Veno-Arterial Extracorporeal Membrane Oxygenation in Adults with Septic Shock

Survivors and non-survivors were compared for 20 adults supported with veno-arterial extracorporeal membrane oxygenation (VA ECMO) for refractory septic shock from 2012-2018. The primary outcome was hospital survival. Secondary outcomes were ECMO associated complications and survival to decannulation. Median age was 53.5 (IQR 42.0-61.3). At ≤ 24 hours prior to cannulation, median SOFA score was 17.5 (IQR 15 - 19) and 17 patients (85%) had new cardiac dysfunction. Median left ventricular ejection fraction (LVEF) was 20% (IQR 10-38). Thirteen patients had a mixed (cardiogenic and distributive) or cardiogenic shock profile (65%), 7 had a distributive shock profile (35%), and 17 (85%) survived to decannulation. Fourteen (70%) survived to hospital discharge and median cerebral performance category score was 1 (IQR 1-2). No differences were found in age, comorbid conditions, time from shock onset to cannulation, peak flow rate on ECMO, ECMO complications, shock profile, LVEF, or vasoactive-inotrope score (VIS). More patients in the distributive shock profile experienced limb ischemia complications (n=3, 42.9%) compared to the cardiogenic and mixed shock profiles (n=1, 7.7%). Survivors to hospital discharge had a lower SOFA score. VA ECMO support may be a beneficial therapy for refractory septic shock and could be considered in select adult patients.

Electrostatic Ion-Acoustic Shock Waves in a Magnetized Degenerate Quantum Plasma

A theoretical investigation has been carried out to examine the ion-acoustic shock waves (IASHWs) in a magnetized degenerate quantum plasma system containing inertialess ultra-relativistically degenerate electrons, and inertial non-relativistic positively charged heavy and light ions. The Burgers equation is derived by employing the reductive perturbation method. It can be seen that under the consideration of non-relativistic positively charged heavy and light ions, the plasma model only supports the positive electrostatic shock structure. It is also observed that the charge state and number density of the non-relativistic heavy and light ions enhance the amplitude of IASHWs, and the steepness of the shock profile is decreased with ion kinematic viscosity. The findings of our present investigation will be helpful in understanding the nonlinear propagation of IASHWs in white dwarfs and neutron stars.

Linear stability of shock profiles for a quasilinear Benney system in ℝ2 × ℝ+

Following Dias et al. [Vanishing viscosity with short wave-long wave interactions for multi-D scalar conservation laws, J. Differential Equations 251 (2007) 555–563], we study the linearized stability of a pair [Formula: see text], where [Formula: see text] is a shock profile for a family of quasilinear hyperbolic conservation laws in [Formula: see text] coupled with a semilinear Schrödinger equation.

Overshoot dependence on the cross-shock potential

Coherent downstream oscillations of the magnetic field in shocks are produced due to the coherent ion gyration and quasiperiodic variations of the ion pressure. The amplitude and the positions of the pressure maxima and minima depend on the cross-shock potential and upstream ion temperature. Two critical cross-shock potentials are defined: the critical gyration potential (CGP), which separates the cases of increase or decrease in the component of the velocity of the distribution center along the shock normal, and the critical reflection potential (CRP), above which ion reflection becomes significant. In a weak, very low upstream kinetic-to-magnetic pressure ratio, β, the shocks' CRP exceeds the CGP. For potentials below the CGP, the first downstream maximum of the magnetic field is shifted farther downstream and is larger than the second maximum. For higher potentials, the first maximum occurs just behind the ramp and is lower than the second maximum. With the increase in the upstream temperature, the CGP exceeds the CRP. For potentials below the CRP, the effects of ion reflection are negligible and the shock profile is similar to that of very low-β shocks. If the potential exceeds the CRP, ion reflection is significant, the magnetic field increase toward the overshoot becomes steeper, and the largest peak occurs at the downstream edge of the ramp.

Overshoot dependence on the cross-shock potential

Coherent downstream oscillations of the magnetic field in shocks are produced due to the coherent ion gyration and quasi-periodic variations of the ion pressure. The amplitude and the positions of the pressure maxima and minima depend on the cross-shock potential and upstream ion temperature. Two critical potentials are defined: the critical gyration potential (CGP) which separates the cases of increase or decrease of the normal velocity of the distribution center, and the critical reflection potential (CRP) above which ion reflection becomes significant. In weak very low β shocks CRP exceeds CGP. For potentials below CGP the first downstream maximum of the magnetic field is shifted farther downstream and is larger than the second one. For higher potentials the first maximum occurs just behind the ramp and is lower than the second one. With the increase of the upstream temperature CGP exceeds the CRP. For potentials below CRP the effects of ion reflection are negligible and the shock profile is similar to that of very low β shocks. If the potential exceeds CRP ion reflection is significant, the magnetic field increase toward the overshoot becomes steeper, and the largest peak occurs at the downstream edge of the ramp.

Whistler precursor and intrinsic variability of quasi-perpendicular shocks

The structure of a whistler precursor in a quasi-perpendicular shock is studied within two-fluid approach in one-dimensional case. The complete set of equations is reduced to the KdV equation, if no dissipation is included. With a phenomenological resistive dissipation the structure is described with the KdV–Burgers equation. The shock profile is intrinsically time dependent. For sufficiently strong dissipation, temporal evolution of a steepening profile results in generation of a stationary decaying whistler ahead of the shock front. With the decrease of the dissipation parameter, whistler wave trains begin to detach and propagate toward the upstream and the ramp is weakly time dependent. In the weakly dissipative regime the shock front experiences reformation.