Different mechanisms of oxygenator failure and high plasma von Willebrand factor antigen influence success and survival of venovenous extracorporeal membrane oxygenation

OBJECTIVE

Failure of membrane oxygenator (MO) function of venovenous extracorporeal membrane oxygenators (VV ECMO) remains problematic. The development of device-induced coagulation disorder (COD) or worsened gas transfer (WGT) necessitates a system exchange. The aim was to correlate von Willebrand factor antigen (vWF:Ag) with the predisposition to MO failure and mortality.

METHODS

Laboratory parameters (inflammation, coagulation) and ECMO-related data from 31 VV ECMO patients were analyzed before and after the first MO exchange. Study groups were identified according to the exchange reasons (COD, WGT) and the extent of vWF:Ag (low, ≤425%; high, >425%).

RESULTS

vWF:Ag remained unchanged after system exchange. High vWF:Ag was associated with systemic endothelial activation of older and obese patients with elevated SOFA score, increased norepinephrine and higher requirement of continuous renal replacement therapy without an effect on MO runtime and mortality. Including the mechanism of MO failure (COD, WGT), various patient group emerged. COD/low vWF:Ag summarized younger and less critically ill patients that benefit mainly from ECMO by a significant improvement of their inflammatory and coagulation status (CRP, D-dimers, fibrinogen) and highest survival rate (91%). Instead, WGT/high vWF:Ag presented older and more obese patients with a two-digit SOFA score, highest norepinephrine, and aggravated gas transfer. They benefited temporarily from system exchange but with worst survival (33%).

CONCLUSIONS

vWF:Ag levels alone cannot predict early MO failure and outcome in VV ECMO patients. Probably, the mechanism of clotting disorder in combination with the vWF:Ag level seems to be essential for clot formation within the MO. In addition, vWF:Ag levels allows the identification different patient populations In particular, WGT/high vWF:Ag represented a critically ill population with higher ECMO-associated mortality.

Comparison of hollow-fiber membrane oxygenators in terms of pressure drop of the membranes during normothermic and hypothermic cardiopulmonary bypass in neonates

The objective of this study was to investigate the effects of two hollow-fiber membrane oxygenators, the Capiox SX10 and the Lilliput 901, on pressure drop of the membranes during normothermic and hypothermic cardiopulmonary bypass (CPB) in neonates.

Methods: Twenty-six congenital heart surgery patients (n=13 in each group) with a mean weight of 3 kg were included in this study. Pressure drops of the membranes, pre- and post-oxygenator extracorporeal circuit pressures (ECC) were recorded during normothermic CPB, hypothermic CPB (208C) and after rewarming. There were no differences between the groups in mean arterial pressure, pump flow rate, temperature, duration of CPB, cross- clamp time or the severity of the surgical repairs.

Results: Pressure drop of the Capiox SX10 oxygenator was significantly lower during normothermic (329/10 versus 559/16 mmHg, p B/0.001), hypothermic (389/15 versus 729/18 mmHg, p B/0.001) and post-rewarming (429/13 versus 729/21 mmHg, p B/0.001) periods compared to the Lilliput oxygenator. In the Capiox group, the pre-oxygenator ECC pressure was also significantly lower during normothermic CPB (1429/27 versus 1849/43 mmHg, p B/0.01), hypothermic CPB (1629/30 versus 1999/38 mmHg, p B/0.01) and after rewarming periods (1729/32 versus 2129/42 mmHg, p B/0.01). Post-oxygenator pressures in the Capiox group were also lower than in the Lilliput group, but results were not statistically significant.

Conclusions: These results suggest that the Capiox SX10 hollow-fiber membrane oxygenator produced significantly lower membrane pressure drops and pre- and post-oxygenator ECC during normothermic and hypothermic CPB. Thus, blood trauma with the Capiox during extracorporeal circulation may be significantly lower compared to the Lilliput. Further studies, including the level of complements, platelets, neutrophils and cytokines, with these oxygenators are warranted.

Performance of polymethyl pentene oxygenators for neonatal extracorporeal membrane oxygenation: a comparison with silicone membrane oxygenators

Objective: To review the performance of polymethyl pentene versus silicone oxygenators in terms of efficiency in priming and oxygenation, oxygenator resistance, requirements for coagulation proteins and consumption of blood products, for neonatal extracorporeal membrane oxygenation (ECMO) patients.

Study design: Forty consecutive neonates were selected retrospectively pre- and post-introduction of the new polymethyl pentene (PMP) oxygenators. They formed two equal groups. After calculation of the sample size, data were collected from ELSO registry forms and patient records. Results were analysed using parametric and non-parametric tests.

