Stephanie Øyasæter

Hypoxemia and reoxygenation with 21% or 100% oxygen in newborn pigs : changes in blood pressure, base deficit, and hypoxanthine and brain morphology

ABSTRACT: To study whether room air is as effective as 100% O2 in resuscitation after hypoxia, hypoxemia (Pao2 2.3–4.3 kPa) was induced in newborn pigs (2–5 d old) by ventilation with 8% O2 in nitrogen. When systolic blood pressure had fallen to 20 mm Hg, animals were randomly reoxygenated with either 21% O2 (group 1, n = 9) or 100% O2 (group 2, n = 11) for 20 min followed by 21% O2 in both groups. Controls (group 3, n = 5) were ventilated with 21% O2 throughout the experiment. Base deficit peaked at 31 ± 5 mmol/L (mean ± SD) for both hypoxic groups at 5 min of reoxygenation and then normalized over the following 3 h. There were no statistically significant differences between the two groups during reoxygenation concerning blood pressure, heart rate, base deficit, or plasma hypoxanthine. Hypoxanthine peaked at 165 ± 40 and 143 ± 42 μmol/L in group 1 and 2 (NS), respectively, and was eliminated monoexponentially in both groups with an initial half-life for excess hypoxanthine of 48 ± 21 and 51 ± 27 min (NS), respectively. Blinded pathologic examination of cerebral cortex, cerebellum, and hippocampus after 4 d showed no statistically significant differences with regard to brain damage. We conclude that 21% O2 is as effective as 100% O2 for normalizing blood pressure, heart rate, base deficit, and plasma hypoxanthine after severe neonatal hypoxemia in piglets and that the extent of the hypoxic brain damage is similar in the two groups.

Glucagon deficiency causing severe neonatal hypoglycemia in a patient with normal insulin secretion.

Summary: In the presented patient glucagon secretion was not stimulated by hypoglycemia or by infusion of alanine, whereas insulin secretion responded normally to changes in blood glucose and alanine concentrations. The administration of exogenous glucagon evoked an abnormally strong and prolonged hyperglycemic response. Gluconeogenesis was severely impaired, but there was no accumulation of the main gluconeogenic precursors. This was explained by the deficiency of substrates for these precursors, and by shunting into other pathways than gluconeogenesis.The hypoglycemia was easy to control neonatally, whereas the condition at 3 months of age was critical. Treatment with glucagon resulted in a clinical improvement already observed the first day, whereas blood glucose normalized in 2–3 days. After 1 week the improvement was striking. The prompt initial effect of glucagon was ascribed to increased lipolysis, the delayed glucose rise to an induction of gluconeogenesis. At reexamination the rate of gluconeogenesis had increased 3 times. Glucagon treatment caused significant increase in pyruvate, free fatty acids, and insulin, whereas the alanine concentration fell. The subcutaneous injection of 0.1 mg zinc protamine glucagon per kg body weight resulted in a plasma level of about 900 pg/ml shortly after the injection, with a subsequent exponential fall. The K value was 13.5%/hr.A brother and a sister probably died from hypoglycemia, and the closely related Pakistani parents had a partly deficient glucagon secretion. An autosomal recessive inherited disorder is suggested.Speculation: Congenital glucagon deficiency would be expected to cause hypoglycemia, but no such case has so far been well documented. In this paper a patient with severe, persistent, neonatal hypoglycemia caused by an isolated glucagon deficiency is presented. This and similar cases may provide valuable information about the physiologic role of glucagon.

A new biochemical method for estimation of postmortem time.

Hypoxanthine (Hx) is formed by hypoxic degradation of adenosine monophosphate (AMP) and might be elevated due to antemortem hypoxia. However, it also increases after cessation of the life processes. Until now measurements of potassium in corpus vitreous humor have been used by forensic pathologists to determine postmortem time. In this study the influence of postmortem time and temperature on vitreous humor Hx and potassium levels were compared. Repeated sampling of vitreous humor was performed in 87 subjects with known time of death and diagnosis. The bodies were kept at either 5 degrees C, 10 degrees C, 15 degrees C or 23 degrees C. Hx was measured by means of HPLC and potassium by flame photometry. In 19 subjects from whom samples were obtained within 1.5 h after death, the normal level of Hx could be estimated to be 7.6 mumol/l and that of potassium to be 5.8 mmol/l. The spread of the potassium levels measured shortly after death was much greater than for the corresponding Hx levels. In the four temperature groups the Hx level increased 4.2, 5.1, 6.2 and 8.8 mumol/l per h, respectively, whereas the corresponding figures for potassium were 0.17, 0.20, 0.25 and 0.30 mmol/l per h. The vitreous humor concentration of both Hx and potassium increases fairly linearly after death. The slopes are steeper with increasing temperature. Since the scatter of the levels is greater for potassium than for Hx, the latter parameter seems to be better suited for the determination of time of death in cases without antemortem hypoxia, especially during the first 24 h.

