Neonatal and pediatric extracorporeal membrane oxygenation using nonocclusive blood pumps: the Vienna experience

40 years neonatology : An academic life

BACKGROUND

A complete review of the development of neonatology in the last 40 years would probably require a compendium with several volumes, to bring to view the remarkable improvements in survival rates and neurodevelopmental outcomes of ill babies in Austria, most industrial countries and to some extent worldwide. The challenge I had to solve here was to integrate my own contributions to the field of neonatology during this period and particularly the contributions of my team from the Division of Neonatology and Pediatric Intensive Care Medicine, Department of Pediatrics and Adolescence Medicine, Medical University Vienna where I was working first as an intern and resident and later had the privilege to become head of department.

AIM

This very personal review was conceived to showcase the milestones of neonatology where, in my opinion, our department made some meaningful contributions in research and clinical practice during the past 40 years.

METHODS

A total of 10 areas of interest were selected which most likely influenced survival rates of preterm infants born at increasingly younger gestational ages and ameliorated long-term clinical and neurodevelopmental outcomes, including: 1) Construction and continuous modernization of neonatal intensive care units (NICUs). 2) Installation of the "Regionalization Program for NICUs in Vienna". 3) Treatment of respiratory distress syndrome (RDS) of premature babies. 4) Fine tuning of glucose metabolism for growth and outcome. 5) Neurodevelopmental care. 6) Neonatal hematology. 7) Infection control. 8) The toxoplasma screening program. 9) The newborn screening program. 10) Quality control: the Vermont Oxford Neonatal Network (VONN).

RESULTS

Over the past four decades advancements in research and technology have allowed a transformative development of neonatal medicine. Survival rates without increased morbidity for very premature infants with gestational ages reaching to what we consider nowadays the border of viability have constantly increased. In my professional life as a neonatologist in Austria I have had the possibility to support and shape some of these developments together with my team.

CONCLUSION

As we look ahead it is imperative to build upon the progress made, harnessing the power of science and technology to further improve the survival and quality of life for preterm infants in Austria and worldwide. At the same time, neonatology must continue to prioritize ethical reflection and education, fostering a culture of integrity, interdisciplinary collaboration, and the development of guidelines and protocols that uphold ethical standards while addressing the evolving needs and complexities of neonatal medicine.

Computer-assisted numerical analysis for oxygen and carbon dioxide mass transfer in blood oxygenators

A two-dimensional numeric simulator is developed to predict the nonlinear, convective-reactive, oxygen mass exchange in a cross-flow hollow fiber blood oxygenator. The numeric simulator also calculates the carbon dioxide mass exchange, as hemoglobin affinity to oxygen is affected by the local pH value, which depends mostly on the local carbon dioxide content in blood. Blood pH calculation inside the oxygenator is made by the simultaneous solution of an equation that takes into account the blood buffering capacity and the classical Henderson-Hasselbach equation. The modeling of the mass transfer conductance in the blood comprises a global factor, which is a function of the Reynolds number, and a local factor, which takes into account the amount of oxygen reacted to hemoglobin. The simulator is calibrated against experimental data for an in-line fiber bundle. The results are: (i) the calibration process allows the precise determination of the mass transfer conductance for both oxygen and carbon dioxide; (ii) very alkaline pH values occur in the blood path at the gas inlet side of the fiber bundle; (iii) the parametric analysis of the effect of the blood base excess (BE) shows that (.)V(CO₂) is similar in the case of blood metabolic alkalosis, metabolic acidosis, or normal BE, for a similar blood inlet P(CO₂), although the condition of metabolic alkalosis is the worst case, as the pH in the vicinity of the gas inlet is the most alkaline; (iv) the parametric analysis of the effect of the gas flow to blood flow ratio (QG/QB) shows that (.)V(CO₂) variation with the gas flow is almost linear up to QG/QB = 2.0. (.)V(O₂) is not affected by the gas flow as it was observed that by increasing the gas flow up to eight times, the (.)V(O₂) grows only 1%. The mass exchange of carbon dioxide uses the full length of the hollow-fiber only if Q(G) /Q(B)> 2.0, as it was observed that only in this condition does the local variation of pH and blood P(CO₂) comprise the whole fiber bundle.

Increased hemolysis from saline pre-washing RBCs or centrifugal pumps in neonatal ECMO

OBJECTIVES

Hemolysis is a significant complication of extracorporeal membrane oxygenation (ECMO), with a reported incidence of 12.2%. The aims of this study were (1) to investigate hemolysis caused by saline-washed versus unwashed RBCs, (2) to determine in vitro the effects of saline washing on erythrocyte hemolytic markers and (3) to investigate hemolysis by centrifugal versus roller pumps.

