Effects of inhaled nitric oxide and extracorporeal membrane oxygenation on pulmonary hemodynamics and lymph flow in oleic acid lung injury in sheep

Extracorporeal membrane oxygenation (ECMO) and the acute respiratory distress syndrome (ARDS): a systematic review of pre-clinical models

OBJECTIVES

Extracorporeal membrane oxygenation (ECMO) is an increasingly accepted means of supporting those with severe acute respiratory distress syndrome (ARDS). Given the high mortality associated with ARDS, numerous animal models have been developed to support translational research. Where ARDS is combined with ECMO, models are less well characterized. Therefore, we conducted a systematic literature review of animal models combining features of experimental ARDS with ECMO to better understand this situation.

DATA SOURCES

MEDLINE and Embase were searched between January 1996 and December 2018.

STUDY SELECTION

Inclusion criteria: animal models combining features of experimental ARDS with ECMO.

EXCLUSION CRITERIA

clinical studies, abstracts, studies in which the model of ARDS and ECMO has been reported previously, and studies not employing veno-venous, veno-arterial, or central ECMO.

DATA EXTRACTION

Data were extracted to fully characterize models. Variables related to four key features: (1) study design, (2) animals and their peri-experimental care, (3) models of ARDS and mechanical ventilation, and (4) ECMO and its intra-experimental management.

DATA SYNTHESIS

Seventeen models of ARDS and ECMO were identified. Twelve were published after 2009. All were performed in large animals, the majority (n = 10) in pigs. The median number of animals included in each study was 17 (12-24), with a median study duration of 8 h (5-24). Oleic acid infusion was the commonest means of inducing ARDS. Most models employed peripheral veno-venous ECMO (n = 12). The reporting of supportive measures and the practice of mechanical ventilation were highly variable. Descriptions of ECMO equipment and its management were more complete.

CONCLUSION

A limited number of models combine the features of experimental ARDS with ECMO. Among those that do, there is significant heterogeneity in both design and reporting. There is a need to standardize the reporting of pre-clinical studies in this area and to develop best practice in their design.

Passive leg raising can predict fluid responsiveness in patients placed on venovenous extracorporeal membrane oxygenation

Introduction

In ICUs, fluid administration is frequently used to treat hypovolaemia. Because volume expansion (VE) can worsen acute respiratory distress syndrome (ARDS) and volume overload must be avoided, predictive indicators of fluid responsiveness are needed. The purpose of this study was to determine whether passive leg raising (PLR) can be used to predict fluid responsiveness in patients with ARDS treated with venovenous extracorporeal membrane oxygenation (ECMO).

Methods

We carried out a prospective study in a university hospital surgical ICU. All patients with ARDS treated with venovenous ECMO and exhibiting clinical and laboratory signs of hypovolaemia were enrolled. We measured PLR-induced changes in stroke volume (ΔPLRSV) and cardiac output (ΔPLRCO) using transthoracic echocardiography. We also assessed PLR-induced changes in ECMO pump flow (ΔPLRPO) and PLR-induced changes in ECMO pulse pressure (ΔPLRPP) as predictors of fluid responsiveness. Responders were defined by an increase in stroke volume (SV) > 15% after VE.

Results

Twenty-five measurements were obtained from seventeen patients. In 52% of the measurements (n = 13), SV increased by > 15% after VE (responders). The patients' clinical characteristics appeared to be similar between responders and nonresponders. In the responder group, PLR significantly increased SV, cardiac output and pump flow (P < 0.001). ΔPLRSV values were correlated with VE-induced SV variations (r² = 0.72, P = 0.0001). A 10% increased ΔPLRSV predicted fluid responsiveness with an area under the receiver operating characteristic curve (AUC) of 0.88 ± 0.07 (95% confidence interval (CI₉₅): 0.69 to 0.97; P < 0.0001), 62% sensitivity and 92% specificity. On the basis of AUCs of 0.62 ± 0.11 (CI₉₅: 0.4 to 0.8; P = 0.31) and 0.53 ± 0.12 (CI₉₅: 0.32 to 0.73, P = 0.79), respectively, ΔPLRPP and ΔPLRPO did not predict fluid responsiveness.

Conclusions

In patients treated with venovenous ECMO, a > 10% ΔPLRSV may predict fluid responsiveness. ΔPLRPP and ΔPLRPO cannot predict fluid responsiveness.

Effects of inhaled aerosolized iloprost and inhaled NO on pulmonary circulation and edema formation in ovine lung injury

Although inhaled NO (iNO) has been shown to lower pulmonary pressures and edema accumulation in experimental acute lung injury, its clinical use has been questioned because of a lack of improvement in outcome, rebound phenomena, and potential toxicity. We investigated the effects of aerosolized iloprost, a stable prostacyclin analogue, compared with iNO on pulmonary pressures and lung edema in 20 female sheep with oleic acid lung injury. The most effective dose of iloprost was determined in healthy animals before the experiment. Anesthetized and ventilated sheep received a central venous oleic acid infusion and were continuously infused with Ringer lactate to achieve a positive fluid balance (5 mL.kg(-1).h(-1)). In the iNO group (n = 6), iNO (20 ppm) was administered continuously for 8 h. Animals in the iloprost group (n = 6) received aerosolized iloprost (40 microg 2 h(-1)). Animals in the control group (n = 6) had no further intervention. Oleic acid infusion was associated with impaired oxygenation, pulmonary hypertension, and lung edema in all groups. Although iNO significantly decreased pulmonary vascular resistance index, effective pulmonary capillary pressure, and extravascular lung water index, these parameters were unaffected by iloprost. Oxygenation index (Pao2/Fio2) increased significantly both during NO and iloprost inhalation but also tended to improve in the control group over time. In contrast to iNO, the investigated dose of iloprost was ineffective to attenuate acute lung injury-induced changes in pulmonary hemodynamics and lung edema in this experimental model.