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Pediatric Extracorporeal Life Support Using a Third Generation Diagonal Pump

Speth, Marlene; Münch, Frank; Purbojo, Ariawan; Glöckler, Martin; Toka, Okan; Cesnjevar, Robert A.; Rüffer, André

doi: 10.1097/MAT.0000000000000385
Pediatric Circulatory Support
Free

This study reports a single-centre experience of the Medos Deltastream diagonal-pump (DP3) for extracorporeal cardiac, pulmonary, or combined support in a single-center pediatric cohort. Twenty-seven consecutive patients with 28 runs of the DP3 between January 2013 and June 2014 were included for analysis. Median patient age, weight, and duration of support were 278 days (range: 0 days–14.2 years), 7.2 kg (range: 2.5–39 kg), and 8 days (range: 2–69 days). Midline sternotomy (n = 20, 71.4%) or cervical approaches (n = 8, 28.6%) were used for cannulation. The DP3 was employed for either veno-arterial extracorporeal life support (ECLS, n = 16), veno-venous extracorporeal membrane oxygenation (ECMO, n = 5), or ventricular assist devices (right ventricular assist device [RVAD], n = 1; left ventricular assist device [LVAD], n = 1; and univentricular assist device [UNIVAD], n = 5). Three patients initially supported with ECLS were switched to UNIVAD and one patient with UNIVAD was changed to ECLS. Required flow for neonates (n = 8) ranged between 0.2 and 0.75 L/min. Irreversible pump damage occurred in one patient during deairing after air block. Successful weaning, 30 day and hospital survival were 89.3% (n = 25), 85.7% (n = 24), and 71.4% (n = 20). All patients on UNIVAD, who did not require further extracorporeal respiratory assist, survived. In conclusion, the DP3 can be used for individual patient demands and adapted to their most suitable method of support. Meticulous flow adjustments render this pump highly effective for extracorporeal support particularly in pediatric patients.

From the *Department of Pediatric Cardiac Surgery, and Department of Pediatric Cardiology, University-Hospital Erlangen, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Erlangen, Germany.

Submitted for consideration December 2015; accepted for publication in revised form April 2016.

The study was performed in fulfillment of the requirement for obtaining the degree “Dr. med.”

Disclosure: André Rüffer served as board member and lectured for Xenios Pediatrics.

Correspondence: André Rüffer, MD, Department of Pediatric Cardiac Surgery, University Hospital Erlangen, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Loschgestraße 15, 91054 Erlangen, Germany. Email: andre.rueffer@uk-erlangen.de.

Whether conventional therapy of patients with acute, potentially reversible pulmonary, cardiac, or combined organ failure does not prove successful, timely extracorporeal support can be potentially lifesaving.1 Veno-venous ECMO is an end-stage therapy for isolated pulmonary failure in patients where artificial CO2 removal and increase in arterial oxygenation is needed.2–5 Veno-arterial extracorporeal life support (ECLS) can be used in patients with combined cardio respiratory failure6,7 and is commonly implanted as a bailout therapeutic intervention in children with low cardiac output or sudden cardiac arrest after cardiac surgery.8,9 It may also be employed as a bridge to transplantation.10 A ventricular assist device (VAD) can be used in patients with isolated ventricular failure, but still with sufficient ventilation as a bridge to decision or bridge to recovery.11–13

In the late 1980s, centrifugal pumps were introduced as an alternative to the “classical” standard roller pump.14 Rotary pumps are either axial or centrifugal pumps, and diagonal pumps are a combination of both technologies.15 The Deltastream diagonal pump (DP3; Medos Medizintechnik AG, Heilbronn, Germany) is the third generation of a diagonal rotational pump which has undergone significant changes in design and handling. The metal shaft and sealing ring have been removed from the magnetically coupled pump head. Heat generation is prevented by less shear stress from the bearing, resulting in less blood trauma.15 The minimal priming volume is 16 ml16–18 and, like the DP1,13 pump settings are able to create a pulsatile flow.15,17 The ideal working range is between 2,000 and 8,000 unit/min, achieving flow ranges between 0 and 7 L/min. Flow can be managed in 10 ml steps or by 50 rotations per min (rpm) down to zero-flow without imminent backflow, as it is the case in nonocclusive pumps.10 The DP3 is coupled to a console (MDC, Medos Medizintechnik AG, Heilbronn, Germany) which includes safety features offering both a bubble sensor and four pressure sensors to control flow and pressure within the system.

Since 2013 exclusively the DP3 has been used for cardiac, pulmonary, or combined extracorporeal support for pediatric patients in our hospital and with this study we aim to share our experience of its performance.

