In vitro and in vivo assessment of oxygenator blood volume for the prediction of clot formation in an ECMO circuit (theory and validation).

INTRODUCTION: Clotting is one of the major causes of mortality and morbidity during extracorporeal membrane oxygenation (ECMO). A large meta-analysis study suggests that 29% of patients require the oxygenator to be replaced during ECMO. As clots usually form in the oxygenator, the oxygenator blood volume (OXBV) decreases over time. The currently used pressure gradient as a predicator of clot formation is unreliable. OBJECTIVE: The aim of this study was to develop and validate ultrasound dilution technology in a quantitative assessment of clotting, using measurements of OXBV. METHODS: OXBV was measured using the ELSA monitor (Transonic Systems Inc., Ithaca, NY, USA) from the transit time of a saline bolus passing through the oxygenator as recorded by a sensor placed after the oxygenator. The accuracy and reproducibility (coefficient of variation [CV]) of OXBV measurement and its independence from ECMO flow was assessed in vitro in lambs and from a clinical data archive. RESULTS: The in vitro accuracy compared with volumetric measurements of OXBV of 22-134 ml at flows of 300-700 ml/min was -0.8±6.6%. For an OXBV of 355 ml at flows of 1020-7000 ml/min, accuracy was -0.4±1.6%. In 88 animal OXBV measurements, the CV was 1.49±1.12%. For an OXBV of 153 (range 42-387 ml), clinical measurements at flow ranged from 210-5960 ml/min, with a CV of 3.20±2.44 %. CONCLUSION: Dilution technology has the ability to accurately and reproducibly assess the clotting process in the oxygenator. Larger studies are needed to establish guidelines for the prediction of imminent clotting and may help to avoid unnecessary circuit changes.

Therapeutic hypothermia for neonatal encephalopathy and extracorporeal membrane oxygenation.

This case series describes the clinical management of 5 infants who underwent whole-body cooling during extracorporeal membrane oxygenation (ECMO). In all 5 infants, systemic hypothermia was maintained during ECMO with acceptable clinical outcomes.

A tale of two bridges: effect of the bloodless bridge on renal function and blood pressure in neonates managed with venoarterial extracorporeal membrane oxygenation.

OBJECTIVE: To investigate if a change in bridge design of the extracorporeal membrane oxygenation (ECMO) circuit had an impact on renal function and blood pressure in neonates requiring venoarterial ECMO support. DESIGN: : Retrospective chart review. SETTING: A tertiary care neonatal intensive care unit and ECMO center. PATIENTS: The medical records of neonates admitted to the neonatal intensive care unit and treated with venoarterial ECMO were reviewed. Data were collected on 50 consecutive neonates treated previous to (prebridge group) and following (postbridge group) transition to a new bridge design on the ECMO circuit. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Gestational age, gender, racial distribution, and use of hypertensive therapy were similar between the two groups. Daily blood urea nitrogen, serum creatinine, urine output, fluid balance, and average and maximum systolic and mean arterial blood pressures were recorded for the first 3 days on bypass. The postbridge group had lower maximum mean arterial blood pressure and systolic blood pressure on day 2 of ECMO and lower average mean arterial blood pressure and systolic blood pressure on days 2 and 3 of ECMO. These differences remained significant after controlling for covariates in a multiple regression model. A higher percentage of patients were hypertensive (mean arterial blood pressure >60) in the prebridge group compared with the postbridge group. There were no differences in blood urea nitrogen, serum creatinine, fluid balance, and urine output between the two groups. CONCLUSIONS: Patients managed on venoarterial ECMO after the transition to the "bloodless" bridge had less hypertension compared with those managed before the bridge change. This may reflect improved maintenance of renal perfusion associated with transition to an ECMO bridge design that does not require intermittent circulation with associated arterial-venous shunting.

Significant Correlation between Regional Tissue Oxygen Saturation and Vital Signs of Critically Ill Infants.

