Novel mRNA isoforms and mutations of uridine monophosphate synthetase and 5-fluorouracil resistance in colorectal cancer.

The drug fluorouracil (5-FU) is a widely used antimetabolite chemotherapy in the treatment of colorectal cancer. The gene uridine monophosphate synthetase (UMPS) is thought to be primarily responsible for conversion of 5-FU to active anticancer metabolites in tumor cells. Mutation or aberrant expression of UMPS may contribute to 5-FU resistance during treatment. We undertook a characterization of UMPS mRNA isoform expression and sequence variation in 5-FU-resistant cell lines and drug-naive or -exposed primary and metastatic tumors. We observed reciprocal differential expression of two UMPS isoforms in a colorectal cancer cell line with acquired 5-FU resistance relative to the 5-FU-sensitive cell line from which it was derived. A novel isoform arising as a consequence of exon skipping was increased in abundance in resistant cells. The underlying mechanism responsible for this shift in isoform expression was determined to be a heterozygous splice site mutation acquired in the resistant cell line. We developed sequencing and expression assays to specifically detect alternative UMPS isoforms and used these to determine that UMPS was recurrently disrupted by mutations and aberrant splicing in additional 5-FU-resistant colorectal cancer cell lines and colorectal tumors. The observed mutations, aberrant splicing and downregulation of UMPS represent novel mechanisms for acquired 5-FU resistance in colorectal cancer.

Vasopressin versus epinephrine during cardiopulmonary resuscitation of asphyxiated newborns: A study protocol for a prospective, cluster, open label, single-center, randomized controlled phase 2 trial - The VERSE-Trial.

Introduction: Current neonatal resuscitation guidelines recommend the use of epinephrine during neonatal cardiopulmonary resuscitation (CPR). However, newborns receiving epinephrine continue to have high rates of mortality and neurodevelopmental disability. The infrequent need for neonatal CPR, coupled with an inability to consistently anticipate which newborn infants are at risk of requiring CPR, explains the lack of high-quality evidence (i.e., large randomized clinical trials) to better guide healthcare providers in their resuscitative effort. Therefore, we need neonatal data to determine the optimal vasopressor therapy during neonatal CPR. The current pilot trial will examine the efficacy of vasopressin versus epinephrine during CPR of asphyxiated newborn infants. Methods and analysis: The trial will be a prospective, cluster, open label, single-center, randomized controlled trial on two alternative cardiovascular supportive medications. This study will assess the primary outcome of time to return of spontaneous circulation (ROSC) in newborns requiring CPR in the delivery room who were treated with either vasopressin (intervention) or epinephrine (control). Secondary outcomes such as infant mortality and other clinical outcome measures will also be collected. An estimated 20 newborns will be recruited, and comparisons will be made between asphyxiated infants treated with either drugs. Ethics and dissemination: This study has been approved by the Research Ethics Board at the University of Alberta (June 16, 2023). Study findings will be published in peer-reviewed journals, presented at conferences, and communicated to relevant participants and stakeholders.Trial registration: ClinicalTrial.gov Identifier: NCT05738148. Registered February 21, 2023.

Id-1 induces cell invasiveness in immortalized epithelial cells by regulating cadherin switching and Rho GTPases.

Epithelial-mesenchymal transition (EMT), characterized by cadherin switching, contributes to cancer metastasis. Our recent study showed that Id-1 (inhibitor of differentiation-1) promotes metastasis in esophageal cancer cells, but whether the invasive and metastatic dynamics can be induced early in the carcinogenesis process is still unclear. Immortalization is regarded as the initial stage in the malignant transformation of normal cells. In this study, we investigated the role and mechanisms of Id-1 in inducing EMT and cell invasiveness in immortalized esophageal epithelial cells. We found that immortalized epithelial cells expressed higher endogenous levels of Id-1 compared with normal cells. Ectopic Id-1 expression inhibited the differentiation of immortalized esophageal epithelial cells and promoted cadherin switching, which was accompanied by increased adhesiveness to extracellular matrix, cell motility, migratory potential and matrix metalloproteinase-dependent invasiveness. GTPase activity assays showed that over-expression or short-hairpin RNA knockdown of Id-1 led to corresponding changes in Rac1 activity, whereas RhoA activity was significantly decreased with Id-1 depletion. Inhibitors targeting Rac1, RhoA, and Rho kinase suppressed the invasiveness of Id-1-expressing NE2-hTERT cells. Knockdown of N-cadherin in Id-1-over-expressing cells inhibited cell invasiveness and down-regulated RhoA activity. These data suggest that the Id-1-induced invasive potential may be regulated through the N-cadherin-RhoA axis and Rac1 activation.

