Bilateral pulmonary artery banding in higher risk neonates with hypoplastic left heart syndromeCentral MessagePerspective

Objectives: Limited data on performing bilateral pulmonary artery banding (BPAB) before stage 1 Norwood procedure suggest that some patients may benefit through the postponement of the major cardiopulmonary bypass procedure. The objective of this study was to evaluate the effectiveness of BPAB in the surgical management of high-risk patients with hypoplastic left heart syndrome (HLHS). Methods: A retrospective review of all high-risk neonates with HLHS who underwent BPAB at our institution was performed. No patients, including those with intact or highly restrictive atrial septum (IAS), were excluded. Results: Between October 2015 and April 2021, 49 neonates with HLHS (including 6 with IAS) underwent BPAB, 40 of whom progressed to the Norwood procedure. Risk factors for not progressing to the Norwood procedure after BPAP include low birth weight (P = .043), the presence of multiple extracardiac anomalies (P = .005), and the presence of genetic disorders (P = .028). Operative mortality was 7.5% (3/40). IAS was associated with operative mortality (P = .022). Conclusions: The strategy of BPAB prestage 1 Norwood procedure was successful in identifying at-risk patients and improving Norwood survival. Although not all patients will need this hybrid approach, a significant number can be expected to benefit from this tactic. These results support the need for a substantial hybrid strategy, in addition to a primary stage 1 Norwood surgical strategy, in the management of HLHS

Elimination of substances from the brain parenchyma: efflux via perivascular pathways and via the blood-brain barrier.

This review considers efflux of substances from brain parenchyma quantified as values of clearances (CL, stated in µL g-1 min-1). Total clearance of a substance is the sum of clearance values for all available routes including perivascular pathways and the blood-brain barrier. Perivascular efflux contributes to the clearance of all water-soluble substances. Substances leaving via the perivascular routes may enter cerebrospinal fluid (CSF) or lymph. These routes are also involved in entry to the parenchyma from CSF. However, evidence demonstrating net fluid flow inwards along arteries and then outwards along veins (the glymphatic hypothesis) is still lacking. CLperivascular, that via perivascular routes, has been measured by following the fate of exogenously applied labelled tracer amounts of sucrose, inulin or serum albumin, which are not metabolized or eliminated across the blood-brain barrier. With these substances values of total CL ≅ 1 have been measured. Substances that are eliminated at least partly by other routes, i.e. across the blood-brain barrier, have higher total CL values. Substances crossing the blood-brain barrier may do so by passive, non-specific means with CLblood-brain barrier values ranging from  1000 for water and CO2. CLblood-brain barrier values for many small solutes are predictable from their oil/water partition and molecular weight. Transporters specific for glucose, lactate and many polar substrates facilitate efflux across the blood-brain barrier producing CLblood-brain barrier values > 50. The principal route for movement of Na+ and Cl- ions across the blood-brain barrier is probably paracellular through tight junctions between the brain endothelial cells producing CLblood-brain barrier values ~ 1. There are large fluxes of amino acids into and out of the brain across the blood-brain barrier but only small net fluxes have been observed suggesting substantial reuse of essential amino acids and α-ketoacids within the brain. Amyloid-β efflux, which is measurably faster than efflux of inulin, is primarily across the blood-brain barrier. Amyloid-β also leaves the brain parenchyma via perivascular efflux and this may be important as the route by which amyloid-β reaches arterial walls resulting in cerebral amyloid angiopathy