The effect of respiratory activity, non-invasive respiratory support and facemasks on aerosol generation and its relevance to COVID-19.

Respirable aerosols (< 5 µm in diameter) present a high risk of SARS-CoV-2 transmission. Guidelines recommend using aerosol precautions during aerosol-generating procedures, and droplet (> 5 µm) precautions at other times. However, emerging evidence indicates respiratory activities may be a more important source of aerosols than clinical procedures such as tracheal intubation. We aimed to measure the size, total number and volume of all human aerosols exhaled during respiratory activities and therapies. We used a novel chamber with an optical particle counter sampling at 100 l.min-1 to count and size-fractionate close to all exhaled particles (0.5-25 µm). We compared emissions from ten healthy subjects during six respiratory activities (quiet breathing; talking; shouting; forced expiratory manoeuvres; exercise; and coughing) with three respiratory therapies (high-flow nasal oxygen and single or dual circuit non-invasive positive pressure ventilation). Activities were repeated while wearing facemasks. When compared with quiet breathing, exertional respiratory activities increased particle counts 34.6-fold during talking and 370.8-fold during coughing (p < 0.001). High-flow nasal oxygen 60 at l.min-1 increased particle counts 2.3-fold (p = 0.031) during quiet breathing. Single and dual circuit non-invasive respiratory therapy at 25/10 cm.H2 O with quiet breathing increased counts by 2.6-fold and 7.8-fold, respectively (both p < 0.001). During exertional activities, respiratory therapies and facemasks reduced emissions compared with activities alone. Respiratory activities (including exertional breathing and coughing) which mimic respiratory patterns during illness generate substantially more aerosols than non-invasive respiratory therapies, which conversely can reduce total emissions. We argue the risk of aerosol exposure is underappreciated and warrants widespread, targeted interventions.

The introduction of quanta SC+ to critical care for haemodialysis during the COVID-19 pandemic

Background: Of 800 patients treated annually in 19 ICU beds (catchment 500,000) 120 require renal replacement therapy (RRT) delivered by Baxter Prismaflex® (continuous veno-veno haemodiafiltration (CVVHDF)). With the onset of the COVID19 pandemic significant increased incidence of acute kidney injury (AKI) requiring RRT & existing intermittent haemodialysis (IHD) patients contracting COVID19 requiring ICU support raised concerns regarding RRT ICU capacity. Additionally a worrying national shortage of CVVHF/HDF consumables & new machines to deliver this requirement;all critical drivers to seek local solutions for RRT provision beyond usual capability Methods: A kidney unit neighbour described their successful experience trialling SC+ in home IHD patients. Translation of SC+ from home use to safe IHD treatment in ICU was quickly apparent alongside ease of supporting technical infrastructure set up & minimal training requirements. Immediate availability & fiscal acceptability of purchasing 4 Quanta SC+ and 2 supporting RO machines were critical determinants in making IHD a realistic & sustainable solution to desperate RRT shortages. Provision of expert technical support and clinical nurse specialist facilitation expedited training of ICU workforce & enabled swift implementation Results: 27 ICU nurses were trained in 3 weeks (23 in 14 days). Between 22/4/20 & 17/5/20 8 patients (range 37-63 yrs, median 53.5;7/8 known IHD, 1/8 AKI;7/8 COVID19 positive) received 20 treatments (1-5/patient) using SC+ in ICU. An agreed ICU IHD protocol was co-designed gaining consensus in an unfamiliar territory of provision of IHD in ICU & differing clinical perspectives in IHD prescription in a critical care setting Conclusions: At a time of unprecedented national shortage of dialysis machines & increased RRT need associated with COVID19, Quanta provided an effective solution for safe provision of IHD in ICU. Ease of use with training delivered in <6 hours enabled ICU nurses to effectively treat patients independent of dialysis nurses allowing continuity of the chronic HD programme. Learnings identified the importance of training, enabling rapid growth of a critical mass of expertise & confidence. Critical elements included mastering unfamiliar technique, establishing infrastructure, procurement & team communication enabled by online & face-to-face troubleshooting support.