Results: Neonatal PMP (N-PMP) oxygenators were smaller, faster and easier to prime. They were less efficient than silicone oxygenators, especially in carbon dioxide elimination, and, therefore, required higher sweeps. The preservation of coagulation proteins was significantly better, but there was no reduction in the consumption of blood products, despite having less than half the surface area and significantly lower blood path resistance.

Conclusion: Small PMP oxygenators (Medos Hilite 800 LT) provide adequate gas exchange and offer technical advantages in terms of more efficient priming, reduced haemodynamic resistance and better control and preservation of coagulation proteins than silicone oxygenators.

[Extracorporeal membrane oxygenation treatment of a neonate with severe low cardiac output syndrome following open heart surgery]

OBJECTIVE

To summarize the experience of extracorporeal membrane oxygenation (ECMO) to rescue a neonate with severe low cardiac output syndrome following open heart surgery.

METHODS

The patient was a male, 2 d, 2.8 kg, G3P2 full-term neonate with gestational age 40 weeks, born by Cesarean-section with Apgar score of 10 at 1 min. He was admitted due to severe dyspnea with oxygen desaturation and heart murmur on the second day after birth. Physical examination showed clear consciousness, cyanosis, dyspnea, RR 70 bpm and a grade II/6 heart murmur. Bp was 56/45 mm Hg (1 mm Hg = 0.133 kPa) and SpO2 around 65%. Blood WBC 13.1 x 10(9)/L, N 46.1%, Hb 238 g/L, Plt 283 x 10(9)/L, CRP < 1 mg/L. Echocardiographic findings: TGA + ASD + PDA with left ventricular ejection fraction (LVEF) of 60%. After supportive care and prostaglandin E1 (5 ng/kg/min) treatment, his condition became stable with SpO2 85 - 90%. On the 6(th) day of life, the baby underwent an arterial switch procedure + ASD closing and PDA ligation. The time of aorta clamp was 72 mins. The cool 4:1 blood cardioplegia was given for 2 times during aortal clamp. Ultrafiltration was used. The internal and external volumes were almost equal and the electrolytes and blood gas and hematocrit (36%) were normal during extracorporeal bypass. Due to a failure (severe low cardiac output) to wean from cardiopulmonary bypass (263 min) with acidosis (lactate 8.8 mmol/L), low blood pressure (< 39/30 mm Hg), increased LAP (> 20 mmHg), bloody phlegm, decreased urine output [< 1 ml/(kg.h)], a V-A ECMO was used for cardio-pulmonary support. ECMO setup: Medtronic pediatric ECMO package (CB2503R1), carmeda membrane oxygenator and centrifugal pump (bio-console 560) were chosen. Direct cannulation of the ascending aorta (Edward FEM008A) and right atrium (TF018090) was performed using techniques that were standard for cardiopulmanory bypass. The ECMO system was primed with 400 ml blood, 5% CaCl(2)1g, 5% sodium bicarbonate 1.5 g, 20% mannitol 2 g, albumin 10 g, and heparin 5 mg. The blood was re-circulated until the temperature was 37 degrees C and blood gases and the electrolytes were in normal range. The patient was weaned from bypass and connected to V-A ECMO. Management of ECMO: the blood flow was set at 150 - 200 ml/kg/min. Venous saturation (SvO2) was maintained at the desired level (75%) by increasing and decreasing extracorporeal blood flow. Systemic blood pressure was maintained at 76/55 - 80/59 mm Hg by adjusting blood volume. Hemoglobin was maintained between 120 - 130 g/L. Platelet count was maintained at > 75,000/mm3 and ACT was maintained at 120 - 190 s. The mechanical ventilation was reduced to lung rest settings (FiO2 35%, RR 10 bpm, PIP 16 cm H(2)O, PEEP 5 cm H2O) to prevent alveolar collapse. Inotropic drug dosages were kept at a low level.

RESULTS

The patient was successfully weaned from ECMO following 87 hours treatment. LVEF on day 1, 2 and 3 following ECMO were 20%, 34% and 43% respectively. The circulation was stable after weaning from ECMO with Bp 75/55 mm Hg, HR 160 bpm and LAP 11 mm Hg under inotropic drug suppor with epinephrine [(0.2 microg/(kg.min)], dopamine [(8 microg/(kg.min)], milrinone [(0.56 microg/(kg.min)]. The blood gases after 1 h off-ECMO showed: pH 7.39, PaO2 104 mm Hg, PaCO2 45 mm Hg, lactate 3.8 mmol/L, Hct 35%, K(+) 3.8 mmol/L, Ca(++) 1.31 mmol/L. The serum lactate was normal after 24 h off-ECMO. On day 22 off-ECMO, the baby was successfully extubated and weaned from conventional ventilator. On day 58, the patient was discharged. Serial ultrasound imaging studies revealed no cerebral infarction or intracranial hemorrhage during and after ECMO. At the time of hospital discharge, the patient demonstrated clear consciousness with good activity, normal function of heart, lung, liver and kidney. However, more subtle morbidities, such as behavior problems, learning disabilities should be observed ria long term follow-up. The main ECMO complications were pulmonary hemorrhage, bleeding on the sternal wound, tamponade, hemolysis and hyperbilirubinemia.

