Invasive mechanical ventilation in patients with acute respiratory distress syndrome receiving extracorporeal support: a narrative review of strategies to mitigate lung injury.

Veno-venous extracorporeal membrane oxygenation is indicated in patients with acute respiratory distress syndrome and severely impaired gas exchange despite evidence-based lung protective ventilation, prone positioning and other parts of the standard algorithm for treating such patients. Extracorporeal support can facilitate ultra-lung-protective ventilation, meaning even lower volumes and pressures than standard lung-protective ventilation, by directly removing carbon dioxide in patients needing injurious ventilator settings to maintain sufficient gas exchange. Injurious ventilation results in ventilator-induced lung injury, which is one of the main determinants of mortality in acute respiratory distress syndrome. Marked reductions in the intensity of ventilation to the lowest tolerable levels under extracorporeal support may be achieved and could thereby potentially mitigate ventilator-induced lung injury and theoretically patient self-inflicted lung injury in spontaneously breathing patients with high respiratory drive. However, the benefits of this strategy may be counterbalanced by the use of continuous deep sedation and even neuromuscular blocking drugs, which may impair physical rehabilitation and impact long-term outcomes. There are currently a lack of large-scale prospective data to inform optimal invasive ventilation practices and how to best apply a holistic approach to patients receiving veno-venous extracorporeal membrane oxygenation, while minimising ventilator-induced and patient self-inflicted lung injury. We aimed to review the literature relating to invasive ventilation strategies in patients with acute respiratory distress syndrome receiving extracorporeal support and discuss personalised ventilation approaches and the potential role of adjunctive therapies in facilitating lung protection.

Measurement of extravascular lung water to diagnose severe reperfusion lung injury following pulmonary endarterectomy: a prospective cohort clinical validation study.

The measurement of extravascular lung water is a relatively new technology which has not yet been well validated as a clinically useful tool. We studied its utility in patients undergoing pulmonary endarterectomy as they frequently suffer reperfusion lung injury and associated oedematous lungs. Such patients are therefore ideal for evaluating this new monitor. We performed a prospective observational cohort study during which extravascular lung water index measurements were taken before and immediately after surgery and postoperatively in intensive care. Data were analysed for 57 patients; 21 patients (37%) experienced severe reperfusion lung injury. The first extravascular lung water index measurement after cardiopulmonary bypass failed to predict severe reperfusion lung injury, area under the receiver operating characteristic curve 0.59 (95%CI 0.44-0.74). On intensive care, extravascular lung water index correlated most strongly at 36 h, area under the receiver operating characteristic curve 0.90 (95%CI 0.80-1.00). Peri-operative extravascular lung water index is not a useful measure to predict severe reperfusion lung injury after pulmonary endarterectomy, however, it does allow monitoring and measurement during the postoperative period. This study implies that extravascular lung water index can be used to directly assess pulmonary fluid overload and that monitoring patients by measuring extravascular lung water index during their intensive care stay is useful and correlates with their clinical course. This may allow directed, pre-empted therapy to attenuate the effects and improve patient outcomes and should prompt further studies.

The effect of high-flow nasal oxygen on hospital length of stay in cardiac surgical patients at high risk for respiratory complications: a randomised controlled trial.