Hypoxia - Reoxygenation in neonatal cardiac arrest: Results from experimental models.

In this review, we summarize the results of studies that investigated the effects of hypoxia and reoxygenation in cardiac arrest, including the use of different fractions of inspired oxygen, in neonatal animals. The studies were heterogenous in terms of anaesthetic regimens, and definitions of cardiac arrest and circulatory recovery. Cardiopulmonary resuscitation with 100% oxygen increased oxidative stress in maturing rats. Studies in fetal/neonatal lambs and post-transitional neonatal piglets indicate no consistent differences between ventilation with 21% vs. 100% oxygen with regards to recovery times, oxygen damage or adverse events. If 21% oxygen is as effective as 100% oxygen in newborn infants with cardiac arrest requiring chest compression, the use of 21% instead of 100% oxygen could reduce morbidity and mortality in asphyxiated infants. Unanswered questions include what is the most optimal cerebral oxygen delivery during reperfusion, as well as oxygenation targets after return of spontaneous circulation.

Novel interventions to reduce oxidative-stress related brain injury in neonatal asphyxia.

Perinatal asphyxia-induced brain injury may present as hypoxic-ischemic encephalopathy in the neonatal period, and disability including cerebral palsy in the long term. The brain injury is secondary to both the hypoxic-ischemic event and the reoxygenation-reperfusion following resuscitation. Early events in the cascade of brain injury can be classified as either inflammation or oxidative stress through the generation of free radicals. The objective of this paper is to present efforts that have been made to limit the oxidative stress associated with hypoxic-ischemic encephalopathy. In the acute phase of ischemia/hypoxia and reperfusion/reoxygenation, the outcomes of asphyxiated infants can be improved by optimizing the initial delivery room stabilization. Interventions include limiting oxygen exposure, and shortening the time to return of spontaneous circulation through improved methods for supporting hemodynamics and ventilation. Allopurinol, melatonin, noble gases such as xenon and argon, and magnesium administration also target the acute injury phase. Therapeutic hypothermia, N-acetylcysteine2-iminobiotin, remote ischemic postconditioning, cannabinoids and doxycycline target the subacute phase. Erythropoietin, mesenchymal stem cells, topiramate and memantine could potentially limit injury in the repair phase after asphyxia. To limit the injurious biochemical processes during the different stages of brain injury, determination of the stage of injury in any particular infant remains essential. Currently, therapeutic hypothermia is the only established treatment in the subacute phase of asphyxia-induced brain injury. The effects and side effects of oxidative stress reducing/limiting medications may however be difficult to predict in infants during therapeutic hypothermia. Future neuroprotection in asphyxiated infants may indeed include a combination of therapies. Challenges include timing, dosing and administration route for each neuroprotectant.

Effects of different durations of sustained inflation during cardiopulmonary resuscitation on return of spontaneous circulation and hemodynamic recovery in severely asphyxiated piglets.

OBJECTIVE: We previously demonstrated that sustained inflation (SI) during chest compression (CC) significantly reduces time to return of spontaneous circulation (ROSC) when compared to 3:1 compression:ventilation (C:V) ratio during neonatal resuscitation. However, the optimal length of SI during CC to improve ROSC and hemodynamic recovery in severely asphyxiated piglets is unknown. AIM: To examine if different lengths of SI will improve ROSC and hemodynamic recovery in severely asphyxiated piglets. INTERVENTION AND MEASUREMENTS: Thirty newborn piglets (1-3 days) were anesthetized, intubated, instrumented and exposed to 30-min normocapnic hypoxia followed by asphyxia. Piglets were randomized into four groups: 3:1 C:V (n = 8), CC with an SI duration of either 20 s (CC+SI 20) (n = 8) or 60 s (CC+SI 60) (n = 8), and a sham group (n = 6). Cardiac function, carotid blood flow, cerebral and renal oxygenation as well as respiratory parameters were continuously recorded throughout the experiment. MAIN RESULTS: When compared with 3:1 group, both CC+SI 20 and CC+SI 60 groups had significantly shorter ROSC time (p = 0.002). All three intervention groups had similar hemodynamic recovery by the end of 4 h observation period. There was no difference in lung injury markers among all experimental groups. However, when compared to the sham group, the concentrations of IL-6 (thalamus) and IL-6 + IL-8 (frontoparietal cortex) of the 3:1 C:V group were significantly higher, respectively. CONCLUSIONS: Even though relatively less animals achieved ROSC, CC during SI significantly improved ROSC time compared to 3:1 C:V in asphyxiated newborn piglets. However, there was no difference in ROSC characteristics and hemodynamic recovery between two CC+SI groups.

