James E. Lynch

Wang-Zwische double lumen cannula-toward a percutaneous and ambulatory paracorporeal artificial lung.

We are developing a high performance double lumen cannula (DLC) for a minimally invasive, ambulatory and percutaneous paracorporeal artificial lung (PAL). The Wang-Zwische (W-Z) DLC was designed for percutaneous insertion into the Internal Jugular (IJ) vein with a drainage lumen open to both the superior vena cava (SVC) and the inferior vena cava (IVC) maximizing venous drainage. A separate collapsible but nondistensible membrane infusion lumen open to the right atrium (RA) achieves minimal recirculation allowing for total gas exchange. The W-Z DLC prototypes are made by a proprietary dip molding process with the “molded in” flat wire spiral stainless steel spring resulting in a flexible yet kink resistant thin wall (0.1 mm) outer cannula with one piece construction. With the ultra thin membrane infusion lumen collapsed, an introducer shaft fits tightly within the drainage lumen to facilitate insertion with placement at the SVC-RA-IVC junction. The W-Z DLC prototypes were tested while connected to a compact pump-gas exchanger circuit in three sheep (2 acute and one 15 day performance study). Insertion was simple, using standard percutaneous insertion techniques. Recirculation was as low as 2%. The 15 day performance study demonstrated our prototype 26 Fr W-Z DLC can achieve 2 L/min blood flow with minimal recirculation. The W-Z DLC design minimizes recirculation rate, maximizes flow lumen cross-sectional area, and maximizes achievable blood flow to enhance gas exchange performance allowing for one site percutaneous venovenous support.

Will CESAR answer the adult ECMO debate

Over the past 30 years, extracorporeal membrane oxygenation (ECMO), in both venoarterial and venovenous confi guration, has become the standard of care for neonates with severe respiratory failure and for postoperative support after congenital heart repair. However, the use of ECMO in adults is not so straightforward. The ECMO experience in adults has been confi ned to a few highly specialised centres due to the associated expense and training necessary as well as the disappointing results reported in the only two randomised trials. Recent positive anecdotal experience in hundreds of patients in Europe with the iLA system for CO2 removal, improvements in ECMO technology and management, and the many changes in critical care since the 1980s cause many to question if it is time to re-evaluate ECMO’s role in the care of the severely ill adult. In The Lancet today, Giles Peek and colleagues present the results of the much anticipated (and debated) CESAR trial of ECMO in adults. This study screened 766 patients for inclusion, of whom 180 were randomised (90 to management and ECMO at Glenfi eld Hospital and 90 to conventional management as practised at the participating tertiarycare centres). Intent-to-treat analysis was used for survival and cost analysis. The CESAR trial showed a 16% survival benefi t without severe disability for patients in the ECMO referral group over conventional management. ECMO referral therefore seems benefi cial as part of an overall management algorithm in the critically ill patient compared with conventional ventilation alone. More patients in the ECMO referral group than in the control group survived, but this diff erence was not statistically signifi cant (relative risk 0·73, 95% CI 0·52–1·03, p=0·07). Three of the patients in the control group were lost to disability follow-up, reducing the group to 87. One patient in the control group was severely disabled. Five patients in the ECMO referral group died during or involving transport. A strength of the study design is the fact that the transport risk was included in the comparison. Only 68 of the 90 patients in the ECMO referral group were actually placed on ECMO; 14 of 17 survived with critical care management alone, and 43 (63%) of 68 survived to 6 months. It is important therefore to understand that the relative risk benefi t reported is not for ECMO treatment but for referral to a single ECMO-capable hospital for ECMO assessment and management if criteria are met. The single referral center, however, leads to a potential weakness of this study; possibly, improved care at the single ECMO hospital led to the relative risk observed. This point restricts the generalisability of this study; ECMO referrals to other ECMO-capable hospitals might not see the same improvements. Survival without severe disability in patients referred for ECMO assessment was at twice the length of stay and twice the cost. Important issues include use of local conventional management rather than a standard critical-care protocol addressing diuresis, low-tidalvolume ventilation, use of steroids and antibiotics, and fl uid management. As seen in several trials in acute respiratory syndrome, including the ARDSNet study, the usual observed survival with critical-care protocol involving a low tidal volume is about 60%. Will this trial change clinicians’ opinion of adult ECMO? To clinicians who have witnessed fi rst-hand ECMO’s ability to salvage an unstable life that would presumably be lost without it, today’s study will represent the sentinel paper on adult ECMO for years to come. After all, 63% of patients who were dying survived to 6 months with ECMO referral. The study involved hundreds of clinicians and years of planning in the design and execution, resulting in the largest (and best) randomised trial of adult ECMO referral so far published. Most proponents of ECMO will conclude that patients treated

Venovenous carbon dioxide removal in chronic obstructive pulmonary disease: experience in one patient.

Chronic obstructive pulmonary disease (COPD) is the fourth leading cause of death in the United States. Acute exacerbations of COPD account for up to 84% of the total economic cost of this disease. The altered mechanics of the COPD patient represent a unique challenge to the clinician instituting assisted ventilation in this population. We developed an alternative mode of limited extracorporeal support termed Venovenous carbon dioxide removal (VVCO2R). We report our first case using VVCO2R, a 42-year-old white woman with a history of COPD and asthma, who was a heavy smoker at the time of admission. We utilized a compact, low flow pediatric extracorporeal circuit interposed with a low resistance gas exchange device. Venovenous carbon dioxide removal allowed for a reduction in the patients minute ventilation to 30% of baseline with improved arterial blood gases (ABGs), a reduction in peak airway pressures and improvement in her hyperinflation. Our experience demonstrates that this system can effectively remove CO2 safely in a single cannula venous configuration while maintaining minimal anticoagulation. We believe this system could potentially be utilized in any medical or surgical intensive care unit.