STUDY DESIGN

(1) To evaluate the effect of pre-transfusion saline-washing versus non-washing, the peak plasma-free hemoglobin (FHb) and total bilirubin in the first 3 days versus the next 4 days of ECMO were compared (2) Pre- and postsaline-washed RBCs were analyzed for K+ hemoglobin, mean corpuscular volume, FHb and hemolysis at baseline and after 4 h of storage at 4 degrees C. (3) Over 10 000 neonatal ECMO cases were retrospectively reviewed to study the effect of pump type on hemolysis.

RESULTS

(1) The washed blood group had significantly more hemolysis within the first 3 days of ECMO. (2) Immediately after saline washing, the K+ and Hb concentrations were significantly decreased compared with unwashed blood, and these differences were maintained after 4 h. The osmotic fragility of washed RBCs after 4 h of storage at 4 degrees C was significantly higher than at baseline. (3) Hemolysis was reported more often in the centrifugal than in the roller pump group.

CONCLUSIONS

(1) Using unwashed RBCs decreased hemolysis within the first 3 days of ECMO. (2) Saline washing, while decreasing the concentration of K+ in the plasma, significantly increases RBC membrane osmotic fragility. (3) Hemolysis is linked to the use of centrifugal pumps.

Quantitative Electroencephalography Values of Neonates During and After Venoarterial Extracorporeal Membrane Oxygenation and Permanent Ligation of Right Common Carotid Artery

Venoarterial extracorporeal membrane oxygenation (ECMO) in neonates commonly needs neck vessel cannulation leading to ligation of right common carotid artery (RCCA) in some cases. Quantitative electroencephalography (EEG) measurements provide reproducible data of cerebral function. The aim of this case-control study was to test whether ligation of the RCCA results in EEG changes after ECMO weaning. Ten mechanically ventilated neonates not treated with ECMO were eligible as control patients. Seven ECMO patients receiving similar sedoanalgesia were investigated during and after ECMO and RCCA ligation. Dominant frequency, absolute alpha, theta, delta, and total powers of right and left frontocentral and temporooccipital derivations were calculated. Dominant frequency did not differ among groups. Power was found to be significantly decreased in all frequency bands during ECMO. After weaning from ECMO, EEG differences between the ECMO and control groups disappeared in spite of permanent RCCA ligation. It is concluded that ligation of the RCCA per se does not result in quantitative EEG changes.

Pediatric cardiopulmonary bypass devices: trends in device use for cardiopulmonary bypass and postcardiotomy support

Cardiopulmonary bypass (CPB) devices and techniques have continuously evolved. We have conducted surveys that chronicle the changes in CPB devices and techniques used at North American pediatric cardiac surgery centers since 1989. The aim of this article is to describe trends in cardiopulmonary bypass device use during cardiac surgery and changes in the devices used for extracorporeal life support (ECLS) following cardiac surgery for pediatric patients. The diffusion of innovation in pediatric cardiovascular surgery has not been solely driven by the availability of scientific evidence to support change but rather it has often been related to other factors that influence clinicians willingness to change including; tradition, ease of use, and cost related pressures. The current CPB systems used for cardiac surgery are more homogenous than in previous years. Most centers use a heparin coated or modified surface system comprised of a "hard shell" open venous reservoir, a roller pump, a hollow fiber membrane oxygenator, and arterial line filter. ECLS systems comprised of hollow fiber oxygenators and centrifugal pumps for are gradually replacing the classical ECLS circuit, servo regulated roller pumps and silicone rubber membranes. Nearly 40% of centers use these alternate components in their ECLS systems. Costs, utility, safety and measurable benefit to the patient should guide decisions related to device selection.

Development of disposable self-regulating blood pumps and automatically-controlled portable extracorporeal membrane oxygenation systems for neonatal extracorporeal membrane oxygenation

For safer and simpler neonatal ECMO management, the authors have been developing an innovative, automatically-controlled ECMO machine using self-regulating blood pumps. The newest model is an air-driven, tube-type blood pump. A pair of blood pumps are placed in parallel and actuated alternately with compressed air. The pump flow is automatically regulated in accordance with hemodynamic changes of the body. The need for a venous reservoir is eliminated because the circuit does not generate excessive negative pressure when there are shortages of draining blood. Therefore, the priming volume of the circuit is only 85 ml. This ECMO apparatus has three driving modes, one of which is a "delay" mode. This enables the pump flow to easily be varied from 10 to 500 ml/min under automatic control, and it can be used when the pump flow is decreased for weaning. This newest ECMO apparatus was clinically used in 3 neonates with severe lung hypoplasia and persistent fetal circulation. The ECMO duration was 139 h to 168 h, and the maximum ECMO flow 71.3 to 109.0 ml/min/kg. Thanks to the self-regulation, intensive observation of the circuit was not necessary during ECMO. Damage to blood cells was less significant, and the use of blood products was only minimal (15.7 ml/kg/day) because a large volume of blood to stabilize the pump performance was not necessary. In conclusion, the automatically-controlled ECMO apparatus worked well without complications by changing the ECMO flow automatically in accordance with hemodynamic changes. This automatic ECMO system required fewer personnel expenditures and was also favorable in terms of hematological findings.