Tidal volume delivery during continuous chest compressions and sustained inflation.

OBJECTIVE: To determine the distending pressure needed to achieve sufficient tidal volume (VT) delivery during continuous chest compressions (CC) superimposed by sustained inflation (SI) (CC+SI). DESIGN: Randomised animal/manikin trial. SETTING: University laboratory. SUBJECTS: Cadaver piglets/manikin. INTERVENTIONS: SI distending pressures of 5, 10, 15, 20, 25 and 30 cm H2O were delivered in random order during CC+SI for 2 min each. MAIN OUTCOME MEASURES: VT, gas flow and airway pressure. Spearman's r for distending pressure and VT. RESULTS: Distending pressure and VT correlated in cadaver piglets (r=0.83, p<0.001), manikin (r=0.98, p<0.001) and combined data (r=0.49, p<0.001). VT was delivered during chest recoil during CC in both models. In cadaver piglets, a distending pressure ∼25 cm H2O was needed to achieve an adequate VT. CONCLUSIONS: Chest recoil generates VT depending on an adequate distending pressure. This has previously been demonstrated in adult animals. A pressure of ∼25 cm H2O is needed to achieve an adequate VT delivery.

Assessment of endotracheal tube placement in newborn infants: a randomized controlled trial.

OBJECTIVE: International resuscitation guidelines recommend clinical assessment and exhaled CO2 to confirm tube placement immediately after intubation. However, exhaled CO2 devices can display false negative results. In comparison, any respiratory function monitor can be used to measure and display gas flow in and out of an endotracheal tube. However, neither method has been examined in detail. We hypothesized that a flow sensor would improve the assessment of tracheal vs esophageal tube placement in neonates with a higher success rate and a shorter time to tube placement confirmation when compared with the use of a quantitative end-tidal CO2 (ETCO2) detector. STUDY DESIGN: Between December 2013 and September 2014, preterm and term infants requiring endotracheal intubation were eligible for inclusion and randomly allocated to either ETCO2 ('ETCO2 group') or flow sensor ('flow sensor group'). All infants were analyzed according to their group at randomization (that is, analysis was by intention-to-treat). RESULT: During the study period, a total of 110 infants (n=55 for each group) were randomized. Successful endotracheal tube placements were correctly identified in 100% of cases by the flow sensor compared with 72% of cases with the ETCO2 detector within 10 inflations (P<0.05). The median (interquartile range) number of inflations needed to identify successful tube placement was significantly lower in the flow sensor group with 2 (1 to 3) inflations vs 8 (6 to 10) inflations with the ETCO2 detector (P<0.001). CONCLUSION: A flow sensor would improve the assessment of successful endotracheal tube placement with a higher success rate and a shorter time compared with an ETCO2 detector.

Matrix metalloproteinase-2 contributes to ischemia-reperfusion injury in the heart.

BACKGROUND: Matrix metalloproteinases (MMPs) contribute to collagen degradation and remodeling of the extracellular matrix after myocardial infarction; however, their role in myocardial dysfunction immediately after ischemia and reperfusion is unknown. METHODS AND RESULTS: We measured the release of MMPs into the coronary effluent of isolated, perfused rat hearts during aerobic perfusion and reperfusion after ischemia. Aerobically perfused control hearts expressed pro-MMP-2 and MMP-2, as well as an unidentified 75-kDa gelatinase. These enzymes were also detected in the coronary effluent. After 20 minutes of global no-flow ischemia, there was a marked increase in pro-MMP-2 in the coronary effluent that peaked within the first minute of reperfusion. The release of pro-MMP-2 into the coronary effluent during reperfusion was enhanced with increasing duration of ischemia and correlated negatively with the recovery of mechanical function during reperfusion (r(2)=0.99). MMP-2 antibody (1.5 to 15 microg/mL) and the inhibitors of MMPs doxycycline (10 to 100 micromol/L) and o-phenanthroline (3 to 100 micromol/L) improved whereas MMP-2 worsened the recovery of mechanical function during reperfusion. CONCLUSIONS: These results show that acute release of MMP-2 during reperfusion after ischemia contributes to cardiac mechanical dysfunction. The inhibition of MMPs may be a novel pharmacological strategy for the treatment of ischemia-reperfusion injury.

