Timothy W. Willcox

Extracorporeal Membrane Oxygenation for Treating Severe Cardiac and Respiratory Failure in Adults: Part 2: Technical Considerations

i a N THIS SECOND OF 2 articles on the use of extracorporeal membrane oxygenation (ECMO) for treating severe cardiac nd respiratory failure in adults, the physiology, technical coniderations, and complications of this technique are reviewed. lthough ECMO remains a technically and logistically deanding undertaking, recent advances in the design of circuit omponents, particularly the oxygenator, have improved the ase of use and durability of the technique, such that extracororeal support can be maintained relatively safely for several eeks.

Venous air in the bypass circuit: a source of arterial line emboli exacerbated by vacuum-assisted drainage

BACKGROUND Arterial emboli cause neurocognitive deficits in cardiac surgical patients. Carotid artery emboli, detected ultrasonically, have been observed after venous air entrainment into the cardiopulmonary bypass circuit. We investigated in vitro the extent to which venous air affected emboli detected in the arterial line downstream from a 40-microm filter. METHODS Using salvaged clinical cardiopulmonary bypass circuits, fixed volumes of air were introduced into the venous return line at unrestricted rates and at fixed rates using gravity venous drainage and vacuum-assisted venous drainage. Emboli counts were recorded distal to the arterial line filter using a 2-MHz pulsed-wave Doppler monitor. Emboli counts were similarly recorded after the introduction of carbon dioxide into the venous return line instead of air. RESULTS The number of emboli rose with increasing volumes of entrained venous air (p < 0.001), and there was an almost tenfold increase with vacuum-assisted venous drainage (p < 0.0001) compared with gravity venous drainage. Venous air was entrained at a significantly faster rate under vacuum-assisted venous drainage (p < 0.0001). When the entrainment rate of venous air was fixed, the difference in emboli numbers recorded for gravity and assisted venous drainage was not significant. There was a significant reduction in arterial line emboli when carbon dioxide rather than air was entrained under both vacuum-assisted and gravity drainage (p < 0.001). CONCLUSIONS Entrained venous air during cardiopulmonary bypass is a potential hazard, particularly during vacuum-assisted venous drainage. Every effort should be made to avoid venous air entrainment.

Venovenous Extracorporeal Membrane Oxygenation in Adults: Practical Aspects of Circuits, Cannulae, and Procedures

NTEREST IN extracorporeal membrane oxygenation (ECMO) for treating severe respiratory failure in adults has increased substantially in the last 5 years. There are several reasons for this increase. The first reason is the publication of the CESAR study in 2009, which showed improved survival in adults with severe acute respiratory distress syndrome (ARDS) randomized to consideration of ECMO compared with patients treated conventionally.1 Second is the H1N1 influenza pandemic of 2009 and 2010, which resulted in a substantial increase in the use of ECMO for treating severe respiratory failure. 2 The outcome from ECMO in this group of patients was excellent, with reported survival rates of 68% to 77%. 3-5 The third factor has been improvements in the equipment used for ECMO; in particular, the introduction of polymethylpentene (PMP) oxygenators, second-generation centrifugal pumps, and cannulae specifically designed for ECMO. Finally, ECMO increasingly is being used for patients undergoing surgical correction of critical airway obstruction (eg, tracheal papilloma).6,7 There are 2 basic forms of ECMO: venoarterial (VA) and venovenous (VV). VA ECMO supports the lungs and the heart (left and right ventricles), whereas VV supports the lungs only. In adults, VA ECMO is used for treating acute cardiac and cardiorespiratory failure. For acute cardiac failure, ECMO may be used instead of a ventricular assist device (VAD), as a bridging technique either to recovery or to a long-term VAD. Historically, VA ECMO also was used for treating respiratory failure in adults 8 and is still used commonly for treating neonatal respiratory failure. 2 However, VV ECMO is now the preferred mode of extracorporeal support for adults with ARDS because it avoids 2 important disadvantages associated with VA ECMO: the need for arterial cannulation and upper-body hypoxemia. Upper-body hypoxemia occurs in patients with respiratory failure but good cardiac function who are supported with peripheral VA ECMO in which the arterial cannula is placed in the femoral artery. Oxygenated blood from the ECMO circuit perfuses the lower body, but deoxygenated blood, passing through the nonfunctioning lungs and ejected from the left ventricle, perfuses the upper body (coronary arteries and cerebral circulation).

Cerebral Protection by Lidocaine During Cardiac Operations: A Follow-Up Study

BACKGROUND A previous study showed less postoperative neurocognitive impairment in open-chamber cardiac surgery patients given lidocaine for 48 hours after induction of anesthesia. In the present study, we aimed to test the benefit of a 12-hour infusion in a broader group of cardiac surgery patients, including those undergoing coronary artery bypass graft surgery. METHODS This was a randomized, double-blind, intention-to-treat trial. Before cardiac surgery, 158 patients completed 7 neurocognitive tests and a self-rating scale for memory. They received a 12-hour infusion of either lidocaine in a standard antiarrhythmic dose or placebo, beginning at induction of anesthesia. The cognitive tests and memory scale were repeated at postoperative weeks 10 and 25. A deficit in any cognitive test was defined as a decline in score by more than or equal to the preoperative group standard deviation. RESULTS All tests were completed by 118 and 107 patients at 10 and 25 weeks, respectively. The proportions of patients in the lidocaine and placebo groups exhibiting a deficit in one or more tests were as follows: 45.8% versus 40.7% at 10 weeks, and 35.2% versus 37.7% at 25 weeks (not significant). There were no significant differences between groups in self-ratings of memory function or length of intensive care unit or hospital stay. CONCLUSIONS Lidocaine was not neuroprotective. The result of the previous trial may represent a type 1 error. Alternatively, benefit may be more likely for open-chamber surgery patients exposed to larger numbers of emboli or with a longer lidocaine infusion.

Best Practice for Cardiopulmonary Bypass in the High-Risk Elderly Patient

The management of cardiopulmonary bypass has evolved over the last 50 years resulting in a largely consistent approach to both adult and pediatric perfusion. Very little has been written or prospectively researched on the best practice for cardiopulmonary bypass in the high-risk elderly patient, despite the challenge this patient cohort presents compared to the general adult population and the rapidly increasing number of such patients undergoing cardiac surgery. We propose a framework for perfusion strategies for the high-risk elderly patient from our current understanding of cardiopulmonary bypass. It should stimulate discussion for a consensus on perfusion strategies for the elderly and encourage further research into perfusion variables as they relate to the outcome of patients of advanced age.