Current status of extracorporeal membrane oxygenation for severe respiratory failure

Pharmacokinetics and Extracorporeal Membrane Oxygenation in Adults: A Literature Review

Extracorporeal membrane oxygenation is a rapidly emerging treatment for respiratory or cardiac failure and is used as a bridge to recovery, transplant, or destination therapy. Adult patients receiving extracorporeal membrane oxygenation also receive significant amounts of pharmacotherapy. Although the body of literature on extra-corporeal membrane oxygenation in general is extensive, only a few publications focus on pharmacokinetic changes related to extracorporeal membrane oxygenation in adults. Understanding pharmacokinetics in adult patients receiving extracorporeal membrane oxygenation is important to correctly select and dose medications in this patient population. This article reviews published studies of the effects of extracorporeal membrane oxygenation on pharmacokinetics in adults.

Veno-venous ECMO: a synopsis of nine key potential challenges, considerations, and controversies

Background

Following the 2009 H1N1 Influenza pandemic, extracorporeal membrane oxygenation (ECMO) emerged as a viable alternative in selected, severe cases of ARDS. Acute Respiratory Distress Syndrome (ARDS) is a major public health problem. Average medical costs for ARDS survivors on an annual basis are multiple times those dedicated to a healthy individual. Advances in medical and ventilatory management of severe lung injury and ARDS have improved outcomes in some patients, but these advances fail to consistently “rescue” a significant proportion of those affected.

Discussion

Here we present a synopsis of the challenges, considerations, and potential controversies regarding veno-venous ECMO that will be of benefit to anesthesiologists, surgeons, and intensivists, especially those newly confronted with care of the ECMO patient. We outline a number of points related to ECMO, particularly regarding cannulation, pump/oxygenator design, anticoagulation, and intravascular fluid management of patients. We then address these challenges/considerations/controversies in the context of their potential future implications on clinical approaches to ECMO patients, focusing on the development and advancement of standardized ECMO clinical practices.

Summary

Since the 2009 H1N1 pandemic ECMO has gained a wider acceptance. There are challenges that still must be overcome. Further investigations of the benefits and effects of ECMO need to be undertaken in order to facilitate the implementation of this technology on a larger scale.

Intestinal epithelial apoptosis initiates gut mucosal injury during extracorporeal membrane oxygenation in the newborn piglet

Neonates and young infants exposed to extracorporeal circulation during extracorporeal membrane oxygenation (ECMO) and cardiopulmonary bypass are at risk of developing a systemic inflammatory response syndrome with multi-organ dysfunction. We used a piglet model of ECMO to investigate the hypothesis that epithelial apoptosis is an early event that precedes villous damage during ECMO-related bowel injury. Healthy 3-week-old piglets were subjected to ECMO for up to 8 h. Epithelial apoptosis was measured in histopathological analysis, nuclear imaging, and terminal deoxynucleotidyl transferase dUTP nick end labeling. Plasma intestinal fatty acid-binding protein (I-FABP) levels were measured by enzyme immunoassay. Intestinal mast cells were isolated by fluorescence-assisted cell sorting. Cleaved caspase-8, caspase-9, phospho-p38 MAPK, and fas ligand expression were investigated by immunohistochemistry, western blots, and reverse transcriptase-quantitative PCR. Piglet ECMO was associated with increased gut epithelial apoptosis. Extensive apoptotic changes were noted on villus tips and in scattered crypt cells after 2 h of ECMO. After 8 h, the villi were denuded and apoptotic changes were evident in a majority of crypt cells. Increased circulating I-FABP levels, a marker of gut epithelial injury, showed that epithelial injury occurred during ECMO. We detected increased cleaved caspase-8, but not cleaved caspase-9, in epithelial cells indicating that the extrinsic apoptotic pathway was active. ECMO was associated with increased fas ligand expression in intestinal mast cells, which was induced through activation of the p38 mitogen-activated protein kinase. We conclude that epithelial apoptosis is an early event that initiates gut mucosal injury in a piglet model of ECMO.

Establishment of an animal model of extracorporeal membrane oxygenation in rabbits

OBJECTIVE

This study was undertaken to establish an animal model of extracorporeal membrane oxygenation in rabbits.

METHODS

Ten New Zealand white rabbits weighing 2573±330 g were used in this study. Extracorporeal membrane oxygenation was established in these animals through cannulation of the right carotid artery and jugular vein for arterial perfusion and venous return. The components of the perfusion circuit were specially designed. Arterial blood pressure was measured with a blood pressure meter through cannulation of the right femoral artery. The heart rate and blood gas parameters were also monitored by electrocardiography and a blood gas analyzer (Radiometer ABL800, Bronshøj, Denmark), respectively.