Renal dopamine receptors: mechanisms of action and developmental aspects.

Dopamine is important for renal perfusion, natriuresis, and the control of blood pressure. Modulation of the activities of adenylyl cyclase, phospholipase C and protein kinases is involved in the signal transduction pathway of dopamine. Peripheral dopamine receptors are classified as the DA1 and DA2 subtypes on the basis of synaptic localization and their pharmacological profiles. In the kidney, DA1 receptors are localized in the medial layer of the renal vasculature and along the nephron; DA2 receptors are found in the glomerulus and the nerves surrounding renal blood vessels. While DA1 receptor stimulation results in renal vasodilatation and natriuresis, DA2 receptors may play a synergistic role in the DA1 modulated natriuresis. There is increasing evidence that these effects of dopamine are attenuated in younger than in older animals. Future studies should be directed to identify the ontogenic differences in vascular and tubular dopamine receptors (density and affinity) and their coupling mechanisms, in order to evaluate the role of dopamine which is frequently used in the management of shock in newborns.

Temporal effects of prolonged hypoxaemia and reoxygenation on systemic, pulmonary and mesenteric perfusions in newborn piglets.

OBJECTIVE: Temporal effects of prolonged hypoxaemia and reoxygenation, on the systemic pulmonary and mesenteric circulations in newborn piglets, were investigated. METHODS: Two groups [control (n = 5), hypoxaemic (n = 7)] of 1-3 day old anaesthetised piglets were instrumented with ultrasound flow probes placed to measure cardiac, hepatic arterial flow and portal venous flow indices, and catheters inserted for measurements of systemic and pulmonary arterial pressures. Hypoxaemia with arterial oxygen saturation 40-50% was maintained for 3 h, followed by reoxygenation with 100% inspired oxygen. RESULTS: Cardiac index was transiently elevated at 30-60 min of hypoxaemia (23% increase from baseline 158 +/- 39 ml/kg/min), along with increases in stroke volume but not heart rate. A significant decrease in systemic vascular resistance after 30 min of hypoxaemia was followed by hypotension at 180 min of hypoxaemia. Progressive pulmonary hypertension with significant vasoconstriction was found after 30 min of hypoxaemia. The hypoxaemic mesenteric vasoconstriction was transient with a 37% decrease in portal venous flow index at 15 min of hypoxaemia (29 +/- 12 vs. 46 +/- 18 ml/kg/min of baseline, p < 0.05). The hepatic arterial to total hepatic oxygen delivery ratio increased significantly during hypoxaemia. In contrast to the significant increase in systemic oxygen extraction throughout hypoxaemia, elevation in mesenteric oxygen extraction decreased after 30 min of hypoxaemia associated with modest decreases in oxygen consumption. Following reoxygenation, the pulmonary hypertension was partially reversed. Cardiac index decreased further (130 +/- 39 ml/kg/min) with reduced stroke volume, persistent systemic hypotension and decreased systemic oxygen delivery. CONCLUSIONS: We demonstrated differential temporal changes in systemic, pulmonary and mesenteric circulatory responses during prolonged hypoxaemia. Cautions need to be taken upon reoxygenation because the neonates are at risk of developing myocardial stunning, persistent pulmonary hypertension and necrotising enterocolitis.

Rescuer fatigue during simulated neonatal cardiopulmonary resuscitation.

OBJECTIVE: To assess development of fatigue during chest compressions (CCs) in simulated neonatal cardiopulmonary resuscitation (CPR). STUDY DESIGN: Prospective randomized manikin crossover study. Thirty neonatal healthcare professionals who successfully completed the Neonatal Resuscitation Program performed CPR using (i) 3:1 compression:ventilation (C:V) ratio, (ii) continuous CC with asynchronous ventilation (CCaV) at a rate of 90 CC per min and (iii) CCaV at 120 CC per min for a duration of 10 min on a neonatal manikin. Changes in peak pressure (a surrogate of fatigue) and CC rate were continuously recorded and fatigue among groups was compared. Participants were blinded to pressure tracings and asked to rate their level of comfort and fatigue for each CPR trial. RESULT: Compared with baseline, a significant decrease in peak pressure was observed after 72, 96 and 156 s in group CCaV-120, CCaV-90 and 3:1 C:V, respectively. CC depth decreased by 50% within the first 3 min during CCaV-120, 30% during CCaV-90 and 20% during 3:1 C:V. Moreover, 3:1 C:V and CCaV were similarly preferred by healthcare professionals. CONCLUSION: Similarly, 3:1 C:V and CCaV CPR were also fatiguing. We recommend that rescuers should switch after every second cycle of heart rate assessment during neonatal CPR.