BACKGROUND: Near-infrared spectroscopy (NIRS) has been used to non-invasively measure specific tissue oxygen saturation (StO2) continuously. Cerebral autoregulation status can be derived from NIRS and arterial blood pressure. The relationship of both cerebral and somatic StO2, fractional tissue oxygen extraction (FTOE), and cerebro-splanchnic oxygenation ratio (CSOR) with measured vital sign parameters for Neonatal Intensive Care Unit (NICU) patients has not been well studied. OBJECTIVE: The aims of this study are to determine if significant relationships of brain and somatic StO2, brain and somatic FTOE, and CSOR parameters with vital signs for neonates exist and assess relationship between pressure passivity index, cerebral autoregulation, and mean blood pressure (MBP). DESIGN/METHODS: Neonates weighing < 5 kg, preferentially with an arterial catheter, were enrolled in the study. FORE-SIGHT Elite (CASMedical Systems, Inc., Branford, CT, USA) cerebral and somatic NIRS sensors were placed over the abdominal right upper quadrant and right frontal-temporal area of the forehead for 24 h. Vital signs including arterial MBP were recorded simultaneously from the patients' bedside monitor. Data were averaged into 60 s windows and analyzed using linear regression. Results were stratified by gestational age (GA), birth weight (BW), and presence of brain abnormality. RESULTS: Data were obtained from 27 subjects (GA 22.2-42 weeks). Two subjects did not have an arterial line, thus they were not included in the MBP measurements. There were ~28,000-31,000 paired data points per comparison. Significant positive and negative correlations (p value < 0.0001) were noted between NIRS parameters and vital signs. When stratified by BW, there was a positive correlation between brain StO2 (StO2B) and MBP in the <1,500 g BW group (r = 0.193) and a negative correlation in >1,500 g group (r = 0.057). Brain and somatic FTOE in <1,500 g BW revealed a negative correlation with MBP (r = 0.172 and r = 0.086, respectively). In patients with an abnormal brain scan, a positive correlation was noted between StO2B and MBP (r = 0.354), and a negative correlation was noted between FTOE-B and MBP (r = 0.305). Generated pressure passive index plots suggested good cerebral autoregulation at low normal MBP ranges for lower weight and GA subjects. CONCLUSION: There is a significant correlation between cerebral and somatic StO2 and FTOE with measured vital sign parameters in NICU patients.

Clinical and pathologic implications of extending the spectrum of maternal autoantibodies reactive with ribonucleoproteins associated with cutaneous and now cardiac neonatal lupus from SSA/Ro and SSB/La to U1RNP.

While the relationship between maternal connective tissue diseases and neonatal rashes was described in the 1960s and congenital heart block in the 1970s, the "culprit" antibody reactivity to the SSA/Ro-SSB/La ribonucleoprotein complex was not identified until the 1980s. However, studies have shown that approximately 10-15% of cases of congenital heart block are not exposed to anti-SSA/Ro-SSB/La. Whether those cases represent a different disease entity or whether another antibody is associated has yet to be determined. Moreover, the cutaneous manifestations of neonatal lupus have also been identified in infants exposed only to anti-U1RNP antibodies. In this review, we describe what we believe to be the first case of congenital heart block exposed to maternal anti-U1RNP antibodies absent anti-SSA/Ro-SSB/La. The clinical and pathologic characteristics of this fetus are compared to those typically seen associated with SSA/Ro and SSB/La. Current guidelines for fetal surveillance are reviewed and the potential impact conferred by this case is evaluated.

Altered cerebrovascular responses after exposure to venoarterial extracorporeal membrane oxygenation: role of the nitric oxide pathway.

BACKGROUND: Previous studies in our laboratory on newborn lambs have shown cerebral autoregulation impairment after exposure to venoarterial extracorporeal membrane oxygenation (VA ECMO), with additional studies showing an altered cerebrovascular response to NG-nitro-L-arginine methyl ester in lamb cerebral vessels in this same model. OBJECTIVE: To further study the mechanisms involved in altered cerebrovascular responses in vessels exposed to VA ECMO. DESIGN: Prospective study. SETTING: Research Animal Facility at Children's National Medical Center, Washington, DC. SUBJECT: Newborn lambs, 1-7 days of age, 4.76 +/- 0.8 kg (n = 10). METHODS: Animals randomly assigned two groups, control and VA ECMO, were anesthetized, ventilated, heparinized, and kept in a normal physiologic condition. Control animals were continued on ventilatory support, whereas animals in the VA ECMO groups were placed on VA ECMO, with bypass flows maintained between 120 and 200 mL x kg x min(-1) for 2.5 hrs. Isolated third-order branches of the middle cerebral arteries were studied for myotonic reactivity to increasing intraluminal pressure changes, response to acetylcholine, an endothelium-dependent vasodilator, 3-morpholinyl-sydnoneimine chloride, an endothelium-independent vasodilator, and serotonin, a direct vascular vasoconstrictor. Arterial caliber was monitored using video microscopy. RESULTS: Myogenic constriction response was significantly decreased in the VA ECMO group compared with the control group (p = .03). Intraluminal acetylcholine caused concentration-dependent arterial dilation in the control group, whereas it resulted in vasoconstriction in the VA ECMO group (p = .008). There were no significant differences in dilation responses to 3-morpholinyl-sydnoneimine chloride and contractile responses to serotonin among the groups. CONCLUSION: Cerebral arteries exposed to VA ECMO had impaired myogenic responses combined with altered endothelial function. The endothelial alteration seems to be mediated through the nitric oxide pathway, with recovery noted after addition of a nitric oxide donor. It can be postulated that these changes may reflect the mechanisms for the impairment of cerebral autoregulation previously reported in this lamb model.

