Pulmonary hypertension attenuates the dynamic preload indicators increase during experimental hypovolemia

Rodent models of pulmonary embolism and chronic thromboembolic pulmonary hypertension

Pulmonary embolism (PE) is the third most prevalent cardiovascular disease. It is associated with high in-hospital mortality and the development of acute and chronic complications. New approaches aimed at improving the prognosis of patients with PE are largely dependent on reliable animal models. Mice, rats, hamsters, and rabbits, are currently most commonly used for PE modeling because of their ethical acceptability and economic feasibility. This article provides an overview of the main approaches to PE modeling, and the advantages and disadvantages of each method. Special attention is paid to experimental endpoints, including morphological, functional, and molecular endpoints. All approaches to PE modeling can be broadly divided into three main groups: 1) induction of thromboembolism, either by thrombus formation in vivo or by injection of in vitro prepared blood clots; 2) introduction of particles of non-thrombotic origin; and 3) surgical procedures. The choice of a specific model and animal species is determined based on the objectives of the study. Rodent models of chronic thromboembolic pulmonary hypertension (CTEPH), which is the most devastating complication of PE, are also described. CTEPH models are especially challenging because of insufficient knowledge about the pathogenesis and high fibrinolytic activity of rodent plasma. The CTEPH model should demonstrate a persistent increase in pulmonary artery pressure and stable reduction of the vascular bed due to recurrent embolism. Based on the analysis of available evidence, one might conclude that currently, there is no single optimal method for modeling PE and CTEPH.

Noninvasive assessment of fluid responsiveness for emergency abdominal surgery in dogs with pulmonary hypertension: Insights into high-risk companion animal anesthesia

Objective

Optimizing cardiac stroke volume during high-risk surgical anesthesia is of particular interest with regard to a therapeutic target to reduce the incidence of postoperative complications. However, intensive fluid management in critically ill small animals with pulmonary hypertension (PH) has been empirically performed, and thus it can be challenging. Stroke volume variation (SVV) has been used as a dynamic preload predictor of fluid responsiveness. We hypothesized that if SVV exhibited robust reliability in the setting of hemodynamically unstable condition, it would provide more precise information on fluid resuscitation to translate it into veterinary anesthesia. Thus the aim of this study was to investigate the utility of SVV measured by the electrical velocimetry (EV) method for predicting fluid responsiveness in dogs with PH.

Methods

Sixteen dogs undergoing emergency abdominal surgery and diagnosed with PH secondary to myxomatous mitral valve disease (MMVD) on preoperative transthoracic echocardiogram were included. Dogs were randomly assigned to 2 groups with and without inotropic cardiac support with dobutamine. Hemodynamic measurements including stroke volume and SVV derived from the EV device were performed under general anesthesia before (baseline) and after surgery (fluid challenge with a colloid solution defined by a SV increase of ≥ 10%).

Results

In both groups, SVV elevated significantly after abdominal surgery compared with baseline. In dobutamine infused group, the SVV values decreased significantly after fluid challenge (P < 0.05) with a greater number of responders than saline infused control group (P < 0.01). Receiver operating curve analysis of SVV confirmed high positive predictive value for dogs during dobutamine infusion (P < 0.05; cut-off value of 15%; specificity 90%, sensitivity 82%).

Conclusions

Noninvasive EV monitoring may be useful for the prediction of fluid responsiveness in critically ill dogs with left-sided heart failure-related PH. This normalization of dynamic preload indices, which could be achieved more precisely under inotropic support, may prevent further detrimental consequence of fluid loading.

End-Expiratory Occlusion Test During Increase of Vasomotor Tone in a Rabbit Model of Hemorrhage

End-expiratory occlusion test (EEOT) has been proposed as a preload responsiveness test that overcomes several limitations of pulse pressure (PPV) and stroke volume (SVV) variations. We compared the ability of EEOT versus SVV and PPV to predict fluid responsiveness during the increase of the vasomotor tone in a rabbit model of hemorrhage. Ten rabbits were anesthetized, paralyzed, and mechanically ventilated during basal load (BL), after progressive blood withdrawal (BW), and after volume replacement. Other two sets of data were obtained during vasomotor increase by phenylephrine (PHE) infusion in BL and BW. We estimated the change of stroke volume (∆SV_EEOT) and aortic flow (∆AoF_EEOT) during the EEOT. PPV and SVV were obtained by the variation of beat-to-beat PP and SV, respectively. Baseline PPV, SVV, ∆SV_EEOT, and ∆AoF_EEOT increased significantly after BW, with a decrease of aortic flow (P < 0.05). PHE induced a significant decrease of PPV and SVV, but without affecting ∆SV_EEOT, and ∆AoF_EEOT. We conclude that ∆SV and ∆AoF during EEOT kept the ability to predict fluid responsiveness during PHE infusion in a rabbit hemorrhage model. This result may suggest the advantage of EEOT with respect to SVV and PPV in predicting fluid responsiveness during vasomotor tone increase.

Acute Right Ventricular Dysfunction in Intensive Care Unit

The role of the left ventricle in ICU patients with circulatory shock has long been considered. However, acute right ventricle (RV) dysfunction causes and aggravates many common critical diseases (acute respiratory distress syndrome, pulmonary embolism, acute myocardial infarction, and postoperative cardiac surgery). Several supportive therapies, including mechanical ventilation and fluid management, can make RV dysfunction worse, potentially exacerbating shock. We briefly review the epidemiology, pathophysiology, diagnosis, and recommendations to guide management of acute RV dysfunction in ICU patients. Our aim is to clarify the complex effects of mechanical ventilation, fluid therapy, vasoactive drug infusions, and other therapies to resuscitate the critical patient optimally.