Mask ventilation with two different face masks in the delivery room for preterm infants: a randomized controlled trial.

BACKGROUND: If an infant fails to initiate spontaneous breathing after birth, international guidelines recommend a positive pressure ventilation (PPV). However, PPV by face mask is frequently inadequate because of leak between the face and mask. Despite a variety of available face masks, none have been prospectively compared in a randomized fashion. We aimed to evaluate and compare leak between two commercially available round face masks (Fisher & Paykel (F&P) and Laerdal) in preterm infants <33 weeks gestational age in the delivery room. METHODS: Infants born at the Royal Alexandra Hospital from April to September 2013 at <33 weeks gestational age who received mask PPV in the delivery room routinely had a flow sensor placed between the mask and T-piece resuscitator. Infants were randomly assigned to receive PPV with either a F&P or Laerdal face mask. All resuscitators were trained in the use of both face masks. We compared mask leak, airway pressures, tidal volume and ventilation rate between the two groups. RESULTS: Fifty-six preterm infants (n=28 in each group) were enrolled; mean±s.d. gestational age 28±3 weeks; birth weight 1210±448 g; and 30 (52%) were male. Apgar scores at 1 and 5 min were 5±3 and 7±2, respectively. Infants randomized to the F&P face mask and Laerdal face mask had similar mask leak (30 (25-38) versus 35 (24-46)%, median (interquartile range), respectively, P=0.40) and tidal volume (7.1 (4.9-8.9) versus 6.6 (5.2-8.9) ml kg(-1), P=0.69) during PPV. There were no significant differences in ventilation rate, inflation time or airway pressures between groups. CONCLUSION: The use of either face mask during PPV in the delivery room yields similar mask leak in preterm infants <33 weeks gestational age.

Paralog chromatography.

As a mixed mode ligand, a small peptide can mimic an antibody's paratope (antigen recognition site). This report describes the construction of a representative set of paratope analogs, or "paralogs," which can be conjugated to a chromatographic sorbent to combine desirable characteristics of traditional high-performance liquid chromatography columns with the specificity of a moderate affinity antibody. The broad utility of this novel set of protein separatory reagents is illustrated on the complex mixture of proteins in a yeast lysate.

Nitric oxide and platelet function: implications for neonatology.

Nitric oxide (NO) is a mediator that modulates vessel wall tone and hemostatic-thrombotic balance. Platelet function is regulated by NO generated from platelets, endothelial cells and leukocytes. Nitric oxide has been shown to inhibit platelet adhesion, aggregation, and stimulate disaggregation of preformed platelet aggregates. Many of the effects of NO are mediated by its stimulation of guanylate cyclase and the formation of cyclic GMP and its subsequent transduction mechanism. In vivo, NO is likely to interact with prostacyclin, metabolites of ecto-nucleotidase, and lipoxygenase to modulate platelet function in a synergistic manner. An imbalance of NO production (deficiency or overproduction) has been implicated in the pathogenesis of various vascular disorders including thrombosis, atherosclerosis, septicemia, and ischemia-reperfusion injury. It is likely that some of detrimental effects of NO are mediated through its reaction with superoxide anion to form the potent oxidant, peroxynitrite. Nitric oxide gas and NO donors are used for the pharmacological treatment of various vascular disorders. Because inhaled NO has been documented to improve systemic oxygenation and reduce the need for extracorporeal membrane oxygenation, it has been widely used in neonates with severe hypoxemia. An inhibition of platelet function, resulting in a prolonged bleeding time, has been shown in adults receiving inhaled NO. Because bleeding complications may occur in high-risk infants, it is important to evaluate the effect of inhaled NO on platelet function and its correlation with clinical consequences such as intracranial hemorrhage. For these reasons, hemostasis should be carefully monitored during the administration of inhaled NO to critically ill neonates.

Early childhood neurodevelopment in very low birth weight infants with predischarge apnea.