Diving seals, ischemia-reperfusion and oxygen radicals

The cardiovascular adaptations of seals that contribute to their ability to tolerate long periods of diving asphyxial hypoxia result in episodic regional ischemia during diving and abrupt reperfusion upon termination of the dive. These conditions might be expected to result in production of oxygen-derived free radicals and other forms of highly reactive oxygen species. Seal organs vary during dives with respect to the degree and persistence of ischemia. Myocardial perfusion is reduced and intermittent; kidney circulation is vigorously vasoconstricted. Heart and kidney tissues from ringed seals (Phoca hispida) and domestic pigs (Sus scrofa) were compared in reactions to experimental ischemia. Resulting production of hypoxanthine, indicative of ATP degradation, was higher in pig than in seal tissues. Activity of superoxide dismutase (SOD), an oxygen radical scavenger, was higher in seal heart. We suggest that these results indicate enhanced protective cellular mechanisms in seals against the potential hazard of highly reactive oxygen forms. SOD activity was unexpectedly higher in pig kidney.

Effects of hypoxemia and reoxygenation with 21% or 100% oxygen in newborn piglets: extracellular hypoxanthine in cerebral cortex and femoral muscle.

OBJECTIVE To determine whether reoxygenation with an FIO2 of 0.21 (21% oxygen) is preferable to an FIO2 of 1.0 (100% oxygen) in normalizing brain and muscle hypoxia in the newborn. DESIGN Prospective, randomized, animal study. SETTING Hospital surgical research laboratory. SUBJECTS Twenty-six anesthetized, mechanically ventilated, domestic piglets, 2 to 5 days of age. INTERVENTIONS The piglets were randomized to control or hypoxemia groups. Hypoxemia was induced by ventilating the piglets with 8% oxygen in nitrogen, which was continued until mean arterial pressure decreased to <20 mm Hg. After hypoxemia, the piglets were further randomized to receive reoxygenation with an FIO2 of 0.21 (21% oxygen group, n = 9) or an FIO2 of 1.0 for 30 mins followed by an FIO2 of 0.21 (100% oxygen group, n = 9), and followed for 5 hrs. The piglets in the control group were mechanically ventilated with 21% oxygen (n = 8). MEASUREMENTS AND MAIN RESULTS We measured extracellular concentrations of hypoxanthine in the cerebral cortex and femoral muscle (in vivo microdialysis), plasma hypoxanthine concentrations, cerebral arterial-venous differences for hypoxanthine, acid base balances, arterial and venous (sagittal sinus) blood gases, and mean arterial pressures. The lowest pH values of 6.91 +/- 0.11 (21% oxygen group, mean +/- SD) and 6.90 +/- 0.07 (100% oxygen group) were reached at the end of hypoxemia and then normalized during the reoxygenation period. Plasma hypoxanthine increased during hypoxemia from 28.1 +/- 9.3 to 119.1 +/- 31.9 micromol/L in the 21% oxygen group (p < .001) and from 32.6 +/0- 14.5 to 135.0 +/- 31.4 micromol/L in the 100% oxygen group (p <.001). Plasma hypoxanthine concentrations then normalized over the next 2 hrs in both groups. In the cerebral cortex, extracellular concentrations of hypoxanthine increased during hypoxemia from 3.9 +/- 2.8 to 20.2 +/- 7.4 micromol/L in the 21% oxygen group (p < .001) and from 5.9 +/- 5.0 to 25.1 +/- 7.1 micromol/L in the 100% oxygen group (p < .001). In contrast to plasma hypoxanthine, extracellular hypoxanthine in the cerebral cortex increased significantly further during early reoxygenation, and, within the first 30 mins, reached maximum values of 24.9 +/- 6.3 micromol/L in the 21% oxygen group (p < .01) and 34.8 +/- 10.9 micromol/L in the 100% oxygen group (p < .001). This increase was significantly larger in the 100% oxygen group than in the 21% oxygen group (9.7 +/- 4.7 vs. 4.7 +/- 2.6 micromol/L, p < .05). There were no significant differences between the two reoxygenated groups in duration of hypoxemia, hypoxanthine concentrations in femoral muscle, plasma hypoxanthine concentrations, pH, or mean arterial pressure. The cerebral arterial-venous difference for hypoxanthine was positive both at baseline, at the end of hypoxemia, and after 30 mins and 300 mins of reoxygenation, and no differences were found between the two reoxygenated groups. CONCLUSIONS Significantly higher extracellular concentrations of hypoxanthine were found in the cerebral cortex during the initial period of reoxygenation with 100% oxygen compared with 21% oxygen. Hypoxanthine is a marker of hypoxia, and reflects the intracellular energy status. These results therefore suggest a possibly more severe impairment of energy metabolism in the cerebral cortex or an increased blood-brain barrier damage during reoxygenation with 100% oxygen compared with 21% oxygen in this newborn piglet hypoxia model.