RESULTS

The rabbit model of extracorporeal membrane oxygenation was established successfully. The hemodynamic and blood gas parameters were changed within an acceptable range during the extracorporeal membrane oxygenation process. The specially designed miniature membrane oxygenator was sufficient to meet the extracorporeal membrane oxygenation needs in this animal model.

CONCLUSION

The rabbit model of extracorporeal membrane oxygenation established through right carotid artery and jugular vein cannulation is feasible, easily operated and economical. It is an ideal model for further research of the pathophysiology and organ protection offered through the application of extracorporeal membrane oxygenation.

Predicting major adverse events after cardiac surgery in children

OBJECTIVES

To develop a reliable predictor of major adverse events after pediatric cardiac surgery, with the aim of reducing mortality of cardiac extracorporeal life support through earlier, more accurate patient selection.

DESIGN

Prospective observational study.

SETTING

Tertiary level pediatric intensive care unit.

PATIENTS

Fifty-two children undergoing open heart surgery considered above-average risk based on preoperative assessment.

INTERVENTIONS

None; strictly observational study.

MEASUREMENTS AND MAIN RESULTS

A wide range of measurements was made at 3, 6, 9, 12, and 24 hrs after surgery, including: oxygen consumption, central venous pressure and oxygen saturation (Scvo2), cardiac output (Fick), heart rate, arterial pressure, arterial lactate, urine output, core-toe temperature gradient, and derived hemodynamic variables. Six children had major adverse events; three needed extracorporeal life support, two died. There were no correlations between routine postoperative measurements (blood pressure, pulse, temperature gradient, central venous pressure) and any measure of cardiac function, and neither group of variables predicted adverse outcomes. Lactate (>8 mmol/L) and Scvo2 (<40%) had high sensitivity (both 73.7%) and specificity (96.3% and 95.4%, respectively), for predicting major adverse event but positive predictive values for both were low (63.6% and 58.3%, respectively). The ratio of the two had better predictive power than the individual values. When the ratio (Scvo2, %)/(lactate, mmol/L) fell below 5, the positive predictive value for major adverse event was 93.8% (sensitivity 78.9%, specificity 90.5%). The effect was present at all postoperative time points.

CONCLUSIONS

Lactate and Scvo2 are the only postoperative measurements with predictive power for major adverse events. Forming a ratio of the two (Scvo2/lactate), seems to improve predictive power, presumably by combining their individual predictive strengths. Both measures have excellent specificities but lower sensitivities. Predictive power of single measures is only fair but can be improved, in high risk patients, by monitoring repeated measures over time.

Beneficial outcome after prostaglandin-induced post-partum cardiac arrest using levosimendan and extracorporeal membrane oxygenation

BACKGROUND

Administration of high doses of prostaglandins is a frequently performed and effective method for the treatment of atonic uterine haemorrhage in order to increase uterine muscle tone. Rarely, however, these drugs may cause life-threatening complications including bronchospasm, acute pulmonary oedema and myocardial infarction caused by coronary spasms.

METHODS

We discuss the management of a patient suffering post-partum atonic uterine bleeding, catecholamine-resistant cardiac arrest and fulminant pulmonary failure due to deleterious side-effects of treatment with prostaglandins.

RESULTS

During therapy resistant cardiopulmonary resuscitation, the addition of levosimendan to standard medications resulted in a prompt stabilization of haemodynamics. Subsequent treatment of pulmonary failure was successfully managed with ECMO.

CONCLUSION

Although levosimendan is not approved for pharmacological treatment of cardiopulmonary arrest, the beneficial effects in this patient suggest an important role of calcium sensitization and vasodilation during prostaglandin-induced cardiac arrest.

Hemodynamic effects of pumpless extracorporeal membrane oxygenation (ECMO) support for chronically pressure-overloaded right heart failure in a canine experimental model

PURPOSE

This study was done to evaluate the hemodynamic effects of a pumpless implantable extracorporeal membrane oxygenation (ECMO) circuit between the right ventricle (RV) and left atrium (LA) in a chronic canine model with an RV pressure overload.

METHOD

We created a model of right-sided heart failure by pulmonary artery banding in ten dogs for a duration of more than 3 months. After demonstrating that the RV pressure increased, a bypass circuit was created between the RV and LA with an in-line oxygenator. Both the hemodynamics and gas exchange were measured.