Evaluation of Dry Sensors for Neonatal EEG Recordings.

PURPOSE: Neonatal seizures are a common neurologic diagnosis in neonatal intensive care units, occurring in approximately 14,000 newborns annually in the United States. Although the only reliable means of detecting and treating neonatal seizures is with an electroencephalography (EEG) recording, many neonates do not receive an EEG or experience delays in getting them. Barriers to obtaining neonatal EEGs include (1) lack of skilled EEG technologists to apply conventional wet electrodes to delicate neonatal skin, (2) poor signal quality because of improper skin preparation and artifact, and (3) extensive time needed to apply electrodes. Dry sensors have the potential to overcome these obstacles but have not previously been evaluated on neonates. METHODS: Sequential and simultaneous recordings with wet and dry sensors were performed for 1 hour on 27 neonates from 35 to 42.5 weeks postmenstrual age. Recordings were analyzed for correlation and amplitude and were reviewed by neurophysiologists. Performance of dry sensors on simulated vernix was examined. RESULTS: Analysis of dry and wet signals showed good time-domain correlation (reaching >0.8), given the nonsuperimposed sensor positions and similar power spectral density curves. Neurophysiologist reviews showed no statistically significant difference between dry and wet data on most clinically relevant EEG background and seizure patterns. There was no skin injury after 1 hour of dry sensor recordings. In contrast to wet electrodes, impedance and electrical artifact of dry sensors were largely unaffected by simulated vernix. CONCLUSIONS: Dry sensors evaluated in this study have the potential to provide high-quality, timely EEG recordings on neonates with less risk of skin injury.

Validation of the CAS neonatal NIRS system by monitoring vv-ECMO patients: preliminary results.

The CAS neonatal NIRS system determines absolute regional brain tissue oxygen saturation (SnO2) and brain true venous oxygen saturation (SnvO2) non-invasively. Since NIRS-interrogated tissue contains both arterial and venous blood from arterioles, venules, and capillaries, SnO2 is a mixed oxygen saturation parameter, having values between arterial oxygen saturation (SaO2) and cerebral venous oxygen saturation (SvO2). To determine a reference for SnO2, the relative contribution of SvO2 to SaO2 drawn from a brain venous site vs. systemic SaO2 is approximately 70:30 (SvO2:SaO2). If the relationship of the relative average contribution of SvO2 and SaO2 is known and does not change to a large degree, then NIRS true venous oxygen saturation, SnvO2, can be determined non-invasively using SnO2 along with SaO2 from a pulse oximeter.

Are Immune Modulating Single Nucleotide Polymorphisms Associated with Necrotizing Enterocolitis?

