Point-of-care Ultrasound to Assess Hemodynamic Contributors to Acute Kidney Injury in Pediatric Patients With Cerebral Malaria: A Pilot Study.

BACKGROUND: Acute kidney injury is common in severe malaria and is independently associated with mortality. The pathogenesis of acute kidney injury (AKI) in severe malaria remains incompletely understood. Ultrasound-based tools such as point-of-care ultrasound (POCUS), ultrasound cardiac output monitors (USCOMs) and renal arterial resistive index (RRI) can be used to detect hemodynamic and renal blood flow abnormalities contributing to AKI in malaria. METHODS: We conducted a prospective study of Malawian children with cerebral malaria to determine the feasibility of using POCUS and USCOM to characterize hemodynamic contributors to severe AKI (Kidney Disease: Improving Global Outcomes stage 2 or 3). The primary outcome was feasibility (completion rate of study procedures). We also assessed for differences in POCUS and hemodynamic variables for patients with or without severe AKI. RESULTS: We enrolled 27 patients who had admission cardiac and renal ultrasounds and USCOM. Completion rates were high for cardiac (96%), renal (100%) and USCOM studies (96%). Severe AKI occurred in 13 of 27 patients (48%). No patients had ventricular dysfunction. Only 1 patient in the severe AKI group was determined to be hypovolemic ( P = 0.64). No significant differences in USCOM, RRI or venous congestion parameters were detected among patients with and without severe AKI. Mortality was 11% (3/27) with the 3 deaths occurring in the severe AKI group ( P = 0.056). CONCLUSIONS: Ultrasound-based cardiac, hemodynamic and renal blood flow measurements appear to be feasible in pediatric patients with cerebral malaria. We were unable to detect hemodynamic or renal blood flow abnormalities contributing to severe AKI in cerebral malaria. Larger studies are needed to corroborate these findings.

Transcranial doppler velocities in a large healthy population of African children.

Background and purpose: Transcranial doppler ultrasound (TCD) is a tool that diagnoses and monitors pathophysiological changes to the cerebrovasculature. As cerebral blood flow velocities (CBFVs) increase throughout childhood, interpretation of TCD examinations in pediatrics requires comparison to age matched normative data. Large cohorts of healthy children have not been examined to develop these reference values in any population. There is a complete absence of normative values in African children where, due to lack of alternate neuroimaging techniques, utilization of TCD is rapidly emerging. Materials and methods: A prospective study of 710 healthy African children 3 months-15 years was performed. Demographics, vital signs, and hemoglobin values were recorded. Participants underwent a complete, non-imaging TCD examination. Systolic (Vs), diastolic (Vd), and mean (Vm) flow velocities and pulsatility index (PI) were calculated by the instrument for each measurement. Results: Vs, Vd, and Vm increased through early childhood in all vessels, with the highest CBFVs identified in children 5-5.9 years. There were few significant gender differences in CBFVs in any vessels in any age group. No correlations between blood pressure or hemoglobin and CBFVs were identified. Children in the youngest age groups had CBFVs similar to those previously published, whereas nearly every vessel in children ≥3 years had significantly lower Vs, Vd, and Vm. Conclusions: For the first time, reference TCD values for African children are established. Utilization of these CBFVs in the interpretation of TCD examinations in this population will improve the overall accuracy of TCD as a clinical tool on the continent.

Mechanisms of Transcranial Doppler Ultrasound phenotypes in paediatric cerebral malaria remain elusive.

BACKGROUND: Cerebral malaria (CM) results in significant paediatric death and neurodisability in sub-Saharan Africa. Several different alterations to typical Transcranial Doppler Ultrasound (TCD) flow velocities and waveforms in CM have been described, but mechanistic contributors to these abnormalities are unknown. If identified, targeted, TCD-guided adjunctive therapy in CM may improve outcomes. METHODS: This was a prospective, observational study of children 6 months to 12 years with CM in Blantyre, Malawi recruited between January 2018 and June 2021. Medical history, physical examination, laboratory analysis, electroencephalogram, and magnetic resonance imaging were undertaken on presentation. Admission TCD results determined phenotypic grouping following a priori definitions. Evaluation of the relationship between haemodynamic, metabolic, or intracranial perturbations that lead to these observed phenotypes in other diseases was undertaken. Neurological outcomes at hospital discharge were evaluated using the Paediatric Cerebral Performance Categorization (PCPC) score. RESULTS: One hundred seventy-four patients were enrolled. Seven (4%) had a normal TCD examination, 57 (33%) met criteria for hyperaemia, 50 (29%) for low flow, 14 (8%) for microvascular obstruction, 11 (6%) for vasospasm, and 35 (20%) for isolated posterior circulation high flow. A lower cardiac index (CI) and higher systemic vascular resistive index (SVRI) were present in those with low flow than other groups (p < 0.003), though these values are normal for age (CI 4.4 [3.7,5] l/min/m2, SVRI 1552 [1197,1961] dscm-5m2). Other parameters were largely not significantly different between phenotypes. Overall, 118 children (68%) had a good neurological outcome. Twenty-three (13%) died, and 33 (19%) had neurological deficits. Outcomes were best for participants with hyperaemia and isolated posterior high flow (PCPC 1-2 in 77 and 89% respectively). Participants with low flow had the least likelihood of a good outcome (PCPC 1-2 in 42%) (p < 0.001). Cerebral autoregulation was significantly better in children with good outcome (transient hyperemic response ratio (THRR) 1.12 [1.04,1.2]) compared to a poor outcome (THRR 1.05 [0.98,1.02], p = 0.05). CONCLUSIONS: Common pathophysiological mechanisms leading to TCD phenotypes in non-malarial illness are not causative in children with CM. Alternative mechanistic contributors, including mechanical factors of the cerebrovasculature and biologically active regulators of vascular tone should be explored.