RESULTS

The effects of a pulmonary bypass in nine dogs were studied. Approximately half of the RV output was passively shunted through the bypass circuit, and a marked reduction in the RV pressure and recovery from right heart failure were observed. After a complete ligation of the main pulmonary artery, five of the nine dogs survived more than 6 h. The RV pressure did not change significantly, but the cardiac output and blood pressure gradually decreased. The blood gas state was sufficiently maintained throughout the experiment.

CONCLUSION

The present study indicates the hemodynamic benefit of a partial pumpless ECMO system in dogs with chronically pressure-overloaded right heart failure; however, the experimental preparation of the total pumpless ECMO circuit proved to be unstable.

Methodology for Predicting Oxygen Transport on an Intravenous Membrane Oxygenator Combining Computational and Analytical Models

A computational methodology for accurately predicting flow and oxygen-transport characteristics and performance of an intravenous membrane oxygenator (IMO) device is developed, tested, and validated. This methodology uses extensive numerical simulations of three-dimensional computational models to determine flow-mixing characteristics and oxygen-transfer performance, and analytical models to indirectly validate numerical predictions with experimental data, using both blood and water as working fluids. Direct numerical simulations for IMO stationary and pulsating balloons predict flow field and oxygen transport performance in response to changes in the device length, number of fibers, and balloon pulsation frequency. Multifiber models are used to investigate interfiber interference and length effects for a stationary balloon whereas a single fiber model is used to analyze the effect of balloon pulsations on velocity and oxygen concentration fields and to evaluate oxygen transfer rates. An analytical lumped model is developed and validated by comparing its numerical predictions with experimental data. Numerical results demonstrate that oxygen transfer rates for a stationary balloon regime decrease with increasing number of fibers, independent of the fluid type. The oxygen transfer rate ratio obtained with blood and water is approximately two. Balloon pulsations show an effective and enhanced flow mixing, with time-dependent recirculating flows around the fibers regions which induce higher oxygen transfer rates. The mass transfer rates increase approximately 100% and 80%, with water and blood, respectively, compared with stationary balloon operation. Calculations with combinations of frequency, number of fibers, fiber length and diameter, and inlet volumetric flow rates, agree well with the reported experimental results, and provide a solid comparative base for analysis, predictions, and comparisons with numerical and experimental data.

Flow Mixing Enhancement from Balloon Pulsations in an Intravenous Oxygenator

Computational investigations of flow mixing and oxygen transfer characteristics in an intravenous membrane oxygenator (IMO) are performed by direct numerical simulations of the conservation of mass, momentum, and species equations. Three-dimensional computational models are developed to investigate flow-mixing and oxygen-transfer characteristics for stationary and pulsating balloons, using the spectral element method. For a stationary balloon, the effect of the fiber placement within the fiber bundle and the number of fiber rings is investigated. In a pulsating balloon, the flow mixing characteristics are determined and the oxygen transfer rate is evaluated. For a stationary balloon, numerical simulations show two well-defined flow patterns that depend on the region of the IMO device. Successive increases of the Reynolds number raise the longitudinal velocity without creating secondary flow. This characteristic is not affected by staggered or non-staggered fiber placement within the fiber bundle. For a pulsating balloon, the flow mixing is enhanced by generating a three-dimensional time-dependent flow characterized by oscillatory radial, pulsatile longitudinal, and both oscillatory and random tangential velocities. This three-dimensional flow increases the flow mixing due to an active time-dependent secondary flow, particularly around the fibers. Analytical models show the fiber bundle placement effect on the pressure gradient and flow pattern. The oxygen transport from the fiber surface to the mean flow is due to a dominant radial diffusion mechanism, for the stationary balloon. The oxygen transfer rate reaches an asymptotic behavior at relatively low Reynolds numbers. For a pulsating balloon, the time-dependent oxygen-concentration field resembles the oscillatory and wavy nature of the time-dependent flow. Sherwood number evaluations demonstrate that balloon pulsations enhance the oxygen transfer rate, even for smaller flow rates.