There has been increased interest in the prophylactic and therapeutic use of high-flow nasal oxygen in patients with, or at risk of, non-hypercapnic respiratory failure. There are no randomised trials examining the efficacy of high-flow nasal oxygen in high-risk cardiac surgical patients. We sought to determine whether routine administration of high-flow nasal oxygen, compared with standard oxygen therapy, leads to reduced hospital length of stay after cardiac surgery in patients with pre-existing respiratory disease at high risk for postoperative pulmonary complications. Adult patients with pre-existing respiratory disease undergoing elective cardiac surgery were randomly allocated to receive high-flow nasal oxygen (n = 51) or standard oxygen therapy (n = 49). The primary outcome was hospital length of stay and all analyses were carried out on an intention-to-treat basis. Median (IQR [range]) hospital length of stay was 7 (6-9 [4-30]) days in the high-flow nasal oxygen group and 9 (7-16 [4-120]) days in the standard oxygen group (p=0.012). Geometric mean hospital length of stay was 29% lower in the high-flow nasal group (95%CI 11-44%, p = 0.004). High-flow nasal oxygen was also associated with fewer intensive care unit re-admissions (1/49 vs. 7/45; p = 0.026). When compared with standard care, prophylactic postoperative high-flow nasal oxygen reduced hospital length of stay and intensive care unit re-admission. This is the first randomised controlled trial examining the effect of prophylactic high-flow nasal oxygen use on patient-centred outcomes in cardiac surgical patients at high risk for postoperative respiratory complications.

Physiological controversies and methods used to determine fluid responsiveness: a qualitative systematic review.

Accurate assessment of intravascular fluid status and measurement of fluid responsiveness have become increasingly important in peri-operative medicine and critical care. The objectives of this systematic review and narrative synthesis were to discuss current controversies surrounding fluid responsiveness and describe the merits and limitations of the major cardiac output monitors in clinical use today in terms of usefulness in measuring fluid responsiveness. We searched the MEDLINE and EMBASE databases (2002-2015); inclusion criteria included comparison with an established reference standard such as pulmonary artery catheter, transthoracic echocardiography and transoesophageal echocardiography. Examples of clinical measures include static (such as central venous pressure) and dynamic (such as stroke volume variation and pulse pressure variation) parameters. The static parameters measured were described as having little value; however, the dynamic parameters were shown to be good physiological determinants of fluid responsiveness. Due to heterogeneity of the methods and patient characteristics, we did not perform a meta-analysis. In most studies, precision and limits of agreement (bias ±1.96SD) between determinants of fluid responsiveness measured by different devices were not evaluated, and the definition of fluid responsiveness varied across studies. Future research should focus on the physiological principles that underlie the measurement of fluid responsiveness and the effect of different volume expansion strategies on outcomes.

Extracorporeal membrane oxygenation in acute massive pulmonary embolism: a systematic review.

Massive pulmonary embolism (PE) can present with extreme physiological dysfunction, characterised by acute right ventricular failure, hypoxaemia unresponsive to conventional therapy and cardiac arrest. Consensus regarding the management of patients with persistent shock following thrombolysis is lacking. Our primary objective was to describe the application of extracorporeal membrane oxygenation (ECMO) in the treatment of acute massive PE. We were unable to identify any randomised controlled trials (RCTs) comparing ECMO with other support systems in the setting of massive PE. We reviewed case reports and case series published in the past 20 years to evaluate the mortality rate and any poor prognostic factors. Overall survival was 70.1% and none of the definitive treatment modalities was associated with a higher mortality (thrombolysis - OR - 0.99, P - 0.9, catheter embolectomy - OR - 1.01, P - 0.99, surgical embolectomy - OR - 0.44, P - 0.20). Patients who had ECMO instituted whilst in cardiorespiratory arrest had a higher risk of death. (OR - 16.71, P - 0.0004). When compared with other causes of cardiac arrest, patients who survived a massive PE presented a good neurological outcome (cerebral performance category 1 or 2).

Acute right heart syndrome in the critically ill patient.

Acute right heart syndrome is a sudden deterioration in right ventricular performance, resulting in right ventricular failure and confers significant in-hospital morbidity and mortality. In critically ill patients, the syndrome is often undiagnosed and untreated, as these patients do not usually exhibit the common clinical manifestations of the condition, making the diagnosis challenging for the intensivist. In this narrative review we focus on the pathophysiology of acute right heart syndrome, in critical illness, diagnostic modalities used to assess right ventricular function and management of acute right heart syndrome, including mechanical ventilation strategies and circulatory support.