Biomimetic stiffening of cell-laden hydrogels via sequential thiol-ene and hydrazone click reactions.

Hydrogels with dynamically tunable crosslinking are invaluable for directing stem cell fate and mimicking a stiffening matrix during fibrosis or tumor development. The increases in matrix stiffness during tissue development are often accompanied by the accumulation of extracellular matrices (e.g., collagen, hyaluronic acid (HA)), a phenomenon that has received little attention in the development of dynamic hydrogels. In this contribution, we present a gelatin-based cell-laden hydrogel system capable of being dynamically stiffened while accumulating HA, a key glycosaminoglycans (GAG) increasingly deposited by stromal cells during tumor progression. Central to this strategy is the synthesis of a dually-modified gelatin macromer - gelatin-norbornene-carbohydrazide (GelNB-CH), which is susceptible to both thiol-norbornene photopolymerization and hydrazone click chemistry. We demonstrate that the crosslinking density of cell-laden thiol-norbornene hydrogels can be dynamically tuned via simple incubation with aldehyde-bearing macromers (e.g., oxidized dextran (oDex) or oHA). The GelNB-CH hydrogel system is highly cytocompatible, as demonstrated by in situ encapsulation of pancreatic cancer cells (PCC) and cancer-associated fibroblasts (CAF). This unique dynamic stiffening scheme provides a platform to study tandem accumulation of HA and elevation in matrix stiffness in the pancreatic tumor microenvironment. STATEMENT OF SIGNIFICANCE: Hydrogels permitting on-demand and secondary crosslinking are ideal for mimicking a stiffening tumor microenvironment (TME). However, none of the current dynamic hydrogels account for both stiffening and accumulation of hyaluronic acid (HA), a major extracellular matrix component increasingly deposited in tumor stromal tissues, including pancreatic ductal adenocarcinoma (PDAC). The current work addresses this gap by developing a dynamic hydrogel system capable of simultaneously increasing stiffness and HA accumulation. This is achieved by a new gelatin macromer permitting sequential thiol-norbornene (for primary network crosslinking) and hydrazone click chemistry (for bioinert or biomimetic stiffening with oxidized dextran (oDex) or oHA, respectively). The results of this study provide new insights into how dynamically changing physicochemical matrix properties guide cancer cell fate processes.

Dynamic Click Hydrogels for Xeno-Free Culture of Induced Pluripotent Stem Cells.

Xeno-free, chemically defined poly(ethylene glycol) (PEG)-based hydrogels are being increasingly used for in vitro culture and differentiation of human induced pluripotent stem cells (hiPSCs). These synthetic matrices provide tunable gelation and adaptable material properties crucial for guiding stem cell fate. Here, sequential norbornene-click chemistries are integrated to form synthetic, dynamically tunable PEG-peptide hydrogels for hiPSCs culture and differentiation. Specifically, hiPSCs are photoencapsulated in thiol-norbornene hydrogels crosslinked by multiarm PEG-norbornene (PEG-NB) and proteaselabile crosslinkers. These matrices are used to evaluate hiPSC growth under the influence of extracellular matrix properties. Tetrazine-norbornene (Tz-NB) click reaction is then employed to dynamically stiffen the cell-laden hydrogels. Fast reactive Tz and its stable derivative methyltetrazine (mTz) are tethered to multiarm PEG, yielding mono-functionalized PEG-Tz, PEG-mTz, and dualfunctionalized PEG-Tz/mTz that react with PEG-NB to form additional crosslinks in the cell-laden hydrogels. The versatility of Tz-NB stiffening is demonstrated with different Tz-modified macromers or by intermittent incubation of PEG-Tz for temporal stiffening. Finally, the Tz-NB-mediated dynamic stiffening is explored for 4D culture and definitive endoderm differentiation of hiPSCs. Overall, this dynamic hydrogel platform affords exquisite controls of hydrogel crosslinking for serving as a xeno-free and dynamic stem cell niche.

Sulfamethoxazole-Trimethoprim and Hyperkalemia in an Infant.

Hyperkalemia is a potentially life-threatening electrolyte abnormality in both children and adults. In the setting of elevated serum potassium concentrations, cardiac conduction disturbances and cardiac arrest may occur. In the pediatric intensive care unit (PICU) setting, the differential diagnosis of hyperkalemia may be extensive including increased potassium intake or administration, increased endogenous production, decreased renal excretion, and intracellular to extracellular shifts related to changes in acid-base status. We present a 4-month-old infant who developed hyperkalemia during the recovery phase of her PICU course for respiratory failure. A thorough investigation demonstrated that the hyperkalemia was most likely the result of the commonly used antibiotic, trimethoprim-sulfamethoxazole (Bactrim®). Potential etiologies of hyperkalemia in the PICU patient are discussed and previous reports of hyperkalemia associated with trimethoprim-sulfamethoxazole presented.