5 results
Safety of tracheal intubation in the presence of cardiac disease in paediatric ICUs
- Eleanor A. Gradidge, Adnan Bakar, David Tellez, Michael Ruppe, Sarah Tallent, Geoffrey Bird, Natasha Lavin, Anthony Lee, Vinay Nadkarni, Michelle Adu-Darko, Jesse Bain, Katherine Biagas, Aline Branca, Ryan K. Breuer, Calvin Brown III, Kris Bysani, Guillaume Emeriaud, Sandeep Gangadharan, John S. Giuliano, Jr, Joy D. Howell, Conrad Krawiec, Jan Hau Lee, Simon Li, Keith Meyer, Michael Miksa, Natalie Napolitano, Sholeen Nett, Gabrielle Nuthall, Alberto Orioles, Erin B. Owen, Margaret M. Parker, Simon Parsons, Lee A. Polikoff, Kyle Rehder, Osamu Saito, Ron C. Sanders, Jr, Asha Shenoi, Dennis W. Simon, Peter W. Skippen, Keiko Tarquinio, Anne Thompson, Iris Toedt-Pingel, Karen Walson, Akira Nishisaki, For National Emergency Airway Registry for Children (NEARKIDS) Investigators and Pediatric Acute Lung Injury and Sepsis Investigators (PALISI)
-
- Journal:
- Cardiology in the Young / Volume 28 / Issue 7 / July 2018
- Published online by Cambridge University Press:
- 25 April 2018, pp. 928-937
-
- Article
- Export citation
-
Introduction
Children with CHD and acquired heart disease have unique, high-risk physiology. They may have a higher risk of adverse tracheal-intubation-associated events, as compared with children with non-cardiac disease.
Materials and methodsWe sought to evaluate the occurrence of adverse tracheal-intubation-associated events in children with cardiac disease compared to children with non-cardiac disease. A retrospective analysis of tracheal intubations from 38 international paediatric ICUs was performed using the National Emergency Airway Registry for Children (NEAR4KIDS) quality improvement registry. The primary outcome was the occurrence of any tracheal-intubation-associated event. Secondary outcomes included the occurrence of severe tracheal-intubation-associated events, multiple intubation attempts, and oxygen desaturation.
ResultsA total of 8851 intubations were reported between July, 2012 and March, 2016. Cardiac patients were younger, more likely to have haemodynamic instability, and less likely to have respiratory failure as an indication. The overall frequency of tracheal-intubation-associated events was not different (cardiac: 17% versus non-cardiac: 16%, p=0.13), nor was the rate of severe tracheal-intubation-associated events (cardiac: 7% versus non-cardiac: 6%, p=0.11). Tracheal-intubation-associated cardiac arrest occurred more often in cardiac patients (2.80 versus 1.28%; p<0.001), even after adjusting for patient and provider differences (adjusted odds ratio 1.79; p=0.03). Multiple intubation attempts occurred less often in cardiac patients (p=0.04), and oxygen desaturations occurred more often, even after excluding patients with cyanotic heart disease.
ConclusionsThe overall incidence of adverse tracheal-intubation-associated events in cardiac patients was not different from that in non-cardiac patients. However, the presence of a cardiac diagnosis was associated with a higher occurrence of both tracheal-intubation-associated cardiac arrest and oxygen desaturation.
Stability characteristics of a counter-rotating unequal-strength Batchelor vortex pair
- Kris Ryan, Christopher J. Butler, Gregory J. Sheard
-
- Journal:
- Journal of Fluid Mechanics / Volume 696 / 10 April 2012
- Published online by Cambridge University Press:
- 06 March 2012, pp. 374-401
-
- Article
- Export citation
-
A Batchelor vortex represents the asymptotic solution of a trailing vortex in an aircraft wake. In this study, an unequal-strength, counter-rotating Batchelor vortex pair is employed as a model of the wake emanating from one side of an aircraft wing; this model is a direct extension of several prior investigations that have considered unequal-strength Lamb–Oseen vortices as representations of the aircraft wake problem. Both solution of the linearized Navier–Stokes equations and direct numerical simulations are employed to study the linear and nonlinear development of a vortex pair with a circulation ratio of . In contrast to prior investigations considering a Lamb–Oseen vortex pair, we note strong growth of the Kelvin mode coupled with an almost equal growth rate of the Crow instability. Three stages of nonlinear instability development are defined. In the initial stage, the Kelvin mode amplitude becomes sufficiently large that oscillations within the core of the weaker vortex are easily observable and significantly affect the profile of the weaker vortex. In the secondary stage, filaments of secondary vorticity emanate from the weaker vortex and are convected around the stronger vortex. In the tertiary stage, a transition in the dominant instability wavelength is observed from the short-wavelength Kelvin mode to the longer-wavelength Crow instability. Much of the instability growth is observed on the weaker vortex of the pair, although small perturbations in the stronger vortex are observed in the tertiary nonlinear growth phase.
