Hypoxia in the pulmonary vein increases pulmonary vascular resistance independently of oxygen in the pulmonary artery

INTRODUCTION

Hypoxic pulmonary vasoconstriction (HPV) can be a challenging clinical problem. It is not fully elucidated where in the circulation the regulation of resistance takes place. It is often referred to as if it is in the arteries, but we hypothesized that it is in the venous side of the pulmonary circulation.

METHODS

In an open thorax model, pigs were treated with a veno-venous extra corporeal membrane oxygenator to either oxygenate or deoxygenate blood passing through the pulmonary vessels. At the same time the lungs were ventilated with extreme variations of inspired air from 5% to 100% oxygen, making it possible to make combinations of high and low oxygen content through the pulmonary circulation. A flow probe was inserted around the main pulmonary artery and catheters in the pulmonary artery and in the left atrium were used for pressure monitoring and blood tests. Under different combinations of oxygenation, pulmonary vascular resistance (PVR) was calculated.

RESULTS

With unchanged level of oxygen in the pulmonary artery and reduced inspired oxygen fraction lowering oxygen tension from 29 to 6.7 kPa in the pulmonary vein, PVR was doubled. With more extreme hypoxia PVR suddenly decreased. Combinations with low oxygenation in the pulmonary artery did not systematic influence PVR if there was enough oxygen in the inspired air and in the pulmonary veins.

DISCUSSION

The impact of hypoxia occurs from the alveolar level and forward with the blood flow. The experiments indicated that the regulation of PVR is mediated from the venous side.

An Ovine Model of Awake Veno-Arterial Extracorporeal Membrane Oxygenation

Background: Large animal models are developed to help understand physiology and explore clinical translational significance in the continuous development of veno-arterial extracorporeal membrane oxygenation (VA-ECMO) technology. The purpose of this study was to investigate the establishment methods and management strategies in an ovine model of VA-ECMO. Methods: Seven sheep underwent VA-ECMO support for 7 days by cannulation via the right jugular vein and artery. The animals were transferred into the monitoring cages after surgery and were kept awake after anesthesia recovery. The hydraulic parameters of ECMO, basic hemodynamics, mental state, and fed state of sheep were observed in real time. Blood gas analysis and activated clotting time (ACT) were tested every 6 h, while the complete blood count, blood chemistry, and coagulation tests were monitored every day. Sheep were euthanized after 7 days. Necropsy was performed and the main organs were removed for histopathological evaluation. Results: Five sheep survived and successfully weaned from ECMO. Two sheep died within 24-48 h of ECMO support. One animal died of fungal pneumonia caused by reflux aspiration, and the other died of hemorrhagic shock caused by bleeding at the left jugular artery cannulation site used for hemodynamic monitoring. During the experiment, the hemodynamics of the five sheep were stable. The animals stayed awake and freely ate hay and feed pellets and drank water. With no need for additional nutrition support or transfusion, the hemoglobin concentration and platelet count were in the normal reference range. The ECMO flow remained stable and the oxygenation performance of the oxygenator was satisfactory. No major adverse pathological injury occurred. Conclusions: The perioperative management strategies and animal care are the key points of the VA-ECMO model in conscious sheep. This model could be a platform for further research of disease animal models, pathophysiology exploration, and new equipment verification.

Levosimendan to Facilitate Weaning From Cardiorespiratory Support in Critically Ill Patients: A Meta-Analysis

Background: Cardiopulmonary support, as extracorporeal membrane oxygenation (ECMO) or mechanical ventilation (MV), is crucial for ICU patients. However, some of these patients are difficult to wean. Therefore, we aimed to assess the efficacy and safety of levosimendan in facilitating weaning from cardiorespiratory support in this patient population. Methods: We searched for potentially relevant articles in PubMed, Embase, China National Knowledge Infrastructure, Wanfang, and the Cochrane database from inception up to Feb 30, 2021. Studies focusing on weaning data in MV/ECMO adult patients who received levosimendan compared to controls were included. We used the Cochrane risk of bias tool or the Newcastle-Ottawa Quality Assessment Scale to evaluate the study quality. The primary outcome was the weaning rate from MV/ECMO. Secondary outcomes were mortality, duration of MV, and ICU stay. Subgroup analysis, sensitivity analysis, and publication bias were also conducted. Results: Eighteen studies with 2,274 patients were included. The quality of the included studies was low to moderate. Overall, levosimendan effectively improved weaning rates from MV/ECMO [odds ratio (OR) = 2.32; 95%CI, 1.60-3.36; P < 0.00001, I 2 = 68%]. Subgroup analyses confirmed the higher successful weaning rates in ventilated patients with low left ventricular ejection fractions (OR = 4.06; 95%CI, 2.16-7.62), patients with ECMO after cardiac surgery (OR = 2.04; 95%CI, 1.25-3.34), and patients with ECMO and cardiogenic shock (OR = 1.98; 95%CI, 1.34-2.91). However, levosimendan showed no beneficial effect on patients with MV weaning difficulty (OR = 2.28; 95%CI, 0.72-7.25). Additionally, no differences were found concerning the secondary outcomes between the groups. Conclusions: Levosimendan therapy significantly increased successful weaning rates in patients with cardiopulmonary support, especially patients with combined cardiac insufficiency. Large-scale, well-designed RCTs will be needed to define the subgroup of patients most likely to benefit from this strategy.

