A computational fluid dynamics assessment of 3D printed ventilator splitters and restrictors for differential multi-patient ventilation

BACKGROUND

The global pandemic of novel coronavirus (SARS-CoV-2) has led to global shortages of ventilators and accessories. One solution to this problem is to split ventilators between multiple patients, which poses the difficulty of treating two patients with dissimilar ventilation needs. A proposed solution to this problem is the use of 3D-printed flow splitters and restrictors. There is little data available on the reliability of such devices and how the use of different 3D printing methods might affect their performance.

METHODS

We performed flow resistance measurements on 30 different 3D-printed restrictor designs produced using a range of fused deposition modelling and stereolithography printers and materials, from consumer grade printers using polylactic acid filament to professional printers using surgical resin. We compared their performance to novel computational fluid dynamics models driven by empirical ventilator flow rate data. This indicates the ideal performance of a part that matches the computer model.

RESULTS

The 3D-printed restrictors varied considerably between printers and materials to a sufficient degree that would make them unsafe for clinical use without individual testing. This occurs because the interior surface of the restrictor is rough and has a reduced nominal average diameter when compared to the computer model. However, we have also shown that with careful calibration it is possible to tune the end-inspiratory (tidal) volume by titrating the inspiratory time on the ventilator.

CONCLUSIONS

Computer simulations of differential multi patient ventilation indicate that the use of 3D-printed flow splitters is viable. However, in situ testing indicates that using 3D printers to produce flow restricting orifices is not recommended, as the flow resistance can deviate significantly from expected values depending on the type of printer used.

TRIAL REGISTRATION

Not applicable.

Determinants of non-adherence to anti-TB treatment in high income, low TB incidence settings: a scoping review

BACKGROUND: Improving adherence to anti-TB treatment is a public health priority in high-income, low incidence (HILI) regions. We conducted a scoping review to identify reported determinants of non-adherence in HILI settings.METHODS: Key terms related to TB, treatment and adherence were used to search MEDLINE, EMBASE, Web of Science, PsycINFO and CINAHL in June 2019. Quantitative studies examining determinants (demographic, clinical, health systems or psychosocial) of non-adherence to anti-TB treatment in HILI settings were included.RESULTS: From 10,801 results, we identified 24 relevant studies from 10 countries. Definitions and methods of assessing adherence were highly variable, as were documented levels of non-adherence (0.9-89%). Demographic factors were assessed in all studies and clinical factors were frequently assessed (23/24). Determinants commonly associated with non-adherence were homelessness, incarceration, and alcohol or drug misuse. Health system (8/24) and psychosocial factors (6/24) were less commonly evaluated.CONCLUSION: Our review identified some key factors associated with non-adherence to anti-TB treatment in HILI settings. Modifiable determinants such as psychosocial factors are under-evidenced and should be further explored, as these may be better targeted by adherence support. There is an urgent need to standardise definitions and measurement of adherence to more accurately identify the strongest determinants.

Coping with COVID-19: ventilator splitting with differential driving pressures using standard hospital equipment

The global COVID‐19 pandemic has led to a worldwide shortage of ventilators. This shortage has initiated discussions on how to support multiple patients with a single ventilator (ventilator splitting). Ventilator splitting is incompletely tested, experimental and the effects have not been fully characterised. This study investigated the effect of ventilator splitting on system variables (inspiratory pressure, flow and volume) and the possibility of different ventilation targets for each limb using only standard hospital equipment. Experiments were conducted on two test lungs with different compliances (0.02 l.cmH₂O⁻¹ and 0.04 l.cmH₂O⁻¹). The ventilator was used in both pressure and volume control modes and was set to ventilate the low compliance lungs at end‐tidal volumes of 500 ± 20 ml. A flow restrictor apparatus consisting of a Hoffman clamp and tracheal tube was connected in series to the inspiratory limb of the high compliance test lungs and the resistance modified to achieve end‐tidal volumes of 500 ± 20 ml. The restriction apparatus successfully modified the inspiratory pressure, minute ventilation and volume delivered to the high compliance test lungs in both pressure control (27.3–17.8 cmH₂O, 15.2–8.0 l.min⁻¹ and 980–499 ml, respectively) and volume control (21.0–16.7 cmH₂O, 10.7–7.9 l.min⁻¹ and 659–498 ml, respectively) ventilation modes. Ventilator splitting is not condoned by the authors. However, these experiments demonstrate the capacity to simultaneously ventilate two test lungs of different compliances, and using only standard hospital equipment, modify the delivered pressure, flow and volume in each test lung.