Long-term ex vivo bovine experiments with the Gyro C1E3 centrifugal blood pump

Centrifugal blood pumps are used widely for cardiopulmonary bypass, as ventricular assist devices, and for extracorporeal membrane oxygenation (ECMO). However, there is no centrifugal blood pump that is suitable for long-term ECMO. The authors developed the Gyro C1E3 centrifugal blood pump (Kyocera Corporation, Kyoto, Japan), which has superior antithrombogenic, antitraumatic, and hydraulic features in comparison with the conventional centrifugal blood pumps. Five ex vivo long-term durability tests of the Gyro C1E3 were performed using healthy miniature calves. The ECMO circuit was composed of a prototype hollow fiber silicone membrane oxygenator and a Gyro C1E3 pump. Venous blood was drained from the left jugular vein of a calf, passed through the oxygenator and infused into the left carotid artery using a Gyro C1E3. Ex vivo studies were performed from 7 to 15 days at a blood flow rate of 1 L/min. During this period, the Gyro C1E3 demonstrated a stable performance without exchanging the pump. Bleeding complications were the major reason for termination of each experiment. Rotational speed was maintained around 2,000 rpm. All five calves demonstrated neither abnormal signs nor abnormal blood examination data throughout the experiment. Neither clot nor thrombus formations were found during the necropsy in the cannula or pump nor were infarctions observed in any of the major organs. In conclusion, the Gyro C1E3 showed a stable and reliable performance during long-term ex vivo bovine experiments under the conditions tested.

Hemolytic characteristics of oxygenators during clinical extracorporeal membrane oxygenation

A connection was previously reported between the hemolytic characteristics associated with oxygenators and the pressure drop measurements in the blood chamber under experimental conditions simulating their use in cardiopulmonary bypass. We examined this association during extracorporeal membrane oxygenation (ECMO) conditions. Three oxygenators for ECMO or pediatric cardiopulmonary bypass (Menox EL4000, Dideco Module 4000, and Mera HPO-15H) were evaluated. Fresh blood from healthy Dexter strain calves anticoagulated with citrate phosphate dextrose adenine solution was used. The blood flow was fixed at 1 L/min, similar to that in ECMO. The Normalized Index of Hemolysis for Oxygenators (NIHO) has been modified according to the American Society of Testing and Materials standards, as was previously reported. The NIHO value was the lowest in the Menox (0.0070+/-0.0009) and increased from Menox to Dideco (0.0113+/-0.0099) to Mera (0.0164+/-0.0043); however, there were no significant differences among the oxygenators. This NIHO value has a close correlation to the pressure drop. In conclusion, this evaluation method is also applicable to comparison of the biocompatibility performance of different types of clinically available oxygenators for ECMO.

Use of plasma lactate to predict early mortality and adverse outcome after neonatal extracorporeal membrane oxygenation: a prospective cohort in early childhood

OBJECTIVE

To examine the use of plasma lactate levels to predict mortality and neurodevelopmental outcome of neonates treated with extracorporeal membrane oxygenation.

DESIGN

Prospective cohort study.

SETTING

Two level III neonatal intensive care units in Canada and the United States.

PATIENTS

Seventy-four neonates requiring extracorporeal membrane oxygenation in two neonatal intensive care units from 1994 to 1996.

INTERVENTIONS

Differences in clinical and biochemical measurements, including serial lactate levels between three outcome groups (early deaths, adverse survivors, and normal survivors) were compared using analysis of variance. We also examined the predictive relationship between plasma lactate levels and the outcome at neonatal intensive care unit discharge and at 18-24 months postnatal age by backward, stepwise regression and Fisher's exact test.

MEASUREMENTS AND MAIN RESULTS

Fifteen (20%) neonates died before neonatal intensive care unit discharge (early deaths), with seven additional deaths before follow-up, which are included in the adverse survivors group. Among 49 early childhood survivors (22 +/- 7 months), 27 were disabled or delayed with Mental and Performance Developmental Indices of 70 +/- 21 and 72 +/- 22, respectively. Early deaths had higher plasma lactate levels and were more acidemic than adverse and normal survivors, who were not different from each other (p <.05). Plasma lactate and the lowest arterial pH independently predicted 42% of the variance of the outcome ( p<.001). A peak lactate level of >or=25 mM predicted early mortality (sensitivity, 47%; specificity, 100%; positive and negative predictive values, 100% and 88%, respectively; p<.001), whereas a level of >or=15 mM predicted adverse outcome (sensitivity, 35%; specificity, 91%; positive and negative predictive values, 89% and 38%, respectively; p<.05). The predictability of plasma lactate was significantly improved in 45 neonates without congenital diaphragmatic hernia or lethal anomalies (sensitivity of 100% for early mortality, negative predictive value of 63% for adverse outcome). CONCLUSIONS In addition to assessing tissue oxygenation, plasma lactate may facilitate the decision-making process by providing early predictive information about the outcome of neonates treated with extracorporeal membrane oxygenation.

Effects of arteriovenous extracorporeal therapy on hemodynamic stability, ventilation, and oxygenation in normal lambs

OBJECTIVE

To evaluate hemodynamic stability and gas exchange in a neonatal animal model of pumpless arteriovenous extracorporeal membrane oxygenation (AV-ECMO) with extracorporeal shunt flow of up to 15% of cardiac output during variable ventilation and oxygenation.