Hypoxanthine, xanthine, and uric acid in newborn pigs during hypoxemia followed by resuscitation with room air or 100% oxygen.

ObjectiveTo determine if resuscitation with room air is as effective as resuscitation with an Fio2 of 1.0. DesignProspective, randomized laboratory study. SettingExperimental laboratory (neonatal or delivery ward). SubjectsTwenty piglets, 1 to 2 wks of age. InterventionsPiglets were randomized into two groups. Both groups underwent hypoxemia for 2 hrs and then underwent reoxygenation for 1 hr (group 1 with an Fio2 of 1.0 and group 2 with an Fio2 of 0.21). Measurements and Main ResultsHypoxanthine, xanthine, uric acid, Pao2, oxygen saturation, pH, base excess or deficit, and arterial pressure. During hypoxemia (Pao2 26 to 49 torr [3.5 to 6.5 kPa]), the mean hypoxanthine concentrations increased (p < .02) from 26.1 to 115.4 μmol/L in plasma, from 20.9 to 81.7 μmol/L in cerebrospinal fluid, and from 12.9 to 21.5 μmol/L in vitreous humor. Xanthine concentrations changed in a similar way, whereas uric acid concentrations increased only in plasma.During reoxygenation, hypoxanthine concentrations increased both in cerebrospinal fluid and in the vitreous humor. Final concentrations in these two fluid areas were 81.8 and 39.4 μmol/L, respectively (p < .02). Xanthine concentrations increased similarly. In plasma, hypoxanthine and xanthine concentrations decreased during reoxygenation. The final mean concentration of hypoxanthine was 76.8 μmol/L (p < .02). No change in plasma or cerebrospinal fluid uric acid concentrations were found during reoxygenation. The other measurements varied throughout the experiment, but no differences were found between the groups. ConclusionsThere were no significant differences between the two treatment groups at any stage in the experiments. In this porcine model of hypoxemia, resuscitation with room air was as effective as was resuscitation with an Fio2 of 1.0, when circulating concentrations of oxypurines were used as an end-point.

Ascorbic acid enhances hydroxyl radical formation in iron-fortified infant cereals and infant formulas

Abstract Infant cereals and formulas are usually fortified with iron to prevent iron deficiency. To enhance iron bioavailability, supplemental ascorbic acid is recommended. Ascorbic acid is considered to be an antioxidant in vivo, but has pro-oxidant effects when exposed to non-protein-bound iron. We measured formation of free radicals in cereals and infant formulas after addition of ascorbic acid. The production of hydroxyl radicals was assessed by hydroxylation of salicylic acid to 2,5-dihydroxybenzoic acid (2,5-DHBA). Production of 2,5-DHBA increased with increasing ascorbic acid doses added. Addition of 0.8 mM ascorbic acid to breast milk produced less radicals (0.03 ± 0.05 μM) than addition of ascorbic acid to low-iron formula (0.13 ± 0.08 μM, P = 0.019), medium-iron formula (0.34 ± 0.12 μM, P < 0.0001) or high-iron formula (0.44 ± 0.08 μM, P < 0.0001). Even when iron content in breast milk was adjusted to a level comparable with that of formulas, production of 2,5-DHBA was lower. Breast milk seems to contain substances that reduce hydroxyl radical formation. Conclusion Supplemental ascorbic acid causes hydro-xyl radical formation in iron-fortified infant nutrients in vitro.