Necrotizing enterocolitis (NEC) is a devastating gastrointestinal emergency. The purpose of this study is to determine if functional single nucleotide polymorphisms (SNPs) in immune-modulating genes pre-dispose infants to NEC. After Institutional Review Board approval and parental consent, buccal swabs were collected for DNA extraction. TaqMan allelic discrimination assays and BglII endonuclease digestion were used to genotype specific inflammatory cytokines and TRIM21. Statistical analysis was completed using logistic regression. 184 neonates were analyzed in the study. Caucasian neonates with IL-6 (rs1800795) were over 6 times more likely to have NEC (p = 0.013; OR = 6.61, 95% CI 1.48-29.39), and over 7 times more likely to have Stage III disease (p = 0.011; OR = 7.13, (95% CI 1.56-32.52). Neonates with TGFß-1 (rs2241712) had a decreased incidence of NEC-related perforation (p = 0.044; OR = 0.28, 95% CI: 0.08-0.97) and an increased incidence of mortality (p = 0.049; OR = 2.99, 95% CI: 1.01 - 8.86). TRIM21 (rs660) was associated with NEC-related intestinal perforation (p = 0.038; OR = 4.65, 95% CI 1.09-19.78). In premature Caucasian neonates, the functional SNP IL-6 (rs1800795) is associated with both the development and increased severity of NEC. TRIM21 (rs660) and TGFß-1 (rs2241712) were associated with NEC- related perforation in all neonates in the cohort. These findings suggest a possible genetic role in the development of NEC.

Follow-up study of adolescents exposed to di(2-ethylhexyl) phthalate (DEHP) as neonates on extracorporeal membrane oxygenation (ECMO) support.

Di(2-ethylhexyl) phthalate (DEHP) is used to make polyvinyl chloride (PVC) plastic tubing soft and flexible. Animal data show that adverse effects of DEHP exposure may include reduced fertility, reduced sperm production in males, and ovarian dysfunction in females. Known treatments that involve high DEHP exposures are blood exchange transfusions, extracorporeal membrane oxygenation (ECMO), and cardiovascular surgery. Although potential exposure to DEHP in ECMO patients is significant, the exposure has not been associated with short-term toxicity. To evaluate long-term toxicity, we undertook a study of neonatal ECMO survivors to assess their onset of puberty and sexual maturity. We evaluated 13 male and 6 female subjects at 14-16 years of age who had undergone ECMO as neonates. All subjects had a complete physical examination including measurements for height, weight, head circumference, and pubertal assessment by Tanner staging. The testicular volume and the phallic length were measured in male participants. Laboratory tests included thyroid, liver, and renal function as well as measurements of luteinizing hormone, follicle-stimulating hormone, testosterone for males, and estradiol for females. Except for one patient with Marfan syndrome, the rest had normal growth percentile for age and sex. All had normal values for thyroid, liver, and renal functions. Sexual hormones were appropriate for the stage of pubertal maturity. Our results indicate that adolescents exposed to significant quantities of DEHP as neonates showed no significant adverse effects on their physical growth and pubertal maturity. Thyroid, liver, renal, and male and female gonadal functions tested were within normal range for age and sex distribution. Key Words: DEHP, ECMO, toxicity.

The use of intratracheal pulmonary ventilation and partial liquid ventilation in newborn piglets with meconium aspiration syndrome.

OBJECTIVE: To determine whether intratracheal pulmonary ventilation (ITPV) combined with partial liquid ventilation (PLV) improves oxygenation and ventilation at lower mean airway and peak inspiratory pressures when compared with conventional mechanical ventilation in a piglet model of meconium aspiration syndrome. DESIGN: Prospective, randomized, interventional study. SETTING: Animal Research Laboratory at the Children's National Medical Center, Washington, DC. SUBJECTS: Twenty newborn piglets, 1 to 2 wks of age, 1.8-2.8 kg in weight. INTERVENTION: The animals were anesthetized, paralyzed, and intubated with a 4.0 mm (internal diameter) endotracheal tube via a tracheostomy and were ventilated. Catheters were placed in the femoral artery and vein. Seven milliliters per kilogram of 20% human meconium was insufflated into the lungs over 30 mins. Dynamic pulmonary compliance was measured before and after instillation of meconium. Animals were ventilated to maintain arterial blood gases in a normal range, that is, pH = 7.35-7.45, Paco(2) = 40-45 torr (5.3-6.0 kPa), and Pao(2) = 70-90 torr (9.3-12.0 kPa). Ventilator settings were increased as needed to a maximum setting of Fio(2) = 1.0, peak inspiratory pressure (PIP) = 40 cm H(2)O, positive end-expiratory pressure = 5 cm H(2)O, and intermittent mandatory ventilation = 60 bpm. After a period of stabilization, 30 mL/kg of perflubron (Liquivent; Alliance Pharmaceutical Corp., San Diego, CA) was given intratracheally over 30 mins and the animals were randomized to either ITPV or control group. Measurements and RESULTS: Arterial blood gases were taken every 30 mins, and ventilatory settings were adjusted to achieve the targeted blood gas parameters. The animals' temperature, arterial blood pressure, heart rate, and oxygen saturation were monitored continuously. There was a significant decrease in the dynamic pulmonary compliance measurements in both groups immediately after meconium instillation. Compliance measurements after meconium instillation were similar in both groups (0.67 +/- 0.23 mL/cm H(2)O/kg ITPV; 0.88 +/- 0.46 mL/cm H(2)O/kg conventional, p =.17), indicating a similar degree of injury before the administration of perflubron. PIP and mean airway pressures were not significantly different at baseline; however, there was significant difference in PIP at 0, 2, and 4 hrs after administration of perflubron (p <.05). The maximum PIP and mean airway pressure were seen in both groups after meconium instillation before perflubron administration, with a mean PIP of 29.0 +/- 4.6 cm H(2)O in ITPV and 28.8 +/- 2.1 cm H(2)O in control. Mean airway pressure was significantly different between the two groups at 0, 1, 2, 3, and 4 hrs after perflubron administration. Lung pathology showed a uniform distribution of meconium in animals of both groups. The alveolar spaces were relatively clear of meconium and appeared to be well preserved. CONCLUSION: The results of this study indicate that ITPV combined with PLV allows for effective ventilation and oxygenation in piglets with meconium aspiration syndrome at lower mean airway pressure and PIP compared with conventional ventilation combined with PLV.

