No Differences in Cerebral Immunohistochemical Markers following Remote Ischemic Postconditioning in Newborn Piglets with Hypoxia-Ischemia.

BACKGROUND: Despite therapeutic hypothermia, neonates with hypoxic-ischemic encephalopathy still develop neurological disabilities. We have previously investigated neuroprotection by remote ischemic postconditioning (RIPC) in newborn piglets following hypoxia-ischemia (HI). The aim of this study was to further investigate potential effects of RIPC on cerebral immunohistochemical markers related to edema, apoptosis, and angiogenesis. METHODS: Brain expression of aquaporin 4, caspase-3, B-cell lymphoma 2, and vascular endothelial growth factor was analyzed by immunohistochemistry in 23 piglets, randomly selected from a larger study of RIPC after HI. Twenty animals were subjected to 45 minutes of HI and randomized to treatment with and without RIPC, while three animals were randomized to sham procedures. RIPC was conducted by four conditioning cycles of 5-minute ischemia and reperfusion. Piglets were euthanized 72 hours after the HI insult. RESULTS: Piglets subjected to HI treated with and without RIPC were similar at baseline and following the HI insult. However, piglets randomized to HI alone had longer duration of low blood pressure during the insult. We found no differences in the brain expression of the immunohistochemical markers in any regions of interest or the whole brain between the two HI groups. CONCLUSION: RIPC did not influence brain expression of markers related to edema, apoptosis, or angiogenesis in newborn piglets at 72 hours after HI. These results support previous findings of limited neuroprotective effect by this RIPC protocol. Our results may have been affected by the time of assessment, use of fentanyl as anesthetic, or limitations related to our immunohistochemical methods.

Short-term outcomes of remote ischemic postconditioning 1 h after perinatal hypoxia-ischemia in term piglets.

BACKGROUND: We aimed to assess remote ischemic postconditioning (RIPC) as a neuroprotective strategy after perinatal hypoxia-ischemia (HI) in a piglet model. METHODS: Fifty-four newborn piglets were subjected to global HI for 45 min. One hour after HI, piglets were randomized to four cycles of 5 min of RIPC or supportive treatment only. The primary outcome was brain lactate/N-acetylaspartate (Lac/NAA) ratios measured by magnetic resonance spectroscopy at 72 h. Secondary outcomes included diffusion-weighted imaging and neuropathology. RESULTS: RIPC was associated with a reduction in overall and basal ganglia Lac/NAA ratios at 72 h after HI, but no effect on diffusion-weighted imaging, neuropathology scores, neurological recovery, or mortality. CONCLUSIONS: The selective effect of RIPC on Lac/NAA ratios may suggest that the metabolic effect is greater than the structural and functional improvement at 72 h after HI. Further studies are needed to address whether there is an add-on effect of RIPC to hypothermia, together with the optimal timing, number of cycles, and duration of RIPC. IMPACT: RIPC after HI was associated with a reduction in overall and basal ganglia Lac/NAA ratios at 72 h, but had no effect on diffusion-weighted imaging, neuropathology scores, neurological recovery, or mortality. RIPC may have a selective metabolic effect, ameliorating lactate accumulation without improving other short-term outcomes assessed at 72 h after HI. We applied four cycles of 5 min RIPC, complementing existing data on other durations of RIPC. This study adds to the limited data on RIPC after perinatal HI and highlights that knowledge gaps, including timing and duration of RIPC, must be addressed together with exploring the combined effects with hypothermia.

Continuous versus short-term infusion of cefuroxime: assessment of concept based on plasma, subcutaneous tissue, and bone pharmacokinetics in an animal model.

The relatively short half-lives of most ß-lactams suggest that continuous infusion of these time-dependent antimicrobials may be favorable compared to short-term infusion. Nevertheless, only limited solid-tissue pharmacokinetic data are available to support this theory. In this study, we randomly assigned 12 pigs to receive cefuroxime as either a short-term or continuous infusion. Measurements of cefuroxime were obtained every 30 min in plasma, subcutaneous tissue, and bone. For the measurements in solid tissues, microdialysis was applied. A two-compartment population model was fitted separately to the drug concentration data for the different tissues using a nonlinear mixed-effects regression model. Estimates of the pharmacokinetic parameters and time with concentrations above the MIC were derived using Monte Carlo simulations. Except for subcutaneous tissue in the short-term infusion group, the tissue penetration was incomplete for all tissues. For short-term infusion, the tissue penetration ratios were 0.97 (95% confidence interval [CI], 0.67 to 1.39), 0.61 (95% CI, 0.51 to 0.73), and 0.45 (95% CI, 0.36 to 0.56) for subcutaneous tissue, cancellous bone, and cortical bone, respectively. For continuous infusion, they were 0.53 (95% CI, 0.33 to 0.84), 0.38 (95% CI, 0.23 to 0.57), and 0.27 (95% CI, 0.13 to 0.48) for the same tissues, respectively. The absolute areas under the concentration-time curve were also lower in the continuous infusion group. Nevertheless, a significantly longer time with concentrations above the MIC was found for continuous infusion up until MICs of 4, 2, 2, and 0.5 µg/ml for plasma and the same three tissues mentioned above, respectively. For drugs with a short half-life, like cefuroxime, continuous infusion seems to be favorable compared to short-term infusion; however, incomplete tissue penetration and high MIC strains may jeopardize the continuous infusion approach.