Apnea commonly occurs in preterm infants and may persist beyond term. We prospectively investigated the relationship between apnea that persisted beyond 35 weeks post-conceptional age and subsequent neurodevelopment in early childhood. Between January, 1990-November, 1993, we performed predischarge respiratory recordings, using 24-hr, 4-channel pneumography, at 35 weeks or more of postconceptional age in 164 infants (birth weight, <1,250 g; gestational age, < or = 32 weeks), who subsequently underwent multidisciplinary neurodevelopmental assessment at 15-64 (median 24) months of adjusted age. The duration of initial artificial ventilation for respiratory distress syndrome and the grade of intraventricular hemorrhage were independent predictors of neurodevelopmental outcome. Mean oximetry desaturation and frequency of predischarge apnea correlated with mental and motor developmental scores. Mean oximetry desaturation during apnea was an independent predictor for motor score in the total population, and for both mental and motor scores in 50 infants with grade 3 or 4 intraventricular hemorrhage, but not in 114 infants without grade 3 or 4 intraventricular hemorrhage. Despite its limited predictability for early childhood neurodevelopment, predischarge respiratory recordings may be useful in predicting subsequent neurodevelopment of high-risk preterm infants, especially those with severe intraventricular hemorrhage.

Plasma lactate as a predictor of early childhood neurodevelopmental outcome of neonates with severe hypoxaemia requiring extracorporeal membrane oxygenation.

Although plasma lactate concentration has been widely used as an indicator of tissue hypoxia, no clinical study has been conducted to relate these values to the neurological outcome of sick neonates. Seventeen consecutively cared for and surviving neonates with severe hypoxaemia requiring extracorporeal membrane oxygenation (ECMO) were evaluated at a mean age of 19.6 months. The serial plasma lactate concentrations were significantly correlated with the scores of the Bayley Scales of Infant Development. Admission and peak plasma lactate of < or = 15 mmol/l predicted favourable outcome (MDI and PDI > 70 and no disability): sensitivity 100%, specificity 88%, positive predictive value 90%, and negative predictive value 100%. Plasma lactate values could help predict neurodevelopmental outcome in these sick neonates.

Tonometry to estimate intestinal perfusion in newborn piglets.

AIM: To determine the correlation between gastric intramucosal pH and superior mesenteric artery (SMA) flow in newborn piglets. METHODS: Fourteen newborn piglets were randomly assigned to either a control or to an epinephrine group which received 0,1,2,4,0 microg/kg/min of epinephrine for 60 minutes, each dose. Gastric tonometry was performed, SMA flow was measured, and intramucosal pH and the ratio of tonometer pCO(2) over arterial pCO(2) (rCO(2)) were calculated. RESULTS: Intramucosal pH decreased over time in both groups, but tended to be lower in the epinephrine group. With increasing dose of epinephrine, SMA flow decreased; this in turn increased rCO(2) (p = 0.04) with a tendency to decrease intramucosal pH (p = 0.06). CONCLUSIONS: Gastric tonometry may be useful in human neonates to evaluate gut ischaemia.

Sensorineural hearing loss in survivors of neonatal extracorporeal membrane oxygenation.

From February 1989 to January 1994, nine of 63 (14.3%) survivors of neonatal extracorporeal membrane oxygenation developed bilateral sensorineural hearing loss. Seven of nine children were tested and passed initial or repeat clinical auditory brainstem response evaluation completed before discharge from neonatal intensive care. Hearing loss was suspected and confirmed between 6-36 and 10-48 months of age, respectively. We recommend regular audiologic follow-up for these high-risk infants until bilateral thresholds for hearing can be obtained.

Quantification of recirculation by thermodilution during venovenous extracorporeal membrane oxygenation.

PURPOSE: The aim of this study was to determine whether recirculation could be quantified by a thermodilution technique during venovenous (VV) extracorporeal membrane oxygenation (ECMO) in a rabbit model. METHODS: Five New Zealand white rabbits, mean weight, 4.5 (range, 3.7 to 5.7) kg, were anesthetized, instrumented, cannulated with a double-lumen catheter, and placed on VV ECMO. Serial injections of ice-cold saline were performed at the arterial arm of the circuit, and the resultant temperature change at various pump flows was measured at the venous arm of the circuit using a thermistor-tipped catheter and a cardiac output computer. Results were compared with the respective 100% recirculation measured with all the circuit flow passing through the bridge. RESULTS: Using linear regression, recirculation percentage could be calculated as: 19 + 0.1 x pump flow (R2 = 0.81, P < .005). Recirculation correlated positively with pump flow. Variability between results at each flow was less than 10%. CONCLUSIONS: Recirculation can be quantified during VV ECMO by measuring the change in temperature in the venous arm using a cardiac output computer after injection of a known quantity of ice-cold saline in the arterial side of the circuit. The effect of interventions to reduce recirculation can be assessed conveniently and reliably.