DESIGN

Prospective study.

SETTING

Research laboratory in a hospital.

SUBJECTS

Seven lambs (5.5 +/- 0.6 kg, mean +/- sd).

INTERVENTIONS

The lambs initially were anesthetized by 50 mg/kg ketamine intravenously. After tracheostomy, the lambs were mechanically ventilated and paralyzed by using 1 mg/kg vecuronium bromide followed by 0.1 mg.kg(-1).hr(-1). One femoral vein was cannulated with a pulmonary artery flotation catheter and used for cardiac output and pulmonary artery pressure measurements. A femoral artery was cannulated for measuring mean arterial blood pressure, measuring heart rate, and blood sampling for gas exchange analyses. Finally, the right internal jugular vein and carotid artery were cannulated and used for the AV-ECMO. Normothermia (38 +/- 0.5 degrees C), fluid balance (5 mL.kg(-1).hr(-1) normal saline), and anesthesia (5 mg.kg(-1).hr(-1), intravenous ketamine) were maintained. Ventilator settings were adjusted to establish a baseline Paco2 (25-35 mm Hg) at an Fio2 of 0.4. The AV-ECMO circuit was established by using a hollow fiber oxygenator, primed with maternal sheep blood (150-200 mL).

MEASUREMENTS AND MAIN RESULTS

The physiologic effects of the AV-ECMO shunt were evaluated at 15, 25, and 40 mL.kg(-1).hr(-1) ECMO flow, corresponding roughly to 4%, 8%, and 15% of the cardiac output values. The baseline minute volume was maintained during stepwise increases in arteriovenous shunt. A significant increase in endogenous cardiac output occurred at arteriovenous shunt of 25 and 40 mL.kg(-1).hr(-1) (analysis of variance followed by Tukey-Kramer multiple comparisons test), which was attributed to a significant increase of 30% in the heart rate. Effective cardiac output (difference between the thermodilution value and the AV-ECMO flow rate) and mean arterial blood pressure were not significantly changed. CO2 removal, measured at 15% arteriovenous shunt, was significantly increased with decreasing ventilation to 25% and 50% of the baseline (analysis of variance and Tukey-Kramer test). Oxygenation through the membrane was measured after reducing inspired Fio2 from 0.4 to 0.21, 0.15, and 0.10 with 15% arteriovenous shunt and baseline minute ventilation. Oxygen delivery by the oxygenator was significantly increased at Fio2 of 0.10, providing a maximum of 19.5% of the total oxygen consumption at an arterial hemoglobin-oxygen saturation of 60%.

CONCLUSIONS

Healthy lambs are capable of maintaining effective cardiac output in the presence of moderate arteriovenous shunts (15%). AV-ECMO may provide efficient ventilatory support in the neonatal population with hypercapnia. The amount of oxygen delivery with AV-ECMO depends on arterial desaturation.

Flow and Oxygen Transfer Characteristics of an Intravenous Membrane Oxygenator: A Computational Study

Spectral element computational simulations of the conservation of mass, momentum and species equations are performed to investigate the flow and oxygen transfer characteristics of an Intravenous Membrane Oxygenator (IMO). The simulations consider a three-dimensional IMO computational model consisting of equally-spaced fibers, an elastic balloon with non-permeable walls positioned longitudinally within the vena cava, and a Newtonian and time-dependent incompressible flow. Flow characteristics and oxygen transfer parameters are determined for operating conditions of a stationary and a pulsating balloon. For the stationary balloon configuration the flow is two-dimensional, parallel, laminar and without secondary flows for the Reynolds number range of 5.7-455.2. Evaluations of the oxygen transfer characteristics for the stationary balloon indicate that the main transport mechanisms are diffusion and convection in the crosswise and streamwise directions, respectively. Additionally, evaluations of oxygen transfer rates and Sherwood numbers in this Reynolds number range indicate that the oxygen transfer rate reaches an asymptotic limit at relatively moderate Reynolds numbers. For the pulsating balloon, flow characteristic results demonstrate the existence of a strong secondary flow around the fiber, and between the balloon and the fiber. This secondary flow induces oscillatory crosswise and streamwise velocities and a seemingly random spanwise flow which enhances the flow mixing as well as the transport of oxygen from the fiber surface to the bulk flow.

