracorporeal membrane oxygenation.