Hypoxanthine, Xanthine, and Uric Acid Concentrations in the Cerebrospinal Fluid, Plasma, and Urine of Hypoxemic Pigs

ABSTRACT: The concentrations of hypoxanthine, xanthine, and uric acid in plasma and cerebrospinal fluid (CSF), as well as the urinary output of hypoxanthine and xanthine, were measured in four groups of pigs (three groups with different degrees of hypoxemia and one control group). During hypoxemia with arterial O2 tension between 2.1 and 3.0 kPa [group 1, fractional inspired oxygen (FiO2)=0.08], hypoxanthine increased in CSF from a mean basal value of 18.1 to 39.3 µmol/L at death (p < 0.02), in plasma from 25.4 to 103.6 µmol/L (p < 0.05), and in urine from 21.3 to 87.1 nmol/kg/min (p < 0.02). Xanthine changed in a similar way: in CSF from 4.0 to 10.6 /nmol/L (p<0.02), in plasma from 0.7 to 48.1 µmol/L (p<0.02), and in urine from 4.0 to 12.6 nmol/kg/min (p<0.05). Uric acid increased in CSF from 2.7 to 11.6 µmoI/L (p <0.05), and in plasma from 15.4 to 125.0 µmol/L (p<0.02). During hypoxemia with arterial O2 tension between 3.0 and 4.0 kPa (group 2, FiO2=0.11), hypoxanthine increased in the CSF from 14.7 to 42.9 µmol/L (p<0.02). Plasma hypoxanthine increased from 20.3 to a maximum of 44.1 µmol/ L (p<0.02), but decreased to initial values by the time of death. The urinary excretion of hypoxanthine increased from 13 to 54 nmol/kg/min (p<0.02). Xanthine increased in the CSF from 3.9 to 13.3µmol/L (p< 0.02), in plasma from 0.6 to 36.6 µmol/L (p <0.02), and in urine from 6 to 25 nmol/kg/min (p < 0.02). Uric acid increased in CSF from 3.1 to 16.3 jumol/L (p< 0.02), and in plasma from 15.3 to 208 µmol/L (p<0.0 0.02). During milder hypoxemia with arterial O2 tension between 4.3 and 5.6 kPa (group 3, FiO2=0.14), or in the control group (group 4, FiO2K=0.21), neither of the metabolites changed significantly.

Hypoxanthine, xanthine, and uric acid concentrations in plasma, cerebrospinal fluid, vitreous humor, and urine in piglets subjected to intermittent Versus continuous hypoxemia

ABSTRACT: Infants with sudden infant death syndrome have higher hypoxanthine (Hx) concentrations in their vitreous humor than infants with respiratory distress syndrome and other infant control populations. However, previous research on piglets and pigs applying continuous hypoxemia has not been able to reproduce the concentrations observed in infants with sudden infant death syndrome. To test whether intermittent hypoxemia could, in part, explain this observed difference, Hx, xanthine (X), and uric acid were measured in vitreous humor, urine, plasma, and cerebrospinal fluid in newborn piglets during intermittent hypoxemia (IH) or continuous hypoxemia (CH) of equal degree and duration. Urinary Hx excretion was significantly higher (p < 0.04) in the IH group after 60 min of hypoxemia. The vitreous humor Hx increase was significantly higher in the IH group (from 21.0 ± 7.8 to 44.1 ± 25.5 μmol/L, p < 0.01 versus baseline) than in the CH group (from 16.4 ± 4.2 to 23.2 ± 7.3 μmol/L, p < 0.05 versus baseline) (p < 0.05 IH versus CH). X increased significantly more (p < 0.05) in vitreous humor in the IH group than in the CH group. No differences between the two groups were found in plasma and cerebrospinal fluid for either Hx, X, or uric acid. We conclude that vitreous humor Hx and X increases more during IH than during CH.

Raised plasma hypoxanthine levels as a prognostic sign in preterm babies with respiratory distress syndrome treated with natural surfactant

Plasma hypoxanthine concentration was measured in twelve preterm babies with respiratory distress syndrome (RDS) treated with 200 mg/kg of a porcine surfactant (Curosurf). Five of the babies died within one week and seven survived the neonatal period. Surviving babies had no significant changes in plasma hypoxanthine concentration throughout a one hour study period following the administration of surfactant. By contrast, in nonsurvivors the mean plasma hypoxanthine concentrations increased from 6.8 mumol/l before surfactant administration to 14.2 mumol/l 15 minutes after surfactant treatment. Survivors had a mean maximal increase in plasma hypoxanthine of 1.9 mumol/l 15-30 min factor surfactant treatment compared with 9.4 mumol/l in nonsurvivors (p < 0.05). The babies who developed intracranial hemorrhage had significantly higher maximal plasma hypoxanthine increase (mean 9.6 mumol/l) compared with babies who did not develop intracranial hemorrhage (mean 1.1 mumol/l) (p < 0.01). The combination of high PaO2 and high hypoxanthine concentration could lead to an increased production of oxygen radicals which might be harmful. We conclude that plasma hypoxanthine concentration may serve as an indicator of the prognosis in preterm babies treated with natural surfactant. Further, it seems important to reduce oxygen supplementation as soon as surfactant is given to possibly limit oxygen radical production.