Venoarterial versus venovenous ECMO for neonatal respiratory failure.

Extracorporeal membrane oxygenation (ECMO) continues to be an important rescue therapy for newborns with a variety of causes of cardio-respiratory failure unresponsive to high-frequency ventilation, surfactant replacement, and inhaled nitric oxide. There are approximately 800 neonatal respiratory ECMO cases reported annually to the Extracorporeal Life Support Organization; venoarterial ECMO has been used in approximately 72% with a cumulative survival of 71% and venovenous has been used in 28% with a survival of 84%. Congenital diaphragmatic hernia is now the most common indication for ECMO. This article reviews the development of the two types of extracorporeal support, venoarterial and venovenous ECMO, and discusses the advantages of each method, the current selection criteria, the procedure, and the clinical management of neonates on ECMO.

Genomics in premature infants: a non-invasive strategy to obtain high-quality DNA.

We used a cost-effective, non-invasive method to obtain high-quality DNA from buccal epithelial-cells (BEC) of premature infants for genomic analysis. DNAs from BEC were obtained from premature infants with gestational age ≤ 36 weeks. Short terminal repeats (STRs) were performed simultaneously on DNA obtained from the buccal swabs and blood from the same patient. The STR profiles demonstrated that the samples originated from the same individual and exclude any contamination by external DNAs. Whole exome sequencing was performed on DNAs obtained from BEC on premature infants with and without necrotizing enterocolitis, and successfully provided a total number of reads and variants corroborating with those obtained from healthy blood donors. We provide a proof of concept that BEC is a reliable and preferable source of DNA for high-throughput sequencing in premature infants.

Trisomy 21 in one of extremely low birth weight twins.

Prematurity is frequently seen in the neonatal intensive care unit, and trisomy 21 is an often diagnosed neonatal disorder. We report a unique case of extremely premature twins, one of whom was ultimately diagnosed with trisomy 21. We were able to examine the neonatal courses and outcomes of these twins, which were similar despite the presence of trisomy 21 in one twin. This is the first report comparing the neonatal course of an infant with trisomy 21 to an unaffected twin in patients born so prematurely, and demonstrates the difficulty of making the diagnosis of trisomy 21 based solely on physical examination in premature infants.

Improved oxygenation with reduced recirculation during venovenous ECMO: comparison of two catheters.

