Stefania Crotti

Computed tomography in adult respiratory distress syndrome: what has it taught us?

Computed tomography (CT) has played an important role in improving our knowledge of the pathophysiology of the adult respiratory distress syndrome (ARDS), and in determining the morphological and functional relationships of different manoeuvres commonly used in the therapeutic management of this syndrome (changes in body position, application of positive end-expiratory pressure (PEEP) and mechanical ventilation). During the early phase of the disease, the ARDS lung is characterized by a homogenous alteration of the vascular permeability. Thus, oedema accumulates evenly in all lung regions with a nongravitational distribution (homogenous lung). The increased lung weight, due to increased oedema, causes a collapse of the lung regions along the vertical axis, through the transmission of hydrostatic forces (compression atelectasis). Thus, the lesions appear mainly in the dependent lung regions (dishomogeneous lung). During inspiration, at plateau pressure, the pulmonary units reopen and, if the PEEP applied is adequate, they stay open during the following expiration. Adequate PEEP is equal to or higher than the hydrostatic forces compressing that unit. Prone position is another manoeuvre which allows previously collapsed lung regions to reopen and, conversely, compresses previously aerated regions, reversing the distribution of gravitational forces. During late ARDS, there is less compression atelectasis and the lung undergoes structural changes, due to the reduced amount of oedema. This is usually associated with CO2 retention and the development of emphysema-like lesions. In conclusion, computed tomography is not only a research tool, but a useful technique which allows a better understanding of the progressive change in strategy needed to ventilate the adult respiratory distress syndrome lung at different stages of the disease.

Extracorporeal membrane oxygenation with spontaneous breathing as a bridge to lung transplantation

OBJECTIVES A large number of transplantation centres consider extracorporeal membrane oxygenation as an inappropriate option for bridging critical patients to lung transplantation. Technical improvements such as the introduction of a polymethylpentene membrane, new centrifugal pumps and heparin-coated circuits have led to a safer application of extracorporeal membrane oxygenation, and an increasing number of centres are reporting their positive experiences. The aim of this study was to review our practice in bridging critical candidates to lung transplantation with extracorporeal membrane oxygenation, by comparing patients with invasive mechanical ventilation with patients with spontaneous breathing. METHODS The records of candidates for lung transplantation treated with extracorporeal membrane oxygenation have been revised. RESULTS From February 2008 to 2012, 11 patients who experienced an abrupt worsening of their respiratory conditions were treated with extracorporeal membrane oxygenation; mean age: 33.9 ± 13.2 years, male/female ratio: 5/6, 6 patients were affected by cystic fibrosis, 2 had chronic rejection after transplantation, 2 had pulmonary fibrosis and 1 had systemic sclerosis. Seven patients were awake, while 4 patients received invasive mechanical ventilation. The sequential organ failure assessment score significantly increased during bridging time and this increase was significantly higher in the intubated patients. All the patients had bilateral lung transplantation. Spontaneously breathing patients showed a tendency to require a shorter duration of invasive mechanical ventilation, intensive care unit stay and hospital stay after transplantation. One-year survival rate was 85.7% in patients with spontaneous breathing vs 50% in patients with invasive mechanical ventilation. CONCLUSIONS Extracorporeal membrane oxygenation in spontaneously breathing patients is a feasible, effective and safe bridge to lung transplantation.

Organ Allocation Waiting Time During Extracorporeal Bridge to Lung Transplant Affects Outcomes

BACKGROUND The use of extracorporeal membrane oxygenation (ECMO) as a bridge to lung transplant (LTX) is still being debated. METHODS We performed a retrospective two-center analysis of the relationship between ECMO bridging duration and survival in 25 patients. Further survival analysis was obtained by dividing the patients according to waiting time on ECMO: up to 14 days (Early group) or longer (Late group). We also analyzed the impact of the ventilation strategy during ECMO bridging (ie, spontaneous breathing and noninvasive ventilation [NIV] or intubation and invasive mechanical ventilation [IMV]). RESULTS Seventeen of 25 patients underwent a transplant (with a 76% 1-year survival), whereas eight patients died during bridging. In the 17 patients who underwent a transplant, mortality was positively related to waiting days until LTX (hazard ratio [HR], 1.12 per day; 95% CI, 1.02-1.23; P = .02), and the Early group showed better Kaplan-Meier curves (P = .02), higher 1-year survival rates (100% vs 50%, P = .03), and lower morbidity (days on IMV and length of stay in ICU and hospital). During the bridge to transplant, mortality increased steadily with time. Considering the overall outcome of the bridging program (25 patients), bridge duration adversely affected survival (HR, 1.06 per day; 95% CI, 1.01-1.11; P = .015) and 1-year survival (Early, 82% vs Late, 29%; P = .015). Morbidity indexes were lower in patients treated with NIV during the bridge. CONCLUSIONS The duration of the ECMO bridge is a relevant cofactor in the mortality and morbidity of critically ill patients awaiting organ allocation. The NIV strategy was associated with a less complicated clinical course after LTX.