Percutaneous extracorporeal arteriovenous carbon dioxide removal improves survival in respiratory distress syndrome: a prospective randomized outcomes study in adult sheep

OBJECTIVE

Arteriovenous carbon dioxide removal (AVCO(2)R) uses a simple arteriovenous shunt for CO(2) removal to minimize barotrauma/volutrauma from mechanical ventilation. We performed a prospective randomized outcomes study of AVCO(2)R in our new, clinically relevant model of respiratory distress syndrome.

METHODS

Adult sheep (n = 18) received an LD(50) severe smoke inhalation and 40% third-degree burn. When respiratory distress syndrome developed (PaO (2)/FIO (2) < 200 at 40 to 48 hours), animals were randomized to the AVCO(2)R (n = 9) or sham group (n = 9) for 7 days. Ventilator management protocols mandated reductions in minute ventilation, first tidal volume to peak inspiratory pressure less than 30 cm H(2)O, then respiratory rate when PaCO (2) was less than 40 mm Hg. PaO (2) was kept above 60 mm Hg by adjusting FIO (2). When FIO (2) was 0.21, animals were weaned.

RESULTS

The study required 2946 animal-hours of critical care with 696 AVCO(2)R hours. One died in each group during model development. AVCO(2)R flow from 820 mL/min to 970 mL/min (11% to 14% cardiac output) removed CO(2) at a rate of 92 to 116 mL/min (mean 103 mL/min; 93%-97% of CO(2) production). Heart rate, mean arterial pressure, cardiac output, and pulmonary arterial wedge pressure remained relatively constant. Within 48 hours, AVCO(2)R allowed significant ventilator reductions versus baseline in the following measurements: tidal volume (420 to 270 mL), peak inspiratory pressure (25 to 14 cm H(2)O), minute ventilation (13 to 5 L/min), respiratory rate (26 to 16 breaths/min), and FIO (2) (0.88 to 0.35). Ventilator-free days with AVCO(2)R were 3.9 versus 0.2 (P <.01) for sham animals, and ventilator-dependent days with AVCO(2)R were 2.4 versus 6.2 (P <.01) for the 3 sham survivors. All 8 AVCO(2)R animals and 3 of 8 sham animals survived 7 days after randomization.

CONCLUSIONS

Percutaneous AVCO(2)R achieved significant reduction in airway pressures, increased ventilator-free days, decreased ventilator-dependent days, and improved survival in a sheep model of respiratory distress syndrome.

The current status of neonatal extracorporeal membrane oxygenation

Marked changes have occurred in the practice of neonatal extracorporeal membrane oxygenation (ECMO) since the first survivor in 1975. Coagulation management has been markedly refined, new catheters allow ECMO to be done either in a venoarterial or venovenous (VV) mode, depending on cardiac function in the infant. A new design of the VV catheter will allow this technique to be used in more infants in the future. New therapies for respiratory failure have changed the complexion of the population being treated with ECMO. The 34 to 36 week gestation infant with respiratory distress syndrome and/or pulmonary hypertension rarely needs ECMO therapy due to the effectiveness of surfactant and high frequency oscillation. Present day survival for infants treated with ECMO for many diagnostic categories ranges between 90% to 100%. The effects of new interventions must be evaluated with regard to their effect on morbidity when being considered prior to ECMO. Neuro-developmental outcome is encouraging, but does indicate that ECMO and the near-miss ECMO patients need to be followed closely into school age. The number of patients being treated per ECMO center has dropped significantly over the last 10 years from 18 to 9. This brings forward the question about regional needs for ECMO Centers and how to assure that centers have enough patients to maintain their clinical competencies. The challenge for the future is where to place ECMO as a therapy. Should it remain a rescue therapy? Or should there now be a trial comparing ECMO to conventional therapies, with morbidity and cost of care as the outcome variables?

Rapid cardiopulmonary support for children with complex congenital heart disease

BACKGROUND

Extracorporeal membrane oxygenation has limitations in children with congenital heart disease (prolonged setup times, increased postoperative blood loss, and difficulty during transport). We developed a miniaturized cardiopulmonary support circuit to address these limitations.

PATIENTS AND METHODS

The cardiopulmonary support system includes a preassembled, completely heparin-coated circuit, a BP-50 Bio-Medicus centrifugal pump, a Minimax plus membrane oxygenator, a Bio-Medicus flow probe, and a Bio-trend hematocrit/oxygen saturation monitor. Short tubing length permits a 250-mL bloodless prime in less than 5 minutes. From 1995 to 1997, 23 children with congenital heart disease were supported with this technique.