The role of neuronal GABA(A) receptor subunit mutations in idiopathic generalized epilepsies

Rare GABA(A) receptor gamma2 and alpha1 subunit mutations of pathogenic effect have been described segregating in families with "monogenic" epilepsies. We now report globally on the genetic variation contained within all 16 neuronal GABA(A) receptor subunit genes from the one patient cohort. The cohort consists of GEFS(+), FS, and IGE subgroups as either sporadic cases or index cases from small families, with one index case from one large IGE family. The rarity of mutations and coding variation in general across all of the subunits suggests a low tolerance for mutations affecting GABA mediated neuronal inhibition. Characterization of the broader channelopathy load associated with susceptibility to these common epilepsies mostly with complex genetics will need to be expanded beyond the family of GABA(A) receptor subunits to all families of neuronal ion channels and their interacting molecules by systematic mutation detection associated with functional investigation of their naturally occurring genetic variations.

Calcified plaque is common in the carotid and femoral arteries of dialysis patients without clinical vascular disease

BACKGROUND

Cardiac and vascular mortality are common in end-stage renal disease (ERSD) and are often attributed to accelerated atherosclerosis.

SUBJECTS AND METHODS

We studied 24 non-diabetic ESRD patients without cardiac or vascular disease (M = 12, F = 12) and 24 age-, sex- and race-matched healthy controls. All underwent B-mode ultrasound for carotid and femoral intima media thickness (IMT) and plaque (% stenosis) together with blood pressure (BP), and echocardiograms to determine left ventricular mass.

RESULTS

Both BP and mean IMT were similar in patients and controls. However, discrete plaque was present in 71% (17/24) of patients compared with 21% (5/24) of controls (P = 0.001), and % stenosis was greater in patients (carotid 12.2 +/- 11% vs 2.3 +/- 5.9%, P < 0.0004; femoral 16.4 +/- 19.1% vs 3.1 +/- 6.4%, P < 0.003). Plaque was soft/atheromatous in 3 of the 5 controls, but not in any of the 17 patients (P = 0.007), all of whom had calcified lesions. BP and cholesterol were not correlated with IMT or plaque in patients, but in control subjects carotid IMT was correlated with systolic BP (r = 0.66, P < 0.0005) and diastolic BP (r = 0.45, P < 0.03). In patients, the only independent variables related to vascular morphology were serum albumin which was inversely related to IMT (P < 0.03) and to plaque (carotid P < 0.05, femoral P < 0.02) and age, which was related to femoral plaque only (P < 0.04). Left ventricular end-diastolic internal dimension, not LVMI, correlated positively with carotid IMT (P < 0.04).

CONCLUSION

Our results show that calcified plaque is common in ESRD patients and hypoalbuminaemia may be an associated factor.

Effectiveness of single and annual applications of potassium fertilizer on mown pasture in southeastern South Australia

In south-eastern South Australia, experiments lasting three years were conducted at 22 sites to compare the effects of single and annual applications of KCl on mown subterranean clover-rye grass pastures. Data from the sites were analyzed using the model

Seasonal response of pasture to nitrogen fertilizer in the Mt. Lofty Ranges, South Australia

Ammonium nitrate (0 to 200 kg ha-1 N) was applied to new areas of pure grass (Lolium perenne and Dactylis glomerata) and of mixed clover and grass (Trifolium subterraneum, L. perenne and D. glomerata) at monthly intervals from autumn (April) to late winter (August.) at a site in the Mt. Lofty Ranges, South Australia, and the pasture harvested 1 and 2 months after each application. As fertilizer applications were delayed, pasture yield responded increasingly to nitrogen. When 100 kg ha-1 was applied to grass, yield increases measured 2 months later ranged from 2 to 25 kg D.M. kg-1 N for the May and August applications respectively. Mixed pasture was less responsive than grass to later applications, because nitrogen suppressed the increasingly vigorous clover growth ; with 100 kg ha-1 N, response 2 months after the August application was 16 kg D.M. kg-1 N. Applied nitrate and ammonium disappeared rapidly from the top 30 cm of soil. Only after the May and June dressings, when rainfall was light, did significant quantities persist for one month. Some of the nitrogen loss was from leaching. Herbage harvested after two months accounted for 17 to 48 per cent of nitrogen applied at 100 kg ha-1, the largest recovery following the July dressing. The relatively small responses to high rates of nitrogen in mid winter indicate that other factors, possibly light energy, limited the potential growth of the pasture. The results suggest that nitrogen could be used either to increase the supply of grazing in early spring or the production of hay in late spring, especially where pastures lack clover.