Artificial lung as an alternative to mechanical ventilation in COPD exacerbation

To the Editors: Acute exacerbation of chronic obstructive pulmonary disease (COPD) is commonly treated with different kinds of noninvasive positive pressure devices, ranging from helmet or face-mask continuous positive airway pressure (CPAP) to noninvasive pressure support ventilation (NPPV), or Bi-PAP [1]. The use of positive end-expiratory pressure (PEEP) and NPPV often results in the successful treatment of COPD patients with respiratory distress [1, 2]. If, despite maximal medical management, respiratory distress and gas exchange deteriorate with increasing tachypnoea and acidosis, and with altered level of consciousness, then tracheal intubation and mechanical ventilation (MV) become mandatory [3]. However, tracheal intubation and MV have several detrimental side-effects that may concur to determine the high morbidity and mortality reported in COPD patients requiring them [3, 4]. Indeed, the increase in airway resistance, the prolonged time required for lung emptying and the resulting dynamic hyperinflation, named auto-PEEP [4], are the most important physiological alterations during COPD exacerbation. In this condition, the application of MV could increase lung hyperinflation and lead to barotrauma and circulatory failure [4, 5]. Furthermore, tracheal intubation is usually associated with the need for sedation. The side-effects of intubation, sedation and MV may initiate a vicious circle, often resulting in a very difficult or impossible weaning. In this report, we describe a patient with severe exacerbation of COPD, in whom after failure of noninvasive ventilation, we decided to treat the respiratory acidosis, tachypnoea and ventilatory fatigue by removing CO2 with an artificial lung. This avoided the need for tracheal intubation and MV, leaving the patient in spontaneous breathing. In September 2010, a 72-yr-old, female heavy …

Awake extracorporeal membrane oxygenation (ECMO): pathophysiology, technical considerations, and clinical pioneering

Venovenous extracorporeal membrane oxygenation (vv-ECMO) has been classically employed as a rescue therapy for patients with respiratory failure not treatable with conventional mechanical ventilation alone. In recent years, however, the timing of ECMO initiation has been readdressed and ECMO is often started earlier in the time course of respiratory failure. Furthermore, some centers are starting to use ECMO as a first line of treatment, i.e., as an alternative to invasive mechanical ventilation in awake, non-intubated, spontaneously breathing patients with respiratory failure (“awake” ECMO). There is a strong rationale for this type of respiratory support as it avoids several side effects related to sedation, intubation, and mechanical ventilation. However, the complexity of the patient–ECMO interactions, the difficulties related to respiratory monitoring, and the management of an awake patient on extracorporeal support together pose a major challenge for the intensive care unit staff. Here, we review the use of vv-ECMO in awake, spontaneously breathing patients with respiratory failure, highlighting the pros and cons of this approach, analyzing the pathophysiology of patient–ECMO interactions, detailing some of the technical aspects, and summarizing the initial clinical experience gained over the past years.

Total respiratory support with tidal flow extracorporeal circulation in adult sheep

A novel pressure gated tidal flow extracorporeal circulation (TF ECC) device was developed, and it was hypothesized that it could provide total respiratory support in apneic adult sheep without adverse hemodynamic or cardiac effects. The circuit consisted of a single lumen cannula, computer driven tubing occluders gated by circuit pressure, a nonocclusive peristaltic blood pump, a spiral coiled membrane lung, and a heat exchanger. Six paralyzed, anesthetized adult sheep were instrumented and TF ECC was instituted via cannulation of the right atrium. Total respiratory support was provided by the circuit during an apneic period of 6 hours. Echocardiography was performed with the animal instrumented (baseline) and after 2 hours of TF ECC. Circuit blood tidal volume was 172.6 ± 18.0 cc, resulting in a TF ECC flow of 71.1 ± 10.1 cc/kg/min. At the end of the study period, PaCo2 was 35.5 ± 7.6 mmHg, pa O2) was 91.2 ± 30.6 mmHg, and pulmonary artery oxygen saturation (SPAO2) was 95 ± 5%. Hemodynamic stability was maintained with no significant differences at baseline and after 6 hours in mean arterial pressure, mean pulmonary artery pressure, or heart rate noted. Echocardiographic evaluation showed preserved fractional shortening of the left ventricular (LV) septal-lateral dimension (baseline 32.4 ± 11.4 %; 2 hours 34.8 ± 8.4 %). This study demonstrates TF ECC provides total respiratory support without adverse hemodynamic effects, and preserved LV function. ASAIO Journal 1997; 43:M811-M816.

ECMO as a Bridge to Lung Transplant

Patient candidates to lung transplant could die awaiting organ allocation due to the worsening of their end-stage respiratory failure. In recent years, the outcome improvement after lung transplant, a more accurate patient selection and the technological development of simpler and safer extracorporeal systems, has made the use of extracorporeal membrane oxygenation (ECMO) as bridge to lung transplant possible in the critically ill patients. The correct choice of the extracorporeal configuration in function to the pathophysiologic characteristics of the end-stage respiratory failure permits performing lung transplants, even in more severe patients, decreasing perioperative morbidity and mortality.