RESULTS

Overall survival to discharge was 48% (11 of 23 patients). Survival to discharge was 80% (4 of 5) in the preoperative support group, 20% (1 of 5) in the postoperative failure to wean from cardiopulmonary bypass group, 44% (4 of 9) in the group placed on support postoperatively after transfer to the intensive care unit, and 50% (2 of 4 patients) in the nonoperative group. Neonatal cardiopulmonary support survival to discharge was 46% (6 of 13 patients).

CONCLUSIONS

This pediatric cardiopulmonary support system is safe and effective. Advantages over conventional extracorporeal membrane oxygenation include rapid setup time, decreased postoperative blood loss, and simplified transport.

Pulmonary failure after Norwood procedure: indication for extracorporeal membrane oxygenation? A case report

Today some authors consider univentricular repair a contraindication for postoperative cardiac extracorporeal membrane oxygenation (ECMO). The question is whether or not ECMO is indicated as pulmonary support in case of an overwhelming pulmonary infection during the postoperative course after a Norwood procedure. During the prolonged weaning period after a Norwood procedure using a 4 mm aortopulmonary shunt, proven respiratory syncytial virus (RSV) bronchiolitis occurred at the time of expected weaning from artificial ventilation. Venovenous ECMO was able to improve oxygenation, but when pulmonary opacification failed to resolve, ECMO was terminated after 12 days.

Reduced ventilator pressure and improved P/F ratio during percutaneous arteriovenous carbon dioxide removal for severe respiratory failure

OBJECTIVE

To evaluate the effect of percutaneous arteriovenous carbon dioxide removal (AVCO2R) on ventilator pressures and P/F ratio in a clinically relevant large-animal model of severe respiratory failure.

SUMMARY BACKGROUND DATA

AVCO2R was developed as a simple arteriovenous shunt with a commercially available low-resistance gas exchange device of sufficient surface area for near-total CO2 removal. With an AV shunt 10% to 15% of cardiac output, AVCO2R allows a reduction in ventilator airway pressures without hypercapnia or the complex circuitry and monitoring required for conventional ECMO.

METHODS

AVCO2R was applied to a new, clinically relevant large-animal model of severe respiratory failure created by smoke inhalation and cutaneous flame bum injury. Adult sheep (n = 9, 38+/-6 kg) received a 40% total body surface area, third-deinsufflation. After injury, all animals were placed on volume-controlled mechanical ventilation to achieve PaO2 > 60 mmHg and PacO2 < 40 mmHg. Animals were placed on AVCO2R within 40 to 48 hours of injury when the PaO2/FiO2 was <200. Animals underwent cannulation of the carotid artery and jugular vein with percutaneous 10F arterial and 14F venous cannulas. Shunt flow was continuously monitored using an ultrasonic flow probe and calculated as a percentage of cardiac output.

RESULTS

AVCO2R flows of 800 to 900 ml/min (11% to 13% cardiac output) achieved 77 to 104 ml/min of CO2 removal (95% to 97% total CO2 production) while maintaining normocapnia. Significant reductions in ventilator settings were tidal volume, 421.3+/-39.8 to 270.0+/-6.3 ml; peak inspiratory pressure, 24.8+/-2.4 to 13.7+/-0.7 cm H2O; minute ventilation, 12.7+/-1.4 to 6.2+/-0.8 L/min; respiratory rate, 25.4+/-1.3 to 18.4+/-1.8 breaths/min; and FiO2, 0.88+/-0.1 to 0.39+/-0.1. The P/F ratio increased from 151.5+/-40.0 at baseline to 320.0+/-17.8 after 72 hours.

CONCLUSIONS

Percutaneous AVCO2R allows near-total CO2 removal and significant reductions in ventilator pressures with improvement in the P/F ratio.

A centrifugal pump driven tidal flow extracorporeal membrane oxygenation system tested with neonatal mock circulation

In 1993, Chevalier published his experiences with tidal flow venovenous extracorporeal membrane oxygenation (ECMO) featuring a single lumen cannula, non-occlusive roller pump, and alternating clamps. Using a neonatal mock circulation (NMC), which enables different hemodynamic states for neonatal ECMO research, the tested hypothesis was that it is possible to create a centrifugal pump driven tidal flow neonatal venovenous ECMO system. Additionally, the resulting hemodynamic effects in a condition of circulatory impairment were investigated. The ECMO circuit tested was assembled using a pediatric centrifugal pump head, a distensible reservoir, and a rotary clamp separating drainage from the injection phase. Using the NMC, end tidal volumes, mock circulation flow, and arterial and venous pressures were measured at different pump speeds after the drainage and injection phases. Effective venovenous ECMO flow (evvEF) was calculated. Mock circulation baseline values (ECMO clamped) were compared to values during tidal flow ECMO. At 3,000 rpm, a centrifugal pump speed of 75 ml/kg/min evvEF was reached, and it increased with higher pump speeds. At this point, the end tidal mock circulation flow (representing cardiac output) after drainage differed significantly from that during the injection phase (p < 0.01) but not from the baseline value. The end tidal arterial and venous pressures after the drainage phase were found to be significantly decreased compared to the baselines (p < 0.01). In conclusion, a centrifugal pump driven tidal flow venovenous ECMO system can be created enabling sufficient tidal volumes. Tested in the described NMC simulating posthypoxic circulatory impairment, significant hemodynamic effects could be demonstrated. Animal experiments for confirmation are necessary.