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Materials and Methods

Patients

The local ethics committee was notified and the institutional review board provided approval for data collection. Parental consent was waived. All consecutive pediatric patients (<16 years) who received extracorporeal mechanical support with the DP3 between January 2013 and June 2014 were retrospectively included in the analysis.

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Material

All mechanical support systems in our institution are implanted by pediatric cardiac surgeons and maintained by a perfusionist. The DP3 rotational pump is controlled via a MDC console. Membrane oxygenators are used according to calculated flow and included the Hilite LT800 for flow rates <800 ml/min, the Hilite LT2400 for 800–2,000 ml/min (Medos) and the A.L.One ECMO oxygenator (Eurosets, Medolla, Italy) for flow rates >2,000 ml/min.

For arterial cannulation, straight 8–12 F Maquet cannulas 163608–12 (Maquet, Rastatt, Germany), 14–16 F Medtronic-Paediatric One Piece cannulas 77014–16, and 18–22 F Medtronic EOPA cannulas 77418–22, and for venous cannulation, straight 12–32 F Medtronic cannulas 66012–032 were inserted (Medtronic, Meerbusch, Germany). For double lumen venous cannulation, the 13–19 F Avalon cannula (Maquet) was employed.

Exclusively laminar flow was used. Full flow of the mechanical system (ECLS and VAD) was adapted to the body surface area of the patient (L/m2/min) and multiplied by a factor of 3.0 for patients <5 kg, 2.8 (L/m2/min) for patients between 5 and 10 kg, and 2.6 (L/m2/min) for patients >10 kg. Extracorporeal membrane oxygenation was aimed at 30–40% of the estimated full flow.

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General Considerations on Mechanical Support

An overview regarding the principles of mechanical support and their cannulation sites is given in Figure 1. The thoracic approach is suitable for all modes of VAD support: via the left atrium and aorta for left ventricular assist device (LVAD; F igure 2A), or right atrium and pulmonary artery for right ventricular assist device (RVAD; Figure 2B). In patients with single ventricle physiology and systemic-to-pulmonary shunt a UNIVAD system can be employed after cannulation of the common atrium and the ascending aorta. Sternotomy is applied for the deployment of ECLS after arterial cannulation of the aorta and single venous or biatrial cannulation of the right or right and left atrium (Figure 2C). Alternatively, the cervical approach is considered for ECLS allowing simultaneous cardiopulmonary resuscitation (CPR) during the surgical preparation of the internal carotid artery and internal jugular vein. For isolated ECMO support, the Avalon cannula is advanced percutaneously into the right atrium via the right internal jugular vein (Figure 2D).

Figure 1

Figure 1

Figure 2

Figure 2

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Monitoring

A clinical multidisciplinary bedside visit was performed two times per day. Frontal cortex oxygen saturation and end organ perfusion in the kidneys was monitored continuously using near-infrared spectroscopy (INVOS 5100C, Covidien, Neustadt/Donau, Germany).19 Activated partial thromboplastin time was maintained at 60–80 seconds. In case of visible thrombi in the support system, increased platelet transfusion requirements and increasing levels of fibrin degradation products (D-dimers), total mechanical support system exchange (except cannulas) was implemented. Macrohematuria raised suspicion of pump induced damage of corpuscular blood components. Device weaning was monitored by transthoracic or transesophageal echocardiography and assessment of respiratory or cardiac ischemic markers indicating cardiac or pulmonary recovery.20

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Statistical Analysis

Descriptive data for continuous variables are reported as median with ranges or mean ± standard deviation. Categorical variables are presented as numbers or percentages. Patients who underwent cardiac surgery before initiation of mechanical support were defined as post cardiotomy patients. Patients who survived for more than 24 hours after the removal of the mechanical support system were counted as successfully weaned patients. All deaths up to 30 days after the implantation of the mechanical support system or during hospital stay are categorized as early or hospital mortality.

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Results

Patients

Twenty-seven patients receiving 28 runs with the DP3 were included in the study. Median age and weight were 278 days (range: 0 days–14.2 years) and 7.2 kg (range: 2.5–39 kg). The majority of patients were younger than 1 year (neonates 28.6% [n = 8]; infants 25% [n = 7]). One patient with heterotaxy received mechanical support treatment twice: after the correction of a total anomalous pulmonary venous connection and deployment of an aortopulmonary shunt (patient 171), and 4 months later post diagnostic cardiac catheterization (patient 172).