Symmetry breaking and instability mechanisms in medium depth torsionally driven open cylinder flows
- STUART J. COGAN, KRIS RYAN, GREGORY J. SHEARD
-
- Journal:
- Journal of Fluid Mechanics / Volume 672 / 10 April 2011
- Published online by Cambridge University Press:
- 14 February 2011, pp. 521-544
-
- Article
- Export citation
-
A numerical investigation was conducted into the different flow states, and bifurcations leading to changes of state, found in open cylinders of medium to moderate depth driven by a constant rotation of the vessel base. A combination of linear stability analysis, for cylinders of numerous height-to-radius aspect ratios (H/R), and nonlinear stability analysis and three-dimensional simulations for a cylinder of aspect ratio 1.5, has been employed. Attention is focused on the breaking of SO(2) symmetry. A comprehensive map of transition Reynolds numbers as a function of aspect ratio is presented by combining a detailed stability analysis with the limited existing data from the literature. For all aspect ratios considered, the primary instabilities are identified as symmetry-breaking Hopf bifurcations, occurring at Reynolds numbers well below those of the previously reported axisymmetric Hopf transitions. It is revealed that instability modes with azimuthal wavenumbers m = 1, 3 and 4 are the most unstable in the range 1.0 < H/R < 4, and that numerous double Hopf bifurcation points exist. Critical Reynolds numbers generally increase with cylinder aspect ratio, though a decrease in stability occurs between aspect ratios 1.5 and 2.0, where a local minimum in critical Reynolds number occurs. For H/R = 1.5, a detailed characterisation of instability modes is given. It is hypothesized that the primary instability leading to transition from steady axisymmetric flow to unsteady three-dimensional flow is related to deformation of shear layers that are present in the flow, in particular at the interfacial region between the vortex breakdown bubble and the primary recirculation.
Cylinders with square cross-section: wake instabilities with incidence angle variation
- GREGORY J. SHEARD, MATTHEW J. FITZGERALD, KRIS RYAN
-
- Journal:
- Journal of Fluid Mechanics / Volume 630 / 10 July 2009
- Published online by Cambridge University Press:
- 10 July 2009, pp. 43-69
-
- Article
- Export citation
-
The wakes behind square cylinders with variation in incidence angle are computed over a range of Reynolds numbers to elucidate the three-dimensional stability and dynamics up to a Reynolds number of Re = 300, based on the projected height of the inclined square cylinder. Three-dimensional instability modes are predicted and computed using a linear stability analysis technique and three-dimensional simulations, respectively. Depending on the incidence angle, the flow is found to transition to three-dimensional flow through either a mode A instability, or a subharmonic mode C instability. The mode A instability is predicted as the first-occurring instability at incidence angles smaller than 12° and greater than 26°, with the mode C instability predicted between these incidence angles. At a zero-degree angle of incidence, the wake instabilities closely match modes A, B and a quasi-periodic mode predicted in earlier studies behind square and circular cylinders. With increasing angle of incidence, the three-dimensional wake transition Reynolds number first increases from Re = 164 as the mode A instability weakens, before decreasing again beyond an incidence angle of 12° as the wake becomes increasingly unstable to the mode C instability, and then again to the mode A instability as the incidence angle approaches 45°. A spanwise autocorrelation analysis from computations over a cylinder span 20 times the square cross-section side length reveals that beyond the onset of three-dimensional instabilities, the vortex street breaks down with patterns consistent with spatio-temporal chaos. This effect was more pronounced at higher incidence angles.
Elliptic instability in a strained Batchelor vortex
- LAURENT LACAZE, KRIS RYAN, STÉPHANE LE DIZÈS
-
- Journal:
- Journal of Fluid Mechanics / Volume 577 / 25 April 2007
- Published online by Cambridge University Press:
- 19 April 2007, pp. 341-361
-
- Article
- Export citation
-
The elliptic instability of a Batchelor vortex subject to a stationary strain field is considered by theoretical and numerical means in the regime of large Reynolds number and small axial flow. In the theory, the elliptic instability is described as a resonant coupling of two quasi-neutral normal modes (Kelvin modes) of the Batchelor vortex of azimuthal wavenumbers m and m + 2 with the underlying strain field. The growth rate associated with these resonances is computed for different values of the azimuthal wavenumbers as the axial flow parameter is varied. We demonstrate that the resonant Kelvin modes m = 1 and m = −1 which are the most unstable in the absence of axial flow become damped as the axial flow is increased. This is shown to be due to the appearance of a critical layer which damps one of the resonant Kelvin modes. However, the elliptic instability does not disappear. Other combinations of Kelvin modes m = −2 and m = 0, then m = −3 and m = −1 are shown to become progressively unstable for increasing axial flow. A complete instability diagram is obtained as a function of the axial flow parameter for several values of the strain rate and Reynolds number.
The numerical study considers a system of two counter-rotating Batchelor vortices in which the strain field felt by each vortex is due to the other vortex. The characteristics of the most unstable linear modes developing on the frozen base flow are computed by direct numerical simulations for two axial flow parameters and compared to the theory. In both cases, a very good agreement is obtained for the most unstable modes. Less unstable modes are also identified in the numerics and shown to correspond to peculiar resonances involving Kelvin modes from branches of different labels.