Remote ischemic postconditioning increased cerebral blood flow and oxygenation assessed by magnetic resonance imaging in newborn piglets after hypoxia-ischemia.

Background: We have previously investigated neurological outcomes following remote ischemic postconditioning (RIPC) in a newborn piglet model of hypoxic-ischemic encephalopathy. The aim of this study was to further investigate potential mechanisms of neuroprotection by comparing newborn piglets subjected to global hypoxia-ischemia (HI) treated with and without RIPC with regards to measures of cerebral blood flow and oxygenation assessed by functional magnetic resonance imaging. Materials and methods: A total of 50 piglets were subjected to 45 min global HI and randomized to either no treatment or RIPC treatment. Magnetic resonance imaging was performed 72 h after the HI insult with perfusion-weighted (arterial spin labeling, ASL) and oxygenation-weighted (blood-oxygen-level-dependent, BOLD) sequences in the whole brain, basal ganglia, thalamus, and cortex. Four sham animals received anesthesia and mechanical ventilation only. Results: Piglets treated with RIPC had higher measures of cerebral blood flow in all regions of interest and the whole brain (mean difference: 2.6 ml/100 g/min, 95% CI: 0.1; 5.2) compared with the untreated controls. They also had higher BOLD values in the basal ganglia and the whole brain (mean difference: 4.2 T2*, 95% CI: 0.4; 7.9). Measures were similar between piglets treated with RIPC and sham animals. Conclusion: Piglets treated with RIPC had higher measures of cerebral blood flow and oxygenation assessed by magnetic resonance imaging in the whole brain and several regions of interest compared with untreated controls 72 h after the HI insult. Whether this reflects a potential neuroprotective mechanism of RIPC requires further study.

Learning Curves for Training in Ultrasonography-Based Examination of Umbilical Catheter Placement: A Piglet Study.

BACKGROUND: The training required for accurate assessment of umbilical catheter placement by ultrasonography (US) is unknown. OBJECTIVE: To describe the learning curve and provide an estimate of the accuracy of physicians' US examinations (US skills) and self-confidence when examining umbilical catheter tip placement. METHODS: Twenty-one physicians with minimal experience in US completed a 1.5-hour eLearning module. Ten piglets with catheters inserted in the umbilical vessels were used as training objects. Following eLearning each physician performed up to twelve 10-min US examinations of the piglets. Expert examinations were reference standards. Sensitivity and specificity of physicians' skills in detecting catheter tip placement by US was used to describe the learning curve. Self-confidence was reported by Likert scale after each examination. RESULTS: Physicians' detection of a correctly placed and misplaced umbilical artery catheter tip increased by an odds ratio of 1.6 (95% CI: 1.1, 2.3) and 3.6 (95% CI: 1.7, 7.8) per examination performed. A sensitivity of 0.97 (95% CI: 0.80, 0.99) and specificity of 0.95 (95% CI: 0.84, 0.99) was reached after 6 examinations. For the venous catheter, US skills in detecting a misplaced catheter tip increased with an odds ratio of 2.4 (95% CI: 1.2, 4.8) per US examination. Overall, performance and self-confidence plateaus were reached after 6 examinations. CONCLUSION: We found steep learning curves for targeted US examination of umbilical catheter placement. eLearning followed by 6 examinations was found to be adequate training to perform with a sufficiently high accuracy and self-confidence to allow for point-of-care use.

A Piglet Model of Neonatal Hypoxic-Ischemic Encephalopathy.

Birth asphyxia, which causes hypoxic-ischemic encephalopathy (HIE), accounts for 0.66 million deaths worldwide each year, about a quarter of the world's 2.9 million neonatal deaths. Animal models of HIE have contributed to the understanding of the pathophysiology in HIE, and have highlighted the dynamic process that occur in brain injury due to perinatal asphyxia. Thus, animal studies have suggested a time-window for post-insult treatment strategies. Hypothermia has been tested as a treatment for HIE in pdiglet models and subsequently proven effective in clinical trials. Variations of the model have been applied in the study of adjunctive neuroprotective methods and piglet studies of xenon and melatonin have led to clinical phase I and II trials(1,2). The piglet HIE model is further used for neonatal resuscitation- and hemodynamic studies as well as in investigations of cerebral hypoxia on a cellular level. However, it is a technically challenging model and variations in the protocol may result in either too mild or too severe brain injury. In this article, we demonstrate the technical procedures necessary for establishing a stable piglet model of neonatal HIE. First, the newborn piglet (< 24 hr old, median weight 1500 g) is anesthetized, intubated, and monitored in a setup comparable to that found in a neonatal intensive care unit. Global hypoxia-ischemia is induced by lowering the inspiratory oxygen fraction to achieve global hypoxia, ischemia through hypotension and a flat trace amplitude integrated EEG (aEEG) indicative of cerebral hypoxia. Survival is promoted by adjusting oxygenation according to the aEEG response and blood pressure. Brain injury is quantified by histopathology and magnetic resonance imaging after 72 hr.