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Approaches and Types of Mechanical Support

Type of mechanical support, support indication, and outcome are stated in Table 1. Approaches and initial methods of support are shown in Figure 3. The cervical approach was chosen for eight (28.6%) DP3 runs and the remaining 20 (71.4%) were managed via sternotomy.

Table 1

Table 1

Figure 3

Figure 3

Primary and secondary pulmonary failure was supported by cervical ECMO via Avalon cannula (n = 5), apart from two patients (patients 7 and 16). The first was stabilized via cervical ECLS as she presented with cardio respiratory failure 6 months after cardiac surgery. The second suffered from streptococcal pneumonia with pneumothoraces despite multiple chest tubes and was supported by thoracic ECLS, to treat lung fistulae.

Patients with cardiac failure were usually approached by sternotomy and supported by ECLS (n = 19). Exceptions were made in two of those patients, who were cannulated via neck vessels because of ongoing CPR: patient 172 was resuscitated 4 months after Glenn-take down during cardiac catheterization; patient 15 was rewarmed after drowning and CPR over 75 minutes. In addition, VADs were implanted in four patients with isolated cardiac failure and sufficient pulmonary function (patients 4, 17,1 22, 24).

Four patients were changed to a different support device during the course of the treatment. Patient 22 received UNIVAD after he failed to wean off bypass. As his oxygen saturation dropped later on the same day, an oxygenator had to be implanted and he was switched to ECLS on ICU. Patients 5, 18, and 23 were first treated with ECLS, and then changed to UNIVAD as their lungs recovered after 5, 5, and 4 days, respectively.

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Technical Protocol

Mean duration of support was 12 ± 15 days (median: 8 days [range: 2–69 days]). Flow ranges for neonates were considerably lower for ECMO therapy (range: 0.2–0.3 L/min) than for ECLS support (range: 0.4–0.75 L/min).

The average running time of a singular support system without exchange was 5 days (range: 0–20 days). In total, 37 exchanges of mechanical support systems were conducted in 13 patients. The median system exchange rate was 0 per patient (range: 0–8). There was no hemolysis related exchange of the pump head.

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Outcome

Weaning from extracorporeal support was successful in 89.3% (n = 25) of all DP3 runs. The 30 day survival was 85.7% (n = 24) and hospital survival accounted to 71.4% (n = 20; Figure 4).

Figure 4

Figure 4

All patients with pulmonary indication survived, except patient 20 with myelodysplastic syndrome, who received ECMO because of respiratory failure after bone marrow transplantation. Both patients with biventricular morphology and DP3-VAD survived. Moreover, all patients with UNIVAD, who did not need further extracorporeal respiratory assist (n = 4), were discharged. Patient 22 with coronary sinusoids was switched from UNIVAD to ECLS and died of cardiac failure despite successful weaning. Further six patients with primary ECLS died in hospital: In patient 1, aortic cannula dislocation led to urgent thoracotomy and system exchange but sufficiently stable circulation was not achieved. Patient 3 was successfully weaned from the device, extubated, and transferred to the ward but died later because of sudden circulatory arrest. In patient 10, upper caval rupture after balloon dilatation resulted in an air block after urgent rethoracotomy with a system standstill. The pump was damaged during CPR and deairing, and had to be exchanged. The patient could be weaned from the device, but expired later in hospital. In patient 13, increasing venous under pressure resulted in successive flow deregulation of the pump down to zero flow. Further mechanical support was abandoned after ineffective CPR. In two patients, ECLS was discontinued as the patients developed brain edema: Patient 172 had grave, congenital heart pathology, and ECLS in the context of post catheterization CPR; in patient 8, ECLS was implanted during CPR as bridge to EXCOR Pediatric (BerlinHeart GmbH, Germany) for decompensated dilated cardiomyopathy. Patient 15, who was rewarmed via cervical ECLS after drowning and CPR over 75 min, developed a left-sided hemiplegia with a right medial cerebral artery infarction confirmed on computed tomography (CT).

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Discussion

Nomenclature

There is a lack of uniform nomenclature to distinguish between distinct extracorporeal therapies for cardiac, pulmonary, or cardiopulmonary failure.

Some authors in the field use ECLS17,21,22 or ECMO2–6,8–10,12,13,15,18–20,23 as all-inclusive terms, or use va-ECMO/vv-ECMO3,5 to differentiate by vessel cannulation. The German Society for Cardiovascular Engineering suggests the use of specific terminology (i.e., VAD, ECMO, and ECLS7,11,16,24) to differentiate between extracorporeal treatment scenarios, to enable precision in communication, maximize quality of treatment, and improve patient outcome. This will be reflected in the society’s newest guidelines, which are currently under review.