Total arteriovenous CO2 removal: simplifying extracorporeal support for respiratory failure

BACKGROUND

To reduce the complexity, complications, and cost of conventional extracorporeal membrane oxygenation, we have developed a technique of simplified arteriovenous extracorporeal CO2 removal (AVCO2R) with a low-resistance membrane gas exchanger for total CO2 removal to provide lung rest in the setting of severe respiratory failure.

METHODS

We initially used AVCO2R in healthy animals to quantify the gas exchange capabilities of the system and establish ventilator management protocols for the subsequent studies of AVCO2R in a large animal model of respiratory failure secondary to a severe smoke inhalation injury.

RESULTS

In healthy sheep the maximum spontaneous arteriovenous flow ranged from 1,350 to 1,500 mL/min, whereas CO2 removal plateaued at a blood flow of approximately 1,000 mL/min in which 112 +/- 3 mL/min CO2 was removed, allowing an 84% reduction in the minute ventilation of from 6.9 +/- 0.8 L/min to 1.1 +/- 0.4 L/min (p < 0.01) without triggering hypercapnia. A subsequent reduction in extracorporeal flow at a reduced minute volume led to the development of hypercapnia only if it decreased to less than 500 mL/min. We also applied AVCO2R in mechanically ventilated sheep with a severe smoke inhalation injury and removed 95% (111 +/- 4 mL/min) of the total CO2 production. This allowed the minute ventilation to be reduced by 95% and the peak inspiratory pressures by 52% (both p < 0.05) over 6 hours and produced no adverse hemodynamic effects. The partial pressure of arterial oxygen was maintained above 100 mm Hg at a maximally reduced minute volume. The mean AVCO2R flow was 1,213 +/- 29 mL/min, averaging 27% +/- 1% of the cardiac output.

CONCLUSIONS

We conclude that AVCO2R in a simple arteriovenous shunt is a less complicated technique than extracorporeal membrane oxygenation and is capable of total CO2 removal that allows a significant reduction in the minute ventilation and peak airway pressure during severe respiratory failure.

Prolonged hemodynamic stability during arteriovenous carbon dioxide removal for severe respiratory failure

OBJECTIVE

The effects of prolonged arteriovenous carbon dioxide removal on hemodynamics during severe respiratory failure were evaluated in adult sheep with severe smoke inhalation injury.

METHODS

Adult female sheep (n = 6,33.8 +/- 5.2 kg) were subjected to intratracheal cotton severe smoke insufflation to a mean carboxyhemoglobin level of 83% +/- 3%. Twenty-four hours after injury, a low-resistance 2.5 m2 membrane oxygenator was placed in a carotid-to-jugular pumpless arteriovenous shunt at unrestricted flow to allow complete carbon dioxide removal and reductions in ventilator support. Animals remained conscious, and heart rate, cardiac output, mean arterial pressure, and pulmonary arterial pressure were measured at baseline, after injury, and daily during support with the arteriovenous carbon dioxide removal circuit for 7 days.

RESULTS

All animals survived the study period. Carbon dioxide removal ranged from 99.7 +/- 13.7 to 152.2 +/- 16.2 ml/min, and five (83%) of the six animals were successfully weaned from the ventilator before day 7. During full support with the arteriovenous carbon dioxide removal circuit, shunt flow ranged from 1.24 +/- 0.06 to 1.43 +/- 0.08 L/min and accounted for 20.1% +/- 1.4% to 25.9% +/- 2.4% of cardiac output. No statistically significant changes in heart rate, cardiac output, mean arterial pressure, or pulmonary artery pressure were demonstrated over the study course despite the extracorporeal shunt flow.

CONCLUSIONS

Arteriovenous carbon dioxide removal as a simplified means of extracorporeal gas exchange support is relatively safe without adverse hemodynamic effects or complications.