OBJECTIVES: To determine whether the new double-lumen catheter made by OriGen Biomedical (Austin, TX) for venovenous (VV) extracorporeal membrane oxygenation (ECMO) would reduce recirculation and improve oxygenation during VV ECMO when compared with the Kendall double-lumen catheter (Kendall Healthcare Products, Mansfield, MA). DESIGN: Prospective intervention study. SETTING: The animal research laboratory at Children's National Medical Center, Washington, DC. SUBJECTS: Nine newborn lambs one to seven days old and weighing 4.4 +/- 0.8 kg. INTERVENTION: Animals were anesthetized, intubated, and ventilated. The ductus arteriosus was ligated. Femoral arterial and venous, cephalic jugular vein, and pulmonary artery catheters were placed. After systemic heparinization, the catheter to be tested, an OriGen catheter, was placed in the right internal jugular vein and advanced into the right atrium. The animal was placed on ECMO and stabilized, with the ventilator settings decreased to a peak inspiratory pressure of 15-20 cmH2O, peak end-expiratory pressure of 5 cmH2O, rate of 15-25 breaths/min, and a fractional inspired oxygen concentration of 0.21-0.30. ECMO flows were increased in 100-ml increments from 200 to 600 ml/min with measurements taken 15 min after each change. The OriGen catheter was removed, the Kendall catheter was placed, and the studies were repeated. MEASUREMENTS AND MAIN RESULTS: Heart rate, mean blood pressure, PaO2, jugular cerebral oxygen saturation, pulmonary artery oxygen saturation, pump venous oxygen saturation, and postmembrane circuit pressures were measured at each study period. The OriGen catheter improved oxygenation, with higher systemic PaO2, higher pulmonary artery and cerebral oxygen saturations, and lower pump venous oxygen saturations (indicating less recirculation). With the OriGen catheter, PaO2 levels ranged from 69 +/- 18 mmHg [9.2 +/- 2.4 kPa] to 114 +/- 45 mmHg [15.2 +/- 6.0 kPa], compared range from 61 +/- 15 mmHg [8.1 +/- 2.0 kPa] to 87 +/- 34 mmHg [11.5+/-4.5 kPa] for the Kendall catheter. These findings indicate that, at all flow rates studied, less recirculation occurred with the OriGen catheter than with the Kendall catheter. The postmembrane pressures were significantly lower for the OriGen catheter at any given flow (from 30 +/- 5 to 122 +/- 18 mmHg) when compared with the Kendall catheter (from 77+/- 16 to 330+/-78 mmHg). CONCLUSIONS: These findings indicate that the OriGen catheter resulted in a reduction of recirculation, thereby resulting in an improvement in oxygenation while on VV ECMO. The lower postmembrane pressure potentially could reduce the risk of ECMO circuit complications such as tubing rupture, bleeding complications, as well as hemolysis. This new catheter makes VV ECMO more effective and represents a design that could be used for neonatal and/or pediatric ECMO.

Comparison of the effect of venovenous versus venoarterial extracorporeal membrane oxygenation on renal blood flow in newborn lambs.

UNLABELLED: Venovenous extracorporeal membrane oxygenation (VV ECMO) using double lumen catheters is an alternative to venoarterial (VA) ECMO and allows for total blood flow using the patient's cardiac output in comparison to partial blood flow provided during VA ECMO. OBJECTIVE: To compare the effects of VV versus VA ECMO on renal blood flow. DESIGN: Prospective study. SETTING: Research laboratory in a hospital. SUBJECT: Newborn lambs 1-7 days of age (n = 15). INTERVENTIONS: In anesthetized, ventilated lambs, femoral artery and vein were cannulated for monitoring and renal venous blood sampling. An ultrasonic flow probe was placed on the left renal artery for continuous renal blood flow measurements. Animals were randomly assigned to control (non-ECMO), VV ECMO and VA ECMO groups. After systemic heparinization, the animals were cannulated and studied at bypass flows of 120 mL/kg/min (partial bypass) for two hours in both ECMO groups and 200 mL/kg/min (full bypass) for an additional 30 min in the VA group. Changes in blood pressure and renal flow on ECMO and during ECMO bridge unclamping were recorded continuously. Plasma renin activity (PRA) levels were sequentially sampled. RESULTS: Systemic blood pressure was not different in VV or VA ECMO at partial bypass flow. However, systemic blood pressure increased significantly at maximal bypass flow in the VA ECMO group. There was no change in renal flow in either VV or VA ECMO groups. PRA levels did not correlate with bypass flow change. During unclamping of the ECMO bridge, blood pressure and renal flow drop significantly in the VA group, but not in the VV group. CONCLUSION: VV and VA ECMO at partial bypass flows had comparable effect on blood pressure, renal blood flow and PRA level in this short-term study. However, unclamping of the ECMO bridges did differentially affect blood pressure and renal blood flow between VV and VA groups. We speculate that this repeated acute change in long-run VA ECMO support may play a role in the persistent hypertension seen in some patients.