CONCLUSION

ECMO is an effective option of cardio-pulmonary support for neonate with low cardiac output syndrome following open heart surgery.

Oxygenation index for extracorporeal membrane oxygenation: is there predictive significance?

Although extracorporeal membrane oxygenation (ECMO) is known to improve survival in neonates with respiratory failure, there has been a significant decrease in the use of ECMO in recent years. Alternative modalities such as high-frequency oscillatory ventilation (HFOV), inhaled nitric oxide (iNO), and surfactant therapy are associated with this decline. The criteria for the initiation of ECMO, developed about 20 years ago, are likely no longer relevant. We examined the predictive significance of the oxygenation index (OI) as a patient entry criterion for ECMO use. We sought a critical OI level predicting death or chronic lung disease (CLD) with and without ECMO use. We also examined whether patients with certain OIs are more likely to have worse outcomes. One hundred and seventy-four term-newborn admissions between 1995 and 2000 requiring mechanical ventilation were enrolled in the study. Receiver operating curve analysis was performed to find a cutoff value of OI for ECMO initiation. Mortality rates and CLD probability were compared to the worst OIs. Our 6-year ECMO administration experience showed that an OI of 33.2 is a suitable cutoff value for ECMO initiation with high sensitivity and specificity as a predictive criterion. The critical OI value associated with the CLD risk when ECMO is not used is in the 40s. OI is a good predictor of CLD; the probability of CLD increases with higher OIs. Our data support the trend toward the use of new interventions over ECMO, especially for patients with OI scores of less than 33.2. Only when the probability of ventilator-associated lung injury becomes significant is it better to consider ECMO than conventional modalities.

A survey of cardiopulmonary bypass perfusion practices in Australia in 1992

Twenty-four cardiopulmonary bypass (CPB) perfusion units around Australia were surveyed to determine the characteristics of CPB perfusion as practised in Australia in 1992. Twenty completed survey forms were received. Findings were compared with those of a similar study performed by one of the authors for the year 1986. The field of CPB perfusion continues to expand both in terms of numbers of cases and increasing technological complexity. The major technological changes evident are the now clear dominance of membrane over bubble oxygenators and the proliferation of inline SvO2 monitoring devices. The greatest change in practice has been to the virtually universal use of cardioplegia. There remains considerable variation in the composition of the cardioplegia solutions used in the responding units. A range of minimum perfusion pressures for CPB is noted, whereas most units employ similar minimum perfusion flows. Methods of central nervous system and renal protection are mainly hypothermia and diuretics, respectively, with a scattering of other techniques. Staffing of CPB perfusion units is essentially unchanged since 1986 and at least five units had no medical perfusionist appointed in 1992.

Extracorporeal membrane oxygenation selection criteria: partial pressure of arterial oxygen versus alveolar-arterial oxygen gradient

Extracorporeal membrane oxygenation (ECMO) has dramatically increased the survival rate of hypoxemic neonates who are unresponsive to maximum conventional medical therapy. Because ECMO involves multiple risks, including ligation of the right common carotid artery and right internal jugular vein, ECMO candidates should be neurologically intact neonates with a high probability of death despite maximum conventional ventilatory support. Currently, criteria based on the calculated alveolar-arterial oxygen gradient (A-aDO2) have replaced the neonatal pulmonary insufficiency index for predicting mortality and, thus, ECMO eligibility. A retrospective review of death prediction for the 26 months prior to the initiation of an ECMO program revealed a sensitivity of 67% and a specificity of 96% using the criterion of a PaO2 of less than 50 mm Hg for four hours. An equivalent A-aDO2 criterion of greater than or equal to 630 for four hours produced a sensitivity of 61% and a specificity of 96%. Prediction of mortality in neonates with sepsis was poor regardless of the criteria used. Excluding the deaths due to sepsis increased the sensitivity to 86% and 79% using criteria based on PaO2 and A-aDO2, respectively. It is concluded that the use of criteria based on PaO2 is equivalent to criteria based on A-aDO2 for predicting mortality. Criteria based on PaO2 may, however, decrease both the false-negative rate (patients with an elevated PCO2) and the false-positive rate (patients with intentionally induced hypocarbia secondary to hyperventilation alkalosis).