A novel strategy for cardiopulmonary support during lung transplantation

Contemporary modalities for cardiopulmonary support during lung transplantation include traditional cardiopulmonary bypass (CPB) and venoarterial extracorporeal membrane oxygenation (VA-ECMO). While highly effective, both are associated with morbidities such as arteriopathy and bleeding diathesis. In this report, we describe a novel approach for cardiopulmonary support during double lung transplantation in a patient with end-stage lung disease, pulmonary hypertension and moderate right ventricle (RV) dysfunction, using a percutaneous dual lumen cannula placed via the jugular vein which allowed us to achieve both RV bypass and membrane oxygenation. The cannula was left in place to provide ongoing RV support and the patient was successfully decannulated at bedside on post-operative day (POD) 2. Lack of arterial cannulation, percutaneous access, and bedside decannulation are benefits of this strategy, rendering this approach a useful addition to the armamentarium for CPB techniques in lung transplantation.

Traumatic ventricular septal defect and flail tricuspid valve: successful management by an extracorporeal membrane oxygenator-supported hybrid approach

We report the successful management of a critically ill patient with a traumatic ventricular septal defect (VSD) and flail tricuspid valve sustained in a motorcycle accident. Multiple orthopedic injuries prevented emergency cardiac surgery. The patient was stabilized by venous arterial extracorporeal membrane oxygenator support which allowed initial orthopedic repair. Repair of his cardiac injuries was then accomplished using a hybrid approach of percutaneous VSD closure using an Amplatzer post myocardial infarction VSD occluder which was also coil embolized followed by surgical tricuspid valve replacement.

Novel multi-functional life support system

Concepts of cardiopulmonary support (CPS), extracorporeal membrane oxygenation (ECMO), and ventricular support (VS) have been thoroughly studied and refined. These perfusion adjuncts often require multiple devices, skill sets, and significant financial burden to purchase, maintain, deploy, and use. We describe a novel system that is rapidly deployable, user-friendly, portable, safe, and economical. Over a 1-year period we have used a multi-functional life support system (MLS) in the cardiac catheterization laboratory, cardiovascular intensive care unit, and cardiac surgical suites. Further, we have conducted multiple transports within the hospital and one to an alternate facility. Applications have included ECMO, cardiopulmonary resuscitation-supported cardiogenic shock, high risk percutaneous coronary intervention (PCI), valvuloplasty, right ventricular assist device transition to ECMO post cardiotomy, left ventricular assist device transition to ECMO, ventricular septal defect closure, and ECMO transition to conventional cardiopulmonary bypass (CPB). Duration of support has ranged from approximately 39 minutes to several days.

KEYWORDS

extracorporeal membrane oxygenation (ECMO), percutaneous ventricular assist device, cardiopulmonary support, portable cardiopulmonary life support, ventricular assist.

Transport of critically ill children on cardiopulmonary support assistance

OBJECTIVE

To report two patients helicopter transport on mechanical cardiopulmonary support to a transplant center.

SETTING

Cardiac intensive care unit (CICU) and transport helicopter.

PATIENTS

A 9 kg and 22 kg children who suffer cardiac deterioration needing air transport on mechanical cardiopulmonary support.

INTERVENTIONS AND RESULTS

CPS was initiated to support these patients failing cardiac function. Transport on CPS of these two patients to a transplant institution was accomplished after determining that heart transplantation would be their more likely chance for recovery.

CONCLUSION

A cardiac deterioration event that will lead to the need for heart transplantation can be acute and sudden sparing no time for early referral to a transplant center. It is necessary for heart centers to have a plan of action to provide inter-hospital transport on cardiopulmonary support (CPS). This protocol can involve transport by the referral institution, the receiving institution or a third institution.

In vitro characterization and performance testing of the ension pediatric cardiopulmonary assist system

In the last 40 years, mechanical circulatory support devices have become an effective option for the treatment of end-stage heart failure in adults. Few possibilities, however, are available for pediatric cardiopulmonary support. Ension Inc. (Pittsburgh, PA) is developing a pediatric cardiopulmonary assist system (pCAS) intended to address the limitations of existing devices used for this patient population. The pCAS device is an integrated unit containing an oxygenator and pump within a single casing, significantly reducing the size and blood-contacting surface area in comparison to current devices. Prototype pCAS devices produce appropriate flows and pressures while minimizing priming volume and preparation time. The pCAS was tested on a mock circulation designed to approximate the hemodynamic parameters of a small infant using a 10-Fr. extracorporeal membrane oxygenation inflow cannula and an 8-Fr. extracorporeal membrane oxygenation outflow cannula. Revision 4 of the device provided a flow rate of 0.42 L/min at 6,500 RPM. Revision 5, featuring improved impeller and diffuser designs, provided a flow rate of 0.57 L/min at 5,000 RPM. The performance tests indicate that for this cannulae combination, the pCAS pump is capable of delivering sufficient flows for patients <5 kg.