Unmasking the Impact of Oxygenator Induced Hypocapnia on Blood Lactate in Veno-Arterial Extracorporeal Membrane Oxygenation

Extracorporeal membrane oxygenation (ECMO) is often associated with disturbances in acid/base status that can be triggered by the underlying pathology or the ECMO circuit itself. Extracorporeal membrane oxygenation is known to cause hypocapnia, but the impact of reduced partial pressure of carbon dioxide (pCO2) on biomarkers of tissue perfusion during veno-arterial (VA)-ECMO has not been evaluated. To study the impact of low pCO2 on perfusion indices in VA-ECMO, we placed Sprague-Dawley rats on an established VA-ECMO circuit using either an oxygen/carbon dioxide mixture (O2 95%, CO2 5%) or 100% O2 delivered through the oxygenator (n = 5 per cohort). Animals receiving 100% O2 developed a significant VA CO2 difference (pCO2 gap) and rising blood lactate levels that were inversely proportional to the decrease in pCO2 values. In contrast, pCO2 gap and lactate levels remained similar to pre-ECMO baseline levels in animals receiving the O2/CO2 mixture. More importantly, there was no significant difference in venous oxygen saturation (SvO2) between the two groups, suggesting that elevated blood lactate levels observed in the rats receiving 100% O2 were a response to oxygenator induced hypocapnia and alkaline pH rather than reduced perfusion or underlying tissue hypoxia. These findings have implications in clinical and experimental extracorporeal support contexts.

Factor XII promotes the thromboinflammatory response in a rat model of venoarterial extracorporeal membrane oxygenation

BACKGROUND

Factor XII (FXII) is a multifunctional protease capable of activating thrombotic and inflammatory pathways. FXII has been linked to thrombosis in extracorporeal membrane oxygenation (ECMO), but the role of FXII in ECMO-induced inflammatory complications has not been studied. We used novel gene-targeted FXII- deficient rats to evaluate the role of FXII in ECMO-induced thromboinflammation.

METHODS

FXII-deficient (FXII-/-) Sprague-Dawley rats were generated using CRISPR/Cas9. A minimally invasive venoarterial (VA) ECMO model was used to compare wild-type (WT) and FXII-/- rats in 2 separate experimental cohorts: rats placed on ECMO without pharmacologic anticoagulation and rats anticoagulated with argatroban. Rats were maintained on ECMO for 1 hour or until circuit failure occurred. Comparisons were made with unchallenged rats and rats that underwent a sham surgical procedure without ECMO.

RESULTS

FXII-/- rats were maintained on ECMO without pharmacologic anticoagulation with low resistance throughout the 1-hour experiment. In contrast, WT rats placed on ECMO without anticoagulation developed thrombotic circuit failure within 10 minutes. Argatroban provided a means to maintain WT and FXII-/- rats on ECMO for the 1-hour time frame without thrombotic complications. Analyses of these rats demonstrated that ECMO resulted in increased neutrophil migration into the liver that was significantly blunted by FXII deficiency. ECMO also resulted in increases in high molecular weight kininogen cleavage and complement activation that were abrogated by genetic deletion of FXII.

CONCLUSIONS

FXII initiates hemostatic system activation and key inflammatory sequelae in ECMO, suggesting that therapies targeting FXII could limit both thromboembolism and inopportune inflammatory complications in this setting.

An in vivo animal model to study chronic adriamycin cardiotoxicity: a P-31 nuclear magnetic resonance spectroscopy investigation

The mechanism responsible for adriamycin induced cardiotoxicity is unknown. We have developed an in vivo rabbit model for use with P-31 nuclear magnetic resonance spectroscopy which allows serial investigations of the drug's effects on myocardial metabolism. Eleven animals were studied over a 10 week period and changes in intracellular pH and phosphate metabolites were observed. The magnitude of changes in pH and inorganic phosphate were the best indicators of the severity of the cardiomyopathy. The results are consistent with an adriamycin induced degeneration of myofibrils rather than a severe metabolic impairment.

Modulation by cortisol of adrenocorticotropin-induced activation of adrenal function in fetal sheep

We examined the hypothesis that cortisol (F) modulates the activation of adrenal function induced by treating fetal sheep in vivo with pulsatile ACTH (P-ACTH). Chronically catheterized sheep fetuses were infused in utero for 100 h between day 127 and day 131 of pregnancy with P-ACTH; P-ACTH plus metopirone; P-ACTH plus metopirone plus F; P-ACTH plus metopirone plus dexamethasone, or saline (controls). After 100 h, basal and ACTH-stimulated output of 11-desoxycortisol (S), F, and progesterone from collagenase-dispersed fetal adrenal cells was measured. Adrenal cells from fetuses treated with P-ACTH in vivo had significantly greater basal and stimulated (delta) outputs of F and S in vitro than controls. These effects were attenuated in fetuses pretreated with P-ACTH plus metopirone. Concurrent in vivo treatment with ACTH plus metopirone plus F restored basal and delta outputs of F and S to values that were not significantly different from those after P-ACTH alone. In vivo treatment with dexamethasone in addition to P-ACTH plus metopirone significantly raised basal outputs of F and S, but the cells were unresponsive to ACTH in vitro. Basal output of progesterone was significantly greater after in vivo P-ACTH plus metopirone plus dexamethasone, but no treatment raised delta progesterone output over controls. These results support a role for glucocorticoids in modulating ACTH-induced activation of adrenal function in late gestation fetal sheep.

Wrist driven flexor hinge orthosis: linkage design improvements

Wrist driven flexor hinge orthosis (WDFHO) linkage movements were analyzed graphically for existing kit form orthoses and modified orthoses. The graphical analysis indicated improved function by increased torque and resultant pinch force in modified orthoses. A geometric solution to pivot point location which will allow clinicians and orthotists to properly locate the linkage pivot points for WDFHOs was developed. Improved function was documented in 5 orthoses converted from kit form linkages to modified linkages.

Relation between diurnal changes in peripheral plasma progesterone, cortisol, and estriol in normal women at 30-31, 34-35, and 38-39 weeks of gestation

To determine the relation of diurnal changes in plasma progesterone to those in cortisol and estriol we measured the concentrations of progesterone, cortisol and estriol in samples of plasma taken at 30- to 60-min intervals throughout 24 h from women at 30-31, 34-35, and 38-39 weeks of gestation. Plasma progesterone showed a significant diurnal rhythm at 30-31 and at 34-35 weeks of pregnancy, with troughs at 04.30-10.00 h. Major peaks occurred between 15.30 and 02.30 h. There was no diurnal rhythm in progesterone at 38-39 weeks. Plasma progesterone showed a significant negative correlation with plasma cortisol at 30-31 and 34-35 but not at 38-39 weeks. Plasma progesterone showed a significant positive correlation with estriol at 34-35 and at 38-39 weeks. We suggest that daily fluctuations in plasma progesterone may be related to the concentration of plasma cortisol, either directly by competition for binding sites on transcortin, or indirectly after modulation of fetal pituitary-adrenal function by maternally derived glucocorticoid.