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Outcome

To date, this is the largest single centre serial study with the DP3 for extracorporeal mechanical support in a pediatric patient cohort.18,25 Compared with other studies, our pediatric patient cohort was heterogeneous comprising patients with pulmonary, postcardiotomy and other support indications, with both single and biventricular morphology. Of all seven patients with isolated respiratory support, only one patient with myelodysplastic syndrome (patient 20) could not be weaned from the device. This confirms other observations, which show that respiratory mechanical support offers higher chances of survival than cardiac assist22 but is often limited in patients with hematologic disorder.21 All patients, who were treated with VAD and did not require further extracorporeal respiratory support, survived. A waiver of the oxygenator has many advantages as around 90% reduction in surface area makes the patient prone to less coagulopathy, inflammatory reaction, and thrombembolic events.12 Extracorporeal life support ECLS patients are a much sicker patient group, as they suffer from combined cardio respiratory failure. All ECLS patients apart from two could be weaned from the device, yet only 63% could be discharged from hospital.

In literature, successful weaning rates from transient extracorporeal support range between 69% and 79% and the survival to hospital discharge rate is even lower, between 34% and 63%.9,12,19,22–24 In our cohort, almost all patients who survived at least 24 hours after mechanical support discontinuation (89.3%) also survived the first 30 days post mechanical support implantation. The gap between successful weaning and hospital survival (71.4%) may anticipate the sometimes still palliative character of extracorporeal support therapy as aspects influencing the outcome are mainly based on the underlying disease.

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Assist-Related Complications

In this study, only the thoracic and cervical approach were used and therefore compartment syndrome, fasciotomy, or amputation of lower extremity, sometimes coincidental after cannulation of femoral vessels, did not occur.18

Technical complications comprised aortic cannula dislocation which could not adequately be managed (patient 1), and an air block leading to pump exchange because of damage of the pump during deairing (patient 10). Hence, pump failure was in first line user and not hardware induced. We did not observe long-standing macrohematuria indicating pump-induced corpuscular trauma under support system therapy.

A system standstill occurred in patient 13, resulting from venous under pressure. Stepwise down regulation of the DP3 prevented suction or rupture of the atrial wall and eliminated backflow from the aorta into the system. Nevertheless, immediate sufficient correction of hypovolemia or adequate positioning of the venous cannula might have saved the patient.

Neurologic complications were eminent in three patients (patients 5, 15, and 172), who had undergone prolonged CPR. Patient 15 was cannulated via neck vessels and developed signs of hemiplegia. It is unclear whether hemodynamic arrest before support, cerebral embolism, or the cannulation of one common carotid artery can be associated with diminished cerebral perfusion and hence induce cerebral ischemia. Reports on this cannulation technique usually refer to newborn or infant circulatory support, without giving any indication until what age this approach is safe.2

Small sized blood clots in the venous line or pump compartment of the system usually pass through the pump and accumulate in the oxygenator without endangering the patient. Despite the lack of this filtering mechanism by the oxygenator in patients with VAD no thrombosis or embolisms were observed even in this patient group. Lifetime of a support system in our cohort was usually dependent on the oxygenator, and terminated by system exchange on basis of elevated fibrin degradation products or increased platelet transfusion requirements.

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Performance of the DP3

It was shown that calculated low flow rates needed for support particularly in neonates can be maintained over a long period of time. Even though other pumps offer the possibility of pulsatile flow15,17 or zero flow, it is the prevention of backflow and features for pressure, bubble, and flow control offering fine adjustments down to zero, which make the DP3 safe. Compared with its predecessors heat generation was abandoned and the DP3 treats corpuscular blood more gentle. Critical elements of construction related to the whole system are the connecting tubes, which conically increase from the venous 1/4 inch to 3/8 inch at the pump entrance. This may predispose to turbulent flow and thrombus formation.

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Limitations

Limitations are inherent in the nature of a single centre, retrospective study with a relatively small cohort and short observation period. Comparison to other support systems was not made. In our unit, markers of hemolysis (haptoglobin or free hemoglobin) are not part of routine laboratory chemistry control.

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Conclusions

In a heterogeneous pediatric cohort, the Deltastream DP3 pump has proofed to be a versatile and safe tool in mechanical support therapy, which can be adapted to the individual circumstances and necessities of the patient, even in low-flow ranges.

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References

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Keywords:

extracorporeal life support; extracorporeal membrane oxygenation; diagonal pump; DP3; congenital heart disease

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