Percutaneous venovenous CO2 removal with regional anticoagulation in an ovine model.

Extracorporeal CO2 removal may reduce minute ventilation requirements and allow for better tolerance of low tidal volume ventilating strategies in patients with severe respiratory insufficiency. Conventional extracorporeal gas exchange is labor-intensive, expensive, and usually requires systemic anticoagulation. In this study, a simplified venovenous circuit was developed by using regional citrate anticoagulation to avoid potential complications associated with systemic heparin. Five healthy adult sheep underwent percutaneous placement of a double-lumen 18F catheter into the internal jugular vein. The extracorporeal circuit consisted of a hollow fiber oxygenator and a variable speed roller pump. Regional anticoagulation consisted of a continuous citrate infusion to the inflow limb of the circuit. Systemic calcium levels were maintained by calcium chloride infusion through a central line. CO2 transfer was measured at varying levels of blood and gas flow. CO2 transfer ranged from 31 ml/min (500 ml/min blood flow; 2 l/min gas flow) to 150 ml/min (1000 ml/min blood flow; 15 l/min gas flow) and was directly proportional to blood flow and gas flow (p < 0.05). Normocapnia was maintained despite a 75% reduction in minute ventilation. At 24 hours, there was no significant clot formation in the circuit.

A survey for pain and sedation medications in pediatric patients during extracorporeal membrane oxygenation

Routine administration of large amounts of pain and sedative medication is common to critically ill pediatric patients undergoing extracorporeal membrane oxygenation (ECMO) for cardiopulmonary failure. It has been our experience that pediatric patients are the most difficult age group in which to achieve an ideal pain and sedative control due to the narrow margin of safety. The purpose of this study was to determine the general practice guideline used for pain and anxiolytic pharmacotherapy for pediatric patients at ECMO centers. We sent a survey questionnaire to all ECMO centers in the USA that treat pediatric respiratory failure patients. Of the 46 responding centers (including telephone follow-ups), 37 (80%) centers had an active pediatric ECMO programs for patients with severe respiratory failure. Fentanyl was the most commonly used pain medication and continuous infusion, administered directly to the patient, was preferred. Subjective effectiveness of various pharmacological agents was variable without clear consensus; however, midazolam was considered to be the most effective agent used.

Complete respiratory support with AVCO2R and CPAP-mimic ventilation for total gas exchange in sheep.

The altered respiratory mechanics in patients with chronic obstructive pulmonary disease (COPD) present unique challenges with regard to treatment during an acute exacerbation that often leads to respiratory support with mechanical ventilation. Alternative therapies are badly needed to reduce morbidity and mortality associated with mechanical ventilator use. We hypothesized that arteriovenous carbon dioxide removal (AVCO2R) coupled with continuous positive airway pressure (CPAP) would achieve total gas exchange eliminating the need for intubation/mechanical ventilation, thus reducing baro/volutrauma. This hypothesis was tested in six adult sedated apneic sheep with AVCO2R administered through a simple arteriovenous (AV) shunt for CO2 removal. Because it is impractical to apply a CPAP mask to conscious sheep, the CPAP was mimicked in intubated/sedated sheep by positive end-expiratory pressure (PEEP) of 5–10 mmH2O with negligible ventilation. The AVCO2R and CPAP-mimic maintained Pao2 and Paco2 in the normal physiological ranges. The CO2 removal was 120–150 ml/min through AVCO2R with AV blood flow of 1.1–1.5 L/min. A high fraction of inspired oxygen percentage (Fio2) level (89 ± 3%) was required to achieve 40 ± 7% O2 in the small bronchus. Thus, AVCO2R and CPAP-mimic achieved total gas exchange in anesthetized sheep and may be a potential option for acute COPD exacerbation in humans.

Turning the Dial to Futility

Affi liations: From the Chest Department, Taipei Veterans General Hospital. Financial/nonfi nancial disclosures: The authors have reported to CHEST that no potential confl icts of interest exist with any companies/organizations whose products or services may be discussed in this article. Correspondence to: Kun-Ta Chou, MD, Chest Department, Taipei Veterans General Hospital, No. 201, Section 2 Shih-Pei Rd, Taipei 112, Taiwan; e-mail: ale1371@yahoo.com.tw

ECMO to Artificial Lungs: Advances in Long-Term Pulmonary Support

Lung disease is the fourth leading cause of death (one in seven deaths) in the United States. Acute respiratory distress syndrome (ARDS) affects approx 150,000 patients a year in the US; an estimated 16 million Americans are afflicted with chronic lung disease, accounting for 100,000 deaths per year. Medical management is the standard of care for initial therapy, but is limited by progression of the disease. Chronic mechanical ventilation is readily available, but it is cumber-some, expensive, and often requires tracheotomy with loss of upper airway defense mechanisms and normal speech. Lung transplantation is an option for fewer than 1,000 patients per year because demand has steadily outgrown supply.